COSMOS Galaxy and X-ray Group Membership Catalogs

Matt George

Current version: see IRSA for the official versions of these catalogs, where they will be available for the long term.

*** Last updated 2011 November 15

The catalogs have been updated with some changes to column names to follow IRSA formatting guidelines (z->redshift, *MMGG_SCALE*->*MMMGs*, proj_dist*->dist*, Mstar*->SM*). Sorry if that breaks your code - you might try the ALIAS option with mrdfits in IDL if you don't want to adopt the new column names. Also, a column (MMGGS_ZBEST) that was inadvertantly missing from the previous version has been added - it gives the MMGGscale flag for the "zbest" selection (i.e. spectroscopic redshifts replacing photo-zs when available). Thanks to Viola Allevato for catching that. The rest of the content in the catalogs is unchanged so I'm calling this version "20110914a".



There are two catalogs in this release, one for group properties and one for galaxy properties. Information is drawn from a number of sources:

We consider galaxies with MAG_AUTO<24.2 (ACS F814W band) and groups with z<1. The galaxy magnitude cut is set by the K-band completeness limit of ~24 since a detection is required for stellar mass estimates. Photoz uncertainties also rise steeply beyond this magnitude.

The galaxy catalog contains ACS photometric parameters, stellar masses, photoz information, and group membership associations. The group catalog contains X-ray properties, lensing-calibrated masses, quality flags, aggregate member galaxy statistics, and coordinates for the center of each group.

We expect that this is the version of the catalog that will be made publicly available at IRSA. Please let us know if you find problems or have suggested changes to be made.

Reading Files

The catalogs are in the FITS binary table format with data stored in the first extension. I/O packages for reading this file format are available in a variety of languages including IDL, C, and Python.

As an example, to read the catalogs in IDL:

group_file = "/path/to/catalogs/cosmos_xgroups_20110914a_public.fits"
group = mrdfits(group_file, 1)
gal_file = "/path/to/catalogs/cosmos_xgroup_galaxies_20110914a_public.fits"
gal = mrdfits(gal_file, 1)

To check the contents of these data structures in IDL once they have been loaded:

help, group, /str
help, gal, /str

Version History