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Published January 1, 2010 | Published
Journal Article Open

The Density Field of the 10k zCOSMOS Galaxies


We use the current sample of ~10,000 zCOSMOS spectra of sources selected with I_(AB) < 22.5 to define the density field out to z ~ 1, with much greater resolution in the radial dimension than has been possible with either photometric redshifts or weak lensing. We present the new algorithm that we have developed (ZADE) to incorporate objects not yet observed spectroscopically by modifying their photometric redshift probability distributions using the spectroscopic redshifts of nearby galaxies. We present a number of tests on mock catalogs used to justify this approach. The ZADE algorithm allows us to probe a broader range of galaxy environments and reduce the Poisson noise in the density field. The reconstructed overdensity field of the 10k zCOSMOS galaxies consists of cluster-like patterns surrounded by void-like regions, extending up to z ~ 1. Some of these structures are very large, spanning the ~50 h^(–1) Mpc transverse direction of the COSMOS field and extending up to Δz ~ 0.05 in redshift. We present the three-dimensional overdensity maps and compare the reconstructed overdensity field to the independently identified virialized groups of galaxies and clusters detected in the visible and in X-rays. The distribution of the overdense structures is in general well traced by these virialized structures. A comparison of the large-scale structures in the zCOSMOS data and in the mock catalogs reveals an excellent agreement between the fractions of the volume enclosed in structures of all sizes above a given overdensity between the data and the mocks in 0.2 < z < 1, although in the data these overdense regions are in generally larger contiguous structures.

Additional Information

© 2010 American Astronomical Society. Print publication: Issue 1 (2010 January 1); received 2008 November 28; accepted for publication 2009 November 10; Published 2009 December 14. This work has been supported in part by a grant from the Swiss National Science Foundation and by grant ASI/COFIS/WP3110I/026/07/0. We thank M. G. Kitzbichler and S. D. M. White for providing themock catalogs (Kitzbichler & White 2007).

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Published - Kovac2010p6759Astrophys_J.pdf


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