The Faint End Slopes Of Galaxy Luminosity Functions In The COSMOS 2-Square Degree Field

TL;DR

This study analyzes the faint-end slope of galaxy luminosity functions in the COSMOS field, revealing how it varies with galaxy type and redshift, and providing insights into the population of faint dwarf galaxies.

Contribution

It presents the first detailed measurement of the faint-end slope of the V-band luminosity function across different galaxy spectral types and redshifts in the COSMOS survey.

Findings

Faint-end slope alpha ranges from -1.24 to -1.12 across redshifts.

Steeper slopes (~ -1.9) for starburst galaxies at low redshift.

Slopes become shallower (~ -0.5) for early-type galaxies at higher redshift.

Abstract

We examine the faint-end slope of the rest-frame V-band luminosity function (LF), with respect to galaxy spectral type, of field galaxies with redshift z<0.5, using a sample of 80,820 galaxies with photometric redshifts in the Cosmic Evolution Survey (COSMOS) field. For all galaxy spectral types combined, the LF slope, alpha, ranges from -1.24 to -1.12, from the lowest redshift bin to the highest. In the lowest redshift bin (0.02<z<0.1), where the magnitude limit is M(V) ~ -13, the slope ranges from ~ -1.1 for galaxies with early-type spectral energy distributions (SEDs), to ~ -1.9 for galaxies with low-extinction starburst SEDs. In each galaxy SED category (Ell, Sbc, Scd/Irr, and starburst), the faint-end slopes grow shallower with increasing redshift; in the highest redshift bin (0.4<z<0.5), the slope is ~ -0.5 and ~ -1.3 for early-types and starbursts respectively. The steepness of alpha at lower redshift could be qualitatively explained by large numbers of faint dwarf galaxies, perhaps of low surface brightness, which are not detected at higher redshifts.