SSPM24. Fumbling Through Fornax
By Scott Mellish, 2001
Fornax as a constellation was brought into existence by Lacaille in 1752. It precedes the mighty river Eridanus and actually is tucked into a bend in the said river.
There are not many bright stars in Fornax with a glowing at only some mag. 4. The entire area of the constellation is some 398 sq deg.
I find this whole region of sky to be one of the most exhilarating and awesome regions for Galaxy hunters, for here lie some of the most remarkable extragalatic nebulae the eye can behold.
Also there is the so-called Fornax System, a rather faint visually challenging dwarf galaxy which is a member of the local group. Edwin Hubble located two globular clusters in this object way back in 1939. Since then, the number has increased to 5. A few of these Globulars are visible in amateur telescopes, the brightest being NGC 1049.
The Fornax galaxy cluster is a fairly compact grouping of 18 or so galaxies, with a fair few fainter objects thrown in for good measure. A good wide-field eyepiece should be able to fit at least nine galaxies into one field, which gives you an idea as to the richness of this cluster. The brightest member of the Fornax cluster is the galaxy NGC1316. In the eyepiece it does appear to be an obvious elliptical galaxy in shape, but it is listed as being a spiral of uncertain classification, at least according to the Shapley-Ames catalogue. This rather strange galaxy is identified with the strong radio source called "Fornax A". The second-brightest galaxy in the cluster is the spherical system NGC 1399; this is an EO galaxy of around mag. 11.0. The less conspicuous object NGC 1404 should reside in the same field, some 8' to the south.
The glorious barred spiral NGC 1365 is ranked as the third-brightest object, and would doubtless be regarded as among the finest of its type. As you can see in the first image, this is a beautiful object and is the pick of the bunch without question.
The resolution achieved here is mind-boggling and only further strengthens the fact that this is one very impressive galaxy.
Burham's Celestial Handbook has this to say of NGC 1365: "Probably the finest object of its type in the southern sky. The bright central bar, measuring about 3' in length, has an actual extent of some 45 000 light years, while the long faint curving spiral arms sweep out for even greater distances at both ends of the bar. With a computed absolute magnitude of about -20, this is one of the most luminous of all known barred spirals. A supernova was recorded in the system in 1957".
And from Hartung's Astronomical Objects For Southern Telescopes we have this description: "This barred spiral nebula is the best object of its type for the southern observer. Photographs disclose very well-marked bar features in an elliptical system 6.8' x 3.2' which 30cm shows as a bright round diffuse centre across which is a broad faint bar about 3' long in pa. 70deg. From the ends of this come streams of faint nebulosity, from the p. end in pa. 20deg and from the f. end in pa. 200deg, so that the general shape is that of a large open imperfect ellipse with dark areas on either side of the bar. Smaller apertures show correspondingly less but 15cm indicates the bright central region clearly".
In the sketch done in the 16inch (third image) at 210x mag. you can see that this is indeed a very handsome galaxy. The bright core in itself would have to be some 1.0' x 1.0' in size, and the lovely articulate spiral arms turn sharply at each end of the central bar and protrude out in elegant sweeping curves. Both the arms form a scythe shape that the grim reaper would be proud of.
In the 23' field this lovely galaxy makes an exquisite view in the eyepiece, its size and brightness make it a treasure to behold in almost any sized telescope.
Not as pretty, but somewhat brighter is the rotund pairing of NGC 1316 and NGC 1317. The rather odd looking NGC 1316 has the distinction of being also known as 'Fornax A', indicating its presence as a strong radio source.
In the 16inch at 210x mag. this is a bright and very prominent pair that make a lovely contrast with each other. As can be seen in the DSS image (fourth image) you can probably see what I am on about.
Hartung's has this to say of this handsome pair: "In a field with a few scattered stars are two conspicuous nebulae. One is an elliptical haze about 3' x 2' in pa. 60deg with very bright nucleus easily extended into a long band by the prism; the other about 6.5'N is round, less bright, about 40" across and rising much to the centre which is extended by the prism. Both are classed as spiral systems and 10.5cm shows them plainly"
In the accompanying sketch you may see what is visible in the eyepiece at 210x mag. A very distinct and softly luminous pair of oval shaped galaxies of about mag. 10.0 for 1316 and mag. 11.0 for 1317. The pair sticks out like the proverbial you know what in the eyepiece field and are very conspicuous indeed. The sketch I did of this object may give some idea of what to expect when observing this pair (fifth image). In the eyepiece at 210x mag. what is seen is two all-too-evident galaxies, there is sparse detail visible apart from a pair of quite dominant and round cores, with the core of NGC 1316 by far the most prominent feature of this pairing. I guess the most disappointing feature of both NGC 1316 / 1317 is their lack of interesting features with such bright galaxies. I would even so much as suggest that NGC 1316 is actually boring to some extent. However, do not let this detract you from observing these two very enjoyable galaxies. They are indeed two of the 'gems' of Fornax.
In the David Malin book "Catalogue of the Universe" there is some further reference to these two objects. NGC 1316 is basically described as follows: "The brightest radio source in the small southern constellation of Fornax has been identified with the larger of the two galaxies. The larger galaxy's catalogue number is NGC 1316, and the galaxy at the top of the picture is its companion NGC 1317" this is describing the view of the accompanying photograph in the said book. It continues on as follows; "The central regions of NGC 1316 are devoid of spiral structure. However, the dust lanes visible within the galaxy suggest that it is not an elliptical, and the classification of lenticular has been adopted. Unlike most lenticular galaxies, however, the faint outer reaches of NGC 1316 have a totally irregular outline, as seen on the deep exposure negative photograph (page 41 of the book this information was taken from). This reveals that NGC 1317 seems to lie within the boundary of NGC 1316; however, the structure of the outer material is not disturbed near NGC 1317. This suggests that NGC 1317 is not actually involved, and instead lies either in the front of or behind the radio galaxy".
The description by Malin now continues as to the nature of the radio emissions emanating from NGC 1316 as follows: "The radio source is triple. Radio lobes lie one to each side of NGC 1316, and their centres are marked by crosses (you will have to imagine this with one of the pictures featured in this article). A weak third source is coincident with the nucleus of the galaxy, confirming the identification between Fornax A and NGC 1316. Radio sources in lenticular galaxies are rather rare, and most sources with radio properties like Fornax A are associated with elliptical galaxies. "NGC 1316 lies at rather over 100 million light years from us. The radio lobes extend 20 arc minutes on either side of the galaxy, which corresponds to a distance of at least 500,000 light years from their parent galaxy"
So without going into much more detail, I will conclude this post mortem, and leave you with the thought of a nice crystal clear night, out there trying to sort your way through all the lovely galaxies that are in abundance in the constellation of Fornax.