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

• Published in: The Astrophysical journal Vol. 844; no. 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: Journal Article
• Language: English
• Published: Philadelphia IOP Publishing 01-08-2017; University of Chicago Press
• 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

Abstract
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.