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 (Lya), performed with the Hubble Space Telescope, that comprise the backbone of the Lyman alpha Reference Sample (LARS). We present images of 14 starburst galaxies at redshifts 0.028 < z < 0.18 in continuum-subtracted Lya, Halpha, and the far ultraviolet continuum. We show that Lya is emitted on scales that systematically exceed those of the massive stellar population and recombination nebulae: as measured by the Petrosian 20 percent radius, RP20, Lya radii are larger than those of Halpha by factors ranging from 1 to 3.6, with an average of 2.4. The average ratio of Lya-to-FUV radii is 2.9. This suggests that much of the Lya light is pushed to large radii by resonance scattering. Defining the "Relative Petrosian Extension" of Lya compared to Halpha, ξ_ext = RP20_Lya / RP20_Ha, we find ξ_ext to be uncorrelated with total Lya luminosity. However ξ_ext 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 Lya photons throughout the interstellar medium and drive a large extended Lya halo.

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

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• Impact of star formation history on the measurement of star formation rates
• Lyman alpha Emitting Galaxies in the Nearby Universe
• Linking Ly-alpha and Low-Ionization Transitions at Low Optical Depth
• A Semi-Analytical Line Transfer (SALT) model to interpret the spectra of galaxy outflows
• The LyAlpha Line Profiles of Ultraluminous Infrared Galaxies: Fast Winds and Lyman Continuum Leakage
• The Lyman alpha reference sample: IV. Morphology at low and high redshift
• The Lyman Alpha Reference Sample: III. Properties of the Neutral ISM from GBT and VLA Observations
• The Properties of Lyman Alpha Nebulae: Gas Kinematics from Non-resonant Lines
• Lyman Alpha and MgII as Probes of Galaxies and their Environments
• Physical properties and evolutionary state of the Lyman alpha emitting starburst galaxy IRAS 08339+6517