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The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyα Emission of High-redshift Galaxies

Reddy, Naveen A. and Topping, Michael W. and Shapley, Alice E. and Steidel, Charles C. and Sanders, Ryan L. and Du, Xinnan and Coil, Alison L. and Mobasher, Bahram and Price, Sedona H. and Shivaei, Irene (2022) The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyα Emission of High-redshift Galaxies. Astrophysical Journal, 926 (1). Art. No. 31. ISSN 0004-637X. doi:10.3847/1538-4357/ac3b4c.

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We perform joint modeling of the composite rest-frame far-UV and optical spectra of redshift 1.85 ≤ z ≤ 3.49 star-forming galaxies to deduce key properties of the massive stars, ionized interstellar medium (ISM), and neutral ISM, with the aim of investigating the principal factors affecting the production and escape of Lyα photons. Our sample consists of 136 galaxies with deep Keck/LRIS and MOSFIRE spectra covering, respectively, Lyβ through C iii] λλ1907, 1909 and [O ii], [Ne iii], Hβ, [O iii], Hα, [N ii], and [S ii]. Spectral and photoionization modeling indicates that the galaxies are uniformly consistent with stellar population synthesis models that include the effects of stellar binarity. Over the dynamic range of our sample, there is little variation in stellar and nebular abundance with Lyα equivalent width, W_λ(Lyα), and only a marginal anticorrelation between age and W_λ(Lyα). The inferred range of ionizing spectral shapes is insufficient to solely account for the variation in W_λ(Lyα); rather, the covering fraction of optically thick H i appears to be the principal factor modulating the escape of Lyα, with most of the Lyα photons in down-the-barrel observations of galaxies escaping through low column density or ionized channels in the ISM. Our analysis shows that a high star-formation-rate surface density, Σ_(SFR), particularly when coupled with a low galaxy potential (i.e., low stellar mass), can aid in reducing the covering fraction and ease the escape of Lyα photons. We conclude with a discussion of the implications of our results for the escape of ionizing radiation at high redshift.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Reddy, Naveen A.0000-0001-9687-4973
Shapley, Alice E.0000-0003-3509-4855
Steidel, Charles C.0000-0002-4834-7260
Sanders, Ryan L.0000-0003-4792-9119
Du, Xinnan0000-0001-5554-5444
Coil, Alison L.0000-0002-2583-5894
Price, Sedona H.0000-0002-0108-4176
Shivaei, Irene0000-0003-4702-7561
Alternate Title:The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyman Alpha Emission of High-Redshift Galaxies
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 August 11; revised 2021 November 17; accepted 2021 November 17; published 2022 February 9. We acknowledge support from NSF AAG grants AST1312780, 1312547, 1312764, and 1313171; grant AR13907 from the Space Telescope Science Institute; and grant NNX16AF54G from the NASA ADAP program. This work made use of v2.2.1 of the Binary Population and Spectral Synthesis (BPASS) models, as described in Eldridge et al. (2017) and Stanway & Eldridge (2018), and v17.02 of the Cloudy radiative transfer code (Ferland et al. 2017). We wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, most of the observations presented herein would not have been possible.
Group:Astronomy Department
Funding AgencyGrant Number
Subject Keywords:Stellar abundances; Interstellar abundances; H II regions; High-redshift galaxies; Interstellar medium; Star formation
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Stellar abundances (1577); Interstellar abundances (832); H II regions (694); High-redshift galaxies (734); Interstellar medium (847); Star formation (1569)
Record Number:CaltechAUTHORS:20220209-266204000
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Official Citation:Naveen A. Reddy et al 2022 ApJ 926 31
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113350
Deposited By: George Porter
Deposited On:09 Feb 2022 20:46
Last Modified:09 Feb 2022 20:46

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