Measuring the Mean Free Path of HI Ionizing Photons at $3.2\leq z\leq4.6$ with DESI Y1 Quasars

The mean free path of ionizing photons ($\lambda_\mathrm{mfp}^{912}$) in the intergalactic medium (IGM) is a crucial quantity in modelling the ionization state of IGM and the extragalactic ultraviolet background (EUVB), and is widely used in hydrodynamical simulations of galaxies and reionization. We construct the largest quasar spectrum dataset to date -- 12,595 $\mathrm{S/N}>3$ spectra -- using the Y1 observation of Dark Energy Spectroscopic Instrument (DESI) to make the most precise model-independent measurement of the mean free path at $3.2\leq z\leq 4.6$. By stacking the spectra in 17 redshift bins and modelling the Lyman continuum profile, we get a redshift evolution $\lambda_\mathrm{mfp}^{912}\propto(1+z)^{-4.27}$ at $2\leq z\leq 5$, which is much shallower than previous estimate $\lambda_\mathrm{mfp}^{912}\propto(1+z)^{-5.4}$. We then explore the sources of systematic bias, including the choice of intrinsic quasar continuum, the consideration of Lyman series opacity and Lyman limit opacity evolution and the definition of $\lambda_\mathrm{mfp}^{912}$. Combining our results with estimates of $\lambda_\mathrm{mfp}^{912}$ at higher redshifts, we conclude at high confidence that the evolution in $\lambda_\mathrm{mfp}^{912}$ steepens at $z \approx 5$. We interpret this inflection as the transition from the end of HI reionization to a fully ionized plasma which characterizes the intergalactic medium of the past $\sim10$ billion years.

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Journal
arXiv (Cornell University)
Published
2024-11-24
DOI
https://doi.org/10.3847/2041-8213/adb48f
Primary Topic
Galaxies: Formation, Evolution, Phenomena
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article
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article

Measuring the Mean Free Path of HI Ionizing Photons at $3.2\leq z\leq4.6$ with DESI Y1 Quasars

P. Martini, A. Muñoz-Gutiérrez, J. Moustakas, Jason Xavier Prochaska et al.
arXiv (Cornell University)
Galaxies: Formation, Evolution, Phenomena
article

Measuring the Mean Free Path of HI Ionizing Photons at $3.2\leq z\leq4.6$ with DESI Y1 Quasars

P. Martini, A. Muñoz-Gutiérrez, J. Moustakas, Jason Xavier Prochaska, A Kremin, Benjamin Alan Weaver, David Sprayberry, D. Bianchi, Ignasi Pérez-Ràfols, Axel de la Macorra, Zechang Sun, E. Sanchez, Siwei Zou, Jeffrey A. Newman, Satya Gontcho A Gontcho, G. Tarlé, Cheng Zhao, Zheng Cai, Arjun T. Dey, Steven P. Ahlen, R. Miquel, Aaron Meisner, David H. Brooks, Hailin Zou, Graziano Rossi, P. Doel, G. Gutierrez, M. Schubnell, J. E. Forero-Romero, K. Honscheid, E. Gaztañaga, T. Claybaugh, S. Juneau, Anning Gao
article en

Abstract

The mean free path of ionizing photons ($\lambda_\mathrm{mfp}^{912}$) in the intergalactic medium (IGM) is a crucial quantity in modelling the ionization state of IGM and the extragalactic ultraviolet background (EUVB), and is widely used in hydrodynamical simulations of galaxies and reionization. We construct the largest quasar spectrum dataset to date -- 12,595 $\mathrm{S/N}>3$ spectra -- using the Y1 observation of Dark Energy Spectroscopic Instrument (DESI) to make the most precise model-independent measurement of the mean free path at $3.2\leq z\leq 4.6$. By stacking the spectra in 17 redshift bins and modelling the Lyman continuum profile, we get a redshift evolution $\lambda_\mathrm{mfp}^{912}\propto(1+z)^{-4.27}$ at $2\leq z\leq 5$, which is much shallower than previous estimate $\lambda_\mathrm{mfp}^{912}\propto(1+z)^{-5.4}$. We then explore the sources of systematic bias, including the choice of intrinsic quasar continuum, the consideration of Lyman series opacity and Lyman limit opacity evolution and the definition of $\lambda_\mathrm{mfp}^{912}$. Combining our results with estimates of $\lambda_\mathrm{mfp}^{912}$ at higher redshifts, we conclude at high confidence that the evolution in $\lambda_\mathrm{mfp}^{912}$ steepens at $z \approx 5$. We interpret this inflection as the transition from the end of HI reionization to a fully ionized plasma which characterizes the intergalactic medium of the past $\sim10$ billion years.

arXiv (Cornell University)
Boston University (US), Institució Catalana de Recerca i Estudis Avançats (ES), Fermi National Accelerator Laboratory (US), Hiroshima Shudo University (JP), High Energy Accelerator Research Organization (JP), Kavli Institute for the Physics and Mathematics of the Universe (JP), University of Pittsburgh (US), Institute for High Energy Physics (ES), University of Milan (IT), University of Michigan (US), Sejong University (KR), National Solar Observatory (US), Institut d'Estudis Espacials de Catalunya (ES), Institut Català de Ciències del Clima (ES), Lickenbrock (US), Michigan United (US), Unidades Centrales Científico-Técnicas (ES), Mylan (Switzerland) (CH), National Astronomical Observatories (CN), Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (ES), State Library of Ohio (US), University College London (GB), University of Portsmouth (GB), Universidad Nacional Autónoma de México (MX), Siena College (US), Netherlands Institute for Radio Astronomy (NL), Universitat Politècnica de Catalunya (ES), Tsinghua University (CN)
National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, Ministerio de Ciencia, Innovación y Universidades, National Natural Science Foundation of China, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Office of Science, Science and Technology Facilities Council, Division of Astronomical Sciences
Openalex Percentile: Top 84%
Galaxies: Formation, Evolution, Phenomena
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