Galex/COSMOS Prior-based Photometry Catalog Definitions

COSMOS Overview

The COSMOS Archive serves data taken for the Cosmic Evolution Survey (COSMOS) project. COSMOS is an astronomical survey designed to probe the formation and evolution of galaxies as a function of cosmic time (redshift) and large scale structural environment. The survey covers a 2 square degree equatorial field with imaging by most of the major space-based telescopes (Hubble, Spitzer, GALEX, XMM, Chandra) and a number of large ground based telescopes (Subaru, VLA, ESO-VLT, UKIRT, NOAO, CFHT, and others).

IRSA serves the COSMOS archive using the following search methods:

GALEX/COSMOS Prior-based Photometry Catalog, version 3

This catalog was created using u*-band priors and the EM-algorithm. Appropriate references for a description of the method are:

Guillaume, M., Llebaria A., Aymeric, D., Arnouts, S., & Milliard, B. 2006, Proceedings of the SPIE, Volume 6064, pp. 332-341

This is the current reference, and contains all the basics of the method and algorithm. A more specific reference for this catalog will be available soon.

Zamojski, Arnouts, Vibert, Schiminovich & Milliard (2008, in preparation)

The algorithm was run on the four NUV and the four FUV GALEX images covering the COSMOS field. It was run on the "-int" images (intensity maps) obtained as a product of the GALEX pipeline processing, version 1.61.

The u*-band mosaic image and SExtractor catalog used as priors in this run were generously provided by Henry McCracken (IAP) and are based on CFHT-u* observations of the COSMOS field. These are NOT included with the release. People interested in the priors should contact both Henry and myself for more information.

GALEX/COSMOS Prior-based Photometry Catalog Column Definitions

Gator serves the COSMOS June 2008 Galex Catalog (27 columns [23 delivered + 5 IRSA-created], 414,924 data rows). The column descriptions can be found below.

Column Name Data Type Units Description
NUMBER int   ID of the object in the u*-band prior catalog. This is NOT the same as the ID in the general COSMOS photometry catalog.
ra float degrees Right ascension J2000
dec float degrees Declination J2000
POINTING_NUV int   NUV image from which the photometry was measured (GALEX covers the COSMOS field in 4 pointings)
POINTING_FUV int   FUV image from which the photometry was measured (GALEX covers the COSMOS field in 4 pointings)
X_NUV float pixels X position of object in the NUV image (1 pixel ~ 1.5")
X_FUV float pixels X position of object in the FUV image (1 pixel ~ 1.5")
Y_NUV float pixels Y position of object in the NUV image (1 pixel ~ 1.5")
Y_FUV float pixels Y position of object in the FUV image (1 pixel ~ 1.5")
BKG_NUV float counts/s Level of the NUV background around object
BKG_FUV float counts/s Level of the FUV background around object
FLUX_NUV float counts/s Measured NUV flux of the object
FLUX_FUV float counts/s Measured FUV flux of the object
FLUXERR_NUV float counts/s Error in the NUV flux measurement
FLUXERR_FUV float counts/s Error in the FUV flux measurement
MAG_NUV float   NUV AB-magnitude corresponding to the measured flux
MAG_FUV float   FUV AB-magnitude corresponding to the measured flux
MERR_NUV float   NUV magnitude error
MERR_FUV float   FUV magnitude error
MAG_PRIOR float   u*-band magnitude used as prior to start the iterative algorithm. This is a MAG_AUTO with additional deblending, and can differ from the u*-band aperture magnitude in the general COSMOS photometry catalog.
MASK_NUV int   0 means ok. 1 means that the photometry of the object could be problematic due to either a nearby bright object, or image defects.
MASK_FUV int   0 means ok. 1 means that the photometry of the object could be problematic due to either a nearby bright object, or image defects.
CLASS_STAR float   SExtractor output parameter from u*-band prior catalog. Objects with a CLASS_STAR > 0.8 were modeled with a simple PSF whereas the ones with a CLASS_STAR < 0.8 were modeled with a profile based on their u*-band image convolved with the GALEX PSF.