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Optically Selected Compact Stellar Regions and Tidal Dwarf Galaxies in (Ultra)-Luminous Infrared Galaxies

This thesis work is devoted to the analysis of compact star forming regions (knots) in a representative sample of 32 (U)LIRGs. The project is based mainly on optical high angular resolution images taken with the ACS and WFPC2 cameras on board the HST telescope, data from a high spatial resolution simulation of a major galaxy encounter, and with the combination of optical integral field spectroscopy (IFS) taken with the INTEGRAL (WHT) and VIMOS (VLT) instruments. A few thousand knots -a factor of more than one order of magnitude higher than in previous studies- are identified and their photometric properties are characterized as a function of the infrared luminosity of the system and of the interaction phase. These properties are compared with those of compact objects identified in simulations of galaxy encounters. Finally, and with the additional use of IFS data, we search for suitable candidates to tidal dwarf galaxies, setting up constraints on the formation of these objects for the (U)LIRG class. Knots in (U)LIRGs are likely to contain sub-strucutre. Evidence is found that in ULIRGs they are intrinsically more luminous than in less luminous interacting systems due to size-of-sample effects. Furthermore, their sizes and masses are similar to stellar complexes or clumps detected in galaxies at z > 1, unlike local stellar complexes. The star formation in (U)LIRGs is charaterized by a luminosity function with a slope consistent with α= 2, independent of the luminosity of the system. However, it may flatten slightly due to, as simulations suggest, higher knot formation rates at early phases of the interaction. Candidates to tidal dwarf galaxies are identified in the sample. With a production rate of 0.1 candidates per (U)LIRG system, only a few fraction (< 10%) of the general dwarf satellite population could be of tidal origin.