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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 421323.0, MPI für Astronomie / Publikationen_mpia
3D Lyα radiation transfer. III. Constraints on gas and stellar properties of z ~ 3 Lyman break galaxies (LBG) and implications for high-z LBGs and Lyα emitters
Authors:Verhamme, A.; Schaerer, D.; Atek, H.; Tapken, C.
Date of Publication (YYYY-MM-DD):2008
Title of Journal:Astronomy and Astrophysics
Start Page:89
End Page:111
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:Aims. The aim of our study is to understand the variety of observed Lyalpha line profiles and strengths in Lyman Break Galaxies (LBGs) and Lyalpha emitters (LAEs), the physical parameters governing them, and hence derive constraints on the gas and dust content and stellar populations of these objects. Methods: Using our 3D Lyalpha radiation transfer code including gas and dust, MCLya, we fit 11 LBGs from the FORS Deep Field with redshifts between 2.8 and 5. A simple geometry of a spherically expanding shell of H I is adopted. Results: The variety of observed Lyalpha profiles is successfully reproduced. Most objects show outflow velocities of V_exp ~ 150-200 km s-1; two objects are most likely quasi-static. The radial H I column density ranges from N_HI ~ 2 × 1019 to 7 × 1020 cm-2. Our Lyalpha profile fits yield values of E(B-V) ~ 0.05-0.2 for the gas extinction. We find indications for a dust-to-gas ratio higher than the Galactic value, and for a substantial scatter. The escape fraction of Lyalpha photons is found to be determined primarily by the extinction, and a simple fit formula is proposed. In this case a measurement of EW(Lyalpha)obs can yield E(B-V), if the intrinsic Lyalpha equivalent width is known (or assumed). Intrinsic EW(Lyalpha)int ~ 50-100 Å are found for 8/11 objects, as expected for stellar populations forming constantly over long periods (⪆10-100 Myr). In three cases we found indications of younger populations. Our model results also allow us to understand observed correlations between EW(Lyalpha)obs and other observables such as FWHM(Lyalpha), E(B-V), SFR(UV) etc. We suggest that most observed trends of Lyalpha, both in LBGs and LAEs, are driven by variations of N_HI and the accompanying variation of the dust content. Ultimately, the main parameter responsible for these variations may be the galaxy mass. We also show that there is a clear overlap between LBGs and LAEs: at z ~ 3 approximately 20-25% of the LBGs of Shapley et al. (2003, ApJ, 588, 65) overlap with ~23% of the LAEs of Gronwal et al. (2007, ApJ, 667, 79). Radiation transfer and dust effects explain the increase of the LAE/LBG ratio, and a higher percentage of LBGs with strong Lyalpha emission with increasing redshift.
Free Keywords:line: profiles; radiative transfer; galaxies: starburst; galaxies: ISM; galaxies: high-redshift; ultraviolet: galaxies
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2008A%26A...491...89... [ID No:1]
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