Dariush, Ali A. and Raychaudhury, Somak and Ponman, Trevor J. and Khosroshahi, Habib G. and Benson, Andrew J. and Bower, Richard G. and Pearce, Frazer (2010) The mass assembly of galaxy groups and the evolution of the magnitude gap. Monthly Notices of the Royal Astronomical Society, 405 (3). pp. 1873-1887. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20100714-144515261
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We investigate the assembly of groups and clusters of galaxies using the Millennium dark matter simulation and the associated Millennium gas simulations, and semi-analytic catalogues of galaxies. In particular, in order to find an observable quantity that could be used to identify early-formed groups, we study the development of the difference in magnitude between their brightest galaxies to assess the use of magnitude gaps as possible indicators.We select galaxy groups and clusters at redshift z = 1 with dark matter halo mass M(R_(200)) ≥ 10^(13) h ^(−1)M_⊙, and trace their properties until the present time (z = 0). We consider only the systems with X-ray luminosity L_(X,bol) ≥ 0.25 × 10^(42) h ^(−2) erg s^(−1) at redshift z = 0. While it is true that a large magnitude gap between the two brightest galaxies of a particular group often indicates that a large fraction of its mass was assembled at an early epoch, it is not a necessary condition. More than 90 per cent of fossil groups defined on the basis of their magnitude gaps (at any epoch between 0 < z < 1) cease to be fossils within 4 Gyr, mostly because other massive galaxies are assembled within their cores, even though most of the mass in their haloes might have been assembled at early times. We show that compared to the conventional definition of fossil galaxy groups based on the magnitude gap Δm_(12) ≥ 2 (in the R-band, within 0.5R_(200) of the centre of the group), an alternative criterion Δm_(14) ≥ 2.5 (within the same radius) finds 50 per cent more early-formed systems, and those that on average retain their fossil phase longer. However, the conventional criterion performs marginally better at finding earlyformed groups at the high-mass end of groups. Nevertheless, both criteria fail to identify a majority of the early-formed systems.
|Additional Information:||© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 February 20. Received 2010 January 16; in original form 2009 November 2. The Millennium simulations used in this paper was carried out by the Virgo Supercomputing Consortium at the Computing Center of the Max-Planck Society in Garching. The semi-analytic galaxy catalogues used in this study are publicly available at http://galaxycatalogue. dur.ac.uk:8080/MyMillennium/. The Millennium Gas Simulations were carried out at the Nottingham HPC facility, as was much of the analysis required by this work. The SDSS-DR4 group catalogue of Yang et al. (2007) used in this study is publicly available at http://www.astro.umass.edu/xhyang/Group.html. AAD gratefully acknowledges Graham Smith, Malcolm Bremer and the anonymous referee for helpful discussions. The 2dFGRS group catalogue data (Yang et al. 2005, 2007) used in this study was kindly provided by Frank C. van den Bosch and X. Yang.|
|Subject Keywords:||hydrodynamics; methods: numerical; galaxies: formation; galaxies: kinematics and dynamics; cosmology: theory|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||05 Aug 2010 17:58|
|Last Modified:||26 Dec 2012 12:14|
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