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Object of the Week, April 18 2021 — NGC 5474
NGC 5474 = VV 344b
Peculiar galaxy in Ursa Major
RA (J2000): 14 05 02
Dec (J2000): +53 39 44
V mag: 10.8
NGC 5474 is a satellite of M 101 and is believed to be responsible for the tidal distortion of M 101 (See the 2015 OOTW by Howard Banich). It lies only 0.74° away from M 101, which corresponds to a distance of ~300 kly from M 101 in real space [1]. It is brighter than the threshold to be considered a dwarf galaxy, so I imagine it to be sort of roughly analogous to the LMC for visual observers in M 101. It is 1.5x brighter than the LMC [1].
The galaxy has a distinctly off-center bulge, shifted to the north from the center of the visual halo of the galaxy. The point around which the matter rotates, though, lies just south of the bulge. The distribution of stars in this galaxy is also strongly asymmetric from what is typically expected. It's seemingly well-accepted that M 101 has contributed to some of these peculiar features, resulting from an interaction ~300 Myr ago. In fact, there is some vague evidence [2] for a bridge of matter between M 101 and NGC 5474 in radio wavelengths. However, [1] (which is the primary reference for this OOTW) argues that M 101 alone is not enough to explain everything, and perhaps NGC 5474 consumed a dwarf satellite in the past, or is interacting with something that's harder to observe. In any case, it looks like the story of this interesting galaxy is not settled yet.
What drew me to this galaxy? It was this peculiar blue-green thing "outside" the galaxy in an SDSS image (which I've marked with red cross-hairs):
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SIMBAD thinks it's a galaxy, but that's surely not right. The paper [1] has an H-alpha image which shows that this knot glows brightly in H-alpha. Steve Gottlieb pointed out that the knot has a Hodge-Kennicutt designation, NGC 5474: [HK83] 27. This knot is my "challenge object" offering for this week. The galaxy also has many more knots sprinkled over it, which might be good targets for a large telescope.
NGC 5474: [HK83] 27
HII region in NGC 5474
RA (J2000): 14 04 58.3
Dec (J2000): +53 41 29
NED link: http://ned.ipac.caltech.edu/cgi-bin/...&img_stamp=YES
I first observed NGC 5474 from very good skies in central Texas in April 2016. I noted a "Distinct off-center core, reminiscent of a nebula" along with this caricature (200x power):
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But more recently (March 12 2021), I gave it a shot under light-polluted skies at Fremont Peak ~1 hour south of San Jose, CA, USA. Despite the decent seeing and high surface brightness of the nebulosity [HK83] 27, I was unable to detect it, even with a nebula filter. In a 6mm Delos (~350x), the galaxy itself readily showed a faint core, followed in a few moments by a fainter halo fanning out to the south. The halo was distinctly mottled, and with averted vision, a few sizable patches of mottling could be intermittently held. Not sure if I changed eyepieces after this, but upon closer inspection, I noticed that the halo was lopsided to the south-east, and on one occasion sensed a C-shaped structure in it (only one was sensed, not two -- corroborates more with the picture in the paper [1] than the other pictures I've seen). The C-shape was a very weak observation, as were the specific patches of mottling, although the mottling itself was evident.
I'm sure y'all have some amazing observations of this object and the knots in it. If not, as always
Give it a go, and let us know!
References:
[1] The strange case of the peculiar spiral galaxy NGC 5474
[2] The HI Environment of the M 101 Group
