NGC 1622 in Eridanus

January 2019 - Galaxy of the Month

NGC 1622, along with NGC 1618 and NGC 1625 form a nice triplet just north of the bright star Nu Eri.

The discovery history of the group is quite interesting as they are all relatively bright galaxies. NGC 1618 was found by William Herschel in 1786, NGC 1625 by John Herschel in 1827 whilst reobserving his fathers’ discoveries and NGC 1622 by George Stoney whilst using Lord Rosse’s 72” at Birr in 1850.

NGC 1622 was also independently discovered by d’Arrest on the 1st Jan 1862 using the 11” Refractor at Copenhagen, no New Year’s Eve’s parties for him! You would have thought that William could have picked up NGC 1625 as well, although NGC 1622 may have been to faint for him. Perhaps scattered light from Nu Eri impacted his observations.

John Herschel originally thought that the discoveries by Stoney and d’Arrest were two separate objects and added them into the GC as such (numbers 881 and 878). Dreyer spotted the error and merged both into NGC 1622.

The galaxies may form a physical system as they all have similar redshifts. All three are spiral galaxies with an inclination close to edge on, with the exception of NGC 1618 which is rather wider open.

None of the galaxies show any obvious signs of interactions, although the outer disk of NGC 1622 does appear to show quite a strong warp. NGC 1625 also seems to show a slight warp in its disk and also appears to have a galaxy superimposed on its disk. Given the radial velocity of the object it may well be a dwarf galaxy associated with NGC 1625. The group would appear to be about 220 million light years away.

All the galaxies in the group appear to be barred spirals which is relatively unusual. Of the three it would appear that NGC 1618 is the one most actively forming stars at this time.

The group is tight enough that it will fit in the field of a modern hyperwide eyepiece at medium power. The Night Sky Observer's Guide (NSOG) suggests that it is a tough target for 8-10” telescopes but should be easy in 14-18” ones.

I suspect the main challenge seeing the galaxies here is going to be keeping the 4th magnitude star Nu Eri out of the field whilst looking for the galaxies, a similar challenge to that with NGC 404 and Mirach in And. The galaxies are quite faint and may well require a telescope in the 40-cm plus category to show well, especially from UK skies.

If these are not enough of a challenge then the compact group Hickson 30 lies only 20’ north of NGC 1622. Hickson 30 contains no NGC galaxies, although the brightest galaxies are around 14th magnitude so it should be visible in larger scopes.

Owen Brazell - Galaxy Section Director