The Star Formation History of the Universe
(Note: all figures from Madau and Dickenson, ARAA 2014)
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
- Measure the UV and FIR luminosities of galaxies as a function of redshift, then build luminosity functions.
Galaxy luminosity functions in the rest frame ultraviolet (left) and far-infrared (right):
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, after extinction correction (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 (data points) compared to integrated SFR (solid line):
2) Type II (massive star) core-collapse supernovae rate as a
function of redshift (data points), compared to derived SFR (solid line):
3) Combine SFR fit with metallicity evolution model to predict average metallicity of the universe.
Zb = rho(metals)/rho(baryon)