Finding Distant Ionized Gas Clouds and Using them to Explore our Milky Way Galaxy
Stars with masses greater than ten times that of our Sun shine for only about 10 million years before they detonate in titanic supernova explosions that spew into space heavy elements forged by nuclear reactions in their cores. During their lives, massive stars ionize the gas that surrounds them, creating an ionized hydrogen (H II) region. Professor Thomas Bania, former BU graduate students Loren Anderson (an assistant professor at West Virginia University) and Dana Balser (a staff scientist at NRAO), and Robert Rood (University of Virginia, deceased) have used the Green Bank Telescope (GBT, operated by the National Radio Astronomy Observatory, NRAO), to discover previously unknown H II regions in distant locations inside our Milky Way Galaxy. During FY13, Professor Bania and collaborators have extended the survey to search for HII regions in the newly discovered Outer Scutum-Centarus (OSC) Arm.
In order to detect fainter H II regions, Prof. Bania’s team migrated the H II Region Discovery Survey (HRDS) to the Arecibo Observatory (operated by the National Astronomy and Ionospheric Center), the largest radio telescope in the world (1000 feet in diameter). The technique that they employ is to search for hydrogen-recombination lines in the spectra of candidate H II regions that were beyond the reach of the GBT. Professor Bania’s team has discovered more than 600 regions in the Milky Way where massive stars form, more than doubling the number of such known regions. The newly discovered regions include the most distant sites of massive-star formation known in the Milky Way. Future generations of stars and planets form from massive stars. This census changes our view of how the chemical elements that massive stars produce enrich interstellar space. This new census provides targets for observational studies of galactic chemical evolution that will be made by NSF-supported instruments such as the Karl Jansky Very Large Array (VLA) and the Atacama Large Millimeter Array (ALMA).