mrt 132013

March 13, 2013

Arp 297, a quartet of galaxies in Boötes

NGC 5752, NGC 5753, NGC 5754 and NGC 5755

Image Credit & Copyright: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Arp 297 is a quartet of galaxies, consisting of NGC 5752, NGC 5753, NGC 5754 and NGC 5755, which looks like a compact group but actually consists of two galaxy pairs at quite different distances, located in the constellation of Boötes, the Herdsman.

The name “Arp 297” derives from being included in Arp’s Atlas of Peculiar Galaxies, a catalog of 338 peculiar galaxies, drawn up by Halton Arp in the years from 1962 through 1967 and published by the California Institute of Technology. Arp’s catalog was based only on the visual appearance of galaxies and groups of galaxies, and not whether they were actually physically related to each other.

In this image we see the bright interacting pair NGC 5754 (the large galaxy on the bottom) and NGC 5752 (the much smaller one to its right), and the two galaxies NGC 5253 (top right) and NGC 5255 (just above the center).

NGC 5754 and NGC 5752, both barred spiral galaxies, lie at a distance of roughly 200 million light-years, while NGC 5753, a spiral galaxy, and NGC 5755, a huge barred spiral, lie much further away at distances of about 450 million light-years.

NGC 5753 (of about 80 thousand light-years across) and NGC 5755 (of some 170 thousand light-years across) do not seem to be interacting at this time, although the very different sizes of NGC 5755’s two spiral arms and its long tidal tails suggests a previous close encounter.

The internal structure of NGC 5754 (of about 75 thousand light-years across) has hardly been disturbed by the encounter, including a quite normal selection of star clusters for a bright spiral galaxy. This galaxy has wide outer arms that does show tidal features, as does the symmetry of the inner spiral pattern and the kinked arms just beyond its inner ring.

In contrast, the small companion NGC 5752 (about 45 thousand light-years across) has undergone a starburst event, with a rich population of massive and luminous star clusters clumping around the core and intertwined with the intricate dust lanes. The energy release from the massive stars is driving an outflow of gas. The contrasting reactions of the two galaxies to their interaction are due to their very different masses and sizes.

Gravitational interaction between these two galaxies, has produced a long tidal tail (of about 275,000 light-years long) extending from NGC 5752. The stars and dust in the tail are presumably material stripped out of NGC 5752 during their closest approach which occurred about 250 million years ago, in which NGC 5752 crossed the disk plane of NGC 5754 at an angle of about 60°.

This image is taken in April 2012 with the SBIG STX16803 CCD Camera on the 32-inch Schulman Telescope (RCOS) at the Mount Lemmon SkyCenter, using the Astrodon Gen II filter. North is to the top.

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