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ASTRO: VV 699 (NGC 1721-5-8) NGC 1725 Unusual and peculiar Galaxies



 
 
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Old March 31st 12, 08:09 AM posted to alt.binaries.pictures.astro
Rick Johnson[_2_]
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Default ASTRO: VV 699 (NGC 1721-5-8) NGC 1725 Unusual and peculiar Galaxies

VV699 is a triple galaxy system in Eridanus about 170 to 200 million
light-years distant. The three are NGC 1721, NGC 1725 and NGC 1728.
Their redshifts put them at a distance of 205, 178 and 171 million
light-years. Since they appear to be possibly interacting these
differences may just reflect their relative motion more than a true
distance difference. I find no other distance estimates for them.

NGC 1721 appears the most disturbed. NED classes it (R')SAB(s)0^0^ pec
while the NGC Project says more simply S0. I can't fathom that one.
The inner core does have some elements of an SO but you have to ignore
the huge outer spiral arms or is it arm. I see an arm coming from the
NW ansa of the inner disk but the other end is too obscured by NGC 1725
to see what is going on there. I suppose it is possible the eastern arm
is just a continuation of the western one though I doubt that.

NGC 1725 is classed S0 by NED and E-S0 by the NGC project. These both
seem reasonable to me. It doesn't seem disturbed. So is it really
interacting with the others? There's no papers on this trio that
address this issue. They are just catalog listings or physical
descriptions. Ellipticals are dense so can cause interaction without
showing much distortion themselves. That may be the case here.

NGC 1728 is classed as Sa pec with spectral emission lines by NED and
simply as Sa by the NGC project. The disk is warped so I can understand
the peculiar label NED gives it. The warped disk indicates interaction
with some galaxy. Is it both the other two or just NGC 1721? Again
nothing addressing this turned up in my search.

I imaged this field twice. First time NGC 1723 at the top was just out
of frame with its faint large arm just in the edge of the field looking
just like a halo from a bright star. It wasn't until I went to process
the image that I looked at that area on the POSS plates and found it was
the edge of a galaxy. Back to the telescope a year later to retake it
with this neat spiral in the field. I never did process the first attempt.

NGC 1723 is classed as SB(r)a pec by NED and SB by the NGC Project. The
two arms that come off the very strong bar nearly touch to make a
complete ring hence the (r) designation at NED. Add in the huge
distorted arm outer arm structure and it well deserves its "pec" label.
With a redshift virtually the same as that of NGC 1728 and nearly that
of NGC 1725 it very likely interacted with the VV699 trio some time in
the past. Is it the cause of NGC 1721's outer ring-like arms?

The VV catalog calls the trio isolated. But if you check my annotated
image or keep reading you'll find that isn't the case. The few other
galaxies for which NED has redshift data are also in this distance range.

2MFGC 04079 to the west of NGC 1721 is at 200 million light-years about
the same as NGC 1721. NED has no classification for it. 2MFGC 04080 to
the southwest is in the 2 micron flat galaxy catalog though it doesn't
look all that flat to me. It is the third galaxy in the field to sport
a redshift of 171 million light-years. In red light and IR light it
does look far flatter than in blue light so that may be the way it got
into that catalog. NED doesn't classify it but does say it is 0.4 by
0.3 minutes in size, hardly flat. But their red light POSS I image
shows it very flat. Odd.

The only other galaxy in the field with redshift data is the edge on
spiral MCG -02-13-031 at 168 million light-years. Again a member of
this rapidly expanding group. NED classes it as SB(s)c? indicating the
arm structure is very hard to determine with such an edge on view. It's
disk seems slightly warped as well. NED says it has some HII emission
lines in its spectra. This would indicate it contains regions of active
star formation.

14" LX200R @ F/10, L=4X10 RGB=2X10X3, STL-11000XM, Paramount ME

Rick
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Prefix is correct. Domain is arvig dot net

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