The Star Formation History of the Universe
How do we measure the star formation history of the universe?
Young massive stars emit in the ultraviolet, so ultraviolet light is a tracer of star formation.
Surrounding dust can absorb and be heated by the young stars, then radiate in the far infrared, so FIR light is a tracer of star formation.
Measure the UV and FIR luminosities of galaxies as a function of redshift, then build luminosity functions.
(Note: all figures from
Madau and Dickenson, ARAA 2014
Galaxy luminosity functions in the (rest frame) ultraviolet and far-infrared:
How to convert these to star formation rates?
Integrate over the luminosity function to get a total UV or FIR luminosity from all galaxies.
Need to adopt extinction correction (UV)
Need to adopt an initial mass function to connect UV/FIR emission to total star formation rate
Corrections have significant uncertainties to them.
Estimating extinction correction by comparing (uncorrected) UV and FIR star formation rates.
Left: Star formation rate, Right: Inferred extinction (magnitudes)
Combined datasets (blue/green points = UV, red/purple points = FIR)
Remember, this is NOT the SFR history of individual galaxies, it's the integrated SFR history of the universe.
1) Integrating the star formation history over time should give the stellar mass of the universe
Stellar mass function of galaxies:
Total stellar mass compared to integrated SFR:
2) Type II (massive star) core-collapse supernovae rate as a function of redshift, compared to SFR
3) Combine SFR fit with metallicity evolution model to predict average metallicity of the universe.