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IC 1101 and Abell Galaxy Cluster 2029

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#1 Redbetter

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Posted 12 March 2019 - 10:14 AM

I finally got a clear night, so I went to a high altitude site for some DSO observing starting at midnight.  Temps ran in the mid 20's, excellent transparency, frost, poor seeing, and strong breeze.  Late on the agenda was IC 1101 and a search for some members of the extensive cluster of galaxies surrounding this behemoth.  I had made some finder charts a few weeks ago down to 18 B mag, but didn't expect to see anything past 17 B...which in theory meant only a handful of targets were likely to be visible, and most of them far from the center of the cluster.  But the universe had some surprises waiting...

 

IC 1101 was found easily in the 20" at 156x.  Despite being 1 billion light years away, this thing is enormous considering the distance!  It is the apparent size of some close Local Group galaxies.  It trails off rapidly in visual magnitude, so the best views were at mid power where the surface brightness was more apparent.  At high power the extent was less visible.  This one should not be too difficult to detect with any large aperture scope.  Unfortunately I did not get a good estimate of the size because of this "now you see me, now you don't" aspect.

 

The seeing limited me to 278x effective.  Past that the stellar images broke down badly making it difficult to resolve galaxies vs. stars.  My table of 54 B mags appears to be more conservative than anticipated.  Looking at the B and g magnitude, the visual level is typically~1 mag brighter for galaxies like these. 

 

The breeze and poor seeing limited views nearest the core, as well as some of the faintest targets.  Nevertheless in a fairly small inner section of the cluster I detected 13 galaxies all the way to 18.15 B.   Ironically, I didn't even target the brighter targets further out that I expected to resolve.  I could have, but I was becoming more and more chilled by the wind so I called it a night.  I want to revisit in decent seeing to see if I can resolve more near the core at 350 to 500x.  There is far more of this cluster visible than I suspected.


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#2 IVM

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Posted 12 March 2019 - 09:05 PM

Very nice. Looking at Wikisky, there is a marvelous thin, blue edge-on just S of IC 1101 that is not in any common catalog. Its extent is almost comparable with IC 1101. Did you see it? Only the tiny round core might be visible on a red plate, so blue the disk is. The core is cataloged as USNO-A2 0900-07928732.


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#3 quazy4quasars

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Posted 12 March 2019 - 09:29 PM

  I tried for that with the 25 a couple of times: It eluded me. Its so thin- it may only pop in under really excellent conditions, if at all.


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#4 Redbetter

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Posted 13 March 2019 - 12:06 AM

Very nice. Looking at Wikisky, there is a marvelous thin, blue edge-on just S of IC 1101 that is not in any common catalog. Its extent is almost comparable with IC 1101. Did you see it? Only the tiny round core might be visible on a red plate, so blue the disk is. The core is cataloged as USNO-A2 0900-07928732.

I noticed that one when making my finder charts, but did not detect it last night.  I was also fascinated by its edge on (?) shape and color in images--it is #27 on my finder chart.  It is listed as AGC 251824 or SDSS J151054.61+054314.7.  Hyperleda has it at 17.55 V mag, which is probably close to accurate comparing to the others nearby.  AGC 251824 is a foreground galaxy several times less distant based on velocity.  That is why it looks so out of place and out of scale.  I could probably detect it with another half magnitude of reach, but the thin disk would almost certainly still be invisible. 

 

I think the others I saw were closer to 17 visual despite being listed at up to 18.15 B in the case of PGC 1288950.  (That one is more easily detected because of the ~16th mag star next to it that looks non stellar because of the close proximity.)  I am probably going to go back through my list and use the g and r band values to estimate better visual magnitudes for all of these.  I expect the dimmest I saw to be close to 17.0 V rather than ~18 B. 


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#5 Redbetter

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Posted 13 March 2019 - 03:53 AM

Here are the members observed so far (a couple were marginal/hard to resolve) along with the V mag calculated from the SDSS g and r mags.

  • PGC 54157  (16.68)
  • 2MASX J15105275+0543296  (16.78)
  • PGC 54175 (16.69)
  • PGC 54173  (16.95)
  • PGC 54174  (16.95)
  • PGC 1288950 (17.38)
  • PGC 54178 (16.18)
  • PGC 54162 (16.83)
  • CGCG 19-65 (16.39)   
  • PGC 1289895 (16.94)
  • PGC 54190 (16.72)
  • PGC 54192 (17.05)
  • PGC 1289572 (17.12)

Four others were attempted and definitely not seen, while two others may have been seen a few times: PGC 1288469 at 17.18 V mag and PGC 1289259 at 17.14 V.


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#6 quazy4quasars

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Posted 13 March 2019 - 01:11 PM

  IC1101 is, by even a conservative estimate, about 400 times as far away as M31. (1 Billion / 2.5 million = 400)

 

Apparent brightness decreases by the square of the distance, so M31 would appear less than 1/100,000 as bright as it does, if it were placed out where IC1101 is.  to put it a better way, it would be visible, but much, much smaller, with a long axis of well under an arc minute. The inner part (the part we most easily see) would appear much smaller still, maybe 10 arcsec or so, on a good night. 

 

  Given  a V of 3.5 (simbad),  M31 would appear as a ~16 mag non-point source at that distance. Not so easy!  If we then allow our newly relocated M31 to partake of the expansion of the Universe, The "low" redshift of z .077 would shift its visible spectrum to the red by a few hundred angstroms, so we would lose perhaps another .2  magnitude of visibility, giving V~16.2. (Those photons are not just reddened;  their arrival time intervals are also lengthened. -Their source is receeding at 23.000 kilometeres per second! -bummer.)  

 

  Presumably, then, Our own Milky Way Galaxy would appear at about V of ~17, (since our own galaxy is presumed to be only half as luminous as M31, that means M31 is just over (minus).8 mag brighter than the Milky way)

 

 The point I'm making is that those truly faint fuzzzies that Redbetter glimpsed and listed above are comparable to or even brighter than our own Milky Way Galaxy, even though they are ellpticals... note: from our position within the dusty disk, we can't see the total brightness of the milky way; not by a long shot.

 

Assuming V ~ 13.7 for IC1101, then it is throwing at least 20 times the visible luminosity of our own humble Milky Way Galaxy. Not bad for a "red and dead" elliptical with no spiral arms, no star forming regions, no hot young blue giants...   and remember, the Milky Way and Andromeda are the two largest, and brightest galaxies in the Local Group.   We're no slouches ourselves, as galaxies go. Far from it. 

 

Food for thought!


Edited by quazy4quasars, 13 March 2019 - 04:48 PM.

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#7 Redbetter

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Posted 13 March 2019 - 06:19 PM

Yes, I went through a similar calculation using the absolute magnitudes and concluded the same thing.  They may or may not be as bright/brighter than the MW galaxy but they are in the same range. 

 

The "easiest" one to detect  near IC 1101 was PGC 54178.  At ~ 16.2 V mag and well placed in a wide space between/south of two 14 mag stars, I could see it as soon as I looked at the spot.  Very very faint, very very small, but oval with orientation apparent.  I would anticipate this being within range of a 16" scope for my eye, perhaps even detectable in a 12" since it is somewhat higher surface brightness and that helps a lot.   

 

The first one I looked for and detected was PGC 54157 at ~16.7 mag.  When I saw it in averted vision without difficulty I realized there might be far more visible than I had expected.   It also has rather substantial surface brightness although not as much as the other.  Average or low surface brightness galaxies are much more difficult to detect at a given magnitude.  Following this galaxy is PGC 1288058 which I didn't really look for or see because it is about 1.7 MPSAS worse surface brightness, and about 17.4 V mag...I hadn't even assigned it a number on the chart.

 

Later this Spring I hope to get some good seeing, that is the period that is usually best here.  That would allow me to use 357 to 500x to see if I can see some of the dimmest/smallest companions.  357x was just too much for conditions on Monday night.  I tried it a few times but it was making things worse.



#8 quazy4quasars

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Posted 14 March 2019 - 02:12 PM

Yes, I went through a similar calculation using the absolute magnitudes and concluded the same thing.  They may or may not be as bright/brighter than the MW galaxy but they are in the same range. 

 

The "easiest" one to detect  near IC 1101 was PGC 54178.  At ~ 16.2 V mag and well placed in a wide space between/south of two 14 mag stars, I could see it as soon as I looked at the spot.  Very very faint, very very small, but oval with orientation apparent.  I would anticipate this being within range of a 16" scope for my eye, perhaps even detectable in a 12" since it is somewhat higher surface brightness and that helps a lot.   

 

The first one I looked for and detected was PGC 54157 at ~16.7 mag.  When I saw it in averted vision without difficulty I realized there might be far more visible than I had expected.   It also has rather substantial surface brightness although not as much as the other.  Average or low surface brightness galaxies are much more difficult to detect at a given magnitude.  Following this galaxy is PGC 1288058 which I didn't really look for or see because it is about 1.7 MPSAS worse surface brightness, and about 17.4 V mag...I hadn't even assigned it a number on the chart.

 

Later this Spring I hope to get some good seeing, that is the period that is usually best here.  That would allow me to use 357 to 500x to see if I can see some of the dimmest/smallest companions.  357x was just too much for conditions on Monday night.  I tried it a few times but it was making things worse.,

 

  when I last went for PCG 37477 (in Abell 1413, another giant BCG, way out at z~.141), I could just see its elongated shape, a little larger with AV- and some dim fuzzies (pops?) to the S-SW of the core that is an associated group of "average" ellipticals, -barely, with AV,  in 25". The seeing was good for 360x, at a "pretty dark" site in the Southern Diablo Range,  I'm interested in your impressions of that one, Red-  along with that of CGCG 122-067 -and of Abell 1689 if you find yourself inclined, for the sake of comparison. That's probably as far as I'll ever go with deep Galaxies/GXs. 


Edited by quazy4quasars, 14 March 2019 - 02:52 PM.


#9 uwe_glahn

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Posted 14 March 2019 - 05:02 PM

Nice reminder of a spectacular galaxy. 25 galaxies sounds very good.

 

Some years ago I took the inner 6' field with my 27-inch and got 8 companions beside the IC. Lots of fun. But I wish I had much more aperture to also catches the innermost patches.

 

sketch: 27", 419x, NELM 6m5+, Seeing III

IC1101.jpg


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#10 quazy4quasars

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Posted 15 March 2019 - 12:25 AM

 That...is glorious.  Thanks, Uwe!



#11 Redbetter

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Posted 15 March 2019 - 02:49 AM

  when I last went for PCG 37477 (in Abell 1413, another giant BCG, way out at z~.141), I could just see its elongated shape, a little larger with AV- and some dim fuzzies (pops?) to the S-SW of the core that is an associated group of "average" ellipticals, -barely, with AV,  in 25". The seeing was good for 360x, at a "pretty dark" site in the Southern Diablo Range,  I'm interested in your impressions of that one, Red-  along with that of CGCG 122-067 -and of Abell 1689 if you find yourself inclined, for the sake of comparison. That's probably as far as I'll ever go with deep Galaxies/GXs. 

CN had a hiccup...hopefully this won't double post:

 

I haven't observed the one in Abell 1413 although it looks like a worthy target.  From what I saw looking up some magnitudes of the more prominent companions I suspect they are out of range for my 20", but could be in range of a 25" for my eye.  Then again, on a night of superb seeing and transparency, who knows?  There may be another quarter or half magnitude in reach or even more.

 

I noted CGCG 122-67 as "not bright or obvious.  Took a couple of passes before seen w/ 16 [T5 at 156x]  More apparent w/9, but low surface brightness.  Stellar core vvf with brightening to middle.  Oval w/ ~16 mag star on NW edge of main glow."  I didn't see any companions.  Looking at Wikisky now there are two candidates over an arc minute from the galaxy: SDSSJ094500.49+225237.5 at ~17.4 V mag, and  2MASX J09444821+2252278 at ~17.6.  There is perhaps another further out and of considerably lower surface brightness, 2MASX J09450353+2250115 at ~17.8 V mag.   I doubt even the brightest of these would be visible in my scope, but given the right conditions and carefully searching for it...maybe?  They all have similar velocities to CGCG 122-67.


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#12 Redbetter

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Posted 15 March 2019 - 03:32 AM

Nice reminder of a spectacular galaxy. 25 galaxies sounds very good.

 

I only logged 14 for certain (if one counts IC 1101), and two more possible.  I had a list of 55 total to target, most much further out, so the #27 I referred to was the associated number on my chart rather than in sequence observed/attempted.  I am widening my magnitude screen for the outer galaxies in light of how this past session went.  The vast majority on the "too observe list" in the surrounding region have close enough velocities to be associated with the group in some fashion, although a few are clearly interlopers several times nearer to us.

 

There is a fair chance that much of the success in going deeper than I anticipated was extremely good transparency.  While seeing was limiting, I suspect it will be hard to top that night's transparency in the near future.   Stars at 5 degrees of elevation in Centaurus were quite bright (although I did not target Omega Centauri through the trees there, I have done it before at other local sites) so extinction was minimal.   On the other hand, the gegenschein and zodiacal bands were not as prominent as I would have expected for a really good night this time of year, so it wasn't a match for what a full Bortle 1 or borderline 1-2 site locally will do either.

 

It was one of those "pinch yourself" sessions though.  When I started seeing galaxy after galaxy marked on my chart I began to wonder if I was having a vivid dream and was about to awaken to find myself home in bed.  The same thing happens when fishing at times...I get on a mess of fish and am reeling in beauties and begin to wonder if it is a dream or real.  Those moments rarely last long and are often followed by moments of dread (in this case just a minor bout with flu that I could feel coming on that night.)  I had a fishing session like that as a storm was brewing just before the Joplin tornado struck 150 miles south...reeled in the biggest bass I ever caught, and on light tackle, actually broke my line as I landed it and it was flopping on the bank.  Same thing happened to me near the Des Moines river when I pulled in an enormous catfish along my kayak and tried to extract the treble hooks from it on very light gear, not daring to lift it more than half out after it towed me around for awhile.  About 2 hours later we had to pack our tent/gear quickly and flee because a vicious storm was blowing in and the local sheriff had given the campground warning.  Just beat the storm on the way out.


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