S-COSMOS IRAC GO2 Delivery   
27May2007
O. Ilbert + M.Salvato + S-COSMOS team 

I. Basic Information

Telescope:             Spitzer
Instrument:            IRAC
PI:                    David B. Sanders
Program Title:         SCOSMOS
Program ID:            20070
IRAC Bands:            3.6, 4.5, 5.8 amd 8 um
SSC Software Version:  S14.0.0
See SSC website for S14.0 data issues and Calibration.

II. Products

READme                       (this file)
IRAC_0407_IRSA.tbl         catalog for sources having total flux in 3.6um >1uJ [uJ]
irac_ch1_gO2_sci.fits      3.6um image  [MJ/sr] 
irac_ch1_g02_cov.fits      3.6um coverage map [MJ/sr]
irac_ch1_g02_unc.fits      3.6um uncertainty map
irac_ch2_gO2_sci.fits      4.5um image [MJ/sr]
irac_ch2_g02_cov.fits      4.5um coverage map[MJ/sr]
irac_ch2_g02_unc.fits      4.5um uncertainty map
irac_ch3_gO2_sci.fits      5.8um image [MJ/sr]
irac_ch3_g02_cov.fits      5.8um coverage map[MJ/sr]
irac_ch3_g02_unc.fits      5.8um uncertainty map
irac_ch4_gO2_sci.fits      8.0um image [MJ/sr]
irac_ch4_g02_cov.fits      8.0um coverage map[MJ/sr]
irac_ch4_g02_unc.fits      8.0um uncertainty map



Columns of the catalog:
    

 1             ID                      unique IRAC 3.6um ID number      null
 2           Xcoo     X coordinates in pixels on IRAC 3.6um mosaic       pix
 3           Ycoo     Y coordinates in pixels on IRAC 3.6um mosaic       pix
 4            BKG                  Background at centroid position        uJ
 5         Thresh             Detection threshold above background        uJ
 6       flux_max                       Peak flux above background        uJ
 7        RA_2000            Right ascension of barycenter (J2000)       deg
 8       DEC_2000                Declination of barycenter (J2000)       deg
 9            CXX                     Cxx object ellipse parameter    x^(-2)
10            CYY                     Cyy object ellipse parameter    x^(-2)
11            CXY                     Cxy object ellipse parameter    x^(-2)
12              A                     Profile RMS along major axis       pix
13              B                     Profile RMS along minor axis       pix
14          Theta                           Position angle (CCW/x)       deg
15           FLAG                                  SExtractor flag      null
16      flux_c1_1                  Flux  in 3.6um in 1.4" aperture        uJ
17       err_c1_1                                            error        uJ
18      flux_c1_2                  Flux  in 3.6um in 1.9" aperture        uJ
19       err_c1_2                                            error        uJ
20      flux_c1_3                  Flux  in 3.6um in 2.9" aperture        uJ
21       err_c1_3                                            error        uJ
22      flux_c1_4                  Flux  in 3.6um in 4.1" aperture        uJ
23       err_c1_4                                           error         uJ
24          fl_c1                 data quality flag in 3.6um image      null
25      flux_c2_1                  Flux  in 4.5um in 1.4" aperture        uJ
26       err_c2_1                                            error        uJ
27      flux_c2_2                  Flux  in 4.5um in 1.9" aperture        uJ
28       err_c2_2                                            error        uJ
29      flux_c2_3                  Flux  in 4.5um in 2.9" aperture        uJ
30       err_c2_3                                            error        uJ
31      flux_c2_4                  Flux  in 4.5um in 4.1" aperture        uJ
32       err_c2_4                                            error        uJ
33          fl_c2                 data qiality flag in 4.5um image      null
34      flux_c3_1                  Flux  in 5.8um in 1.4" aperture        uJ
35       err_c3_1                                            error        uJ
36      flux_c3_2                  Flux  in 5.8um in 1.9" aperture        uJ
37       err_c3_2                                            error        uJ
38      flux_c3_3                  Flux  in 5.8um in 2.9" aperture        uJ
39       err_c3_3                                            error        uJ
40      flux_c3_4                  Flux  in 5.8um in 4.1" aperture        uJ
41       err_c3_4                                            error        uJ
42          fl_c3                 data quality flag in 5.8um image      null
43      flux_c4_1                  Flux  in 8.0um in 1.4" aperture        uJ
44       err_c4_1                                           error         uJ
45      flux_c4_2                  Flux  in 8.0um in 1.9" aperture        uJ
46       err_c4_2                                           error         uJ
47      flux_c4_3                  Flux  in 8.0um in 2.9" aperture        uJ
48       err_c4_3                                           error         uJ
49      flux_c4_4                  Flux  in 8.0um in 4.1" aperture        uJ
50       err_c4_4                                        error on         uJ
51          fl_c4                      quality flag in 8.0um image      null



Notes on the images 
(1) Images are color corrected
(2) images are in MJ/sr, pixel scale of 0.6"/px: they are dithered with a factor of 0.65
(3) The astrometry has as an accuracy of 0.5" (2MASS catalog used as reference)
(4) To transform the images in  uJ/pix  the conversion factor  8.4616 has been used.


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.   

     Note on Flags:
     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<K<14 and flag=2 for K<10.  The latter case is more unreliable 
     as the background is more strongly affected by saturated stars.  In IRAC  
     channels 2,3 and 4, objects can also be assigned flag=2 if they fall out 
     of the observed region (past the image borders).  The project advises
     against using objects with flag=2.  For objects with flag=1, it should be 
     noted that the source characterization step (with a Gaussian filter) is 
     different from that in the full catalog (done with a Mexican hat filter).

 (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 microns to AB magnitude, please use:

         -2.5 log(flux) + 23.9

     To go from flux in microns 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