Thursday, 8 August 2013

Extragalactic objects - Beyond M31 and M33

As I'm preparing a little presentation of "EXTRAGALACTIC OBJECTS IN ANDROMEDA AND TRIANGULUM GALAXIES" to our annual Deep Sky Meeting, I thought to myself, why not dump some of that stuff in it here? As the goodies in Andromeda and Triangulum galaxies have already been discussed in the Blog, here are some of the  fancy objects included in the intro of the presentation.

Artist's impression of SagDEG
Image courtesy of NASA
If you consider SagDEG and Canis Major Dwarf as extragalactic and "not enough bound to the Milky Way", the hunt for the extragalactic objects becomes quite a lot easier. With SagDEG (size 7.5° x 3.6°), one can simply spot M54 (NGC 6715) with a pair of binoculars and say they've logged an object from another galaxy. With this in mind, it is interesting to point out that it was Charles Messier in 1778 who was the first person to have spotted an extragalactic object from another galaxy! Is it true? Of course not. 30 Doradus (NGC 2070) was seen by Nicolas Louis de Lacaille back in 1751 as well as the Aboriginals who must have spotted this object hundreds of years before Lacaille. How about the bulky 12°  x 12° Canis Major Dwarf? As with SagDEG, you can cheat a bit and consider the galaxy as extragalactic and simply spot one of these globular clusters: M79, NGC 1851, NGC 2298 or NGC 2808. The brightest star in the galaxy, that I managed to find out about, is EIS 7873 at magnitude 16.2. 

Large Magellanic Cloud
Credit & Copyright: Marco Lorenzi
No matter how you look at it, you don't have to cheat with the Large Magellanic Cloud (Nubecula Major / PGC 17223). This irregular galaxy was noted by al-Sufi (964) and Vespucci (1501) prior to Magalhães but I suppose "Large al-Sufi Cloud" or "Large Aboriginal Cloud" doesn't rhyme quite as well as “Large Magellanic Cloud”. Anyway, LMC harbors the brightest object in another galaxy (the brightest extragalactic object is of course LMC itself). It contains the gigantic (over 25 times larger than the Orion Nebula!) H II region 30 Doradus (Tarantula nebula / NGC 2070) which shines at an impressive magnitude of 4.0[1]. Considering it is an easy naked eye object, the typical apparent magnitude of 8.0 (v) can be considered far too faint. The brightest star in LMC and also the brightest extragalactic star in the sky is S Doradus at 9.5 (v) magnitude (8.6 to 11.5 var). SMC (Nubecula Minor / NGC 292) comes far behind but it contains the conspicious H II region NGC 346 with a magnitude of
6.0-6.5 (v)[2]. The brightest single star in SMC is HD 5980 at 11.3 (v) magnitude which is located inside NGC 346.

After these two (or four, you little cheater...) it becomes a bit trickier. In the Andromeda-piece the extragalactic globular clusters in Fornax Dwarf (Spheroidal) where mentioned. Of the bunch the brightest one is  NGC 1049 @ 12.6 (v) magnitude so it can be spotted even with small apertures. Despite the bright globular clusters, the brightest single stars in Fornax Dwarf are only around 19th magnitude! The hunt for individual stars becomes easier with NGC 6822 (Barnard's galaxy). The brightest stars shine around 15th magnitude so resolving the galaxy should be fairly easy but identifying a star that actually is part of NGC 6822 and seeing it (not just a bunch of resolved stars) is going to be annoying. Oh, and don't forget to bag the brightest H II region in NGC 6822: IC 1308 which shines at around 14th magnitude. Don't get freaked out by the larger aperture sightings of it by Jakiel, Gottlieb, Polakis[3]. IC 1308 is quite visible even with medium apertures.

For globular cluster hunters, here's a list of brightest extragalactic globular clusters.
Host galaxy
Mag (v)

Fornax Dwarf
NGC 1049
Andromeda galaxy
NGC 205 (M 110)
Triangulum galaxy
NGC 147
Hodge 3
NGC 185
Hodge 5
NGC 2403
Messier 81
[PR95] 50225

[1] Stephen O'Meara. Deep-Sky Companions: The Caldwell Objects: page 406.
[2] Visual magnitude estimate by Timo Karhula.