Starship Asterisk*

I started processing the GALEX mosaic of M31 after looking at some of the data and realizing there's a lot of potential for a fresh look. Some famous GALEX imagery was processed a bit harshly, losing some fainter details in all the contrast.

What I thought I would get was a softer image overall with a smoother glow to the stars and galaxy. What I ended up finding was some hidden cirrus. I had no idea this was here! It's only easy to view in the FUV (far ultraviolet) channel. If it's there in the NUV (near ultraviolet) then it's pretty hard to see. So what we have is hidden galactic cirrus finally revealed. At first I couldn't believe it was cirrus and thought it was some kind of oddball instrumental thing. Lo and behold, it's really there.

I'm guessing it's nothing unique to the area around Andromeda. The stuff must be everywhere.
http://geckzilla.com/astro/M31_GALEX_FUD.jpg (changed to link because image > 1MB)

Interesting. Are you sure that's cirrus, Geck? Couldn't it be a widely scattered population of hot stars?

If it's cirrus, why would it be bright in the far ultraviolet?

Ann

geckzilla wrote:I started processing the GALEX mosaic of M31 after looking at some of the data and realizing there's a lot of potential for a fresh look. Some famous GALEX imagery was processed a bit harshly, losing some fainter details in all the contrast.

What I thought I would get was a softer image overall with a smoother glow to the stars and galaxy. What I ended up finding was some hidden cirrus. I had no idea this was here! It's only easy to view in the FUV (far ultraviolet) channel. If it's there in the NUV (near ultraviolet) then it's pretty hard to see. So what we have is hidden galactic cirrus finally revealed. At first I couldn't believe it was cirrus and thought it was some kind of oddball instrumental thing. Lo and behold, it's really there.

I'm guessing it's nothing unique to the area around Andromeda. The stuff must be everywhere.
http://geckzilla.com/astro/M31_GALEX_FUD.jpg (changed to link because image > 1MB)

I think I've seen several papers in recent years about very tenuous, very hot intergalactic material being observed in far UV, and how this helps account for some of the "missing mass" (the mismatch between observed luminous matter and the assumed amount of ordinary matter).

I can see the cirrus now. It didn't look like cirrus on my work computer.

Ann

Yeah, I'm pretty sure it's cirrus. Sorry it's hard to see. I tried to put a wide, dark background so the any white from your browser wouldn't drown it out. It's much easier to see when there are no competing bits of white being emitted by your monitor. It also helps to have a good screen without the sun behind you.

Chris Peterson wrote:I think I've seen several papers in recent years about very tenuous, very hot intergalactic material being observed in far UV, and how this helps account for some of the "missing mass" (the mismatch between observed luminous matter and the assumed amount of ordinary matter).

I'm quite astonished to find it there since I've not once seen it presented by any GALEX imagery. I have to imagine either they don't think anyone cares or GALEX imagery is so rarely processed by other individuals, maybe whoever has already done so didn't notice it or didn't process it very well.

I've got a completed mosaic up here:

GALEX Andromeda Mosaic by Judy Schmidt, on Flickr

I've said it before but your processing is excellent, you have the soul of an artist! There is definitely faint galactic cirrus in this region of the sky, there was a widefield image of M31 and M33 by Rogelio Bernal Andreo which showed it but it isn't available on his website anymore.

starsurfer wrote:I've said it before but your processing is excellent, you have the soul of an artist! There is definitely faint galactic cirrus in this region of the sky, there was a widefield image of M31 and M33 by Rogelio Bernal Andreo which showed it but it isn't available on his website anymore.

I think that, in visible light, the cirrus tends to be dominated by Andromeda's extended light. It is visible somewhat in the near ultraviolet channel, but even in that one the stars begin to dominate. It is only in the far ultraviolet where many stars are dim that the cirrus is revealed. I do not think this is a case of integrated flux nebula where the light from billions of stars faintly illuminates it but rather that it is glowing in UV light itself. Hence, Rogelio's imagery or even the deepest astrophotography may fail to render it.

geckzilla wrote:

starsurfer wrote:I've said it before but your processing is excellent, you have the soul of an artist! There is definitely faint galactic cirrus in this region of the sky, there was a widefield image of M31 and M33 by Rogelio Bernal Andreo which showed it but it isn't available on his website anymore.

I think that, in visible light, the cirrus tends to be dominated by Andromeda's extended light. It is visible somewhat in the near ultraviolet channel, but even in that one the stars begin to dominate. It is only in the far ultraviolet where many stars are dim that the cirrus is revealed. I do not think this is a case of integrated flux nebula where the light from billions of stars faintly illuminates it but rather that it is glowing in UV light itself. Hence, Rogelio's imagery or even the deepest astrophotography may fail to render it.

I meant that the cirrus is associated with our galaxy and shares the same line of sight. Also I found Rogelio's image on an obscure website called APOD.

Cool, it does seem like a good match in visible light, though Rogelio's cirrus is very blurry.