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Old 18-04-2021, 11:45 AM
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GUS.K (Ivan)
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Observing the Fourcade-Figueroa Shred and NGC 5237.

So while observing galaxies around centaurus A on Wednesday night, came across this object on my Uranometria chart 184, and after starhopping to it, found nothing. Next morning, after searching the net, found out that this object and NGC 5237, could be the remnants of the galaxy that merged with Centaurus A. Last night was clear so made another attempt at this object ,and after a star hop and a bit of back and fourth with the chart finally spotted a very, very faint streak of light and tapping the scope and using averted vision, was able to confirm the spot. NGC 5237 on the other hand was easy, after a quick star hop from centaurus A, spotted it straight off with direct vision. The hypothesis is that 500 million years ago a galaxy shredding event took place, where a spiral galaxy (similar in size to our own) got too close to NGC 5128 and part of the outer dust ,gas and stars of the spiral arms was pulled in towards Centaurus A ( the material encircling it), while the core (NGC 5237) and some of the disk material ( probably a spiral arm, The Fourcade-Figueroa shred) was ejected. The core remained relatively unscathed, the shred shows signs of star burst activity and is non rotational. Both these objects on their own don't offer much to the observer, but taken in with viewing centaurus A and in context with the related story ( if true) makes for a rewarding observation, worth the hassle to track down.
Some detail

NGC 5237 (the core)
Dist 9 MLys
Mag 12.5
SB 13.6
RA 13 37 38.8
Dec -42 50 51
size 1.9'x 1.6'

ESO 270-17
PGC 47847
Dist approx 24 MLys
Mag 11.4
SB 14.2
RA 13 34 47.3
Dec -45 32 51

size 11,5'x 1.4'
Attached is a finder chart for anyone interested, and to a site with more info https://sandandstars.co.za/2019/05/0...igueroa-shred/
There are also reports from other observers from IIS, CN and DSF on the net.
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Click for full-size image (IMG_20210418_071131[7111] (3).jpg)
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Last edited by GUS.K; 18-04-2021 at 01:27 PM.
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Old 18-04-2021, 08:07 PM
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Rainmaker (Matt)
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Well spotted Ivan , you must have had good conditions. I've only seen 270-17 once and only in my previous 18. I'm going to have to try with the current scope next time out and away from Canberra's lightdome..
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Old 18-04-2021, 10:07 PM
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ngcles
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Hi Ivan & All,

Yes, as Ivan has noted ESO 270-17 is a possible/probable merger remnant/shred remaining from the merger event that gave Centaurus A* its current appearance. NGC 5237 is the possible merger remnant core. At first glance, ESO 270-17 looks like an edge-on spiral but it is definitely not rotating, has no core and is slowly stretching along its major axis.

This is the 1992 paper that results from supercomputer simulations that demonstrates in principle, that a prograde merger between a massive lenticular galaxy like NGC 5128 and a dust-rich spiral can produce a result not unlike what we see with these three objects (currently).

https://academic.oup.com/mnras/artic.../4/689/1092606

Observing notes from 1999 under a Bortle 2 sky (Mudgee Star Party):

PGC 47847 (ESO 270-17) Gx Centaurus
31cm x186: An extremely faint galaxy of very, very LSB but large. In a pretty starry field as an ill-defined streak, almost non-existent patch of weakest gossamer 6' x 1' in PA 110 with a line of stars not superimposed but running beside it magnitudes 10-11. Does not grow to the axis or the core. Very, very difficult object at threshold.

I don't have a note using 46cm, but I do recall re-observing it a few times about 10 years ago at x185. It was still a very difficult object of exceedingly LSB but a bit easier to see than with 31cm. I have looked at it once with 63.5cm at x156 and it is much more definite, still very LSB, maybe 8' long with a slightly brighter centre.

Best,

L.

P.S ESO 274-1, an edge-on spiral in Lupus is also a probable member of the M83/Centaurus A* group. A little easier to see than ESO 270-17 but in a field with a veritable blizzard of stars.

PGC 54392 (ESO 274-1) Gx Lupus (1999)
31cm x186: A quite difficult object of extremely LSB. Visible N of a magnitude 8 star by 14'. In a field with a gazillion other faint stars. In PA 45 as a very long diaphanous streak of gossamer 7-8' x 1' in PA 45. Small slightly brighter portion near the centre, otherwise of consistent LSB except that the tips are even fainter than most of the halo. Quite a number of faint stars and threshold stars are superimposed. Very, very lovely!
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Old 19-04-2021, 08:21 AM
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GUS.K (Ivan)
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Quote:
Originally Posted by Rainmaker View Post
Well spotted Ivan , you must have had good conditions. I've only seen 270-17 once and only in my previous 18. I'm going to have to try with the current scope next time out and away from Canberra's lightdome..
Thanks Matt, conditions were quite average, humidity was hovering around 100 percent, I spent 3 hours out that night and constantly wiping the scope down, water was dripping of the upper cage. Predictions were for cloud, but ended up being clear, but cold and humid, not the best conditions but wasn't sure how the next few days were going to turn out. Let us know how you go with the observation.
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Old 19-04-2021, 08:31 AM
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GUS.K (Ivan)
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Quote:
Originally Posted by ngcles View Post
Hi Ivan & All,

Yes, as Ivan has noted ESO 270-17 is a possible/probable merger remnant/shred remaining from the merger event that gave Centaurus A* its current appearance. NGC 5237 is the possible merger remnant core. At first glance, ESO 270-17 looks like an edge-on spiral but it is definitely not rotating, has no core and is slowly stretching along its major axis.

This is the 1992 paper that results from supercomputer simulations that demonstrates in principle, that a prograde merger between a massive lenticular galaxy like NGC 5128 and a dust-rich spiral can produce a result not unlike what we see with these three objects (currently).

https://academic.oup.com/mnras/artic.../4/689/1092606

Observing notes from 1999 under a Bortle 2 sky (Mudgee Star Party):

PGC 47847 (ESO 270-17) Gx Centaurus
31cm x186: An extremely faint galaxy of very, very LSB but large. In a pretty starry field as an ill-defined streak, almost non-existent patch of weakest gossamer 6' x 1' in PA 110 with a line of stars not superimposed but running beside it magnitudes 10-11. Does not grow to the axis or the core. Very, very difficult object at threshold.

I don't have a note using 46cm, but I do recall re-observing it a few times about 10 years ago at x185. It was still a very difficult object of exceedingly LSB but a bit easier to see than with 31cm. I have looked at it once with 63.5cm at x156 and it is much more definite, still very LSB, maybe 8' long with a slightly brighter centre.

Best,

L.

P.S ESO 274-1, an edge-on spiral in Lupus is also a probable member of the M83/Centaurus A* group. A little easier to see than ESO 270-17 but in a field with a veritable blizzard of stars.

PGC 54392 (ESO 274-1) Gx Lupus (1999)
31cm x186: A quite difficult object of extremely LSB. Visible N of a magnitude 8 star by 14'. In a field with a gazillion other faint stars. In PA 45 as a very long diaphanous streak of gossamer 7-8' x 1' in PA 45. Small slightly brighter portion near the centre, otherwise of consistent LSB except that the tips are even fainter than most of the halo. Quite a number of faint stars and threshold stars are superimposed. Very, very lovely!
Thanks Les. Reading up about this object, I did see your previous observations. Definitely One of the harder objects to spot. I can only imagine how difficult it would be in a 12 inch scope, even in Bortle 1 or 2 skies. Thanks for the observation notes and info about ESO 274-1.
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