Colliding Galaxies and the NGC 5529 group

[Steve Gottlieb]

I wanted to mention I have a featured observing article titled "Galaxies in Collision" in the May issue of Sky & Tel, which should be out shortly. It includes a number of interacting Arp pairs including the Antennae (cover photo) and other interesting duos such as the Mice, the Tadpole, the Heron, the Grasshopper and more. Some of these are fairly well known and others are more obscure. All the observations were made courtesy of Jimi's 48-inch.

In the same issue, Howard Banich has an observing article on NGC 5529 and its challenging neighbors. Perhaps Howard will mention more about the article. So quite a bit to chew on for deep sky observers!

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[Jimi Lowrey]

Howard I thought I would tell you I was able to catch a glimpse of Kregel B near NGC 5529 tonight. I had 4 really good pops and several slight pops at the right location. I spent a long time on it to get the results that I had. I used a 6MM ZAO @813X with my head covered in my observing hood. The seeing was sub par.

[Howard B]

Hi Jimi,

Thanks for the heads up - Kregel B is a tough one, and obviously tougher than I imagined! I'll keep trying anyway if I get a chance this spring but I won't hold my breath.

Did the brightness of 5529 get in the way or could you keep it out of the field with the 6mm ZAO? Also, could you see if it was elongated or did you just barely see just a faint shapeless smutz?

[Jimi Lowrey]

Howard with the 6MM ZAO 5529 was out of the field. On the few really good pops I got Kregel B appeared larger than the images show it to be. I often see this happen at the eyepiece of the 48" although I am not sure why. Kregel B had no shape and appeared as a featureless smutz.

[Norman]

Hi Jimi,

the phenomenon that very weak galaxies at the edge of visibility appear much bigger than they are in reality i am having very often - even not having 48" ;-)

Some other observers i talked to experienced the same. Must be some kind of psychological thing. Worth having some research on it in my opinion.

btw: nice articles - thanks for the hint!

CS!
Norman

[Jimi Lowrey]

Norman I see this phenomenon a lot. It would be interesting to know what is the cause is it real or a illusion?

[Norman]

Hi Jimi,

i am really no expert in this stuff - but it might be an eye-physio-issue. Kind of "inadequate stimulation" or something like that. A term of biology. Don´t know if it fits here, probably not -but putting the eye under pressure there might occur some kind of flashes e.g.. Is meant to be just an example of in which ways our body is pulling our leg sometimes. Shortly: kind of illusion, of course. But nothing personalized - it´s more a physio - so general thing i guess.

Could be that too much of the rods are stimulated in border-situations and pretend a bigger area. Maybe Reiner Vogel is reading here - could be that he has got some input to that phenomenon. Parallel to that it would be interesting to know what other observers say or have experienced. Is it really a general phenomenon or just with a few people?

I hope my english it not too bad to get expressed what i mean :-))

CS
Norman

[Howard B]

I see this a lot too - not every time, but most of the time. I've also wondered if its a photographic thing, at least partially. Perhaps some photos under-represent the size and/or width of some objects.

[FaintFuzzies]

I also see this sometimes with my 22" and 30" scopes.

[Norman]

maybe one idea:

I just read about the rods and cones in wikipedia :-)

Resolution by the rods is worse than with the cones. So bad resolution means unsharp/ defocussed. And defocussed stars appear bigger than focussed ones. The weaker the object, the less sharp. Having a brighter object, the pic is better defined - sharper. maybe also some cones contribute to the picture now. So it is better resolved - sharper, smaller.

Could this be the right explanation?

CS
Norman

edit: cons replaced by cones ;-)

[akarsh]

Tells me that I have a long way to go, because I've never documented this phenomenon.

Very curious -- I wonder what causes it.

Is this something discussed in Roger Clarke's book? I haven't seen it there.

Regretting missing Kregel B by a day :D,
Akarsh

[akarsh]

Here's what I have from a few hours ago with the "cheating" telescope (Jimi's 48"). Conditions not good enough to even dream of Kregel B. All of this was guided by Steve.

NGC 5529 and company, 13mm (375x):

NGC 5529: Beautiful edge on spiral. The dark lane is not as obvious as in NGC 891 (duh!) but can be seen distinctly at times of good seeing, especially with averted vision.

CGCG 191-71: Next brightest in the line. The galaxy was spotted without any trouble in the 48"

LEDA 2076904: Seen above the CGCG galaxy. Would place this third in the league. The object is not too hard and was seen within several seconds of arriving at the eyepiece.

SDSSCGA 240: (Did not observe the faintest fourth member; see SIMBAD). This is the "collisional ring" that Jimi may have referred to. The three cores observed were of almost equal brightness and comparable to SDSS J141513.30+361007.2 in both compactness and brightness, or possibly a bit brighter and a bit more diffuse. The cores were condensed, though, relative to other galaxies in the field. The collisional ring seemed to sport a slight brightening on the east-north-east, but no real features were visible.

SDSS J141513.30+361007.2 This galaxy further to the south of PGC 50925 is compact and relatively easy. (This is apparently not on Howard's list, Steve told me about this)

PGC 50925 (mistaken NGC): This one is a low surface brightness galaxy. It is not easy. Whoever mistook _this_ for an NGC was presumably under the influence of controlled substances. But definitely not at the limit of visibility. Looks like a relatively large uniform patch.

MCG +6-31-85B (PGC 50950): This MCG was surprisingly hard for an MCG. Is it really an MCG? It appeared to have a more compact and higher surface brightness core than LEDA 2076904, but it was still overall much harder to see, which is somewhat confusing.

SDSS J141555.30+361333.9: This is the "SDSS" on Howard's article. This object was the hardest to say and I can only put an 85% confidence on having seen this. Hardest by far, did not appear to have a very codensed core. Low surface brightness.

[wvreeven]

Akarsh mentiones Roger Clark and I was thinking about his work as well. One thing I learned from him is that the eye (or brain) needs very faint objects to be larger to be distinguished. Compare it to reading a paper in poor light. You need to put the paper close to your eyes to be able to see the letters. Maybe a reverse thing is going on here. Since the galaxies are very faint, the brain assumes they are much larger for otherwise not visible? I am just guessing here...


Clear skies, Wouter

[Steve Gottlieb]

Here's what I have from a few hours ago with the "cheating" telescope (Jimi's 48"). Conditions not good enough to even dream of Kregel B. All of this was guided by Steve.

NGC 5529 and company, 13mm (375x):

....snip

MCG +6-31-85B (PGC 50950): This MCG was surprisingly hard for an MCG. Is it really an MCG? It appeared to have a more compact and higher surface brightness core than LEDA 2076904, but it was still overall much harder to see, which is somewhat confusing.

This faint galaxy is in the MCG, but I believe the "B" designation means it is mentioned in the notes section of the MCG to NGC 5529 = MCG +6-31-75. In fact MCG +6-31-75A corresponds with PGC 50925 -- the mistaken NGC that is referred to in Howard's Sky & Tel article.

As far as the magnitude for -75B, The SDSS lists a g-mag of 17.2 and a r-mag of 16.5. This suggests ~16.8V and ~17.6B. But the redshift is .067, which implies the light-travel time is ~900 million years, so it is far in the background of the NGC 5529 group.

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[Daniel_Sp]

Hi Steve,
I'm currently in Honolulu and got an issue! Thanks for the hint!

[Curtin]

Hi Steve,
I'm currently in Honolulu and got an issue! Thanks for the hint!

That's awesome Steve. I have my copy.