IC Galaxies in Pavo

Most observers overlook the plethora of galaxies in the southern constellation of Pavo, other than the spectacular face‐on spiral NGC 6744. And, even then, they get stung by the published magnitude of 8.3. Since this galaxy is very large, 13’x20’, the light is spread over a large area, producing a surface brightness of just 14.1! No wonder it’s difficult to see in a telescope smaller than 12”.

The lesson here is to also look at the surface brightness (SB) of any extended object, when compiling your observing plan.

This month, I thought I would highlight some galaxies that are often off the beaten path. These belong to the IC catalog. Two Index Catalogs (IC) were published as supplements to the New General Catalog (NGC). They were compiled, as was the NGC, by John Dreyer. The first (IC I), published in 1895, added 1,529 new star clusters, nebulae, and galaxies; the second (IC II), published in 1908, listed a further 3,857 objects. Today, the IC Catalog contains the entries from both original catalogs. AstroPlanner software lists over 100 IC catalog galaxies, in Pavo, visible within the capabilities of medium sized telescopes.

The 5 brightest IC galaxies in Pavo are listed in the following table.

Object Type Mag Surface Brightness Size (arcmin)
IC 5071 Galaxy 12.6 13.4 0.8 x 3.4
IC 5096 Galaxy 12.5 12.8 0.5 x 3.2
IC 4721 Galaxy 11.8 13.8 1.5 x 5.2
IC 5052 Galaxy 10.6 12.2 0.9 x 5.6
IC 4871 Galaxy 13.3 13.5 0.4 x 3.5

IC5052 is one of the largest and brightest in this collection. We view this galaxy edge‐on, and spiral galaxies are viewed from this angle, it is very difficult to fully understand their properties and how they are arranged. IC 5052 is actually a barred spiral galaxy – its pinwheeling arms do not begin from the centre point but are instead attached to either end of a straight "bar" of stars that cuts through the galaxy's middle.

Approximately two thirds of all spirals are barred, including the Milky Way.

In the 16" telescope, at 152x, this galaxy appears as a beautiful, narrow edge‐on streak with little or no central concentration. It is very elongated. It displays a slightly bulging core, with one half seemingly brighter than the other. The almost face‐on spiral, 11.4 mag NGC 6943 lies 43' to the northwest.

IC4721 is a large spiral, 89 million light years away. Classified as an SBc spiral, the view is inclined to us; and because of its large size, it has the largest SB of the galaxies in this collection. Try using a hoodie to protect your eyes from all stray light. Then, also look for its 14.5 mag companion IC4721A, just 2’ south of the core. Another galaxy, 13.6 mag IC4720 is only 9’ to the northwest.