HCG 61 = The Box
Compact Group of Galaxies
RA: 12 12 26
Dec: +29 09 57
This compact group comprises of four galaxies, all with NGC designations:
NGC designation Redshift (z) Distance (Mly) Size Mag (V) NGC 4169 0.0127 170 1.8' × 0.9' 12.34 NGC 4173 0.0037 33 5.0' × 0.7' 13.3 NGC 4174 0.0134 175 0.82' × 0.5' 13.6 NGC 4175 0.0131 182 (or 118?) 1.8' × 0.4' 13.4
In the above table, all data is from NED except for the magnitudes which are from SIMBAD. There is stark ambiguity between the redshift-based (182 Mly) and the redshift-independent (118 Mly) distance to NGC 4175. The 118 Mly distance is based on 3 references in NED, all three using the Tully-Fisher relation.
Of course, it is evident from the redshifts that NGC 4173 is a foreground galaxy, whereas the remaining three (likely) form a bonafide group with a distance of about 180 Mly.
There isn't much literature on the group as a whole, and I did not dig deep into the individual galaxies. One reference indicates that this is a relatively gas-rich group and notes the disturbed morphology of NGC 4175. That NGC 4175 has something interesting going on can be seen by looking at the POSSII Blue image:
HCG61.png
DSS2 Blue image of HCG 61. The cross hairs mark the knot in NGC 4175
I'm not sure what the knot marked in the above image is, but perhaps this is related to the disturbed morphology discussed in the reference. The legacy survey image seemingly doesn't give more insight into this knot:
HCG61Legacy.png
Legacy survey image of the group
This deep image from the Legacy survey however does show what look like tidal disturbances in NGC 4174 and NGC 4169, perhaps a result of their interaction.
Incidentally, SIMBAD lists a background (8.8 Gyr light travel) quasar of 20th mag shining through NGC 4173, named 2XMMi J121226.7+291117, perhaps a real challenge for Jimi Lowrey's 48".
This object was on my mind because of a recent observation made at a star party in south India, on the night of Jan 13 2024 using Jagan Gorti's 16" Hubble Optics telescope equipped with a Baader Hyperion zoom eyepiece. I logged "Spotted all 4 galaxies, a-c were continuous direct vision with a being brightest. d was hardest, continuous AV, elongated." The conditions were of subpar transparency and perhaps best described as Bortle 4. However, the beautiful arrangement of galaxies was well-appreciated by many of the visual observers gathered on the field.
But of course, this group is too amazing for me to have not observed it before. Surprisingly, I've only logged it twice in the past. On 29th March 2014, I observed the group from Bortle 2 skies in central Texas (near Pontotoc, TX) using my 18". I described it as "Easy, bright and nice!" while marking that NGC 4173's elongation was easily seen.
But the more interesting observation was a birthday treat on my 28th birthday! Through Jimi Lowrey's 48" telescope, I described the group as spectacular. My observation marks a "mild knot?" on NGC 4175 right where the knot lies, and notes a "sensation of a dark lane all through".
I am looking forward to seeing all the beautiful sketches you have of this group. Whereas most of you have seen it already, this group is perhaps worth re-visiting. If you haven't seen it yet, all the more reason to
GIVE IT A GO AND LET US KNOW
Clear Skies
Akarsh
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