Daily Image
23-08-2018
A better radio view of M81 and M82
| Submitter: | Erwin de Blok |
| Description: | M81 and M82 are two well-known galaxies in the northern sky, and together with NGC 3077 form the M81 triplet. They have been been extensively observed in the radio, and observations of their neutral hydrogen (HI) distribution, done with the VLA in the early '90s, have become the poster child for showing the importance of interactions between galaxies. Those old observations were made some 25 years ago, and cover only a small part of the volume of the triplet. In fact, recent single-dish observations show that there is twice as much HI present in the group than previously observed with the VLA. We therefore decided to revisit this group, again using the VLA whose capabilities have improved enormously over the past decades. We covered a 3 x 3 degree area surrounding M81 with 105 pointings, increasing the survey area by almost a factor of ten. These new observations also increased the spatial and velocity resolution significantly, so that these new observations can now resolve individual HI clouds around these galaxies. The left-hand image shows our new high-resolution HI mosaic in blue, superimposed on a Sloan Digital Sky Survey colour image. M81 is in the center, M82 toward the top, NGC 3077 is visible on the left, and dwarf galaxy NGC 2976 at the bottom-right. The spiral arms in M81 are clearly visible, as is the chaotic HI distribution around M82, and the offset HI near NGC 3077. Throughout the field, bright and faint HI streams and filaments are visible, connecting these galaxies. The right-hand image shows only the HI distribution. Here the complexity of the HI filaments and clouds is clearly visible. These observations are described in a paper recently accepted for the Astronomical Journal by de Blok et al., also available at https://arxiv.org/abs/1808.02840 . |
| Copyright: | (c) Erwin de Blok |
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