Evolution of smale scale systems of galaxies: X-ray detected E+S galaxy pairs
- Author(s)
- Ruth Grützbauch, Roberto Rampazzo, Ginevra Trinchieri, Werner Zeilinger
- Abstract
In the framework of a hierarchical evolutionary scenario, X-ray detected, mixed-morphology (E+S) galaxy pairs could represent a way station in the coalescence process of physical groups into isolated ellipticals. Since the merging timescales of bright group members are shorter than both, the merging timescales of the group's dwarf galaxy population and the cooling timescale of the X-ray halo of a rich group (Ponman et al 1994, Nature 369, 462), the result of the evolutionary path of a merging galaxy group could resemble an isolated elliptical with extended X-ray emission and a surrounding group-like dwarf galaxy population. Indeed, prototypical objects with these characteristics, supporting the evolutionary link between groups and giant ellipticals, are found (Mulchaey & Zabludoff 1999 ApJ 514, 133), but however, this link is far from being demonstrated. To illuminate the different phases of the coalescence process of groups, we started a study of mixed morphology galaxy pairs taken from the Reduzzi & Rampazzo (1995, Astr. Lett. Comm. 30, Nos. 1-6, 1) catalogue showing similar optical but very different X-ray characteristics. XMM-Newton observations show that two of the pairs from the sample are embedded in extended, group-like X-ray emission (r = 110 kpc for RR 143 and r = 134 kpc for RR 242), while for the other two pairs the L X/LB ratios of the individual members are consistent with the lowest X-ray-to-optical luminosity ratio objects, for which the emission is produced by the evolved stellar population (eg. considering the Ciotti et al (1991, ApJ 376, 380) models). In order to clarify whether the members of poor groups and pairs lie in a common gravitational potential, the X-ray data are complemented with optical observations using the wide field imager (WFI) at the 2.2m MPG/ESO telescope. The 34' × 33' frames centered on each pair were searched for a faint galaxy population possibly associated with the pair. The properties of this population may not only be connected to the pair's X-ray properties, its existence would also argue in favor of the evolutionary scenario described above. The presence of a large number of faint objects (as expected in X-ray detected poor groups) would influence the group's mass distribution and crossing and merging timescales and therefore the whole pair/group evolution. The candidate group member galaxies were selected using the SourceExtractor (Bertin & Arnouts 1996, AAS, 117, 393). To exclude possible background objects, we applied a color-restriction based on the color-magnitude relation of the Coma cluster. Surface photometry was performed on the resulting sample of ˜ 100 -170 candidates per pair using the gal fit algorithm (Peng et al 2002, AJ 124, 266). A one component Sersic law, where œ(r) ~ r1/n, was fitted to the galaxies' surface brightness profiles. As expected for dwarf galaxies, the distribution of sersic indices peaks at n ˜ 1. In order to compare the spatial distribution of this candidate group population with the extended X-ray emission, we compute the projected number density for each galaxy position (in galaxies Mpc -2) and construct an iso-density contour map for each pair (see Figure A 09). Œ 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- Osservatorio Astronomico, INAF Osservatorio Astronomico di Brera
- Journal
- Astronomische Nachrichten
- Volume
- 326
- Pages
- 492
- ISSN
- 0004-6337
- Publication date
- 2005
- Austrian Fields of Science 2012
- 103003 Astronomy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/9a295465-9957-4905-9c2e-e909ce551e15