Arp 215, NGC 2782, is thought to be the result of two galaxies that have almost merged. The core is still elongated and appears double at some wavelengths. The debris of the merger hasn't yet merged with the resulting galaxy but likely will. It is classed as SAB(rs)a and is a starburst galaxy. Some consider it a Seyfert 1 galaxy. Others say this is an illusion due to the massive star formation going on in its merging nuclei. The galaxy is about 125 million light-years distant and is found in southwest Lynx, north of 38 Lynx.

It is peculiar enough to make Arp's catalog under his class: Galaxies (not classifiable as E or S); adjacent loops. Not having today's multiple wavelength data he didn't likely didn't know it was a merger situation. He just knew there were no galaxies in the area that could have interacted with it so it's distortion was without an obvious explanation.

While the edge on spiral (SBb) to the southeast, UGC 4872, may seem to be involved it is three times as far away at 380 million light-years.

As there's quite a bit of information on the background galaxies thanks to the SDSS, I've made an annotated version showing the distance in billions of light-years to the more distant galaxies and quasars. Note the one west of Arp 215 at 3.9 billion light-years is the upper object. There's a star about 3" south. The galaxy is at magnitude 21.0 in visual (SDSS G filter) light. Limiting magnitude on the posted image is about 22.5. It goes a bit below 23 on the Lum FITS. The image is not as deep as I'd have liked. Transparency wasn't very good these nights though seeing was fairly good.

Sometimes the SDSS data base in NED mystifies me. Below and a bit right of Arp 215 are two galaxies, one at 1.3 and the other 1.9 billion light-years. The galaxy in the middle isn't in the database. But if you look closely just to the left of it near its northern end is a very dim star, below 22nd magnitude. The SDSS puts at the location of the galaxy, noting it is a star and lists its magnitude as 20.4 which is way too bright for the star but dimmer than the anonymous galaxy. It is noted with a question mark in the annotated image. I included it to point out the more distant objects in the image.

There's one quasar identified in the image as well. Most of the galaxies with red shift data are between 1.2 and 1.4 billion light-years.

SDSS image:
http://astronomerica.awardspace.com/SDSS-18/NGC2782.php

There are a few HST frames in the archive but they need so much work to salvage and don't appear to add much to this discussion I didn't try to salvage them.

Arp's image is one of his best. Core does appear possibly double rather than just a short bar.
http://nedwww.ipac.caltech.edu/level...ig_arp215.jpeg

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

Full image with slightly less compression
http://www.spacebanter.com/attachmen...tid=2664&stc=1

Rick

Attached Images

	ARP215L4X10RGB2X10X3r-8.jpg (142.6 KB, 19 views)
	ARP215L4X10RGB2X10X3r-ID.jpg (104.4 KB, 16 views)

Love the halo look.

First let me say that your images of Arp 215 (NGC 2782) and UGC 4872 are outstanding work, Rick!

With that said, let me just say NED couldn't give a proper classification if it were handed to them on a silver platter. Actually, there really isn't any proper classification for this galaxy using the standard de Vaucouleurs classifications. What I see here are tidal tails, a dust lane in disarray as a result of the merger and an HII region (i.e. the starburst arc) resulting from the merger or to put it another way, this is a cosmic train-wreck!

You're not the only one, Rick who is mystified by NED's classifications of galaxies. I classified galaxies for a little over 2 years, and I can tell you that NED is a royal mess!

Whether or not it is a Seyfert 1 galaxy would be determined spectroscopically and not visually, unless I am misunderstanding what you're saying. Specific types of AGN have a unique spectroscopic signature.

Here's a diagram from Bill Keel's site depicting the distinctions among the various flavors of AGN:

http://www.astr.ua.edu/keel/agn/spectra.gif

And here's a link to the page from Bill Keel's site from where I got the illustration:

http://www.astr.ua.edu/keel/agn/spectra.html

Bill really knows his stuff when it comes to the spectra of AGN.

Eric

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The Seyfert 1 question comes from spectroscopic notes at NED. Some say they see only a starburst at the core causing the spectral details others see as Seyfert 1. I was just reporting the disagreement and not passing judgment on either. I done some photometric work with an astronomer at the University of Texas helping with his AGN correlating rapid brightness changes across the entire spectrum, radio to x-ray, and am somewhat familiar with the subject.

When it comes to many of the galaxies in Arp's catalog standard classification systems certainly are inadequate. Train-wreck is about as close as you can come. Wait a billion or two years and maybe they will start to fit again. Seems each paper on these comes to a different classification. What source do you prefer?

Rick

Actually, I use The de Vaucouleurs Atlas of Galaxies by Ronald J. Buta, Harold G. Corwin, Jr., and Stephen C. Odewahn. I do my own classifying, because I don't trust any of the databases, like NED or SIMBAD, etc. I might look at NED for comparison to my own classification, but that is all. I will say about NED what Winston Churchill said about democracy: it is the worst database except for all of the rest! LOL

Eric

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Just to clarify things - "NED's classifications" don't exist as any claimed standard. NED is a compilation of what everyone has done in the literature and databases; when it lists a classification, that is not claimed to be anything more than indicative and may just be the first one filled in for a particular object. When it matters, there is no substitute for going to the source! (Having a human being look carefully over all incoming information for consistency and rationality is something they had to give up on some years ago, since there are few people working on NED and the incoming data volume is already too high to keep up with in a steady state).

Maybe the best way to view NED is as a very large and quite convenient set of pointers to what has been published (including electronic data collections). Comparisons with certain online services suggest themselves but are almost too much of a cheap shot, given the amount of work it takes to keep NED going. (All these young whipperspanners not remembering what it was like back in the days of quill pens - I just recently brought myself to throw away some file boxes of large index cards with Polaroids and pencil notations on galaxy samples from old projects.)

Point well taken, Bill.

Eric

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Excellent detail in the main galaxy, and the edge on spiral is interesting also. I like how your processing always brings out fine detail in the galaxies without making the core too bright.

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Actually, I have to correct myself. I had forgotten that there are classifications for interacting galaxies in the de Vaucouluers system of galaxy classification. After further investigation, I have come up with a classification which I believe fits this peculiar galaxy. It's very close to the NED classification with a couple of slight differences. I agree with you Rick that the core looks elongated and in some wavelengths looks like a double core, which is reasonable considering that this is a merger that still is in the merging process. My classification would be as follows:

SA(rs)a pec

Like I said, it's very close to the NED classification. To some degree, when you get into the fine details of galaxy classification, the classification can be somewhat subjective. Now, the person who did the classification that is in NED may have been using an older version of the de Vaucouluers system than I or just saw the galaxy differently. But, I can't say that the NED classification is that far off. And some of it is subject to interpretation.

Eric

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Hi Rick, A very impressive image of these Galaxies and excellent info. Clear Skies my friend.

Hi Rick:
As always, privileged information and excellent photos.
Many grettings
Cesar

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Thanks all for making this a very interesting and informative thread. Love it when that happens!

Rick

We couldn't have done without you, Rick.

Eric

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