Evolutionary properties of the low-luminosity galaxy population in the NGC5044 Group

TL;DR

This study investigates the properties and evolution of low-luminosity galaxies in the NGC 5044 Group, revealing their composition, star formation activity, metallicity, and age, and placing the group between galaxy clusters and looser galaxy clumps.

Contribution

It provides detailed multicolour photometry, morphological classification, and spectroscopic analysis of faint galaxies in NGC 5044, highlighting their evolutionary state and group environment influence.

Findings

Dwarf ellipticals and irregulars dominate the luminosity function.

Star formation activity is moderate and pervasive among dwarf ellipticals.

Dwarf ellipticals share sub-solar metallicity and are mostly old systems.

Abstract

With this third paper of a series we present Johnson-Gunn B,g,V,r,i,z multicolour photometry for 79 objects, including a significant fraction of the faintest galaxies around NGC5044, assessing group membership on the basis of apparent morphology and low-resolution optical spectroscopy to estimate redshift for 21 objects. Together, dE's and Im's provide the bulk of the galaxy luminosity function, around M(g)\sim-18.0, while the S0 and dSph components dominate, respectively, the bright and faint-end tails of the distribution. This special mix places the NGC 5044 group just "midway" between the high-density cosmic aggregation scale typical of galaxy clusters, and the low-density environment of looser galaxy clumps like our Local Group. The bright mass of the 136 member galaxies with available photometry and morphological classification, amounts to a total of 2.3x10^{12}M_sun while current SFR within the group turns to be about or higher than 23M_sun/yr. In this regard, a drift toward bluer integrated colours is found to be an issue for dE's pointing to a moderate but pervasive star-formation activity even among nominally "quiescent" stellar systems. Through Lick narrow-band index analysis, dwarf ellipticals are found to share a sub-solar metallicity (-1.0 < [Fe/H] <-0.5) with a clear decoupling between Iron and alpha elements, as already established also for high-mass systems. Both dE's and dS0's are consistent with an old age, about one Hubble time, although a possible bias, toward higher values of age, may be induced by the gas emission affecting the Hbeta strength.