Object of the Week, March 18 2018 -- NGC 4054, a cosmic collision in Ursa Major

NGC 4054 = VV 136

Constellation: Ursa Major

RA: 12 03 12 Dec: +57 53 36

Mag: ~15.2

Type: Galaxy triplet

NGC 4054, aka VV 136, was discovered by William Herschel on April 17, 1789 and described as "extremely faint and small." Herschel only noted a single nebula through his 18-inch speculum reflector, but in 1959 Russian astronomer Boris Vorontsov-Velyaminov catalogued NGC 4054 as a triple system (VV 136) in his Catalogue and Atlas of Interacting Galaxies.

NED (NASA-IPAC Extragalactic Database) only shows 9 references and no special notes on this system, so it has been ignored by professional astronomers.

I last observed it on April 20th last year at 488x and all 3 members were easily visible within a 1/2 arcminute circle. VV 136a is the largest member, but VV 136b (just southeast) has the highest surface brightness with an extremely bright core. VV 136c on the northeast edge is the faintest member but was direct vision and elongated in the eyepiece.


Attachment 2937

While doing some research on this object, I noticed on the SDSS image what appears to be an anonymous object squeezed between two others. It seems like I always learn something new about an object when I go to write an OOTW. If you observe NGC 4054, let us know how many objects you can resolve. I know I'm looking forward to reobserving to see if I can resolve the anonymous galaxy (labeled on image).

PANSTARRS image
Attachment 2938

GIVE IT A GO AND LET US KNOW!

Here's my observation of NGC 4054 from June of 2016. I also resolved the B component through a 16-inch SCT back in 2007, though it was quite small and I missed VV 136C.

24-inch (322x): the western and largest component (VV 136A) of the triple system NGC 4054 appeared faint, small, slightly elongated, ~20" x 15", low surface brightness. The southeast component (VV 136B) was smaller but displayed a significantly higher surface brightness. It was noted as fairly faint, very small, elongated ~12" x 9" E-W. The centers of these small galaxies are separated by just 15". VV 136C, the northeast component, was not seen.

One of my favorites from the Herschel catalog. I read in Mark Bratton's book about the possible 4th component when I first observed the group, but to date have not seen it.

April 2016. "Like a nebulous triple star." 12", 230x, SQM 21.8-21.9, seeing 7/10.
Last night. Sketch below. 20", 360 and 500x, SQM 21.5, seeing 4/10.

Attachment 2940

I took another look at NGC 4054 last night after moon set under clear transparent skies. The seeing was below average for here though.

I was looking forward to see if I could resolve the anon galaxy. At 610x the seeing was a little soft but was comeing and going and at brief times the view was ok. The bright star like core of VV 136b was washing out the view with the sub par conditions. I did have a couple of pops but nothing I would log as a positive observation. I think it is going to take high power and good seeing to catch this little bugger. I will keep at it!

Ran Aladin on it with SIMBAD and NED. The NW knot in VV 136a, which looks red on SDSS, is mag 20.4g galaxy 2MASX J12031176+5753408, redshift unknown. The SE knot (just N of VV 136b) is mag 19.6g star SDSS J120313.72+575331.2. The former is in NED and SIMBAD. The latter is in NED. The "star" is barely printing through in the 2MASS data. If the red object is indeed a galaxy, it should be far in the background to the approx. 450 Mly VV. The SDSS and 2MASX star-galaxy criteria are nothing to put much stock in in a specific case like this, but this is what the catalogs are saying.

Also miss the forth galaxy Jimi but I think it is beyond me reach. Nevertheless, interesting compact trio indeed with some nice companion galaxy field.

27", 419x-586x, NELM 6m5+, Seeing III
Attachment 2943

The 4th galaxy that Jimi refers to is SDSS J120313.75+575331.5 (in DR12), the tiny one just north of VV 136b. SDSS photometry (DR12) gives g = 17.09 and r = 17.26, which suggests V ≈ 17.2. But the r-mag is almost always brighter than the g-mag, so perhaps these numbers are not reliable.

Quote:

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Originally Posted by Ivan Maly

One of my favorites from the Herschel catalog. I read in Mark Bratton's book about the possible 4th component when I first observed the group, but to date have not seen it.

April 2016. "Like a nebulous triple star." 12", 230x, SQM 21.8-21.9, seeing 7/10.
Last night. Sketch below. 20", 360 and 500x, SQM 21.5, seeing 4/10.

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Great observation and sketch, Ivan. I'm impressed you picked up the 3rd (NE) component VV 136c in your 12-inch. SDSS gives g = 17.25 and r = 16.77, suggesting V ≈ 17.0!

Is the object type for SDSS J120313.75+575331.5 "galaxy"? It is not in NED but when mapped is identical to the SDSS star that I mention.

Thanks, Steve. Vm 17.0 doesn't sound too scary for the well-baffled SCT I was using under such excellent conditions, but the description I left after that brief look at the survey magnification did not imply a full resolution of the components, only that there was something ternary about the object's appearance.

Quote:

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Originally Posted by Ivan Maly

Is the object type for SDSS J120313.75+575331.5 "galaxy"? It is not in NED but when mapped is identical to the SDSS star that I mention.

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Here's the SDSS page. Yes, the object type is given as "galaxy" in SDSS Data Release 12.

Thanks, I see it now. The classification changed from "star" to "galaxy" between DR7 and 8, but was apparently retained in NED. The "photoZ" estimates between the releases have been all over the place, including an early value (DR6) that was commensurate with the VV triplet z (0.039 vs. 0.034), but the last three (DR12-14) place the galaxy far in the background (photoZ=0.12). And the history of the classifications is the opposite for the 2MASX object that I mentioned. Needless to say, visual inspection of the images agrees with the later classification of both, although the weakness of the object N of VV 136b in 2MASS is puzzling.

This is interesting. I looked at my notes from 7yrs ago when I observed this group with my 12.5” as part of my Herschel 2500 quest. I don’t pre look things up before observing so actually noted VV136b as a bright star that detracted from the glow/structure of NGC 4054. I think this is funny. I guess the next time I’m out I’ll need to check this out again with my 20”. It won’t be a big deal as I’m already working this area of the sky as I tidy up the final couple hundred of the Herschels.