ARP312

ARP 312/HOLM 758 is a group of galaxies in northern Hercules located about 525 million light-years away. It falls under Arp's category Group Character: Groups of Galaxies. There are several Arp galaxies in this area northeast of M92. While the galaxies of Arp 312 have about the color of elliptical galaxies they are a bit bluer than most leading me to wonder if these were spirals and have interacted sufficiently to eject their dust and gas so are turning into elliptical galaxies. I find very little on this group so this is pure speculation on my part.

How many of the galaxies Arp considered to be in the group is also a bit difficult to determine. NED seems to list only 2, the two northern ones sharing a common halo of stars. Webb and Kanipe include the bright galaxy to the southwest. Arp included the one to the northeast by a star in his photo. His comment reads; "Diffuse connection between central members of the group." Obviously, the two brighter members show a common halo. Look closely and it extends to the southwestern one as well. That would be 3 members, not just "central" ones. So is Arp referring only to the two with the obvious halo and considering the northeast and southwestern ones members not sharing a "diffuse connection?"

The three major galaxies are: MCG+8-31-4, the southeastern one; MCG+8-31-5, the largest of the group; and MCG+8-31-6 the easternmost galaxy of the three. The one hiding behind the star to the northeast is 2MASX J16495421+4643284 a strong IR emitting galaxy. But that applies to the other three as well as they too are in the 2MASX catalog which was conducted at the 2 micron IR/microwave wavelength. I find redshift data only on MCG+8-31-5. I'd assume the three in the MCG catalog are all about the same distance due to the common halo. Most everything else in the area is a mystery, unfortunately. No one seems to even be trying to classify any of the 4.

While this area has been surveyed by the Sloan project no redshift data for the entire field was found in NED. There are lots of interesting galaxies but while I can put names on them that is about all I can do so I haven't bothered to prepare an annotated version. The bright star is a 7th magnitude K2 star that gave me fits when processing this image.

Sloan image:
http://astronomerica.awardspace.com/SDSS-12/MCG8-31-4.php
Their image really shows what a pain that K2 star was!

Arp's image:
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp312.jpeg

Besides the normal full image I've attached a cropped version at 0.5" per pixel, twice my normal resolution.

14" LX200R @ f/10, L=4x10 RGB=2x10x3, STL-11000XM, Paramount ME

Related Designations for ARP312

ARP313

ARP 313 is a trio of interacting galaxies. The biggest member in the center is NGC 3995, to the west (right is NGC 3994. The glow-worm like the galaxy to the northwest (upper right) is NGC 3991. Redshift data shows these to be about 150 to 157 million light years from us. NGC 3994, the undistorted one having a redshift that could indicate that it is a good 5 million light years closer thus explaining why it shows so much less distortion. Still, it is a LINER galaxy which indicates something is going on. LINER stands for Low Ionization Nuclear Emission Region. A very complicated way of saying that the core of the galaxy has emission lines indicating there's a lot of gas in the core that is slightly ionized -- that is not many of the electrons are missing but more than you'd expect. The cores of most galaxies are pretty dust and gas free. That is out in the disk of the galaxy where we live. But in galaxies that have interacted with others or that have really active cores due to a hungry black hole, it is seen. Since NGC 3994 doesn't seem to have an active black hole the LINER status would indicate it is feeling the interaction with the other two. Also if you look closely you can see some tidal arms coming off the north and south ends of it. Unfortunately, again taken in moonlight, I can only bring out a hint of this without making the image very noisy. I've attached a crude stretch to show this halo. It appears to connect to NGC 3995 but that is mostly noise from the moon and not real. I need a moon free night to tell more.

NGC 3995 and NGC 3991 are certainly interacting as shown by the very weird nature of both as well as the very blue colors in both indicating massive new stars have formed in these galaxies in the last few million years. Considering the galaxies are at least 10 billion years old this is very young astronomically speaking.

NGC 3991 and 3995 were discovered by Heinrich d'Arrest on February 5, 1864 while he found NGC 3994 on April 6, 1864.

Arp's image: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp313.jpeg

14" LX200$ @ f/10 L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for ARP313

ARP314

Late last summer I started to have problems with elongated stars. I had to throw out frames and retake them to eliminate this. I couldn't track down the problem. This is probably the most affected image. Retaking didn't help, I just had more elongated stars. I was getting desperate. I decided to regrease the gears and see if that helped. I also had a bad USB cable that needed replacing. These route through the axes. I opened the Dec axis' compartment to pull out the bad cable and found it totally packed with sunflower seeds some little critter (mouse or vole most likely) had stashed there. Once the seeds were removed my oval stars went away. I plugged the openings around the cables with steel wool and set traps. Traps didn't trip or have bait eaten so I assume the critter had already met up with one of the owls that hang around here, great horned and barred. I never retook it. The tracking problems were quick so only distorted brighter objects. Galaxies seem to have been immune to the quick excursions caused by the seeds. Even tiny star forming regions in the "shock wave" like features of the two highly distorted galaxies are well resolved.

Arp 314 is classed by Arp under groups of galaxies. Most sources say it is a three galaxy group leaving off the one to the southeast that appears to be creating some sort of shock front full of star forming regions. Arp did include it in his photo and mentions it in his comment saying "Faint filament leads SE to faint dwarf." So I think he was including it yet most catalogs don't include it. Maybe that's because there's no redshift data so it's possible it is at a very different distance. Possible but doubtful what with its odd distortion and that arm leading toward it. Or maybe he was referring to the condensation at the end of the filament. It isn't cataloged anyplace I could find as a separate object but maybe that is what he means.

Arp 314 is in the constellation of Aquarius just west of Arp 223 under the Circlet of Pisces. It is about 150 million light-years distant, only about 8 million light years more distant than nearby Arp 223. Since orbital velocities in galaxy groups can easily cause even greater redshift differences it's quite likely these are part of the same galaxy "local group."

The northern galaxy is MCG -01-58-009 and is classed as (R')SA(s)bc? pec. The galaxy with the tidal arm is MCG -01-58-010 classed as SB(rs)cd: pec. The third member all agree on is the odd elongated one to the south of MCG -01-58-010. It is MCG -01-58-011 classed as (R')SB(s)dm pec. The fourth galaxy that NED and others don't consider part of Arp 314 for some reason is basically anonymous. It has only been cataloged by aN automatic plate measuring survey with the UK Schmidt camera as APMUKS(BJ) B225548.75-040459.3. The extended PGC lists it as PGC1066529. It lists a magnitude of 17.1 while the APMUKS listing shows it as 16.3. That's quite a difference but could but due to the color this was measured in. It hasn't been classified nor studied that I can find yet seems to be a very interesting galaxy. What is causing that odd arc of new stars "in front" of it? MCG -01-58-011 seems to have a similar arc of new star forming regions to its west as well. MCG -01-58-009 is the only one that only looks sort of messed up. At least its spiral structure is somewhat in tact. That's certainly not the case with the 3 others.

There's a cute little comma of 5 galaxies in the upper left corner just right of a fairly bright star. Two are in the APMUKS catalog, all are otherwise anonymous. Four are about the same brightness. Are they a small group? Brightest is about 20th magnitude.

The obvious asteroid in the upper right corner is (12324) Van Rompaey at magnitude 16.8. Much harder to see toward the lower right corner is 2005 QC1 at magnitude 19.3

Arp's image
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp314.jpeg

Hubble hasn't seen fit to explore this system.

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

Related Designations for ARP314

ARP315

Arp 315/Abell 779 is a group of galaxies in southern Lynx. Arp 315 is just 3 of the 83 galaxies in the Abell 779 galaxy cluster that mark the heart and is likely the anchor of the group. Arp put them in his Group of Galaxies category. The three in his atlas are NGC 2830, NGC 2831 and NGC 2832 right to left. They don't appear to be interacting so are likely further apart than our perspective makes it appear. His comment reads: "Companion E [NGC 2831] is quite compact."

The group is about 300 million light-years from us. NGC 2832 dominates the group. It is obviously a cD galaxy ("central Dominant), also under Yerkes galaxy classification, it means by the c that it is a super giant galaxy and the D that it is diffuse (elliptical), galaxy. NED classes it as E2+2 while the NGC project says E4. NGC 2831 is classed as E0 by both. NGC 2830 is simply S under the NGC Project and SB0/a: per NED. It appears to be nearly edge on.

NGC 2825 was discovered on April 3, 1831 by John Herschel
NGC 2826, 2831 and 2832 were discovered on March 13, 1850 by George Stoney
NGC 2830 was discovered by William Herschel on December 7, 1875 but isn't in either H400 program

I've prepared an annotated image that shows both the catalog entry and redshift distance per NED using 5 year WMAP data. There is quite a spread likely indicating rather high orbital velocities of the galaxies in the group. Including the identification rather than just the distance greatly increased the file size as well as making it hard to put in labels without overwriting other objects. If the object isn't a member of the group I only show its nature (Q-quasar, G-galaxy) and distance. Those without a label had no distance data in NED so I couldn't determine if it was a cluster member or not. A few weren't in NED's database. I noted one of these, a rather bright one, with a question mark. Why these don't make the catalog is still a mystery to me. No one seems to know the answer, at least no one has told me.

Looking around the image there are a lot of galaxy pairs and triples, many of which appear to be interacting others just line of sight pairs. There's a lot going on all over this image if you go looking for it.

There's one asteroid in the image, (230947) 2004 XY54 at magnitude 18.5

Arp's image
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp315.jpeg

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

Related Designations for ARP315

ARP316

I was going through all my Arp images trying to get them organized. I found some of my very early ones, back when I was just taking interesting galaxies and paying no attention to the Arp catalog, were very poorly processed. This one is one of them. Arp 316 consists of 3 galaxies NGC 3187, NGC 3190 and NGC 3193 and is located between two stars of the sickle of Leo. NGC 3185 is part of the Hickson 44 group but apparently not part of Arp 316. Arp classifies it under "Group Character: Groups of galaxies. A redundant classification. Reminds me of when I was in college working for an accounting firm. Bookkeeping was done by IBM punch cards on a mechanical rather than computer system. The firm with the equipment forced all users to the same expense categories. There were 9 possible classifications in three levels defined by the numbers 1-9. Each refined the previous category. 9 was Other, 9 under that was Miscellaneous and 9 under that was Misc. I was told that I could never use account 999 for obvious reasons. So they did Arp one better with redundant classes.

The main galaxies of the group include NGC 3185 at the bottom (not part of Arp 316). It is classed as SB(r)a and is thought to be about 70 million light-years away.

NGC 3187 is the wide armed spiral, SBc pec, and is thought to be about 85 million light-years away. Note how the upper arm has lots of fine detail but the bottom one looks all "windswept" and fuzzy. Must have happened in the tidal interaction that gave it such wide spread arms in the first place though I can't recall seeing this effect before. Notes indicate it is interacting with NGC 3190 and maybe NGC 3185.

The big spiral in the center with the very weird dust lanes is NGC 3189 (lower part) and NGC 3190, rest of it. Most sources just use the NGC 3190 designation, however. It is classed as Sa pec LINER and is thought to be 73 million light-years away. Note the two planes to its dust lanes. There's the main lane which at the NW end suddenly seems to separate and go off at a different angle for a short ways. Then toward the other end, it splits with a fine lane resuming about the same plane as the odd piece at the other end. But they don't point at each other, just that they seem to be at about the same angle in relation to the main band. Very odd. Lots of tidal spray around the galaxy as well. This may be the result of a merger that hasn't yet been pulled into one plane.

The upper galaxy is NGC 3193 E2 LINER and has a redshift distance of 79 million light-years but there are indications it is really about 96 million light-years away.

This group is also known as Hickson 44. NGC 3185 and 3187 were discovered by George Stoney in January 1850. Sorry I couldn't find a more precise date. The other two NGC 3190 and 3193 were discovered by William Herschel on March 12, 1784. I find it odd he didn't find the first two as they are seen in my 10" f/5 scope though 3187 is more difficult than the other three. Both of Herschel's galaxies are in the original H400 program. My notes from April 15, 1985 under humid but fair skies at up to 150x reads: "3190: Oval galaxy, gradually brighter toward the center. This galaxy is not a winner except when you take the other three into account. Does form a nice high power pair with NGC 3193. 3193: Small, not quite circular galaxy near a field star. Forms a high power pair with 3190. It has a large bright core with a tight halo about it." It appears this group is photographically much better than seen visually, at least through the humidity I was dealing with that night.

The blue spiral toward the SE corner is LSBC D500-05 an Sc spiral, LSBC stands for Low Surface Brightness Catalog. The galaxy is listed with a redshift that puts it about 200 million light-years away. Thus it must be a rather large galaxy.

Blue galaxy well west of NGC 3190, halfway to the edge of the image is LEDA 086788 an Sc galaxy at about 100 million light years which puts it at least in the vicinity of Arp 316.

The tiny SO like galaxy between NGC 3190 and NGC 3193 is SDSS J101811.88+215130.0. I find no info on it other than the note "candidate dwarf".

The much larger fuzz blob to the southeast of NGC 3193 is SDSS J101833.31+215138.2. There's little on it, however.

Most of the other blue fuzzies aren't even listed in NED which surprises me as this is an area covered by the SDSS yet they aren't in it either.

ARP 316 as a whole is listed by NED at a distance of 78 million light years by redshift.

This was taken on a night of better than normal seeing. So I was able to get a lot of detail in these galaxies. But what really strikes me about the image is that the spread of faint objects is very uneven. There's an area around the 3 upper galaxies and one bright star that has a lot of faint objects in it. But the rest of the image has far less. You normally don't think of dust in Leo but it seems like something could be reducing the background except in that one area. It appears most of the objects in this "enhanced" area are galaxies. I searched NED for some galaxy clusters in the area and came up with two but they are centered near NGC 3187 or a bit above it. Still, they show a distance of over 2 billion light years which does seem to fit. They are NSC J101747+215255 and 400d J1018+2154. They are likely seeing the same group. There's not much data on either as to size density or galaxy count.

Arp's image of the group taken this time with the 48" Schmidt telescope due to the area being too great for the 200" field of view, is at:
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp316.jpeg

The SDSS image:
http://astronomerica.awardspace.com/SDSS-21/NGC3193-90-87.php

14" LX200R @ f/10, L=5x10' RGB=2x10', STL-11000XM, Paramoune ME

Related Designations for ARP316

ARP317

Arp 317 is also known as the Leo Triplet. It consists of three galaxies, NGC 3628, M65 and M66. M66 by itself is also Arp 16. Unfortunately, my field of view is too small to include all three even in a mosaic of two images as the distance between the two Messier objects and NGC 3628 is just too great. For a view that shows all three in one image see: http://cseligman.com/text/atlas/ngc3628wide.jpg

While many sources consider all three galaxies to be interacting Arp's comment only dealt with two, M66 and NGC 3628 when he wrote: "Both galaxies on east show signs of interaction." M66 has large plumes as well as some large H alpha regions I picked up even without the aid of an H alpha filter. NGC 3628 is rather famous for a long streamer of stars coming off its northeast end heading east. Unfortunately, I took my image of it when I first was getting into digital imaging and had no idea I needed to manage the system noise of my camera. The result was that I lost the streamer due to severe system noise covering it up thanks to my short exposure time. For some reason, I've never gotten around to retaking it. NGC 3628 is often called the Hamburger Galaxy due to its wide, dark dust lane reminding some of a hamburger patty in a bun. I can't say that it works for me but I'm not a big hamburger fan in the first place (sorry McDonald's, Burger King, etc.)

I've included my image of M65 and 66 though you will see that also at Arp 16. I was fortunate enough to catch M65 with a supernova though it was fading when I finally got around to imaging the pair. NGC 3628 has a redshift distance of about 55 million light-years at NED but an average of about 15 non-redshift measurements says it is only about 35 million light-years distant. NED classifies it as SAb pec sp;HII LINER. M65 has a redshift distance of about 53 million light-years but a non-redshift distance of 42 million light-years. It is classified by NED as SAB(rs)a LINER. M66 has a redshift distance of 50 million light-years but a non-redshift distance of 31 million light-years. It is classified as SAB(s)b;LINER Sy2. Even though the non-redshift distances to these three don't agree all that closely compared to the redshift distances most sources put their distances at about 35 million light-years.

NGC 3628 was discovered by William Herschel on April 8, 1784. It is in the original H400 observing program. My comments from the night of April 16, 1985, under fair but humid conditions using my 10" f/5 at up to 100x is pretty bare bones. It reads: "Large, edge on galaxy with a hint of a dust lane. Forms a triple at low power with M65 and M66." How that huge dark dust lane was reduced to a "hint of a dust lane" I don't know. M 65 and M66 were discovered by Charles Messier on March 1, 1780, though many books and articles incorrectly attribute their discovery to Pierre Méchain. You can thank Admiral Smyth for creating this error which was picked up by others over and over again.

Arp's image with the 48" Schmidt telescope:
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp317.jpeg

NGC 3628: 14" LX200R @ f/10, L=8x5' RGB=2x10', STL-11000XM, Paramount ME
M65 and 66: 14" LX200R @ f/10, L=4x10 RG=2x10' B=4x10', STL-11000XM, Paramount ME

Related Designations for ARP317

ARP318

Arp 318 is a group of 4 galaxies also known as Hickson 16. It is in the constellation of Cetus and is about 160 million light years distant. Hickson 16 consists of 4 galaxies but Arp 318 may consist of 5. Depends on your source. Arp's image only includes 4 of the 5. The 5th is too far for the 200" to image it with the others. With other large objects, Arp went with the 48" Schmidt photo, however. Since he didn't here I'll assume 4 is correct but the 5th is in my image so won't escape my covering it.

The 4 galaxies, right to left are, NGC 833 (HCG16B), NGC 835 (HCG16A), NGC 838 (HCG16C) and NGC 839 (HCG16D). Hickson lettered them brightest to dimmest. NGC 833 is classed as (R')Sa:pec;Sy2 LINER so has an active nucleus likely caused by its interaction with NGC 835. NGC 835 shows tidal plumes from the interaction. It is classed SAB(r)ab: pec LINER with some sources saying it too is a Seyfert 2 galaxy. Its ring like arm and overall shape is somewhat akin to some galaxies thought to have taken a direct center hit by another galaxy. Usually, the ring is further out and more complete. Something has sure clobbered it, Maybe NGC 833.

NGC 838 is also disturbed showing some rather strong dust features. It is classed as SA(rs)0^0 pec: Sbrst. Its classification as a starburst galaxy indicates it too has been altered by an encounter. I'm leaning toward it being the bullet that hit NGC 835 if indeed it was hit by one. With those huge dark dust clouds, it could be in starburst mode for some time. The final galaxy of the four, NGC 839 is classed as Spec sp; LINER Sy2. It too has an active nucleus. It appears to have a bright ring structure as well with a very dark cloud. It's not as red as those in NGC 838 probably indicating less UV light from young stars is hitting it. The UV light causes dust to give off a reddish light called Extended Red Emission. The lack of UV hitting it likely is due to it not being a starburst galaxy and thus not having sufficient supermassive stars to give off the unneeded light. Or the cloud is located such that it is blocked from such light. It's hard to tell. In any case, it, like the other 3, has obviously had a close encounter of the galactic kind. All four were discovered by William Herschel on November 28, 1785. None are in either H400 observing program.

The 5th galaxy is in the lower left corner of my image. It is NGC 848 and has a redshift putting it at 171 million light years, about the same as the other 4 so it is most certainly part of the group. It carries the uncertain classification of (R')SB(s)ab pec? Sbrst. Note the large plumes, especially to the north. So it has also been rather strongly jostled about by one or more of the other 4 galaxies but seems to be making a run for it rather than take further beatings. (I'm typing this with the help of a 12-year-old granddaughter, the anthropomorphic slant is hers though she doesn't know the meaning of the word.) This galaxy was discovered by Ormond Stone In December 1885. While I've seen it included as part of HCG 16 it is too far away to meet Hickson's compact group definition. Its inclusion is an error.

Arp's comment about this 4 galaxy entry is: "Faint, diffuse streamers, peculiar galaxies.

I've included an annotated image showing distances in billions of light years to those objects that NED has redshift data for. G is for galaxy and Q for quasar. QC means quasar candidate and P after the distance means it was determined photographically. This is done by noting the point at which the redshifted UV light suddenly drops off. Theory says this happens at a particular frequency for a resting source. By how far this point is shifted toward the red its redshift and thus distance can be estimated. Of course, if something unforeseen alters the UV spectrum this could be in error though it is usually considered a valid indicator of distance and is how most of Hubble's deep field images are evaluated for their galactic distances. The label is immediately right of the object when possible. When that would cover up something the label is moved to a clear space and a line is drawn to the object.

Usually, distant galaxies are quite reddened but this image has a surprising number of galaxies over a billion light years distant that are still blue to white in color.

This image doesn't go nearly as deep as normal as two subframes were lost to clouds and I didn't realize it at the time. This data loss makes going deep too noisy due to under sampling of the photons I was collecting.

Arp's image:
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp318.jpeg

14" LX200R @ f/10, L=3x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for ARP318

ARP319

Arp 319 is better known as Stephan's Quintet. It is really a group of 4 galaxies with a 5th galaxy in the foreground though there is a true fifth member Arp didn't include it. The interloper galaxy is NGC 7320. It is apparently the largest of the group and the bluest. It is really a member of the so-called "Deer Lick" group located less than a degree away. It is located only some 40 million light-years away while the other 4 are about 270 million light-years from us. At one time this group was put forth by some to disprove redshift as a distance measure to the universe. Since NGC 7320 is close it has a small redshift while the other 4 have a large redshift. But if all were at the same distance then redshift was called into question. It took Hubble to answer this for sure. It could resolve stars in NGC 7320 but only massive star clusters in the others. This was consistent with the redshift distances and it is now accepted that 7320 is a Deer Lick member seen in front of the far more distant group. Actually, we do have 5 members of this distant group. To the left, a bit is a barred spiral whose arms make a nice ring, NGC 7320C. It is now known to be a member of the group and may be responsible for some of the tidal plumes. So there really are 5 galaxies in Stephan's quintet, just that one isn't the one we thought was a member for many years.

For a shot taken with a far larger telescope on Kitt Peak than mine see: http://www.noao.edu/image_gallery/html/im0414.html

Actually, there are several more members of the group. Just that like 7320 is well away from its group these other members aren't as close by. One is LEDA 141041 even further east than the first 5. Then there's the very awkwardly named [WYV2002] 6 in the upper left corner of the image. Just out of the image due east of the cluster is NGC 7320B yet another member of the group. These are the only ones I found with redshift values to show they are very likely group members. In the lower part of the image is NGC 7320A which looks almost a twin of NGC 7320B I missed catching. Both these last two are members of the 2MASS flat galaxy catalog. On the west side of the image is the S0 looking galaxy PGC 69218. It too has no redshift data but could possibly be a member of the group.

I find it interesting that while NGC 7320 is now known not to be a member NGC 7320B and NGC 7320C are members (as may be 7320A). The annotated image identifies the galaxies that have redshifts and those two without redshift data that might be members of the group as well as the interloper, NGC 7320 itself. There's one quasar in the image hard to pick out from NGC 7319 appearing more like a bright spot in the galaxy. Also, a star forming knot in the tidal plume coming from NGC 7319 is listed in NED as a separate galaxy though I think it is just a star cloud in the plume, one of several in that plume.

So how did this group come to be so tidally damaged? There are many theories. A note at NED summarizes them this way: "To explain the peculiar morphology of Stephan's Quintet, a number of different interaction scenarios have been suggested. Some of these scenarios involve ram pressure stripping during a head-on collision between two galaxies. For example, Peterson & Shostak (1980) suggest that a head-on collision between NGC 7318B and NGC 7319 removed the gas and caused the radio continuum ridge between them. A different scenario was suggested by Shostak et al. (1984): a prograde tidal encounter of NGC 7320C and NGC 7319 occurred, pulling gas out of these galaxies, creating the long tail south of NGC 7319. This was followed by a high-speed collision between NGC 7318A and NGC 7318B. Other scenarios involve a collision between an "intruder galaxy" (usually NGC 7318B) and intragalactic gas that had previously been tidally stripped or ram pressure-stripped in an earlier encounter between two different galaxies in the group (van der Hulst & Rots 1981; Moles et al. 1997). Moles et al. (1997) suggest that a direct collision between the outlying galaxy NGC 7320C and NGC 7319 occurred in the recent past (10^8^ yr ago), removing a large quantity of gas from these galaxies. After this event, NGC 7318B entered the group at high velocity, colliding with this stripped gas and triggering star formation." Pick one of your choosing or come up with another. Seems to be still open for more ideas. Look up Arp 7319 at NED and read the notes for even more suggestions from users of the radio part of the spectrum.

What I never saw mentioned is that NGC 7320 seems to have its own plume extending to the southeast (left and some down). Is it from NGC 7320 or is it really from NGC 7318B but mostly hidden by NGC 7320 until it finally appears after passing behind it? I found nothing on this feature.

Arp's image: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp319.jpeg

14" LX200R @ f/10, L=6x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for ARP319

ARP320

Arp 320/Copeland's Septet is a group of 7 galaxies though you'll see 9 main galaxies in the center of the field. A finder chart of the 7 that are members of the "official" septet http://www.ngcicproject.org/dss/n/3/n3753.jpg
Note the blob above the label for NGC 3754 is a plate defect so you won't see it in my image. It is also known as Hickson 57. The main galaxy in the group is NGC 3753 also known as ARP 320. The reason for so many names is just that each astronomer has some reason to study it and puts it in their catalog. Before long there are a ton of catalog entries for the same thing. Besides NGC 3753 is also known as: UGC 06602, VV282a, KUG1135+222, CGCG127-012S, CGCG1135.4+2216, MCG+04-28-010, PGC03616, UZC J113753.8+215852 and [BDG09] J113753.9+215853 to name a few. The group is also known as Copeland's septet, HCG 057, WBL 343-005, USGC U404 and UZC-CG 142, RSCG 43 and others. Confused yet?

The group is about 410 to 440 million light years distant and somewhat red. I suspect this is due to lots of dust between us and the group though one galaxy does show some blue color. But two of the redder galaxies have "retired" nuclei. This means star formation has virtually ceased though some emission lines of LINER galaxies are still seen. This usually is interpreted to mean they are about to become red and dead galaxies. Several papers mention this color problem but none I saw gives an answer or even a guess as to why the group but for NGC 3754 is so red. Some of it was discovered by Ralph Copeland on February 9, 1874 (NGC 3746, 3750 and 3753) and the rest on April 5, 1874 (NGC 3745, 3748, 3751 and 3754). He got their position rather wrong by about 1.5 minutes of Right Ascension and about 15 arcmin of NPD. Enough that my field would have missed it using Copeland's position. But since no other group is in the area and its description fits his identification is certain. As to why 4 were found in April and 3 in February, I couldn't discover.

Just under NGC 3748 is PGC 36010 an S0/a galaxy that some consider part of Arp 320 but Copeland didn't see so it is not Copland's Octet. It is part of HCG 57 however. Look around the annotated image and you will see quite a few other galaxies, mostly dwarfs compared to the seven in the septet, also at the 410 to 440 million light-year distance indicating this is quite a large group.

It is quite obvious NGC 3753 is interacting with NGC 3750 by the huge plumes it has. I suppose the vertical one off the west end may be coming from NGC 3750. NGC 3753's southeastern plume almost looks like it is sticking its tongue out. Its dust lane is quite disturbed. Often a sign it ate something recently. While SLOAN shows a point source object just northwest of its upper end it doesn't show any entry for the plume. I thought it might be some low surface brightness dwarf that just happened to line up with NGC 3753 but apparently, it is just a plume. Assuming it is a plume and including the northwestern plume, I measure the full size at 300,000 light-years. Measuring just the bright disk I get 110,000 light-years.

NGC 3748 shows plumes as well indicating it did interact with one of the galaxies in the group but which one? Including plumes, it is 162,000 light-years across. The disk is much smaller at 55,000 light-years. NGC 3746 I measure at 135,000 light-years in size. I measure NGC 3750 at 140,000 light-years, NGC 3751 at 145,000 light-years and NGC 3745 at 90,000 light-years including the faint plume, mainly to the east. Omitting the plume I get 40,000 light-years making it the smallest of the 7.

The asteroid to the lower left (southeast) is (30376) 2000 JE65 at magnitude 17.7.

Arp's image: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp320.jpeg

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

Related Designations for ARP320

ARP321

Arp 321, Hickson 40, is a tight group of 5 galaxies, 3 of which are certainly interacting. Most catalogs list them as a through e but can't agree as to which is which. I'm following Hickson's lettering in my annotated image since it fits a NED note that is interesting. Part of it is reproduced below.

"All galaxies in the group, except galaxy e, are radio sources (Menon & Hickson 1985). The most relevant structure of the group is the triplet formed by galaxy b with the two spirals c and e. These last galaxies provide further examples of disk "eroded" by interaction with a close companion. In particular, the southern spiral arm of galaxy e forms a characteristic stream of matter toward the two companions, indicating that the triplet is indeed a physical association. This fact is also confirmed by the presence in galaxy b of a small nuclear jet pointing towards galaxy c (UMT) and by the unusual behavior of profiles of both galaxies. Actually, the luminosity, ellipticity, and position angle profiles of galaxy b suggest its classification as a disky elliptical or S0 galaxy. On the contrary, its a_4_ profile shows a strong boxiness also noted by Rubin et al. (1991). This could suggest that the close interaction may change the shape of the galaxy more rapidly than its radial light distribution and, in this framework, galaxy b of this group could represent an intermediate stage of a merging process.

"The most luminous member of the group (galaxy a) is another example of dubious classification between S0 and disky elliptical. In fact, even if the luminosity profile is well represented by the r^1/4^ law, the geometrical profiles (especially the ellipticity profile) are typical of an SO galaxy seen at an intermediate inclination angle. Also in the field of this group, some small diffuse objects are visible, mostly around the galaxy a."

The galaxies are located in Pisces near the Circlet and are a bit over 300 million light-years distant. Actually, there's a 6th member of the group LEDA 082490. It shows the same redshift distance and does seem to have a bit of distortion at its ansae so may have had a run in with the others sometime in the past.

Arp classed this one under his rather redundant class Group character: Groups of galaxies. His comment: "Sharp absorption lane in connection to S galaxy."

They are classed at NED as:
a) E1
b) SA(r)0 pec
c) SB(rs)b pec
d) SB(s)0/a pec
e) SAB(s)a pec
LEDA 082490 S(0)

This field is not covered by the Sloan survey so most of the galaxies in the image have no redshift data and most are anonymous.

Arp's image:
http://nedwww.ipac.caltech.edu/level5/Arp/Figures/big_arp321.jpeg

I've included an annotated 2x enlargement of the group to show a-e and LEDA 082490.

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

Related Designations for ARP321