Galaxies NGC 1721, NGC 1723, NGC 1725, and NGC 1728

A Galaxy Group in Eridanus

NGC 1721 Galaxy Group

A 15 minute exposure taken under poor sky conditions with STL-1301E CCD camera thru Kopernik's 20-inch F/8.1 telescope. The field of view is 15x13 arc minutes, with North at the top.

The negative version below has the galaxies identified and just begins to show the very dim outer arms of NGC 1723 and outer ring of NGC 1721.

NGC 1721 Galaxy Group - Negative image with galaxies identified.

This group of four galaxies is in the Constellation of Eridanus. Three appear very close and were included by Vorontsov and Velyaminov in their 1968 catalog of peculiar interacting galaxies. Otherwise, there is not much published in the professional papers on these galaxies.

All four galaxies have similar red shifts, but there is some difference. This might reflect relative motion inside the galaxy group, or they may not be all that close in space. However, two of the three in the close group have rather strange shapes, as does the fourth galaxy. NGC 1723 (top of Koperik image) is a little separated from the others. It has a theta shaped inner ring and bar, plus two very dim spiral arms, one of which is very spread out. (These arms just barely show in the Kopernik image.) NGC 1728 is a nearly edge-on Spiral Galaxy with a peculiar distorted shape. NGC 1721 is a Barred Spiral Galaxy with two very dim and narrow spiral arms that seem to form a pseudo outer ring (again, just barely seen in the Kopernik image). NGC 1725, the center galaxy of the triplet, is a Lenticular Galaxy. There is also one small dim background galaxy in the image.

NGC 1721:

  • Magnitude: 12.9
  • RA: 04h 59m 17.4s
  • Dec: -11° 07' 08" Epoch 2000
  • Size: (mins) 2.3' x 1.2'
  • Constellation: Eridanus
  • Type: (R')SAB(s) pec, Pseudo Outer Ring,
  • Mixed Barred Non-Barred Spiral Galaxy, S-shaped, peculiar.
  • NGC 1723:

  • Magnitude: 12.5
  • RA: 04h 59m 25.9s
  • Dec: -10° 58' 52" Epoch 2000
  • Size: (mins) 3.2' x 2.0'
  • Type: SB(r)a pec Barred Spiral Galaxy, Inner Ring, peculiar.
  • NGC 1725:

  • Magnitude: 12.3
  • RA: 04h 59m 22.9s
  • Dec: -11° 07' 57" Epoch 2000
  • Size: (mins) 2.8' x 1.8'
  • Type: SO, Lenticular Galaxy.
  • NGC 1728:

  • Magnitude: 13.7
  • RA: 04h 59m 27.8s
  • Dec: -11° 07' 22" Epoch 2000
  • Type: Sa pec sp, Edge-on Spiral Galaxy, peculiar, spindle shaped.

  • George Normandin, KAS

    December 26th, 2009