THE HETDEX PILOT SURVEY. II. THE EVOLUTION OF THE Ly{alpha} ESCAPE FRACTION FROM THE ULTRAVIOLET SLOPE AND LUMINOSITY FUNCTION OF 1.9 < z < 3.8 LAEs
- Department of Astronomy, University of Texas at Austin, Austin, TX (United States)
- Texas Cosmology Center, University of Texas at Austin, Austin, TX (United States)
- Max Planck Institute for Extraterrestrial Physics, Garching (Germany)
- Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA (United States)
- George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX (United States)
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ (United States)
- McDonald Observatory, Austin, TX (United States)
- Astrophysikalisches Institut Potsdam, Postdam (Germany)
We study the escape of Ly{alpha} photons from Ly{alpha} emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by The Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. For 89 LAEs with broadband counterparts we measure ultraviolet (UV) luminosities and UV slopes, and estimate E(B - V) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SFRs). Comparison between the observed Ly{alpha} luminosity and that predicted by the dust-corrected SFR yields the Ly{alpha} escape fraction. We also measure the Ly{alpha} luminosity function and luminosity density ({rho}{sub Ly{alpha}}) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of {rho}{sub Ly{alpha}.} We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Ly{alpha} escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Ly{alpha}) > (3-6) x 10{sup 42} erg s{sup -1} (0.25-0.5 L*), have a mean (E(B - V)) = 0.13 {+-} 0.01, implying an attenuation of {approx}70% in the UV. They show a median UV uncorrected SFR = 11 M{sub sun} yr{sup -1}, dust-corrected SFR = 34 M{sub sun} yr{sup -1}, and Ly{alpha} equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Ly{alpha} escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Ly{alpha} escape fraction in LAEs correlates with E(B - V) in a way that is expected if Ly{alpha} photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Ly{alpha} EW with dust, due to a clumpy multi-phase interstellar medium (ISM), is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Ly{alpha} can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Ly{alpha} escape fraction of LAEs from z {approx} 4 to 2. We see hints of a drop in the number density of LAEs from z {approx} 4 to 2 in the redshift distribution and the Ly{alpha} luminosity function, although larger samples are required to confirm this. The mean Ly{alpha} escape fraction of the overall galaxy population decreases significantly from z {approx} 6 to z {approx} 2, in agreement with recent results. Our results point toward a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z {approx} 6 and 2, reducing their Ly{alpha} escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Ly{alpha} photons is reached by z {approx} 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.
- OSTI ID:
- 21578331
- Journal Information:
- Astrophysical Journal, Vol. 736, Issue 1; Other Information: DOI: 10.1088/0004-637X/736/1/31; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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