How does one identify the common galaxy absorption lines (e.g. Na, Mg, K, etc.) and emission lines (H-alpha, O III, S II, etc.) by just looking at a galaxy spectrum (like the one below)? I need to know how to do this because I want to calculate the redshifts of galaxies using the emitted wavelengths from the SDSS table.

enter image description here

  • $\begingroup$ are all lines going to be shifted the same amount? $\endgroup$ – Theologos K May 15 '20 at 13:28
  • $\begingroup$ @TheologosK To first order, yes, but various radiative transfer effects may cause some lines to be redshifted or blueshifted relative to the overall, "systemic", shift. These shifts are important to identify some physical processes, such as galactic outflows. $\endgroup$ – pela May 15 '20 at 14:37

You need to compare it with the spectrum of a similar galaxy at a known redshift, that would probably enable you to identify features with known rest wavelengths.

If you can find such a template, then the best way of estimating a redshift for a galaxy spectrum like this, consisting of mostly weak and blended absorption features, is to cross-correlate your template galaxy with this one. The cross-correlation "lag" gives you the difference in redshift.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.