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Originally Posted by John Hothersall
Great effort and a very good in depth thread.
John.
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Thanks John.
It has been a most informative thread.
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Originally Posted by madbadgalaxyman
To compare with Steven's 'long-wavelength' UV, and also to compare with the GALEX satellite FUV-only image which was attached in my previous post (far-ultraviolet essentially isolates only very young and very hot and very luminous stars) ;;
here is another GALEX image which sums the two filters/bandpasses used by Galex (this image displays far-ultraviolet plus near-ultraviolet bands).
Note that far-ultraviolet and near-ultraviolet in the context of GALEX observations have different meanings to the same terms when used elsewhere.
In this display, the galex FUV band displays as blue-white and the galex NUV band displays as yellow.
This image offers very good discrimination between;
- the dust lane
and
- the young hot OB stars (which appear as blue-white)
and
- the old stars of the spheroidal component of NGC 5128, which appear as yellow
Attachment 139927
(This image was obtained using the excellent GalexView 'virtual telescope' interface for the GALEX images)
One thing to bear in mind is that the GALEX far-ultraviolet band is extremely extremely sensitive to the light of the OB stars found in blue knots within galaxies; a vanishingly faint knot of blue stars which is seen in a visible-light image can light up brightly in the GALEX FUV band. |
A couple of observations Robert.
The transparency of the dust belt increases again as one goes from NUV to MUV and FUV as seen in the Galex image.
Opacity is caused by scattering of photons which is a function of photon wavelength and the particle size of the scattering medium.
NUV wavelengths and particle size has maximized the degree of opacity.
Perhaps it explains the dearth of NUV images due to the lack of belt detail.
The other point is the confusion over terminology.
From Galex.
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DETECTORS: Two 65 millimeter diameter, microchannel plate detectors. Far ultraviolet sensitive to light with wavelengths 135 to 175 nanometers. Near ultraviolet sensitive to light with wavelengths 175 to 280 nanometers.
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Long wavelength UV (NUV) is classified in the region of 300-400nm.
I'm not sure for the reasons behind the Galex definition but the NUV data in the Galex image isn't really NUV but more like MUV.
Regards
Steven