The Properties of the Heterogeneous Shakhbazyan Groups of Galaxies in the SDSS - Astrophysics > Cosmology and Nongalactic AstrophysicsReport as inadecuate




The Properties of the Heterogeneous Shakhbazyan Groups of Galaxies in the SDSS - Astrophysics > Cosmology and Nongalactic Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: We present a systematic study of the sub-sample of Shakhbazyan groups SHKscovered by the Sloan Digital Sky Survey Data Release-5 SDSS-5. SHKs probe anenvironment with characteristics which are intermediate between those of looseand very compact groups. Surprisingly, we found that several groups identifyingalgorithms e.g. Berlind et al. 2006, Tago et al. 2008 miss this type ofstructures. Using the SDSS-5 spectroscopic data and the photometric redshiftsderived in D-Abrusco et al. 2007, we identified possible group members inphotometric redshift space and derived, for each group, several individualproperties. We also combined pointed and stacked Rosat All Sky Survey data toinvestigate the X-ray luminosities of these systems. Our study confirms thatthe majority of groups are physical entities with richness in the range 3-13galaxies, and properties ranging between those of loose and compact groups. Weconfirm that SHK groups are richer in early-type galaxies than the surroundingenvironment and the field, as expected from the morphology-density relation andfrom the selection of groups of red galaxies. Furthermore, our work supportsthe existence of two sub-classes of structures, the first one being formed bycompact and isolated groups and the second formed by extended structures. Wesuggest that while the first class of objects dwells in less dense regions likethe outer parts of clusters or the field, possibly sharing the properties ofHickson Compact Groups, the more extended structures represent a mixture ofcore+halo configurations and cores of rich clusters. X-ray luminosities forSHKs are generally consistent with these results and with the expectations forthe L X-sigma v relation, but also suggest the velocity dispersions reported inliterature are underestimated for some of the richest systems.



Author: D. Capozzi, E. De Filippis, M. Paolillo, R. D'Abrusco, G. Longo

Source: https://arxiv.org/



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