Cloud and Star Formation in Disk Galaxy Models with Feedback

TL;DR

This study uses hydrodynamic simulations with feedback mechanisms to analyze star formation, gas dynamics, and cloud properties in galactic disks, revealing how feedback influences turbulence, cloud formation, and star formation rates.

Contribution

It introduces a feedback implementation in cloud-scale star formation models, showing how feedback affects turbulence, cloud mass, and star formation efficiency in galactic disks.

Findings

Feedback reduces dense gas fraction and star formation rate.

Cloud cutoff masses are consistent with observations (~a few million solar masses).

Star formation rate surface density scales with gas surface density with an index ~2.

Abstract

We include feedback in global hydrodynamic simulations in order to study the star formation properties, and gas structure and dynamics, in models of galactic disks. We extend previous models by implementing feedback in gravitationally bound clouds: momentum is injected at a rate proportional to the star formation rate. This mechanical energy disperses cloud gas back into the surrounding ISM, truncating star formation in a given cloud, and raising the overall level of ambient turbulence. Propagating star formation can however occur as expanding shells collide, enhancing the density and triggering new cloud and star formation. By controlling the momentum injection per massive star and the specific star formation rate in dense gas, we find that the negative effects of high turbulence outweigh the positive ones, and in net feedback reduces the fraction of dense gas and thus the overall star formation rate. The properties of the large clouds that form are not, however, very sensitive to feedback, with cutoff masses of a few million solar masses, similar to observations. We find a relationship between the star formation rate surface density and the gas surface density with a power law index ~2 for our models with the largest dynamic range, consistent with theoretical expectations for our model of disk flaring. We point out that the value of the "Kennicutt-Schmidt" index depends on the thickness of the disk. With our simple feedback prescription (a single combined star formation event per cloud), we find that global spiral patterns are not sustained; less correlated feedback and smaller scale turbulence appear to be necessary for spiral patterns to persist.