ASTRO: Arp 225 What a mess this one is

Arp 225/NGC 2655 is a nearby strange galaxy in Camelopardalis. Red
shift puts it about 65 million light-years away though a Tully estimate
says more like 80. I'm going to go with the closer figure as even that
distance makes it a huge galaxy some 170,000 light-years across. The
more distant estimate makes it about 210,000 light-years across. I
doubt it is that big.

It is obviously a highly disturbed galaxy. Arp put it in his class for
galaxies with amorphous spiral arms. He said of it: "Very faint diffuse
outer arms, absorption one side of nucleus." NED classes it as
SAB(s)0/a while the NGC Project says S0/Sa. Several papers call it a
Seyfert 2 galaxy. I found only one paper addressing the "amorphous"
arms. It refers to LEDA 3085822 which is the large rther evenly faint
blob to the northwest (about 2 O'clock) near the upper right corner of
the enlarged, cropped image. The paper refers to it as An 0849+78.
http://adsabs.harvard.edu/cgi-bin/bi...6AS..117..343K It
says: "An 0849+78 is located at the extension of an outer spiral arm of
NGC 2655 and seems to be connected to it by a very faint bridge. Its
isophotes are of regular shape; a faint elongated nucleus is marginally
visible. The light profile is probably non-exponential, but its outer
part is poorly determined due to the uncertainties in background
subtraction. The HI observations show that An 0849+78 is confused by NGC
2655, at V_h_ = 1400 km/s. To calculate the absolute characteristics we
use for An 0849+78 the distance of NGC 2655. If An 0849+78 is a bound
(dwarf spheroidal) companion of NCC (sic) 2655, its survival in the
gravitational field of the bright galaxy is problematic. New multicolour
photometry and HI observations are needed."

So it could be the "arms" are really the tidal tail of a dwarf galaxy
being totally pulled apart by NGC 2655. NED gives the "blob" almost the
same redshift as Arp 225 which supports this idea. The dust near the
core then likely is from this now almost annihilated galaxy. While I
found no paper willing to go this far it seems the most reasonable
explanation of what is going on here. Besides the above paper another
would go this far: " NGC 2655 = Arp 225 is an Sa galaxy which shows
traces of a strong interaction or merger event: faint outer stellar
loops, extended HI-envelope (Huchtmeier & Richter 1982). The bulge in
NGC 2655 is especially large (Table 4). The central dust-structure
(Erwin et al. 1996) is probably the reason for the disturbed fit
residuum there."
http://adsabs.harvard.edu/cgi-bin/bi...6A...368...16M

Yet another paper coming close to saying these loops are due to galaxies
being destroyed is:
http://iopscience.iop.org/1538-3881/135/1/99 but put on your hip waders
if you haven't already.

There is an odd, likely background galaxy seen right through the outer
parts of Arp 225 almost directly north of the core. It might be two
galaxies superimposed or even a star and galaxy. This is almost
certainly a background object(s). In any case the two look somewhat
like a comet. The only thing NED shows at almost that position (about
1" different) from its centroid is the infrared source 2MASXi
J0855445+781451. It doesn't indicate this is a galaxy but it just might
me this object In fact it has very little on this field which is common
for these galaxies up near the celestial pole. It has a red shift for
only one other galaxy, UGC 04701, the nice Sd: near edge on spiral east
of Arp 225. It has about the same redshift as the other two so the are
likely part of a group. Two thirds of a degree east of Arp 225 and well
out of my image is a very nice spiral NGC 2715 also with a similar
redshift. It is a nice spiral showing little sign of being disturbed.
It went on my to-do list once I could reach this far north but weather
last year prevented any of its photons being captured.

Arp's image:
http://ned.ipac.caltech.edu/level5/A...ig_arp225.jpeg

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

Rick
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