Title:

A Spitzer View Of Massive Star Formation And AGNs At High Redshift



Emeric LeFloc'h
IfA



Abstract:

Although they are rare objects in the present day Universe, Luminous
Infrared (IR) Galaxies played a significant role in the evolution of
structures at high redshift. I will discuss how the Spitzer Space
Telescope has revolutionized our knowledge on the contribution of this
population to the history of star formation and supermassive black
hole growth. I will particularly emphasize results on the evolution of
IR-luminosity functions up to z~1 as well as the discovery of a
population of 2<z<3 galaxies exhibiting the largest mid-IR
luminosities ever measured at such redshifts. These sources contain
powerful dusty active nuclei, which also underlines the difficulties
to interpret IR surveys when starbursts and AGNs are not carefully
distinguished. Avoiding these limitations, an independent approach for
probing massive star formation based on cosmic GRBs will be
presented. I will show that Spitzer has revealed so far a weak overlap
between GRB-selected star-forming galaxies and luminous dusty
starbursts. Possible scenarios will be described to explain this
result.