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Arp 63 and Arp 129



 
 
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  #1  
Old December 14th 16, 08:17 PM
WA0CKY WA0CKY is offline
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Default Arp 63 and Arp 129

Arp 63/NGC 2924 is a multiple galaxy in northwestern Leo about 320 million light-years from us. Arp puts it in his category for spiral galaxies with small, high surface brightness companions on its arm. It appears to have two, one at each end. Arp was silent as to which he meant but most sources say it is the western one, PGC 27534 (listed under its SDSS position in the annotated image). Problem is there's no redshift data on this one while the one at the eastern end, PGC 1990710 has a redshift that does match that of the spiral galaxy. But is its connection only an illusion due to our line of sight or is it real? Are both true companions? To my eye both show distortions that could indicate they are both interacting with the main galaxy. Many sources list this as a triple galaxy. NED and Seligman classifies the spiral as SB(s)c pec? while the NGC Project says is is Sc/SBc. Only Seligman classifies PGC 1990710 saying it is SB? pec.

The galaxy was discovered by Johann Palisa on March 27, 1886. Somehow he missed the much brighter pair of galaxies that is Arp 129 just to the northeast. Since his position and description matches Arp 63 there's no question he meant Arp 63 rather than 129 as some sources claim.

Arp 129 is in Arp's category for Elliptical and elliptical like galaxies close to and perturbing spirals. It is in the same field with Arp 63 so I'm just using the same image for both. Arp did the same with his image of these two as both fit within the corrector on the 200" scope he used.

While much brighter than NGC 2944 that is Arp 63 this pair didn't receive an entry in the NGC catalog. The elliptical like galaxy is on the east and is PGC 27546. Seligman classifies it as a lenticular galaxy SB0?. The spiral it is said by Arp to be perturbed is PGC 27547 which Seligman classifies as SAB(rs)bc? pec. Note too that while the PGC galaxies are numbered from west to east these two are reversed for some reason. It could be that in the LEDA catalog the spiral was classed as elliptical and the elliptical as spiral. This is only a wild guess on my part. The pair are also about 310 to 320 million light-years distant by redshift though there's a slight difference with the spiral having a slightly less (nearer) redshift. Still it does appear they are or did interact. Though the lenticular galaxy shows little distortion and the pulled out arm of the spiral could be "natural" and not due to any interaction at all with the lenticular. I doubt it but it is possible. It does appear to my eye that the spiral is closer same as redshift indicates. But how much closer is unknown.

While nearly all my full size images (2004x1336 pixels) are displayed at 1" per pixel this one was taken half frame at 0.5" per pixel and is displayed at that resolution even though the night didn't really support more than about my normal 1" resolution.

14" LX 200R @ f/10, L=6x10'x1, RGB=2x10'x1, STL-11000XM, Paramount ME

Rick
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Last edited by WA0CKY : December 14th 16 at 08:20 PM.
  #2  
Old December 20th 16, 10:48 PM
slilge slilge is offline
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Rick,

great field with two such interesting objects/pairs in it.
Are you imaging unbinned and then decide if the image "needs" software binning or are you choosing the binning mode for each object?

Stefan
  #3  
Old December 21st 16, 09:07 AM
WA0CKY WA0CKY is offline
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I see I forgot to mention this was another long lost file on the hard drive. It was taken in 2009. Back then I normally imaged at 1" per pixel (binned 2x2) as most nights didn't support 0.5 pixels. Since then I've found most nights do support 0.8" per pixel and even 0.67" at times and I can get similar S/N ratio not binned in the same time as read noise of the camera is only very slightly decreased by binning with 40 minutes of data. So for the last few years (since you've seen me often cropping an image to 0.8" I software bin to 1" for the display image as even 0.8" is getting too big for some forums and monitors. Then crop a smaller image, usually 800x800 at 0.8 or 0.67 if the night supports it.

Rick

Quote:
Originally Posted by slilge View Post
Rick,

great field with two such interesting objects/pairs in it.
Are you imaging unbinned and then decide if the image "needs" software binning or are you choosing the binning mode for each object?

Stefan
 




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