Star Formation in Disk Galaxies. II. The Effect of Star Formation and Photoelectric Heating on the Formation and Evolution of Giant Molecular Clouds

TL;DR

This study uses high-resolution galaxy simulations to examine how star formation and photoelectric heating influence giant molecular cloud formation, properties, and evolution, revealing environmental impacts on cloud dynamics and star formation rates.

Contribution

It demonstrates the significant role of diffuse photoelectric heating in shaping GMC properties and star formation, with detailed comparisons to observed cloud populations.

Findings

Photoelectric heating suppresses ISM fragmentation and alters cloud rotation.

Cloud lifetimes range from 0 to 20 Myr with high infant mortality.

Simulated cloud properties align with observations, but star formation rates are higher due to missing feedback.

Abstract

We investigate the effect of star formation and diffuse photoelectric heating on the properties of giant molecular clouds (GMCs) formed in high resolution (~< 10 pc) global (~ 20 kpc) simulations of isolated Milky Way-type galaxy disks. The clouds are formed through gravitational fragmentation and structures with densities n_H>=100cm^-3 are identified as GMCs. Between 1000-1500 clouds are created in the simulations with masses M > 10^5 Msolar and 180-240 with masses M > 10^6 Msolar in agreement with estimates of the Milky Way's population. We find that the effect of photoelectric heating is to suppress the fragmentation of the ISM, resulting in a filamentary structure in the warm gas surrounding clouds. This environment suppresses the formation of a retrograde rotating cloud population, with 88% of the clouds rotating prograde with respect to the galaxy after 300 Myr. The diffuse heating also reduces the initial star formation rate, slowing the conversation of gas into stars. We therefore conclude that the interstellar environment plays an important role in the GMCs evolution. Our clouds live between 0-20 Myr with a high infant mortality (t' < 3 Myr) due to cloud mergers and star formation. Other properties, including distributions of mass, size and surface density agree well with observations. Collisions between our clouds are common, occurring at a rate of ~1/4 of the orbital period. It is not clear whether such collisions trigger or suppress star formation at our current resolution. Our star formation rate is a factor of 10 higher than observations in local galaxies. This is likely due to the absence of localized feedback in our models.