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What Makes a Lyman-alpha Emitter?
  Astronomy and astrophysics

Friday 17 April 2015
from 10:30 to 11:30
at FB41
Speaker : Alex Hagen (Penn State University)
Abstract : We compare the physical and morphological properties of z ∼ 2 Lyα emitting galaxies (LAEs) from the HETDEX Pilot Survey and narrow band studies with those of z ∼ 2 optical emission line galaxies (oELGs) identified via HST WFC3 infrared grism spectroscopy. Both sets of galaxies extend over the same wide range in stellar mass (7.5 < logM/M⊙ < 10.5), size (0.5 < R < 3.0 kpc), and star-formation rate (∼ 1 < SFR < 100M⊙ yr−1). Remarkably, in all physical and morphological parameters: stellar mass, half light radius, UV slope (β), star formation rate, ellipticity, nearest neighbor distance, star formation surface density (ΣSFR), and specific star formation rate, there are no statistically significant differences between these populations. In particular, in the case of the UV slope, which parametrizes reddening, the lack of difference suggests that Lyα emission is not significant modulated by dust, as is usually assumed. We develop a simple model of Lyα emission that connects LAEs to all high-redshift star forming galaxies where Lyman-α escapes through a fraction of the galaxy and is thus only observable on a fraction of sightlines. We find a average Lyman-α escape solid angle of ΩLyα = 2.4 ± 0.8 steradians, and find this value consistent with those we calculate from other studies. We then compare our models’ predictions with those of computational models. Furthermore, we find both oELGs and LAEs fall above a linear extrapolation of the "main sequence" of star forming galaxies, which could demonstrate that these galaxies are experiencing a starburst, or that there is a change in the main sequence slope at low stellar masses. This could demonstrate that both oELGs and LAEs are drawn from the same star-bursting subset of high-z star-forming galaxies.

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