Object of the Week October 6, 2019 – Hickson 97 = Shkh 30

[Steve Gottlieb]

Type: Compact Galaxy Group
Constellation: Pisces
Central position: 23 47 23 -02 19 34 (2000)
Members: 5+
Distance: ~300 million l.y. (z = .022)

HCG 97.SDSS.jpg


If you enjoy observing compact groups, HCG 97 presents 5 galaxies ranging from V = 13.0 to 15.6 and presents a nice challenge for a range of apertures. Furthermore, it's the brightest of the 377 Shakhbazian compact groups of compact galaxies (Shkh 30).

The main quintet was discovered by E.E. Barnard on 28 Oct 1889 at Lick Observatory. At the time, Barnard was observing Brooks Comet (1889V) with the 36-inch Clark refractor. He didn't publish the discovery, though, until 1906 while he was at Yerkes Observatory. His sketch (below) clearly identifies all 5 members of the quintet. Don't try to match up Barnard's letter designations with Paul Hickson's - there's no correlation. Also note his sketch has south up, so you'll need to mentally rotate it 180° to match the SDSS image.

The Shakbazian numbering goes deeper and includes 6 through 11 as well as A through D, (letters added later), for a total of 15 galaxies. One or more of these, though, may be background galaxies.

Barnard sketch.jpg


All 5 members of HCG 97 are visible in an 18" scope in good conditions, though one is tough. The brightest member is 13th magnitude IC 5357 = HCG 97A = Shkh 30-1. I recorded it in my old 18" as "moderately bright, elongated 4:3 NNW-SSE, 0.8'x0.6', broad concentration. Located 3' NW of a mag 10.5 star (with IC 5351 attached)."

IC 5359 = HCG 97B = Shkh 30-5 is a thin edge-on and fainter than you'd expect for the "B" component. It was quite a dim streak in my 18", about 50" in length with a very low, uniform surface brightness. Interestingly, Barnard didn't sketch it as an edge-on in the 36-inch. It's marked with a "K" on his sketch.

IC 5351 = HCG 97D = Shkh 30-2 is interesting because it's attached on the north side of a 12th magnitude star, which partly masks the galaxy! You might also see the nucleus of the galaxy if its not washed out by the star.

The faintest member (15.6V) of the quintet is IC 5352 = HCG 97E = Shkh 30-4, which was a threshold object in my 18". I took a look at it two weeks through my 24-inch and still there was no details. Just a small, round 12" patch. Hickson failed to identify his HCG 97E as IC 5352, and this omission is continued today by HyperLEDA and SIMBAD.

Besides the quintet, there are a couple of MCGs about 12' SE (MCG -1-60-40 and -41) that you should also check out (-41 is easier). And in excellent conditions - and large enough aperture - it might be possible to glimpse one of the much fainter Shkh members. Barnard mentioned "there are probably a number more nebulae here." He was right!

This labeled image is from Rick Johnson, who passed away earlier this year, and often posted his images of obscure galaxies and groups on CloudyNights.

RJ2.jpg

As always,

"Give it a go and let us know!
Good luck and great viewing!"

[wvreeven]

Very interesting to read that there are more galaxies in the group than the "famous five", if only just visually! When I observed this galaxy group back on October 8, 2015, I wasn't aware of the fainter companions. Also I was using SkyTools 3 Pro which in some cases, for historical reasons IIRC, disagrees with some NGC and IC designations used by other sources. It labels IC 5352 as PGC 72405, something that Simbad actually agrees with but Wolgang Steinicke and DeepSkyLog don't. I am not expert on the history of certain object identifiers, so in order to stay in line with the identifiers posted here I'll use IC 5352. Please don't take this as a rant against SkyTools nor any other sources of historical information concerning object identifiers!

My observations with my 20" telescope read:

At 545x I can see all five members:
IC 5351: At 545x this galaxy appears very much elongated and is the one but hardest galaxy in the group.
IC 5352: At 545x the hardest one to spot in this group. North of IC 5357 lies a faint star. West of this star I thought I saw a smudge but this sometimes is visible as a very faint double star. Just north of the line between this star and double star I have seen a few times a very, very faint smudge.
IC 5356: At 545x faintly visible without a brighter central part.
IC 5357: At 545x I see an elongated smudge with a bright central region. It is the brightest galaxy of the group.
IC 5359: At 545x this galaxy is hard to see due to a bright star close by. I see a faint smudge next to the star.

[Steve Gottlieb]

Thanks for posting your observations, Wouter. These mirror my notes pretty closely.

As far as nearby galaxies, MCG -01-60-041 (to the southeast of HCG 97) is easier than the fainter members of the quintet, so check it out if you revisit the group. Looking at the dim galaxies displayed in the SDSS image, the one just south of IC 5356 might be glimpsed in a 20" or larger scope in superb conditions, but I haven't seen it.

Fortunately, Barnard left us with his sketch and positions of the group, so the identifications (specifically IC 5352) are not in doubt. I've rotated his sketch so north is up and can be compared directly with the SDSS image.

IC 5352.jpg

[Uwe Glahn]

Nice finding Steve.
I once took exactly this historic sketch during a talk to estimate the limiting range of the 36-inch but as you mentioned the observation was a quick look and Barnard could probably see much deeper with his eyes and the 36-inch.
For the comparison I do two observation and sketches with a 14.5-inch and my larger 27-inch. I don't add my descriptions here which can be found in my Hickson project. A funny project to re-observe Barnard's findings.

sketch: 14.5", 283x, NELM 6m5+, Seeing III
HCG97.jpg

sketch: 27", 419x, NELM 6m5+, Seeing IV
HCG97_27.jpg

[Steve Gottlieb]

Thanks for posting the sketches, Uwe.

I believe a good check on the limiting range of the 36-inch are the 17 IC galaxies discovered by Barnard and Burnham in 1890 in Abell 1783 (IC 918, 919, 921-3, 925, 926, 928-32, and 934-38).

Unfortunately, the identifications are somewhat guesswork due to inaccurate positions, but there are certainly some quite faint galaxies in this cluster that were discovered visually.

[Uwe Glahn]

Thanks Steve for the reminder of Barnard's IC 928-group. Its on my list since several years.
And yes, you could be right. With the double IC 918 or the faint IC 925 he reaches around 18vmag. That is what I estimated when I check the power of the old 36-inch Lick Refractor. And that is what he has to see when he found star H in the Trapezium and saw the star as a double.

[Steve Gottlieb]

Agreed. And the fact that he noticed and perhaps sketched these dim galaxies (I haven't seen his logbook) while scanning the field suggests he could have reached at least 0.5 vmag fainter if he had prior knowledge.

[NGC7702]

Hi All,

Interesting thread and Hickson group.

I observed it on 29th October 2018 (before my operation for cataracts in August 2019) with my 25" f/5.

I missed noticing IC 5352 on a night with good transparency but pretty poor seeing (4/10). Interestingly, the annotated image supplied by Steve above is at a variance with Megastar (using the Realsky DSS overlay) that says IC 5352 is "unknown" at RA: 23h 47m 24.0s Dec: -02° 16' 00" but plots PGC 72405 very close by at RA: 23h 47m 19.8s Dec: -02° 16' 52" Mag: 16.6. When searching Simbad, PGC 72405 is recognised while IC 5253 isn't. NED holds they are the same object. In any event, I missed it on a night of poor seeing where I was limited to x195 magnification. However ...

In observing IC 5356, my notes read: IC 5356 is probably second brightest, small, round about 20” - 30" diameter across, growing broadly and slightly to centre. There are a couple of faint magnitude 15.5 stars < 1' S and E-W of each other. This maybe a pair though the eastern-most one, in moments of better seeing looks non-stellar. On SkyMap and it certainly looks like a small very distant galaxy but no assigned designation. A further search on NED revealed it to be a galaxy -- 2MASS J23472322-0221475 and to have a R/V (+5991) consistent with it being part of the physically bound group with the others. A magnitude supplied by NED was 17.18, but no information on what wavelength.

In one of the images above it is identified as SHK 030:07 0.25. It is a bit odd I picked this one up, but missed PGC 72405 / IC 5362. Has anyone else picked up 2MASS J23472322-0221475 ?

As for the balance of the members:

IC 5351: IC 5351 has a magnitude 13.5 star superimposed or perhaps just on edge to the S, because of that difficult to determine size, maybe almost 30" diameter, seems to grow weakly to centre.

IC 5357: IC 5357 is the brightest galaxy in the compact galaxy group Hickson 97 with IC 5351 1.25’ SW, IC 5356 3’ S and IC 5359 3.75’ SE. This compact group is gathered around the magnitude 11 star GSC 5252:792 which is 2.75’ SE of IC 5357. IC 5357 is probably the brightest of the group small, round or possibly off-round halo in PA 150, probably 50" x 40" of goodish S.B growing broadly and slightly to centre where there is a small slightly brighter zone.

IC 5359: IC 5359 is of very LSB -- an edge on spindle galaxy, 40" x 5" in PA 135 growing weakly to the axis near centre, no other structure. Very faint.


Best,

L.

[Steve Gottlieb]

In observing IC 5356, my notes read: IC 5356 is probably second brightest, small, round about 20” - 30" diameter across, growing broadly and slightly to centre. There are a couple of faint magnitude 15.5 stars < 1' S and E-W of each other. This maybe a pair though the eastern-most one, in moments of better seeing looks non-stellar. On SkyMap and it certainly looks like a small very distant galaxy but no assigned designation. A further search on NED revealed it to be a galaxy -- 2MASS J23472322-0221475 and to have a R/V (+5991) consistent with it being part of the physically bound group with the others. A magnitude supplied by NED was 17.18, but no information on what wavelength.

In one of the images above it is identified as SHK 030:07 0.25. It is a bit odd I picked this one up, but missed PGC 72405 / IC 5362. Has anyone else picked up 2MASS J23472322-0221475 ?

I certainly missed this small galaxy in my 24" observation (only logged the nearby mag 15 star), though I'm in good company. Barnard apparently didn't notice this galaxy with his 36-inch observation at Lick!