A. Buzzoni, S. A. Cellone, P. Saracco, E. Zucca
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.
View original:
http://arxiv.org/abs/1112.4493
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