title: Voyager measurements of hydrogen Lyman-α diffuse emission from the Milky Way.
abstract: Doppler-shifted hydrogen Lyman-alpha (Lyα) emission from galaxies is currently measured and used in cosmology as an indicator of star formation. Until now, the Milky Way emission has not been detected, owing to far brighter local sources, including the H (hydrogen) glow, i.e., solar Lyα radiation backscattered by interstellar atoms that flow within the solar system. Because observations from the Voyager spacecraft, now leaving the heliosphere, are decreasingly affected by the H glow, the ultraviolet spectrographs are detecting Lyα diffuse emission from our Galaxy. The surface brightness toward nearby star-forming regions is about 3 to 4 rayleighs. The escape fraction of the radiation from the brightest H II regions is on the order of 3% and is highly spatially variable. These results will help in constraining models of Lyα radiation transfer in distant galaxies.
authors.affiliation: Galaxies, Etoiles, Physique, Instrumentation (GEPI), Observatoire de Paris, CNRS, Université Paris Diderot, Place Jules Janssen, Meudon, France. rosine.lallement@obspm.fr
authors.forename: Rosine
authors.initials: R
authors.lastname: Lallement
authors.forename: Eric
authors.initials: E
authors.lastname: Quémerais
authors.forename: Jean-Loup
authors.initials: JL
authors.lastname: Bertaux
authors.forename: Bill R
authors.initials: BR
authors.lastname: Sandel
authors.forename: Vlad
authors.initials: V
authors.lastname: Izmodenov