The Thermal Proximity Effect: A New Probe of He II Reionization History and the Quasar Lifetime

Abstract

Despite decades of effort, the timing and duration of He II reionization, as well as its morphology and the properties of the quasars believed to drive it, are still not well constrained. In this paper we present a new method to study both He II reionization and quasars via the thermal proximity effect -- the photoelectric heating of the intergalactic medium around quasars when their hard radiation doubly ionizes helium. We post-process a SPH simulation with 1D radiative calculations, and study how the thermal proximity effect depends on the amount of singly ionized helium, $x_{\mathrm{HeII},0}$, which prevailed in the IGM before the quasar turned on, and the characteristic lifetime $t_{\mathrm{Q}}$ for which quasars shine. We find that the amplitude of the temperature boost in the quasar environment depends on $x_{\mathrm{HeII},0}$, with a characteristic value of $\Delta T\simeq 10^4\mathrm{K}$ for an initially singly ionized IGM ($x_{\mathrm{HeII},0}=1.0$), whereas the size of the thermal proximity zone is sensitive to quasar lifetime $t_{\mathrm{Q}}$, with typical sizes of ~100 cMpc for luminous quasars shining for $t_{\mathrm{Q}}=10^8$ yr. This temperature boost is manifest as a change in the thermal broadening of H I absorption lines near the quasar. We introduce a new method based on measuring the Ly$\alpha$ forest power spectrum as a function of distance from the quasar, and conduct Bayesian MCMC analysis to demonstrate that the thermal proximity effect should be easily detectable. For a mock dataset of 50 quasars at z~4, we predict that one can measure $x_{\mathrm{HeII},0}$ to a precision $\approx 0.04$, and $t_{\mathrm{Q}}$ to a precision of $\approx 0.1$ dex. By applying our formalism to existing high-resolution Ly$\alpha$ forest spectra of quasars at $3.1\lesssim z\lesssim 5.0$, one should be able to detect the thermal proximity effect, and reconstruct the full reionization history of He II.

23 pages, 16 Figures, accepted to ApJ, two sections and one figure added

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Cited by in corpus (20)

• Quantitative Constraints on the Reionization History from the IGM Damping Wing Signature in Two Quasars at z > 7
• Predicting Quasar Continua Near Lyman-$\alpha$ with Principal Component Analysis
• The Role of Galaxies and AGN in Reionising the IGM - I: Keck Spectroscopy of 5 < z < 7 Galaxies in the QSO Field J1148+5251
• The 21cm bispectrum as a probe of non-Gaussianities due to X-ray heating
• Detecting and Characterizing Young Quasars II: Four Quasars at $z\sim 6$ with Lifetimes $<10^4$ years
• Intensity mapping with SDSS/BOSS Lyman-alpha emission, quasars and their Lyman-alpha forest
• Time-dependent behaviour of quasar proximity zones at $z\sim 6$
• The first measurement of the quasar lifetime distribution
• Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn
• Constraints on QSO emissivity using H I and He II Lyman alpha forest
• Evidence for Short $\sim 1$ Myr Lifetimes from the He II Proximity Zones of $z\sim 4$ Quasars
• Modeling the HeII Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration
• How proper are Bayesian models in the astronomical literature?
• Mapping quasar light echoes in 3D with Lyα forest tomography
• Dating individual quasars with the HeII proximity effect
• Ly$\alpha$ forest power spectrum as an emerging window into the epoch of reionization and cosmic dawn
• Photometric IGM Tomography: Efficiently Mapping Quasar Light Echoes with Deep Narrow Band Imaging
• High-redshift AGN population in radiation-hydrodynamics simulations
• New simulation of QSO X-ray heating during the Cosmic Dawn
• Measuring photo-ionization rate and mean free path of HeII ionizing photons at $2.5\le z\le 3.6$: Evidence for late and rapid HeII reionization Part-II