The rise and fall of the star formation histories of blue galaxies at
  redshifts 0.2<z<1.4
  Popular cosmological scenarios predict that galaxies form hierarchically from
the merger of many progenitors, each with their own unique star formation
history (SFH). We use a sophisticated approach to constrain the SFHs of 4517
blue (presumably star-forming) galaxies with spectroscopic redshifts in the
range 0.2 < z < 1.4 from the All-Wavelength Extended Groth Strip International
Survey (AEGIS). This consists in the Bayesian analysis of the observed galaxy
spectral energy distributions with a comprehensive library of synthetic spectra
assembled using realistic, hierarchical star formation and chemical enrichment
histories from cosmological simulations. We constrain the SFH of each galaxy in
our sample by comparing the observed fluxes in the B, R, I and Ks bands and
rest-frame optical emission-line luminosities with those of one million model
spectral energy distributions. We explore the dependence of the resulting SFHs
on galaxy stellar mass and redshift. We find that the average SFHs of high-mass
galaxies rise and fall in a roughly symmetric bell-shaped manner, while those
of low-mass galaxies rise progressively in time, consistent with the typically
stronger activity of star formation in low-mass compared to high-mass galaxies.
For galaxies of all masses, the star formation activity rises more rapidly at
high than at low redshift. These findings imply that the standard approximation
of exponentially declining SFHs widely used to interpret observed galaxy
spectral energy distributions may not be appropriate to constrain the physical
parameters of star-forming galaxies at intermediate redshifts.
