Isolated Elliptical Galaxies
Published on Jan 15, 2008 at 8:35 pm.
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Filed under conference blogging, galaxies.
While at the AAS conference last week, one of the posters that I looked at was being presented by Mike Fanelli, from nearby TCU, along with Pam Marcum (also at TCU), and a graduate student, Chris Fuse.
It has been a long standing debate about where isolated elliptical galaxies come from. For many years, it was assumed that galaxies either formed as elliptical galaxies or else they formed as spiral galaxies. Then, astronomers began to realize that many ellipticals could be the result of collisions between spirals, and the larger ellipticals are likely due to the merger of other galaxies (including spirals). But, the isolated ellipticals were a problem. There was nothing nearby to explain a collision or interaction. Another problem is that of the very few isolated elliptical galaxies know, most are very blue, indicating star formation is occurring (or has recently occurred). That is important because star formation usually occurs in spiral galaxies rather than elliptical galaxies (rule of thumb statement: not an absolute).
Well, as graduate student Chris Fuse explained to me, he and his professors believe that they have found an interesting correlation between these isolated elliptical galaxies and a type of galaxy cluster called a Hickson Compact Group.
Hickson compact clusters have a very similar X-ray signature (in terms of luminosity and energy) to the isolated elliptical galaxies. There is another small galaxy cluster called a fossil group. Fossil groups are more like an elliptical galaxy with a satellite or two. It had previously been suggested that fossil groups are what Hickson groups evolve into. However, the research presented on this poster suggests otherwise. They found that fossil groups tended to have higher luminosity and energy X-rays than either the Hickson groups or the isolated ellipticals. That seems to suggest that Hickson groups and isolated ellipticals share a common origin, and fossil groups have a different origin.
 -Astroprof
