Arp 282 -- Infall and attraction

[RickJ]

Arp 282 is an interesting interacting pair just under 200 million light years from us. It consists of a large but distorted spiral, NGC 169 and a small companion with tidal arms, IC 1559. Ned calls the small companion a SAB pec though I see no hint of spiral structure. Most papers I saw classed it as E3 or S0 which makes more sense to me. Arp classed the pair as Group character: infall and attraction, whatever that means. He explained a bit saying "Companion appears to rain into the nucleus of spiral." The famous Whale galaxy, Arp 181/NGC 4631, is similarly classed by Arp. My image of that is archived at: http://www.spacebanter.com/attachment.php?attachmentid=2508&stc=1

Distortions to NGC 169 include a core that is well west (left) of center as something seems to have drawn the arms on th east side way away from the core. Likely the companion passed by this side sometime in the past. While the companion seems to be "falling" into the core it likely is well in front of the galaxy after looping around the east end. The orbit is likely unstable and the two will eventually combine sometime in the future. NGC 169 seems to have a large bulge of halo stars "above" (north) of the plane of the galaxy. This would indicate the companion has made several passes at different angles to cause both tidal distortions.

Note at NED makes the following comments on the pair: "These two galaxies have dramatically different colors; galaxy A has very blue, star-forming colors; galaxy B displays the colors of a reddened elliptical, yet has a disk morphology." I assume A is IC 1559 and B NGC 169. Another note says: "Pair in contact, made up of NGC 0169 and IC 1559 MRK 0341 = IC 1559, a small peculiar lenticular."

The MGC catalog says of IC 1559: "It is of elliptical shape with the major axis having stubby ends. The continuous spectrum is diffuse in the blue-violet region and becomes brighter in the ultraviolet. H{alpha} is observed."

I had a lot of problems processing this image due to the bright star, SAO 78148, right beside the pair. It is a K2 giant of 6th magnitude and cast all sorts of junk across the image that was a major pain to deal with.

The third member of this group, 11 arc minutes to the SW (lower right) is NGC 160. It is at about the same distance as Arp 282. It is classed as SA0(r) pec. One note says of it: "Very small nucleus, isolated at center of faint double (R). Non-interacting pair with NGC 0169." That is, it has a double ring structure. I assume that refers to the inner yellowish band around the core as well as the bright bluish outer edge to the galaxy. Normally the outer edge of a spiral fades away but this one ends abruptly after a narrow suddenly brighter rim. Some stars are seen outside this bright rim at either end but they also seem to end abruptly rather than fade into the background. So did it interact with Arp 282 sometime in the distant past to get this odd structure?

Above NGC 160 and right of the bright star is UGC 354 at 240 million light years. A bit farther than the others but possibly a group member. Note that some catalog listings incorrectly show it as NGC 162. The Sky's data base has this error. The description of NGC 162 however shows it to be a very different object. It reads: eF, stellar, 160 sp which translates to extremely Faint, starlike, NGC 160 south preceding. But UGC 354 certainly isn't starlike, nor extremely faint nor is NGC 160 preceding it across the sky but following it. Thus most feel that NGC 162 is one of many stars incorrectly thought to be faint galaxies when seen at the very limit of visibility in scopes of the era. It is likely the star east (left) of the top edge of NGC 160.

These 4 are the only galaxies in the field that NED shows redshift data. About 15 more galaxies are cataloged in NED (all IR emitting in the 2MASX catalog) though a few also carry extended LEDA designations. Thus most of the galaxies in the image are anonymous as far as I can tell.

Arp's photo with the 200" Hale telescope is at:
http://nedwww.ipac.caltech.edu/level5/Arp/Figures/big_arp282.jpeg

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

Rick

[JAICOA]

Very Nice Rick, On your image the distorted arms are seen much more then on the 200in plate. The colors on the image is as impressive also very nice fov. Great info as always. Clear Skies.

[RickJ]

Looks to me like Arp used a red sensitive emulsion for his shot so didn't pick up the bluer parts. At the time he was taking these images there was no good emulsions for a visual spectrum result. They were either blue or red sensitive. He would have to pick one. Also the dynamic range of the films he was forced to use was very narrow. Expose for the faint arms and the core would be so burned in little detail would be seen. It was burned in almost too much as it was. Today's CCD's have a far wider dynamic range than was available at the time he assembled his catalog. As the noise in CCD's comes down the range will continue to improve greatly in the future. If today's detectors were available in the 50's imagine how much further along our knowledge would be!

Rick

[seeker372011]

awesome image and your commentary, as always, is really informative; that's a wonderful body of work you are building up.

[andyschlei]

Fantastic as usual.

[Glom]

Wow that is awesome. Is that real colour?

[RickJ]

Except for the glare around bright stars, especially that 6th magnitude one the color is as close to correct as I can make it. It is probably saturated more than the eye would see it since things are so dim to the eye the color cone cells in our eye are not contributing much. Getting closer in some magical space ship wouldn't help. We are so close to our own Milky Way Galaxy we see it from inside yet don't see color in the Milky except in color images. As we get closer the galaxies get bigger at the same rate their over all brightness increases so stay the same brightness as our eye sees it. I color balance based on stars similar in type and temperature to our own sun which we see as white though is really somewhat yellow. There are better more complicated ways of doing it (B-V balance based on SDSS data for instance as this assures a calibration star is in the image if the area has been included in the data) but the difference is usually very small. The main thing is to properly compensate for loss of blue (and to some extent green) due to scattering in our atmosphere. As the object gets lower in the sky it gets redder same as a setting sun. This can be modeled fairly accurately and is how this image was color balanced as there were no sun like stars within the frame.

However the orange glare from that 6th magnitude star covered the entire image. Removing it and not making things thus too blue was difficult. I may still have a bit too much blue in the image. While I applied the normal G2 balance for this part of the sky there were none in the image itself to be sure I compensated for the glare properly. So if someone would turn off that star I probably would have the color balance a bit more accurate.

There are many web pages devoted to various methods of G2 color balance if you are interested in going deeper into the subject. B-V balancing may take a bit of research as it is quite new. Process is essentially the same however but not built into image processing software like G2 balance is.

Rick