Object of the Week, October 29, 2017: Arp 140, an obscure interacting pair of galaxies in Cetus

Object of the Week, October 29, 2017: Arp 140, an obscure interacting pair of galaxies in Cetus

Arp 140 = NGC 274 and NGC 275
RA: 00 51 04
DEC: -07° 4' 06"
Type: SAB(r)0- pec (NGC 274), S pec (NGC 275)
Size: 1.5' x 1.5' (NGC 274), 1.6' x 1.1' (NGC 275).
Mag: V = 12.8 (NGC 274), and 12.5 (NGC 275).

Autumn, with its cool days, and clear, crisp, nights is an ideal time of the year to explore the skies for galaxies. The summer milky, with its thick, dusty, starry clouds is disappearing in the southwest, and the spectacular winter constellations are just rising in the east, too low to steal the attention from the galaxies that dot the fall sky. And it was during such an exploration that I “discovered” today’s object of the week a few weeks ago: The double galaxy NGC 274 and 275.

Attachment 2733
Arp 140 from the The STScI Digitized Sky Survey

Although these two galaxies seem to interact, not much is known about their astrophysics. Arp included them in his famous catalog as the 140th entry, under the classification “material emanating from elliptical galaxies”. NGC 274 is an lenticular galaxy while NGC 275 is a spiral, both approximately 88 million light years away. Very deep photos and studies at various wavelengths beyond visual indicate that there are long Hydrogen tidal tails as a result of the interaction between the two galaxies.

So, what can be seen in a telescope regarding this complex system? I stumbled upon this galaxy pair on a late August evening, while exploring the area around Diphda (Beta Ceti) with my 18”. The low magnification view was quite surprising because it looked rather cometlike, as in a comet with a round core and an elliptical, but diffuse tail. Increasing the magnification revealed a fascinating pair of galaxies, one (NGC 274) round with a bright, not quite stellar, core, and a second (NGC 275) elliptical, fainter but larger patch of light, directly in contact with the brighter round glow. Careful scrutiny at 275x revealed a slight brightening around the periphery of the ellipse, more distinct on the north side of the galaxy. This brightening corresponds well to structure visible in deep photos of NGC 275. Near to the Arp 140 pair is another edge-on spiral, NGC 273, readily visible in my 18” at all magnifications.

Attachment 2734
Arp 140 as sketched through my 18" Dob at 275X.

I searched for observations of Arp 140 throughout my library and the internet, but they are quite scarce. Apparently, they are very obscure, although they lie in the same region of the sky with showpieces such as NGC 253, NGC 246, and NGC 247. David Tosteson, in the “Arp Atlas of Peculiar Galaxies” by Kanipe and Webb, mentions that through his 25”, “NGC 274 is brighter and round, touching fainter and elongated NGC275 which is not brighter toward middle”. Alvin Huey, in his “Observing the Arp Peculiar Galaxies” , notes that NGC 275 is a “bright slightly elongated patch with an irregular core, which seems to be “torn up””, while his observation of NGC 274 agrees with mine and Tosteson’s. Mark Bratton, in his “Complete Guide to the Herschel Objects” mentions again similar observations for NGC 274, but he says that NGC 275 is “grainy in texture” in his 15”. Apparently, the challenge is to get as much detail as possible out of NGC 275’s elliptical blob of light!

Being 12th magnitude, these galaxies are visible in smaller apertures, but with significantly less detail visible. I was able to detect them at 142X in my 5” APO refractor, but I could not resolve them as a pair, rather they were visible as a faint tiny patch of oblong light with a brightening on one edge (NGC 274 I guess!). Luginbuhl and Skiff mention very similar observations with a 6”, and that separation may be achieved with 10 inches. Although detectable in my 5”, I believe it would need excellent conditions for the pair to be detected in a 4” scope, but it should be doable.

So, next time you are out during a dark, moonless night, turn your scope to the southwest edge of Cetus, locate this beautiful pair of galaxies, and….

GIVE IT A GO AND LET US KNOW!!!

It's a familiar object although I can't find any detailed description in my notes. 274 is supposedly a W. Herschel discovery, but I am pretty sure he saw both and cataloged them as one. That's how I observed them, as a Herschel object. The view I remember in 12" of the pair was unresolved but of two very unequal parts. At least traces of the SW arm in 275 should be detectable in 16 under good conditions and with effort, looking at the SDSS.

My notes with my 20” from southern France:

NGC 274: bright and oval.
NGC 275: At 427x seen with NGC 274 forming Arp 140. Oval, connects with NGC 274, sometimes a stellar nucleus is visible, from the nucleus a strangely shaped star forming region runs away. The bar-shaped part almost perpendicular to the line between the two nuclei is best visible, ending in a knot. The part emerging from the nucleus running towards one end of the bar and the bar running away from the bright know are visible too but much harder to see.

My notes from 2011 with my 28 inch scope:

"Nice Arp! Almost like there are three galaxies here, all within a common envelope. 408x, 21.40 SQM."

Attachment 2735 Attachment 2736

A good guess is that the appearance of three galaxies is because two of the brighter spots are part of NGC 275, perhaps the brighter end of the central bar and the core?

Hi folks,

this is quite an interesting arp... using my 12" around 5 years ago i found shape interesting enough to make a - very - raw sketch ;-)

It shows an quite obvious triangular shape at the weaker part. I do not know magnification anymore - might be either 133x or 200x to that time.
North is up...

Attachment 2737

I cannot remember having split the two - maybe slightly ... because i made a cut between the two parts... However... main interesting thing for me was the shape of the weaker part - the roundish triangle... Sky was of NELM 7m+, 6000 ft above sea level.

CS!

Norman

Here's I recorded NGC 275 a few years back. I was impressed with its unusual structure

24" (10/5/13): at 375x appeared moderately to fairly bright, elongated ~5:3 NW-SE, ~45"x27". Very unusual patchy, irregular appearance! A brighter elongated N-S patch (or arm) is on the east end. Also the southwest border is slightly brighter with a sharp, curving edge. This edge is more prominent at the NW end of the galaxy, where it merges with NGC 274 just northwest.

This arp I observed last autumn with 16" in the bavarian alps - very good transparancy and seeing during the whole night. 274 was only a bright, round ball, but its close neighbour 275 showed a lot of detail. Anvil- or triangle-like shape with two peaks at southern side, while the northern edge is sharp and almost straight.
Some arcminutes in the north, there also was NGC 273; longish, E-W-orientated and without any structure.
https://image.jimcdn.com/app/cms/ima...2089/image.jpg

I observed this pair after a lot of weak and/or diffucult galaxies - so it seemed to me like a colourful firework of details and structures :-)

Nice pair, one of the few objects I remember very good even when the observation is 12 years ago.

At a nearly perfect night in the High Austrian Alps I remember that the details of NGC 275 very difficult to assign in my older 16-inch and I sort them to a folk structure with a brighter bar towards NGC 274. A newer observation with 27-inch shows a knot like structure similar Howard sketched.

16", 360x, NELM 7m0+
Attachment 2741