NGC 4945 Seyfert Galaxy

[ChrisM]

NGC 4945 is a spiral galaxy in Centaurus, ~ 12 million light years distant. It contains many X-ray sources and its bright nucleus is possibly due to a black hole and associated accretion disk.

11 x 60 sec subs
D7000 @ ISO 1600
Processed in PixInsight, with minimal cropping.

I was aiming to get a lot more data but the clouds beat me.

Second image added after application of PI's Local Histogram Equalisation.

Chris

[h0ughy]

nice details and colours

[strongmanmike]

Wow, that's excellent Chris and yes just needs more exposure...bloody clouds, oh and have I mentioned the wind :whistle:

A D7000 huh?..Hmmm? I have one of those...sure be faster than having to do L R G B....

Nice job indeed

Mike

[multiweb]

Plenty of details in that shot. Nicely done. :thumbsup:

[Larryp]

Looks good, Chris:thumbsup:

[madbadgalaxyman]

Chris,

I totally agree with Mike, a really excellent result, and without having to take exposures of great length.

"Way back when astronomical dinosaurs roamed the Earth" I used to struggle with chemical-based light detectors, and I gave up on it after a while.
But this new and remarkably-sensitive imaging technology is seriously tempting me to get back into astro-imaging!

cheers,
Robert

[ChrisM]

Thanks all for the comments.
Mike, at least the wind can blow the clouds away. In the dome, I don't find the wind an issue, even at a very long FL. If I were you I would stick with the FLI!

Chris

[ChrisM]

Thanks Robert. Using my every-day DSLR is a quick and simple way of getting some results, even though they're not in the same league as others who are using LRBG and fast astrographs. I have limited my exposures to 60 seconds for now since the scope is not guided.

The seeing here is usually fair at best, and clear-sky time is short, so for the moment I'm happy shooting a few easy targets. If you already have a DSLR, why not give it a go?

Chris

[madbadgalaxyman]

Not so long ago, your "modest" image of N4945 would have been regarded as amongst the best. Imaging technology, and also the skill levels of those using the newest imaging technology, have been developing very fast.

NGC 4945 is very hard to figure out;
it is even more edge-on in orientation than NGC 253, so nearly all of the internal structure that is seen in images of N4945 is foreshortened and "one thing is on top of the other, due to the effects of our angle of viewing"
N4945 does seem to be later in the Hubble Sequence than is NGC 253 ( NGC 253 has an apparent Hubble classification of SBc, but it is arguably an SBb galaxy, which can be seen in infrared observations that remove much of the dust and confusion).

The multiplicity of assigned Hubble types in the literature for NGC 4945 (e.g. Sc, Scd, Sd) is an indicator that there is little to go on, as far as actual identifiable structure, at least when this galaxy is imaged at visible wavelengths. However, the significant amount of observed semi-chaotic structure could be telling us that this galaxy is closer to type Sd than to type Sc. Consistent with an assigned Hubble Type of Scd is evidence for very vigorous star-formation in this galaxy, as shown by the "feathered" appearance of the ionized gas in this H-alpha image from Jorn Rossa's 2001 PhD thesis; the ionized gas looks like it is being blown out of the disk-plane by the effects of multiple (hot, young, very luminous) OB stars!

136957

This enigmatic galaxy continues to be something of mystery. Perhaps most instructive is the near-infrared image of NGC 4945 from 2MASS:

136958

A reasonable interpretation of this NIR image is that this galaxy has two main spiral arms. I also have an 870 micron (sub-millimetre) image of this galaxy (which is a very low-extinction regime), and this image is also consistent with the existence of two primary spiral arms in NGC 4945. Note also the small, but very intense, central region of this galaxy.
(From images made at visible wavelengths, it is impossible to say anything definite about the central part of this galaxy, due to heavy foreground dust within this galaxy)

[ChrisM]

Robert, that NIR image is very revealing with much more detail evident. I have much to learn about galaxies, but by photographing a few and with input from others such as yourself, I am sure to understand them better.
Thanks, Chris

[madbadgalaxyman]

The background light is better able to get through the dust (both the general 'diffuse' screen of dust within a spiral galaxy, and also the individual dark nebulae in a galaxy) in infrared detection. At 2 micrometers (2000 nanometers), extinction is only about 1/9 that which you get when you image at 500nm (blue visible light). However, imaging longward of 1 micrometer requires specialized CCDs.

Also, the O and B -type stars (luminous & young stars which recently formed) that dominate the appearance of the rather chaotically distributed clumps in the spiral arms, are much less prominent when imaging in the infrared.

Thus, Infrared images of galaxies remove much of the confusion that results from a heavy distribution of chaotic dust clouds and a rather chaotic distribution of very luminous stars.

Some of our members have had success, imaging in the very-near infrared at 700nm to 1000 nm (which is the longest wave that standard CCDs can detect) with objects in which there is only a relatively modest amount of dust extinction of the background light.

There is a sense in which the dust and the very luminous stars in spiral galaxies are "sort of like icing on a cake"; in that a chaotic distribution of Dust Clouds and bright eye-catching Stellar Clumps does not have to mean that a galaxy is seriously disturbed or distorted; the underlying mass distribution of a galaxy, as shown in infrared imaging, can still be totally regular and symmetric!!

cheers,
Bad Galaxy Man

[madbadgalaxyman]

Oh, and while I'm at it, here is one more Hydrogen Alpha image of NGC 4945, at a different scaling;

137009

This image, which was taken with the Magellan Baade telescope and MMTF in 2006, shows H-alpha emission from the massive UV-luminous stars that trace some of the spiral arms. Also, it looks like this image (probably) does show the cone of H-alpha emission near to the nucleus, which marks an outflow of gas from the active central region of this galaxy.

[ChrisM]

Thanks for the additional information Robert. I'm looking forward to exploring more galaxies!
Chris

[madbadgalaxyman]

I think you did very well when imaging this interesting galaxy.

Obviously, short exposures can sometimes be better at capturing very fine details in an object, if they happen to be taken during periods of good seeing;
this could be one reason why your image shows more detail than some of the longer exposures made of this galaxy.

Your Processed version that you added later has a slightly artificial look;
Obviously, astronomical images are always a combination of artefacts (pseudo-morphology that exists in the image but not in the object itself) and real morphology that exists in the real universe.