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Old 18-11-2020, 05:28 PM
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madbadgalaxyman (Robert)
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The aforementioned images (in the webpage showing several images at various wavelengths) were from an initial survey that is associated with the ongoing PanSTARRS survey.

They are indeed in the photometric ugriz system.

Here is an attempt to display the g band image (approximately , this filter admits blue and visual wavelengths) at a realistic linear scale.
(We tend to lose the trend of changing surface brightness with increasing distance from the centre of a galaxy, in most displayed images)

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In this image, which tends to emphasize the younger material, such as the luminous OB stars in spiral arms, this galaxy looks pretty much like a normal dwarf spiral of type Sd or Sdm.
The spheroidal/elliptical component is not in evidence.
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Now here is the same image, this time displayed in a way that emphasizes some of the outer knots of blue supergiant stars, with this galaxy again looking pretty normal for a low luminosity spiral galaxy.

Click image for larger version

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Now here is the z band (near-infrared)(near 866nm) image of this galaxy, which tends rather to emphasize the space distribution of the older stars in a galaxy.
(the parallel lines are image artefacts)

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Voila!
The old stellar distribution looks like a completely different galaxy!

Indeed, if I only had this image, I might conceivably classify this as a dwarf spheroidal galaxy, albeit a dusty one with a certain amount of current star formation.
(not that I am in any way an authority on the classification of dwarf galaxies)


So you see what I mean about the duality or dichotomy of structure within a disk galaxy?


On balance, the visual appearance of this galaxy, in the standard blue/visual bandpass, is consistent with that of a spiral that is very late in the Hubble Sequence, but I don't know enough about these sorts of galaxies to say whether or not this particular galaxy is anomalous.

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Oh, and by the way, it is a commonplace for the near-infrared Hubble Class of a galaxy to be different from its Hubble Class as derived from Visual bandpass images.

Last edited by madbadgalaxyman; 18-11-2020 at 05:54 PM.
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