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

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.Comment: 25 pages with 19 figure & 8 tables - To appear in the Monthly Notices of the Royal Astronomical Society (in press) See http://www.bo.astro.it/~eps/buz10602/10602.html for a complete overview of the projec

The anatomy of the NGC 5044 group - I. Group membership and dynamics

We use a combination of new AAOmega multi-object wide-field spectroscopic observations and literature data to define 111 spectroscopically confirmed members of the massive NGC 5044 group with M_B <= -13.5 mag, providing a three-fold increase in group members over previous analyses of this group. We find the group to have a dynamical mass of 9.2 x 10^13 solar masses, placing it on the border between rich groups and poor clusters. However, comparison to the L_x-sigma and L_x-mass relations shows it more closely follows cluster scaling relations. Using a combination of crossing time, X-ray contours and line-of-sight velocity profile we are able to preclude growth of the NGC 5044 group via major sub-group mergers within the last ~1 Gyr. While the majority of dynamical indicators for the group suggest it is virialised, we find evidence for a small, dynamically distinct sub-group at 1.4 Mpc from the group centre, suggesting that the NGC 5044 group is the dominant structure in its local environment, and is currently accreting smaller groups.Comment: 18 pages, 17 figures, accepted by MNRAS. Updated to match proof versio