Ubiquitous giant Ly $\alpha$ nebulae around the brightest quasars at $z\sim3.5$ revealed with MUSE

TL;DR

This study uses MUSE to reveal that giant Ly α nebulae are common around bright quasars at z~3.5, showing consistent properties and suggesting widespread cold, dense gas in quasar environments.

Contribution

First blind survey with MUSE demonstrating the ubiquity and properties of giant Ly α nebulae around high-redshift quasars, overcoming previous detection limitations.

Findings

Giant Ly α nebulae (>100 kpc) are present around all surveyed quasars.

Surface brightness profiles follow a power-law with slope ~-1.8.

Gas around quasars is likely cold, dense, and widespread within 50-200 kpc.

Abstract

Direct Ly $\alpha$ imaging of intergalactic gas at $z\sim2$ has recently revealed giant cosmological structures around quasars, e.g. the Slug Nebula (Cantalupo et al. 2014). Despite their high luminosity, the detection rate of such systems in narrow-band and spectroscopic surveys is less than 10%, possibly encoding crucial information on the distribution of gas around quasars and the quasar emission properties. In this study, we use the MUSE integral-field instrument to perform a blind survey for giant Ly $\alpha$ nebulae around 17 bright radio-quiet quasars at $3<z<4$ that does not suffer from most of the limitations of previous surveys. After data reduction and analysis performed with specifically developed tools, we found that each quasar is surrounded by giant Ly $\alpha$ nebulae with projected sizes larger than 100 physical kpc and, in some cases, extending up to 320 kpc. The circularly averaged surface brightness profiles of the nebulae appear very similar to each other despite their different morphologies and are consistent with power laws with slopes $\approx-1.8$. The similarity between the properties of all these nebulae and the Slug Nebula suggests a similar origin for all systems and that a large fraction of gas around bright quasars could be in a relatively "cold" (T$\sim$10$^4$K) and dense phase. In addition, our results imply that such gas is ubiquitous within at least 50 kpc from bright quasars at $3<z<4$ independently of the quasar emission opening angle, or extending up to 200 kpc for quasar isotropic emission.