November 2013 - Galaxy of the Month

NGC 1055 in Cetus

NGC 1055 was first discovered by William Herschel in 1783 from Slough. It is an edge on spiral galaxy not dissimilar to M104 (the Sombrero) in Virgo. The dark dust lane and bright star forming regions are believed come from its interaction with the nearby spiral galaxy M77. Indeed a low power eyepiece view will show both galaxies in the same field as they are only separated by about half a degree (a full moons width).

There is a nice image showing galaxies at NASA's APOD. The interaction with M77 also means that NGC 1055 is a bright infra-red and radio source. Images in the ultraviolet by the GALEX satellite show the blue star forming regions very clearly even though they may be overshadowed by the dust lanes. The disk as indicated by the dust lanes appears warped which is also probably a result of the interaction. NGC 1055’s nuclear region also shows some of the properties expected form a LINER galaxy although it is not clear if it is one. It does appear quite boxy and large.

Current distance measurements place NGC 1055 at 45—60 million light years and if this is so then the spatial distance between M77 and NGC 1055 is probably only about 500,000 light years, less than a quarter of the distance between ourselves and M31. This distance would also give NGC 1055 a diameter of about 100,000 light years, comparable in size to our own Milky Way.

Detailed images of NGC 1055 show structures in its halo that may well be star streams from disrupted companion galaxies.

NGC 1055 is one of the dominant members along with M77 of a small group of galaxies known as the M77 group which also includes the galaxies NGCs 1055 (type Sb) and 1073 (type SABc), as well as UGCs 2161 (DDO 27, type Im), 2275 (DDO 28, type Sm - designating a morphological type between spirals and irregulars) and 2302 (DDO 29, type Sm), and the irregular galaxy UGCA 44 and the SBc barred spiral Markarian 600.

NGCs 1087 (Sc), 1090 (S-), and 1094 (SABb-) although nearby on the sky are actually background galaxies, as their much higher redshift indicates.

The M77 group is about the same distance from us as the Virgo cluster but in a different direction. Visually NGC 1055 maybe more challenging to get details out of than images may suggest and although it may be seen in relatively small telescopes to see any detail is likely to require a telescope of 30cm or above aperture in typical UK skies.

Owen Brazell - Galaxy Section Director