Analysis of methods for detecting the proximity effect in quasar spectra

Abstract

Using numerical simulations of structure formation, we investigate multiple methods of determining the strength of the proximity effect in the HI Lyalpha forest. We analyze three high resolution (~10kpc) redshift snapshots (z=4,3,2.25) of a Hydro-Particle-Mesh simulation to obtain realistic absorption spectra of the HI Lyalpha forest. We begin our analysis investigating the intrinsic biases thought to arise in the widely adopted standard technique of combining multiple lines of sight when searching for the proximity effect. We confirm the existence of this biases. We then concentrate on the analysis of the proximity effect along individual lines of sight. We construct the proximity effect strength distribution (PESD) and confirm that the PESD inferred from a simple averaging technique accurately recovers the input strength of the proximity effect at all redshifts. Moreover, the PESD closely follows the behaviors found in observed samples of quasar spectra. However, the PESD obtained from our new simulated sight lines presents some differences to that of simple Monte Carlo simulations. After developing three new theoretical methods of recovering the strength of the proximity effect on individual lines of sight, we compare their accuracy to the PESD from the simple averaging technique. All our new approaches are based on the maximization of the likelihood function, albeit invoking some modifications. The new techniques presented here fail to recover the input proximity effect in an un-biased way. Thus, employing complex 3D simulations, we provide strong evidence in favor of the proximity effect strength distribution obtained from the simple averaging technique, as method of estimating the UV background intensity, free of any biases.

12 pages, 14 figures, accepted by the Astrophysical journal

References in corpus (8)

• A Direct Precision Measurement of the Intergalactic Lyman-alpha Opacity at 2<z<4.2
• A Measurement of Small Scale Structure in the 2.2 < z < 4.2 Lyman-alpha Forest
• A Direct Measurement of the IGM Opacity to HI Ionizing Photons
• An unbiased measurement of the UV background and its evolution via the proximity effect in quasar spectra
• A Flat Photoionization Rate at 2<z<4.2: Evidence for a Stellar-Dominated UV Background and Against a Decline of Cosmic Star Formation Beyond z~3
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Cited by in corpus (5)

• Measurements of the UV background at 4.6 < z < 6.4 using the quasar proximity effect
• Probing the environment of high-z quasars using the proximity effect in projected quasar pairs
• Cosmic Reionization on Computers: Physical Origin of Long Dark Gaps in Quasar Absorption Spectra
• Cosmological radiative transfer for the line-of-sight proximity effect
• Probing Large Scale Ionizing Background Fluctuation with Lyman $\alpha$ Forest and Galaxy Cross-correlation at z=2.4