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The Properties and Evolution of Star Forming Regions Over Cosmic Time

Presentation #333.06D in the session Molecular Clouds, HII Regions, and the ISM II.

Published onJun 29, 2022
The Properties and Evolution of Star Forming Regions Over Cosmic Time

Studying the progression of star formation is critical to understanding the regulation of galactic environments and the evolution of galaxies over cosmic time. Integral Field Spectrograph (IFS) observations of individual galaxies at high redshift, z~1-3, revealed unique kiloparsec-scale “clumps” of concentrated star formation. The relationships between clump size, luminosity, and velocity dispersion are often explored to provide insight into the processes driving clump formation, but the results have varied.

To investigate the source of these differences, I collated a comprehensive sample of local and high-z clumps with a wide range of properties. I developed a Bayesian Markov Chain Monte Carlo code to robustly explore the size-luminosity relationship (and multi-parameter relationships) of star-forming clumps while accounting for intrinsic scatter and measured uncertainties in both dimensions. I find neither evidence of redshift evolution nor selection biases influencing the scaling relationships. Instead, there is evidence of a break in the relationship based on the star formation rate surface density for both local and high-z star forming regions. The resulting differences in slope can be due to either differences in formation mode (Toomre vs. Jeans collapse) or in the geometry of the clump and host galaxy disk.

In order to constrain the size-luminosity scaling relationships on small scales, I observed a sample of compact HII regions in our nearest starburst galaxy, IC 10, with the Keck Cosmic Web Imager (KCWI) IFS. Earlier imaging of the HII regions indicated that they would follow the same scaling relationships, but with this unprecedented resolution IC 10’s HII regions are in fact offset to higher luminosity and velocity dispersion for a given size. The resolved kinematic information afforded by these observations shows that these HII regions are likely not virialized, and instead are young and expanding. Even in the most compact HII regions primarily ionized in some cases by single B stars, warm gas pressure caused by photoionization heating provides the dominant contribution to outward pressure and expansion of the HII regions. These observations at unprecedented few parsec resolution have provided more insight to the scaling relations as well as allowed for a unique and detailed study into the mechanisms of feedback in the starburst environment.

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