The Star Formation-Gas Density Relation in Four Galactic GMCs: Effects of Stellar Feedback

TL;DR

This study maps four galactic GMCs to analyze the relationship between gas density and star formation, considering stellar feedback effects, and compares findings with previous models to understand star formation processes.

Contribution

It provides new detailed maps of GMCs with LTE analysis, accounting for CO freeze-out, and explores the impact of stellar feedback on the gas density-star formation relation.

Findings

YSO surface density scales with gas surface density (exponent 0.9-1.9)

GMCs show power-law tails in gas column density PDFs

Mach number distributions suggest feedback influences turbulence levels

Abstract

We present maps of 4 galactic giant molecular clouds (GMCs) in the J=2-1 emission of both CO and $^{13}$CO. We use an LTE analysis to derive maps of the CO excitation temperature and column density and the distribution of total molecular gas column density, $\Sigma_{gas}$. The depletion of CO by freeze-out onto cold dust grains is accounted for by an approximation to the results of Lewis et al. (2021) which were derived from far-IR observations with {\it Herschel}. The surface density of young stellar objects (YSOs) is obtained from published catalogs. The mean YSO surface density exhibits a power-law dependence on $\Sigma_{gas}$, with exponents in the range 0.9 to 1.9. Gas column density probability distribution functions (PDFs) show power-law tails extending to high column densities. The distributions of sonic Mach number, $M_S$ are sharply peaked at $M_S \sim 5 - 8$ for 3 GMCs; a fourth has a broad distribution up to $M_S =30$, possibly a result of feedback effects from multiple OB stars. An analysis following the methodology of Pokhrel et al. (2021) finds that our sample of GMCs shows power-law relations that are somewhat shallower than found by Pokhrel et al. (2021) for the star formation rate vs. $<\Sigma_{gas}>$ and vs. $<\Sigma_{gas}>/t_{ff}$ in a different sample of clouds. We discuss possible differences in the two samples of star-forming clouds and the effects of stellar feedback on the relation between gas density and star formation rate.