ASTRO: Arp 178 revisited

This is a reshoot with twice the exposure time under a bit better
seeing. It didn't pick up much more of the plumes than the first but
detail in the galaxy is far better. Some of the text below is from the
initial post but there is something new in this image so keep reading as
it is near the end. It is not in the original nor is it an asteroid or
other solar system object.

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 are rotating the same way. It is just
the core being off center from the first ring that create this illusion.
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 5614 is
quite likely the remains of a galaxy torn asunder 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 several more are at
2.1 to 2.2 million light years and may make a third group.

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.

The smudge of a galaxy north northeast of Arp 178 is SDSS
J142418.67+245549.8. NED says it is only about 6" of arc across though
it is about 24" across in my image. NED also gives it a far too faint
magnitude. It has no redshift data. Except that its position exactly
matches that of NED I'd think they were talking about a different galaxy.

Southeast of Arp 178, below a galaxy at 2.2 billion light-years is an
object marked by a question mark. NED lists it at 22nd magnitude.
Indeed it is 22nd magnitude (barely visible) on my first image of this
field but it is 19.5 magnitude on this image or 10 times brighter than
that in my first image. There is a galaxy at that position. That got
me wondering if a supernova had been seen at that position. Yep, it is
PTF11dwn. PTF stands for Palomar Transient Factory. 11 is the year
(apparently they don't worry about 2100 and beyond). The letters dwn
denote its position in objects the PTF turns up. First is a, additional
letters are used as needed. Since it turns up a lot of other things
than supernova the next one it found was PTF11egs rather than PTF11dwo.
I didn't look up what that would be. The supernova is a type 1A at
magnitude 19.5. It is in SDSS J142422.29+344833.8. It was discovered on
May 23rd. My independent discovery was on June 5th, 13 days later. I
wonder how many others like this are lurking on my images I'll never
know about since I have no comparison image. Even if I did finding, it
is highly unlikely. Only because it was near a galaxy I was annotating
did I notice it. When comparing the NED image of the field that extra
star in my image confused me for a bit. Otherwise I'd never have
noticed it.

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

My original post to this news group is archived at:
http://www.spacebanter.com/showthread.php?t=171726
for those wishing to compare the two images for the supernova.

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

Rick
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