The Nature of Fossil Galaxy Groups: Are They Really Fossils?

La Barbera, F.; de Carvalho, R. R.; de la Rosa, I. G.; Sorrentino, G.; Gal, R. R.; Kohl-Moreira, J. L.
Bibliographical reference

The Astronomical Journal, Volume 137, Issue 4, pp. 3942-3960 (2009).

Advertised on:
4
2009
Number of authors
6
IAC number of authors
1
Citations
45
Refereed citations
42
Description
We use SDSS-DR4 photometric and spectroscopic data out to redshift z ~ 0.1 combined with ROSAT All Sky Survey X-ray data to produce a sample of 25 fossil groups (FGs), defined as bound systems dominated by a single, luminous elliptical galaxy with extended X-ray emission. We examine possible biases introduced by varying the parameters used to define the sample, and the main pitfalls are also discussed. The spatial density of FGs, estimated via the V/V MAX test, is 2.83 × 10-6 h 3 75 Mpc-3 for LX > 0.89 × 1042 h -2 75 erg s-1 consistent with Vikhlinin et al., who examined an X-ray overluminous elliptical galaxy sample (OLEG). We compare the general properties of FGs identified here with a sample of bright field ellipticals generated from the same data set. These two samples show no differences in the distribution of neighboring faint galaxy density excess, distance from the red sequence in the color-magnitude diagram, and structural parameters such as a 4 and internal color gradients. Furthermore, examination of stellar populations shows that our 25 FGs have similar ages, metallicities, and α-enhancement as the bright field ellipticals, undermining the idea that these systems represent fossils of a physical mechanism that occurred at high redshift. Our study reveals no difference between FGs and field ellipticals, suggesting that FGs might not be a distinct family of true fossils, but rather the final stage of mass assembly in the universe.
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Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology
We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.
Ignacio
Martín Navarro