Fornax Cluster

Field containing both Fornax A and NGC 1365.

Field containing both Fornax A (NGC 1316) and the beautiful barred spiral NGC 1365. These are the two largest members of the Fornax Cluster of galaxies, which is the second nearest cluster (the nearest one being the Virgo Cluster). The Fornax Cluster consists of 108 members spread in a dense core of galaxies around NGC 1399 (not visible), the edge of which can be seen in the lower-right part of the image. A subcluster is located 3° to the south-west, (upper-left in the image), around Fornax A. Research indicates that the cluster is about 60Mly distant, and measures 4.5Mly.

As soon as dusk fell during my trip to Namibia in august '16 all attention would be on the majestic milky way, about to pass overhead. The combined light of billions of sun-like stars, shining overhead, lightens up the sky so brightly that it casts shadows on the ground, and makes it feel like it's not quite fully dark outside yet, as if the moon were still in the sky somewhere.

The milky way would set at 3am in the west, forming a an almost perfectly horizontal band along the horizon. The sky has become noticeably darker, and it would seem as if it were possible to look deeper into space now that the distracting milky way with its multitude of bright stars in Centaurus has gone under.

The darkening sky soon gives way to a sea of very faint stars, not quite visible when trying to look directly at them, but barely perceptible with peripheral vision. With the void come unfamiliar constellations, like Caelum, Reticulum, and, wedged between the mighty constellation Eridanus and Sculptor, the constellation Fornax.

There, far away from the plane of the milky way, distant wonders become visible. One such wonder is the Fornax Cluster, a grouping of at least 108 1)Substructure and dynamics of the Fornax Cluster individual galaxies. Unlike its larger twin the Virgo Cluster, this one contains two relatively large galaxies, beautifully barred spiral NGC 1365 and lenticular/elliptical galaxy NGC 1316.

The core of the Fornax Cluster is centered around NGC 1399, a giant cD-type galaxy. Only the outskirts of the core of the cluster is visible in lower right of the field. A smaller sub-cluster is located 3 degrees to the south-west, near giant elliptical galaxy NGC 1316. In this wide field image, at least 45 galaxies are visible.

NGC 1316 is the brightest galaxy in Fornax. A strong radio source, it is also called 'Fornax A'. Like NGC 1365, it studied extensively because of its interest to the cosmological distance scale, which recently put it at 62.9 MLy. This galaxy is currently in the process of merging with other galaxie(s), which result in the large stellar streams wrapped around the core.

NGC 1365, member of FA

NGC 1365, a giant spiral galaxy, is probably also a member of the Fornax Cluster. A significant effort has been placed on determining the exact distance to it because of its importance in the cosmological distance scale 2)Distance and membership of the Fornax Cluster, NED, link. It's distance has been determined to be 60Mly ± 2Mly. This makes it a truly gigantic spiral galaxy, given its apparant size of 11.2', its real size is in the order of 300kly, compared to about 100kly for the milky way.

ESO 357-28 & ESO 357-27

NGC1326A & NGC1326B, a couple of field galaxies merging resulting in vigorous star formation. The largest (NGC1326B) one measures 3.2', the smaller one (NGC1326A) 1.5'. Their brightness is about 14.4 magnitude.

Slightly northeast of Fornax A is a beautiful couple NGC1326A/B in the process of merging. The density waves cause new rounds of vigorous star formation, as evidenced by the blue color of hot, young stars. The smaller one actually shows evidence of a curved tidal stream of young, hot stars being ejected from the host galaxy. I don't know if this pair is actually part of the Fornax Cluster.

ESO 301-11

ESO 301-11, a very interesting looking irregular galaxy. The brightest core measures just 44", with a hint of a faint halo stretching out to 1.2'.

Just 23' southeast of Fornax A lies a little known (apparently) gem. This irregular shaped blob, dotted with a few bright knots, is actually a distant, irregular galaxy going by the catalog designation of ESO 301-11 or LEDA 12706. The HST observed this galaxy once in 1995, with a 80s exposure (link), and shows the edge being dotted with bright sources. It looks like a starburst galaxy. I'd love to learn more about this peculiar object!

The following excerpts are 150% crops of the original detailing the largest members that form the core of the Fornax Cluster. The scale is 1.3"/pixel, and each image spans about 6.5'.

NGC1326

NGC1326

NGC 1381

NGC 1389

NGC 1381

NGC 1381

NGC 1387

NGC 1387

NGC 1336

NGC 1336

NGC 1386

NGC 1386

NGC 1379

NGC 1379

NGC 1369

NGC 1369

NGC 1375

NGC 1375

NGC1310

NGC 1310

ESO 357-24

ESO 357-24

ESO 357-27

ESO 357-27

ESO 358-16

ESO 358-16

Finally, a selection of interesting field objects that are unrelated to the Fornax Cluster.

Cluster around FCC B613

Cluster around FCC B613

GRB 930331B

Near this bright star, on 31 march 1993, BATSE detected a gamma ray burst (GRB). No afterglow was detected. This picture also shows no hint of any background galaxy.

Unknown cluster of galaxies

Unknown cluster of galaxies

References   [ + ]

1. Substructure and dynamics of the Fornax Cluster
2. Distance and membership of the Fornax Cluster, NED, link

Image information

Galaxies, Tivoli 2016