Object of the Week May 12, 2013 -- MCG Galaxy Chain near M51

[Steve Gottlieb]

NED aliases: NSC J131822+471007 = [YSS2008] 264

Canes Venatici

Position (brightest member)
RA 13 18 26.1
DEC +47 13 23

Size: 7'
Mag: 15.3-16.2(V)

Type: Galaxy Chain

Galaxy chains have appeared several times in the OOTW -- Shakhbazian 166 and HCG 55 in Draco, UGC 3274 in Orion, HCG 56 in Ursa Major. Why? Well, they're unusual objects, fun to try to bust apart, and well worth several visits as better conditions can resolve new members.

This OOTW does not go by any popular name, but you'll find it less than two degrees west of M51! Furthermore, it lies just northwest of a mag 8 star (HD 115809), so it's a snap to find. I think the lack of a popular name has contributed to its obscurity -- though its similar in difficulty to many Hickson compact groups.

NED gives two designations for the chain -- NSC J131822+471007 and [YSS2008] 264. The first is from the 2003 paper "Northern Sky Optical Cluster Survey" in AJ, 125, 2064. The second is from the 2008 paper "A Spectro-Photometric Search for Galaxy Clusters in SDSS" in Astrophysical Journal Supplement, 176, 414. This study was based on SDSS Digital Release 5.

The chain consists of 5 MCG galaxies - MCG +8-24-102/103/104/105/106, which are oriented nearly N-S and span 7'. The first four have similar redshift (about z = .056), but MCG +8-24-106 = UGC 8364 is a foreground object at half the distance. The SDSS study revealed 7 members (labeled on the image below) within a radius of 1.7 million light years (.52 Mpc).

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My first view of this chain was in my 18-inch Starmaster in May 2010. I didn't have a detailed chart or image at the time but picked up 3 of the 5 members in the chain -- MCG +08-24-102, -103 and -105. I'm pretty sure at least 4 in the chain should be visible in this aperture, though UGC 8364 will be a challenge. In April 2011 I took in look in Jimi Lowrey's 48-inch and all 5 members were easily picked up, as well as a few additional members.

18-inch (280x): MCG +08-24-102 appeared very faint, very small, round, 12"-15" diameter. Forms a close pair with MCG +08-24-103 1.5' N. MCG +08-24-103 was featureless, just an extremely faint and small knot, ~10" diameter. MCG +08-24-105 was the faintest member I noticed and appeared again as a featureless dim knot, ~10" diameter, just 2.8' WNW of mag 8.1 HD 115809.

48-inch (488x): MCG +08-24-103 appeared fairly faint, small, slightly elongated E-W, 15"x10", bright core. Similar MCG +08-24-102 lies 1.5' S and also appeared fairly faint, small, round, bright core. MCG +08-24-104, 1.9' further SSE, was logged as fairly faint, very small, round, 15" diameter, bright core. Forms a close pair with 2MASX J13182879+4711120, a compact companion 26" SSW. MCG +08-24-105 appeared moderately bright, fairly small, elongated nearly 3:2 N-S, 20"x14". Forms a close "pair" with a mag 17 star just 8" W. Finally, MCG +08-24-106 = UGC 8364 appeared very faint, extremely thin 5:1 SW-NE, 30"x6", very low surface brightness. Situated 1.2' SSE of MCG +08-24-105 and just 2.3' WSW of mag 8.1 HD 115809, which makes viewing more difficult.

2MASX J13182879+4711120 is located just 26" SSW of MCG +08-24-104 and appeared very faint, very small, round, 8" diameter, stellar nucleus. 2MASX J13183912+4711011, 1.2' ESE of MCG +08-24-104, was very faint, 10"x6" NW-SE. 2MASX J13185089+4709452 (missing from Megastar) is located just 1.4' NNE of the mag 8.1 star. Despite the glare of the bright star, it was easily picked up as a faint, very small, round glow.

I'd be interested in hearing how many of these galaxies can be picked up in various apertures.

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"GIVE IT A GO AND LET US KNOW"

GOOD LUCK AND GREAT VIEWING!

[Jimi Lowrey]

Great OOTW pick Steve this is one that flies below the radar. I have wounderd why Hickson did not have this one in his catalog? If you have not seen this I highly recommended it next time you are near M51.

[reiner]

Hi Steve,

thanks for showing us this group. It looked interesting and I put it on my to-do-list. Last night was the first opportunity to give it a try with my 22" (out weather condititions in southern Germany had been a bit suboptimal for the last months :-( ).

The star pattern was easy to find, but at a first glance no galaxy was visible at all. It took some time with averted vision until the first galaxy could be discerned. That was 102 which appeared to me to be the *easiest* of the group (being not easy at all), accessible from that triangle of stars. Neighboring 103 was a bit tougher and took some time to be seen with confidence. Switching to the brighter star at the other end, I could resolve 105, being equally difficult as 103. I was not sure about 104. Something appeared to pop in and out over time, but I would not say that I saw it with confidence. Sky conditions were OK, but not great.

This is a challenging group and a lot of fun hunting the single galaxies.

[Steve Gottlieb]

Thanks for posting your observation, Reiner. Out of curiosity, do you take SQM readings when you observe? As a reference, the site where I observe this chain typically has SQM reading of 21.5-21.6, with 21.4 on a sub-par night and 21.7 on an excellent night. It does seem recently, though, conditions have been sub-par to average -- don't know if this is related to solar activity.

[reiner]

No, I don't take SQM readings. There had been some hype here about SQMs several years ago, but that has changed. For my observing locations in southern Germany, SQM readings do not correlate well with perceived sky quality (reflected by the observability of difficult deep sky objects). Our skies are limited mostly by transparency (rather the lack of it), and not by light pollution. And SQM readings do not correlate well with transparency.

Last summer, we had had a discussion here as well in how far increasing sky glow had picked up with increasing solar activity. Uwe might tell you more about this, I had not followed it closely.

The last two nights, I had an fst of around 6.0. At 48° N, we do not have yet those true "white nights", but nevertheless, I have the feeling that it does not get fully dark. In winter, my location has usually fst 6.5, and reaches 7.0 in very few exceptional nights.

[RolandosCY]

Hi everybody,

Last night we had (finally!) some decent observing conditions. Unfortunately, our "seaside" site which gives us amazing views of the southern horizon has been destroyed by three little "surfing clubs" (!) which sprang up, so with only a few hours available for observing we picked our alternative site on a private ranch to which I have access. From this ranch the best skies are at the zenit and to the north to west. With M51 being superbly placed, I decided to give a go to this challenging galaxy chain with my 18".

It was very easy to locate the field (I would have never thought a few years ago that I would be using M51 as a star-hopping stone for nearby galaxies!). The bright star on one side of a 294X field with the little triangle on the other side were very characteristic. The only problem, at first, was the ... lack of galaxies!!!! No galaxy was visible! On goes the DSA hoodie, deep breaths, and I try again. Yes! With averted vision I suspect something. It is on and off, between the bright star and the triangle, nearer to the bright star. I can hold it with averted vision most of the time (I do lose it momentarily). At some point it kind of goes. Another deep breath, here it is again, I can hold it better now with averted vision. I do have the impression that the extremely faint patch of light I see there is lumpy, but I cannot really say that I can see individual galaxies. It is a general lumpiness in a patch of light slightly above the sky brightness. Fellow DSF member NicosCY also confirms that he can see something in the area but cannot really pin it down.

I did try a bit more on this chain, hoping I would finally be able to "break" it down to individual galaxies, but to no avail. as the time moved on I could hold the fuzzy brightness with averted vision all the time, but I was never really able to say that I could split the galaxies. Based on the photographs I believe what I perceived was the combined light of -102 and -103. I hope to be able to re-observe this group in early July from darker mountain skies, before M51 starts to dive to the west.

The above observation was made with my 18" Obsession and a TV Nagler 7mm, under SQM 21.0 skies...

[RolandosCY]

I was lucky enough to have a second go on this group last night, from the same exact locality, but with significantly improved conditions, especially in regards of transparency ( and the SQM improved to 21.15 from 20.98 last night). Knowing the exact field, it was just a matter of concentrating hard and taking all necessary precautions to prevent stray light (thanks Dragan for the Hoodie!). Initially all I could see was again what appeared to be a general brighter patch to the northwest of the distinct asterism. I tried increasing the magnification to 488X but I could no longer locate the brightness. Back to 294X I could again perceive the glow. It was definitely easier to see and hold than during the previous evening, but I would not call it easy!

By taking deep breaths and keeping HD 115809 out of the field of view I slowly started to see two distinct roundish glows where I could see the general glow before. After spending several minutes I could steadily hold with averted vision two very faint spots. I took a break, walked around, returned to the eyepiece, and again I could steadily hold with direct vision two very faint smudges (like slightly out of focus stars) at the same location. With direct vision the two smudges would initially disappear, only to re-appear as an on-off general glow in that area - practically what I could see with averted vision the previous evening.

I had yet another 10 minute rest and I tried again with the same results. The two spots would disappear with direct vision, or if HD 115809 was in the field. I tried hard to see other potential candidate galaxies of the chain, but to no avail. The presence of the asterism on top (south) of the field, the 8th mag star to the north, and a pair of 16th mag stars north of the asterism were helpful to "anchor" the correct position of the galaxies on the sketch I produced. The positions correspond to MCG +8-24-102 and -103. Needless to say, the galaxies appear much brighter than real in the sketch! Thanks to Steve Gottlieb for pointing out this treasure!

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[bearkite]

Was able to give this a look this past Saturday from High Knob Overlook in North Central Pennsylvania. Decent transparency (5/5) and seeing (4/5) with SQM of 21.15 at the time of the observation.

Cut from my ST3 Log:

<<<<<<<<<<SNIP>>>>>>>>>>
TeleVue Delos 6mm, 351x
MCG 8-24-106 Observed as very faint edge on in format. Took very carefull averted vision to resolve. Confirmed by Josh Wright. LEDA 2293741 and LEDA 2293849 observed as stellar, no extension with averted vision. MCG 8-24-103 resolved as extremely faint smudge with averted vision. No stellar core.
<<<<<<<<<<SNIP>>>>>>>>>>

Having spent a significant amount of time chasing Hicksons I found this chain to be difficult at best. The odd thing was the two LEDA's in the middle of the chain. I assumed they were field stars and was surprised that they appear to be stellar cores for those two galaxies. Can't have two side-by-side galaxies that just happen to align with field stars... Right?

And Steve... 21.4 is a sub-par night? I have GOT to get back west. These Pennsylvania skies are killing me...

[Steve Gottlieb]

Thanks for posting your observation, Lou. It's interesting we picked up different objects -- I missed the edge-on UGC 8364 = MCG +08-24-106 in my 18" (also CZ optics), but found MCG +08-24-102 brighter than nearby MCG +08-24-103 (1.5' separation), though both were visible.

The two LEDA galaxies you noted as stellar are actually fainter than all 5 MCG's. Here are the mags I could dig up...

LEDA 2293741 = 2MASX J13182555+4710490
V = 17.3 (computed using g and r mags in SDSS Data Release 9)
B = 18.0 (from HyperLeda)

LEDA 2293849 = 2MASX J13182879+4711120
V = 16.9
B = 17.6
logged as "very faint, very small, round, 8" diameter, stellar nucleus" in the 48-inch

> And Steve... 21.4 is a sub-par night? I have GOT to get back west. These Pennsylvania skies are killing me...

Mark Johnston and I were back to same site on Saturday night and I believe the SQM readings were in the 21.55 range (Mark may have more accurate figures), but the seeing was miserable so still sub-par! Nevertheless, I'll post some observations in the next day or two of several KTG triplets and ROSE quartets from the past two weekends.

[Howard B]

Here's my observation and sketch from the 2013 GSSP:

"All five galaxies are seen, and the two by the brightest field star are the most difficult. Putting the star outside the fov makes both much easier to see. It took me a while to start this observation because about a dozen people stopped by for a look at M51, and after they left the circular baffle in the scope came loose! I quickly put both baffles where they normally go and was back in business in a few minutes this all added up to about an hour delay to this observation. 253x - 408x, 21.65 SQM."

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[akarsh]

Unaware of this thread, I posted my observations here: http://www.deepskyforum.com/showthread.php?852-The-quot-MCG-chain-quot
Very interesting object.