Contributed Talk - Splinter Stars

Tuesday, 14 September 2021, 09:20   (virtual Stars)

A systematic determination of the evolutionary timescale of successive phases of star formation and gas dispersal by stellar feedback

Jaeyeon Kim
Heidelberg University

Stars form in the densest regions of molecular clouds. Recent theoretical works show that, quickly after the onset of star formation, giant molecular clouds are effectively disrupted by feedback from massive stars in the form of photoionisation, winds, supernovae, and radiation pressure, exposing the young stellar population. However, how and when these newly born clusters emerge from their natal gas, terminating embedded phase of star formation, is still observationally ill-constrained. We apply a recently developed statistical method to six nearby galaxies using CO, Spitzer 24mic, and Halpha emission as tracers of the molecular clouds, embedded star formation, and exposed star formation, respectively, with the goal of measuring how long massive stellar populations remain embedded within their natal cloud. We find that the embedded phase of star formation, composed of a heavily obscured and partially exposed phase, lasts for 2-7 Myr, constituting 20-40% of the cloud lifetime. The duration of the heavily obscured phase of star formation (with visible CO and 24mic emission, but no Halpha emission detected) is found to be relatively constant among our sample of galaxies, with an average of 2.9 +/-0.9 Myr. The duration of the partially exposed star-forming phase (with visible CO, 24mic, and Halpha emission) varies more significantly, ranging from 1 to 5 Myr. At the end of this phase, the molecular clouds are destroyed by stellar feedback from young massive stars, leaving 24mic emission to be detectable for another 1-6 Myr. The short duration between the onset of massive star formation and cloud disruption suggests that pre-supernova feedback such as photoionization and winds from massive stars is important in disrupting molecular clouds. The duration of each phase we measure does not show statistically significant correlations with galactic environments such as metallicity, molecular gas, and star formation rate surface density. In the near future with MIRI onboard JWST, the method will be applied to 19 main sequence galaxies from PHANGS, allowing us to explore the first stages of star formation in a much wider range of galaxy properties.