Other
Scientific paper
Mar 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006phdt........22l&link_type=abstract
PhD Thesis
Other
1
Starburst Galaxies, Massive Stars, Wolf-Rayet Stars, Stella Popuiations, Synthesis Techniques
Scientific paper
In this work we apply several stellar population synthesis techniques to investigate the stellar populations of star-forming galaxies. We also address how the morphology and gas abundance dictates the possible scenarios or star forming regimes - continuous or instantaneous. We are mainly interested in massive star formation and in techniques to detect them. This work is divided in three parts. In part I we discuss the Starburst99 code and the new low-metallicity library of stars that we added to the code. This new library (Z = 1/4 Z_&sun;) extended the Starburst99 code to the low-metallicity regime. We note that the synthetic fits are improved by employing the new low-metallicity library. In part II we apply a synthesis code to a large sample of HII and nuclear Starburst galaxies. We find that many of the properties of these galaxies can be summarized and understood by using the population vector vec{x}, whose components represent the contribution of base elements with known ages and metalicities. We can combine age components with similar ages: vec{x} = (x_Y, x_I, x_O); where x_Y, x_I, x_O are components respectively representing the young, intermediate and old populations. By properly combining different age components we define the average age of the galaxy weigthed by the light as atflux. We find that this representation is a powerfull way to describe the star-forming properties of this sample of HII and nuclear Starburst galaxies. The ages of the galaxies described using atflux relate to several other properties. In particular, we relate T_{Flux} to the equivalent width of Hβ W^{obs}_{Hβ} and we find that T_{Flux} is a ``natural clock'' which correctly describes the way W^{obs}_{Hβ} decreases with time. In part III we observed a sample of 32 Starburst galaxies in the optical and infrared to study massive star-formation in the high metalicity regime. In particular we try to understand if the formation of Wolf-Rayet stars is favored in any way at high metalicity. Previous Wolf-Rayet galaxies were found in low-metlicity environments and we would like to understand if this is a selection effect or a true difference between low and high metalicity galaxies. We studied the stellar populations of our sample by using both the Starburst99 and the STARLIGHT codes. We also investigate the properties of the Wolf-Rayet bump (a clear indication of stars with M > 25 M_&sun;) centered at 4640 Å and we derive the numbers of Nitrogen and Carbon Wolf-Rayet stars. We find that large populations of Wolf-Rayet stars are preferably found in very young galaxies, indicating that the age of these systems is an important factor in the detection of such stars.
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