Hickson 61, The Box

Object Description

Hickson 61
Hickson 61: Crop from Sloan Digitized Sky Survey [147]

In 1981 Paul Hickson presented his systematic search for groups of galaxies on the photo plates of the POSS to the public. In order to be classified by him as a galaxy group, at least four members should be identifiable, which had to be reasonably compact and isolated from the rest. The catalog contains 100 groups of galaxies.

The galaxy group with NGC 4169, which is the brightest of the four, has the number 61 in Paul Hickson's Atlas of Compact Groups of Galaxies and is also labeled The Box (not to be confused with NGC 6309, Box Nebula). The name is appropriate because the four galaxies form approximately a rectangle to one another. The four galaxies show no trace of interaction on the POSS photo plates.[96]

The galaxy NGC 4169 in the southwest corner is of the compact type S0, the intermediate stage between a spiral galaxy and a barred spiral galaxy. We look at it from the side, because its axis of rotation is inclined by 70 degrees to our line of sight. The escape speed in relation to the local group is around 3800 km/s. With a Hubble constant of 75 km/s/Mpc, this means a distance of around 170 million light years. [134]

Hickson 61
Hickson 61: Galaxy Group in Coma Berenices; 500/2500mm-Newton + SBIG ST-6; 6x30s; Bülach Observatory; © 22. 7. 1996 Stefan Meister

In the case of the elongated galaxy NGC 4173 in the northern corner, we look exactly at the edge, which makes it difficult to determine its type. In the Deep-Sky Field Guide to Uranometria 2000.0 [22] you can find the type SBd and in the Lyon-Meudon Extragalactic Database [134] the type Scd. Both are very open systems with sweeping spiral arms. NGC 4173 is moving away at a speed of only 1000 km/s, which equates to a distance of only 43 million light years. So it doesn't seem to belong to the group, but she still included Paul Hickson. NGC 4173 is also a bit out of line because of its low surface brightness.

NGC 4174 at the southern corner is by far the smallest of the four galaxies, but still much brighter than NGC 4173. In this spiral galaxy, too, we are almost looking at the edge, because the angle between the axis of rotation and the viewing direction is about 72 degrees. It shows the same escape speed as NGC 4169, so also the same distance. [134]

The galaxy NGC 4175 in the west of the group of four is a spiral galaxy of type S or Sb, roughly like M 31. The angle of inclination is 86 degrees, so we are almost looking at the edge. Their escape speed is somewhat higher with about 3900 km/s relative to the local group, which equates to a distance of 170 million light years. [134]

«Catalogue of Principal Galaxies (PGC)», Paturel et al. 1989 [144]
NameRA [hms]Dec [dms]mTypeDim [']Btot [mag]HRV [km/s]PA [°]
NGC 4169, HICK 61A12 12 18.9+29 10 49L M1.8 x .913.23808153
NGC 4173, HICK 61B12 12 21.5+29 12 24S M5.0 x .713.41105134
NGC 4174, HICK 61D12 12 26.9+29 08 57S M.8 x .314.4398050
NGC 4175, HICK 61C12 12 30.6+29 10 09S M1.8 x .414.23938130

Finder Chart

The galaxy quartet is not that easy to find among the vast numbers of galaxies in the Coma/Virgo cluster. About four degrees west and one degree north of 4.4 mag bright star γ Comae Berenices are started using a large field eyepiece to search for the star patterns shown in the 1° close-up. Since the quartet of galaxies appears faint and inconspicuous, an eyepiece with a field of view of around 15 arc minutes is recommended.

Chart Hickson 61
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

References

22«The Deep Sky Field Guide to Uranometria 2000.0» by Murray Cragin, James Lucik and Barry Rappaport; Willmann-Bell, Inc.; ISBN 0-943396-38-7
96Objekte der Saison: NGC 4169/73/74/75 von Klaus Veit; Interstellarum2/96, S.52
134Lyon-Meudon Extragalactic Database (LEDA); leda.univ-lyon1.fr
144Catalogue of Principal Galaxies (PGC); Paturel G., Fouque P., Bottinelli L., Gouguenheim L.; Astron. Astrophys. Suppl. Ser. 80, 299 (1989); cdsarc.unistra.fr/viz-bin/cat/VII/119 (2021-02-18)
147Aladin Lite; aladin.u-strasbg.fr/AladinLite (2020-12-23)
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form