Physical properties and scaling relations of molecular clouds: the impact of star formation

Abstract

Using hydrodynamical simulations of a Milky Way-like galaxy, reaching 4.6 pc resolution, we study how the choice of star formation criteria impacts both galactic and Giant Molecular Clouds (GMC) scales. We find that using a turbulent, self-gravitating star formation criteria leads to an increase in the fraction of gas with densities between 10 and $10^{4}{\, \rm {cm^{-3}}}$ when compared with a simulation using a molecular star formation method, despite both having nearly identical gaseous and stellar morphologies. Furthermore, we find that the site of star formation is effected with the the former tending to only produce stars in regions of very high density ($>10^{4}{\, \rm {cm^{-3}}}$) gas while the latter forms stars along the entire length of its spiral arms. The properties of GMCs are impacted by the choice of star formation criteria with the former method producing larger clouds. Despite the differences we find that the relationships between clouds properties, such as the Larson relations, remain unaffected. Finally, the scatter in the measured star formation efficiency per free-fall time of GMCs remains present with both methods and is thus set by other factors.

Giant molecular cloud catalogues for PHANGS-ALMA: methods and initial results

“…Guszejnov et al (2020) further showed that, in their simulation set, these GMC scaling relationships and distributions of properties exhibited little variation for an isolated galaxy over cosmic time. More recent work has also proposed using variations in the scaling relationships and mass distributions to critically evaluate the star formation models in the star-forming clouds (Fujimoto et al 2019;Grisdale 2021;Li et al 2020) In this work, as well as S18 and Sun et al (2020b), we have identified variations in cloud properties with environment that can be used as additional points of comparison with simulations. In uniformly characterizing GMCs across several galaxies, we find a range of cloud properties and modest changes in the scaling relationships that can give context to any discrepancies between simulations and the canonical cloud population.…”

The Life and Times of Giant Molecular Clouds

“…Simulations of idealized, isolated GMCs tend to find somewhat higher ff , in some cases where feedback is ineffective reaching values as high as in the earlier pre-feedback simulations (Grudić et al 2018), but simulations using initial surface densities, virial parameters, and magnetic field strengths comparable to those of observed GMCs tend to give ff 0.1 (Kim et al 2021b). Simulations of GMCs embedded in full galactic simulations, which capture environmental effects but at the price of lower resolution and heavier reliance on subgrid treatments of feedback, generally give median values of ff ∼ 0.01, albeit with scatters of ∼ 0.5 dex (Semenov et al 2016;Grisdale et al 2019;Grisdale 2021).…”

On the viability of determining galaxy properties from observations – I. Star formation rates and kinematics

“…bursty SFR is expected for the star formation prescription employed in NEWHORIZON (see Grisdale 2021 ). At the time of our analysis ( z = 2) G1 is undergoing a small burst in SFR , we note that despite this burst the galaxy is not a 'starburst' galaxy.…”