NGC 2585 in Hydra

February 2019 - Galaxy of the Month

In 1886, whilst observing with the 26.3” refractor at the University of Virginia’s Leander McCormick Observatory, Frank Muller came across a group of what he believed were four new nebulae.

Unfortunately the observers at the Leander McCormick observatory were notorious for their poor reported positions for newly discovered nebulae and in this case the positions that he gave Dreyer were at least an arc-minute out.

Based on the descriptions Muller gave however, Dreyer was able to associate three of the nebulae with a small group of galaxies which later became catalogued as NGC 2583, NGC 2584 and NGC 2585. The fourth object that Muller discovered was later determined to be a triple star, although the number NGC 2586 has sometimes been erroneously assigned to another nearby galaxy MCG -1-22-12.

Two of the galaxies, NGC 2584 and NGC 2585 appear to form a physical pair and show signs of tidal interactions. They were given the number 1225 in the extended VV (Vorontsov-Velyaminov) catalogue of interacting galaxies. As the extended catalogue was never published in a journal (only online) the VV numbers beyond 835 are not included in the main extragalactic databases such as NED.

There is conflicting information about whether NGC 2583 forms part of the group but its distance and redshift suggest it probably doesn’t.

The two NGC galaxies are going to be challenging to see visually as they are at around 13-14th magnitude. If they are not challenging enough then there are two other galaxies that appear in the same field as NGC 2584/5 that have catalogue numbers from the MCG (Morphological Catalogue of Galaxies) catalogue at around 15th magnitude as MCG -1-22-6 and MCG -1-22-7.

There are suggestions that they may also form part of a physical group with NGC 2584/5. Their redshifts are quite similar to the main pair, although the redshift of MCG-1-22-6 is perhaps a little further from that of NGC 2583. The redshift of NGC 2585 is around 6868 km/s whilst that of MCG-1-22-6 is 6590. Similar to the issues with NGC 2583 however, if the distances/redshifts associated with them are correct then it is perhaps unlikely unless the group is very widely spread in space. At a stretch MCG-1-22-12 (the galaxy erroneously assigned NGC 2586) could also be part of the group as its redshift is similar to that of NGC 2585. The group is not assigned any number in either the WBL or LGG catalogues which suggests that they at least did not see it as a physical cluster.

The group is very small and will be challenging to find as, despite the fact it lies in the northern part of Hydra as it does not rise much above the 30 degree (one airmass) altitude line as seen from the southern UK.

It is tight enough that all the galaxies in the main group should appear in the field of a medium power (say 250x) eyepiece. MCG-1-22-12 is slightly further away but even then it should fit in the same field as the others with a modern hyperwide eyepiece at say 200x. It may be worth using this kind of power to help darken the sky background and try and bring the galaxies out.

NGC 2585 is a barred spiral galaxy and NGC 2584 is an Sc spiral with lots of ongoing star formation and as they both appear to be face-on spirals probably only the core will show. NGC 2583 is an elliptical galaxy. As always when observing galaxies try and find a dark site with little light pollution.

Owen Brazell - Galaxy Section Director