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Title: A New Method to Measure the Post-reionization Ionizing Background from the Joint Distribution of Ly α and Ly β Forest Transmission

Abstract

The amplitude of the ionizing background that pervades the intergalactic medium (IGM) at the end of the epoch of reionization provides a valuable constraint on the emissivity of the sources that reionized the universe. While measurements of the ionizing background at lower redshifts rely on a simulation-calibrated mapping between the photoionization rate and the mean transmission of the Lyα forest, at z ≳ 6 the IGM becomes increasingly opaque and transmission arises solely in narrow spikes separated by saturated Gunn–Peterson troughs. In this regime, the traditional approach of measuring the average transmission over large ~50 Mpc/h regions is less sensitive and suboptimal. In addition, the five times smaller oscillator strength of the Lyβ transition implies that the Lyβ forest is considerably more transparent at z ≳ 6, even in the presence of contamination by foreground z ~ 5 Lyα forest absorption. We present a novel statistical approach to analyze the joint distribution of transmission spikes in the cospatial z ~ 6 Lyα and Lyβ forests. Our method relies on approximate Bayesian computation (ABC), which circumvents the necessity of computing the intractable likelihood function describing the highly correlated Lyα and Lyβ transmission. We apply ABC to mock data generated from amore » large-volume hydrodynamical simulation combined with a state-of-the-art model of ionizing background fluctuations in the post-reionization IGM and show that it is sensitive to higher IGM neutral hydrogen fractions than previous techniques. As a proof of concept, we apply this methodology to a real spectrum of a z = 6.54 quasar and measure the ionizing background from 5.4 ≤ z ≤ 6.4 along this sightline with ~0.2 dex statistical uncertainties.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3];  [4]
  1. Max Planck Inst. for Astronomy, Heidelberg (Germany)
  2. Max Planck Inst. for Astronomy, Heidelberg (Germany); Univ. of California, Santa Barbara, CA (United States). Dept. of Physics
  3. Max Planck Inst. for Astronomy, Heidelberg (Germany); Heidelberg Univ. (Germany). International Max Planck Research School for Astronomy and Cosmic Physics
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1493254
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 855; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; diffuse radiation; intergalactic medium; statistical methods

Citation Formats

Davies, Frederick B., Hennawi, Joseph F., Eilers, Anna-Christina, and Lukić, Zarija. A New Method to Measure the Post-reionization Ionizing Background from the Joint Distribution of Ly α and Ly β Forest Transmission. United States: N. p., 2018. Web. doi:10.3847/1538-4357/aaaf70.
Davies, Frederick B., Hennawi, Joseph F., Eilers, Anna-Christina, & Lukić, Zarija. A New Method to Measure the Post-reionization Ionizing Background from the Joint Distribution of Ly α and Ly β Forest Transmission. United States. https://doi.org/10.3847/1538-4357/aaaf70
Davies, Frederick B., Hennawi, Joseph F., Eilers, Anna-Christina, and Lukić, Zarija. 2018. "A New Method to Measure the Post-reionization Ionizing Background from the Joint Distribution of Ly α and Ly β Forest Transmission". United States. https://doi.org/10.3847/1538-4357/aaaf70. https://www.osti.gov/servlets/purl/1493254.
@article{osti_1493254,
title = {A New Method to Measure the Post-reionization Ionizing Background from the Joint Distribution of Ly α and Ly β Forest Transmission},
author = {Davies, Frederick B. and Hennawi, Joseph F. and Eilers, Anna-Christina and Lukić, Zarija},
abstractNote = {The amplitude of the ionizing background that pervades the intergalactic medium (IGM) at the end of the epoch of reionization provides a valuable constraint on the emissivity of the sources that reionized the universe. While measurements of the ionizing background at lower redshifts rely on a simulation-calibrated mapping between the photoionization rate and the mean transmission of the Lyα forest, at z ≳ 6 the IGM becomes increasingly opaque and transmission arises solely in narrow spikes separated by saturated Gunn–Peterson troughs. In this regime, the traditional approach of measuring the average transmission over large ~50 Mpc/h regions is less sensitive and suboptimal. In addition, the five times smaller oscillator strength of the Lyβ transition implies that the Lyβ forest is considerably more transparent at z ≳ 6, even in the presence of contamination by foreground z ~ 5 Lyα forest absorption. We present a novel statistical approach to analyze the joint distribution of transmission spikes in the cospatial z ~ 6 Lyα and Lyβ forests. Our method relies on approximate Bayesian computation (ABC), which circumvents the necessity of computing the intractable likelihood function describing the highly correlated Lyα and Lyβ transmission. We apply ABC to mock data generated from a large-volume hydrodynamical simulation combined with a state-of-the-art model of ionizing background fluctuations in the post-reionization IGM and show that it is sensitive to higher IGM neutral hydrogen fractions than previous techniques. As a proof of concept, we apply this methodology to a real spectrum of a z = 6.54 quasar and measure the ionizing background from 5.4 ≤ z ≤ 6.4 along this sightline with ~0.2 dex statistical uncertainties.},
doi = {10.3847/1538-4357/aaaf70},
url = {https://www.osti.gov/biblio/1493254}, journal = {The Astrophysical Journal (Online)},
issn = {1538-4357},
number = 2,
volume = 855,
place = {United States},
year = {2018},
month = {3}
}

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Cited by: 17 works
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Works referencing / citing this record:

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Anomaly in the Opacity of the Post-reionization Intergalactic Medium in the Ly α and Ly β Forest
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