The Star Formation History of Redshift z~2 Galaxies: The Role of The Infrared Prior

TL;DR

This study introduces a new SED-fitting method incorporating IR luminosity as a prior to accurately determine star formation rates, stellar masses, and ages of z~2 galaxies, revealing insights into dust formation and galaxy evolution.

Contribution

The paper develops a novel SED-fitting technique that includes IR luminosity and a variable extinction law, improving estimates of galaxy physical parameters at high redshift.

Findings

SFRs range from a few to 1000 solar masses per year.

Older stellar populations are found in less luminous, less massive galaxies.

Dust forms rapidly within tens of Myr and is prevalent in luminous galaxies.

Abstract

We build a sample of 298 spectroscopically-confirmed galaxies at redshift z~2, selected in the z-band from the GOODS-MUSIC catalog. By exploiting the rest frame 8 um luminosity as a proxy of the star formation rate (SFR) we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the galaxy physical parameters. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable RV . Then we exploit such a new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 1000 solar mass per year, the masses from one billion to 400 billion solar masses, while the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age easurements of highly attenuated objects indicate that dust must form within a few tens of Myr and be copious already at ~100 Myr. In addition, we find that low luminous galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known 'downsizing' scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed mass-to-light ratios.