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 min	density 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

• J-Ks Histogram of All XSC
  
• Ks < 10.0 mag, J-Ks Histogram
  
• 10.0 < Ks < 11.0 mag, J-Ks Histogram
  
• 11.0 < Ks < 12.0 mag, J-Ks Histogram
  
• 12.0 < Ks < 12.5 mag, J-Ks Histogram
  
• 12.5 < Ks < 13.0 mag, J-Ks Histogram
  
• 13.0 < Ks < 13.5 mag, J-Ks Histogram
  
• 13.5 < Ks < 14.0 mag, J-Ks Histogram
  
• Ks > 14.0 mag, J-Ks Histogram
  

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

• J-H vs. H-Ks for All XSC using Hess Diagram
  
• J-H vs. H-Ks for density < 3.2 using Hess Diagram
  
• J-H vs. H-Ks for 3.2 < density < 3.6 using Hess Diagram
  
• J-H vs. H-Ks for 3.6 < density < 4.0 using Hess Diagram
  
• J-H vs. H-Ks for density > 4.0 using Hess Diagram
  

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:

8.0 < Ks < 11.0 mag, 2000 total sources
11.0 < Ks < 12.5 mag, 2000 total sources
12.5 < Ks < 13.5 mag, 2000 total sources
13.5 < Ks < 14.0 mag, 2000 total sources

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.

• density < 3.2, J-H vs. H-Ks
  
• 3.2 < density < 3.6, J-H vs. H-Ks
  
• 3.6 < density < 4.0, J-H vs. H-Ks
  
• density > 4.0, J-H vs. H-Ks
  
• density > 4.0, J-H vs. H-Ks, with expanded axis to show extreme reddening
  

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.

Examples of "Red" Milky Way Objects

• Nebulosity
  
• YSOs
  
• HII Regions
  

  Examples of "Red" Galaxies:

• Markarian 1239, type E/S0 with Sy1.5
  
• Hurt 1, type Sd
  
• Source at (345.401123, -59.222527)
  
• Source at (204.782120, -30.252445) (note bright star confusion; see examples below)
  
• Source at (219.206711, -16.228071)
  
• Source at (0.101620, -12.763147)
  

  Examples of "Blue" Fuzzies:

• NGC 7793, Hubble Type SA(s)d
  
• Comet at (92.836586, 36.640507)
  
• Comet at (213.217377, -15.222510)
  
• Galaxy+star at (192.828003, -30.317444)
  

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.

Examples of Sources with Inaccurate Colors:
• Source at (269.775452, -28.816984: Reason: source corrupted by J-band mask of bright source (to the south) and from neighbor confusion
  
• Source at (346.893738 -0.293708): Reason: source corrupted by J-band horizontal stripe mask
  
• Source at (174.057327,-55.517132): Reason: source in close proximity to bright star (J-band affected)
  
• Source at (230.064285, -69.028946): Reason: source corrupted by J-band diffraction spike
  
• Source at (171.853912, -50.672760): Reason: source corrupted by J-band halo masking
  
• Source at (175.922165, -52.398312): Reason: source corrupted by J-band halo/diffraction spike masking
  
• Source at (130.537003,22.751608): Reason: isophotal photometry incorrect -- aperture is far too large; stellar contamination critical
  
• Source at (139.921173, 80.359772): Reason: isophotal photometry incorrect -- aperture is far too large; stellar contamination critical

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