2MASS Picture of the Week Archive Captions

Atlas Image mosaic, covering 5´ × 5´ on the sky of the galaxy pair NGC 4567 and NGC 4568, aka VV 219 and the "Butterfly Galaxies," in the Virgo Cluster of galaxies. The two spiral galaxies have small separation between them, but the question is whether or not they are gravitationally interacting: Rauscher (1995, AJ, 109, 1608) claims that the lack of discernible tidal signatures argues against interaction, and Xu et al. (2000, ApJ, 541, 644) also find little disturbance in the galaxies' mid-infrared morphologies, while pointing out that maps of neutral hydrogen show two distinct galactic disks (Cayatte et al. 1994, AJ, 107, 1003). Could these galaxies be in the earliest stages of interaction? Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 8´ × 8´ on the sky of Sharpless 269, which is an HII, or ionized hydrogen, region embedded along the front face of a dusty molecular cloud. A number of stellar sources are seen in the 2MASS near-infrared image of the region; some likely very young objects are still obscured by the dust. The region was most recently imaged in the near-infrared by Eiroa & Casali (1995, A&A, 303, 8). The 2MASS color-color and color-magnitude diagrams reveal a number of probable, reddened members of the embedded stellar cluster.


Atlas Image mosaic, covering 1° × 1° on the sky of the Hydra Cluster of galaxies, aka Abell (ACO) 1060. More than a hundred galaxies are seen clustered toward the southern constellation Hydra. The "haloes" around the infrared bright Milky Way foreground stars (HD 92036, a M-type giant to the northeast, and HD 91964, a K-type giant to the southwest; the halo of the brighter star is truncated, due to the 2MASS scan edge) dominate the image. But, compare this 2MASS image with an optical image: In the near-infrared, the optical veneer of recently-formed hot, bright blue stars, the gaseous nebulae, and dark lanes of dust in the cluster's galaxies is stripped away to reveal the bulk of the galaxies' mass, namely, the cool, lower-mass stars. Because these stars have existed for a much longer time and have had time to move away from their birthplaces within the galaxies, the distribution of their infrared light is quite smooth. The morphology for galaxies of different Hubble type (spirals and ellipticals) therefore is more similar in the near-infrared than in the optical. (N.B.: The full mosaic is 13.6 Mb in size! A smaller, 4´´× 4´´-binned, 852-kb version of the mosaic can be obtained here.)


Atlas Image mosaic, covering 20´ × 31´ on the sky of the largest asteroid in the Solar System, 1 Ceres, seen against the Virgo Cluster of galaxies on 2000 Apr 6 UT during routine operations of the northern 2MASS facility on Mt. Hopkins, AZ. The asteroid is seen about 13.7´ west and 25.6´ south of the large spiral galaxy M100. Ceres is quite bright in this image, with Ks=5.50, J-H=0.37, and H-Ks=0.09 mag. Purplish known persistence artifacts trail (in decreasing brightness) due north of the asteroid. The fainter reddish "star" immediately east of due north, and the fainter whitish "star" immediately west of due south of the asteroid are known 2MASS "filter glint" artifacts. Sykes et al. (2000, Icarus, 146, 161) have studied asteroids detected by 2MASS, and the colors for Ceres are consistent with those for other C-type (carbonaceous chondritic) asteroids. The 2MASS Second Incremental Data Release Point Source Catalog contains 3804 associations with known asteroids.


Atlas Image mosaic, covering 15.4´ × 13.6´ on the sky, of the open star cluster, reflection nebula, and HII (or ionized hydrogen) region complex NGC 6595, aka Sharpless 37, which is part of the much larger Sagittarius Star Cloud, Messier 24. The complex is associated with a portion of a dark cloud of dust and molecular gas. The early B-type star, HD 313095 (the brightest blue star, among the small cluster of blue stars, in the region), is likely responsible for most of the ultraviolet photons ionizing Sharpless 37. The cloud, at a distance of about 1.8 kpc (about 5900 light years), is actually quite large and has been recently mapped out in the radio by Saito et al. (1999, PASJ, 51, 819). The cloud, containing about one hundred thousand solar masses of molecular gas, is an active site of massive star formation. Saito et al. conclude that a hole in the neutral hydrogen gas distribution, adjacent to the molecular cloud to the west, may be part of a supershell of gas, created by the action of several supernovae which exploded over the last few million years. It is possible that pressure from this supershell is responsible for the current active star formation. Image mosaic by S. Van Dyk (IPAC).
































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