Centaurus A Radio Galaxy

[MarsG76]

Hello All,

Sharing with you another image that I finished processing as I'm slowly going through my back log of exposures.
This is Centaurus A (NGC 5128), a galaxy in the constellation of Centaurus 13 million lightyears away. NGC 5128 is one of the closest radio galaxies to Earth and is also the fifth-brightest in the sky, making it an ideal amateur astronomy target.
The galaxy is only visible from below very low northern latitudes but is best seen or imaged from the southern hemisphere.

This photo was imaged using a Celestron C8 and a QHY268M at f6.3 1280mm focal length.
Total integration time was 35 hours and 40 minutes, 48x300sec luminance subs through a neodymium filter, 27x120s red, 27x180s green, 27x300s blue, Hα:36x300s, OIII:31x600s & UV:21x1800s filters.

Why 35 hours? Because I spent 10.5 hours on exposing the galaxy through my UVenus filter as an experiment to see if I'll pickup anything more than the usual, aiming for a hint of it's (X-Ray) jets, hoping that there might be some kind of a UV remnant of them captured, but NO such luck... the UV data was extremely weak and all it added to the image was very faint deep blue highlights on a very small number of places... so subtle that the image would not be noticed as having anything less if I didn't expose the UV subs... I'm suspecting that the SCT corrector cuts out most of the UV light too... so failed but and experiment I'm glad I did because otherwise I'd be left wondering.

Thank for looking,
Clear Skies,
MG

Edited July 4, 2023 by MarsG76

[Albir phil]

Not a failure as it stopped you wondering 🤔

[Elp]

Excellent result. I've tried imaging with the f6.3 and it's painfully slow... You've shown great dedication.

[MarsG76]

23 hours ago, Albir phil said:

Not a failure as it stopped you wondering 🤔

A good way to look at it...

[MarsG76]

23 hours ago, Elp said:

Excellent result. I've tried imaging with the f6.3 and it's painfully slow... You've shown great dedication.

I probably don't need that much integration time to result in the same or similar results, but having a permanent telescope setup allows me to spend extra time exposing through each filter... plus the more subs I stack the greater the SNR resulting in less noise to deal with in processing...

I don't think that a C8 at f6.3 is that slow unless comparing to a f2 system like a Hyperstar or RASA with the same primary light gathering mirror... that said, those systems do collect photos from a much wider FOV so I'm not so sure that there would be more signal in an area that is cropped down to the same FOV as is the C8 f6.3 system... although a f2 system at 1280mm focal length would be a beast of a telescope but that would mean that the primary mirror is 2560mm, almost 101", in diameter.

[Elp]

I do have a HS6 and tried Thor's Helmet last, you do lose resolution but gain in the pixel saturation. I've noticed at f6.3 there is far more detail but it's far dimmer so would require more exposure when using reduced.

[MarsG76]

27 minutes ago, Elp said:

I do have a HS6 and tried Thor's Helmet last, you do lose resolution but gain in the pixel saturation. I've noticed at f6.3 there is far more detail but it's far dimmer so would require more exposure when using reduced.

Ah, so there is a trade off in resolution for brightness... I guess it depends what's more important for a particular project... speed or detail... either system has it's advantages and disadvantages. 

[Paul M]

Very nice image. It's a well known object but not one we see here very often!

I could google this, but I'm off out to work...is that a jet bottom center or an artifact?

I guess, not an artifact on an otherwise pristine image!

[symmetal]

Great image with fine detail in the galaxy, which makes it look like a 'Shredded Wheat' 🙂

I think you got your sums wrong on your f2 1280mm focal length scope though, which would have an aperture of 640mm or 25". 😉

Alan

 

[MarsG76]

39 minutes ago, symmetal said:

Great image with fine detail in the galaxy, which makes it look like a 'Shredded Wheat' 🙂

I think you got your sums wrong on your f2 1280mm focal length scope though, which would have an aperture of 640mm or 25". 😉

Alan

 

Yes... I stand corrected.... thanks.

[MarsG76]

1 hour ago, Paul M said:

Very nice image. It's a well known object but not one we see here very often!

I could google this, but I'm off out to work...is that a jet bottom center or an artifact?

I guess, not an artifact on an otherwise pristine image!

It's in other images online, including photos imaged by pros on pro telescopes, so I guess it's a jet...
It's also clear as day on my HAlpha stack, so I say it's not an artifact but a jet/some nebulosity in the FOV.

Edited July 4, 2023 by MarsG76

[pipnina]

Aside from the atmosphere attenuating light exceptionally fast as you move through the 400-300nm range, sensor sensitivity falls off too as a double whammy. And for most commercial amateur telescopes you have a triple-nail in the UV observing coffin where most mirrors are dichroic coated (not aluminium) and have very low reflectance outside the visible spectrum, as per this chart from a listing of the GSO 6" RC you can see that the reflectivity to UV light falls off to only 40% by the time you hit 388nm, and seems to fall very rapidly thereafter. These three factors are likely the reason why any UV image is faint. I suspect venus is only possible to image so readily in the near UV is because it is so very bright.

[MarsG76]

9 minutes ago, pipnina said:

Aside from the atmosphere attenuating light exceptionally fast as you move through the 400-300nm range, sensor sensitivity falls off too as a double whammy. And for most commercial amateur telescopes you have a triple-nail in the UV observing coffin where most mirrors are dichroic coated (not aluminium) and have very low reflectance outside the visible spectrum, as per this chart from a listing of the GSO 6" RC you can see that the reflectivity to UV light falls off to only 40% by the time you hit 388nm, and seems to fall very rapidly thereafter. These three factors are likely the reason why any UV image is faint. I suspect venus is only possible to image so readily in the near UV is because it is so very bright.

Also the coating on the C8 corrector plate rejects a lot of UV wavelength, so we're upto a quadruple whammy.