Properties of Bulgeless Disk Galaxies II. Star Formation as a Function of Circular Velocity

TL;DR

This study investigates the relationship between gas surface density and star formation rate in bulgeless disk galaxies, finding no change in star formation efficiency across a range of circular velocities, challenging previous assumptions about disk stability effects.

Contribution

It provides new evidence that star formation efficiency does not depend on disk stability or dust scale height in bulgeless galaxies, contrary to prior findings.

Findings

No transition in star formation efficiency at v_circ = 120 km/s.

Star formation efficiency is consistent across 46-190 km/s circular velocities.

Disk stability and dust structure do not significantly influence star formation in these galaxies.

Abstract

We study the relation between the surface density of gas and star formation rate in twenty moderately-inclined, bulgeless disk galaxies (Sd-Sdm Hubble types) using CO(1-0) data from the IRAM 30m telescope, HI emission line data from the VLA/EVLA, H-alpha data from the MDM Observatory, and PAH emission data derived from Spitzer IRAC observations. We specifically investigate the efficiency of star formation as a function of circular velocity (v_circ). Previous work found that the vertical dust structure and disk stability of edge-on, bulgeless disk galaxies transition from diffuse dust lanes with large scale heights and gravitationally-stable disks at v_circ < 120 km/s (M_star <~ 10^10 M_sun) to narrow dust lanes with small scale heights and gravitationally-unstable disks at v_circ > 120 km/s. We find no transition in star formation efficiency (Sigma_SFR/Sigma_HI+H2) at v_circ = 120 km/s, or at any other circular velocity probed by our sample (v_circ = 46 - 190 km/s). Contrary to previous work, we find no transition in disk stability at any circular velocity in our sample. Assuming our sample has the same dust structure transition as the edge-on sample, our results demonstrate that scale height differences in the cold interstellar medium of bulgeless disk galaxies do not significantly affect the molecular fraction or star formation efficiency. This may indicate that star formation is primarily affected by physical processes that act on smaller scales than the dust scale height, which lends support to local star formation models.