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NGC 151 AKA NGC 153 A Disturbed Looking Spiral



 
 
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  #1  
Old March 27th 16, 05:58 AM
WA0CKY WA0CKY is offline
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Default NGC 151 AKA NGC 153 A Disturbed Looking Spiral

NGC 151/153 is a disturbed looking spiral in western Cetus about 160 million light-years from our galaxy by redshift while non redshift measurements put it 150 million light-years distant, a very good agreement. Using the latter distance I get a size, including the drawn out arm of about 140,000 light-years. While I call the arm on the left a drawn out arm it ends about 97" of arc from the center of the core but the right hand edge ends at 98" of arc from the core. So the two sides are pretty equal, just that the eastern side is made up of this one arm and a lot of space with few stars while the western side has lots of stars in several arms and arcs giving the impression it extends further east than west when they are quite equal. The illusion was so strong I had to measure it again just to be sure I didn't make a mistake. Still the two sides are very different and that begs for a reason.

Arp had a classification for spirals with high surface brightness companions on an arm. The arm usually appeared drawn out in these galaxies. Oddly Much of the time the companion was only due to line of sight with the companion often much more distant. Sometimes it was a true companion and in others no redshift data was available leaving the issue unanswered. This time we do have a redshift measurement that puts it slightly further away at 210 million light-years. The this leaves the issue a bit ambiguous in that they could be at about the same distance with the companion moving away from NGC 151/153 at a high speed. While possibly the situation a high speed encounter with a galaxy this small wouldn't likely create this much distortion so I have to consider these two as line of sight galaxies until further evidence comes in. Why Arp didn't include this one I don't know. It is a better example than some he did include.

There's nothing else in the field that would be a likely candidate for the odd asymmetry of the galaxy. I didn't check very far outside the field however.

The galaxy was discovered first by William Herschel on November 28, 1785 with Dreyer recording that as NGC 151. On August 9, 1886, over 100 years later, Lewis Swift who got the RA wrong by about 15 to 20 minutes of RA. In fact Swift recorded four "new" objects that night all with a similar time error. Turns out only one was really new the other three already in the NGC. Dreyer caught two of these but missed this galaxy giving it the NGC 153 entry it carries as well as the 151 it earned over a century earlier.

The nights I took this were very poor for transparency and not all that great for seeing. Due to the poor transparency I planned a total retake but after the luminance was taken conditions went from poor to worse and the second round of color had to be rejected. Color balance is a bit questionable due to constantly changing transparency. I hope it is about right at least. Another for the retake list that likely won't happen due to its near -10 degree declination. I don't get many good nights this low.

14" LX200R @ f/10, L=8x10' RGB=2x10', STL-11000XM, Paramount ME

Rick
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Last edited by WA0CKY : March 27th 16 at 07:43 PM. Reason: Correct date Swift found this galaxy
  #2  
Old March 27th 16, 07:44 PM
WA0CKY WA0CKY is offline
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First recorded activity by SpaceBanter: Feb 2008
Posts: 689
Default

I had a typo for the discovery date of the comet by Swift. It was 1886 rather than 1866 as I originally typed it.
Rick

Quote:
Originally Posted by WA0CKY View Post
NGC 151/153 is a disturbed looking spiral in western Cetus about 160 million light-years from our galaxy by redshift while non redshift measurements put it 150 million light-years distant, a very good agreement. Using the latter distance I get a size, including the drawn out arm of about 140,000 light-years. While I call the arm on the left a drawn out arm it ends about 97" of arc from the center of the core but the right hand edge ends at 98" of arc from the core. So the two sides are pretty equal, just that the eastern side is made up of this one arm and a lot of space with few stars while the western side has lots of stars in several arms and arcs giving the impression it extends further east than west when they are quite equal. The illusion was so strong I had to measure it again just to be sure I didn't make a mistake. Still the two sides are very different and that begs for a reason.

Arp had a classification for spirals with high surface brightness companions on an arm. The arm usually appeared drawn out in these galaxies. Oddly Much of the time the companion was only due to line of sight with the companion often much more distant. Sometimes it was a true companion and in others no redshift data was available leaving the issue unanswered. This time we do have a redshift measurement that puts it slightly further away at 210 million light-years. The this leaves the issue a bit ambiguous in that they could be at about the same distance with the companion moving away from NGC 151/153 at a high speed. While possibly the situation a high speed encounter with a galaxy this small wouldn't likely create this much distortion so I have to consider these two as line of sight galaxies until further evidence comes in. Why Arp didn't include this one I don't know. It is a better example than some he did include.

There's nothing else in the field that would be a likely candidate for the odd asymmetry of the galaxy. I didn't check very far outside the field however.

The galaxy was discovered first by William Herschel on November 28, 1785 with Dreyer recording that as NGC 151. On August 9, 1886, over 100 years later, Lewis Swift who got the RA wrong by about 15 to 20 minutes of RA. In fact Swift recorded four "new" objects that night all with a similar time error. Turns out only one was really new the other three already in the NGC. Dreyer caught two of these but missed this galaxy giving it the NGC 153 entry it carries as well as the 151 it earned over a century earlier.

The nights I took this were very poor for transparency and not all that great for seeing. Due to the poor transparency I planned a total retake but after the luminance was taken conditions went from poor to worse and the second round of color had to be rejected. Color balance is a bit questionable due to constantly changing transparency. I hope it is about right at least. Another for the retake list that likely won't happen due to its near -10 degree declination. I don't get many good nights this low.

14" LX200R @ f/10, L=8x10' RGB=2x10', STL-11000XM, Paramount ME

Rick
 




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