How can I recognize H alpha line?

[19matthew89]

Hi everyone!
If I measure a galaxy spectrum in order to compute galaxy redshift, and I know that Balmer's H alpha line is evident in the spectrum, how can I recognize it? In other words, how can I be sure that the peaked line I clearly see on the spectrum is really H alpha line and not another line that I don't know?
I cannot obiously use the wavelength because it'll be shifted...can I use line intensity instead? But the intensity could be attenuated...and so...could I use H alpha shape to recognize it?
I'd be grateful towards you if you could help me.

Thank you

 

[phyzguy]

You really can't be sure you have identified a single line in a redshifted spectrum. But if you have several lines, then you can determine the redshift with high confidence. This is because all of the lines are redshifted by the same factor, so the pattern of the lines is unambiguous. Look at the second figure down on the left (with the caption that begins "Absorption lines in the...") on this page:

http://en.wikipedia.org/wiki/Redshift