The Lyman Alpha Reference Sample : XI. Efficient turbulence-driven Lyα escape and an analysis of IR, CO, and [C II]158 μm

• Context. Lyman-alpha (Ly alpha) is the brightest emission line in star-forming galaxies. However, its interpretation in terms of physical properties is hampered by the resonant nature of Ly alpha photons. In order to remedy this complicated situation, the Lyman Alpha Reference Sample (LARS) was defined, enabling the study of Ly alpha production and escape mechanisms in 14 local star-forming galaxies.Aims. With this paper, we complement our efforts and study the global dust and (molecular) gas content as well as the properties of gas associated with photon-dominated regions. We aim to characterize the interstellar medium of LARS galaxies, allowing us to relate these newly derived properties to quantities relevant for Ly alpha escape.Methods. We observed LARS galaxies with Herschel, SOFIA, the IRAM 30m telescope, and APEX, targeting far-infrared (FIR) continuum and emission lines of [C II]158 mu m, [O I]63 mu m, [O III]88 mu m, and low-J CO lines. Using Bayesian methods we derived dust model parameters and estimated the total gas masses for all LARS galaxies, taking into account a metallicity-dependent gas-to-dust ratio. Star formation rates were estimated from FIR, [C II]158 mu m, and [O I]63 mu m luminosities.Results. LARS covers a wide dynamic range in the derived properties, with FIR-based star formation rates from similar to 0.5-100 M-circle dot yr(-1), gas fractions between similar to 15-80%, and gas depletion times ranging from a few hundred megayears up to more than ten gigayears. The distribution of LARS galaxies in the Sigma(gas) versus Sigma(SFR) (Kennicutt-Schmidt plane) is thus quite heterogeneous. However, we find that LARS galaxies with the longest gas depletion times, that is, relatively high gas surface densities (Sigma(gas)) and low star formation rate densities (Sigma(SFR)), have by far the highest Ly alpha escape fraction. A strong approximately linear relation is found between the Ly alpha escape fraction and the total gas (HI+H-2) depletion time. We argue that the Ly alpha escape in those galaxies is driven by turbulence in the star-forming gas that shifts the Ly alpha photons out of resonance close to the places where they originate. We further report on an extreme [C II]158 mu m excess in LARS 5, corresponding to similar to 14 +/- 3% of the FIR luminosity, which probably is the most extreme [C II]-to-FIR ratio observed in a galaxy (without active nucleus) to date.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

galaxies: evolution

galaxies: starburst

galaxies: irregular

galaxies: ISM

infrared: galaxies

radio lines: galaxies

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)