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

星系可以被认为是恒星形成的“工厂”，在那里，各种过程（如密度波、潮汐力、合并、气体流入）产生了密集的、引力不稳定的气体区域，这些气体随后分裂并坍缩成恒星。根据所涉及的具体过程，这可能导致一个相当恒定的恒星形成速率（SFR）或一个强烈但短暂的事件，主要局限于星系的核心，通常伴随着气体吸积到一个超大质量黑洞上。星爆星系就是后者的例子。在极端情况下，星暴之后是一个漫长的“后星暴”阶段，在这个阶段，恒星的形成基本上是熄灭或“熄灭”的。首席研究员（PI）将带领一个团队使用近红外（NIR）积分场光谱仪在当地大样本的星暴后星系中研究这种淬灭。改进的恒星演化模型也将被测试。拟议的工作还将为本科生提供研究经验和培训，为博士论文提供材料，并向公共领域提供大型天文数据集。该团队将使用11米南非大望远镜（SALT）上的新型近红外积分场光谱仪（NIRWALS）观察50个星暴后星系的样本。一个关键的问题是，恒星形成的猝灭是由较低的SFE引起的，还是由超新星和/或吸积的超大质量黑洞猛烈喷出的气体引起的。近红外氢Paschen发射线将用于测量精确的恒星形成速率，并结合现有的CO数据估计SFE。氦、硫和铁的近红外发射线将被用来揭示激波气体，并确定中央超大质量黑洞是否主动向气体注入能量。该团队将比较星暴后星系的星光与新恒星进化合成模型的预测。这些模型包括对恒星演化后期的改进处理，这些演化后期主导着5亿至20亿年前（大约是观测到的星系爆发后的年龄）恒星群的近红外辐射。正确校准这些模型对于理解星系中恒星质量在宇宙时间内的积累至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.