GalexView- surveying the Sthn sky with UV eyes

[madbadgalaxyman (Robert)]

One of the most interesting "virtual telescopes" on the internet is GalexView, which enables you to view objects, pan, and zoom, over large areas of the southern & northern sky.

This software "telescope" shows you the ultraviolet sky as seen by the GALEX satellite; it is somewhat similar to an electronic star chart, but with imaging data from the GALEX telescope shown in a large screen display.

The address is:
http://galex.stsci.edu/GR6

When you use it, make sure that you:
(1) Click on "full resolution" in the control panel.
(2) Click on the "full screen" icon, which is a very small dark-coloured icon (about the fourth icon from the left), so as to show a bigger display. The icon seems to have a small galaxy on it.
(3) Activate the "display graphics" tick box, which has the effect of putting a red target ring around the object you have asked the telescope to point at. This can be very important, because sometimes, when you ask the telescope to point at an object, it does not exactly centre on it.
(4) De-activate the "display objects" tick box, to remove a multitude of of overlays from the image.

The only deficiency of the displayed images is that the resolution is unpredictable. The images are sometimes extremely noisy, but at other times they have been cleaned up.
Sometimes, depending on precisely what co-ordinates or object you ask the software to point at, GalexView may point to two different versions of the same imaging data.

So...... what can you see in these GALEX images?

- The colour Yellow in the GALEX images codes for near-ultraviolet (NUV) light, which mainly traces an older stellar population in galaxies. For instance: the bulges of spiral galaxies, the light from Elliptical galaxies, the smooth component of spiral arms(old stars & no star formation).
- The colour Blue in these images codes for
far-ultraviolet (FUV) light. This mostly comes from very young and massive stars, e.g. in spiral arms.

The remarkable thing about GALEX images is that the blue channel (FUV) is extremely sensitive to those areas of the universe where massive and hot stars are forming in the universe, today. Often, this current star formation is shown by GALEX to be where we expect it to be, for instance in spiral arms. But at other times, there are massive surprises;
e.g. many gaseous and/or optically-luminous Tidal Tails show evidence for current star formation, and perhaps even the formation of dwarf galaxies. Also, some field S0 galaxies, supposedly "old and red and dead", show evidence for current star formation in the central part of the galaxy.

Note: It can be a waste of time to point this virtual telescope at an elliptical or an S0 galaxy, as it may hardly show anything; these objects typically emit very little ultraviolet light. In contrast, even very-low surface brightness Irregular Galaxies light up like flares in these ultraviolet images!!

Just for fun, here are the GALEX images of NGC 2841 (see the previous discussion about its anomalous outermost extensions) and NGC 1672.





cheers,
madbadgalaxyman

[renormalised (Carl)]

Just read your profile, Rob. Ever thought about doing a degree in astronomy...postgrad even??.