NGC 7793 "Comet Galaxy"

[sjastro]

Visually described as a comet by its discoverer GP Bond in 1850, this object is surprising overlooked due to nearby NGCs 253 and 55 popularity.

Completely messed up the flats so I had to sky glow subtract the background.

LRGB 2 hr L, 1 hr R, 1 hr G, 1 hr B, ST-10XME, BRC-250 scope.

http://users.westconnect.com.au/~sjastro/ngc7793newc.html

Clear skies

Steven

[TrevorW]

Pretty

[Ric]

A lovely capture Steven.

I can see how it could have been originally mistaken for a comet.

[Stevec35]

Nice one Steven. It's certainly an unusual looking galaxy this one.

Cheers

Steve

[RickS]

That's a very nice galaxy!

[sjastro]

Thanks Trevor, Ric, Steve and Rick.

Clear skies

Steven

[strongmanmike]

Nice Job Steve, I remember Spitzer did a famous shot of this galaxy showing it was full of stuff.

Mike

[sjastro]

Thanks Mike.

I recall the Spitzer image.
I'll add some NIR luminance and see if I can capture similar detail to Spitzer.

Clear skies

Steven

[Ross G]

Hi Steven,

A great galaxy photo.

Something I haven't seen before.

Thanks.

Ross.

[sjastro]

Thanks Ross.

Regards

Steven

[telecasterguru]

Cool.

[sjastro]

Thanks for the feedback frank.

Clear skies

Steven

[sjastro]

No visible light was used for luminance.

3 hrs NIR RGB as per visible light NGC 7793,

http://users.westconnect.com.au/~sjastro/ngc7793newNIR.jpg

Attachments shows comparison between NIR luminance (left hand attachment) and visible luminance.

Clear skies

Steven

[midnight]

Very nice work Steven.

Darrin...

[madbadgalaxyman]

Steven,

I really love the very-strong prominence of the Nuclear Star Cluster in your NIR image of NGC 7793

This would have to be one of the most prominent examples of the massive & luminous & compact Stellar Clusters that are the nuclei of many galaxies; this object might even be visually observable!

(( NGC 3603, young Globular Star Clusters, 100,000 Solar Mass young star clusters, Nuclear Star Clusters, etc, were discussed recently in a thread in the science forum about NGC 3603 ))

Best regards,
Robert

[allan gould]

Excellent image Steven of an interesting galaxy.

[gregbradley]

That's an interesting comparison Steven.

Its an interesting galaxy.

Greg.

[madbadgalaxyman]

Hi Greg,

Because NGC 7793 is an Sd-type galaxy and it is not a giant galaxy in terms of its total luminosity, the extinction from dust is small within NGC 7793;
therefore this galaxy is an ideal target for relatively short-wavelength (800nm-1000nm) infrared observations by amateurs;
The light from the central star cluster is a lot more obvious in Steven's NIR image.....so it seems that even short-wavelength NIR imaging is able to "dig out" the cluster from the intervening dust and other confusing material.

Just for fun, here is an NIR image of one of the most unusual and hard-to-understand members of the "mildly-to-moderately perturbed" galaxy population, the galaxy NGC 2442.
This image was taken in J + H + K bandpasses (1.2 microns + 1.6 microns + 2.2 microns) with the Gemini-South telescope:

136502


I am unaware of any amateurs doing 1.2 micron imaging, as it requires specialized equipment;
but don't you love the way that low-extinction >1 micrometer images give a sort of "X-ray" of the complex structure of a galaxy?!

Best regards,
Robert

[sjastro]

Thanks for the comments.

On the subject of luminance imaging in the non visible light spectrum, the dust belt structure of NGC5128 in NIR and long wave UV might make an interesting comparison.

Regard

Steven

[Weltevreden SA]

Robert, you might want to have a look at the 2010 Portegies Zwart paper arXiv1002.1961v1. It's specific to the MW but the IMF data on young massive clusters is extensible to many 'coreless' galaxies like 7793 with poor evidence of a supermassive black hole.

[Weltevreden SA]

This galaxy earns its identity 'peculiar galaxy' for good reason. One would assume those apparent 'bars' would be feeding gas and dust to the core like every other barred spiral. But the core shows little sign of a high-calorie gas and dust diet. So are they really bars? The most energetic star forming regions are in the outer arms. The plot gets even more interesting when Halpha, UV, and IR emission points to a local superbubble (http://arxiv.org/abs/1009.1852) outside the galaxy itself. Magnetic fields (http://arxiv.org/abs/astro-ph/0310462) stirred by the same interaction that shaped the barlike structure and arms have also had a significant impact on the outer halo development of this galaxy. SN1999gn occurred on the rim of the superbubble, further evidence that bubbles formed by multiple SNa one day compress enough gas to form rim clusters, some of whose stars in turn go SN in a few million years. 2442's magnetic 'island' feeds energy and particles into the same region as the superbubble. Our own Carina nebula is a hotbed of SN bubbles breeding new new clusters which have their own SNs, which make even newer bubbles which become new clusters, etc. It differs from the 2442 activity in that Carina has relative little magnetic activity. NGC 2442 might seem an unimpressive S-shaped smudge in our eyepieces, but it has devotees of every photon energy band—radio, microwave, IR, visible, UV, and xray—rushing to their theoretical models and N-body simulators.