Galaxy formation and evolution

Abstract:

Some of the most 'active' galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS) of enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star formation as well as those containing a dominant active galactic nucleus (AGN). Mid-infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid-and farinfrared. This was particularly useful, since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based on ISO data spanning the full range of luminosity and type of active galaxies. © 2005 Springer.

Abstract:

A deep mid- and far-infrared survey in the extended Groth strip (EGS) area gives 3.6 to 8 μm flux densities or upper limits for 253 Lyman break galaxies (LBGs). The LBGs are a diverse population but with properties correlated with luminosity. The LBGs show a factor of 30 range in indicated stellar mass and a factor of 10 range in apparent dust content relative to stellar mass. About 5% of LBGs are luminous at all wavelengths, with powerful emission at rest 6 μm. In the rest 0.9 to 2 μm spectral range these galaxies have stellar spectral slopes with no sign of an AGN power-law component, suggesting that their emission is mainly powered by intensive star formation. Galaxies in this luminous population share the infrared properties of cold Submillimeter Common-User Bolometric Array (SCUBA) sources: both are massive and dusty starburst galaxies at 2 < z < 3; their stellar mass is larger than 10 11 M⊙. We suggest that these galaxies are the progenitors of present-day giant elliptical galaxies, with a substantial fraction of their stars already formed at z ≈ 3. © 2005. The American Astronomical Society. All rights reserved.