# Lyman-Alpha Blobs emit very specific UV light

Himiko has been in the news and I’d like to be sure I have the context of this correct. They can tell the light is 12.9 billion years old by how much it’s red shifted. That’s roughly 800 million years after the big bang. In that time, the universe has expanded by a factor of 8. If the light waves stretch by that factor, that pushes visible light into mid or maybe even far infrared part of the EM spectrum.

Himiko is a Lyman-Alpha Blob. They can tell this by the emission lines that show up in a spectrometer. Lyman-Alpha Blobs emit very specific UV light. Us earthbound observers have a tough time seeing that through our atmosphere. Luckily, it’s so redshifted that the lines end up in the visible or infrared parts of the spectrum.

The distance between us and Himiko is now 8 times greater than when that light started its journey. We started off much closer than 12.9 billion light-years apart and we are now much farther apart. So the angular size of Himiko could be misleading. What I mean is Himiko probably looks much closer than you might guess from the age of its light. It looks like it’s only 4 billion light-years away. And that’s how far it actually was when the light left Himiko.

marcus
Gold Member
Dearly Missed

this is a good calculator example.
put z=7 into wright's calculator

If you are right about the 4 billion LY then you should get that for the "angular size distance".

I get 3.6 billion LY (the distance when the light started out), which is close enough to what you say.
And a present distance of 28.8 billion LY.

z =7 corresponds to an expansion factor of 8, as you said.

Yes! I started with Wright's calculator. Very cool. I should have mentioned that. Plus I did a lot of rounding. I think z=6.6 actually. I just want to be sure I'm not making some obviously wrong assumption about stretching light waves and expansion.

marcus
Gold Member
Dearly Missed

Yes! I started with Wright's calculator. Very cool. I should have mentioned that. Plus I did a lot of rounding. I think z=6.6 actually. I just want to be sure I'm not making some obviously wrong assumption about stretching light waves and expansion.

I don't have more precise information to offer---it looks to me like you are doing fine with whatever sources you have.

I gather that one of the authors is Masami Ouchi. We could look him up and see if there is a technical journal article.

Try this search engine:
http://arxiv.org/find

I tried it and got this:
http://arxiv.org/abs/0807.4174

which estimated the redshift to be z = 6.6, just what you said!
That article was probably published in the ApJ (astrophysical journal). I don't have anything more definite for the time being.

Here's a BBC (non-techical) piece about it:
http://news.bbc.co.uk/2/hi/science/nature/8007844.stm

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