Galaxy of the Month in Draco

• NGC 6340 in Draco

  July 2020 - Galaxy of the Month

  July comes and we are back to lengthening nights, although still no astronomical dark until August here in the UK.

  My choice for this month’s GOM is the strange galaxy NGC 6340 in Draco. Discovered by William Herschel in 1788, NGC 6348 has an anomalous appearance. It appears to be like a lenticular galaxy and the shape suggests that it was the result of a major merger between an elliptical and a spiral galaxy about 12 billion years ago.

  The bulge and inner part of the disk appear to be rotating in a different direction to the stellar disk. It also shows some signs of being a polar ring galaxy with material at right angles to the main disk.

  The distance is also somewhat uncertain but may be of the order of 62 million light-years.

  SIMBAD says it is part of a pair of galaxies but does not suggest what the other galaxy is. It could be one (or both) of the two IC objects in the field, IC 1251 and IC 1254, both galaxies, discovered by Edward Swift using a 16” refractor in 1890. It has been suggested that both IC 1251 and IC 1254 may be part of an interacting group with NGC 6340 as both of them show some signs of gravitational distortion. IC 1251 in particular appears to be furiously forming stars from its image in the UV from the GALEX satellite. If they are at the same distance as NGC 6340 then they are both quite small galaxies.

  NGC 6340 itself also shows some signs of an interaction/merger event perhaps within the last few hundred million years. NGC 6340 also appears to have a low activity AGN at its centre. The disk contains a ring of counter-rotating stars which is part of the reason that it has been suggested that it was involved in a major merger event. Currently NGC 6340 is classified as an S0-a galaxy. One of the best images of the group including NGC 6340 can be found on Adam Block's website.

  Although NGC 6340 is quite bright in terms of its total magnitude it is also quite large so may be a challenge to see in twilight skies. It has certainly been seen in a 25cm telescope from the UK but was not an easy catch. For those with larger telescopes the companions are the objects of interest. If these prove to be too easy then there are a number of other fainter galaxies in the field at around 16th magnitude to try for. These are almost certainly unrelated to NGC 6340 and are much further away.

  The NGC 6340 group is also well covered in the Cambridge Photographic Atlas of Galaxies, available from the Society.

  Owen Brazell - Galaxy Section Director

• July 2015 - Galaxy of the Month

  NGC 6503 in Draco

  

  This image was provided by Bob and Janice Fera. I’d recommend you follow the link to see the rest of their work. You can click on the image for a larger version.

  The bright nights of July from mid northern latitudes make hunting faint galaxies a bit of a challenge so this month’s object is a little brighter than previous GOMs.

  NGC 6503 was discovered by Arthur von Auwers in 1854 using a 2.6” refractor whilst he was a student which is sort of odd then as to why if it was so bright it was missed by William Herschel. NGC 6503 was one of two NGC objects Auwers’s discovered, the other being NGC 4402.

  NGC 6503’s Dreyer code of pF L mE *9 f4 however suggest that it’s large size may have been an issue as perhaps would have been its location close to the pole. Modern references describe this as a high surface brightness object visible in small instruments. NGC 6503 is classified as a dwarf spiral galaxy (SA(s)cd) seen nearly edge on. It is about 30000 light years across and maybe 18 million light years away. This makes it about a third of the size of our Milky Way galaxy. NGC 6503 is an isolated galaxy lying on the edge of the Local Void. The Local Void itself maybe 150 million light years across and contains few stars and galaxies. NGC 6503 appears to have almost no central bulge and a large halo. Its nucleus however is a weak form of AGN known as a LINER which may come from a starved black hole. Here LINER stands for Low Ionization nuclear Emitting Region. Something like 33% of galaxies in our local area appear to have this kind of spectra. There’s rather nice recent image of NGC 6503 taken by Hubble. The Hubble image shows the bright blue stars and HII regions of an active star forming galaxy.

  The location of this galaxy caused it to be named by Steve O’Meara in his Hidden Treasures book the Lost-in-Space galaxy. I am not sure if this nickname will stick. Recent observations however with the Subaru telescope suggest it might not be quite as alone as it appears to have a dwarf companion named NGC 6503-d1. This new galaxy maybe a dwarf Spheroidal and although its location is uncertain it is most likely associated with NGC 6503.

  A sketch of NGC 6503 with a 20cm telescope can be found on Astronomy Sketch of the Day. And there’s an interesting, although perhaps over processed, amateur image too.

  Owen Brazell - Galaxy Section Director

• June 2012 - Galaxy of the Month

  The Draco Triplet

  

  Image Courtesy of Dr. Dietmar Hager, Austria. For more images from Dietmar please visit his Stargazer Observatory website. You can click on the image above for a larger version.

  Not as well-known as the Leo triplet NGC 5981, 5982 and 5985, collectively known as the Draco triplet are a fine group of galaxies high in Draco.

  Unlike the Leo triplet however these galaxies are probably not related and reside at different distances so the triplet is purely a line of sight effect. NGC 5985 is about 120 million light years away, NGC 5982 about 130 million years and the small edge on NGC 5981 about 100 million light years away. However given the errors in astronomical distance measurement they could still be related.

  NGC 5981 is quite a small dwarf galaxy. NGC 5982 and 5985 were found by William Herschel in 1788 but NGC 5981 had to wait until 1850 when it was found by J Stoney at Birr castle, probably with the 72".

  NGC 5985 is an almost face on spiral and probably the easiest of the group so see. It is classified as a Seyfert type 1 galaxy with an active black hole at its nucleus. It is also classified as a LINER.

  NGC 5982 is classified as an elliptical galaxy class E3. Although it looks quiescent now deep images reveal shells surrounding which are the results of a merger with another galaxy. These shells were found in the optical but were among the first to be discovered in the mid infra-red using data from Spitzer. NGC5982 may also be an active galaxy hiding a black hole. The merger probably happened about a billion years ago. Although it is an elliptical galaxy it also contains a young population of stars, perhaps as a result of the merger. Both 5985 and 5982 are visible in telescope as small as 15cm from a dark site.

  NGC 5891 is very much fainter and an edge on spiral galaxy. It may be possible to see the dust lane with large telescopes. It appears smaller than it should and may have a large dark matter halo which has truncated star formation at larger radii. If you find NGC 5981 easy to find then try for NGC 5976, classified as a lenticular and a blue magnitude of 15.8 (so probably about a mag brighter in the visible) this provides a fine challenge to end with. Note however that it was also discovered by Stoney who called it eeF whilst he only thought NGC 5981 was F.

  All four galaxies should fit in the same medium power field but from calculations I think that you may need a telescope with an aperture of 45cm or above to see NGC 5976, certainly from the UK. A good finder image showing the triplet and identifying the galaxies will help.

  Owen Brazell - Galaxy Section Director

• July 2011 - Galaxy of the Month

  NGC 5907

  

  Image copyright ©2006-2008 R Jay GaBany. Click on image for a larger version. For more images from R. Jay GaBany please take a look at his website.

  Summer skies preclude observing faint objects from mid northern latitudes so our galaxy this month is the bright edge on spiral in Draco NGC 5907.

  NGC 5907 was first discovered by William Herschel in 1788 with his 20ft (18.7" mirror) from Slough. It is also known as the Splinter galaxy and is one of the best and brightest of the edge on galaxies, and appears to be a standard SA(s)c.

  It is believed to be part of the galaxy group that includes NGC 5866 (M102). This is a very exclusive group consisting of just the three galaxies NGC 5866, NGC 5907 and NGC 5879. They form an equilateral triangle about a degree on a side. A wide field view showing all three galaxies can be found on the Starry Vistas website.

  NGC 5906 and NGC 5907 are sometimes confused. It appears that NGC 5906 is actually a knot in NGC 5907, although occasionally the galaxy also goes under the same number. This confusion appears to have come from observations made at Birr with the 72".

  NGC 5907 is an interesting galaxy in many ways as it seems to consist of mainly dwarf stars of low metallicity. Very few giant stars have been found in it. The galaxy appears to be about 50 million light years away.

  It became famous in 2008 when an image taken by R Jay GaBany showed tidal streams wrapped around it which may represent the dying orbits of a dwarf galaxy that then became absorbed into the main galaxy maybe 4 billion years ago. These stars streams may orbit as much as 150 thousand pc from the galaxy. This may also be the way that polar ring galaxies form. Our own Milky Way galaxy contains similar star streams that are thought to be the remnants of recently ingested dwarf galaxies showing galactic cannibalism is still alive and well. What makes this image more remarkable is that it was taken by an amateur.

  Recent interactions also seem to have caused NGC 5907 to have a warped disk. The warping galaxy is thought to be the small dwarf galaxy KUG 1513+566. As NGC 5907 is so bright it should be visible in binoculars and small telescopes. Owners of large telescopes might like to look for the 15th magnitude galaxy CGCG 297-11 about 7 arc minutes preceding.

  NGC 5907 has also been home to one supernova in the last 100 years (in 1940).

  Owen Brazell - Galaxy Section Director