The detection and X-ray evolution of galaxy groups at high redshift |
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| Authors: | L R Jones I MHardy A Newsam K Mason |
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| Institution: | School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT; Department of Physics and Astronomy, The University, Southampton SO17 1BJ; Astrophysics Research Institute, Liverpool John Moores University, 12 Quays House, Egerton Wharf, Birkenhead CH41 1LD; Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT |
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| Abstract: | We describe some of the first X-ray detections of groups of galaxies at high redshifts ( z ～0.4) , based on the UK deep X-ray survey of McHardy et al. Combined with other deep ROSAT X-ray surveys with nearly complete optical identifications, we investigate the X-ray evolution of these systems. We find no evidence for evolution of the X-ray luminosity function up to z =0.5 at the low luminosities of groups of galaxies and poor clusters ( L X?1042.5 erg s-1) , although the small sample size precludes very accurate measurements. This result confirms and extends to lower luminosities current results based on surveys at brighter X-ray fluxes. The evolution of the X-ray luminosity function of these low-luminosity systems is more sensitive to the thermal history of the intragroup medium (IGM) than to cosmological parameters. Energy injection into the IGM (from, for example, supernovae or active galactic nuclei winds) is required to explain the X-ray properties of nearby groups. The observed lack of evolution suggests that the energy injection occurred at redshifts z >0.5 . |
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| Keywords: | galaxies: clusters: general X-rays: galaxies |
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