From the "NGC 253 imaged as a dim Dwarf galaxy in Colour" thread.
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I wrote....I have never seen the halo extend deeply in any other amateur or professional image in the visible spectrum.
The pros image the halo in radio, UV and X-ray wavelengths.
One needs to be certain the halo is the real deal rather than a processing artefact.
I've sent the image to the European Southern Observatory for comment.
Given their involvement in the Carina Dwarf galaxy thread, hopefully they will resolve the issue.
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ESO's response as follows. My image marked out by ESO and referenced in the response is in the attachment.
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Olivier Hainaut ESO wrote,
Hello,
Nice work!
Did you start from the original raw FITS files?
It's a little hard to judge on the JPG, so if you could make the final FITS (esp the R and the V ones) available to me, I could have a deeper look. If you work with the JPG or TIF, beware that these images are already heavily processes, and that the noise texture is affected, i.e. you cannot rely on it for further analysis.
What puzzles me is the fact that the disk profile is fairly flat and then drops sharply, but that could very well be the "liberation" curve (ie the response curve you use to go from the FITS to the photoshop or gimp stage -reference to the FITSliberator program) is enhancing that feature.
I don't know which processing you used for the _colour_halo image, but I suspect you used some fairly strong smoothing with some advanced rejection. This causes some strong artefacts around the bright stars: some dark disks centred on the star. So, at that distance, what you see is dominated by the artifacts.
Look at the galaxy, going to-right: there is a ~plateau, then a dark lane, then the background becomes brighter again with artifacts. My guess is that the real halo stops at the end of the plateau, and that at least what comes beyond is not real. Also, for the part within the plateau, I suspect that some of it results from you "boosting" the parametres of the method a little too much. I'd recommend you try again, but seeing what happens is you focus on the getting the region marked in green on my attachment -I marked in red some regions where the artifacts completely dominate, so you could aim at getting these in the background. Then we'll see if the halo extends.
Great work!
oli
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Olivier is looking at this image in the cold hard light of the professional astronomer, it is encouraging he is prepared to invest further time in this image and hasn't rejected the extended halo out of hand.
Steven