Thread: Ic4720/21
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Old 15-09-2013, 05:47 PM
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Shiraz (Ray)
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Location: ardrossan south australia
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Ic4720/21

The largest of the two main galaxies is IC4721, a barred spiral about 80-100 million light years away. The elliptical close to IC4721 is IC4721A (a background galaxy). IC4720 is the smaller spiral separated by about 8.8 arc minutes from IC4721 and apparently at about the same distance.

The “feather” extending from the side of IC4721 is not part of the galaxy, but is a background side-on spiral galaxy that is about 180 million light years further out and can be seen through IC4721. Such fortuitous alignments, including this pair, have been used to estimate the density of galactic material by way of attenuation of light from the background galaxy. There are quite a few other fuzzy blobs, including one at lower left in a line with two main galaxies and one almost at the top of the frame – these two have similar colour to the main galaxies, so could just possibly be related. The thin side-on galaxy in the lower right corner is also intriguing.

The seeing was fairly good at 2.5 arc sec averaged over three fairly short periods, but it really requires a lot more good data to do this target justice. However, this was all that the clouds have allowed, even after including some slightly dodgy data that upset the star shapes. There was also significant sky brightness and galactic extinction, so the final balance was by eye to try to get reasonable stars as well as plausible galaxy colours.

It is now getting a bit late for this RA and, unless the weather patterns change, it is unlikely that there will be another opportunity to image this region for now - will be worth a revisit next winter to do a proper job.
Thanks for looking. Regards Ray

Refs: NED database and associated links and
http://arxiv.org/pdf/1211.6723.pdf

GSO200f4 with RCC1
SX H694
NEQ6

2.25 hours L, ~2 hours RGB total, all 200sec subs at 1x1
heavy crop and reduced by 0.75 (native scale 1.17arcsec/pixel)
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Last edited by Shiraz; 16-09-2013 at 12:04 PM.
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