Measuring the Mean Free Path of H <scp>i</scp> Ionizing Photons at 3.2 ≤ <i>z</i> ≤ 4.6 with DESI Y1 Quasars
Abstract The mean free path of ionizing photons in the intergalactic medium (IGM; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">mfp</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>912</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) is a crucial quantity in modeling the ionization state of the IGM and the extragalactic ultraviolet background, and it is widely used in hydrodynamical simulations of galaxies and reionization. We construct the largest quasar spectrum data set to date—12,595 signal-to-noise ratio > 3 spectra—using the Y1 observations of the Dark Energy Spectroscopic Instrument, to make the most precise model-independent measurement of the mean free path at 3.2 ≤ z ≤ 4.6. By stacking the spectra in 17 redshift bins and modeling the Lyman-continuum profile, we get a redshift evolution <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">mfp</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>912</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>z</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4.27</mml:mn> </mml:mrow> </mml:msup> </mml:math> at 2 ≤ z ≤ 5, which is much shallower than the previous estimate, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">mfp</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>912</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>z</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5.4</mml:mn> </mml:mrow> </mml:msup> </mml:math> . We then explore the sources of systematic bias, including the choice of the intrinsic quasar continuum, the consideration of Lyman-series opacity and Lyman-limit opacity evolution, and the definition of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">mfp</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>912</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . Combining our results with estimates of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">mfp</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>912</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> at higher redshifts, we conclude at high confidence that the evolution in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">mfp</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>912</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> steepens at z ≈ 5. We interpret this inflection as the transition from the end of H i reionization to a fully ionized plasma that characterizes the IGM of the past ∼10 billion yr.
Authors
- D. Brooks (ORCID: https://orcid.org/0000-0002-8458-5047)
- Paul Martini (ORCID: https://orcid.org/0000-0002-4279-4182)
- A. Muñoz-Gutiérrez (ORCID: https://orcid.org/0000-0002-3565-0148)
- S. Juneau (ORCID: https://orcid.org/0000-0002-0000-2394)
- Jeffrey A. Newman (ORCID: https://orcid.org/0000-0001-8684-2222)
- Gregory Tarlé (ORCID: https://orcid.org/0000-0003-1704-0781)
- Jason Xavier Prochaska (ORCID: https://orcid.org/0000-0002-7738-6875)
- Benjamin Alan Weaver (ORCID: https://orcid.org/0000-0003-3687-3463)
- David Sprayberry (ORCID: https://orcid.org/0000-0001-7583-6441)
- D. Bianchi (ORCID: https://orcid.org/0000-0001-9712-0006)
- Ignasi Pérez-Ràfols (ORCID: https://orcid.org/0000-0001-6979-0125)
- Axel de la Macorra (ORCID: https://orcid.org/0000-0002-1769-1640)
- Zechang Sun (ORCID: https://orcid.org/0000-0002-8246-7792)
- Siwei Zou (ORCID: https://orcid.org/0000-0002-3983-6484)
- Anthony Kremin (ORCID: https://orcid.org/0000-0001-6356-7424)
- Eusebio Sanchez (ORCID: https://orcid.org/0000-0002-9646-8198)
- Satya Gontcho A Gontcho (ORCID: https://orcid.org/0000-0003-3142-233X)
- Cheng Zhao (ORCID: https://orcid.org/0000-0002-1991-7295)
- K. Honscheid (ORCID: https://orcid.org/0000-0002-6550-2023)
- Zheng Cai (ORCID: https://orcid.org/0000-0001-8467-6478)
- Arjun T. Dey (ORCID: https://orcid.org/0000-0002-4928-4003)
- J. E. Forero-Romero (ORCID: https://orcid.org/0000-0002-2890-3725)
- Steven P. Ahlen (ORCID: https://orcid.org/0000-0001-6098-7247)
- Aaron Meisner (ORCID: https://orcid.org/0000-0002-1125-7384)
- R. Miquel (ORCID: https://orcid.org/0000-0002-6610-4836)
- John Moustakas (ORCID: https://orcid.org/0000-0002-2733-4559)
- Hu Zou (ORCID: https://orcid.org/0000-0002-6684-3997)
- Graziano Rossi
- P. Doel (ORCID: https://orcid.org/0000-0002-6397-4457)
- G. Gutierrez
- M. Schubnell
- E. Gaztañaga (ORCID: https://orcid.org/0000-0001-9632-0815)
- T. Claybaugh
- Anning Gao
Publication Details
- Journal
- The Astrophysical Journal Letters
- Published
- 2025-03-05
- DOI
- https://doi.org/10.3847/2041-8213/adb48f
- Citations
- 1
- Primary Topic
- Galaxies: Formation, Evolution, Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 1.15