Object of the Week, April 24, 2016 - The Fourcade-Figueroa Shred

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

Attachment 2075

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.

Attachment 2076


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!

Nice and unusual object Steve. I can contribute with 2 observation from Germany ;)

12", 150x, NELM 7m0+ (Hakos/Namibia)
very faint thing with extremely low surface brightness; difficult to detect because of the rich star field; only the central longish part is visible, which runs and ends into a quadrilateral at the west side (which Steve also described) this eastern part could be detected around 2-3' long

28", 190x-260x, NELM 7m5+ (Gamsberg/Namibia)
easy to detect; a quick and dirty observation shows a 7' long streak of light; E side seems to end sharply, W side runs in quadrilateral which merge with the glow of the galaxy and causes visually a brighter part of the galaxy; galaxy itself seems to continue a little bit over the quadrilateral to the west

I heared about this object from a friend a couple of years ago. But I didn't know it was so interesting.

I took a look at it with my 4" (40x, 1.8° field) from Hakos, Namibia in 2012. The conditions were exceptionally good even compared to the very good nights before. I had no intention to draw it and didn't even taken notes. Memories are fading but I remember that I have seen an extremely faint elongated object on the very edge of visibility. Another friend András Papp took a look at it as well, but I don't remember if he confirmed my sort-of observation or not.

But the day after tomorrow we are flying to Hakos for 2 weeks and I will definitely take a better look at it.

Interestingly the DSS image shows quite a few extensions, almost makes it look like a cuttlefish Attachment 2077

Owen

maybe interesting to mention, that this galaxy belongs to the RFGC - the superflat galaxies... nice object choice.

CS
Norman

Quote:

---

Originally Posted by Steve Gottlieb

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

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.

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!

---

Hi Steve,

I am glad my 14" scope was up for the challenge :D !!

As you could appreciate this target makes the list of "tough objects I want to observe" each and every year at Ozsky, which I have been doing for over 10 years. Consequently, I have observed it a lot of times from Coonabarabran (and a few other good sites) over the past 10 years. I have observed it on a couple of occasions in my 14" scope, many times in the 18" scopes, the 25" scopes and the 30" scope. I have never tried to observe it in anything smaller than my 14" scope although I am guessing my 10" scope, which also has a great mirror in it, might do it under good skies.

Even in the larger scopes I don't get much extra detail from it, other than the brighter central bulge becomes a bit more extended. Pumping up the power to around 300X to 350X helps improve contrast and also helps to extend the central bulge a little.

Cheers,
John B

Quote:

---

Originally Posted by Steve Gottlieb

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

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?
GIVE IT A GO AND LET US KNOW!

---

Hi Steve,

I observed quite a few targets in Centaurus from TSP in 2007 in 12" to 36" scopes. My feeling comparing how I see those targets compared to how they appeared at TSP is that to see this target from TSP you will need a scope at least in the 20" to 25" class. For instance observing Omega Centauri (NGC 5139) in Larry Mitchell's 36" scope to me was equivalent to observing it in about an 18" scope from Coonabarabran. Van Robinson (Van has made 5 trips to Coonabarabran) and Andrew Murrell who were with me at the time at TSP, also agreed with my assessment.

Cheers,
John B

Quote:

---

Originally Posted by ausastronomer

Hi Steve,

I am glad my 14" scope was up for the challenge :D !!

As you could appreciate this target makes the list of "tough objects I want to observe" each and every year at Ozsky, which I have been doing for over 10 years. Consequently, I have observed it a lot of times from Coonabarabran (and a few other good sites) over the past 10 years. I have observed it on a couple of occasions in my 14" scope, many times in the 18" scopes, the 25" scopes and the 30" scope. I have never tried to observe it in anything smaller than my 14" scope although I am guessing my 10" scope, which also has a great mirror in it, might do it under good skies.

Even in the larger scopes I don't get much extra detail from it, other than the brighter central bulge becomes a bit more extended. Pumping up the power to around 300X to 350X helps improve contrast and also helps to extend the central bulge a little.

Cheers,
John B

---

Thanks for your comments, John. My first view of Fourcade-Figueroa was actually back in 2002 during my first trip to Australia (this was my 7th!). Les Dalrymple showed it to me in his 12.5-inch from Bargo. But I recall it was definitely a *marginal* observation -- particularly as I didn't know exactly what to look for. So, the view earlier this month was much easier to accomplish, particularly from darker skies.

I contacted Les Dalrymple about his experiences with the F-F Object and here's his reply --

"Yep, have seen it several times. It is a threshold object in pristine conditions (when I had younger eyes) with 31cm. It is still difficult with 46cm. It is a "shredded galaxy" or more correctly a "galaxy shred" as it is not rotating along any axis -- most likely a segment of spiral arm that has escaped Centaurus A*. It is near Centaurus A* and not all of it is visible -- just a small 3' x 1', partly superimposed upon a small rectangle of mag 12-13 stars that make locating it fairly easy. Very, very, LSB.

I have now read your post in the forum and it is spot-on. I did a write-up on the whole M83-Cen A* cluster several years back that was published in one form in S&T and in another form in Australian S&T."

Had a go last night with the 48" from West Texas it just clears the wall of my observatory. I have tracked down this faint streak before. We had SQM readings last night from 21.88 to 21.99 its very low surface brightness and the best view of this faint extended streak was with a 21 Ethos.

We took another look at the Fourcade-Figueroa Object this May's new moon at Hakos, Namibia. This time I haven't seen it in my 4" Newtonian (in fact I doubt that I had seen it last time). But it was not hard at all in the 16" scope. A very long very much elongated object with lots of bright stars in the field. No drawing this time either. Now (2016 May) the conditions were not as good as last time (2012 June). Skyglow was much stronger and both transparency and seeing were a bit poorer.

In 2012 from Coonabarabran I saw the FF thread using a 30". At the time I thought the current theory was that it WAS the remnant galaxy that hit Cent A. But thanks to Steve's mentioning the Thompson paper of 1992 I see that it is now believed the FF object should be "demoted" to the FF thread and that NGC 5237 (which I have not looked for--something for the future) is the main (or at least another) remnant.

I happened to view the Fourcade-Figueroa system on February 10, while on vacation in Western Australia (my 17th trip to the southern hemisphere). I was doing my 16 nights of dusk to dawn "starathon" with my 10-inch SkyWatcher Dobsonian in Wicherina, about 50 kms due east of Geraldton. The SQM-L was typically 21.5-21.9 and my NELM was 7.8 on the best of nights. Centaurus A was a naked eye object. This night was one of the worse, SQM-L only 21.5. I had not heard about Fourcade-Figueroa before but its large and elongated appearance, the location between Omega Centauri and Centaurus A and the strange name made me interested.

Using 50x - 150x magnification (employing a 8-24 mm Baader Hyperion zoom-eyepiece), I saw nothing first and I had to double-check the location in the Uranometria 2000.0 Atlas. After a while, I noticed a faint, elongated ESE-WNW glow ESE of a 11 mag star, which was the NE star of a rectangle of stars. The glow was indeed the core of the very flat Fourcade-Figueroa galaxy. The object was of a very low surface brightness but not difficult to view once it was located.

/Timo Karhula

Hi Steve, and the rest of you. I can also say that I have seen this object. It was also with Andrew Murrell's assistance at this years's Oz-Sky camp at Coonabarrabran, in a 25" Newtonian reflector. I am another of the members of 3RF, and assisted in the running of the Oz-Sky Safari. ESO 270-17 is a fairly faint object, but to me it was the most impressive thing that I saw all week, in part because of the story of the titanic physical forces involved, and also because it is such an unusual object. There is very little information available about this shred, but I found the RC Thomson research paper from 1992, online (which Steve had mentioned) - as you had indicated Steve, the shred is non-rotational, and is now considered an irregular galaxy/galactic shred, similar to the Large Magellanic Cloud, although signifcantly larger. I was interested in the computer modelling in the paper that was used to postulate how NGC 5237 might have collided with Centaurus A and produced the shred that is now seen. Although it is a pretty faint object, even through a 25" scope, it was the highlight of the week for me, and I was quite excited to have seen it.

David Batagol

A new paper has been published on this galaxy:

https://arxiv.org/abs/2106.05133


Wouter