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:

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
intnumber Unique identification number of each source in the catalog.
image_tile
intnumberWhich of the 144 sub-image tiles contains this object. [Tile diagram]
RA
doubledegRight Ascension (J2000.0).
DEC
doubledegDeclination (J2000.0).
x_pix
doublenumberx pixel position on the sub-image tile.
y_pix
doublenumbery pixel position on the sub-image tile.
i_fwhm
doublepixelFWHM in pixels measured on the detection image indicated by auto_flag.
i_max
doubleuJyPeak flux in nJy measured on the detection image indicated by auto_flag.
i_star
doublenumberSextractor 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
doublemagTotal 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
doublemagOffset between 3" aperture magnitudes and the total magnitude. This is the apperture correction for the multi-color photometry.
auto_flag
doublenumberFlag 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
doublemagCFHT u* AB magnitude.
u_mag_err
doublemag1 Sigma error on CFHT u* AB magnitude.
B_mag
doublemagSubaru Bj AB magnitude.
B_mag_err
doublemag1 Sigma error on Subaru Bj AB magnitude.
V_mag
doublemagSubaru Vj AB magnitude.
V_mag_err
doublemag1 Sigma error on Subaru Vj AB magnitude.
g_mag
doublemagSubaru g+ AB magnitude.
g_mag_err
doublemag1 Sigma error on Subaru g+ AB magnitude.
r_mag
doublemagSubaru r+ AB magnitude.
r_mag_err
doublemag1 Sigma error on Subaru r+ AB magnitude.
i_mag
doublemagSubaru i+ AB magnitude.
i_mag_err
doublemag1 Sigma error on Subaru i+ AB magnitude.
z_mag
doublemagSubaru z+ AB magnitude.
z_mag_err
doublemag1 Sigma error on Subaru z+ AB magnitude.
K_mag
doublemagCTIO/KPNO Ks AB magnitude.
K_mag_err
doublemag1 Sigma error on CTIO/KPNO Ks AB magnitude.
i_cfht_mag
doublemagCFHT i* AB magnitude.
i_cfht_mag_err
doublemag1 Sigma error on CFHT i* AB magnitude.
u_sdss_mag
doublemagSDSS u AB magnitude.
u_sdss_mag_err
doublemag1 Sigma error on SDSS u AB magnitude.
g_sdss_mag
doublemagSDSS g AB magnitude.
g_sdss_err
doublemag1 Sigma error on SDSS g AB magnitude.
r_sdss_mag
doublemagSDSS r AB magnitude.
r_sdss_mag_err
doublemag1 Sigma error on SDSS r AB magnitude.
i_sdss_mag
doublemagSDSS i AB magnitude.
i_sdss_mag_err
doublemag1 Sigma error on SDSS i AB magnitude.
z_sdss_mag
doublemagSDSS z AB magnitude.
z_sdss_mag_err
doublemag1 Sigma error on SDSS z AB magnitude.
F814W_mag
doublemagHST F814W magnitude.
F814W_mag_err
doublemag1 Sigma error on HST F814W magnitude.
NB816_mag
doublemagSubaru NB816 magnitude.
NB816_mag_err
doublemag1 Sigma error on Subaru NB816 magnitude.
Ebv
doublenumbere(B-V) for this object position from Schlegel et al. (1998).
Zphot
doublenumberPhotometric Redshift from Mobasher et al. (2007).
Zerr_68_min
doublenumberMinimum photometric redshift at 68% probability.
Zerr_68_max
doublenumberMaximum photometric redshift at 68% probability.
Zerr_95_min
doublenumberMinimum photometric redshift at 95% probability.
Zerr_95_max
doublenumberMaximum photometric redshift at 95% probability.
Tphot
doublenumberPhotometric 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
doublenumberIntrinsic e(B-V) of the object estimated by the photometric redshift code. See Mobasher et al. (2007) for details.
Chisq
doublenumberChi-sq of best fit redshift and photometric type.
Nbands
doublenumberNumber of filters used for in the photometric redshift estimation.
Mv
doublemagAbsolute V band AB magnitude.
D95
doublenumberD95 parameter from Mobasher et al. (2007) Defined as the ratio of the 95% confidence interval to the best fit redshift.
logMass
doublenumberLog base 10 of the stellar mass in units of solar mass. See Mobasher et al. (2007) for more details.
star
doublenumberStar flag based on color and morphology from Capak et al. (2007). 0=Non-Star, 1=Star
B_mask
doublenumberThe 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
doublenumberThe 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
doublenumberThe 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
doublenumberThe 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_maskdoublenumberObject may be over de-blended or a false detection, see Capak et al. (2007) for details. 0=Good Detection, 1=Problematic Detection.