Invited Review at the Conference Lighthouses of the
universe. August 6-10, 2001 (Garching, Germany).
astro-ph/0201476
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Abstract. Ultraluminous galaxies in the local universe (z
0.2) emit the
bulk of their energy in the mid and far-infrared. The multiwavelength
approach to these objects has shown that they are advanced mergers
of gas-rich spiral galaxies. Galaxy-galaxy
collisions took place on all cosmological time-scales, and nearby
mergers serve as
local analogs to gain insight into the physical processes that lead
to the formation and trans-formation of galaxies in the more distant
universe. Here I review multiwavelength observations - with
particular emphasis on recent results obtained with ISO - of mergers
of massive galaxies driving the formation of: 1) luminous infrared
galaxies, 2) elliptical galaxy cores, 3) luminous dust-enshrouded
extranuclear starbursts, 4) symbiotic galaxies that host AGNs, and 5)
tidal dwarf galaxies. The most important implication for studies on the
formation of galaxies at early cosmological timescales is that the
distant analogs to the local ultraluminous infrared galaxies
are invisible in the
ultraviolet and optical wavelength rest-frames and should be detected
as sub-millimeter sources with no optical counterparts.
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