VI. Analysis of the 2MASS Second Incremental Release Catalogs

4. Completeness and Reliability

a. Analysis of PSC Completness and Reliability from Tile Overlaps

(This section is essentially the same as Section VI.1e.)

To evaluate the internal completeness and reliability, we examined the source data for more than 25 regions that were repeated 6 times in rapid succession. The data span a broad range of source density and were obtained on 5 separate nights in 1997 and 1998 from the Northern Facility, as described in http://spider.ipac.caltech.edu/staff/slw/cnr/cnr_results.html. S. Wheelock took these scan data and computed the number of times, N, a source could have been seen compared with the number of times, M, the source actually was seen (ideally, M=6). Wheelock trimmed the areas to ensure adequate geometric overlap. Her analysis of the individual scans can be found at the above URL. We accumulated the counts for all these scans into N/M bins, as shown in Tables 1-3 below. We used this information to generate the completeness and reliability (C&R) numbers given in the tables and in Figures 1, 2, and 3 (J, H, Ks, respectively) following Wheelock's prescription.

Figure 1Figure 2Figure 3

The Level 1 requirements on the Catalog are a differential completeness of 0.99 in the half-magnitude wide bin at the catalog limits (15.3-15.8 mag at J, 14.6-15.1 mag at H, and 13.8-14.3 mag at Ks). The reliability value, at the same magnitude limits, is meant to be 0.9995. It is clear from the tables that the 2MASS data handily meet the completeness requirement. However, the reliability reaches a plateau of about 0.995, which does not improve appreciably at brighter magnitudes. There are two reasons for this effect. First, these source counts have not had the benefit of the rigorous artifact removal that has been applied in the final Catalog. Thus, the reliability numbers are lower limits to the quality of the released Catalog. Second, examination of individual sources deemed unreliable by this type of analysis usually turns up marginally-resolved double stars or galaxies that come and go on different apparitions, depending on seeing and other effects. The reliability in the sense that there is one (or more) infrared sources at the quoted position is considerably closer to the stated requirement than indicated by the numbers in the tables. The best test of actual reliability will come from examination of deep co-added 2MASS images or comparison with external catalogs.

Wheelock is presently extracting the source data from all the scan overlap regions in this Catalog Release. This information, when it is available, will be representative of the completeness of the Catalog as a whole. However, the overlap data will be somewhat harder to analyze, since, with only two coverages (M=2, rather than M=6), it is harder to separate reliability and completeness problems.

Table 1. J-Band C&R

Cumulative

 Sources Sources

Mag TRUE FALSE Completeness dCompl Reliability dRel
15.3 11159 131 0.9981 0.0002 0.9967 0.0005
15.8 15083 206 0.9981 0.0001 0.9961 0.0005
16.3 20121 364 0.9961 0.0002 0.9946 0.0005
16.8 26451 2335 0.9836 0.0003 0.9738 0.0010
17.3 30301 15810 0.9658 0.0004 0.8882 0.0019
Differential Sources Sources

Mag TRUE FALSE Completeness dCompl Reliability dRel
14.8-15.3 2801 31 0.9985 0.0003 0.9971 0.0010
15.3-15.8 3924 75 0.9979 0.0003 0.9944 0.0012
15.8-16.3 5038 158 0.9902 0.0006 0.9902 0.0014
16.3-16.8 6330 1971 0.9440 0.0012 0.9129 0.0037
16.8-17.3 3850 13475 0.8434 0.0028 0.5540 0.0108

Table 2. H-Band C&R
Cumulative Sources Sources

Mag TRUE FALSE Completeness dCompl Reliability dRel
14.6 10333 132 0.9963 0.0002 0.9964 0.0006
15.1 14001 229 0.9940 0.0003 0.9950 0.0006
15.6 18806 752 0.9871 0.0003 0.9878 0.0008
16.1 23837 5629 0.9674 0.0005 0.9387 0.0016
16.6 24923 23747 0.9581 0.0005 0.8303 0.0026
Differential Sources Sources

Mag TRUE FALSE Completeness dCompl Reliability dRel
14.1-14.6 2671 39 0.9933 0.0006 0.9961 0.0012
14.6-15.1 3668 97 0.9877 0.0008 0.9909 0.0016
15.1-15.6 4805 523 0.9670 0.0011 0.9673 0.0026
15.6-16.1 5031 4877 0.8935 0.0020 0.7917 0.0064
16.1-16.6 1086 18118 0.7554 0.0068 0.2349 0.0265

Table 3. Ks-Band C&R
Cumulative Sources Sources

Mag TRUE FALSE Completeness dCompl Reliability dRel
13.8 7004 79 0.9983 0.0002 0.9969 0.0007
14.3 9440 129 0.9982 0.0002 0.9964 0.0006
14.8 13227 221 0.9981 0.0002 0.9955 0.0006
15.3 18291 819 0.9914 0.0003 0.9878 0.0008
15.8 23755 13977 0.9611 0.0005 0.8800 0.0022
Differential Sources Sources

Mag TRUE FALSE Completeness dCompl Reliability dRel
13.3-13.8 1961 25 0.9994 0.0002 0.9962 0.0014
13.8-14.3 2436 50 0.9979 0.0004 0.9948 0.0015
14.3-14.8 3787 92 0.9979 0.0003 0.9935 0.0013
14.8-15.3 5064 598 0.9739 0.0009 0.9682 0.0025
15.3-15.8 5464 13158 0.8595 0.0022 0.6446 0.0081

[Last Updated: 2000 Feb 2 by C.A. Beichman. Modified 2000 Jul 21 by S. Van Dyk.]

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