2MASS Picture of the Week Archive Captions

Atlas Image mosaic, covering 3.33° × 3.33° on the sky of the Small Magellanic Cloud (SMC). The SMC is a dwarf irregular galaxy which, along with the neighboring Large Magellanic Cloud (LMC), is a satellite of our own Milky Way Galaxy. Both the LMC and SMC are much smaller in size and mass than our Galaxy. The SMC, at about 60 kpc, is somewhat farther from us than the LMC. Compare the 2MASS view with that seen by David Malin in the optical. Much of the bar structure can still be seen, and the bright HII region, NGC 346, is prominent. But, where the light in the optical is dominated by young, hot stars, the near-infrared light is dominated by cool, red supergiant and lower-mass red giant stars. The color-color and color-magnitude 2MASS Hess diagrams show the prevalence of these stars, as well as a number of dust-obscured, red asymptotic giant branch stars. Also, compare, in particular, the 2MASS SMC color-magnitude diagram with that found for the LMC using 2MASS by Nikolaev & Weinberg (2000, ApJ, 542, 804): many of the features are the same, including the "contamination" by foreground dwarfs and giants, but the detected SMC stars are correspondingly fainter and fewer in number. The galaxy is so extended that building this mosaic proved to be quite a challenge! The mosaic is binned by 2´´ × 2´´ pixels; the JPG rendition has been further shrunken by a factor of four. Image mosaic by T. Jarrett (IPAC). These data are included in the Second Incremental Data Release!


Atlas Image, covering 8´ × 8´ on the sky of the environment of Supernova 1987A in the Large Magellanic Cloud (LMC). SN 1987A was the closest supernova, or exploding star, to us, at ~50 kpc (163,000 light years), since Kepler's in 1604 (distance < 20,000 light years), which occurred in our own Milky Way Galaxy. SN 1987A is not actually visible in the 2MASS image, since it is quite faint and also difficult to resolve from its two blue neigboring stars, but its position is indicated by the top of the white line on the image. At very high resolution in the optical, the Hubble Space Telescope (HST) first revealed the amazing ring structure around the supernova. From the 2MASS color-color and color-magnitude diagrams, we see that the environment of SN 1987A consists of several different populations of stars. The colored lines on the color-magnitude diagram roughly trace out the LMC populations: green, the many, old (~14 Gyr) red giants; blue, the top of the hot main sequence; and red, the young (~20 Myr), primarily red, supergiant stars. The latter group are predominately from the large stellar association, Lucke-Hodge 90, near the northeast corner of the image. Noticeably lacking are older and dust-obscured asymptotic giant branch stars. The group of stars at J-Ks~0.4 are stars in the Galactic foreground. SN 1987A is beginning to interact with the rings, as seen in recent HST images, and continues to be a wondrous object.


Atlas Image mosaic, covering 15´ × 20´ on the sky of Sharpless 235. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 8´ × 8´ on the sky of Liller 1, which is a globular star cluster in the plane of the Milky Way Galaxy, about 5° from the Galactic center. The cluster, at a distance of 8700 pc (28400 light years) from us, is seen through about 9 magnitudes of visual extinction, rendering it nearly invisible at optical wavelengths. The cluster is relatively metal-rich, that is, the abundance of elements heavier than helium is relatively high, possibly as high as the Sun. The recent near-infrared analysis of Liller 1 by Davidge (2000, ApJS, 126, 105) indicate that the cluster has characteristics in common with stars in the Galactic bulge. The HST/NICMOS photometry by Ortolani et al. (2001, A&A, 376, 878) shows the faint red horizontal branch stars in the cluster for the first time, confirming the high metallicity; the main sequence turnoff is also seen in their analysis, but not clearly enough to estimate the cluster's age. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 1.42° × 1.42° on the sky of Messier 31 (M31), aka the Andromeda Nebula, or Andromeda Galaxy. This is one of the most famous Messier objects in the sky, and certainly one of the most famous galaxies. (For the 2MASS view of other Messier objects, please visit the 2MASSier Gallery.) Two additional galaxies, the much smaller spheroidal objects, are also seen in the 2MASS image mosaic: Messier 32, to the south, and NGC 205, to the northwest, which are satellites of the giant spiral M31. All three are members of the Local Group of galaxies, which includes the Milky Way, the Large Magellanic Cloud, the Small Magellanic Cloud, Messier 33, and other smaller dwarf galaxies. It is through Edwin Hubble's work in the 1920's on M31, which is at a distance of 765 kpc (2,493,900 light years), that we first became aware that other galaxies exist beyond the Milky Way. The Local Group is a gravitationally-bound aggregate of galaxies, which is a subunit of the much larger Local Supercluster of groups and galaxy clusters, including the Virgo Cluster. M31 is so bright and extended on the sky that, at a dark site, it can be seen with the naked eye. The galaxy is so extended that building this mosaic proved to be quite a challenge! The M31 field is included in the Second Incremental Data Release. Image mosaic by T. Jarrett (IPAC). N.B.: The full image mosaic is 20 Mb in size! To obtain this larger version of the mosaic, click here.

































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