Fossil Groups in the Sloan Digital Sky Survey

TL;DR

This study identifies and characterizes fossil galaxy groups in the Sloan Digital Sky Survey by combining optical and X-ray data, estimating their space density and properties.

Contribution

It introduces a novel method for detecting fossil groups using SDSS and ROSAT data, providing the first estimate of their space density.

Findings

34 candidate fossil groups identified

Estimated space density of fossil systems: (1.0 ± 0.6) × 10^{-6} h_{50}^3 Mpc^{-3}

Method combining optical and X-ray data proven effective

Abstract

A search for fossil groups in the Sloan Digital Sky Survey was performed using virtual observatory tools. A cross-match of the positions of all SDSS Luminous Red Galaxies (with r < 19 and measured spectroscopic redshifts) with sources in the ROSAT All-Sky Survey catalog resulted in a list of elliptical galaxies with extended X-ray emission (with a galaxy/ROSAT-source distance of less than 0.5 arcmin in all cases). A search for neighbors of the selected elliptical galaxies within a radius of $0.5 h_{70}^{-1}$ Mpc was conducted taking into account the r-band magnitudes and spectroscopic or photometric redshifts of all objects within this area, leading to a sample of 34 candidate fossil groups. Considering this sample, the estimated space density of fossil systems is $n =(1.0 \pm 0.6) \times 10^{-6}$ $h_{50}^3$ Mpc$^{-3}$.