2MASS Extended Sources in the
Zone of Avoidance

The so-called "zone of avoidance" refers to the area contained within 5 or 10 degrees of the disk plane of the Milky Way. Gas and dust obscures starlight within this region and screens nearly all background extragalactic objects from traditional optical-wavelength surveys; as such, the Galactic plane has historically been avoided by astronomers. 2MASS will penetrate this zone with its near-infrared wavelength detectors, providing a "window" that is 90% free of obscuration (relative to that of optical wavelengths). The large nearby spiral galaxy (seen here) is just one example of a new 2MASS discovery of objects hidden beyond our Galaxy.

The major limitation that 2MASS suffers in the zone of avoidance is "confusion" noise from starlight that, like background galaxies, is suddenly revealed in the near-infrared. The confusion noise becomes appreciable within an area +-5 degrees of the Galactic plane. The end result is a loss of sensitivity as the surface density of stars increases exponentially, and a profusion of multiple surface groupings of stars (doubles, triples, ... etc) that can, under relatively rare circumstances, mimic galaxies and be picked up by the automated extended source detection and extraction routines. The typical reliability of the 2MASS extended source catalog in the Galactic plane ranges from 20 to 80% (compared to >98% well out of the plane), where the primary contaminent is multiple stellar groups.

To demonstrate the ability of 2MASS to find galaxies in the zone of avoidance, probable extended sources (most of which are galaxies or H II regions) from a small area of the sky are shown below. The area corresponds to 53 < Glong < 59 degrees, and -2.5 < Glat < 4.5 degrees, giving a total of ~40 square degrees. This targeted region is illustrated in the "sky" plot of all 2MASS galaxies in the first incremental data release, seen below. The area is populated by both Galactic H II regions, planetary nebulae and extragalactic objects (galaxies).

skyplot of 2MASS galaxies

Figure 1: Sky Plot of the 2MASS Extended Sources in the first incremental public data release. Left panel shows all of the sources. White dots represent new (previously uncatalogued) extended sourcces (most of which are probably galaxies); green dots demark galaxies found in NED (thus, previously catalogued). The dashed red line represents the Galactic plane at Glat = 0 degrees, and the two dotted red lines represents +- 5 degrees Glat. Right panel shows sub-region near the Galactic plane defined by (53 < Glong < 59 deg), (-2.5 < Glat < 4 deg). Verified extended sources (images given below) are denoted with blue filled circles. White points within blue box represent false extended sources (typically multiple stars).

45"-size JHK (3-color) Postage Stamp Images

2MASS Extended Sources Located within Area: 53 < Glong < 59o, -2.5 < Glat < 4.5 Each individual image is about 45 arcsec in width. For a much larger view of one of these fields, see An Infrared Window Through the Milky Way Galaxy

2MASS J+H+Ks	DSS
		(288.569336, 20.708765); Glong = 53.9250, Glat = 4.4976 Estimated Extinction (mag): Av = 4.2 (Ak = 0.42) Size: 10.8", semi-major axis Flux (J,H,Ks mag): 13.84, 12.95, 12.54 Color (J-H, H-K, J-K): 0.89, 0.41, 1.30 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.385803, 23.333241); Glong = 57.0397, Glat = 4.2188 Estimated Extinction (mag): Av = 4.0 (Ak = 0.40) Size: 14.2", semi-major axis Flux (J,H,Ks mag): 13.69, 12.56, 12.02 Color (J-H, H-K, J-K): 1.13, 0.54, 1.67 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(289.078400, 20.192081); Glong = 53.6856, Glat = 3.836 Estimated Extinction (mag): Av = 4.8 (Ak = 0.48) Size: 15.2", semi-major axis Flux (J,H,Ks mag): 13.02, 12.17, 11.73 Color (J-H, H-K, J-K): 0.85, 0.44, 1.28 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.951813, 23.331978); Glong = 57.2822, Glat = 3.7588 Estimated Extinction (mag): Av = 4.5 (Ak = 0.45) Size: 10.6", semi-major axis Flux (J,H,Ks mag): 13.84, 12.87, 12.40 Color (J-H, H-K, J-K): 0.97, 0.47, 1.44 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.366516, 22.092396); Glong = 55.9313, Glat = 3.6554 Estimated Extinction (mag): Av = 4.9 (Ak = 0.49) Size: 11.4", semi-major axis Flux (J,H,Ks mag): 13.37, 12.30, 11.82 Color (J-H, H-K, J-K): 1.07, 0.48, 1.55 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.201202, 21.631920); Glong = 55.4515, Glat = 3.5761 Estimated Extinction (mag): Av = 5.8 (Ak = 0.58) Size: 12.2", semi-major axis Flux (J,H,Ks mag): 13.94, 12.91, 12.38 Color (J-H, H-K, J-K): 1.03, 0.53, 1.57 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.669281, 22.371202); Glong = 56.3096, Glat = 3.5382 Estimated Extinction (mag): Av = 4.4 (Ak = 0.43) Size: 21", semi-major axis Flux (J,H,Ks mag): 12.96, 12.08. 11.73 Color (J-H, H-K, J-K): 0.88, 0.35, 1.23 NED: no entry SIMBAD: IRAS 19206+2216 Probable Nature: ???
2MASS J+H+Ks	DSS
		(290.386078, 21.550463); Glong = 55.4598, Glat = 3.3860 Estimated Extinction (mag): Av = 5.8 (Ak = 0.58) Size: 14.2", semi-major axis Flux (J,H,Ks mag): 13.68, 12.55, 12.07 Color (J-H, H-K, J-K): 1.13, 0.48, 1.61 NED: no entry SIMBAD: no entry Probable Nature: galaxy ** See the Big Picture **
2MASS J+H+Ks	DSS
		(291.046387, 22.137291); Glong = 56.2669, Glat = 3.1202 Estimated Extinction (mag): Av = 4.8 (Ak = 0.48) Size: 14", semi-major axis Flux (J,H,Ks mag): 12.90, 11.99, 11.53 Color (J-H, H-K, J-K): 0.91, 0.45, 1.36 NED: no entry SIMBAD: no entry Probable Nature: galaxy or double star
2MASS J+H+Ks	DSS
		(296.078552, 18.258453); Glong = 55.1629, Glat = -2.8896 Estimated Extinction (mag): Av = 2.3 (Ak = 0.23) Size: 18.4", semi-major axis Flux (J,H,Ks mag): 12.14, 11.22, 10.79 Color (J-H, H-K, J-K): 0.93, 0.42, 1.35 NED: IRAS 19420+1808 Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.638367, 20.906759); Glong = 55.0007, Glat = 2.8766 Estimated Extinction (mag): Av = 6.4 (Ak = 0.64) Size: 16.8", semi-major axis Flux (J,H,Ks mag): 13.03, 12.02, 11.55 Color (J-H, H-K, J-K): 1.01, 0.47, 1.48 NED: no entry SIMBAD: no entry Probable Nature: ???
2MASS J+H+Ks	DSS
		(290.598999, 20.605236); Glong = 54.7169, Glat = 2.7675 Estimated Extinction (mag): Av = 6.66 (Ak = 0.67) Size: 20.6", semi-major axis Flux (J,H,Ks mag): 13.08, 11.89, 11.51 Color (J-H, H-K, J-K): 1.19, 0.38, 1.57 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(291.544556, 21.983480); Glong = 56.3495, Glat = 2.6406 Estimated Extinction (mag): Av = 5.6 (Ak = 0.56) Size: 13.4", semi-major axis Flux (J,H,Ks mag): 14.00, 12.43, 11.88 Color (J-H, H-K, J-K):2.12, 0.55, 1.97 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(296.424805, 19.622694); Glong = 56.5102, Glat = -2.4931 Estimated Extinction (mag): Av = 3.5 (Ak = 0.35) Size: 20", semi-major axis Flux (J,H,Ks mag): 12.59, 11.69, 11.29 Color (J-H, H-K, J-K): 0.90, 0.39, 1.30 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(291.128784, 20.791735); Glong = 55.1151, Glat = 2.4181 Estimated Extinction (mag): Av = 8.0 (Ak = 0.80) Size: 56", semi-major axis Flux (J,H,Ks mag): 10.37, 9.66, 8.72 Color (J-H, H-K, J-K): 0.71, 0.95, 1.66 SIMBAD: PKS B1922+206, HII region Probable Nature: H II region
2MASS J+H+Ks	DSS
		(296.438080, 19.900749); Glong = 56.7574, Glat = -2.3648 Estimated Extinction (mag): Av = 3.7 (Ak = 0.37) Size: 8.2", semi-major axis Flux (J,H,Ks mag): 13.66, 12.64, 12.10 Color (J-H, H-K, J-K): 1.02, 0.54, 1.56 NED: radio source WSRTGP 1943+1945 SIMBAD:IRAS 19435+1946 Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(291.149567, 20.695066); Glong = 55.0390, Glat = 2.3554 Estimated Extinction (mag): Av = 8.6 (Ak = 0.86) Size: 10.8", semi-major axis Flux (J,H,Ks mag): 13.66, 12.47, 11.95 Color (J-H, H-K, J-K): 1.19, 0.52, 1.71 NED: no entry SIMBAD: no entry Probable Nature: galaxy or double star
2MASS J+H+Ks	DSS
		(291.159607, 20.580065); Glong = 54.9420, Glat = 2.2928 Estimated Extinction (mag): Av = 7.9 (Ak = 0.79) Size: 7", semi-major axis Flux (J,H,Ks mag): 14.25, 12.78, 12.13 Color (J-H, H-K, J-K): 1.47, 0.65, 2.12 NED: radio source WSRTGP 1922+2029 within 1' Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(295.401276, 18.500484); Glong = 55.0543, Glat = -2.2115 Estimated Extinction (mag): Av = 3.8 (Ak = 0.38) Size: 15.4", semi-major axis Flux (J,H,Ks mag): 13.39, 12.33, 11.84 Color (J-H, H-K, J-K): 1.06, 0.49, 1.55 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(290.233856, 18.692518); Glong = 52.8647, Glat = 2.1737 Estimated Extinction (mag): Av = 9.4 (Ak = 0.94) Size: 24.6", semi-major axis Flux (J,H,Ks mag): 13.07, 13.72, 11.05 Color (J-H, H-K, J-K): -0.66, 2.68, 2.02 NED: no entry SIMBAD: IRAS 19186+1835 Probable Nature: ??
2MASS J+H+Ks	DSS
		(291.381317, 20.190228); Glong = 54.6967, Glat = 1.9252 Estimated Extinction (mag): Av = 9.6 (Ak = 0.96) Size: 7.8", semi-major axis Flux (J,H,Ks mag): 14.14, 12.70, 12.10 Color (J-H, H-K, J-K): 1.44, 0.60, 2.04 NED: no entry SIMBAD: no entry Probable Nature: galaxy
2MASS J+H+Ks	DSS
		(293.655212, 23.829866); Glong = 58.9035, Glat = 1.8186 Estimated Extinction (mag): Av = 7.1 (Ak = 0.71) Size: 25", semi-major axis Flux (J,H,Ks mag): 12.04, 11.40, 10.80 Color (J-H, H-K, J-K): 0.64, 0.60, 1.24 NED: no entry SIMBAD: IRAS 19325+2343 Probable Nature: H II region
2MASS J+H+Ks	DSS
		(297.110077, 22.143667); Glong = 59.0131, Glat = -1.7794 Estimated Extinction (mag): Av = 5.2 (Ak = 0.52) Size: 8.2", semi-major axis Flux (J,H,Ks mag): 13.43, 12.91, 12.03 Color (J-H, H-K, J-K): 0.51, 0.89, 1.40 NED: PN G059.0-01.7 Probable Nature: Planetary Nebula
2MASS J+H+Ks	DSS
		(292.117401, 19.508265); Glong = 54.4262, Glat = 0.9918 Estimated Extinction (mag): Av = 9.9 (Ak = 0.99) Size: 35.8", semi-major axis Flux (J,H,Ks mag): 11.80, 10.57, 9.71 Color (J-H, H-K, J-K): 1.23, 0.86, 2.09 NED: radio source MG2 J192832+1930 within 1" of object position Probable Nature: galaxy or H II region
2MASS J+H+Ks	DSS
		(294.701691, 23.144455); Glong = 58.7735, Glat = 0.6464 Estimated Extinction (mag): Av = 12.2 (Ak = 1.22) Size: 45", semi-major axis Flux (J,H,Ks mag): 11.99, 10.45, 9.31 Color (J-H, H-K, J-K): 1.54, 1.15, 2.68 NED: radio source IRAS 19366+2301 Probable Nature: H II region
2MASS J+H+Ks	DSS
		(294.631073, 20.422840); Glong = 56.3702 Glat = -0.6327 Estimated Extinction (mag): Av = 13.61 (Ak = 1.36) Size: 7", semi-major axis Flux (J,H,Ks mag): 14.69, 12.92, 10.79 Color (J-H, H-K, J-K): 1.77, 2.13, 3.90 NED: no entry SIMBAD: IRAS 19363+2018 Probable Nature: ??
2MASS J+H+Ks	DSS
		(294.127625, 20.548206); Glong = 56.2487, Glat = -0.1601 Estimated Extinction (mag): Av = 23.85 (Ak = 2.39) Size: 28", semi-major axis Flux (J,H,Ks mag): 11.32, 10.08, 10.46 Color (J-H, H-K, J-K): 1.24, -0.38, 0.86 NED: radio source WSRTGP 1934+2026 within 1" of object position Probable Nature: H II region
2MASS J+H+Ks	DSS
		(292.323456, 17.939505); Glong = 53.1418, Glat = 0.0700 Estimated Extinction (mag): Av = 25.6 (Ak = 2.56) Size: 28", semi-major axis Flux (J,H,Ks mag): 16.32, 12.99, 10.55 Color (J-H, H-K, J-K): 3.33, 2.44, 5.78 NED: no entry SIMBAD: IRAS 19270+1750 ? Probable Nature: H II region
2MASS J+H+Ks	DSS
		(292.337189, 17.955620); Glong = 53.1622, Glat = 0.0663 Estimated Extinction (mag): Av = 25.7 (Ak = 2.57) Size: 7", semi-major axis Flux (J,H,Ks mag): 15.24, 13.38, 11.69 Color (J-H, H-K, J-K): 1.86, 1.70, 3.56 NED: no entry SIMBAD: no entry Probable Nature: ??
2MASS J+H+Ks	DSS
		(292.594238, 18.339275); Glong = 53.6160, Glat = 0.0360 Estimated Extinction (mag): Av = 26.4 (Ak = 2.64) Size: 34", semi-major axis Flux (J,H,Ks mag): 14.59, 12.58, 10.80 Color (J-H, H-K, J-K): 2.01, 1.78, 3.79 NED: no entry SIMBAD: radio source F3R 1872 Probable Nature: H II region
2MASS J+H+Ks	DSS
		(294.669067, 21.823648); Glong = 57.6081, Glat = 0.0240 Estimated Extinction (mag): Av = 24.3 (Ak = 2.43) Size: 24", semi-major axis Flux (J,H,Ks mag): 15.61, 13.45, 11.97 Color (J-H, H-K, J-K): 2.16, 1.48, 3.64 NED: no entry SIMBAD: IRAS 19365+2142 Probable Nature: ??

The 2MASS images represent a "3-color" RGB composite of the J-band, H-band and Ks-band images, where J consists of blue shading, H green shading and Ks red shading.

The DSS image refers to the STScI Digitized Sky Survey. The images of these surveys are based on photographic (optical-wavelength) data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of Caltech, AAO, RAO and ESO.

The images range in size from 30 to 60 arcsec in width.

The position coordinates correspond to the intensity-weighted centroid of the object. The equatorial coordinates are given in units of degrees, as are the Galactic coordinates (Glong, Glat).

The integrated fluxes come from the elliptical isophotal (K-band 20 mag per sq. arcsec isophote) aperture measurements. The size of the object refers to the semi-major axis of this elliptical aperture. The measurement uncertainties encorporate the Poisson flux error, including the confusion noise. We caution, however, that every source in the table is contaminated by flux from foreground stars, which we have attempted to minimize. The error due to this contamination far outweighs the quoted flux uncertainties (and remains largely unknown).

Galactic dust extinction is derived from UCBerkeley composite COBE/DIRBE/IRAS/ISSA maps with the zodiacal foreground and confirmed point sources removed. The extinction is computed using the DIRBE 100 and 240 micron data, inferring the dust temperature, then using the 100 micron map to convert to a grid proportional to dust column density. More information can be found here.

NED refers to the NASA Extragalactic Database, a general all-purpose database warehouse of galaxies, including classic catalogs (e.g., NGC) and the latest deep surveys.

SIMBAD refers to the database "Set of Identifications, Measurements, and Bibliography for Astronomical Data", maintained by Centre de Donnees Astronomiques de Strasbourg, France. It contains catalogs and information relevant to Galactic objects (e.g., stars, H II regions, PN nebulae, etc).