HCG075

HCG 75 is a tight group of 8 galaxies in northwestern Serpens Caput about 550 to 590 million light years distant. One has no distance estimate. Are they really at the same distance or is this just an illusion due to our perspective? I found no non-redshift distance estimates to help here. It is rather likely they are at about the same distance and the difference in redshift values is due to their relative motion around a common center of gravity. Assuming they are about the same distance the group is a bit over 400,000 light-years across. Close enough that I'd expect to see some rather noticeable interaction. While A and B overlap I don't really see any interaction and the others show none other than H is an irregular blue galaxy but this may just be its nature. With no distance estimate of any type, G may be a distant background galaxy of which many are in the image.

While A is the brightest of the galaxies in the group and likely the most massive, B has the largest diameter, which I measure at about 160,000 light-years. I measure A at about 95,000 light-years in size though this is a guess since it is partly lost either behind or in the glare of galaxy B. So I measured the southeastern half and doubled that for a size. Being a tightly packed ball of stars it likely has more mass than the larger disk of galaxy A.

Galaxies G and H are listed at NED as being dwarf candidates. If G is a true member of the group it is a small spherical galaxy about 16,000 light-years across so would be a dwarf. H, however, is much larger, being almost 50,000 light-years across. Far too large to be considered a dwarf. Maybe it got this possible classification before its distance was known. But then it would have had to be considered much closer than the others in the group or else others would have to be dwarf galaxies as well and none are listed that way.

Three other galaxies to the north, northwest and southwest of the group have similar redshifts so are likely members of this group. There are 5 other galaxies near A to the west that may be dwarf members or distant background galaxies. Without redshift data, I can't tell which they are. All these, but for H are red and dead galaxies. In fact, most of the galaxies in this field are red and dead galaxies.

While this field was shot through clouds of varying thickness I think the colors are not far wrong. EXcalibrator said red had to be toned down to get the spectral colors of the stars right, this adjustment wasn't severe. I believe colors to be close to correct. Clouds did limit color in very faint stars and galaxies. Green was hit the worst but most easily compensated for. All bright stars had strong green halos which Hasta La Vista green easily eliminated. Imaging through clouds has been a near constant problem this spring. I'm getting used to it.

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

Related Designations for HCG075

HCG076

Seeing turned poor this night. I searched for something I thought could sort of survive the bad seeing and chose the Hickson 76 group as it consisted of mostly featureless galaxies. Not checking further I put it on the schedule and went to bed. Seeing got worse and it turns out this field was far more interesting than I expected. Now too late to redo it this year I went ahead and processed this low resolution mess. I'll try again next year.

What I didn't realize is that HCG 76 forms the core of the ABELL 2085 galaxy cluster at a bit under a half billion light-years. This cluster virtually fills my field. HCG 76 itself consists of 7 of the brighter members in the core of the ABELL cluster. Three are NGC objects. There is some controversy over 2 of these. It's too long to go into here so I'll just let you look it up at this link: http://www.ngcicproject.org/NGC/NGC_59xx/NGC_5941.htm . The link may be temporary. It is to the NGC Project which shut down upon the death of the fellow administering it. A temporary version is online as I write this. If it changes once the site has been fully restored it shouldn't be hard to find the entry.

In short, I followed the above site for designating the three NGC galaxies in the HCG group even though that puts NGC 5941 east of NGC 5942 so out of RA order. Seligman follows the same system but makes no mention of its problems.

The other NGC galaxy in the frame is the biggest and brightest. It is NGC 5940 and the lone bright, face on spiral. It has a rather odd arm structure on the east side that creates the appearance of a dark vertical stripe or dust lane. I think it more to do with the odd arm structure than obscuring dust. I measure its size at about 130,000 light-years.

All 4 of the NGC galaxies were discovered by Lewis Swift on April 19, 1887. Unfortunately, his positions tended to be rather vague leading to the identity confusion.

The field contains the usual mix of objects that are labeled in the annotated image. To the upper left is an object that is listed as both a galaxy and a quasar. It has a fuzzy image on the SLOAN image with a size greater than that for a point source quasar. Apparently, it is a quasar that doesn't outshine its host galaxy allowing a bit of the galaxy to be seen. It helps that it is about half the distance of most other quasars.

Seeing was very poor. I probably should have reduced it to 1.5" per pixel from my normal 1" per pixel but that made the annotated version hard to read so left it at a very fuzzy 1" per pixel.

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

Related Designations for HCG076

HCG079

This was the most compact group of galaxies known when Seyfert discovered it in 1951. The group consists of only 5 rather than 6 galaxies like the name implies. 4 of them are about 200 million light-years away. The fifth, the small spiral to the east side under others, is well over 4 times as distant so not a member of the group. Three of the group appear to be interacting, the easternmost so distorted it was thought to be two galaxies giving rise to the 6 galaxy count. The extra galaxy is just a large plume, however. The group was first recorded by Édouard Stephan as one galaxy which went into the NGC as NGC 6027. The individual galaxies carry their own letter designation but that varies from catalog to catalog with some using lower case letters and others upper case. All have PGC numbers but again I find some disagreement as to which is which. A quick calculation shows the interacting galaxies occupying an area of space only slightly larger than our galaxy. I do find the southern blue galaxy odd. I suspect it isn't interacting nearly as strongly with the others, if at all.

This is one of my early 2007 images when I did no research on my images though I see I tried to do some for this one and got lost in the various naming conventions I ran into. I don't have time to fight it right now. I'll just add that the galaxy on the far left of my image is PGC 56636. It is at about the same redshift as 4 closer members of HCG 79 so likely part of their local group.

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

Related Designations for HCG079

HCG082

HCG 82 consists of 4 galaxies in far western Hercules west of the Keystone. It consists of 3 NGC galaxies and one PGC galaxy, NGC 6161-6163 and PGC 58231. The three NGC galaxies were discovered by Édouard Stephan on June 30, 1870. Hickson had no distance data when compiling his 100 groups. He assumed most would be related due to their close proximity to each other. In this case, they may be related though their redshift shows a rather wide range of values from about 460 million to 530 million light-year distance, a 70 million light-years difference. This is probably due to their orbital velocities around a common center of gravity and not a real distance difference. An average would put them just under a half billion light-years distant. I measure the group as being about 530,000 light-years across assuming they are all at about the same distance. NGC 6162 is the big one at 185,000 light-years across. NGC 6163, thanks to its wide "wings" is 125,000 light-years in size. NGC 6161, thanks to its plumes is nearly as large as NGC 6162 at 180,000 light-years though I suspect its mass is much less. Also, this size argues strongly against it being an irregular galaxy though its core region with the dust lane is only 65,000 light-years in diameter. PGC 58231 is the baby also at 65,000 light-years. Still a respectable size for a spiral galaxy.

NGC 6161 is listed as an Irregular Magellanic galaxy by NED while Seligman and the NGC project say Sc though Seligman adds a question mark. I see it as a disrupted spiral. I suppose its distortion is due to interaction with one or more of the other galaxies in this group. Only NGC 6163 appears possibly distorted so I'll say it is the cause. But if NED is right it may be just naturally this way.

The annotated image shows a scattering of other galaxies that have a similar redshift to those of HCG 82. All appear to be dwarfs compared to the 4 HCG galaxies. There is the usual mix of distant galaxies and quasars in the field. Nothing caught my eye as interesting, however.

As with many of my spring images, sky conditions were poor when this was taken. At least seeing wasn't all that horrible but there was a thick haze in the sky. 7th magnitude HD 148616, the K0 star to the lower right cast a glare from the haze over the entire image. Removing it was a major pain. Also, the haze severely harmed the blue image to the point it was very noisy. I should have taken more blue frames but the clouds didn't allow it this night and after this, the moon was a major problem. I went with the poor color data though as I've mentioned several times before the color is rather suspect due to high noise in the blue data. Also, clouds were kind to the first green frame but totally eliminated the second green frame. Still, it's one frame had a much higher signal to noise ratio than the two blue frames.

14" LX200R @ f/10, L=4x10' RB=2x10' G=1x10', STL-11000XM, Paramount ME

Related Designations for HCG082

HCG084

HCG 84 is a group of 6 galaxies in Ursa Minor, The Little Dipper, a bit northeast of the bowl. 5 of the galaxies are about three quarters of a billion light-years distant while the 6th is twice as distant at 1.39 billion light-years by redshift. Hickson made the assumption that if a galaxy was similar to the others in the group it likely was the same distance. He knew there'd be exceptions. I measure the size of HCG 84A at just under 200,000 light-years so it is a huge E2 galaxy. Obviously, its gravity is anchoring the group. HCG 84E is the smallest galaxy of the group at only 36,000 light-years. Distant HCG 84F is twice as large at 67,000 light-years, its greater distance making it appear nearly as small.

Hickson apparently lettered the galaxies in a group with A being the brightest and on down the magnitude scale. In this case, 84B and 84C appear reversed with C being 0.04 magnitude brighter than B according to NED. I assume this difference is so small that the magnitudes Hickson had available may have easily been the reverse. Being small and the most distant 84F is the faintest at magnitude 18.42 while A is magnitude 15.77 thus barely visible to say a 20" telescope under dark skies.

Being very far north at 77.75 degrees the field is poorly studied. I found redshift values for only the Hickson group galaxies. NED lists only 19 other galaxies in the area, a couple are out of my field. None have even a magnitude estimate let alone distance data. This makes for a rather sparse annotated image but I felt it needed to identify the members of the group.

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

Related Designations for HCG084

HCG23

HCG 23 contains 5 galaxies and is located in northwestern Eridanus. Unfortunately, it is quite low in my sky. In the fall warm water and cold air above results in both poor seeing and a lot of rising water vapor. Both make imaging this low virtually impossible. This image is obscured by over 2 magnitudes because of these issues.

HCG (Hickson Compact Groups) are a visual group. They need not be related. Usually, most are but often one or more galaxies is just a line of sight member. This group consists of 5 galaxies, A through E. E is the odd man out with a redshift twice that of the other 4 showing it a distant interloper. The other 4 are about 200 to 210 million light-years from us. The fifth being 450 million light-years distant. Also, a compact group is just that -- compact. Other related galaxies are usually in the area, just too distant to meet the compact requirement. Hickson set several requirements for his groups. They must contain 4 or more galaxies that vary no more than 3 magnitudes in brightness. They must be compact enough that the average surface brightness is brighter than 26th magnitude per second of arc. Also, they must be isolated so not the core of a galaxy cluster. For more on this subject see: http://ned.ipac.caltech.edu/level5/Sept01/Hickson/Hickson_contents.html .

There are many other members of the same group that four of the 5 members belong to. This larger not compact group is centered about NGC 1208 on the far right of my image.

Galaxies in compact groups are often interacting, hence the desire to located such groups. Two of the 5 galaxies in this group certainly look like they've interacted. NGC 1215 is a peculiar spiral with an inner ring around the nearly invisible bar that spawns two wide arms that form an outer ring. MCG -02-08-050 has an off center core surrounded by a blue ring. The other two true members, NGC 1214 and NGC 1216 appear rather normal.

I measure NGC 1214 at 90,000 light-years, NGC 1215 at 110,000 light-years, NGC 1216 at 70,000 light-years and MCG -02-08-050 at 34,000 light-years in size. The interloper, MCG -02-08-54 is 70,000 light-years across. But the big galaxy in the image is NGC 1208 at 140,000 light-years, a giant spiral indeed. But the real giant is IC 1880 at over 260,000 light-years in diameter.

NGC 1208 was discovered by William Herschel on January 10, 1785 but isn't in either H400 program.
NGC 1214 and 1215 were discovered by Ormond Stone sometime before October 12, 1886 and by Lewis Swift on October 21, 1886.
NGC 1216 was discovered by Ormond Stone sometime in 1886.

Normally I'd have moved the field east but I wanted to pick up the obvious flat galaxy in the upper left corner. There's no distance info available at NED for it, however.

Conditions for this image were lousy so it is a candidate to be retaken. I doubt that will happen, however.

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

Related Designations for HCG23

HCG71

This field made my to-do list for two reasons. First is the galaxy NGC 5008 which has some fascinating plumes and houses an AGN at its core. Both indicate it has recently interacted with or devoured another galaxy. Also, it is the major galaxy in the Hickson Compact Group 71. I'm slowly working on those that interest me as well. The field is located in Bootes.

NGC 5008 is classified as Scd: by NED; SBc by the NGC Project; and SBc? by Seligman. So does it have a bar or not? Maybe. I can see arguments both ways. Its arm structure is weird for either barred or not barred spirals. While there's a hint of arms starting from a very faint bar they die out quickly and spiral counterclockwise. Other arms start from nothing and go for much further and are often brighter yet spiral clockwise. They are also bluer than those coming off the possible bar. An inner counter-clockwise and outer clockwise spiral pattern with plumes would indicate some sort of merger. I find it odd no one tacked on the peculiar label. By redshift it is some 430 million light-years distant though non-redshift measurements put it slightly further.

It was discovered by Heinrich d'Arrest on May 18, 1862. But unfortunately he recorded its hour angle one hour off and noted the nearby 10th magnitude star as being north when it is south. I've greatly dimmed it in my image so it appears much dimmer but still the brightest of the three to the south as otherwise its glare was very distracting from the galaxy itself. It was then recorded as NGC 5008 at the wrong position. So when Stephane Javelle later found it on June 15, 1895 and recorded its position correctly it became IC 4381. It was only later that d'Arrest's error was discovered and the two realized to be the same galaxy. Then Hickson in recording his compact galaxy groups included it along with IC 4382 and two others (see the annotated image) as his group #71. We now know that while three of these galaxies are likely related and have similar cosmological redshifts HCG 71D has a redshift putting it twice as distant as the other three. I notice NED, while listing all four as part of the group gives the count for the group at 3, not 4. Is it excluding this more distant member?

The other four are IC 4382, HCG 71B, which also houses an AGN and is listed as an Sb edge-on spiral, PGC 50640 which is HCG 71C is listed as an Sbc spiral and the outcast PGC 50641/HCG 71D listed as an S0 galaxy at 910 million light-years. It is also the furthest from the center of the group. There appear to be other galaxies in the area that are members of the group as they too have redshifts very similar to that of NGC 5008. LEDA 214226 to the north may appear to be double in my image but the northern object is a very blue star and ultraviolet source. Then to the northeast is LEDA 1741935 which has a very off-center core making it look like a comet. It too shares about the same redshift. More ordinary looking is LEDA 4405543 to the east-northeast. It is the smallest of the group. To the north-northeast is the very low surface brightness apparently spiral LEDA 4556417. Another dwarf member of the group is LEDA 4404962 far to the north. But even further north is NGC 5498 a large S0-: galaxy that too shares the same redshift and looks possibly the most massive of the group. Others are found outside my field.

NGC 5498 was discovered by Edouard Stephan on May 9, 1882. NED lists it as S0 while the NGC Project says E-S0. It is a very large galaxy some 160,000 light-years in diameter. NGC 5008 is much larger, 280,000 light-years, if you include the plumes but the spiral itself is only 90,000 light-years in diameter. IC 4382 is actually larger at nearly 110,000 light-years but seen edge on appears much smaller. I find it odd it has no dust lane visible. It too was found by Stephane Javelle at the same time as he saw NGC 5008/IC 4381. While he made a one minute error in the position of both their relative positions match perfectly.

HCG 71C, an Sbc spiral is only about 65,000 light-years across. About the size of an average spiral. HCG 71D is about 100,000 light-years across. Only is greater distance makes it appear smaller than the other three. Of the other galaxies related to NGC 5008 and NGC 5498, LEDA 4405543 is the smallest of the group in my frame at about 23 million light-years.

While HCG 71D isn't a true member of the group it does appear to be part of a different group of galaxies seen scattered over the image. However, I found no cataloged group for either of these two other than part of the closer being part of HCG 71. Considering how many strange galaxies are in the closer group I'm surprised it hasn't received any significant attention.

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

Related Designations for HCG71

HERC CLUSTER

The Hercules Cluster, Abell 2151, is a rather unusual galaxy cluster a bit under a half billion light-years distant. It is unusual for its high content of spiral galaxies. Most clusters are mostly elliptical or S0 class galaxies due to most being the result of many galaxy mergers over billions of years. Somehow this cluster has avoided this though even a quick examination of my image shows many spirals in the act of merging or at least colliding. In fact, four of them made Arp's Atlas of Peculiar Galaxies, Arps 71, 122, 172 and 272. of the four only Arp 172 doesn't involve spiral galaxies. Many other galaxy interactions are also seen in my image. I prepared an annotated image but it is so cluttered with labels maybe I shouldn't have labeled as many as I did.

This is one of earliest images and suffers from my inexperience. The data was taken back in 2007. Though reprocessed 9 years later from scratch my calibration frames were crude so loses a lot. I keep saying I'm going to retake it but it never happens. Mostly because seeing is poor when it's best positioned and when seeing is good there are so many things still on my to-do list that have never been taken that it hasn't yet happened.

14" LX 200R @ f/10, L=6x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for HERC CLUSTER

HOAGS OBJ

Hoag's Object is the name this galaxy got when first discovered by Art Hoag in 1950. It is about 600 million light years distant and about the size of a typical large spiral galaxy like our own Milky Way. Hubble imaged it in its high resolution though the image uses false colors so the core is an odd yellow color. Oddly, there's a much more distant ring galaxy seen through the gap between the core and the ring. It shows as only a discoloration in my image.

The Hubble image is at:
http://apod.nasa.gov/apod/ap040815.html

You can read more about these oddball galaxies at:
http://heritage.stsci.edu/2002/21/lucas_files/lucas.html
See the link below for a photo taken at Kitt Peak of this galaxy and read their take on it.
https://www.noao.edu/kpvc/Prog/galaxy1.php

Two satellites went through the field while I was taking this image, one is faint to the right of Hoag's object the other obvious. Back in 2007 when my image was taken I didn't have the ability to easily remove satellites. I've not reprocessed it the data to remove it.

14" LX200R @ f/10, L=4x10' RGB=1x10', STL-11000XM, Paramount ME

Related Designations for HOAGS OBJ

HOLMBERG I

Holmberg I is the first of 9 dwarf galaxies in Holmberg's list of dwarf galaxies, most of which lie somewhat in the area of M 81. Holmberg 1 lies about 2.5 degrees northwest (330°) of M81 and is considered part of the M81 group. It is a very blue, low surface brightness dwarf with little HII emission according to papers I read. That surprised me as the HST image shows some nice nebula in it. Then I noticed the filters used by the HST, Green (centered on the same frequency as most green lasers, 555nm) was assigned to blue with near infrared, 814nm, was assigned to red. Thus the blue nebulae were seen in green light rather than H alpha red. They show as blue fuzzy "stars" in my image and are quite weak in red light. I need to revisit this one in H alpha sometime.

The redshift distance is 10 million light-years but this is highly unreliable so close in. Still, the non-redshift values show it only slightly further. They range from 12.5 to 19.2 million light-years. Three values were derived from the HST images, some of which I used for my rendering. Those are in quite close agreement with the latest having the value of 13.0 million light-years which I show on the annotated image. An older paper puts it at 12 million light-years. New data supports the 13 million light-year distance. Otherwise, the paper is interesting but rather deep. http://iopscience.iop.org/1538-3881/122/6/3070/pdf/1538-3881_122_6_3070.pdf

I got quite a shock when I had NED list the objects of all types in the field with redshift data. It returned only Holmberg I. So I asked for all galaxies or galaxy clusters and quasars or quasar candidates. That returned only three others! One is barely visible on the FITS stack but almost invisible on the processed TIFF file. After JPG compressing it is gone unless you hype the brightness greatly. It is listed as being possibly a dwarf spherical galaxy. Its position is somewhere in a 5 arc second circle but that does include the faint fuzz patch I've marked. The other galaxy right near Holmberg I is bright but near star-like until you look at its PSF. One star is listed as a strong ultraviolet source by the Galex satellite and is considered a candidate quasar though with no redshift and little else I could find on which to make this claim.

When I asked for all objects it did return 3 HII regions. Two agree with tiny blue "stars" in the galaxy in my image.

Of the 9 Holmberg galaxies, I'm yet to catch VI. It is at -21.3° so too low unless I have a one in a thousand night. Holmberg II is filed under Arp 268 and Holmberg IX is in my image of M81 if you are looking for those two. The rest are under their Holmberg designation.

You can read more about Holmberg I at this PDF link. It gets a bit deep and precedes the later distance estimates I used. http://iopscience.iop.org/1538-3881/122/6/3070/pdf/1538-3881_122_6_3070.pdf It indicates the galaxy is undergoing ram pressure stripping.

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

Related Designations for HOLMBERG I