ASTRO: Arp178

Arp 178 consists of three galaxies NGC 5613 (upper), NGC 5614 (lower)
and NGC 5615 (inside NW halo of NGC 5614). These are located in the
constellation of Bootes. NGC 5613 is nearly 400 million light-years
distant while the other two are a bit less than 190 million light-years
away. Arp put these in his category of galaxies with narrow counter
tails. His comment reads: "Ring off center, broad ejected plume from
condensation in ring."

Most papers of the era of Arp's Atlas and prior consider NGC 5614 as
interacting with the northern galaxy (5613). We now know that with 5613
having over twice the redshift this isn't the case. It is unrelated but
worthy of its own entry in the atlas. It is classed as (R)SAB(r)0+ by
NED and the NGC project agrees but leaves off the + sign. At first
glance it appears to have a faint outer ring. But look closely and you
see it is really two very extended spiral arms that nearly overlap. One
starts at the 11 o'clock position and goes around to the 4 o'clock
position. The other starts at 5 o'clock and goes around to the 10
o'clock position. In both cases the ends are further from the core than
the other arm inside it. This may be easier to see in the Sloan image
stretched a bit differently than my image. What caused this? There
seems no likely source. Prior to its redshift being determined it is
easy to conclude that NGC 5614 caused it. Now it is a puzzle.

The main feature here is NGC 5614 a very large tightly wound spiral with
an off center core and huge plume. NED and the NGC Project classes it
as SA(r)ab pec. The plume seems possibly related to NGC 5615. It
certainly is due to a gravitational interaction in the recent past. The
off center core causes Arp's "ring off center" comment. At first I
thought it might be that this was a case of a merger with inner arms
rotating counter clockwise and outer ones turning clockwise but I found
a rotation curve that says all is rotating the same way. It is just the
core being off center from the first ring that create this illusion.
Still I am having a hard time seeing it. Still I believe it a merger in
progress with NGC 5615

The condensation Arp refers to is NGC 5615 and has a redshift that puts
it about 3 million light years more distant than NGC 5614. NGC 5615 is
not classified at NED, NGC project says S? I can't see enough to try
classifying it so have to agree with NED. Is NGC 5614 in the process of
digesting NGC 5615. I saw suggestions of this in early papers but
nothing conclusive. One paper suggests that the tightly wound arms of
NGC 5614 might be due to an unusually massive black hole at its core.
No reason given other than it appears such galaxies tend to have larger
than expected black holes when this has been measured. Pretty
speculative to me. In any case it is an interesting galaxy as is NGC 5613.

After I wrote this Adam Block posted an image of this galaxy taken by
the 32" scope at the Mt. Lemmon Sky Center observatories. It clearly
shows NGC 5615 is broken into several bright cores. It also shows the
bright blue arcs in NGC 5614 far more clearly. I now think 5615 is
quite likely the remains of a galaxy torn assunder by 5615, even the
core of it is being ripped apart by tidal forces. I wrote Adam with
this suggestion and he agreed it is likely the case. The three million
light-year difference in redshift is likely due to relative motion and
difficulty of assigning a redshift based distance to a mess like this.

Another galaxy at about the same distance of NGC 5514-5 is to their NE.
Several galaxies of the same distance as NGC 5513 are in the frame.
It appears they are two different groups. Several galaxies at 1 billion
light-years are also found around the image. While I see several groups
of galaxies in the image only one, the northwest corner is listed as a
galaxy group. That is MaxBCG J215.67259+34.98489, is cataloged. It is
shown to be a group of 20 galaxies in an unknown area. It is listed
with the same position as its apparent anchoring galaxy though their
redshift distances are slightly different. See the annotated image for
these.

Normally I think of NGC galaxies as being closer than say a half billion
light-years, far closer in many cases. But NGC 5609 at 1.31 billion
light-years is an exception. NED lists its green magnitude as 16.3
while the NGC Project puts its visual magnitude at 15.7. Since green is
usually used for this I can't explain the difference. Still this one
should be visible in larger amateur telescopes from a dark site, say a
16" or larger. Young eyes may glimpse it with less aperture if the
brighter magnitude is correct.

Often, in my annotated images, two similar galaxies are side by side.
Only one though has a redshift published. I often get asked "Isn't it
reasonable to assume the other is at the same distance?" No it isn't.
A good example is in the lower corner of my image where two rather
similar galaxes do have red shift data and one is over 3 times further
away than the other yet appears only very slightly smaller. Assumptions
are very dangerous in this business.

Yet again I happened to check a galaxy in my image that NED doesn't seem
to know about. It lists over 5000 galaxies in this field, many too
faint for me to pick up, but see Adam's image which does see them and
more, on this rather poor night. Yet it missed the one in the
northwestern corner of my image marked with a question mark. The star
to its left and a bit north is listed but not the galaxy. Sure wish I
knew why this happens. There are likely others. I don't check very
many for this trait yet find one in a rather high percentage of my
images. Note that most of the faint "stars" in the image are actually
galaxies that are listed in NED but without red shift. Which is good as
otherwise the image would have so many lables as to be useless.

Arp's image
http://nedwww.ipac.caltech.edu/level...ig_arp178.jpeg

Adam Block's image with the 32" telescope at the Mt. Lemmon Sky Center
http://www.caelumobservatory.com/gallery/n5613.shtml

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Rick
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Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".