Collaborative Research: Understanding the extreme diversity of atomic hydrogen depletion times in galaxies

Stars form out of clouds of gas found in galaxies. Most of this gas is in the form of cold atoms of hydrogen, but before stars can form, this gas must undergo several chemical and physical processes that are poorly understood. The investigators leading this proposal will analyze data from both the NSF-funded Green Bank Telescope (GBT) and the Atacama Large Millimeter Array (ALMA), which can be used to measure the amounts of hydrogen gas in a broad sample of galaxies. They will use this to test how the depletion timescales of these gas reservoirs depend on other measured galaxy properties, placing important constraints on the growth of galaxies. At the same time, they will train undergraduate researchers in the techniques of radio astronomy. This program seeks to understand the differences in atomic hydrogen (HI) depletion times using the SDSS-IV’s Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) and HI-MaNGA (21cm follow-up for MaNGA) galaxy surveys to search for evidence of systematic variations due to (1) ionization/heating sources, (2) fractions of diffuse versus dense HI, and (3) internal motions (e.g., velocity dispersion and bulk non-rotational flows), all of which may alter the efficiency with which HI is processed. The investigators will add new data from the GBT and ALMA to quantify the molecular hydrogen (H2) fraction for a subset of galaxies to probe whether long HI depletion times are driven by inefficient H2 formation from HI or inefficient formation of stars out of H2. In parallel with these efforts, the investigator will use the GBT to fully complete the HI-MaNGA survey, improving its legacy value for the astronomical community. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.