Ngc 7552

[Stevec35]

Hi to all

NGC 7552 is the 4th member of the Grus quartet (the one a bit further away from the other three). I thought that it would be a total disaster because the only thing that went reasonably okay was the luminance. During the colour I had appalling seeing and numerous unexplained guiding problems. So I guess this shows that you can generally salvage a LRGB as long as you have good luminance data.

The galaxy itself has a very interesting structure. Maybe there will be a Hubble Heritage image of it one day.

This may be the last RC image for a while as it's coming off the mount soon.

Cheers

Steve

http://members.pcug.org.au/~stevec/ngc7552_STL6303_RC.htm

[gregbradley]

That turned out quite well despite your troubles.

Greg.

[sjastro]

The seeing conditions in southern Victoria have been terrible as well, which has curtailed my own imaging.

Your image Steve however has come out very well.

Regards

Steven

[jjjnettie]

It's a pretty little galaxy to be sure. :D

[John Hothersall]

This galaxy reminds me of 7479 in Pegasus, just love the backgnd galaxies and backgnd galaxies around the actual arms of 7552.

John.

[Stevec35]

Thanks John. It is a busy area for faint galaxies.



Thanks JJ. It is a nice one. Greg did a nice shot of all four recently.



Thanks Steven. Seeing is always bad here in September but lately it seems to be getting worse. Very depressing.



Thanks Greg.

[madbadgalaxyman]

Steve,

I enjoyed your image of N7552.

The nuclear region is good and intense, due to the effects of a very violent burst of star formation.
Radio and infrared observations plainly show a very tight (9 by 7 arcseconds) ring of supergiant star-formation regions surrounding the centre of this galaxy;
I am not sure how much of this would be visible in the optical regime, but probably the ring is well hidden due to the effects of dust extinction.

For those of you reading this thread who don't know the online version of the De Vaucouleurs Atlas of Galaxies, I note that there is a high resolution image of NGC 7552 at:

http://kudzu.astr.ua.edu/devatlas


There are a number of Hubble Space Telescope images of this galaxy available at http://hla.stsci.edu
so, "just for fun and profit", here is a preview, from this website, of an F439W (blue) image taken with the WFPC2 instrument on the HST:

101017

[strongmanmike]

Yeh, that's a great galaxy really and probably deserves more attention than its more famous nearby trio..?

Yep if your Lum is ok then RGB can be complete crap and you can still salvage something :thumbsup:

Mike

[Alchemy]

Your bad is most peoples good.
:thumbsup:

[Ric]

A very nice capture Steve.

I must agree it has a structure about it.

[Stevec35]

Thanks Ric



Thanks Clive. I probably am a bit hard on myself sometimes.



Thanks Mike. Maybe I'll do a mosaic incorporating the other three sometime.



Thanks for the comments and link. Obviously there are HST pictures of it but it appears no one has done a colour pretty picture yet.

[Stevec35]

For anyone interested in taking another look I did my customary day after reprocess of NGC 7552 and was able to bring out even more detail. I've also added a full resolution crop. It's amazing how much detail there is.

Certainly seems a good topic for a professional observatory pretty picture to me.

Cheers

Steve

http://members.pcug.org.au/~stevec/ngc7552_STL6303_RC.htm

[madbadgalaxyman]

Steve,
Your repro is excellent. Buta, in the de Vaucouleurs Atlas of Galaxies, remarks about the complex and unusual structure of the bar.

[Stevec35]

Thanks Robert

[Ross G]

A beautiful galaxy photo Steve.


Ross.

[Stevec35]

Thanks Ross

[atalas]

A great looking galaxy Steve....shot in Canberra light pollution was It?

[mill]

Nicely done Steve and i know what you mean with the weather :thumbsup:
@#%@ clouds :P

[multiweb]

Very nice galaxy and lovely details. :thumbsup:

[richardo]

Very nicely done Steve!
Yes, it looks like some pretty heavy activity happening in and around the nucleus... not to mention all the little galaxies it's devouring!

Rich

[Stevec35]

Thanks Rich. It's certainly a galaxy that deserves to be better known



Thanks Marc



Thanks Martin. The weather has been a problem for a while and there's another La Nina on the way too.



Thanks Louie. Yes, from my backyard observatory in Southern Canberra. Actually the seeing is more of a problem than the light pollution. If you want good seeing then don't come to Canberra.

[Ross G]

Hi Steve,

I love galaxy phtotos and yours is impressive.

Amazing colours and detail.

Thanks.

Ross.

[Stevec35]

Thanks Ross

[Paul Haese]

Nice work Steve. Certainly not seen this one for a while. Really like the field of view, it gives that sense of distance.

[Stevec35]

Thanks Paul

[Martin Pugh]

Yep, like it Steve. Nicely done (recovered).

cheers
Martin

[Stevec35]

Thanks Martin. I've now worked out the guiding problems I've been having. An AOL arrived yesterday so maybe that will help with the seeing.

[madbadgalaxyman]

Hi Steve,

I've been trying to get together a multi-wavelength collection of NGC 7552 images for some time.
The morphology of this galaxy is often compared with that of NGC 7582, yet it seems to me there are undeniable peculiarities in N7552.

This is one of those galaxies for which the old-style photographic process image from the Carnegie Atlas of Galaxies is a good one:

101370

Because this atlas image is reproduced from a blue-sensitive photographic plate, the dust lanes are heavier than they look in most CCD exposures, due to the presence of more extinction (within N7552) than in red light.
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Here's an image at a much longer wavelength, an Near-infrared H-band image (1.6 micrometres) from the OSUBSGS survey, reproduced at a linear scale:

101371

Much of the dust extinction is gone in this image, as most 1.6 micron photons pass through all but the heaviest dust lanes, and furthermore this image emphasizes an older stellar population. It is remarkable how intense the central feature is in this galaxy.
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The intensely bright central region is also well shown in the following near-infrared (J+H+K bands) image from 2MASS:

101372

Also, it can be seen in this image that, despite the confusing and dusty appearance of this galaxy in the optical regime, its bar, as defined by the old mass-dominant stellar population, looks normal..... so the overall distribution of stars within this galaxy is probably not highly disturbed (indeed, the NIR isophotes of the bar are nothing unusual).
Yet, referring back to the Blue-sensitive image of NGC 7552 in the de Vaucouleurs Atlas of Galaxies (see the link in my previous post in this thread), the distribution of dust and Population I material is unusual and possibly disturbed. Young material (e.g. OB stars and dust and molecular gas) within disk galaxies is “kinematically cold” (i.e. low random velocities and high co-ordinated rotation), so it is easily disrupted; and it is always of small mass relative to the total luminous mass of a spiral galaxy.
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NGC 7552 does look interesting in (continuum subtracted) Hydrogen alpha line images.

(( For the uninitiated, I here explain that a galaxy image made with a Hydrogen alpha filter includes not only nebular light, but also some light from the stars of a galaxy (this is called the stellar continuum). But, using a mathematical model, it is possible to turn a raw H-alpha image into a “continuum subtracted” H-alpha image of a galaxy, and such an image includes the H-alpha line only......in other words, an image which shows only nebular light from HII regions ))

So here is an H-alpha (continuum subtracted) image of NGC 7552 by Salman Hameed of Hampshire College (references: 1999, AJ, 118, 730 and 2005, AJ, 129, 2597) :

101373

Despite considerable dimming from dust extinction, the central region of this galaxy is still intense in H-alpha light, undoubtedly due to its circumnuclear ring of OB stars and H-alpha regions. (this is a "circumnuclear starburst")

Here is Hameed's comparison of his H-alpha image (right panel) with a broadband optical image in the left panel :

101374

The H-alpha emission seen along the bar follows the two leading edges of the bar, where models indicate that the interstellar gas within a barred spiral galaxy is shocked into compression (this also causes the characteristic leading edge dust lanes in barred spirals) ;
gas compression here must have formed young and massive stars, which have ionized the interstellar medium in order to make the HII regions that are seen along the bar.
However, the apparent (as observed) asymmetry of this galaxy is considerable, in Hydrogen alpha light.
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I now compare the distribution of H-alpha light (which mainly comes from HII regions and which is a therefore an excellent tracer of where the most massive & hot & luminous stars are), with another good tracer of the distribution of OB stars within a galaxy; far-ultraviolet (FUV) light.

Here is the FUV image of NGC 7552 taken by GALEX, displayed firstly at a Square Root scale and secondly at a linear scale:

101376

101375

To be honest, I don't know exactly what to make of the morphology of this galaxy in FUV light....but extinction will be very high at this wavelength, so many of the regions with OB stars may not be visible from our line-of-sight.

Certainly, any morphological interpretation of NGC 7552 will be tentative, if it is based on visible or ultraviolet wavelength images; there is a lot of obscuring dust evident in this galaxy that can easily hide structures existing behind it.
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best regards, Robert

[Stevec35]

Here's another one Robert:

http://www.capella-observatory.com/ImageHTMLs/Galaxies/NGC7552.htm

Cheers

Steve

[madbadgalaxyman]

Steve,

that's a fine image from Capella Observatory.

While there are plenty of barred spirals with unusual dust distributions (I have in mind the semi-chaotic dust distribution in NGC 2903, which nonetheless overlays an old stellar population that is distributed quite normally)
the unusual dust distribution in NGC 7552 seems to me to be quite singular. For one thing, the irregularity in the dust extends to a very large physical scale

I think that a high angular resolution amateur image would help to elucidate more about this galaxy, but this would be very hard to achieve because the bar is only about two arcminutes across.

"Just for fun and profit", and to show how diverse is the dust morphology in the population of barred spiral galaxies,
I attach an image of NGC 2903:

101455

Additional comment added in edit:
The two major "deeply incised" and "continuous-looking" dust lanes (along the bar) that can be seen in the Capella image look to me like an artefact of their processing. A lot of amateur processing tends to have the effect of making dust lanes look both darker and more continuous than they actually are in the real universe.
The dust lanes seen in your full resolution crop of your N7552 image have a more realistic and "true to life" appearance.

The "over processed" look of some amateur images can sometimes produce "pseudo-morphology" instead of the actual structures that exist in the galaxy itself.

[jase]

Lovely work Steve. Given the issues you note, you've produced a great image. Thanks for sharing this little gem.