May 2017 - Galaxy of the Month
NGC 4536 in Virgo
As the shorter nights come along finding challenging galaxies of the month becomes harder. In fact from mid-May to mid-August we no longer get any astronomical dark in the UK. As such this month’s galaxy is somewhat brighter than usual suspects.
NGC 4536 was first discovered by William Herschel in 1784. Lying roughly 50 million light years away in the constellation of Virgo NGC 4536 is not part of the main Virgo group of galaxies but is part of the Virgo II subgroups, in this case part of the group containing M61. This group is also catalogued as LGG 287. The Virgo II subgroups are part of a long southern tail to the main Virgo cluster. See "An Atlas of the Universe" for more information.
NGC 4536 appears to be undergoing some form of starburst, although there is no obvious interacting galaxy. It is classified as SAB(rs)bc. It will be interesting to know how much of the spiral arms can be seen visually. There is a fine Hubble image of the system. Perhaps as expected, because of all the star formation going on, NGC 4536 also shows up well in the GALEX UV images.
It is possible that NGC 4536 is a mild AGN given the excited lines seen in both the IR and visible. XMM observations also suggest the presence of a million solar mass black hole at the centre. Finding black holes in bulgeless galaxies is unusual.
In 1981 NGC 4536 was home to supernova 1981B, a Type 1a that reached a maximum magnitude of 12.3, well within reach of amateur telescopes.
NGC 4536 is part of the Herschel 400 program so it can be seen with small telescopes of around 20cm aperture. Nearby is the edge on galaxy NGC 4533 and this may prove to be more of a challenge to see visually as it shines dimly at 14.4 (P). It was discovered by Tempel in 1877. It was pretty easy in my 55cm telescope under not great skies so it should be visible in much smaller telescopes, perhaps down to 30cm. It did make a fine sight as a pair with NGC 4536. NGC 4533 is also part of the M61 subgroup.
Also nearby, and part of the same subgroup, is the bright edge on spiral NGC 4527 (also discovered by William Herschel) and for those wanting a real challenge there is the faint edge on IC 3474, discovered photographically by Isaac Roberts in 1892. These others are also part of the same M61 sub group.
The brighter galaxies will fit in the same field of view of a medium power (x130) hyperwide field eyepiece. Jim Thommes has a nice amateur image of the NGC 4536 and NGC 4527 pair.
I know of no visual observations of IC 3474 but at mag 14.9 (B) it should be in reach of some of the larger telescopes. Unfortunately I did not try when I was observing NGC 4536.
Owen Brazell - Galaxy Section Director