Emeric Le Floc'h (IfA)

Title: Luminous starbursts and active nuclei at high redshift: a mid-infrared
perspective

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 present a number of
key results obtained in the mid-IR with the Spitzer Space Telescope
and that revolutionized our understanding of the contribution of
luminous galaxies to the star formation history and the growth of
supermassive black holes. In particular I will discuss their nature
and their relationship within other populations of distant sources
using a multi-wavelength characterization of their spectral
properties, luminosity function, morphology and clustering. I will
emphasize the large contribution of IR-luminous "composite" galaxies
experiencing both star formation and nuclear accretion, which will
finally lead me to underline the difficulties of interpreting 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 revealed a weak overlap between
GRB-selected star-forming galaxies and luminous dusty
starbursts. Possible scenarios will be described to explain this
result.