Status report on analysis of stars in SXDS

Michael Richmond
Aug 9, 2007

For earlier reports in this series, see

My goal is to perform in the SXDS field the same analysis I did for the SDF:

The earlier reports provide many of the details of this procedure. This very short report describes results after updating the Subaru catalogs to incorporate changes to the V-band measurements only.

Third version of catalog based on stellar locus

I have finished my third version of analysis on the SXDS, using a new set of catalogs. These were kindly provided by Tomoki Morokuma on July 26, 2007. The new set differ from the previous ones only in a re-reduction of the V-band images. All the information in the other bands is identical with previous versions. When I examined the stellar locus of the new material, I found that it shifted very slightly due to the new V-band information. The shift is roughly equivalent to a zero-point change in the V-band magnitudes of

     new V-band mag   ~=   old V-band mag  +  0.040

The MD5 checksums for these new versions of the catalogs are

114524 -rw-rw-r--  1 richmond richmond 117149021 Jul 26 00:14 e45c62629de1562de82630a7b19c0b1f
111376 -rw-rw-r--  1 richmond richmond 113924188 Jul 26 00:14 37cc32628723ba29befa3e90c00ffdd8
118608 -rw-rw-r--  1 richmond richmond 121327226 Jul 26 00:14 28970cf712e1aca608e2b6a13361112b
110756 -rw-rw-r--  1 richmond richmond 113293989 Jul 26 00:15 4227447f57cda90fbc9b1af0fd5d55c4
112880 -rw-rw-r--  1 richmond richmond 115463629 Jul 26 00:15 570819e8f6d1753ccc324a131edb1222

As before, I used catalogs of the SXDS images based on the i'-band detections, and worked in a three-dimension space using colors (B-V), (V-R) and (R-i'). I applied the techniques described by

The locus created in this fashion has an ellipsoidal cross-section which may change size and orientation. Following the methods described in Richmond (2005), I used this locus to give a "color classification" to every object in the SXDS catalogs. If the colors of an object -- including observational uncertainties -- fell completely within the locus, I assigned a "color score" of 1.0 to the object, meaning it is consistent with stellar colors. If the colors of an object placed it completely outside the locus, I assigned it a "color score" of 0.0, meaning that is not consistent with stellar colors. Some objects had a location which fell partly within the locus when one included uncertainties; for such object, I assigned a score between 0.0 and 1.0, given by the fraction of the object's error ellipsoid which fell within the locus.

The i'-band catalogs for the five SXDS fields (Center, North, South, East, West) contain many, many objects. I discarded those which had invalid values for at least one magnitude or magnitude uncertainty, which left 780,826 entries. Some of these are repeated measurements of a single object in regions of overlap between two fields. I have not (yet) done anything about repeated entries for the same object.

The results of my classification can be found in the following files.

A few simple statistics

Let me list a few properties of objects classified in the SXDS. I'll also mention some of these properties for stars in the SDF (taken from Properties of stars in the Subaru Deep Field ).

 shape         color       number    fraction   fraction
 score         score       in SXDS    in SXDS    in SDF       name
(out of 10)  (out of 1.0)  (791165)
 5 - 10       0.0 - 1.0    120013     15.2%     11.7%    somewhat stellar shape
 9 - 10       0.0 - 1.0     22818      2.9       3.4     very     stellar shape

 0 - 10       0.5 - 1.0     14421      1.8       1.4     somewhat stellar color
 0 - 10       0.9 - 1.0     10142      1.3       1.1     very     stellar color

 5 - 10       0.5 - 1.0      7831      9.99      0.84    "low-quality" star
 9 - 10       0.9 - 1.0      4309      0.54      0.56    "high-quality" star