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1 Dark Cosmology Centre, The Niels Bohr Institute, Faculty of Science, Københavns Universitet 2 IRAP 3 Stockholm University 4 University of Geneva 5 Departamento de Astrofísica 6 Max Planck Institute for Astronomy 7 Observatoire 8 Macalester College 9 Leibniz-Institut für Astrophysik (AIP) 10 UPMC 11 University of Geneva 12 Dark Cosmology Centre, The Niels Bohr Institute, Faculty of Science, Københavns Universitet
Extended Lyman alpha halos produced at low dust content
We report on new imaging observations of the Lyman alpha emission line (Lyα), performed with the Hubble Space Telescope, that comprise the backbone of the Lyman alpha Reference Sample. We present images of 14 starburst galaxies at redshifts 0.028 <z <0.18 in continuum-subtracted Lyα, Hα, and the far ultraviolet continuum. We show that Lyα is emitted on scales that systematically exceed those of the massive stellar population and recombination nebulae: as measured by the Petrosian 20% radius, R , Lyα radii are larger than those of Hα by factors ranging from 1 to 3.6, with an average of 2.4. The average ratio of Lyα-to-FUV radii is 2.9. This suggests that much of the Lyα light is pushed to large radii by resonance scattering. Defining the Relative Petrosian Extension of Lyα compared to Hα, ξ = R /R , we find ξ to be uncorrelated with total Lyα luminosity. However, ξ is strongly correlated with quantities that scale with dust content, in the sense that a low dust abundance is a necessary requirement (although not the only one) in order to spread Lyα photons throughout the interstellar medium and drive a large extended Lyα halo. © 2013. The American Astronomical Society. All rights reserved.
Astrophysical Journal. Letters, 2013, Vol 765, Issue 2
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