The rise and fall of the star formation histories of blue galaxies at redshifts 0.2<z<1.4

TL;DR

This study uses Bayesian analysis of galaxy spectral energy distributions to reveal that star formation histories of blue galaxies at 0.2<z<1.4 are mass-dependent, with high-mass galaxies showing bell-shaped histories and low-mass galaxies rising steadily.

Contribution

It introduces a comprehensive Bayesian approach to constrain star formation histories of a large galaxy sample using synthetic spectra from cosmological simulations.

Findings

High-mass galaxies have bell-shaped star formation histories.

Low-mass galaxies show steadily rising star formation activity.

Standard exponentially declining SFHs may not be suitable at intermediate redshifts.

Abstract

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.