NGC 7253 = VV 242 = Arp 278
Consists of NGC 7253A = UGC 11984, and NGC 7253B = UGC 11985
Interacting Galaxies in Pegasus
RA: 22:19:28 ("A" component)
Dec: +29:33:45 ("A" component)
B magnitudes: 14.22 ("A" component), 14.81 ("B" component) [1]*
Size: 1.7' x 0.8' ("A"), 1.6' x 0.5' ("B") [2]
Apologies for the late post. Several of us were at GSSP last week and I'm still recovering from camping in the heat!
Background
This week's OOTW should be well-placed just before astronomical twilight in much of the northern hemisphere, and is likely familiar to many members of this forum. The object is an interacting pair of galaxies in Pegasus, lying perhaps about 130 million ly away. The redshift of 0.015 places the pair at a higher distance of about 220 Mly according to Planck 2018 parameters. We can see that it is a true interaction from the distorted morphology of both galaxies and the presence of tails and streams.
A 1987 photometric study from the Byurakan observatory indicates that the galaxies are interacting spirals, as confirmed by the "relatively correct structure of the galaxies in the inner parts, the presence of pronounced nuclei, and presumably, spiral branches (the tail in NGC 7253A and oppositely directed processes in NGC 7253B)" [1]. Since I used machine translation with my iPhone, the exact details may be garbled a bit. The study further goes on to state that they are of morphology Sbc-Sc or SBbc-SBc. They identify 13 condensations which they suggest are HII regions based on their color indices. I have marked them on an image from the Legacy survey below.
NGC7253_Legacy.png
Legacy survey image annotated with condensations identified in reference [1]
(I'm not sure if there are errors in my calculation or the coordinates from the paper are imprecise, but you can see the boxes don't line up with the features very well. I did the precession on a spreadsheet and added some new code to my DSS tool to enable making such plots.)
They identify the "tail" of NGC 7253A, whose length they estimate at 9 kpc, as a deformed spiral branch. They also recognize a tidal filament from NGC 7253B. There are plenty of contour plots if you dig into the reference [1], but in an unusual example of Russian reversal, they are south up.
A more recent study [3] compares this pair with the Taffy Galaxies, except viewed edge-on. They too emphasize evidence of starbursts in both galaxies. This paper has a more refined H-alpha image, which does agree with a few knots from the 1987 study (e.g. 6, 7, 9, 12, 11). I am pasting it below for your convenience:
NGC7253_Halpha.jpg
Finally, there's a Hubble image of this object:
Arp_278.jpg
This one is processed by Judy Schmidt, it is not north up.
Visual Observation
I have made four observations of this object: three with my 18", but I have logs only for two of them. Back in 2015, with the moon interfering mildly, I noted a "comet"-like bushy triangular appearance which resolved into two edge-on galaxies upon further inspection. NGC 7253A was the easier of the two. This was at 295x.
More recently in 2022 June from the excellent skies of the Warner Mountains of California, I marked two edge-on galaxies arranged in a V-shape as if converging on a star. NGC 7253A once again appeared brighter of the two and appeared to thin near the double star lying east of its core. The galaxies appeared to merge at this double star. The symmetry of the interaction with the star field around it was striking.
Both these observations indicate that I missed the fainter extension of NGC 7253B that lies to the north-east of its core. I also did not log the tidal tail of the "A" component.
The latest observation is fresh out of my new light bucket, the 28" f/4 "Black Betty" formerly belonging to Jimi Lowrey that we managed to restore in time for the Golden State Star Party. While I was at a loss for objects that would really shine with aperture, Jimi called out "What about that edge-on interaction that's in Pegasus". I immediately realized what he was talking about, and managed to find its catalog numbers. Then using about 470x, I spied two elongated faint galaxies that appeared to meet nearly perpendicular to each other. The galaxies appeared rather mottled with substantially brighter middles, especially NGC 7253A. This was my last observation of that night, so I was hasty. I also vaguely remember that I lost the object before I could take a more detailed look, as my 28" still needs to be manually tracked. Perhaps under better conditions and with more energy, I should be able to nail down some of the mottling and see if I can catch the faint tidal tail out of NGC 7253A.
I imagine a smaller telescope like a 14", perhaps even smaller, should show the pair. But the challenges for the ultra-large apertures are apparent: the tidal tail and HII regions should be plenty. I know I'll be looking at this pair again, you too might as well
GIVE IT A GO AND LET US KNOW!
[1] The photometric investigation of the interacting system VV 242 (Translated using iPhone translate app)
[2] Wolfgang Steinicke's NGC/IC catalog
[3] Mapping Infrared Enhancements in Closely Interacting Spiral-Spiral Pairs -- I. ISO CAM and ISO SWS Observations (2000)
* The paper [1] talks about "integrated" and "corrected" apparent magnitudes, which I confirmed with the help of a Russian-speaking friend. I'm quoting the "integrated" one, as it lines up with SIMBAD, but I'm not sure what the corrections are.
Reply With Quote
