Galactic Star Formation Rate (SFR)
Naive model: Start with gas mass Mgas at t = 0
Assume SFR ∝ Mgas thereafter
SFR ∝ e-λt
SFR
λ>0
t
Approximate using weighted sequence of single bursts.
Galaxy Colors
Sc
Colors depend on
star formation rate
over past ~108 yr.
Sb
Sa
5 Gyr
10 Gyr
20 Gyr
50 Gyr
Express SFR as timescale: Mstar / SFR.
100 Gyr
200 Gyr
Normal Galaxies
Peculiar Galaxies
Larson & Tinsley (1978)