Modeling the HeII Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration

Abstract

The HeII transverse proximity effect - enhanced HeII Lyα transmission in a background sightline caused by the ionizing radiation of a foreground quasar - offers a unique opportunity to probe the emission properties of quasars, in particular the emission geometry (obscuration, beaming) and the quasar lifetime. Building on the foreground quasar survey published in Schmidt+2017, we present a detailed model of the HeII transverse proximity effect, specifically designed to include light travel time effects, finite quasar ages, and quasar obscuration. We post-process outputs from a cosmological hydrodynamical simulation with a fluctuating HeII UV background model, plus the added effect of the radiation from a single bright foreground quasar. We vary the age $t_{\mathrm{age}}$ and obscured sky fractions ${\Omega }_{\mathrm{obsc}}$ of the foreground quasar, and explore the resulting effect on the HeII transverse proximity effect signal. Fluctuations in IGM density and the UV background, as well as the unknown orientation of the foreground quasar, result in a large variance of the HeII Lyα transmission along the background sightline. We develop a fully Bayesian statistical formalism to compare far UV HeII Lyα transmission spectra of the background quasars to our models, and extract joint constraints on $t_{\mathrm{age}}$ and ${\Omega }_{\mathrm{obsc}}$ for the six Schmidt+2017 foreground quasars with the highest implied HeII photoionization rates. Our analysis suggests a bimodal distribution of quasar emission properties, whereby one foreground quasar, associated with a strong HeII transmission spike, is relatively old $(22\mathrm{Myr})$ and unobscured ${\Omega }_{\mathrm{obsc}}<35\%$, whereas three others are either younger than $(10\mathrm{Myr})$ or highly obscured $({\Omega }_{\mathrm{obsc}}>70\%)$.

19 pages, 6 figures, submitted to ApJ

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Cited by in corpus (22)

• Quantitative Constraints on the Reionization History from the IGM Damping Wing Signature in Two Quasars at z > 7
• Time-dependent behaviour of quasar proximity zones at $z\sim 6$
• Detecting and Characterizing Young Quasars II: Four Quasars at $z\sim 6$ with Lifetimes $<10^4$ years
• The first measurement of the quasar lifetime distribution
• The Evolution of the HeII-Ionizing Background at Redshifts 2.3<z<3.8 Inferred from a Statistical Sample of 24 HST/COS HeII Ly$\alpha$ Absorption Spectra
• Estimating the effective lifetime of the $z\sim 6$ quasar population from the composite proximity zone profile
• Evidence for Short $\sim 1$ Myr Lifetimes from the He II Proximity Zones of $z\sim 4$ Quasars
• Discovery of intergalactic bridges connecting two faint $z\sim 3$ quasars
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• Mapping quasar light echoes in 3D with Lyα forest tomography
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• On the diversity of the jet production efficiency in Swift/BAT AGNs
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• Spectral Signatures of Quasar Ages at z~3
• Constraining the ratio of median pixel optical depth profile around z ~ 4 quasars using the longitudinal proximity effect
• Measurements of quasar proximity zones with the Ly$\alpha$ forest of DESI Y1 quasars