Had to attempt this big bright galaxy and added Ha as most don't but it does contain spots of HII. A bit disappointed with the detail with a large scope as its pretty similar to others here using smaller instruments, but a facinating galaxy all the same.
Its another sensational shot John. It isn't like other smaller scope shots at all. Only comment though is the total exposure is a bit light and it shows in the overall density of the colour. Slightly washed as a result of not enough total exposure. Also, if the total exposure were higher it can be processed more aggressively. Those OOUK optics are really hot.
Maybe I'm missing something, but I see real evidence of apeture in that image, detail galore and overall a very pleasing result. A bit more of a tinker in PS and maybe add a bit more data to it, just to finish it off and I rekon it will be fantastic!
Thanks for the feedback, looked at the raw subs and they are light, I could go for 20mins per sub really to bring out those strange vertical dark lines I sometimes see in professional images. I flipped the image to have North up but clearly the original seems to sit better - in my mind too. May add more but not decided yet.
Wow, I receive a shock on my eyes when I seen your SPLENDID and amazing image ! It is really great shot of 4 hours exposure. So much details in arms and the process is really good. Thank you to share your image with us. It is so beautiful and great to have a look inside this galaxy.
After that, I will also try to shot this galaxy.
Regards.
Franck
Thank you, John, for a fine image. The impression I get is of good angular resolution.
A lot of the so-called "detail" seen in other images of NGC 253 seems to me to be more artefacts of processing instead of the actual structure of this galaxy. But this is not the case in your image....it does not have that "over processed" look which tends to falsify the real-world morphology of a galaxy.
The HII regions look quite small, which would tend to argue against this galaxy being of Hubble type Sc.
The visual wavelengths classification of this galaxy, using blue light images and according to the precepts of Alan Sandage and Gerard de Vaucouleurs, might be type Sc (with just the merest hint of a bar), but the near infrared classification of NGC 253 - a wavelength regime which leaves out most of this galaxy's heavy dust distribution - has been given in the literature as SBb (a strongly barred galaxy).
I would be very interested to see what your H-alpha channel looks like, as the larger HII regions should be good tracers of the spiral structure of this galaxy. Of course, the H-alpha bandpass will also include some light from the stars of this galaxy.
Interestingly, NGC 253 has much redder optical colours, overall, than most spiral galaxies....but this could just reflect the reddening of starlight by the heavy dust screen within this galaxy.
Last edited by madbadgalaxyman; 18-10-2011 at 11:16 AM.
Reason: typo correction & more info
Thanks Robert for the information about this galaxy's classification, the Ha image does show better structure around the nucleus without the star clutter.
John, thanks for displaying the H-alpha bandpass image.
The bar of NGC 253 is only hinted at in broadband optical light (e.g. R or G or B bands, or photometric U, B, V, R), yet this galaxy is quite obviously a barred spiral in your Ha image!
(putting various bands together makes for a pretty picture, but each individual band is probably more informative from the point of view of science.....)
There is obviously still some stellar continuum light in your Ha image, but the nebulae are obvious. I think that your image probably shows H-alpha maxima along the two leading edges of the bar, and that this might be the signature of shocks in which the interstellar gas is compressed into star formation along the leading edge of the bar.
I got quite a buzz from your Ha image...it is better than many of the science images of NGC 253 that have been made in the Ha bandpass!
The overall structure of this galaxy is a lot clearer in Ha than it is in a broader bandpass......it is almost as if you had made an "X-ray" of this galaxy in order to show its most important features.
Thanks Robert for the information about this galaxy's classification, the Ha image does show better structure around the nucleus without the star clutter.
John
John,
I have taken the liberty of increasing the contrast and brightness on your .jpg H-alpha image of NGC 253, as your image shows some very interesting features that are not at all obvious in standard images taken with filters which have a broad bandpass. I hope that's OK!
(see also the optical/NIR comparison for this galaxy in my recent thread in the Science Forum)
The centre of this galaxy hides a very strong burst of recent Star Formation, which has formed tens of thousands of very luminous OB stars. However, I seem to recall that there is at least 7 magnitudes of dust extinction in front of this powerful and very compact feature at the centre of this galaxy.
(so it is not visible in the usual image at visible wavelengths)
At infrared wavelengths, this central feature becomes ever more obvious with progressively increasing wavelength of observation, till the light of the central feature virtually dominates the light of the entire galaxy!! In fact, a large fraction of the very luminous stars in NGC253 are in this very-compact central starburst.
Here is an 8 micron image, and also a 24 micron image, from the Spitzer Space Telescope. Note the incredibly intense central source of light!! (NGC 253 has a notably heavy internal 'screen' of interstellar dust, so the central starburst is usually hidden in normal imaging.)
Also, the true structure of NGC 253 is "plain as day" at longer infrared wavelengths.
Now comparing these IR images with your H-alpha image, it looks to me like you are probably detecting some H-alpha light from the very obscured centralmost region of intense star formation!!
Galaxies have always been 'my thing'. There is so much to be discovered; for instance nothing was known about the internal structure of NGC 253 before infrared observations were made, as it is just too dusty.
When I used to do regular visual observing, I observed galaxies nearly all of the time...
Someone at the Observing Site started screaming and jumping up & down, waving his arms in front of me with the breathless announcement "there is a - 2 magnitude comet blazing in the sky!!".....however, I didn't show the least interest in this news, and I continued observing vanishingly faint galaxies for the rest of the night.
[[ These days, I mostly leave the time-consuming & specialized process of observing & data collection to people like Strongmanmike, leaving me free to spend my time obsessing about galaxy structure and about numerical data in galaxy catalogs. ]]
I think that we all have to get specialized, eventually, in order to make further progress beyond the "intermediate-level amateur astronomer" stage; so I ended up looking at everything in astronomy from the point of view of galaxies.
I certainly greatly admire any amateur who really "knows their stuff" in their particular area of astronomical interest.
Best Regards,
Robert
Last edited by madbadgalaxyman; 15-05-2013 at 12:25 AM.
Wow, I receive a shock on my eyes when I seen your SPLENDID and amazing image ! It is really great shot of 4 hours exposure
