Informations obtainable from spectra

The analysis of a galaxy spectrum is typically based on the measurements of a set of line fluxes and equivalent widths (EW):

where is the flux measured in the line and is the flux in the continuum.

From these easily measurable quantities we can derive two relevant informations:

• Distinguish if the gas is ionized by hot stars or by nonthermal sources. In this way galaxies hosting AGN can be identified even if only an integrated spectrum is available (which is normally the case in high redshift AGN)

• Estimate of the ongoing and past galaxy star formation rate

• Diagnostic diagrams
• Ongoing star Formation rate in normal galactic disk
  • SFR indicator:
  • SFR indicator:
• Dust content and reddening correction
• Past and future star formation rate