TY - JOUR
T1 - Model-independent constraints on the hydrogen-ionizing emissivity at z > 6
AU - Mason, Charlotte A.
AU - Naidu, Rohan P.
AU - Tacchella, Sandro
AU - Leja, Joel
N1 - Funding Information:
The authors thank Charlie Conroy for useful discussions and for providing comments on a draft of this paper. We thank Steve Finkelstein, Fred Davies, and Brad Greig for useful discussions and for providing: the Ṅion model from Finkelstein et al. (2019), and xHI posteriors from Davies et al. (2018) and Greig et al. (2019), respectively. We thank Austin Hoag for sharing the xHI posterior from Hoag et al. (2019). CAM acknowledges support by NASA Headquarters through the NASA Hubble Fellowship grant HST-HF2-51413.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. RPN gratefully acknowledges an Ashford Fellowship and Peirce Fellowship granted by Harvard University. ST is supported by the Smithsonian Astrophysical Observatory through the CfA Fellowship. JL is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1701487.
PY - 2019/10/21
Y1 - 2019/10/21
N2 - Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, N ion) at z = 4-14 from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of Nion, allowing us to flexibly explore the entire prior volume. We infer a declining N ion with redshift at z > 6, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the cosmic microwave background (CMB) optical depth and Ly α and Ly β forest dark pixel fraction produce Nion evolution (d log10 N ion/dz|z=6→8 = -0.31 ± 0.35 dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly α damping of galaxies and quasars produces a more rapid decline: D log10 N ion/dz|z=6→8 = -0.44 ± 0.22 dex, steeper than the declining galaxy luminosity density (if extrapolated beyond MUV ≳ -13), and constrains the mid-point of reionization to z = 6.93 ± 0.14.
AB - Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, N ion) at z = 4-14 from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of Nion, allowing us to flexibly explore the entire prior volume. We infer a declining N ion with redshift at z > 6, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the cosmic microwave background (CMB) optical depth and Ly α and Ly β forest dark pixel fraction produce Nion evolution (d log10 N ion/dz|z=6→8 = -0.31 ± 0.35 dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly α damping of galaxies and quasars produces a more rapid decline: D log10 N ion/dz|z=6→8 = -0.44 ± 0.22 dex, steeper than the declining galaxy luminosity density (if extrapolated beyond MUV ≳ -13), and constrains the mid-point of reionization to z = 6.93 ± 0.14.
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U2 - 10.1093/mnras/stz2291
DO - 10.1093/mnras/stz2291
M3 - Article
AN - SCOPUS:85075174469
VL - 489
SP - 2669
EP - 2676
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -