Galaxy And Mass Assembly (GAMA): Bivariate functions of H$\alpha$ star forming galaxies

TL;DR

This study derives bivariate luminosity and stellar mass functions of Hα star forming galaxies from the GAMA survey, correcting for observational biases and revealing that a significant fraction of red galaxies are dusty star formers.

Contribution

It introduces a method to correct for missing optically faint star forming galaxies and provides the first comprehensive bivariate functions for GAMA Hα star forming galaxies.

Findings

20-30% of red galaxies are star forming, indicating dusty star formation.

The derived functions help estimate local star formation and stellar mass densities.

The sample includes both blue and red galaxy populations, mostly blue.

Abstract

We present bivariate luminosity and stellar mass functions of H$\alpha$ star forming galaxies drawn from the Galaxy And Mass Assembly (GAMA) survey. While optically deep spectroscopic observations of GAMA over a wide sky area enable the detection of a large number of $0.001<{SFR}_{H\alpha}$ (M$_{\odot}$ yr$^{-1}$)$<100$ galaxies, the requirement for an H$\alpha$ detection in targets selected from an $r$-band magnitude limited survey leads to an incompleteness due to missing optically faint star forming galaxies. Using $z<0.1$ bivariate distributions as a reference we model the higher-$z$ distributions, thereby approximating a correction for the missing optically faint star forming galaxies to the local SFR and stellar mass densities. Furthermore, we obtain the $r$-band LFs and stellar mass functions of H$\alpha$ star forming galaxies from the bivariate LFs. As our sample is selected on the basis of detected H$\alpha$ emission, a direct tracer of on-going star formation, this sample represents a true star forming galaxy sample, and is drawn from both photometrically classified blue and red sub-populations, though mostly from the blue population. On average 20-30% of red galaxies at all stellar masses are star forming, implying that these galaxies may be dusty star forming systems.