2MASS XSC Colors

The fiducial elliptical isophotal (20 mag arcsec-2 in the Ks band) mags are used to construct the colors J-H, H-Ks, and J-Ks. The XSC sources (1.65 million total) are sub-divided according to the stellar number density, which measures the surface density of stars that the extended object is projected against.

Density vs. XSC

density mindensity max %XSC |Glat| min |Glat| max
0.0 3.2 73.4% ~25 90
3.2 3.6 19.0% ~10 ~25
3.6 4.0 6.9% ~5 ~10
4.0 4.5 0.7% 0 ~5

a. J-Ks Colors

b. J-H vs. H-Ks Color-Color

For color-color-mag scatter plots, the number of points must be reduced to avoid image saturation. For the following plots, we fix the number of point to 2000 per mag bin interval defined as: where we have chosen the points at random. The plots should be an adequate representative of the XSC as a whole. For reference, we also include the stellar main-sequence and evolved (giant) tracks, shown in green, and the redshift K-correction (assuming SAB type galaxies with no evolution cosmology; adapted from the models of Bruzual & Charlot 1993, McLeod & Rieke 1995), shown in magenta.

c. Discussion of Color Outliers

Sources with colors that significantly deviate from the "norm" are either (1) intrinsically "red", or (2) characterized by one or more inaccurate fluxes.

Intrinsically red sources are mostly confined to the Galactic Plane (see for example the All Sky Distribution of XSC Sources), and include HII regions, nebulosity, star formation regions (with Young Stellar Objects) and other deeply embedded Milky Way objects. Galaxies may also be very red, either from foreground dust extinction or associations with active galactic nuclei (AGN) or even from significantly red-shifted colors (particularly in the H-K color). See Near-Infrared Galaxy Morphology Atlas for discussion of the different Hubble Galaxy Types as imaged in the near-infrared.

Sources with inaccurate colors fall into the catagories of (1) confused sources, (2) fall within the zone of bright star masking, usually the J-band is the worst offender (see Extended Source Spatial Coverage for discussion of bright star masking); (3) isophotal apertures too large (induced by background removal problems, confusion, contamination from bright star artifacts, etc), (4) mis-characterized objects (e.g., pieces of galaxies, artifacts, double galaxies, etc). See also Visual Inspection of Extended Sources.

[Last Updated: 2003 Feb 24; by Tom Jarrett]