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Milky Way
Conference Abstracts of
Talks and Poster Presentations
Abstracts are listed by Session. To access abstracts
by Author, go to the Participants
page and click on a name.
Session 1. HI
Surveys
Invited Review
1.0 Naomi McClure-Griffiths, New
HI Surveys of the Milky Way
Since the first HI surveys of the Milky Way, HI has been a valuable
tool for understanding the structure and dynamics of the Milky Way.
In fact, because of its high filling factor, HI is one of the best
tracers of Galactic dynamics. Despite the obvious value of HI surveys
of the Milky Way these surveys stagnated in the 1970 and 80's while
Galactic surveys in other wave-bands excelled. Recently surveys of
HI in the Galaxy have undergone a resurgence fuelled primarily by
new advances in large-field imaging. In this talk I will present an
overview of the International Galactic Plane Survey (IGPS), a high
resolution HI survey of Galactic plane. The IGPS is an international
project to combine data from the Canadian, Southern and VLA Galactic
plane surveys to create an atlas of Milky Way HI to an angular resolution
of ~1 arcmin, with spectral resolution of ~1 km/s and rms sensitivity
of ~1 K. These surveys, which are nearly complete, cover more than
80% of the stellar disk of the Galaxy and are producing a variety
of exciting results. I will present some work on tracing the distribution
of a population of compact, cold HI clouds and studying small-scale
structural and dynamical aspects of Galactic structure.
Invited Talks
1.1 Juergen Kerp, A New Whole HI Sky Survey
The data reduction for an all-sky galactic 21-cm line survey, merging
the Instituto Argentino de Radioastronomia (IAR) and the Leiden/Dwingeloo
survey databases is approaching its final step. Hopefully the final
version of this survey shall have its premiere in Boston. A data cube
containing the most important part of the Galactic HI line emission
will be shown.
For the first time a sensitive homogeneous all-sky survey with a
spatial resolution of 0.5 degree and a channel width of 1 km/s becomes
available. All data have been corrected for stray-radiation to an
accuracy which is on average comparable to that of the Bell Labs Survey.
This database allows to study details of the Milky Way structure in
high as well as low galactic latitudes. In future it may serve also
as a reference for surveys with higher spatial resolution.
1.2 Jay Lockman, The VLA Galactic Plane
Survey
The VLA Galactic Plane Survey is the latest in a series of surveys
made using aperture synthesis radio telescopes that provide HI line
and continuum measurements with about 1 arcmin spatial resolution
and 1 km/s velocity resolution over large areas at low Galactic latitude.
The VLA survey covers much of the first longitude quadrant, an area
rich in star formation and related phenomena. I will describe the
survey observations, the state of data prosessing, and some of the
first results that it has produced.
Poster Presentations
1.3 John M. Dickey, A New Look at the
HI in the Fourth Quadrant
Using data from the Southern Galactic Plane Survey we have new measurements
of the properties of the Milky Way disk in the fourth quadrant. Our
HI longitude velocity diagram shows new features in the outer Galaxy
that were not clear in earlier surveys. Our resolution of 1.5' allows
much improved measurements of the 21-cm rotation curve, the thickness
of the atomic disk, and the corrugations of the plane. The combination
of Parkes and Compact Array interferometer data provides an unprecedented
combination of resolution and sensitivity to gas on large scales that
allows us to see the inner disk with much improved fidelity.
1.4 Juan Enrique Pradas Simon, X-raying
the galactic interstellar medium
The 3-D structure and composition of the galactic interstellar medium
can be deduced from the soft X-ray absorption observations.
The discovery of a X-ray emitting coronal gas filling the Milky Way
Halo was one of the major breakthroughs of the ROSAT mission. Here
we present evidence, that the diversity of the published values for
temperature and emissivity of this halo gas is due to the analysis
of only the very soft X-ray energy regime from 0.1 to 0.28 keV. In
contrast to previous approaches, we now analyse the data for the whole
ROSAT-PSPC energy window (0.1 keV,2.1 keV) to derive a self-consistent
model of the diffuse X-ray radiation.
We cross-correlate the ROSAT all-sky survey with the HI 21-cm line
all-sky survey provided by the Leiden/Dwingweloo and Instituto Argentino
de Radioastronomia surveys. This approach allows to derive the 3-D
structure of X-ray absorbing and emitting gas and to constrain the
distance to some high- (HVC) and intermediate-velocity cloud (IVC)
complexes.
1.5 Hiroyuki Nakanishi, Three-Dimensional
Distribution of the Neutral Hydrogen Gas in the Milky Way Galaxy
We derived the three-dimensional distribution of HI gas in the Milky
Way Galaxy using the latest HI survey data cubes and rotation curves.
The distance of the HI gas was determined by the kinematic distance
using a rotation curve. We solved the near-far problem in the inner
Galaxy by a fitting method which involves introducing a model of
vertical HI distribution. In our resultant maps we could trace three
prominent arms: the Sagittarius-Carina arm, the Perseus arm, and the
Outer arm. These three arms were found to be logarithmic spiral arms.
The HI disk shows large and asymmetric warping in the outer disk.
We also found that the HI outskirt is largely swelling in the fourth
quadrant, and hence the Galaxy is significantly lopsided. The scale-height
of the HI layer increases with the radius, and is correlated with
the HI volume density at the centroid of the HI layer.
1.6 C.R. Kerton, C.M. Brunt & L.B.G. Knee,
High Spatial Dynamic Range HI Surveys of Nearby Molecular Cloud
Complexes: Probing the origin, structure and destruction of Molecular
Clouds
Recently it has become apparent that a full understanding of the
origins of molecular clouds requires an understanding of the structure
and kinematics of the surrounding and embedded atomic phase gas. I
will report on current and planned HI surveys of the nearby Cepheus
Flare and Perseus molecular cloud complexes being undertaken by HIA.
The approximately one arcminute resolution of these surveys combined
with the wide-field capability of the DRAO synthesis telescope (ST)
will result very high-spatial dynamic range maps of these
regions. High spatial dynamic range is crucial in order to be able
to map out the molecular-atomic interface regions in sufficient detail
and at the same time describe the kinematics of the atomic gas on
large angular scales. Molecular line (CO) data are being obtained
for both regions at comparable resolution to provide data on the molecular
gas phase. Finally, the DRAO ST also provides complementary continuum
total power and polarization data which will allow a unique probe
of the magneto-ionic medium within these regions.
1.7 Ji-hyun Kang, Bon-Chul Koo, Carl Heiles,
Faint HI 21-cm Emission Line Wings at Forbidden Velocities
We present the results of a search for faint HI 21-cm emission line
wings at velocities forbidden by the Galactic rotation in large-scale(l,v)
diagrams of the Galactic plain using the Leiden/Dwingeloo Survey.
These "forbidden-velocity(FV) wings" protrude from their
surroundings over more than 20km/s in limited (< 2 deg) spatial
regions. They are different from high-velocity clouds in the sense
that the wings are extended and not separated from the Galactic HI
emissions. Since the FV wings exist at velocities forbidden by the
Galactic rotation, they must be associated with some dynamical processes.
If we consider that identifying some objects in the Galactic plane
is hampered by the background contamination, it is important to study
the natures of the FV wings because finding FV wings can be another
method to learn about hidden dynamical phenomena of celestial objects.
We have found about 80 FV wings in the region |b|<13 degree and
0<l<250 degree. We have compared their positions with those
of Sharpless' HII regions, supernova remnants, and galaxies, and found
that 75% are not coincident with those objects. We will discuss the
statistical properties of FV wings and their origins.
1.8 Ji-hyun Kang, Bon-Chul Koo, and Naomi McClure-Griffiths,
HI Study of Southern Galactic Supernova Remnants
We searched HI 21 cm line emission from shocked atomic gas associated
with southern supernova remnants (SNRs) using the Southern Galactic
Plane Survey. Among 97 sources, we detected 10 SNRs that have associated
high-velocity HI gas, most of which are quite possibly the gas accelerated
by the SN blast wave. We also detected 5 SNRs that possibly have associated
HI shells. These 5 sources show an excess HI emission significantly
brighter than the surrounding region over a wide (>10 km/s) velocity
interval. We present images of these 15 SNRs. We discuss the results
on two SNRs, G321.9-0.3 and G347.3-0.5.
1.9 Emily Flynn, HI Self Absorption Toward
Molecular Clouds: Theoretical Models
Although 21 cm H I self-absorption is commonly observed toward molecular
clouds, the origin of the cold atomic hydrogen remains unclear. Two
mechanisms have been proposed: (1) photodissociation of molecular
hydrogen on the skins of the molecular clouds exposed to ultraviolet
radiation, or (2) cosmic ray chemistry deep inside the molecular clouds.
We study H I self-absorption toward molecular clouds by modeling the
chemical and thermal structure of molecular clouds exposed to ultraviolet
radiation fields and calculating the radiative transfer of 21 cm radiation
through these model clouds. We use the models of Kaufmann et al. (1999),
as modified by Wolfire et al. (2003), which compute the physical and
chemical conditions in a molecular cloud as a function of extinction
for various ultraviolet radiation fields, densities, and metallicities.
We find that all model molecular clouds contain enough opacity in
cold H I to exhibit self-absorption against strong 21 cm backgrounds
(TB ~50 - 100 K). The H_I absorption opacity is dominated by cold
atomic hydrogen formed by cosmic ray chemistry deep in the interiors
of clouds. If all molecular clouds contain as much cold atomic hydrogen
as the models suggest, then the presence or absence of H I self-absorption
toward a molecular cloud can constrain its location in the Galaxy.
In particular, in the inner Galaxy, the H I self-absorption can be
used to resolve the kinematic distance ambiguity and therefore establish
accurate distances to galactic molecular clouds.
1.10 Felix J. Lockman, The Cloudy
Galactic HI Halo
New 21cm observations reveal that a significant fraction of HI above
the Galactic disk is organized into discrete clouds. The dominant
motion of the clouds is due to galactic rotation. The clouds have
diameters of tens of pc, masses of tens of solar mass (in HI alone)
and often have a two-phase structure with a cool core and hotter shell.
High-resolution observations show that some of the cool gas is clumped
on scales of one pc, and must be <800 K from the linewidth alone.
These clouds are found to distances of at least 1.5 kpc from the plane
and become so abundant at lower latitudes that they blend into an
indistinct group. It is possible that we are observing the return
flow of cool gas condensing from a galactic fountain.
Session 2. Molecular
Surveys
Invited Review
2.0 Jim Jackson, The Boston
University-FCRAO Milky Way Galactic Ring Survey
Using the new SEQUOIA multi-pixel array receiver on the FCRAO 14
m telescope, we are conducting a new molecular line survey of the
inner Galaxy, the Boston University-Five College Radio Astronomy Observatory
Galactic Ring Survey (GRS). The GRS will map 13CO 1-0 emission in
the inner Galaxy from l=15 to 52 degrees and b=-1 to 1 degree. Compared
with previous molecular line surveys of the inner Galaxy, the GRS
offers excellent sensitivity (0.4 K), better spectral resolution (0.21
km/s), the same or better angular resolution (46”), better sampling
(22”), and the use of 13CO (1-0), a better column density tracer
than 12CO.
Theoretical modelling suggests that all molecular clouds contain
significant column densities of cold atomic hydrogen. We have found
that 21 cm H I self-absorption features toward GRS molecular clouds
caused by this cold H I allow us to resolve the long-standing near/far
kinematic distance ambiguity. Because we can measure the distances
to clouds and their embedded infrared young stellar objects and star
clusters, we can establish their masses, sizes, distributions, and
luminosities.
We have also studied MSX infrared dark clouds. These clouds are easily
detected in 13CO emission. We find that many are in fact cores of
larger giant molecular clouds. Because we can establish their kinematic
distances, we can deduce their masses, sizes, and distributions. Their
masses (~few thousand solar masses) and sizes (~few pc) suggest that
these are the intial condensations that will ultimately become OB
clusters or associations. Their radial Galactic distribution peaks
in the 5 kpc ring.
Invited Talks
2.1 Akira Mizuno, Physical properties
of molecular clouds from the galactic center to the galactic warp
In this presentation, we shall present physical properties of molecular
clouds in terms of a galacto-centric distance especially focused on
the galactic center and the galactic warp, the outer edge of the Galaxy.
We carried out deeper and finer observations toward these regions
than toward the other galactic plane objects in order to look into
the two extreme area of our galaxy.
We have carried out CO observations toward the galactic center region
of -10deg<L<10deg and -5deg<B<5deg with a grid spacing
of 4 arcmin, which is focused on the molecular distribution along
the galactic latitude. In the survey, we found several vertical features,
some of which are newly found. The molecular clouds are found to be
confined by the pressure, not by their own self-gravity. We also found
peculiar molecular cloud complex with B = -2deg-- -4deg and L>0deg
with a radial velocity of ~ -100 km/s. These positions and velocities
are located in the forbidden region in the L-V diagram, and the complex
is expected to be ejected from the galactic center due to possible
past energetic events.
We also have made an unbiased survey for molecular clouds in the
Galactic warp. This survey, covering an area of 60 square degrees
at L=252 to 266, has revealed 70 molecular clouds in the outer edge
of the Galaxy at R greater than 14 kpc, only 3 of which were previously
known. The mass of the clouds is significantly smaller than that of
giant molecular clouds in the inner disk, while the cloud mass spectrum
characterized by a power law shows basically no significant difference
all over the Galaxy.
The X factors, N(H_2)/I_{CO}, were derived toward the above two regions
as well as the inner disk region, and the X factors found to have
a positive gradient with a galacto-centric distance.
2.2 Tom Dame, A Large Extension of the
1.2-Meter Galactic CO Survey
The Galactic CO survey of Dame, Hartmann, & Thaddeus (2001; hereafter
DHT) is composed of both large-scale unbiased surveys, mainly concentrated
within 10 deg of the Galactic plane, and targeted observations of
clouds at higher latitudes. Analysis of all-sky IRAS and 21 cm maps
suggests that the DHT survey is nearly complete for clouds larger
than ~1 deg, even though roughly half of the total area at |b| <
30 deg was not observed. In October 2001 we began a new survey of
all of this unobserved area that is accessible to the northern 1.2
meter telescope, approximately 6,600 sq-deg between l = 0 deg and
230 deg, mainly in the latitude range |b| = 10-30 deg. At least 12
hours per day is being dedicated to this large project, which is sampling
every 1/4 deg (every other beamwidth) to an rms sensitivity of 0.19
K at a velocity resolution of 0.65 km/s. As of May 2003, we have obtained
90,000 of the 106,000 spectra required to complete the survey.
While, as expected, the new observations do not substantially change
the DHT map, several dozen relatively small and isolated molecular
clouds at intermediate latitudes have so far been discovered. The
new survey, combined with that of DHT, is being used for a new census
of molecular clouds within 1 kpc of the Sun, updating the work of
Dame et al. (1987).
Poster Presentations
2.3 Youngung Lee, 13CO Molecular Clouds
and Clumps in the Galactic Plane
Using the Bell Laboratories Survey (Lee et al. 2001) in the J=1-0
transition of 13CO, for one third of galactic plane, (l, b) = (-5
to 117, -1 to +1), and our revised cloud identification code (Lee
et al. 1997), 13CO clouds have been identified and cataloged as a
function of threshold temperature. We identified 1,400 of molecular
clouds with 1 K threshold temperature and with a 4-threshold number
of pixels, 629 clouds with 2 K threshold temperature, and 263 clouds
with 3 K. Clouds with the hottest cores (T_R*(13CO) > 3 K) are
confined to the 6 Kpc Molecular Ring (l<40) and l=80 region. In
addition to cloud identification, cloud clump regions can also be
located within the cloud complex. Dense clump regions can be located
using this 13CO survey and then combined with existing UMass-Stony
Brook 12CO data for the first quadrant of the Galactic Plane (l, b)
= (+8 to 89.9, -1 to 1). The optical depth of 13CO can be estimated
for each channel and pixel from the ratio of the 12CO and 13CO brightness
assuming LTE. This estimate would give a lower limit to the true optical
depth under non-LTE conditions.
Numbers of identified clumps are 3,156 with 0.4 threshold 13CO optical
depth, 2,134 with 0.6, 1,190 with 0.8, and 662 with 1.0. It is found
that the hot clumps are heavily crowded between l = 10 to 20. We also
estimate the column density channel by channel (with a velocity step
of 1 km/sec) with LTE assumption, generating the column density cube
data for the first quadrant of the Galactic Plane. The highest column
density is estimated to be 9.3x10^16 cm^-2 ((km/sec)^)-1, which is
one of the densest part of the Galactic Ring region. Good correlationship
is found between 13CO integrated intensity and column density. We
discuss some statistical characteristics of clouds, cores, and the
column density distribution.
2.4 Martin Bruell, The KOSMA large-scale
CO survey of clouds in the Galactic Molecular Ring
We performed with the KOSMA-telescope large-scale observations of
clouds in the Galactic Molecular Ring (GMR) in CO J=3-2, 2-1 and 13CO
2-1 following up on the BU-FCRAO 13CO 1-0 survey (Simon et al., 2001).
The GMR is one of the prominent large scale structures in the Milky
Way and an interesting laboratory to study star formation. Whereas
the 13CO data yield a good measure of the overall column density structure,
the new observations of CO 2-1 provide a picture of the thin extended
gas and the CO 3-2 data show the distribution of the dense and warm
molecular gas. The combination of observations of these lines thus
allows to distinguish between extended, quiescent gas, dense cold
parts, and warm regions, influenced by star formation. In performing
large scale observations we are able to analyse the structure of this
material.
We observed two fields, one at 45-46 deg, one at 30-31 deg in Galactic
longitude. Each field contains clouds at different velocities and
thus nearly at each Galactic radius within the GMR. In total this
survey covers a field of 1.375 squaredegree. The high star-forming
activity in the GMR is known (e.g. van der Walt et al., 1995, Fig.3)
and in fact we found in our sample no single separated cloud without
some connected star-forming activity. Further both fields contain
extended but quiescent foreground sources.
Comparing the structural scaling behaviour in maps of the different
tracers, we studied the effect of star formation on cloud structure
in the GMR. The Delta-variance method (Stutzki et al.,1998, Bensch
et al.2001) of the CO 3-2 maps of the field G45-46 clearly show the
difference in the distribution of warm gas between the GMR-source
and the non star-forming foreground source.
2.5 Chris Brunt, A High Latitude 12CO
and 13CO Survey in the Outer Galaxy
Large scale (~ 200 sq. deg.) imaging of the 12CO and 13CO (J=1-0)
spectral lines at high latitudes (b=5-18) in the Outer Galaxy is being
conducted at FCRAO as part of the Canadian Galactic Plane Survey.
The molecular line survey combines with CGPS (DRAO) imaging of the
HI 21cm line, 21 cm Stokes I, Q and U, 74 cm Stokes I, as well as
HIRES processed IRAS images in all bands, all at comparable (~arcminute)
resolution. I will review the specifications, status and potential
of the molecular line survey as part of the CGPS database.
2.6 Di Li, CI Survey of Rho Oph using SWAS
We have completed a 3 square degree CI $^3$P$_1$-$^3$P$_0$ map of
the \r\ Ophiuchi regions using SWAS. The remarkably stable receiver
and backends systems of SWAS allow for uniformly calibrated data set
on this scale. Combined with \co, \13co, and \c18o\ maps made using
FCRAO, this data set will facilitate a thorough study of the physics
and the chemistry in this nearby star forming region.
2.7 Lorant Sjouwerman, Maria Messineo,
Harm Habing, Alain Omont, Karl Menten, Maartje Sevenster, 86
GHz SiO maser survey and kinematics in the Galactic Bulge
We have searched color-selected AGB stars from the ISOGAL and MSX
mid-IR surveys in the Galactic Bulge and Plane for 86 GHz (J=2-1,
v=1) SiO maser emission with the 30-m IRAM telescope. The SiO masers
instantaneously reveal the line-of-sight velocity of the stars, which
in combination with the less numerous and slightly different population
of OH/IR stars, can be used as kinematic probes of the Inner-Galactic
gravitational potential. Here we present the first results of the
survey.
2.8 Norikazu Mizuno, NANTEN CO Survey
of the Southern Sky: Distribution and Properties of Giant Molecular
Clouds
We will present results of the molecular-cloud survey in the southern
sky conducted by Nagoya University with the NANTEN 4-m millimeter-wave
telescope. The NANTEN telescope is installed at the Las Campanas Observatory
in Chile. Since 1996, we have carried out surveying molecular clouds,
mainly in the J = 1-0 transitions of the CO isotopes 12CO, 13 CO,
and C18O at a beam size of 2.7 arcmin toward more than a million of
points. One of our key projects, the Galactic-plane survey in 12CO,
has almost covered 60deg<l< 200deg, -10deg< b<10deg with
grid spacings of 4 arcmin for |b|< 5deg and of 8 arcmin for the
rest. This survey succeeded to reveal the CO distribution in the Galactic
plane with high spatial resolution and sensitivity, and resulted in
a number of detections of candidates for molecular supershells along
the galactic plane. Some of them are associated with observable indications
of supershells at other wavelengths, including HI, far-infrared, soft
X-ray, and SNRs. The implications of these findings are discussed
in terms of the impact of supershells on star formation in the Galaxy.
Physical properties of the molecular gas toward GMCs are also studied.
In this poster, we will discuss the GMC properties in the context
of star/cluster formation.
2.9 Toshikazu Onishi, NANTEN Observations
of High Latitude Clouds
We have started molecular cloud survey toward high galactic latitude
area with the NANTEN 4m telescope in order to reveal a molecular gas
distribution around the Sun and to study a molecular cloud formation
in low-density interstellar medium. We found tens of high latitude
clouds (HLCs) with the extensive survey by make the best use of the
high-surveying ability of NANTEN. The targets include far-IR excess
clouds over HI emission, cold far-IR clouds, cloud complexes, and
so on. In this poster, we shall present the recent results of HLC
survey by
NANTEN.
As a first step, the survey has been carried out toward the far-infrared
excess clouds of Reach et al.(1998) (Onishi et al. 2001). All the
68 infrared excess clouds that are observable from NANTEN have been
mapped in 12CO(J=1-0). CO emission is detected from 32 infrared excess
clouds. Most of these CO clouds are identified and mapped as high-latitude
clouds for the first time. The CO detection rate is found to be 47%,
much higher than that of the previous study of ~ 13%. The infrared
excess clouds with no CO emission are most likely the molecular hydrogen
cloud because the temperature is similar to or lower than that of
the surrounding HI gas.
We also carried out a CO survey of high galactic latitude molecular
clouds toward HI filaments that contains a molecular cloud complex,
a MBM 53, 54, and 55 region and that toward L~109 and B~-45. These
observations covered the whole area of the HI filament in 12CO(J=1-0)
with a 4 arcmin grid spacing. The filamentary structures are found
to consist of a number of clumpy molecular clouds, and we identified
more than 200 12CO clouds in the regions. In the first complex, we
found a possible molecular cloud-forming region, HLCG92-35, which
is newly detected in this survey (Yamamoto et al. 2003).
2.10 Masahiro Sugimoto, High resolution
survey of molecular clouds in and between the Galactic spiral arms
We are carrying out 13CO J=1-0 survey observations of Sagittarius
arm region (l=38 degree) to investigate relations between the dynamics
of the Galaxy and the properties of molecular clouds. The main science
targets are as follows: (1) Comparison between molecular cloud properties
in the upstream and downstream sides of the arm. (2) Comparison between
clouds in star-forming and non star-forming regions. (3) Determination
of cloud mass function (MF) in an unprecedentedly wide dynamic range.
The survey is on-going, and we have already mapped a 20"*30"
(50*70 pc at 8 kpc) region in the grid spacing of 13."7 (0.45
pc at 6.7 kpc) using the SIS 25-BEam Array Receiver System (BEARS)
installed on NRO 45-m telescope. The observed 13CO distribution shows
three velocity components, corresponding to the near/far Sgr arm and
interarm (terminal velocity). The arm components have clumpy structures.
To the contrary, the interarm component shows clump-less structure
and is distributed broadly. There are differences in the size-linewidth
relation of clumps among these three components, i.e., the size and
linewidth of clumps in the interarm are larger than those in the far
arm. Though the size of clouds in the near arm is similar to those
in the far arm, however, the linewidth is broader.
We will finish this survey (100 pc*1 kpc along the Sgr arm) within
three years.
2.11 Hiro Saito, The study of the dense
molecular clumps in massive star-forming regions
New observations of the 13CO and C18O emission lines have been extensively
made toward the candidate of the 175 protostellar IRAS point sources
in the Centaurus region (308 < l < 324, -2 < b < 2) using
"NANTEN" telescope. In the Centaurus region, there are many
compact optical and radio HII regions. These relatively young objects
indicate that massive stars formation has been occurring in this region
since ~ 10^6 yr ago. Almost all of young objects are distributed at
distances from 3 kpc to 5 kpc.
The observations have revealed about 150 dense molecular clumps whose
mass ranges 5x10^2 Mo to 4x10^4Mo and size ranges 2 pc to 5 pc and
column density ranges 5x10^21 /cm^2 to 5x10^22/cm^2. The luminosity
of IRAS sources associated with the clumps ranges from 500 Lo to 7x10^5
Lo. We find that the luminosity of IRAS sources is well correlated
with the molecular line width, as fitted by a power law, log(Lir)
= 9.2 log(dV). In addition, we compared the luminosity of the IRAS
sources and the ratio Mvir/Mco. The ratio indicates the ratio of the
internal kinetic energy compared to the self-gravitational energy.
We find that Massive stars are therefore formed in the clumps with
small Mvir/Mco ratio. These suggests that the mass of the formed stars
is determined by the internal velocity dispersion of the dense core/clump
and it is necessary for more massive star formation to more gravitationary
relax thesystem.
2.12 Akira Mizuno, NANTEN Galactic
Plane CO Survey Maps
2.13 Sungeun Kim, CO J=7-6 and CO J=4-3
Emission toward the Galactic Center Region
We present position-velocity strip maps of the Galactic Center region
in the CO J=7-6 and J=4-3 transitions observed with the Antarctic
Submillimeter Telescope and Remote Observatory (AST/RO) located at
Amundsen-Scott South Pole Station. Emission from the two rotational
transitions of 12CO was mapped at b=0 deg for 3.5 deg > l >
-1.5 deg, on a 1' grid with a FWHM beamsize of 58'' at 806 GHz and
105'' at 461 GHz. CO J=4-3 and (Ojha et al. 2001) emission from this
region show that these lines are distributed in a manner similar to
CO J=1-0 emission (Stark et al. 1987). The (CO J=4-3)/(CO J=1-0) line
ratio map is almost featureless across the entire Galactic Center
region.
In contrast, the CO J=7-6 emission from the Galactic Center is strongly
peaked toward the Sgr~A and Sgr~B molecular complexes. A Large Velocity
Gradient (LVG)\ analysis shows that aside from the two special regions
Sgr~A and Sgr~B, the photon-dominated regions within a few hundred
parsecs of the Galactic Center region.
2.14 Alexis M. Johnson, James M. Jackson,
Ronak Y. Shah, Robert Simon, Alberto Bolatto, James Di Francesco, The
Structure of GRSMC 45.46+0.05
We present a 13CO J=1-0 image of the star-forming cloud GRSMC 45.46+0.05
using observations taken with the BIMA D-array and corrected for zero-spacing
flux with BU-FCRAO Milky Way Galactic Ring Survey data. The addition
of the interferometer data provides a synthesized beam with a spatial
resolution of 15" by 20", a factor of 2.4 smaller than the
FCRAO alone. For GRSMC 45.46+0.05, which is at a kinematically determined
distance of 6 kpc, this corresponds to 0.5 pc. The improved spatial
resolution enables us to investigate cloud structure over a larger
range of clump masses. We derive a clump mass spectrum using the three
dimensional gaussian decomposition algorithm GAUSSCLUMPS (Stutzki
& Güsten 1990). We compare the higher resolution spectrum
to a lower resolution spectrum of the surrounding region (Simon et
al. 2001) and find no change in the slope of the mass profile. We
find a spectral index a = 1.73±0.07 from our FCRAO observations,
and a = 1.76±0.12 from the combined BIMA D-array and FCRAO
data.
Observations of molecular clouds reveal an internal structure through
clump mass spectra that on large scales appears to be the same from
cloud to cloud and independent of the amount of internal star formation
(Elmegreen & Falgarone 1996, Simon et al. 2001). Prior studies
of cloud structure have been performed primarily with single dish
telescopes, and consequently probe only large scale structures. These
studies show that the clump mass spectrum is well-represented by a
power law of the form dN/dM ~ M-a, with spectral index a ranging from
1.5 - 1.9. Extending our knowledge of the clump mass spectrum down
to smaller masses is important for understanding the bulk of star
formation, which is in low-mass objects (<~1 solar mass). The additional
resolution of interferometric observations is critical to investigate
the behavior of the clump mass spectrum at these smaller masses.
2.15 Christer Watson, Resolving the
Distance Ambiguity Toward Inner Galaxy Massive Star Formation Regions
175 ultracompact (UC) HII regions in the GLIMPSE survey region (|b|
< 1 and 10 < |l| < 70) were observed using the Arecibo, GBT,
and Compact Array telescopes. The objects were observed in H110a (all),
H2CO (Arecibo and GBT) and HI (Compact Array). By analyzing H2CO or
HI absorption against the UC HII region continuum emission, we resolve
the distance ambiguity toward 144 sources. This determination is critical
to measure global physical properties of UC HII regions (e.g. luminosity,
size, mass) and properties of the Galaxy (e.g. spiral structure,\
abundance gradients). We find that the distribution of UC HII regions
in this survey is consistent with a "local spur", the Perseus,
Sagittarius and Scutum arms as delineated by Taylor & Cordes (1993)
and references therein. However, departures from model velocities
produce distance uncertainties only slightly smaller than the proposed
arm separations.
2.16 Esther Aguti, A New CO Survey of
the Nearest and Largest Translucent Molecular Cloud Complex, MBM 53-55
A new very sensitive CO (J=1-0) survey of the area around the nearest
and largest translucent molecular cloud complex, MBM 53-55, has been
completed using the CfA 1.2 m millimeter-wave telescope. A region
extending from l = 97º to 84º and b = -44º to -30º
was observed every ¼º, i.e., roughly every other beamwidth,
to an rms noise of 0.15 per 0.65 km/s channel, and 2968 spectra were
obtained. CO was detected at velocities ranging from -15 to 0 km/s,
and was concentrated in an arc-shaped structure over 10º long.
Comparison with HI data (Hartmann & Burton, 1997) suggests that
this coincides with the edge of an expanding HI shell, a correlation
previously studied by Gir et al (1994). This arc-shaped feature is
also seen in IRAS 100 micron observations (Schlegel et al, 1998) in
this region. A molecular mass of the cloud complex of 1.3 x 10^3 M(sun)
was derived from the velocity-integrated CO intensity, assuming a
distance of 150 pc (Welty et al, 1989; Hearty et al, 1999). The virial
mass computed was 1.15 x 10^4 M(sun), an order of magnitude higher
than the CO derived mass and indicating that the cloud is not gravitationally
bound. Comparison of the CO data with HI and 100 micron observations
also suggests that the cloud is made up of more atomic than molecular
gas, e.g., the derived HI mass of the cloud is 3.4 x 10^3 M(sun),
a factor of almost three higher than the CO mass.
2.17 Loris Magnani, The Galactic Center
in CH
We present observations of the Galactic Center in the 3335 MHz line
of CH. The observations were made with the NRAO 140-foot telescope
and have 9' resolution. Comparisons between the CH observations and
CO(1-0) observations at similar angular resolution reveal interesting
similarities and differences. Given the ability of the 3335 MHz transition
to trace low-density molecular gas, a Galactic CH survey may be the
best way to understand the atomic-molecular transition in the Galaxy.
2.18 Robert Simon, Multi-wavelength
surveys of Galactic star forming regions
The availability of large scale, high angular resolution Galactic
continuum surveys from mm to near-IR wave lengths makes complementary
spectroscopic surveys tracing the main constituents of the dense atomic
and molecular phase (i.e., CI and CO) increasingly more important.
While lower frequency surveys, such as the 13CO 1-0 Galactic Ring
Survey, reveal the bulk of the molecular material typically at low
densities and temperatures, observations of atomic carbon and higher
excited lines of CO isotopomers yield additional important clues on
the excitation conditions, the chemistry, and kinematics in particular
of the star formation sites in the clouds.
As part of an ongoing study, we present the status of a large scale
multi-frequency survey of the Cygnus-X region, one of the most prominent
high mass star forming regions of our Galaxy, including 13CO 3-2,
2-1, and CI lines observed with KOSMA. We discuss results from an
LTE analysis towards selected regions of potential high mass star
formation in context with submm (MAMBO), mid-IR (MSX), and near-IR
(2MASS) continuum observations.
The KOSMA Cygnus X spectral line survey is part of a long term goal
to survey star forming regions throughout the Galaxy, including the
southern hemisphere. For this, a Nagoya-Cologne University collaboration
will move the Nagoya 4m NANTEN telescope to the ALMA site in Chile
and equip it with SMART, the Cologne 8 pixel dual frequency receiver
operating at 490 and 810 GHz. This new instrument will be dedicated
to exploit the exceptional atmospheric conditions at Chajnantor to
survey the southern sky in both CI lines and high excited CO lines.
2.19 Jill Rathborne, R.Y. Shah, R. Simon,
J.M. Jackson, T.M. Bania, D.P. Clemens, M.H. Meyer, A.M. Johnson, E.
Flynn, N. Bonaventura, Identifying nearby molecular clouds
Recent molecular surveys are revealing the complex structure and
dynamics of clouds within the galactic plane. While this is the case,
difficulties often remain in separating molecular clouds along a line
of sight. Identification of
nearby clouds is facilitated through the combination of molecular
datasets and extinction maps. Star counts at optical and infrared
(IR) wavelengths indirectly trace visual extinction, and when morphologically
similar to molecular emission, allow properties of nearby clouds to
be determined. Here we present the methodology and data used to separate
two molecular clouds along the same line of sight (GRSMC 45.46+0.05
and GRSMC 45.60+0.30). We use a combination of optical and near-IR
star count maps (derived from the US Naval Observatory and 2MASS catalogs)
and molecular datasets (from the Columbia, UMASS-Stony Brook and the
BU-FCRAO Galactic Ring Survey).
2.20 Ronak Yogendra Shah, The BU-FCRAO
Galactic Ring Survey: Channel Maps
The Milky Way Galactic Ring Survey (GRS) continues to map J=1->
0 13CO emission in the First Galactic Quadrant with an excellent combination
of sensitivity (0.2 K), angular resolution (45''), and spectral resolution
(0.2 km/s). Here we present the channel maps of our Third Release
data (www.bu.edu/grs), covering 50 square degrees from 15 > l
> 52 and within b
<1. Posters by E. Flynn, A. Johnson, and J. Rathborne address a
subsets of the science obtained with the GRS.
Session 3. Infrared Surveys
Invited Review
3.0 Robert Benjamin, GLIMPSE: a
SIRTF Legacy Project to Map the Inner Galaxy
The Galactic Legacy Infrared Mid Plane Survey Extraordinaire SIRTF
Legacy project will be a fully-sampled, confusion-limited mid-IR survey
of the inner Galaxy. The area defined by 10<|l|<65 (both sides
of Galactic center) and |b|<1 will be mapped with a pixel resolution
of 1.2'' using the IR Array Camera IRAC, at 3.6, 4.5, 4.8, and 8.0
microns.
GLIMPSE will probe the structure of the inner Galaxy as traced by
the spatial distribution of stars and IR-bright star formation regions.
Its data can be combined with other surveys to study gas and dust
in various structures.
GLIMPSE is expected to discover thousands of bright star formation
regions, in the highest resolution relatively unobscured unbiased
Galactic stellar survey to date. This census will yield particular
insight into the physics and statistics of star formation as a function
of age and Galactic environment.
These star formation regions form a well-distributed set of test
particles with which one can map the structure of the central bar,
the molecular ring, and the inner spiral arms. Some of the specific
determinations made possible by the GLIMPSE survey will include: measuring
the stellar disk scale length, constraining the central bar using
the star formation regions at its ends, correlating stellar content
and star formation with studies of the molecular ring to answer whether
the Milky Way is a ringed Galaxy, addressing the number of spiral
arms, and investigating whether stars are formed on their leading
or trailing edges.
The GLIMPSE project will provide a star catalog and mosaicked images
to the Community on a short timescale, stimulating and enabling research
in star formation, Galactic structure, and many other areas of Galactic
astrophysics.
Invited Talks
3.1 Stephan D. Price, Mid-Infrared Survey
of the Galactic Plane
Two major satellite-based mid-infrared surveys were conducted of
the Galactic Plane in the mid-1990s. The Midcourse Space eXperiment
(MSX), a US DoD Ballistic Missile Defense organization satellite,
surveyed the entire plate within |b| < 5° in four spectral
centered at 8.3, 12.1, 14.7 and 21.3 µm at a resolution of 20"
and a sensitivity of 100 mJy at 8.3 µm to 2 Jy at 21.3 µm.
MSX also surveyed about 40 deg.² of the inner Galaxy to a sensitivity
of about 10 times greater. The camera on the Infrared Space Observatory
was used to survey 16 deg² of the inner Galaxy at 7 and 15 µm
to a ~10 mJy sensitivity and 6" resolution under the aegis of
the ISOGAL experiment. ISOGAL also obtained CVF spectra over a small
number of fields, as well as images in other filters. The images and
catalogs produced by these surveys are available to the general astronomical
community and a number of scientific papers have been published that
were based on the survey results.
The surveys reveal the true complexity of the structure in the interstellar
emission along the Galactic Plane. The MSX band intensities and ISO
CVF spectra confirm that the mid-infrared emission from interstellar
dust is dominated by hydrocarbons. MSX and ISO also discovered a new
component of the Galaxy, infrared dark clouds. These clouds are so
cold (T < 15K) that they are seen in absorption against the infrared
background emission along the Galactic Plane, even in the IRAS 100
µm images. Several thousand dark clouds have been identified
from the MSX survey. The clouds are isolated and sharp edged down
to the 6" ISO resolution. The MSX point source catalog was used
to derive the mid-infrared luminosity function of the bulge AGB. The
MSX, and ISOGAL point source catalogs have been used to identify and
characterize OH and SiO masers, while the MSX mid-infrared colors
have been used to distinguish between the early post-AGB stages of
OH masers. Also, associating the MSX and ISOGAL sources with the near-infrared
observations from the soon to be released Two Micron All Sky Survey
(2MASS) provides an invaluable for stellar population analysis; ISOGAL
and sources in the Deep Near Infrared Sky have been combined to separate
sources into populations and to derive the luminosity function of
the inner bulge. Such multiple color infrared information is essential
for deriving interstellar extinction.
The sensitivity and resolution of the MSX images are an excellent
complement to the results from radio surveys. Young stellar objects
and massive young stellar objects are distinguished by their infrared
and radio characteristics. The structure in the mid-infrared MSX images
correlates well with thermal radio emission but is strongly anti-correlated
with non-thermal emission, such as from a super nova remnant, for
example.
The MSX Galactic Plane images will be presented and the scientific
results of the MSX and ISO catalogs and images will be reviewed
3.2 Martin Weinberg, Finding the Milky
Way in 2MASS
The 2MASS full-sky coverage and the relatively low extinction at
J, H and K' is an ideal resource for uncovering the large-scale structural
details of the Milky Way and their relationship to the underlying
stellar populations. I will illustrate the overall features of the
Point Source Catalog and briefly describe preliminary star-count studies
in the Milky Way, the Large Magellanic Cloud, and the Sagittarius
dwarf as examples. Features of these three (nearly) independent systems
are important aids in the daunting task of pinning down the entire
Milky Way. I will then describe early work on the Milky Way itself
including basic structural parameters and the Milky Way bar. Realization
of these data riches with 2MASS and other surveys will require new
computationally optimized methods for theory-data statistical analyses
and I will briefly outline some recent progress.
Poster Presentations
3.3 Ronald Drimmel, Dust Distribution
in the Milky Way
A three-dimensional model of the dust distribution in the Milky Way
is presented based on FIR observations made by the COBE satellite.
This model is a further development of that first presented by Drimmel
& Spergel (2001). Here the molecular ring has been added, which
shows evidence of ellipticity, as well as a central hole in the disk.
Temperature gradients associated with the spiral arms have also been
added. Description of dust within a few kiloparsecs of the Sun, associated
with the local Orion arm, is further constrained by recent observations
of nearby HII regions. Extinction along several lines-of-sight close
to the Galactic plane is confronted with empirical measures using
2MASS data.
3.4 Sabastien Picaud, Triaxial bulge,
thin disc and a possible in-plane bar in the Milky Way
We present here two studies of the inner Milky Way using both the
Besançon model of Galaxy and star counts in near infrared J
and K bands. In the first study, triaxial outer bulge and inner old
thin disc parameters of density are fitted using Besançon simulations
and DENIS data at longitudes between -12 and +8 deg and latitudes
between -4 and 4 deg. The results show that the outer bulge is very
oblate, with an angle from the sun-Galactic center direction of about
10 degrees, and a major axis almost on the Galactic plane, while the
thin disc has a great central hole. Different bulge luminosity functions
are also tested. In the second study, we compare Besançon simulations
with CAIN data at longitudes 15-45 deg and latidudes lower than 2
deg in absolute, and show the existence of an in- plane extra density
of stars at longitudes lower than 27 degrees. The excess stars are
more numerous than disc ones
and locate at a distance from the sun lower than 6 kpc. This extended
over-density might correspond to the top end of a bar having a half-length
of about 4 kpc and a angle from the sun-Galactic center direction
of 45+/-9 deg
3.5 Paola Platania, Full sky study
of the Diffuse Galactic Emission at long wavelengths
Present and future CMB experiments have to face problems when dealing
with foreground emissions and in particular for diffuse Galactic foregrounds.
Here we present a study on one of the most critical foreground contamination
at low CMB frequencies (around 10 GHz) namely the synchrotron emissions.
We reviewed the current status of data and attack the problem of removing
systematic effects in present synchrotron emissions surveys by means
of a technique already applied to clean IRAS plates from their striping.
We obtain the destriped versions of the three largest low frequency
surveys: the 408, 1420 and 2326 MHz maps. This allows us to construct
detailed maps of the spectral index and normalization factor over
the whole observed the sky. By means of a minimization technique,
we reduce the effects of discontinuities due to the combination of
systematics of the three surveys. The distribution of the spectral
indices is well fit by a gaussian function with b
= 2.725 ± 0.214 in the analysis performed with statistical
errors only and b =2.685 0.235 when systematics
are included. This is representative of the Galactic diffuse synchrotron
emission. As the recent WMAP results show, any template of the Galactic
emission is frequency dependent; the comparison between the synchrotron
spectral index map at WMAP frequencies and that derived from the analysis
of radio surveys at ~ GHz frequencies will add information on the
physical processes of electron energy loss and the properties of Galactic
structures.
3.6 Alice C. Quillen, Using 2MASS to
estimate distances to molecular clouds
Molecular clouds are detected in 2MASS number counts as drop outs.
We attempt to estimate distances to these clouds from the 2MASS number
counts.
3.7 Francois Boulanger, Dust evolution
in the Galaxy: from ISO to SIRTF
I will present results from ISO observations illustrating diverse
aspects of dust evolution in the Galaxy: (1) destruction of small
grains by hard photons, (2) shattering of grains into small particles
in turbulent H I clouds and (3) coagulation of small grains into larger
particles in molecular clouds. These three conclusions result from
a comparative analysis of dust and gas observations on selected fields.
SIRTF will soon provide better sensitivity and much wider surveys,
thus statistics, to pursue these investigations.
3.8 Alain Omont, ISOGAL: A deep survey
of the obscured inner Milky Way with ISO at 7 and 15 micron and with
DENIS near-IR data
ISOGAL combines 7 and 15 micron ISOCAM observations - with a resolution
of 6'' - with DENIS IJK data to determine the nature of the sources
and the interstellar extinction. About 16 square degrees of the inner
Galactic disk and bulge were observed with a sensitivity approaching
10-20mJy, detecting ~100,000 sources, mostly AGB stars, red giants
and young stars. The main scientific results already derived or in
progress will be summarized. These include astrometrically calibrated
7 and 15 micron images, determining structures of resolved sources;
identification and properties of interstellar dark clouds; quantification
of the infrared extinction law and source dereddening; analysis of
red giant and (especially) AGB stellar populations in the central
Bulge, determining luminosity, presence of circumstellar dust, mass-loss
rates and source classification; detection of young stellar objects
of diverse types and foreground sources with mid-IR excess.
3.9 Kathleen Kraemer, Large-Scale Observations
of Galactic Star Forming Regions with MSX
We have imaged seven nearby star forming regions with the infrared
telescope on the Midcourse Space Experiment (MSX) at 18" resolution
at 8.3,12.1, 14.7, and 21.3 micron: the Rosette nebula, the Orion
nebula (A and B), W 3, the Pleiades, S 263, G159.6-18.5, and G300.2-16.8.
The large scale of the regions imaged (7.2-50 square degrees) makes
this dataset unique in terms of the combination of field size and
resolution.
3.10 Uriel Giveon, Infrared Colors of
Radio HII regions in the Milky Way
Investigation of the color-space properties of sources in the MSX
Galactic plane catalog reveals two distinct populations - a blue population
composed of mainly evolved stars, masers and molecular clouds, and
a red population composed mainly of sources of nebular nature - HII
regions, planetary nebulae, and unclassified radio sources. We compare
the MSX catalog to 5 GHz VLA maps of the first quadrant of the Galactic
plane (350<l<40, |b| <0.4). A catalog extracted from these
maps was published first by Becker et al., but calibration and reduction
were significantly improved since, resulting in an increase of 60%
in source detection. The comparison resulted in a sample of 491 sources,
out of which we estimate 38 to be false counterparts, all of them
from the MSX red population. These radio sources with infrared counterparts
are found to be extremely bounded to the Galactic plane (FWHM of 12'
or 30 pc), and have thermal continuous radio spectrum (using 1.4 GHz
data). These properties suggest that the sample is dominated by HII
regions, most of them unclassified so far.
3.11 Jill Rathborne, K.J. Brooks, M.G. Burton,
M. Cohen, S. Bontemps, The Giant Pillars of the Carina Nebula
We present results of a multi-wavelength study of the giant pillars
within the Carina Nebula. Combining survey data in the near-IR from
2MASS, mid-IR from MSX, 843 MHz radio continuum maps from the MOST
and follow-up molecular line and continuum observations from the SEST,
we investigate the nature of the pillars and search for
evidence of ongoing star formation within them. We find the giant
pillars are dense molecular structures, with PDRs on their surfaces,
are surrounded by warm dust and have tips with the potential to be
star forming cores. Evidence for ongoing star formation across the
region was found through the identification of many candidate massive
young stellar objects (MYSOs), compact HII regions and embedded clusters.
3.12 Melvin Hoare, The RMS Survey: A
Systematic Search for Massive Young Stars in the Galaxy
We have selected red MSX sources (RMS) that have the colours of massive
young stellar objects (MYSOs). Our aim is to generate a large systematically
selected sample of such objects that will be essentially complete
for young O stars for future study. Other objects such as UCHIIs,
PN, PPN and AGB stars have similar IR colours and a large programme
of ground-based follow-up observations is underway to characterise
the red MSX sources. These include radio continuum observations to
identify photo-ionized nebulae, kinematic distances to measure luminosities,
ground-based mid-IR imaging to confirm stellar sources, near-IR imaging
and spectroscopy to distinguish pre- and post-MS objects. We report
the progress of these campaigns on the 3000 candidates, with initial
indications showing that a substantial fraction are indeed massive
YSOs.
3.13 Barbara Whitney, A 2MASS Gallery
of star formation regions in the GLIMPSE Survey
We will show 2MASS JHK and MSX 8 um images of several star formation
regions that overlap the SIRTF GLIMPSE survey region. The images are
produced from mosaics of the 2MASS and MSX images available from the
NASA/ IPAC Infrared Science Archive. The 2MASS sensitivities are similar
to those expected from GLIMPSE (Benjamin et al. 2003). These two surveys
will combine to provide fluxes in 7 bands from 1-8 um. These images
show the wealth of information that will be provided by these surveys.
3.14 Robert Simon, R.Y. Shah, J.M. Jackson,
T.M. Bania, D.P. Clemens, M.H. Heyer, MSX Infrared Dark Clouds
in the BU-FCRAO Galactic Ring Survey: A Galactic Ring Population
Recent high resolution surveys with the ISO and MSX satellites have
revealed a large number of Galactic clouds with significant extinction
in the mid-infrared. The infrared dark clouds are characterized by
their high column densities and low temperatures. Little is known,
however, about their origin and distribution in the Galaxy. The BU-FCRAO
Galactic Ring Survey (GRS), a high resolution survey of 13CO emission
in the inner Milky Way, makes it possible to derive physical parameters
of IR dark clouds and their parental molecular clouds, such as sizes
and masses, by spectroscopically determining their kinematic distances.
Based on morphological correlation of IR extinction and GRS 13CO emission
in velocity channel maps, we assign radial velocities to the IR dark
clouds throughout the first Galactic quadrant and, assuming they are
at the near kinematic distance, determine their location in the Galaxy.
We find that the majority of the IR dark clouds is concentrated in
the Galactic Ring at a Galactocentric radius of 5 kpc. We suggest
that the most massive IR dark clouds represent high mass proto-clusters,
or OB-associations in the making.
Session 4: Continuum/Optical Surveys
I
Invited Review
4.0 Wyn Evans, Microlensing Surveys
At just 10 years of age, microlensing is the youngest technique in
Galactic Astronomy, but it uniquely has the power to probe directly
the mass distribution rather than light distribution. Microlensing
has already made fundamental contributions to our knowledge of the
Galaxy, for example, by demonstrating that the interior of the Milky
Way is overwhelmingly baryon-dominated, and by showing that dark halos
are not made up of failed stars or red dwarfs. Large-scale microlensing
surveys of the Milky Way provide powerful constraints on the mass
distribution in the bulge, the bar and the spiral arms. As is natural
in such a young subject, there are a number of perplexing puzzles.
First, there is substantial variation in the optical depth results
reported by the differing microlensing surveys of the Inner galaxy.
Secondly, almost all the surveys find that the optical depth towards
the Galactic bulge is much larger than even a barred, baryon-dominated
Galaxy can explain. Thirdly, certain fields apparently show anomalously
large numbers of long duration microlensing events.
Invited Talks
4.1 Zeljko Ivezic, Reaching to the edge
of the Milky Way with SDSS
I will review recent SDSS results on Milky Way structure, discuss
the potential of POSS-SDSS comparison for proper motion studies, and
describe a new sample of several thousand candidate RR Lyrae stars
in the outer halo. These candidates are selected using variability,
colors, and spectroscopy from a region 30 times larger than that used
in previous published SDSS analyses. I will summarize the properties
of the outer halo, including its clumpiness, overall shape, size,
and radial stellar density distribution, inferred from the analysis
of this sample.
4.2 Ron Reynolds, The WHAM Northern
Sky Survey
Observations of faint H-alpha emission have revealed that diffuse,
low density ionized hydrogen gas at a temperature near 10,000 K is
a major component of the interstellar medium of our Galaxy and others.
The existence of this gas has impacted our understanding of the composition
and structure of the the interstellar medium as well as the principal
sources of ionization and heating within disks and halos of galaxies.
The Wisconsin H-Alpha Mapper (WHAM), a remotely controlled Fabry-Perot
observing facility located at Kitt Peak and funded by the National
Science Foundation, has provided for the first time an H-alpha survey
of the distribution and kinematics of this diffuse interstellar HII
in the Milky Way that is comparable to earlier 21 cm surveys of the
HI. The WHAM survey, consisting of 37,565 spectra north of declination
-30, reveals wide-spread ionization spanning an area from well outside
the solar circle to the inner Galaxy, with enormous loops and filaments
of ionized gas reaching more than 1000 pc from the disk in some cases.
Near the Galactic midplane the HII appears to have little relationship
to the HI; however, at higher Galactic latitudes the WHAM survey reveals
a close relationship, both kinematically and spatially, between the
diffuse HII and "warm" (i.e., broad 21 cm component) HI
clouds, including the distinct complexes of HI clouds at intermediate
and high velocities. A survey of the nebular and lines over a more
limited
region of the sky has also made it possible to map the variations
in temperature and ionization state of the gas.
Poster Presenations
4.3 Ronald Drimmel, Estimated star
counts from the GSC-II catalogue
An estimate of point source counts as a function of magnitude is
made over the whole sky using the Guide Star Catalogue II. Corrections
for blending in crowded fields, as well as misclassification, is made.
Comparisons with independent high-resolution data sets, such as from
the Sloan Digital Sky Survey, is used to confirm the method used.
A final sky map of stellar magnitude distributions is produced.
4.4 Robert Benjamin, Inside the Molecular
Ring: Models of Diffuse X-ray Emission from the
Central Five Kiloparsecs of the Milky Way
The ROSAT 3/4 and 1.5 keV all-sky surveys indicate an important X-ray
emission component fills the inner few kiloparsecs of the Milky Way.
This gas has a temperature of about 4 million degrees K , an X-ray
luminosity of 1-3 x 10^39 ergs/s, a vertical scale height of 1.9 kpc
and a radial extent of about 5 kpc. We present models of this emission,
focussing on possiblity that the interstellar bulge region is driving
a Galactic wind. We discuss the constraints on the nature of any such
wind and make predictions for the temperature gradient of the X-ray
emitting
gas in the central Galaxy.
4.5 Sandro Villanova, Giovanni Carraro, A
survey of Probable Open Cluster Remnants in the Galactic Disk
We present preliminary results of an ongoing survey to probe the
physical nature of a sample of open clusters (POCRs, Bica et al 2001)
believed to be in an advanced stage of dynamical evolution. This kind
of object are very important to constrain dynamical N-body models
of clusters evolution and dissolution, and to understand the formation
of the Galactic field stars populations. Moreover they might represent
what remain of much larger old clusters, and therefore they might
be the remnants of very old open clusters, which are of paramount
importance to probe the early stages of the Galactic disk evolution.
4.6 Balar Khalid, Variable stars &
how the Cepheid variables are used as distance indicators
I will focus on the variable stars, specially "pulsating variables";
and I will concentrate on one important class of pulsating stars called
Cepheid variables.
I am not concerned with why the stars pulsate but rather how they
are used as distance indicators, because Cepheids are the best "Standard
candles"; on extragalactic distance scales also they are bright
and easily identified, and most importantly. So the best method of
determine the distance to a galaxy is by finding a Cepheid in the
galaxy and applying the period-luminosity relationship. We will know
also where did this period-luminosity come from? By using the Fitting
method (Chi-square method).
Although the Cepheid variables continue to be powerful indicators
of the cosmic distance scale, astronomers now tend to believe that
the Cepheid in one galaxy may not be physically identical with those
of the same period in another galaxy . the slope of the P-L relation
may be different from one galaxy to the next, depending upon the relative
abudances of the elements in each . the slopes of the P-L relations
for the two populations of stars may not be the same. ( the P-L relation
are not identical at all wavelengths).
From a general consideration of Stefan's law connecting luminosity
L, radius R, and effective temperature Te, and of Ritter's equation
between the pulsation period P and the mean density, one derives that
P = f (L, M, Te). By applying the Theoretical P-L and P-L-C relations
to available BVK data of Cepheids in the Magellanic Clouds, I eventually
obtain Z=0.004, and true distance modulus DM= 19.16 for the SMC; and
Z=0.008, and DM= 18.46 for the LMC.
4.7 Peregrine M. McGehee, Mapping the
Local Dust Distribution with SDSS
The narrow range of M dwarf g-r colors in SDSS photometry permits
study of the three-dimensional dust distribution within 1 kpc. Distances
to early M dwarfs are assigned using reddening-invariant photometric
parallaxes and clouds are identified by statistically significant
shifts in median g-r colors. The observed reddening is compared against
that predicted by Schlegel, Finkbeiner, and Davis (1998).
4.8 Cesare Barbieri, Digital
Archive of the Asiago Schmidt telescopes surveys of the Milky Way
4.9 Stefano Pasetto, A. Vallenari,
G. Bertelli, A. Spagna, C. Chiosi, Kinematics of the Galactic
populations towards the NGP
Recent determination of the mean rotational velocity of halo shown
no substantial agreement. Majewski et al. 1996 find a retrograde velocity
of 55 km/s; Chiba & Beers 2000 derive no substantial rotation
or even a slightly prograde rotation. In addition a population of
halo RR-Lyrae is found at a mean height of Z=5.3 kpc (Kinman et al.
2002) having a substantially retrograde motion. Whether this retrograde
motion is caused by local streaming or it is part of a more widespread
effect it is not yet clear. To address this issue we simulate CMD
and proper motions of a GSCII catalog field at (l,b)=(162.3,86.5)
using a new implementation of the Padova Galaxy Model where kinematic
simulations are included.
4.10 Dana Dinescu, The Yale/San
Juan Southern Proper Motion Catalog 3
We present the third installment of the Yale/San Juan Southern Proper
Motion Catalog, SPM 3. Absolute proper motions, positions, and photographic
B,V photometry\ are given for over 11 million objects, down to a magnitude
of V=17.5. The Catalog covers an irregular area of 3700 square degrees,
between the declinations of -20 and -45 degrees, and excluding the
Galactic plane. All observations were made with the 50-cm double astrograph
of Cesco Observatory in El Leoncito, Argentina. The Catalog is based
on full-plate scans using the USNO Precision Measuring Machine (PMM)
and its image detection and centering software. Almost all SPM fields
for which second-epoch plates are available have been included, excepting
the Galactic plane. The proper-motion precision, for well-measured
stars, is estimated to be 4.0 mas/yr. Unlike previous releases of
the SPM Catalog, the proper motions are on the International Celestial
Reference System by way of Hipparcos Catalog stars, and have an estimated
systematic uncertainty of 0.4 mas/yr.
The recently begun SPM CCD survey program will also be described,
briefly. These observations will provide second-epoch astrometry,
as well as improved photometry, for the remainder of the original
Southern Proper Motion survey, and for future versions of the SPM
Catalog.
This work has been supported by a series of grants from the National
Science Foundation, incuding the current grant, AST-0098548.
Session 5: Continuum/Optical Surveys
II
Invited Review
5.0 Gary Hinshaw, Galactic Emission
in the Wilkinson Microwave Anisotropy Probe (WMAP) Maps
The Wilkinson Microwave Anistropy Probe (WMAP) has mapped the full
sky in five microwave frequency bands from 23 to 94 GHz with sub-degree
angular resolution. While the primary goal of the mission is to measure
the cosmic microwave background anisotropy, the data also provide
a wealth of information about microwave emission from the Milky Way.
We present full sky maps of the synchrotron, free-free, and dust emission
obtained from the first-year data and comment on how these maps inform
our understanding of the interstellar medium.
Invited Talks
5.1 Jim Cordes, A New Model for the
Galactic Electron Density and its Fluctuations
A new model is presented for the Galactic distribution of free electrons
based on work by J. Lazio and J. Cordes. It (a) describes the distribution
of electrons responsible for pulsar dispersion measures and thus provides
a distance scale for pulsars; (b) describes the distribution of electron
density microstructure that underlies interstellar scattering; (c)
can be used to interpret interstellar scattering and scintillation
observations of Galactic objects and of extragalactic objects (compact
AGNs and Gamma-ray burst afterglows); and (d) serves as a preliminary,
smooth spatial model of the warm ionized component of the interstellar
gas. This work builds upon and supersedes the Taylor & Cordes
(1993) model by exploiting new observations and methods, including
(1) a near doubling of the number of dispersion and scattering measurements;
(2) better independent distance measurements; (3) improved measurements
of scattering toward the Galactic center; (4) improved constraints
on the (Galactocentric) radial distribution of free electrons; (5)
redefinition of the Galaxy's spiral arms; (6) modeling of the local
interstellar medium, including the local hot bubble identified by
X-ray and NaI absorption measurements; and (7) an improved likelihood
analysis for constraining the model parameters. For lines of sight
directed out of the Galactic plane, the new model yields substantially
larger values for pulsar dispersion measures, except for directions
dominated by the local hot bubble. Unlike the TC93 model, the new
model provides sufficient electrons to account for the dispersion
measures of the vast majority of known, Galactic pulsars. Future observations
and analysis techniques that will improve the Galactic model will
be discussed, including deep pulsar surveys with Arecibo, VLBI on
large samples of AGNs, and very deep surveys with the Square Kilometer
Array. Constraints on the role of turbulence are expected through
a combination of low-frequency radio astronomy with LOFAR and gamma-ray
observations with GLAST.
5.2 Bryan Gaensler, Radio Synchrotron
Emission from the Milky Way
The pioneering efforts of Jansky and Reber demonstrated that the
disk of the Milky Way was a strong source of radio emission. Single-dish
radio surveys of the Milky Way in the 1950s and 1960s established
that this emission was polarized synchrotron emission, and that it
originated both from diffuse gas in the Galactic plane and from discrete
supernova remnants.
In the last 5-10 years, wide-field imaging capabilities and effective
mosaicing algorithms have made possible a variety of ambitious interferometric
surveys of the Galaxy, resulting in images of unprecedented sensitivity
and resolution. In this talk I will discuss some of the highlights
from these new surveys. Amongst the many new results are the identification
of many new supernova remnants in confused regions, spectacular low
frequency images of the inner Galaxy with the VLA, and some remarkable
new insights into the structure of the Galactic magnetic field from
linear polarization.
5.3 Robert Becker, Richard L White, David Helfand,
A Three-Configuration VLA Galactic Plane Survey at 1400 MHz
VLA time has been awarded to carry out a three configuration survey
of the Galactic Plane at 1400 MHz. In phase I, observations were taken
of a 1.5 degree-wide strip between 19 and 32 degrees Galactic longitude.
Phase II, which began in April, will extend the strip south to a Galactic
longitude of 5 degrees. Each field of the survey is
observed for approximately 10 minutes over the course of 6 hours in
each of the B, C, and D configurations. The resultant images are combined
with low resolution images from the Bonn 100-meter telescope survey
to compensate for the absence of short spacings in the VLA data. Images
from both Phase I and II will be shown. The survey reaches a point
source sensitivity of ~1 mJy over most of the survey area and has
a final resolution of ~5 arcsec. Hundreds of new HII regions and supernova
remnants are visible in the maps. Comparison with the MSX mid-IR images
is extremely useful for separating thermal and nonthermal emission.
The work is supported by NSF grants AST-02-06309 and AST-02-06055
as well as NASA ADP NAG 5-13062.
Poster Presenations
5.4 Marijke Haverkorn, Polarized
radio continuum emission in the Southern Galactic Plane Survey
The Southern Galactic Plane Survey (SGPS, McClure-Griffiths et al.
2001, ApJ 551, 394) is a high-resolution survey at 1.4 GHz of the
fourth quadrant of the Galactic plane observed with the Australia
Telescope Compact Array (ATCA) and the 64m Parkes telescope. The survey
consists of HI and full polarimetric continuum data at a resolution
of about 1 arcmin. Data and analysis of the polarized continuum part
of the SGPS will be presented, in particular the SGPS test region,
a well-analyzed part of the SGPS data. Most of the structure in polarization
is unrelated to structure in total intensity, and therefore must be
produced by Faraday rotation and/or depolarization processes. Polarization
and depolarization give information on the distance of the emission,
on individual objects such as molecular clouds and supernova remnants,
and on the structure of the Galactic magnetic field. The multi-frequency
polarization data allow rotation measures (RM) to be computed, which
provide a unique method to probe the electron-density-weighted magnetic
field strength in the (mostly) warm Galactic ISM. Characteristics
of the turbulence in the warm ISM are studied using structure functions
of RM. The slope of the structure function provides information on
the kind of structure in the medium, whereas breaks in the slope yield
estimates of typical length scales of the structure.
5.5 Adam Fallon, A Multiwavelength Image
of the Milky Way's First Quadrant
We are in the process of constructing a deep, high-resolution, multiwavelength
image of the Galactic plane in the first quadrant. Observations with
the Very Large Array in the B, C, and D configurations have been added
to single dish data in order to obtain an image at 20cm with a sensitivity
of ~2 mJy and a dynamic range of 500:1. In addition, 90cm data have
been obtained, and a comparison with archival 6cm images has been
conducted. Portions of this region have also been covered with the
imaging instruments on XMM-Newton in the 0.3-12 keV band; archival
data from ASCA have also been examined. Finally, we have undertaken
a detailed comparison of the radio data with mid-IR images from the
MSX mission. We are constructing a catalog of the ~1400 discrete and
~100 extended 20cm sources in the region. We will present some early
results from the catalog. Hundreds of new HII regions and dozens of
supernova remnant candidates are apparent in the 13 degrees of longitude
covered to date. We will present a preliminary analysis of the HII-region
flux density distribution, and will describe the utility of this survey
for a variety of projects ranging from a determination of a quantitative
star formation rate for the Galaxy, the
discovery of young supernova remnants, and the improvement of the
model for the free-electron distribution in the plane which is essential
is characterizing the pulsar population.
5.6 Douglas Finkbeiner, Spinning
Dust Results from WMAP and Green Bank
The Wilkinson Microwave Anisotropy Probe (WMAP; 23-94 GHz) and Green
Bank (8, 14 GHz) surveys support the Draine & Lazarian spinning
dust hypothesis. It is possible to fit the Galactic emission in both
surveys with only free-free, soft synchrotron, thermal dust, and spinning
dust.
Session 6: Galactic Structure and Evolution
I
Invited Review
6.0 Gerry Gilmore, The Bulge and halo:
populations and histories
The stellar bulge and halo are more than a context for continuing
disk evolution: they provide an opportunity to disentangle the star
formation and assembly histories of the older stars in the Galaxy,
and to distinguish the distributions of age, chemistry, stars, and
mass. Our nearest stellar bulge remains poorly defined, and less well
understood. It is small, dense, metal-rich, and largely old. The halo
is very rapidly being surveyed, with even the (chemically) earliest
stars identified. It is extended, sparse, metal-poor, largely old,
and perhaps unique in the Local Group. Are these two systems indeed
related, or do they merely code-share?
Invited Talks
6.1 Eve Ostriker, Molecular cloud
formation
The material in giant molecular clouds (GMCs) constitutes a large
proportion of the Milky Way's ISM, and determining how cloud-formation
processes affect the spatial distribution of GMCs is important to
understanding the structure of the Milky Way. Understanding the formation
of GMCs is also key to theories of galactic evolution because it represents
the first stage in the overall process of star formation. Several
lines of evidence point to a need for relatively rapid GMC formation
via coherent dynamical instabilities, and both Parker- and Jeans-
type modes have been proposed as potential cloud-forming mechanisms.
I will discuss recent numerical simulations that investigate these
instabilities directly, using spatially-localized models of the interstellar
medium that self-consistently incorporate rotational shear, self-gravity,
and magnetic fields, as well as the effects of stellar spiral arms.
These models have demonstrated that condensation via gravitational
instability, aided by the magnetic torques, is the most likely candidate
for explaining the formation of GMCs. The models have also shown that
spiral arm ``spurs'' -- clearly seen as regular projections from dust
lanes in external galaxies -- may originate as magneto-gravitational
instabilities of the ISM within the dense portions of stellar spiral
arms. This raises the interesting possibility that spur structures
with similar dynamical origins could potentially be present in the
Milky Way as well.
6.2 Steve Majewski, Accretion and
the Formation of the Galactic Halo
The notion that the Galactic halo should be networked with streams
from the disruption of satellite systems has a long theoretical history.
At long last, observations are catching up to bear out theoretical
models of a highly substructured Milky Way halo. I will review recent
results from surveys of the halo aimed at discerning substructure.
Poster Presentations
6.3 Heidi Newberg, Galactic Halo Substructure
from A-F stars in the SDSS
Results of searches for spatial substructure in the SDSS database,
using primarily A-F stars, will be presented. The distances to groups
of stars are discovered using statistical photometric parallaxes.
With our data we have been able to map spatial structures of halo
stars at distances of 1.5 kiloparsecs to 100 kiloparsecs from the
Sun. Spectroscopic radial velocity/metallicity measurements of identified
structures will be included.
6.4 Peter A. Tarakanov, Abnormal
Fractal Diffusion in Interstellar Medium of Galaxy
As show observations, the molecular clouds in ISM are fractals with
fractal dimension about 2.35. The model of formation of a cloud is
considered by "cloudlets" aggregation, thrown out from stars.
Is shown, that the driving of a cloudlet in the interstellar medium
is well described within the framework of model of a generalized Brownian
motion and, hence, generatored thus cloud should have fractal structure.
It is known, that for cloudy structures of various types (including
atmospheric clouds and L-alpha forest clouds) the fractal dimension
also is close by 2.35. The hypothesis is expressed, that the value
of fractal dimension of a cloud is completely determined by cloudlet
mass modification character, and the constancy of fractal dimension
for clouds of various types is stipulated by proximity of the mass
increment laws of at clouds formation.
By reviewing all population of cloudlets the "microscopic"
exposition of moving is unsuitable. It is possible to describe a generalized
Brownian motion of an ensemble of particles as generalized diffusion
process with a time-dependent factor - the abnormal diffusion.
The connection of the law of cloudlet mass increase, process of the
abnormal diffusion of cloudlets properties and fractal dimension of
structures obtaining as a result of such process is considered. Is
shown, that the fractal dimensionality of formed clouds corresponds
to the "natural" mass increment law following from the supposition
about stochastic collisions of cloudlets.
6.5 Yousaf Butt, Cosmic Ray Acceleration
by Stellar Associations?
The HEGRA Cherenkov telescope array group recently reported a steady
and extended unidentified TeV gamma-ray source lying at the outskirts
of Cygnus OB2. This is the most massive stellar association known
in the Galaxy, estimated to contain ~2600 OB type members alone. It
has been previously argued that the large scale shocks and turbulence
in such associations may play a role in accelerating Galactic cosmic
rays. Indeed, Cyg OB2 also coincides with the MeV-GeV range unidentified
EGRET source, 3EG 2033+4118. We report on the near-simultaneous follow-up
observations of the extended TeV source region with the CHANDRA X-ray
Observatory and the Very Large Array (VLA) radio telescope obtained
in order to explore this possibility. Analysis of the CO, HI, and
IRAS 100 micron emissions shows that the TeV source region coincides
with an outlying sub-group of powerful OB stars which have evacuated
or destroyed much of the ambient atomic, molecular and dust material,
and which may be related to the very high-energy emissions. An interesting
SNR-like structure is also revealed near the TeV source region in
the CO, HI and radio emission maps. Applying a numerical simulation
which accurately
tracks the radio to gamma-ray emission from primary hadrons as well
as primary and secondary e±, we find that the broadband spectrum
of the TeV source region favors a predominantly nucleonic - rather
than electronic - origin of the high-energy flux, though deeper X-ray
and radio observations are needed to confirm this. A very reasonable,
~0.1%, conversion efficiency of Cyg OB2's extreme stellar wind mechanical
luminosity to nucleonic acceleration to ~PeV (10^15 eV) energies is
sufficient to explain the multifrequency emissions.
6.6 Gilberto C. Gomez, A Fake Galactic
Survey
We developed 3D MHD simulations of the large scale response of the
ISM to a spiral perturbation. We tested our results by generating
synthetic maps of the sky and comparing them with real observations.
We succesfully reproduced a variety of characteristics of the observed
l-v and v-b diagrams.
We then turn the procedure around. By placing an imaginary observer
inside this galaxy, we found the characteristics that he/she might
deduce from the observations, and compared them with the real behavior
of the gas in the simulations.
6.7 Antonio Luis Cabrera Lavers, Stellar
distribution of the Galactic disc from NIR color-magnitude diagrams
We analyze the stellar distribution of the Galactic disk via NIR
color-magnitude diagrams built from 2MASS data and the private CAIN-WIRE
survey. Extinction measurements in the K-band are also extracted from
the diagrams, both for supporting stellar counts predictions of the
Besançon and SKY models and for comparing with a three dimensional
model of Galactic extinction. The method is based on extracting a
well-known population from the CMDs (spectral type K2III), providing
a simple empirical way to obtain the stellar density and interstellar
extinction along a line of sight.
6.8 Antonio Luis Cabrera Lavers, Francisco Garzón,
Deep multicolor NIR survey of the Galactic Plane
We present a deep multicolor NIR survey that we are currently building
at the Instituto de Astrofísica de Canarias (Spain) using the
2D NIR camera CAIN at the 1.5m Carlos Sánchez Telescope (TCS).
Selected areas mostly distributed along the Galactic Plane, and some
other below and above it, are scanned with different integration times
to be background and/or confusion limited at J (1.2mm),
H(1.6mm) and K_short(2.1mm)
bands, with limiting magnitudes of 17, 16.5 and 15.2 respectively.
The aim of the survey is obtain deep star counts in some selected
areas to analyze the large scale structure of the Milky Way and some
galactic components, in particular the Galactic bar. We get more than
one magnitude deeper than in 2MASS and DENIS galactic surveys, and
even more in the inner Galaxy (as we are less limited by source confusion
effects) providing a better analysis of those regions where the extinction
is higher. Some of those global analysis are discussed in this contribution.
6.9 Rob Olling & Walter Dehnen, The
Oort Constants Measured from Proper Motions: Solid Evidence for
an Asymmetric Galactic Potential
The Oort constants describe the local variations of the stellar velocity
field. Classically, they can be determined from proper motion data.
We discuss various problems arising with this procedure. A large,
hitherto apparently overlooked, source of systematic error arises
from longitudinal variations of the mean stellar parallax, caused
by intrinsic density inhomogeneities and inter-stellar extinction.
Together with the reflex of the solar motion these variations by MODE
MIXING create contributions to the longitudinal proper motions mu_l(l)
that are indistinguishable from the Oort constants at the 20% level.
We discuss how to correct for this mode mixing using the latitudinal
proper motions mu_b(l). We use about 10^6 stars from the ACT/Tycho-2
catalogs with median proper motion error of ~3 mas/yr/star.
Our results deviate significantly from expectations based on a smooth
axisymmetric equilibrium models, most notably, the non-zero Oort-C
value for old red giant stars. We also find variations of the Oort
constants with the mean color, which correlate nicely with the asymmetric
drift. The latter correlation may indicate a linear dependence of
the Oort constants on time.
The most reliable tracers for the "true" Oort constants
are red giants, which are old enough to be in equilibrium and distant
enough to be unaffected by possible local anomalies. For these stars
we find, after correction for mode-mixing and asymmetric drift effects,
A ~16, B ~ -17, A-B ~ 33, and C ~ -10 km/s/kpc with errors of about1-2
km/s/kpc and external error of perhaps the same order. These values
are consistent with our knowledge of the Milky Way (flat rotation
curve and Omega=A-B ~ 28 +/- 2 km/s/kpc).
6.10 Tyler J. Foster, The Structure
and Rotation of the Outer Galaxy from Column Densities of Neutral Hydrogen
A model of the smooth large-scale distribution of neutral hydrogen
density with Galactocentric radius is presented, and applied to directions
into the plane of the outer Galaxy (longitude range 90 < l <
140). Our models apply to HI seen in emission, which principally traces
the smooth structure of the Galaxy. Non-axisymmetric model components
include the Galactic Warp, and spiral arms. The models trace the cumulative
column density N(HI) versus distance along the line of sight. We compare
the model to the observed N(HI) velocity distribution towards high
latitudes (b=7 degr.) and towards sight lines more directly into the
plane (b=1.7 degr.). We then demonstrate a remapping technique, whereby
the model is fit to the observed column density-versus-velocity relations
towards various lines of sight. The results of this yields the line
of sight velocity field, and Galactic structure parameters.
Applying this analysis to measure the rotation curve of the outer
Galaxy has several advantages, the most important being that we do
not assume that LOS velocities arise from purely circular rotation.
We observe that in the plane a flat rotation curve well describes
the motion of the gas locally (to within ~1.5 kpc), while beyond this
the Galaxy exhibits significant deviation from a flat rotation law.
However, as we observe to higher latitudes (b> 5 degr.) the Galaxy
returns to obeying a flat rotation curve (with R0=8 kpc and v0=220
km/s).
6.11 Ricardo R Munoz, Galactic Halo
6.12 Woong-Tae Kim, Eve C. Ostriker, and James
M. Stone, Magnetorotationally-Driven Galactic Turbulence and
the Formation of Giant Molecular Clouds
Giant molecular clouds (GMCs), where most stars form, may originate
fromself-gravitating instabilities in the interstellar medium. Using
local three-dimensional magnetohydrodynamic simulations, we investigate
ways in which galactic turbulence associated with the magnetorotational
instability (MRI) may influence the formation and properties of these
massive, self-gravitating, clouds. Our disk models are vertically
stratified with both gaseous and stellar gravity, and subject to uniform
shear corresponding to a flat rotation curve. Initial magnetic fields
are assumed to be weak and purely vertical. For simplicity, we adopt
an isothermal equation of state with sound speed $c_s=7\, {\rm km\,
s^{-1}}$. We find that MRI-driven turbulence develops rapidly, with
the saturated-state Shakura \& Sunyaev parameter $\alpha\sim(0.15-0.3)$
dominated by Maxwell stresses. Many of the dimensionless characteristics
of the turbulence (e.g. the ratio of the Maxwell to Reynolds stresses)
are similar to results from previous MRI studies of accretion disks,
hence insensitive to the degree of vertical disk compression, shear
rate, and the presence of self-gravity -- although self-gravity enhances
fluctuation amplitudes slightly. The density-weighted velocity dispersions
in non- or weakly self-gravitating disks are $\sigma_x\sim\sigma_y\sim(0.4-0.6)
c_s$ and $\sigma_z\sim(0.2-0.3)c_s$, suggesting that MRI can contribute
significantly to the observed level of galactic turbulence. The saturated-state
magnetic field strength $\bar B\sim2\mu$G is similar to typical galactic
values. When self-gravity is strong enough, MRI-driven high-amplitude
density perturbations are swing-amplified to form Jeans-mass ($\sim
10^7{\rm\,M_\odot}$) bound clouds. Compared to previous unmagnetized
or strongly-magnetized disk models, the threshold for nonlinear instability
in the present models occurs for surface densities at least 50\% lower,
corresponding to the Toomre parameter $\Qth\sim1.6$. We present evidence
that self-gravitating clouds like GMCs formed under conditions similar
to our models can lose much of their original spin angular momenta
by magnetic braking, preferentially via fields threading near-perpendicularly
to their spin axes. Finally, we discuss the present results within
the larger theoretical and observational context, outlining directions
for future study.
Session 7: Galactic Structure and Evolution
II: The Bar
Invited Review
7.0 Michael Merrifield, The Galactic
Bar
This talk will review the development of our knowledge of the central
bar in the Galaxy, drawing on both the photometric and kinematic data
available from the many extensive surveys of the Milky Way. The properties
of our own bar will be placed in the broader context of barred and
unbarred galaxies, and used to help understand how these systems form
and evolve.
Invited Talks
7.1 Peter Englmaier, Large-scale
Gas Dynamics in the Milky Way: Evidence for 2 Pattern Speeds
We present new gas flow models for the Milky Way inside the solar
circle. Using a mass model derived from the COBE/DIRBE maps and clump
giant star counts and using a parametric model for the spiral arm
pattern in the disk we calculate gas flow and compare to 12-CO observations.
We find that, models with 4 spiral arms fit the observations better
then 2-armed models. We also find, that models with separate pattern
speeds for the bar and spiral arms can explain the gas flow in the
bars corotation region better then single-pattern speed models.
7.2 Konrad Kuijken, Kinematics in the
galactic bulge/bar
Results will be presented from an ongoing HST/WFPC2 proper motion
programme of several galactic bulge fields. Proper motions for some
60,000 stars, with an accuracy better than 20 km/s at 8kpc distance,
have been obtained, and when combined with photometric parallaxes
clearly show a number of features; rotation of the bulge, separation
of disk and bulge populatons, velocity ellipsoid anisotropy, and vertical
velocity dispersion gradients that can be used to derive the vertical
potential gradient on the Galactic minor axis.
Poster Presentations
7.3 Roberta M. Humphreys, The Asymmetric
Thick Disk: A Star Count and Kinematic Analysis
We report a statistically significant asymmetry in the distribution
of thick disk and possibly inner halo stars in the inner region of
the Galaxy. We have compared the star counts in 120 POSS I fields,
40 each above and below the galactic plane in quadrant I with the
40 complementary fields above the plane in quadrant IV. We find a
spatially extended region in quadrant I with a significant excess,
20% to 25%, in the numbers of blue and intermediate colored stars.
While the region of the asymmetric distribution is somewhat irregular
in shape, it is also fairly uniform,
stretching over several hundred square degrees on the sky. It is therefore
a major substructure in the Galaxy due to more than small scale clumpiness
in the thick disk or inner halo. We present three possible explanations
for the asymmetry; the fossil remnant of a merger, a triaxial thick
disk or halo and interaction of the thick disk/inner halo stars with
the bar in the disk. To better understand the possible origin of this
asymmetric distribution we obtained spectra for classification and
velocities for over 700 stars in complemtary regions in quadrants
I and IV. The velocities reveal a clear kinematic signature associated
with the asymmetry feature. While the stars in quadrant IV show motions
close to what we would expect for the thick disk, those in quadrant
I are "lagging" behind their expected velcities. We therefore
conclude that the aymmetry can best be explained as an interaction
with a fast
rotating bar in the disk that induces a "gravitational wake"
trapping and piling up the stars.
7.4 Eduardo Brescansin de Amôres, Numerical
reproduction of longitude-velocity diagrams for the gas in the Galaxy
The longitude-velocity (l-v) diagrams of neutral and molecular hydrogen
constitute important tools for the study of the Galactic structure,
since they provide information about the distribution of the gas and
about the velocity field in the Galaxy. We constructed a model of
gas distribution in the Galaxy that reproduces the l-v diagrams of
both the neutral and molecular hydrogen. The model makes use of the
galactic rotation curve, and starts with a mean axis-symetric radial
distribution of gas. We add to this distribution density excess in
the form of logarithmic spirals, described by the following parameters:
starting point (galactocentric angle and radius), inclination angle,
length, width, and peak density. The arms are Gaussian distributions
in the radial direction, centered at the radius of the spiral. A procedure
has been developed that calculates the amount of gas along a line
of sight a a function of observed velocity, taking into account the
interception of arms, and therefore reproduces the observed spectra.
We compared the predicted spectra with those observed in HI and CO
surveys (Parkes, Leiden, NRAO and Berkeley surveys for HI, and Columbia
survey of CO), at intervals of 10 degrees in longitude. The direct
comparison of spectra complements the model construction of l-v diagrams.
With this procedure we obtained the terminal velocity as a function
of longitude, and we constructed 2D maps of the Galaxy as it would
be seen face-on, with the main spiral structure and details such as
bridges, bifurcations, and segments of arms.
Session 8: Galactic Structure and Evolution
III
Invited Reviews
8.0 Carl Heiles, Physical Properties
of the Galactic HI
We discuss the physical properties of the Galactic HI as gleaned
from measurements of the HI line in emission, absorption, and Zeeman
splitting.
8.1 Francesca Matteucci, The Chemical
Evolution of the Milky Way
I discuss the basic principles of galactic chemical evolution and
apply them to the evolution of the Milky Way. In particular, I present
model results concerning the halo, disk and bulge. From the comparison
of these results with observational constraints I derive some conclusions
on stellar nucleosynthesis, star formation history and timescales
for the formation of the different Galactic components.
Poster Presentations
8.3 Seth Digel and Isabelle Grenier
on behalf of the GLAST LAT collaboration, Modelling the Milky
Way in Gamma Rays for GLAST
The Milky Way is a bright, diffuse source of high-energy gamma rays
that are produced in cosmic-ray interactions with interstellar gas
and radiation. An accurate, detailed model of this emission will be
important for analysis of the data from the Large Area Telescope (LAT)
under development for launch by NASA on GLAST in 2006. The LAT will
study the sky in the 20 MeV-300 GeV energy range. Owing to its angular
resolution, ranging from 3 deg to 0.1 deg with energy, and because
of the limited photon statistics, a model of the pervasive interstellar
emission is needed in order to determine accurate positions for gamma-ray
point sources as well as to distinguish them from unresolved interstellar
clouds. The model will depend on surveys of neutral and ionized gas
and of continuum emission from the infrared through the optical. In
this poster, we will describe how the model will be developed and
what might be learned from LAT data about the interstellar medium
and radiation field of the Milky Way and cosmic-ray origin and propagation
in the light of results from the previous gamma-ray instrument, EGRET.
Regarding the astronomical inputs, the challenges in developing the
model include inverting spectral line surveys into 3-dimensional distributions
of gas, accounting for the cold neutral gas, and modelling the interstellar
radiation field. In addition models for the sources and propagation
of cosmic rays based on current theory will be required. None of these
issues is unique to the LAT model development, and our object is to
identify and adopt the best approaches.
8.4 Yuri N. Mishurov, Corotation resonance
and its influence on the galactic abundance distribution
We consider two effects of the corotation resonance on the features
of radial abundance distribution in the Galaxy: 1) due to peculiarity
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