COSMOS 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:

Spatial search on all images and small catalogs, using Atlas
Advanced search on only the larger catalogs, using Gator

COSMOS I band catalog

This is an I band selected multi-color catalog for 2 square degrees centered on the COSMOS field at 10:00:28.6, +02:12:21. A detailed description of the catalog is given in Capak et. al. (2007) and it is recomended that you read this paper before using the catalog.

The total magnitude (SExtractor mag_auto) for a source must have an AB magnitude of less than i+<25 to appear in the archival catalog. All photometry is in the AB magnitude system and measured in a 3 arc second aperture on PSF-matched images unless otherwise noted. A magnitude of -99 indicates a photometric measurement was not possible due to lack of data, a large number of bad pixels, or saturation. A magnitude of 99.0 indicates no detection. In the case of no detection the error given for the object is the 1 sigma limiting magnitude at the position of the souce.

The photometry is as measured on the images with no corrections applied. We recommend applying the magnitude offsets in Capak et. al. (2007) to obtain the best possible photometry. More details on the photometry are available in Capak et. al. (2007). The Photometric Redshifts included in this catalog are described in Mobasher et al. (2007) and have an accuracy of dz/(1+z)<0.031 at z<1.2 and I<24.

It is important to pay attention to the flag columns at the end of the catalog. The cleanest catalog will have all flags set to 0. The photometry flags indicate the area of the photometry aperture, in square arc seconds, which is in a masked region. A flag of 1 indicates 14 percent of the aperture is masked, so any flagged object should be carefully checked. Objects with a de-blending flag set to 1 are potentially spurious and should not be used for statistical studies. However, the photometry for real sources with a de-blending flag set to 1 is good if they fall outside of masked region.

COSMOS Photometry Catalog Column Definitions

Gator serves the COSMOS January 2006 Photometry Catalog (68 columns [63 delivered + 5 IRSA-created], 438,226 data rows). The column descriptions can be found below.

Column Name	Data Type	Units	Description
ID	int	number	Unique identification number of each source in the catalog.
image_tile	int	number	Which of the 144 sub-image tiles contains this object. [Tile diagram]
RA	double	deg	Right Ascension (J2000.0).
DEC	double	deg	Declination (J2000.0).
x_pix	double	number	x pixel position on the sub-image tile.
y_pix	double	number	y pixel position on the sub-image tile.
i_fwhm	double	pixel	FWHM in pixels measured on the detection image indicated by auto_flag.
i_max	double	uJy	Peak flux in nJy measured on the detection image indicated by auto_flag.
i_star	double	number	Sextractor stellarity parameter measured on the detection image indicated by auto_flag. See Bertin and Arnouts (1996) for a detailed description of this parameter.
i_mag_auto	double	mag	Total i-band magnitude measured on the detection image indicated by auto_flag. The total magnitude given is the mag_auto parameter from SExtractor. See Bertin and Arnouts (1996) for a detailed description of this parameter.
auto_offset	double	mag	Offset between 3" aperture magnitudes and the total magnitude. This is the apperture correction for the multi-color photometry.
auto_flag	double	number	Flag indicating which image the total magnitude (i_mag_auto) was measured from. 1=Subaru i+, 2=CFHT i*, -1=No valid total magnitude
u_mag	double	mag	CFHT u* AB magnitude.
u_mag_err	double	mag	1 Sigma error on CFHT u* AB magnitude.
B_mag	double	mag	Subaru Bj AB magnitude.
B_mag_err	double	mag	1 Sigma error on Subaru Bj AB magnitude.
V_mag	double	mag	Subaru Vj AB magnitude.
V_mag_err	double	mag	1 Sigma error on Subaru Vj AB magnitude.
g_mag	double	mag	Subaru g+ AB magnitude.
g_mag_err	double	mag	1 Sigma error on Subaru g+ AB magnitude.
r_mag	double	mag	Subaru r+ AB magnitude.
r_mag_err	double	mag	1 Sigma error on Subaru r+ AB magnitude.
i_mag	double	mag	Subaru i+ AB magnitude.
i_mag_err	double	mag	1 Sigma error on Subaru i+ AB magnitude.
z_mag	double	mag	Subaru z+ AB magnitude.
z_mag_err	double	mag	1 Sigma error on Subaru z+ AB magnitude.
K_mag	double	mag	CTIO/KPNO Ks AB magnitude.
K_mag_err	double	mag	1 Sigma error on CTIO/KPNO Ks AB magnitude.
i_cfht_mag	double	mag	CFHT i* AB magnitude.
i_cfht_mag_err	double	mag	1 Sigma error on CFHT i* AB magnitude.
u_sdss_mag	double	mag	SDSS u AB magnitude.
u_sdss_mag_err	double	mag	1 Sigma error on SDSS u AB magnitude.
g_sdss_mag	double	mag	SDSS g AB magnitude.
g_sdss_err	double	mag	1 Sigma error on SDSS g AB magnitude.
r_sdss_mag	double	mag	SDSS r AB magnitude.
r_sdss_mag_err	double	mag	1 Sigma error on SDSS r AB magnitude.
i_sdss_mag	double	mag	SDSS i AB magnitude.
i_sdss_mag_err	double	mag	1 Sigma error on SDSS i AB magnitude.
z_sdss_mag	double	mag	SDSS z AB magnitude.
z_sdss_mag_err	double	mag	1 Sigma error on SDSS z AB magnitude.
F814W_mag	double	mag	HST F814W magnitude.
F814W_mag_err	double	mag	1 Sigma error on HST F814W magnitude.
NB816_mag	double	mag	Subaru NB816 magnitude.
NB816_mag_err	double	mag	1 Sigma error on Subaru NB816 magnitude.
Ebv	double	number	e(B-V) for this object position from Schlegel et al. (1998).
Zphot	double	number	Photometric Redshift from Mobasher et al. (2007).
Zerr_68_min	double	number	Minimum photometric redshift at 68% probability.
Zerr_68_max	double	number	Maximum photometric redshift at 68% probability.
Zerr_95_min	double	number	Minimum photometric redshift at 95% probability.
Zerr_95_max	double	number	Maximum photometric redshift at 95% probability.
Tphot	double	number	Photometric type of the object as described in Mobasher et al. (2007). 1=El, 2=Sbc, 3=Scd, 4=Irr, 5=SB3, 6=SB2 Non integer values indicate a type between the integer types.
Rphot	double	number	Intrinsic e(B-V) of the object estimated by the photometric redshift code. See Mobasher et al. (2007) for details.
Chisq	double	number	Chi-sq of best fit redshift and photometric type.
Nbands	double	number	Number of filters used for in the photometric redshift estimation.
Mv	double	mag	Absolute V band AB magnitude.
D95	double	number	D95 parameter from Mobasher et al. (2007) Defined as the ratio of the 95% confidence interval to the best fit redshift.
logMass	double	number	Log base 10 of the stellar mass in units of solar mass. See Mobasher et al. (2007) for more details.
star	double	number	Star flag based on color and morphology from Capak et al. (2007). 0=Non-Star, 1=Star
B_mask	double	number	The area of the photometry aperture in square arc seconds which falls into a masked area on the Bj image. Please refer to the text above for more information on masks and flags.
V_mask	double	number	The area of the photometry aperture in square arc seconds which falls into a masked area on the Vj image. Please refer to the text above for more information on masks and flags.
i_mask	double	number	The area of the photometry aperture in square arc seconds which falls into a masked area on the i+ image. Please refer to the text above for more information on masks and flags.
z_mask	double	number	The area of the photometry aperture in square arc seconds which falls into a masked area on the z+ image. Please refer to the text above for more information on masks and flags.
blend_mask	double	number	Object may be over de-blended or a false detection, see Capak et al. (2007) for details. 0=Good Detection, 1=Problematic Detection.