Abstract
This project is the continuation of our study of faint Low Surface Brightness Galaxies (fLSBs) in one of the densest nearby galaxy regions known, the Coma cluster. Our goal is to improve our understanding of the nature of these objects by comparing the broad band spectral energy distribution with population synthesis models. The data were obtained with the MEGACAM and CFH12K cameras at the CFHT. We used the resulting photometry in 5 broad band filters (u*, B, V, R, and I), that included new u*-band data, to fit spectral models. With these spectral fits we inferred a cluster membership criterium, as well as the ages, dust extinctions, and photometric types of these fLSBs. We show that about half of the Coma cluster fLSBs have a spectral energy distribution well represented in our template library while the other half present a flux deficit at ultraviolet wavelengths. Among the well represented, ~80% are probably part of the Coma cluster based on their spectral energy distribution. They are relatively young (younger than 2.3 Gyrs for 90% of the sample) non-starburst objects. The later their type, the younger fLSBs are. A significant part of the fLSBs are quite dusty objects. fLSBs are low stellar mass objects (the later their type the less massive they are), with stellar masses comparable to globular clusters for the faintest ones. Their characteristics are correlated with infall directions, confirming the disruptive origin for part of them.
Highlights
Faint low surface brightness galaxies are a class of galaxies residing both in rich clusters and in the field
In the Adami et al (2006a) work based on B and R band data, we used statistical arguments and a comparison with blank fields to show that ∼95% of the detected Faint low surface brightness galaxies (fLSBs) were most probably members of the Coma cluster
Even if this result is consistent with a large fraction of the Best fit (BF) fLSBs being genuine Coma members, as previously demonstrated in Adami et al (2006a), the galaxies with a membership probability lower than 67% will be removed from the MS
Summary
Faint low surface brightness galaxies (fLSBs) are a class of galaxies residing both in rich clusters and in the field. This class of galaxies is defined on the basis of its R band total magnitude (MR ≥ −14) and its low surface brightness (R central surface brightness fainter than ∼24, see Adami et al 2006a for more details) While they are not detectable, their presence can strongly constrain both hierarchical galaxy formation and evolution and the amount of dark matter present in clusters The primordial galaxies lying on the CMR would make up the low mass tail of the galaxy mass distribution, as resulting from hierarchical galaxy formation in CDM models (see for example, White & Rees 1978; White & Frenk 1991).
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