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NGC 4633 and 4634 May be Interacting

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#1 Rick J

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Posted 30 May 2017 - 02:30 PM

NGC 4633 is a strange disk galaxy possibly interacting with NGC 4634. The pair are located in southern Coma Berenices.  Their distance is difficult to determine.  By redshift, both are about 28 million light-years distant.  Only NGC 4633 has a non-redshift measurement that comes in at 69 million light-years.  Quite a difference.  If they are interacting then NGC 4634 could also be about 69 million light-years distant.  While I can't find an HST image of NGC 4633 there is one for NGC 4634.  https://www.spacetel...ages/potw1238a/  The text puts it at "about 70 million light-years".  The pair are members of the Virgo Cluster though are on the outskirts of it as most spirals are.  Radial velocities of Virgo Cluster members vary drastically with some even blue shifted indicating high orbital velocities are common in the cluster.  Thus it isn't unusual that redshift gives erroneous values.  Using 69 million light-years I get a size for NGC 4633 of 50,000 light-years and 71,000 for NGC 4634.

Both appear distorted by their interaction.  NGC 4633 is classified at NED as SAB(s)dm: while Seligman says SBd?.  The NGC Project leaves off the question mark.  I classify it as "A Mess" though that isn't a valid classification.  Stil,l it describes it better to my eye.  Likely it was a much better organized barred spiral before it had a run-in with NGC 4634.  Seen edge-on NGC 4634 seems to be a somewhat ordinary edge on galaxy within an oddly unsymmetric halo.  In some ways, it resembles the Hamberger Galaxy, NGC 3628.  Though its dust lane is also far from symmetric extending beyond the disk and into the halo to the northwest and breaking up and disappearing before reaching the southeast end of the inner galaxy.  The HST image doesn't go deep enough to show much of the halo, unfortunately. Also, its color filters result in a somewhat false color image missing the reddish hues that extend into the halo.  Most halos are filled with new hot stars so tend to be blue but this one had a lot of cooler stars in it for some reason.  Note I did push color on these two galaxies more than usual to bring out this oddity.

NGC 4633 was discovered by Edward Swift on April 27, 1887 and entered into the NGC catalog.  Later on November 23, 1900, it was discovered by Arnold Schwassmann.  Due to apparently different coordinates and Dryer not realizing it was a duplicate was entered into the IC catalog as IC 3688.  NGC 4634 was discovered by William Herschel on January 14, 1787, but is not in either of the H400 observing programs.  A Sloan image of this pair can be found at http://skyservice.ph...800&opt=&query=

NED shows a 20.1 magnitude quasar seen through NEG 4634.  I point to its location though it is lost in the glare of the galaxy in my image.  I can't even find it in the HST image linked to above.  There are three asteroid trails in the image.  One ran right over the 20.2 magnitude galaxy, SDSS J124212.15+142124.3.  NED has no distance data for it.  Just east of NGC 4634 is a pair of galaxies that have the same redshift so may be interacting.  The red one, PGC 042739 is shown at NED as being BCD?.  BCD normally stands for blue compact dwarf.  But given its color and distance is neither blue nor a dwarf.  At least they added a question mark.  It may be it got this designation before redshift was measured.  Still, it is obviously quite red compared to its blue companion which should have been quite evident since the mid 50's when the first POSS survey was done in blue and red light.  If there's another meaning for BCD I have never heard of it.  https://ned.ipac.cal...BCD/Agpaz3.html

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

 

Full image at 1" per pixel

 

Annotated

 

Attached cropped image is at 0.8" per pixel

Rick

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#2 PirateMike

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Posted 30 May 2017 - 02:48 PM

I see you have done your homework on this pair. 

 

A very nice image indeed. waytogo.gif



#3 Gipht

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Posted 30 May 2017 - 03:22 PM

Using the size estimates you have,  they would appear to be a minimum of 50 thousand light years apart.  Doesn't this seem like a long ways apart for any significant interaction?  



#4 Rick J

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Posted 31 May 2017 - 04:43 PM

Using the size estimates you have,  they would appear to be a minimum of 50 thousand light years apart.  Doesn't this seem like a long ways apart for any significant interaction?  

Not at all.  In fact, it is rather close, about one Milky Way radius.  I suspect they are quite a bit further apart than that and this is likely their first encounter.  Also just because we measure a distance today it doesn't mean they weren't closer in the past.  The pros that took the HST image say they are interacting.  See my link in the original post.  I'll let you argue with them.

 

Rick



#5 Jim Thommes

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Posted 06 June 2017 - 12:02 AM

Rick,

Cool image, discussion, and history.

 

I would say they are interacting. But the dust lane distortion and what appears to me to be a little disk on NGC 4634 seems more telling than NGC 4633.




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