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OATS-DAUT SEMINAR
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Speaker: Eros Vanzella (INAF - OA Trieste)

Title: Lyman break galaxies at redshift beyond 3 and contribution to the ionizing ultraviolet background
Date: Tuesday, December 7th, 2010
Time: 15:00
Venue: Villa Bazzoni

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Abstract: Recent spectroscopic surveys have allowed to identify star-forming galaxies up to redshift 7.1, approaching the re-ionization epoch. Lyman break galaxies (LBGs) and Lyman alpha emitters (LAEs) show clear trends among spectroscopic features (e.g. Lya line, interstellar absorption lines), physical properties (e.g. stellar mass, dust attenuation) and ultraviolet appearance (e.g. nucleation, effective radius). I will summarize these properties in the first part. In the second part, a new method for the estimation of the contribution to the ultraviolet ionizing background (UVB) from star-forming galaxies is discussed. It is applied to a sample of 102 LBGs in the GOODS Southern field at redshift 3.4 < z < 4.5: the escape fraction of ionizing photons (fesc) for L > L* LBGs is smaller than 5(10)% at 2(3) sigma; if the QSO contribution to UVB is negligible at this redshift, then this imply a possible evolution of fesc with luminosity (i.e. higher for fainter galaxies). Interestingly, a promising "stellar ionizer" (the unique Lyman continuum detection) has been discovered in the sample at z=3.8, the highest redshift currently known with direct Lyman continuum detection. Its spectral features deviate from those of the typical LBGs population. If this kind of sources are common at the epochs of re-ionization (z>=7), they would be extremely difficult to identify spectroscopically with current facilities. The first clear discovery of two LBGs/LAEs at redshift beyond 7 will be also presented.
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contact: Eros Vanzella (OATS)