Lyα Profile, Dust, and Prediction of Lyα Escape Fraction in Green Pea Galaxies

• Published in: The Astrophysical journal 2017-08, Vol.844 (2), p.171
• Main Authors: Yang, Huan, Malhotra, Sangeeta, Gronke, Max, Rhoads, James E., Leitherer, Claus, Wofford, Aida, Jiang, Tianxing, Dijkstra, Mark, Tilvi, V., Wang, Junxian
• Format: Article
• Language: English
• Subjects: Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Correlation; COSMIC DUST; Dust; DWARF STARS; EMISSION; Emission lines; Emitters; FORECASTING; GALAXIES; Intergalactic media; James Webb Space Telescope; Kinematics; LYMAN LINES; MASS; METALLICITY; Optical analysis; Optical properties; Optical thickness; Peas; RADIANT HEAT TRANSFER; Radiative transfer; Sky surveys (astronomy); SPACE; Space telescopes; SPECTRA; Star formation; Stars & galaxies; Stellar mass; TELESCOPES; ULTRAVIOLET RADIATION
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aa7d4d

We studied Lyman- α (Ly α ) escape in a statistical sample of 43 Green Peas with HST /COS Ly α spectra. Green Peas are nearby star-forming galaxies with strong [O iii ] λ 5007 emission lines. Our sample is four times larger than the previous sample and covers a much more complete range of Green Pea properties. We found that about two-thirds of Green Peas are strong Ly α line emitters with rest-frame Ly α equivalent width . The Ly α profiles of Green Peas are diverse. The Ly α escape fraction, defined as the ratio of observed Ly α flux to intrinsic Ly α flux, shows anti-correlations with a few Ly α kinematic features—both the blue peak and red peak velocities, the peak separations, and the FWHM of the red portion of the Ly α profile. Using properties measured from Sloan Digital Sky Survey optical spectra, we found many correlations—the Ly α escape fraction generally increases at lower dust reddening, lower metallicity, lower stellar mass, and higher [O iii ]/[O ii ] ratio. We fit their Ly α profiles with the H i shell radiative transfer model and found that the Ly α escape fraction is anti-correlated with the best-fit N H i . Finally, we fit an empirical linear relation to predict from the dust extinction and Ly α red peak velocity. The standard deviation of this relation is about 0.3 dex. This relation can be used to isolate the effect of intergalactic medium (IGM) scatterings from Ly α escape and to probe the IGM optical depth along the line of sight of each Ly α emission-line galaxy in the James Webb Space Telescope era.