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View Full Version : Object of the Week, April 18 2021 — NGC 5474



akarsh
April 20th, 2021, 07:07 AM
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 (https://www.deepskyforum.com/showthread.php?731-Object-of-the-Week-May-17-2015-M101-NGC-5457-Arp-26)). 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):
4291

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/objsearch?objname=NGC+5474:%5BHK83%5D+27&extend=no&hconst=73&omegam=0.27&omegav=0.73&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&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):
4292

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 (https://www.aanda.org/articles/aa/abs/2020/02/aa37284-19/aa37284-19.html)
[2] The HI Environment of the M 101 Group (https://iopscience.iop.org/article/10.1088/0004-637X/761/2/186/meta)

Raul Leon
April 20th, 2021, 12:03 PM
Hi here's my observation from 6/17/2020: Ngc 5474 dwarf galaxy in Ursa Major; magnitude:10.8 ; size:6.0'x4.9' ; fairly bright and round, with an off center nucleus, that seems to be on the edge of the galaxy. I used a 10mm Ethos at 198x with my 14.5 Starstructure Dob f/4.34293

PeterN
April 20th, 2021, 06:22 PM
Why are the Ha's blue in your attached image? Maybe the image is filtered? In a normal image it is pink and look's like a associated Ha object.

4295

Uwe Glahn
April 20th, 2021, 08:16 PM
Great choice Akarsh. I like the object, already visible in very small aperture and many structures in larger apertures.
The 27-inch shows the first individual HII spots.

sketch: 27", 293x-419x, NELM 6m5+, Seeing III
4296
home (http://www.deepsky-visuell.de/Zeichnungen/NGC5474.htm)

Jimi Lowrey
April 21st, 2021, 01:34 PM
Peter the above image that Akarsh posted is from the SDSS. The SDSS images use 3 filters combined on images the filters are G 4770 angstroms, R 6231 angstroms and I 7625 angstroms. This is why you get the unusual color on some object.

akarsh
April 23rd, 2021, 05:24 PM
Hi Peter, indeed, like Jimi said, the image is from the Sloan Digital Sky Survey. The image there is not true color, but a composite of Sloan filters, `g` `r` and `i` I believe, as Jimi mentions. Incidentally, I remember noting that the `g` band is actually pretty well aligned with the scotopic response of the eye.

This is what M 42 looks like on the SDSS image:
4301

The H-alpha band image (a grayscale image) is in the paper that I linked in the post.

Clear Skies
Akarsh

akarsh
April 23rd, 2021, 06:15 PM
Great choice Akarsh. I like the object, already visible in very small aperture and many structures in larger apertures.
The 27-inch shows the first individual HII spots.

sketch: 27", 293x-419x, NELM 6m5+, Seeing III
4296
home (http://www.deepsky-visuell.de/Zeichnungen/NGC5474.htm)

Uwe, the amount of detail in your sketch is mindblowing as expected! I see that you have caught the knot NGC 5474: [HK83] 27 as well as a few others.

Howard B
April 24th, 2021, 06:41 PM
I have a couple of observations of 5474 to contrast. The first is with my 28-inch:

"Terrific view! Lots of detail in this unusual galaxy near M101. The way off-center core is brightest along its lower edge, with what looks like a dark lane curving right underneath it, ala M64. The faint, triangular shaped fantail below the core has a broadly brighter edge with a slight protrusion directly below the core and vaguely extending towards the core. 253x and 408x, with 253x giving the best view. 21.52 SQM.

4302 4303

48-inch observation:

"Cool detail in this "soup sandwich" galaxy - 9 HII knots! All over low surface brightness, 375x, and 975x - partly cloudy sky."

4304 4305

Robin
April 25th, 2021, 07:27 PM
What a cool galaxy! I observed it 6 years ago with my 12" Dobsonian. At 84x magnification I noted a stellar nucleus that was not symmetric with respect to the shape of the galaxy. At the side facing away from M 101 there was a larger area of the galaxy that was quite diffuse.
Actually, I don't know why I didn't try or didn't take a note using larger magnification.