The Star Formation Demographics of Galaxies in the Local Volume

TL;DR

This study investigates how star formation activity correlates with galaxy properties like luminosity, mass, and morphology in the Local Volume, revealing characteristic transitions linked to galaxy type and size.

Contribution

It identifies two key transition points in galaxy properties related to star formation, providing insights into the physical processes regulating star formation across different galaxy types.

Findings

Star-forming galaxies show two characteristic transitions in luminosity and velocity.

A narrowing of the galaxy locus occurs at specific luminosity and velocity thresholds.

The mean specific star formation rate remains constant between the two transitions.

Abstract

We examine the connections between the current global star formation activity, luminosity, dynamical mass and morphology of galaxies in the Local Volume, using H-alpha data from the 11 Mpc H-alpha and Ultraviolet Galaxy Survey (11HUGS). Taking the equivalent width (EW) of the H-alpha emission line as a tracer of the specific star formation rate, we analyze the distribution of galaxies in the M_B-EW and rotational velocity (V_{max})-EW planes. Star-forming galaxies show two characteristic transitions in these planes. A narrowing of the galaxy locus occurs at M_B~-15 and V_{max}~50 km/s, where the scatter in the logarithmic EWs drops by a factor of two as the luminosities/masses increase, and galaxy morphologies shift from predominately irregular to late-type spiral. Another transition occurs at M_B~-19 and V_{max}~120 km/s, above which the sequence turns off toward lower EWs and becomes mostly populated by intermediate and early-type bulge-prominent spirals. Between these two transitions, the mean logarithmic EW appears to remain constant at 30 A. We comment on how these features reflect established empirical relationships, and provide clues for identifying the large-scale physical processes that both drive and regulate star formation, with emphasis on the low-mass galaxies that dominate our approximately volume-limited sample.