Fourcade-Figueroa Object
ESO 270-017 = Arp-Madore 1331-451 = MCG -07-28-004 = PGC 47847
RA: 13h 34m 47.3s
DEC: -45° 32' 51"
Type: SBm?
Size: 11.5'x1.4'
P.A.: 118°
Mag: V = 11.7, B = 12.2
This unusual galaxy or galaxy remnant was discovered by Argentine astronomer Carlos Raúl Fourcade and the Chilean night assistant Edgardo Javier Figueroa. On the evening of 27 May 1970 they took an photograph of the Centaurus A region using the Curtis-Schmidt camera of the Cerro Tololo Observatory in Chile. While checking the plate Figueroa noticed a large object (~6.5'x1.5') in the corner, which turned out to be previously uncatalogued (a reflection of how the southern skies were still relatively unexplored by 1970).
In the discovery announcement it was suggested that the Fourcade-Figueroa Object not only associated with Centaurus A but possibly ejected as a shred in an earlier catastrophic encounter (the concept of a galaxy shred was introduced earlier by Arp).
A fuller theory (and computer simulation) of the interaction between Centaurus A and a large spiral galaxy resulting in NGC 5237 (the bulge remnant) and the Fourcade-Figueroa Object (the remnant shredded disc) was given by R.J. Thomson in the 1992 paper Galaxy shredding. I - Centaurus A, NGC 5237, and the Fourcade-Figueroa shred. Here's his summary:
"A case study of Centaurus A suggests a shred-forming encounter with a spiral galaxy (about the same size as our own galaxy) took place some 500 million years ago. The associated bulge and shred remnants have been identified as the nearby dwarf elliptical galaxy NGC 5237, and the Fourcade-Figueroa shred. The captured disc material now forms the conspicuous ring of gas and dust which girdles Centaurus A, and probably provides the rule that powers the radio emission we see today.
The shredding model described here provides a constant picture of many aspects of the Centaurus A systems, including the relative positions and velocities of Centaurus A, NGC 5237 and the Fourcade-FIguiroa shred; the orientation and sense of rotation of the dust lane in Centaurus A; the peculiar nature of the interacting dwarf elliptical galaxy NGC 5237; and the orientation and observed non-rotation of the Fourcade-Figuero shred."
I couldn't find many amateur images of the Fourcade-Figueroa Shred but it was included in the Carnegie-Irvine Galaxy Survey
Fourcade-Figueroa.jpg
Despite an total V magnitude of 11.2 (Carnegie-Irvine Survey gives V = 11.7), the surface brightness is very low so this is a tough visual object. It requires dark skies and probably a minimum aperture of 10 or 12 inches. Furthermore, due to a declination of -45.5° U.S. observers above +30° latitude will be fighting haze and atmospheric extinction, so a larger aperture is probably required. Perhaps a target for the upcoming Texas Star Party?
I was able to take a look at the Fourcade-Figueroa Shred 3 weeks ago at the OzSky Star Safari in Coonabarabran, NSW (-31° latitude). I was using a 14-inch f/4.5 dob (Zambuto optics) but knew it wouldn't be an easy object. After the observation I asked Andrew Murrell to verify my observation, as I knew he had observed it before. Here are my notes:
At 160x, an extremely faint, very elongated glow was definitely seen, particularly extending east-southeast of a mag 11 star. The very low surface brightness glow was "pointing" just south of a mag 9 star (HD 118087), which is 8' ESE of the mag 11 star (roughly the center of the Fourcade-Figueroa System), and extended ~2.5'x 0.4'. A short extension on the west-northwest side of the star was difficult to confirm but was marginally glimpsed. The mag 11 near the center forms the northeast vertex of a small quadrilateral (sides 1.2' or less) of mag 10.5, 12.5 and 13 stars. The faintest star is superimposed on west-northwest extension of the galaxy.
The one sketch I found was done by late Scott Mellish with a 22-inch f/5 dob at the Wiruna observing site at Alford NSW. His sketch very much captures the view I had when the galaxy "popped" in the 14-inch, though I didn't see quite as much extension.
Sketch Fourcade-Figueroa.jpg
By the way, NGC 5237 is also an unusual galaxy!
14" (4/2/16 - Coonabarabran, 160x): moderately bright, fairly small, irregularly round (seems to change shape with averted vision). No noticeable core but seems brightest at the west end with careful viewing. On the DSS, it appears I was detecting a blue, starburst region of the galaxy on the northwest side.
I'd very much like to hear from other observers who have viewed this galactic shred from either downunder (Les Dalrymple or Allan Wade?) or from southern U.S. sites.
GIVE IT A GO AND LET US KNOW!
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