II. User's Guide to the 2MASS All-Sky Data Release

3. Extended Source Catalog (XSC)

d. General Properties

i. Extended Source Spatial Coverage

The spatial coverage of extended sources is limited by the presence of foreground stars. Bright stars block out large halo and long diffraction spike areas (see below). The coverage area is computed for each Atlas Image for each band. The typical high |glat| coverage (during the absence of very bright stars) is >98%, thus representing very good spatial coverage overall. An example of the coverage for a 2MASS scan is given below.


The XSC spatial coverage maps are available for download here: Extended Source Spatial Coverage Maps.

All-Sky Coverage Map Previews

The following images show the XSC coverage for 59731 2MASS 6° scans. Each pixel represents the coverage in a single Atlas Image, i.e., 8.5´×17´. Figure 1 shows the all-sky Aitoff projection of the XSC coverage in equatorial coordinates. The color stretch is such that white corresponds to the best coverage (100%) and black to no coverage at all (0%); refer to the color "wedge." The top panel shows the J-band coverage, and the bottom panel shows the Ks-band coverage (and equatorial coordinate grid). Figures 2-5 show J-band coverage only, in right ascension sections. Figure 2 shows the tangent projection of 0h to 6h. Figure 3 shows the Tangent Projection of 6hr to 12hr. Figure 4 shows the Tangent Projection of 12hr to 18hr. Figure 5 shows the Tangent Projection of 18hr to 24hr. Finally, Figure 6 shows the all-sky Aitoff projection of the XSC in galactic coordinates. The top panel shows 0° < glon < 180°, the bottom panel shows 180° < glon < 360°.

Figure 1Figure 2Figure 3

Figure 4Figure 5Figure 6

Example of Spatial Coverage for a 2MASS Scan

Table 1 lists the spatial coverage for the southern hemisphere 2MASS scan ("044") observed 2000 April 22. The coordinates refer to the center of the Atlas Image, size 512´´ × 1024´´. The mean coverage per Atlas Image is specified by "fj" (J-band coverage), "fH" (H-band), and "fK" (Ks-band), normalized to unity.

Example of the Coverage Toward Scorpious (Antares)

Figure 7 shows the J-band coverage toward Scorpius and Antares, where Antares is circled in green. The projection and coordinates are galactic. The coverage toward the 2MASS Atlas Image which includes the supergiant Antares is 9.7%, 13.3%, and 25.2% for J, H and Ks, respectively (i.e., nearly all of the Atlas Image is masked from the extended source pipeline; see example of masking below).

Figure 7

Example of Bright Star Masking

A few examples of GALWORKS "coverage" maps, i.e., masked regions, are shown in Figures 8-15 below. Masked areas are due to bright stars, their artifacts, bad pixels and low coverage areas (usually edges). The masks (right panel images) are coded as:

(Note: the small masked "circles" are due to persistence ghosts and glints, as given by the MAPCOR purge flags.)

Figure 8Figure 9

Figure 10Figure 11

Figure 12Figure 13

Figure 14Figure 15


Figure 16 shows an example of a full GALWORKS coverage cube. The top three panels show the GALWORKS masking for J, H and Ks, respectively, of the Abell 3558 field (J-band Atlas Image), shown in Figure 17. The bottom three panels show the corresponding PIXPHOT coverage for J, H and Ks, respectively. The darkest greyscales correspond to a maximum coverage of 7. The typical coverage is 6. The lighter greyscales correspond to 5 and less coverages.

Figure 16

Figure 17

[Last Updated: 2003 Feb 25; by T. Jarrett]

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