A Lyman alpha halo around a quasar at redshift z=6.4

TL;DR

This study reports the discovery of an extensive, luminous Lyman alpha halo around a high-redshift quasar, revealing complex gas kinematics and suggesting photo-ionization by the quasar within a massive dark matter halo.

Contribution

First detailed spectroscopic observation of a luminous Lyman alpha halo at z=6.4, providing insights into gas distribution and quasar environment in the early universe.

Findings

Lyman alpha halo extends over 15 kpc with high luminosity.

Gas kinematics show no evidence of infall or outflow.

Halo likely caused by quasar photo-ionization within a massive dark matter halo.

Abstract

We present long-slit spectroscopic data which reveals extended Lyman alpha emission around the z=6.417 radio-quiet quasar CFHQS J2329-0301. The Lyman alpha emission is extended over 15 kpc and has a luminosity of > 8 x 10^36 W, comparable to the most luminous Lyman alpha halos known. The emission has complex kinematics, in part due to foreground absorption which only partly covers the extended nebula. The velocity ranges from -500 km/s to +500 km/s, with a peak remarkably close to the systemic velocity identified by broad MgII emission of the quasar. There is no evidence for infall or outflow of the halo gas. We speculate that the Lyman alpha emission mechanism is recombination after quasar photo-ionization of gas sitting within a high-mass dark matter halo. The immense Lyman alpha luminosity indicates a higher covering factor of cold gas compared to typical radio-quiet quasars at lower redshift.