| Precise if your presentation is oral or a poster : | oral |
| Title of your presentation : | The physical nature of high redshift Lyalpha emission galaxies |
| Abstract |
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A significant fraction of high redshift starburst galaxies presents strong Lyalpha emission. Understanding the nature of these galaxies is important to assess the they played in the early Universe and to shed light on the relation between the narrow band selected Lyalpha emitters and the LBGs: are the Lyalpha emitters a subset of the general LBG population? or do they represent the youngest galaxies in their early phases of formation? We therefore studied a sample of UV continuum selected galaxies from z~3.5 to z~6 from the GOODS-South survey, that have been observed spectroscopically and show the Lyalpha line in emission. In particular we investigated their physical properties, such as total masses, ages, SFRs , extiction etc as determined from a spectrophotometric fit to the multiwavelength (U band to mid-IR) SEDs, and their dependence on the emission line characteristics. We find that although most Lyalpha emitters are less massive and younger than the general LBG population, a non negligible fraction contains an evolved stellar population, with ages of several hundreds Myr and up to ~ 1 Gyr. This is inconsistent with most models, that represent Lyalpha emitters as short lived events, i.e. primeval galaxies in their first burst of star formation in essentialluy dust free environments. Models where the vast majority of LBGs has intrinsic Lyalpha emission and where dust is the main physical parameter responsible for the observed variety of line strenghts and profiles, seem to be consistent with the observed trends, such as the absence of massive galaxies with strong line emission, the correlation between Lyalpha strenght and the dust exctinction and the lack of correlation betwen Lyalpha EW and stellar ages. Finally, we find no indication for clumpy dust that would enhance the line EW by selectively extinguishing the continuum emission while allowing the Lyman alpha photons to escape, a scenario that was recently proposed by several authors. |
