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

John H. Bieging and Shuo Kong

Submitted on 9 September 2022


We present maps of 4 galactic giant molecular clouds (GMCs) in the J=2-1 emission of both CO and 13CO. 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, Σgas. 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 Σgas, 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, MS are sharply peaked at MS58 for 3 GMCs; a fourth has a broad distribution up to MS=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. <Σgas> and vs. <Σgas>/tff 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.


Comment: 15 figures, 3 tables, accepted by ApJ

Subject: Astrophysics - Astrophysics of Galaxies