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

3. Extended Source Catalog (XSC)

d. General Properties

ii. All-Sky Images of the XSC

The 2MASS XSC is primarily composed of galaxies, and secondarily of Milky Way objects. Galaxies are detected all across the sky except for regions of the Galactic Plane that are opaque with stars (e.g., Galactic Center in Sagittarius). Galaxies concentrate on several spatial scales, including groups, clusters, and large filamentary superclusters. Milky Way objects are almost exclusively confined to the Galactic Plane, |b| < 3°. See 2MASS XSC Galactic Extended Sources.

The following figures show the Local Universe as traced by the XSC. Figure 1 shows the Aitoff equal-area projection (binned to 18´ pixels) of the integrated XSC flux for Ks < 14.0 mag (~1.7 mJy). The near-infrared J, H, and Ks bands have been combined to form a three-color composite image of the Local Universe. The image orientation is equatorial, centered on 6h right ascension (roughly corresponding to the Galactic anti-center); see Figure 2 for the equatorial coordinate map. The "red" sources defining the Galactic Plane are mostly Milky Way in origin, both heavily dust reddened as well as being intrinsically red (due to strong emission lines in the Ks-band window). The Galactic anti-center region (center of image) is also graced by the Orion and Taurus molecular cloud systems (Orion located just right and down from the center of the image, Taurus just right and up from the center). The filaments and coherent structures throughout the image are extragalactic superstructures. Figure 3 is a chart showing the orientation and locations of known large scale structures, in equatorial orientation. The figure can be directly compared with the Cornell redshift survey images by M. Haynes. Figure 4, for example, is the sky distribution for galaxies with a redshift < 12,000 km/s (z < 0.04).

Figure 1Figure 2Figure 3Figure 4

Figure 5 shows the 2.2-Micron Differentiated View of the Local Universe, Ks-band integrated flux, separated into three (RGB) mag bins: (1) Ks < 11.5 mag, (2) 11.5 < Ks < 12.75, and (3) 12.75 < Ks < 13.5 mag. The first bin represents the brightest and therefore nearest objects (e.g., Local Group), assigned to the blue (B) channel. The second bin represents the realm of the nearby superclusters (e.g., Coma cluster), assigned to the green (G) channel. The third bin represents the most distant XSC objects, filling in the Universe out to a redshift of 0.2 to 0.3, assigned to the red (R) channel. The image has been convolved with a Gaussian filter for additional smoothing (thanks to R. Hurt for this). See Figure 3 for image orientation and a map of the large scale structure.

Figure 5

Figure 6 shows 2MASS Local Universe, i.e., the combined XSC and PSC. See II.3.c2a on The combined XSC and PSC all-sky images for more details.

Figure 6

See the movies page for various representions of the all-sky view of the XSC. (N.B.: the images are large and require reasonably high Internet speed and bandwidth to view.)

Flat "Tan" Projections

The Aitoff projections tend to accentuate linear features near the poles. See, for example, the linear cluster of galaxies near 20h10m -56° (302° -56°) in Figure 2. The following figures show "flat" or tangent projections of some interesting structures: Figure 10 shows a "linear" cluster(s) near 20h10m -56°. Figure 11 shows Abell 3558 of the Shapley Concentration. Figure 12 shows the Coma Cluster. Figure 13 shows the Virgo Cluster, centered at 12.4h +12.7°, with an 8°×8° field-of-view (N.B.: this image is very large, ~9 Mb).

Figure 10Figure 11Figure 12Figure 13

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

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