The Lyman Alpha Reference Sample: Extended Lyman Alpha Halos Produced at Low Dust Content
Abstract
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 P20, 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, ξLyα = R Lyα P20/R Hα P20, we find ξLyα to be uncorrelated with total Lyα luminosity. However, ξLyα 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.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 12310.- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2013
- DOI:
- 10.1088/2041-8205/765/2/L27
- arXiv:
- arXiv:1303.0006
- Bibcode:
- 2013ApJ...765L..27H
- Keywords:
-
- cosmology: observations;
- galaxies: evolution;
- galaxies: formation;
- galaxies: starburst;
- radiative transfer;
- Astrophysics - Cosmology and Extragalactic Astrophysics
- E-Print:
- Published in ApJ Letters ~~ 6 pages using emulateapj, 4 figures ~~ Higher-resolution, larger, nicer jpeg versions of Figures 1 and 2 can be found here: http://xayes.org/pub/press_lars.html