Post-Starbursts as Laboratories: Probing Star Formation Quenching and Late Phases of Stellar Evolution with NIRWALS

Galaxies can be thought of as star forming "factories," where various processes (e.g., density waves, tidal forces, mergers, gas inflows) act to create regions of dense, gravitationally unstable gas, which subsequently fragment and collapse into stars. Depending on the specific process involved, this could result in a fairly constant star formation rate (SFR) or in an intense but short- lived episode, largely confined to the galaxy's nucleus and often accompanied by gas accreting onto a supermassive blackhole. Starburst galaxies are examples of the latter. In extreme cases the starburst is followed by a lengthy 'post-starburst' phase in which star formation is largely extinguished or 'quenched.' The principal investigator (PI) will lead a team investigating this quenching in a large sample of local post-starburst galaxies using a near-infrared (NIR) integral field spectrograph. Improved stellar evolution models will also be tested. The proposed work will also provide research experience and training for undergraduate students, provide material for a PhD thesis, and deliver a large astronomical dataset to the public domain. The team will observe a sample of 50 post-starburst galaxies using a new NIR integral-field spectrograph (NIRWALS) on the 11-meter Southern African Large Telescope (SALT). A key question is whether star formation quenching is caused by a lowered SFE or if it is caused by the violent blow-out of gas by supernova and/or or accreting supermassive blackholes. NIR hydrogen Paschen emission lines will be used to measure accurate star formation rates, with SFE estimated in combination with existing CO data. NIR emission lines of helium, sulfur, and iron will be used to reveal shocked gas and to determine if central supermassive blackholes actively inject energy into the gas. The team will compare post-starburst galaxies’ starlight to predictions of new stellar evolutionary synthesis models. These models include improved treatment of the late stages of stellar evolution that dominate the NIR emission of stellar populations between 0.5 to 2 billion years old (roughly the post-burst age of the observed galaxies). Correctly calibrating these models is critical for understanding the build-up of stellar mass in galaxies over cosmic time. 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.