Ionization bias and the ghost proximity effect near $z\gtrsim 6$ quasars in the shadow of proximate absorption systems

Abstract

The larger-than-expected scatter in the opacity of the Ly$\alpha$ forest suggests that the metagalactic ionizing background is strongly fluctuating at $z>5.5$. Models for ionizing background fluctuations predict a strong positive bias on large scales, so the environments of massive $>10^{12}{\mathrm{M}}_{\odot }$ dark matter halos, e.g. $z\sim 6$ quasar hosts, would be ideal laboratories to constrain the sources of ionizing photons. While the quasars themselves should overwhelm any plausible ionizing photon contribution from neighboring galaxies, proximate damped Ly$\alpha$ absorbers (DLAs) have recently been discovered in the foreground of $z\sim 6$ quasars, and the Ly$\alpha$ forest in the shadow of these DLAs could probe the local ionization environment. Using Gpc${}^3$ simulations of $z=6$ ionizing background fluctuations, we show that while the Ly$\alpha$ forest signal from ionization bias around a quasar host halo should be strong, it is likely suppressed by the associated intergalactic matter overdensity. We also show that the quasar itself may still overwhelm the clustering signal via a "ghost" of the proximity effect from the quasar radiation causing a large-scale bias in the ionizing photon mean free path. This ghost proximity effect is sensitive to the lifetime and geometry of quasar emission, potentially unlocking a new avenue for constraining these fundamental quasar properties. Finally, we present observations of a $z\sim 6$ quasar with a proximate DLA which shows a strong excess in Ly$\alpha$ forest transmission at the predicted location of the ghost proximity effect.

12 pages, 17 figures, submitted to MNRAS

References in corpus (26)

• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Efficient Simulations of Early Structure Formation and Reionization
• Evidence of patchy hydrogen reionization from an extreme Ly$\alpha$ trough below redshift six
• The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at $z\sim 3$
• The first ultraviolet quasar stacked spectrum at z=2.4 from WFC3
• Large Lyman-alpha opacity fluctuations and low CMB tau in models of late reionization with large islands of neutral hydrogen extending to z<5.5
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6
• New constraints on Lyman-α opacity with a sample of 62 quasars at z > 5.7
• Long troughs in the Lyman-$\alpha$ forest below redshift 6 due to islands of neutral hydrogen
• The Opacity of the Intergalactic Medium Measured Along Quasar Sightlines at $z\sim 6$
• HST-COS Observations of AGN. II. Extended Survey of Ultraviolet Composite Spectra from 159 Active Galactic Nuclei
• The Faint End of the z=5 Quasar Luminosity Function from the CFHTLS
• Evidence for Large-Scale Fluctuations in the Metagalactic Ionizing Background Near Redshift Six
• The Evolution of O I over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium
• 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
• Time-dependent behaviour of quasar proximity zones at $z\sim 6$
• Witnessing galaxy assembly at the edge of the reionization epoch
• A metal-poor damped Ly-alpha system at redshift 6.4
• Determining the Nature of Late Gunn-Peterson Troughs with Galaxy Surveys
• Modeling the HeII Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration
• On the Search for Quasar Light Echoes
• Constraints On Duty Cycles Of Quasars At Z $\sim$ 6

Cited by in corpus (9)

• The Cosmic Baryon and Metal Cycles
• Hydrogen reionisation ends by $z=5.3$: Lyman-$\alpha$ optical depth measured by the XQR-30 sample
• A Significantly Neutral Intergalactic Medium Around the Luminous z=7 Quasar J0252-0503
• The X-SHOOTER/ALMA sample of Quasars in the Epoch of Reionization. I. NIR spectral modeling, iron enrichment and broad emission line properties
• Three Lyman-alpha emitting galaxies within a quasar proximity zone at z=5.8
• 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
• Improved treatments of the ionizing photon mean free path in semi-numerical simulations of reionization
• Effects of Small-Scale Absorption Systems on Neutral Islands during the Late Epoch of Reionization