The Star Formation History of Galaxies from Infrared Observations

摘要

We exploit deep surveys performed in the IR and sub-millimeter, as well as the spectral intensity of the extragalactic IR background, to constrain galaxy evolution in an entirely complementary way compared with the usual deep optical-UV searches. These observations indicate high rates of evolution for the comoving IR luminosity density up to redshift z ～ 1. We also report on spectral analyses of these sources, revealing them to involve massive galaxies hosting violent star-bursts. Our inferred evolutionary scheme considers phases of long-lived quiescent and enhanced star formation (SF) taking place during transient events recurrently triggered by interactions and merging. We interpret the strong observed evolution as an increase with z of the rate of galaxy interactions (density evolution) and of their IR luminosity due to the more abundant fuel in the past (luminosity evolution). The evolution of IR emissivity of galaxies from the present time to z ～ 1 is so strong that the constraints by the observed z-distributions and CIRB spectrum impose it to turn-over at z > 1: scenarios in which a relevant fraction of stellar formation occurs at very high-z are not supported by our analysis. We finally notice an interesting match between this epoch of peak SF, as revealed by IR observations, and the epoch when the galaxy mass function shows first signs of a strong negative evolution.