Starbursts and AGN in Luminous Infrared Galaxies

Abstract

Luminous Infrared Galaxies (LIRGs), which emit a significant fraction of their bolometric luminosity in the far-infrared, have L_(IR) ≥ 10^(11)L_ʘ. LIRGs are a mixture of single galaxies, disk galaxy pairs, interacting systems, and advanced mergers which exhibit enhanced star-formation rates and AGN activity compared to normal galaxies. At the highest luminosities (L_(IR) ≥ 10^(12)L_ʘ), Ultraluminous Infrared Galaxies (ULIRGs) may represent an important stage in the formation of QSOs. If the growth of the central black hole preferentially occurs during periods of enhanced star formation, LIRGs and ULIRGs are important laboratories in which to understand both processes. The Great Observatories All-Sky LIRG Survey (GOALS) is aimed at measuring the properties of a large, complete sample of low-redshift LIRGs across the electromagnetic spectrum. With its ability to probe the stars, dust and ionized and molecular gas in LIRGs through mid-infrared imaging and spectroscopy, Spitzer is providing a key component of the GOALS data. In this paper, we summarize the key findings from Spitzer Infrared Spectrograph (IRS) studies of ULIRGs at low and high redshifts, and present early results from GOALS in the context of the co-evolution of starbursts and AGN.

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