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Title: Implications of z ~ 6 Quasar Proximity Zones for the Epoch of Reionization and Quasar Lifetimes

In this paper, we study quasar proximity zones in the redshift range $$5.77\leqslant z\leqslant 6.54$$ by homogeneously analyzing 34 medium-resolution spectra, encompassing both archival and newly obtained data, and exploiting recently updated systemic redshift and magnitude measurements. Whereas previous studies found strong evolution of proximity zone sizes with redshift and argued that this provides evidence for a rapidly evolving intergalactic medium (IGM) neutral fraction during reionization, we measure a much shallower trend $$\propto {(1+z)}^{-1.44}$$. We compare our measured proximity zone sizes to predictions from hydrodynamical simulations post-processed with one-dimensional radiative transfer and find good agreement between observations and theory, irrespective of the ionization state of the ambient IGM. This insensitivity to IGM ionization state has been previously noted, and results from the fact that the definition of proximity zone size as the first drop of the smoothed quasar spectrum below the 10% flux transmission level probes locations where the ionizing radiation from the quasar is an order of magnitude larger than the expected ultraviolet ionizing background that sets the neutral fraction of the IGM. Our analysis also uncovered three objects with exceptionally small proximity zones (two have $${R}_{p}\lt 1$$ proper Mpc), which constitute outliers from the observed distribution and are challenging to explain with our radiative transfer simulations. Finally, we consider various explanations for their origin, such as strong absorption line systems associated with the quasar or patchy reionization, but find that the most compelling scenario is that these quasars have been shining for ≲10 5 years.
Authors:
ORCiD logo [1] ;  [2] ; ORCiD logo [2] ; ORCiD logo [3] ;  [4] ;  [1]
  1. Max Planck Inst. for Astronomy, Heidelberg (Germany); Heidelberg Univ. (Germany)
  2. Max Planck Inst. for Astronomy, Heidelberg (Germany); Univ. of California, Santa Barbara, CA (United States)
  3. Univ. of California, Santa Cruz, CA (United States)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 840; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Max Planck Inst. for Astronomy, Heidelberg (Germany)
Sponsoring Org:
USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC-21); USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; dark ages; reionization; first stars; intergalactic medium; data analysis methods; quasar absorption lines
OSTI Identifier:
1379826