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Laura Pentericci |
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"The Physical and
Morphological Properties of High Redshift Ly-alpha Emitting Galaxies" |
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Understanding the physical nature of Ly-alpha emitters (LAEs) and Lyman-break galaxies (LBGs) and the relation between the two samples is important to assess the role they played in the early Universe and constrain the relative contribution, e.g., to the total stellar mass density. Are the LAEs a subset of the LBG population or is there an evolutionary sequence from one sample to the other, as claimed by several authors? To assess these issues we studied a large sample of color selected galaxies from z~2 to z~6 from the GOODS-S survey. We then investigated their physical and morphological properties and their dependence on the nature of the Ly-alpha emission/absorption characteristics, using the GOODS MUSIC catalog (including 14-band data from U-band to IRAC), as well as the deepest MIPS and X-ray observations available. We find that although galaxies with Ly-alpha emission are less massive and younger than the general LBG population, a non-negligible fraction contains evolved stars with ages of several hundreds Myr and up to ~ 1 Gyr. This is inconsistent with models that represent LAEs as short-lived events, i.e., primeval galaxies in essentially dust-free environments. For our lower redshift subsample (z=2-3) these differences are much less pronounced than at higher z, and there is essentially a continuity of physical properties. Finally, through non-parametric diagnostics which includes asymmetry, concentration, Gini coefficient, second-order moment of the brightest 20% of galaxy pixels, and ellipticity, we have analyzed the HST morphologies of the z~3 galaxies and find no dependence of properties on line emission strength. Models where the vast majority of LBGs have intrinsic Ly-alpha emission and where dust is the main physical parameter responsible for the observed variety of line strengths and profiles, seem to be consistent with most of the observed trends. |