Andromeda Galaxy - how come HII regions not prominent?

[mental4astro (Alexander)]

Hi all,

I've got to thinking for some time now as to why the HII regions in M31 are not prominent at all?

With dust being so prominent in its structure, and the there being tidal influence from its two big satellite galaxies, I would have thought that M31 would be bristling with ruby red HII regions. Yet photographs of M31 show next to none, with most photos of M31 showing none at all. Yet we see spectacular beads of ruby red HII regions in M33 & M83, and these can be observed with the use of filters too.

Might this be a consequence of the blue-shift of it heading towards the MW? I wouldn't have thought that this would have been so significant though.

Might it be that popular culture surrounding the image processing of M31 knocks out these HII regions from the processing? Photos showing bright red HII regions in M31 are not all that common, making me think that processing might need to be really pushed to reveal these. I don't know

I wouldn't have thought that the 13° incline that M31 has towards us would have been sufficient to obscure just about all the HII regions.

Nor have I found any material relating to the direct observation of the HII regions in M31 in the same way that HII regions can be observed in M33 & M83. It might be that I may just need to dig around a lot more for this, but so far I've found none.

Or is there some quirk to M31 where bright HII regions are not so standout as they are in M33 and M83?

Does anyone have more of an understanding about M31 to help me out here, please? I'm sure that this won't be the case when M31 and the Milky Way have their scrag fight in a billion years or so, but that ain't much good to me right now...

Alex.

[glend (Glen)]

Are you referring to narrowband Ha (which is the red parts of the spectrum), or Hb (which is sometimes referred to as HII is in the blue area). If Ha there are many images that show Ha areas in Andromeda, just Google " Andromeda in Ha " and there they are. Ha is a primary component of ionized hydrogen from emission nebula, whereas Hb is a product of short-lived Blue stars that ionise gas clouds with ultraviolet light. Hb is far less common even in the Milky Way.

[rustigsmed (Russell)]

looks to be a bit around
but yes, not really picked up in LRGB that much.
https://www.flickr.com/photos/leonar...ream/lightbox/

[el_draco (Rom)]

M33 & M83 are face on. M31 is edge on, (pretty much). Dust lanes will block a lot and aspect will hide most of the rest but they are definitely there. Really Hi.Res shots show them clearly.

[RickS (Rick)]

Plenty of HII regions visible in M31 in this image of mine: http://www.astrobin.com/full/223013/0/?real=&mod=

M31 is a lot bigger than M33 so it is typically viewed at lower res making the HII regions look relatively smaller.

Cheers,
Rick.

[mental4astro (Alexander)]

Thanks for the replies.

I suspected the dust could be a major culprit in limiting the appearance of these regions.

With respect to astro imaging, it would seem to be entirely a just a more popular way of portraying M31 without the red emission clouds being prominent.

Anyone with visual experience on teasing out these regions?

I'll look to make M31 a primary target at Astrofest too. Fingers crossed for good conditions. An RFT might be just the thing for these maybe.

[astroron (Ron)]

I have observed M31 many times in High resolution in my 16" but have only noticed very small patches that could be H11 regions but they definitely don't stand out visually in the eye piece.
Maybe try with a UHC or O111 filters,may bring out some detail.
Another good target that I have tried for is the globular clusters,but a good map and steady seeing are required to find any of them.
I have only ever confirmed 2 GC's from my site here at Cambroon.
As you say Alex it is worth a try to see if you can tease them out of the spiral arms.
Cheers

[mental4astro (Alexander)]

Pretty good effort pinning two of Andromeda's GC's, Ron. I'm preparing some charts for having a shot at some these too.