L. Guzzo et al. 2007 ApJS 172 254 doi:10.1086/516588
L. Guzzo1,2,3, P. Cassata4,5, A. Finoguenov3, R. Massey6, N. Z. Scoville6,7, P. Capak6, R. S. Ellis6, B. Mobasher8, Y. Taniguchi9,10, D. Thompson6,11, M. Ajiki9, H. Aussel7,12, H. Böhringer3, M. Brusa3, D. Calzetti8, A. Comastri13, A. Franceschini4, G. Hasinger3, M. M. Kasliwal6, M. G. Kitzbichler2, J.-P. Kneib14, A. Koekemoer8, A. Leauthaud14, H. J. McCracken15, T. Murayama9, T. Nagao9, J. Rhodes6,16, D. B. Sanders7, S. Sasaki9, Y. Shioya9, L. Tasca2 and J. E. Taylor6
Show affiliationsWe have identified a large-scale structure at z
0.73 in the COSMOS field, coherently described by the distribution of galaxy photometric redshifts, an ACS weak-lensing convergence map, and the distribution of extended X-ray sources in a mosaic of XMM-Newton observations. The main peak seen in these maps corresponds to a rich cluster with TX = 3.51
keV and LX = (1.56 ± 0.04) × 1044 ergs s-1 (0.1-2.4 keV band). We estimate an X-ray mass within r500 corresponding to M500
1.6 × 1014 M
and a total lensing mass (extrapolated by fitting a NFW profile) MNFW = (6 ± 3) × 1015 M
. We use an automated morphological classification of all galaxies brighter than IAB = 24 over the structure area to measure the fraction of early-type objects as a function of local projected density Σ10, based on photometric redshifts derived from ground-based deep multiband photometry. We recover a robust morphology-density relation at this redshift, indicating, for comparable local densities, a smaller fraction of early-type galaxies than today. Interestingly, this difference is less strong at the highest densities and becomes more severe in intermediate environments. We also find, however, local "inversions" of the observed global relation, possibly driven by the large-scale environment. In particular, we find direct correspondence of a large concentration of disk galaxies to (the colder side of) a possible shock region detected in the X-ray temperature map and surface brightness distribution of the dominant cluster. We interpret this as potential evidence of shock-induced star formation in existing galaxy disks, during the ongoing merger between two subclusters. Our analysis reveals the value of combining various measures of the projected mass density to locate distant structures and their potential for elucidating the physical processes at work in the transformation of galaxy morphologies.
galaxies: clusters: general; galaxies: evolution; large-scale structure of universe; surveys
Issue 1 (2007 September)
Received 2006 April 27, accepted for publication 2007 January 12
L. Guzzo et al. 2007 ApJS 172 254
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