March 26, 2013
Hickson Compact Group 44, a small group of galaxies in Leo
Image Credit: The MASIL Imaging Team
Hickson Compact Group 44 (also known as the NGC 3190 Group) is a small group of bright galaxies containing three spiral galaxies and an elliptical galaxy, located about 60-100 million light-years away in the constellation of Leo.
A Hickson Compact Group (HCG for short) is a collection of four or five gravitational bound galaxies in close physical proximity to one another, published in a list of 100 objects (462 galaxies) by the Canadian astronomer Paul Hickson in 1982. These groups usually contain large quantities of diffuse gas and are dominated by dark matter. Strong galaxy interactions result and merging is expected to lead to the formation of one, most likely elliptical, larger galaxy.
They are among the densest concentrations of galaxies known, comparable to the centers of rich galaxy clusters. Compact groups are worthy of intense study as they provide a rich opportunity to study galaxy interactions and mergers.
Compact groups are relatively short lived entities that form via mergers of galaxies within loose subsystems and groupings. Simulations predict that merging of the group members should proceed rapidly within one billion years. Hickson groups are therefore snapshots at various stages in this merging process. They may represent an intermediate stage between loose groups and individual galaxies. A better understanding of the nature of HCGs could help explain galaxy formation on a larger scale in the early Universe. Compact groups are surprisingly numerous, and may play a significant role in galaxy evolution.
The four members of Hickson Compact Group 44 are NGC 3190 (in the center), 3185 (the lower right), 3187 (the upper right), and NGC 3193 (the upper left). Two dwarf spiral galaxies named PGC 86788 (to the right of the center) and PGC 2806871 (the lower left) are also part of the group but are not included in the Hickson catalog. NGC 3190, together with NGC 3187 and NGC 3193 from Arp 316.
NGC 3190, the dominant member, is a striking spiral galaxy of some 75,000 light-years across with a characteristic dust lane that we see nearly edge-on. NGC 3187 is an S-shaped spiral with a prominent central bar. NGC 3185 is also a barred spiral, but its bar is subtle and much smaller relative to its overall size. NGC 3193 is a good example of an elliptical galaxy.
The galaxies in the Hickson Compact Group 44 are close enough that they interact with each other gravitationally. This causes the individual galaxies to become distorted and in some cases even share material.
If you look closely, you may notice a faint halo around NGC 3190, a considerable warping of its dust lane on the side nearer to NGC 3187, and also a very subtle smudge of light between NGC 3190 and NGC 3193, which is a bridge of stars being shared between the two giants as they embrace in their cosmic dance. Finally, NGC 3187 shows numerous tidal tails well above and below its disk plane, which are also signs of tidal encounters between members of HCG 44.
In this image you can also see a few bright foreground stars and hundreds of tiny yellowish and reddish objects, which are extremely distant galaxies, hundreds of millions of light-years away. North is up.