Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published September 2007 | Published
Journal Article Open

The Cosmic Evolution Survey (COSMOS): A Large-Scale Structure at z = 0.73 and the Relation of Galaxy Morphologies to Local Environment


We 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 T_X = 3.51^(+0.60)_(-0.46) keV and L_X = (1.56 ± 0.04) × 10^(44) ergs s^(-1) (0.1-2.4 keV band). We estimate an X-ray mass within r_(500) corresponding to M_(500) ≃ 1.6 × 10^(14) M_⊙ and a total lensing mass (extrapolated by fitting a NFW profile) M_(NFW) = (6 ± 3) × 10^(15) M_⊙. We use an automated morphological classification of all galaxies brighter than I_(AB) = 24 over the structure area to measure the fraction of early-type objects as a function of local projected density Σ_(10), 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.

Additional Information

© 2007 The American Astronomical Society. Received 2006 April 27; accepted 2007 January 12. We gratefully acknowledge the contributions of the entire COSMOS collaboration consisting of more than 70 scientists. The HST COSMOS Treasury program was supported through NASA grant HST-GO-09822. The COSMOS Science Meeting in 2005 May was supported in part by the NSF through grant OISE-0456439. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the US (NASA). In Italy, the COSMOS project is supported by INAF under PRIN-2005/ and XMM-COSMOS is supported by INAF and MIUR under grants PRIN/270/2003 and Cofin-03-02-23 and by ASI under grant ASI/INAF I/023/05/0. In Germany, the XMM–Newton project is supported by the Bundesministerium für Bildung und Forschung/Deutsches Zentrum für Luft und Raumfahrt, the Max-Planck Society, and the Heidenhain-Stiftung. Part of this work was supported by the Deutsches Zentrum für Luft- und Raumfahrt, DLR project Nos. 50 OR 0207 and 50 OR 0405. L. G. thanks Claudio Firmani and Marco Scodeggio for enlightening discussions on galaxy evolution, Davide Lazzati for invaluable help with IDL routines, and Stefania Giodini for help with the mock samples.

Attached Files

Published - GUZapjss07.pdf


Files (2.0 MB)
Name Size Download all
2.0 MB Preview Download

Additional details

August 22, 2023
October 19, 2023