S-COSMOS Overview

S-COSMOS is a deep infrared imaging survey carried out with the Spitzer Space Telescope. The survey covers the entire 2 square degrees of the Cosmic Evolution Survey (COSMOS) field. The S-COSMOS and COSMOS projects are closely coupled; therefore, their data are served as one large COSMOS Archive using IRSA's general search service, Atlas. S-COSMOS is part of the Spitzer Legacy Program. The data products released are part of the Spitzer General Observer Cycle 2 (GO2) program, including predominantly IRAC products (images and catalog). MIPS data include shallow images/catalogs covering the entire COSMOS field. There are also deep MIPS images covering only a test field of 0.16 sq. degrees for the upcoming GO3 program. The GO3 products will become public in September 2008.

S-COSMOS IRAC Photometry Catalog Definitions

Gator serves the S-COSMOS IRAC 4-channel Photometry Catalog June 2007
(56 columns [51 delivered + 5 IRSA-created], 345,512 data rows).

Please refer to the IRAC data delivery README file for general information on S-COSMOS catalogs and images.

Please read the following notes on the catalog (from README file); column descriptions are listed below.


Notes on the catalog.
(1) The catalog includes photometry in the 4 IRAC channels for all those sources 
     that have a measured flux in IRAC Channel 1 above 1 uJy [micro-Jansky].
     In the catalog, this flux is listed in column #16, "flux_c1_1".
(2) The first 15 columns are standard outputs (Astrometric and geometric  
     parameters) of SExstractor (http://terapix.iap.fr/IMG/pdf/sextractor.pdf)
(3) The following corrections (flux_catalog/correction) should be applied to each
     channel/aperture, in order to obtain the total flux:

         1.4''   1.9''   2.9''   4.1''  

 ch1    0.610   0.765   0.900   0.950
 ch2    0.590   0.740   0.900   0.940
 ch3    0.490   0.625   0.840   0.940
 ch4    0.450   0.580   0.730   0.910

(4) For very faint sources (roughly 4% of the catalog), measured fluxes  
    in the larger apertures will be reported with a negative number or  
    have lower fluxes than those measured in the smaller apertures.  
    These are objects lying near much brighter objects that compromise  
    measurement of the background. Despite the poorer flux measures,  
    these sources have been retained in the catalog since their infrared  
    detections are nonetheless real. For accurate photometry we advise  
    that flux_c#_2 be used whenever it is larger than flux_c#_3 and  
    flux_c#_4 (where #=1,2,3,4 is the IRAC channel number).

(5) Objects close to bright stars or close to the border of the images,
    do not have reliable  measured flux.  Values in flag columns #24 (fl_c1), 
    #33 (fl_c2), #42 (fl_c3) and #51 (fl_c4) indicate whether a source is close
    to a bright star (1 and 2) or not (0). All sources with flag=0 in all the
    4 channels are reliable.   

 (6) Flux errors are computed by SExtractor using an uncertainty map and 
     setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma 
     errors. [Uncertainty maps are created per IRAC channel as part of 
     generating the image mosaics, using MOPEX.]
     
 (7) To go from flux in uJy to AB magnitude, please use:
 
	 -2.5 log(flux) + 23.9
	 
     To go from flux in uJy to Vega magnitude, use:
     
	 -2.5 log (flux) + 23.9 + K
	 
     where K depends on the channel:	
     
          ch 1:   K = -2.788
          ch 2:   K = -3.255
          ch 3:   K = -3.743
          ch 4:   K = -4.372

Column Name Data Type Units Description
id integer n/a unique IRAC 3.6um ID number
xcoo float pixels X coordinates in pixels on IRAC 3.6um mosaic
ycoo float pixels Y coordinates in pixels on IRAC 3.6um mosaic
bkg float uJy [micro-Jansky] Background at centroid position
thresh float uJy [micro-Jansky] Detection threshold
flux_max float uJy [micro-Jansky] Peak flux
ra float degrees Right ascension of barycenter (J2000), as defined in the SExtractor manual.
dec float degrees Declination of barycenter (J2000), as defined in the SExtractor manual.
cxx float pix-2 SExtractor Cxx object ellipse parameter, where cxx, cyy and cxy are used to express the ellipse parameterisation
cyy float pix-2 SExtractor Cyy object ellipse parameter, where cxx, cyy and cxy are used to express the ellipse parameterisation
cxy float pix-2 SExtractor Cxy object ellipse parameter, where cxx, cyy and cxy are used to express the ellipse parameterisation
a float pix SExtractor profile RMS along major axis of the ellipse shape better defining the isophotal profile of the object. a, b, and theta are used to express another set of ellipse parameters.
b float pix SExtractor profile RMS along minor axis of the ellipse shape better defining the isophotal profile of the object. a, b, and theta are used to express another set of ellipse parameters.
theta float degrees SExtractor position angle (counter-clockwise from the X-axis). a, b, and theta are used to express another set of ellipse parameters.
flag integer n/a SExtractor flag (See SExtractor manual) FLAGS contain, coded in additive numbers, all the extraction flags as a sum of powers of 2:
1 The object has neighbours, bright and close enough to 
  significantly bias the MAG AUTO photometry or bad 
  pixels (more than 10% of the integrated area affected),

2 The object was originally blended with another one,

4 At least one pixel of the object is saturated (or very close to),

8 The object is truncated (too close to an image boundary),

16 Object's aperture data are incomplete or corrupted,

32 Object's isophotal data are incomplete or corrupted

64 A memory overflow occurred during deblending,

128 A memory overflow occurred during extraction.
flux_c1_1 float uJy [micro-Jansky] Flux at 3.6um in 1.4" aperture. Divide by 0.610 in order to obtain total flux.
err_c1_1 float uJy [micro-Jansky] Error margin of flux_c1_1. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c1_2 float uJy [micro-Jansky] Flux at 3.6um in 1.9" aperture. Divide by 0.765 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c1_2 float uJy [micro-Jansky] Error margin of flux_c1_2. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c1_3 float uJy [micro-Jansky] Flux at 3.6um in 2.9" aperture. Divide by 0.900 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c1_3 float uJy [micro-Jansky] Error margin of flux_c1_3. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c1_4 float uJy [micro-Jansky] Flux at 3.6um in 4.1" aperture. Divide by 0.950 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c1_4 float uJy [micro-Jansky] Error margin of flux_c1_4. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
fl_c1 integer n/a To improve the detection of blended objects, an agressive detection method using a Mexican hat filter was employed. A drawback of this technique is that it produces many false sources at the borders of bright stars. In order to label these spurious detections, masks have been created at the locations of 2MASS point sources brighter than K=14. IRAC detections that are in a non-masked region are assigned flag=0. An IRAC detection falling into the masked area of a 2MASS object brighter than K=14 is considered a true detection and replaced with its detection using a Gaussian filter instead. Such sources are flagged with 1 or 2; flag=1 for 10
flux_c2_1 float uJy [micro-Jansky] Flux at 4.5um in 1.4" aperture. Divide by 0.590 in order to obtain total flux.
err_c2_1 float uJy [micro-Jansky] Error margin of flux_c2_1. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c2_2 float uJy [micro-Jansky] Flux at 4.5um in 1.9" aperture. Divide by 0.740 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c2_2 float uJy [micro-Jansky] Error margin of flux_c2_2. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c2_3 float uJy [micro-Jansky] Flux at 4.5um in 2.9" aperture. Divide by 0.900 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c2_3 float uJy [micro-Jansky] Error margin of flux_c2_3. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c2_4 float uJy [micro-Jansky] Flux at 4.5um in 4.1" aperture. Divide by 0.940 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c2_4 float uJy [micro-Jansky] Error margin of flux_c2_4. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
fl_c2 integer n/a Data quality flag in 4.5um image (0 = good data, 1-2 = object in masked region). See descrption for "fl_c1" for details on flags.
flux_c3_1 float uJy [micro-Jansky] Flux at 5.8um in 1.4" aperture. Divide by 0.490 in order to obtain total flux.
err_c3_1 float uJy [micro-Jansky] Error margin of flux_c3_1. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c3_2 float uJy [micro-Jansky] Flux at 5.8um in 1.9" aperture. Divide by 0.625 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c3_2 float uJy [micro-Jansky] Error margin of flux_c3_2. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c3_3 float uJy [micro-Jansky] Flux at 5.8um in 2.9" aperture. Divide by 0.840 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c3_3 float uJy [micro-Jansky] Error margin of flux_c3_3. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c3_4 float uJy [micro-Jansky] Flux at 5.8um in 4.1" aperture. Divide by 0.940 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c3_4 float uJy [micro-Jansky] Error margin of flux_c3_4. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
fl_c3 integer n/a Data quality flag in 5.8um image (0 = good data, 1-2 = object in masked region). See descrption for "fl_c1" for details on flags.
flux_c4_1 float uJy [micro-Jansky] Flux at 8.0um in 1.4" aperture. Divide by 0.450 in order to obtain total flux.
err_c4_1 float uJy [micro-Jansky] Error margin of flux_c4_1. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c4_2 float uJy [micro-Jansky] Flux at 8.0um in 1.9" aperture. Divide by 0.580 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c4_2 float uJy [micro-Jansky] Error margin of flux_c4_2. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c4_3 float uJy [micro-Jansky] Flux at 8.0um in 2.9" aperture. Divide by 0.730 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c4_3 float uJy [micro-Jansky] Error margin of flux_c4_3. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
flux_c4_4 float uJy [micro-Jansky] Flux at 8.0um in 4.1" aperture. Divide by 0.910 in order to obtain total flux. Please see Note #4 regarding catalog fluxes in apertures 2, 3 and 4, above.
err_c4_4 float uJy [micro-Jansky] Error margin of flux_c4_4. Error is computed by SExtractor using an uncertainty map and setting the MAP_WEIGHT parameter. The weighting is performed for 1 sigma errors. [Uncertainty maps are created per IRAC channel as part of generating the image mosaics, using MOPEX.]
fl_c4 integer n/a Data quality flag in 8.0um image (0 = good data, 1-2 = object in masked region). See descrption for "fl_c1" for details on flags.