Bosman, SEI; Becker, GD; (2015) Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641. Monthly Notices of the Royal Astronomical Society , 452 (2) pp. 1105-1111. 10.1093/mnras/stv1336.

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Abstract

Signs of damping-wing absorption attenuating the Lyman α emission line of the first known z ∼ 7 quasar, ULAS J1120+0641, recently provided exciting evidence of a significantly neutral intergalactic medium (IGM). This long-awaited signature of reionization was inferred, in part, from a deficit of flux in the quasar's Lyman α emission line based on predictions from a composite of lower redshift quasars. The composite sample was chosen based on its C IV emission line properties; however, as the original study by Mortlock et al. noted, the composite contained a slight velocity offset in C IV compared to ULAS J1120+0641. Here we test whether this offset may be related to the predicted strength of the Lyman α emission line. We confirm the significant (∼10 per cent at rms) scatter in Lyman α flux for quasars of a given C IV velocity and equivalent width found by Mortlock et al. We further find that among lower redshift objects chosen to more closely match the C IV properties of ULAS J1120+0641, its Lyman α emission falls within the observed distribution of fluxes. Among lower redshift quasars chosen to more closely match in C IV velocity and equivalent width, we find that ULAS J1120+0641 falls within the observed distribution of Lyman α emission line strengths. This suggests that damping-wing absorption may not be present, potentially weakening the case for neutral gas around this object. Larger samples of z > 7 quasars may therefore be needed to establish a clearer picture of the IGM neutral fraction at these redshifts.

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