Implications of z ∼ 6 Quasar Proximity Zones for the Epoch of Reionization and Quasar Lifetimes
- Max-Planck-Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
- Lawrence Berkeley National Laboratory, CA 94720-8139 (United States)
We study quasar proximity zones in the redshift range 5.77⩽z⩽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 ∝(1+z){sup −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{sub p}<1 proper Mpc), which constitute outliers from the observed distribution and are challenging to explain with our radiative transfer simulations. 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{sup 5} years.
- OSTI ID:
- 22872739
- Journal Information:
- Astrophysical Journal, Vol. 840, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Hubble space telescope/cosmic origins spectrograph observations of the quasar Q0302–003: Probing the He II reionization epoch and QSO proximity effects
The Thermal Proximity Effect: A New Probe of the He ii Reionization History and Quasar Lifetime