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Inspiraling Halo Accretion Mapped in Lyman-$\alpha$ Emission around a $z\sim3$ Quasar

, , , , , , , and .
(2017)cite arxiv:1709.08228Comment: 39 pages with 27 figures and 5 appendices. Accepted to MNRAS.

Abstract

In an effort to search for Ly$\alpha$ emission from circum- and intergalactic gas on scales of hundreds of kpc around $z\sim3$ quasars, and thus characterise the physical properties of the gas in emission, we have initiated an extensive fast-survey with the Multi Unit Spectroscopic Explorer (MUSE): Quasar Snapshot Observations with MUse: Search for Extended Ultraviolet eMission (QSO MUSEUM). In this work, we report the discovery of an enormous Ly$\alpha$ nebula (ELAN) around the quasar SDSS~J102009.99+104002.7 at $z=3.164$, which we followed-up with deeper MUSE observations. This ELAN spans $\sim297$ projected kpc, has an average Ly$\alpha$ surface brightness $SB_Ly\alpha\sim 6.04\times10^-18$ erg s$^-1$ cm$^-2$ arcsec$^-2$ (within the $2\sigma$ isophote), and is associated with an additional four, previously unknown embedded sources: two Ly$\alpha$ emitters and two faint active galactic nuclei (one Type-1 and one Type-2 quasar). By mapping at high significance the line-of-sight velocity in the entirety of the observed structure, we unveiled a large-scale coherent rotation-like pattern spanning $\sim300$ km s$^-1$ with a velocity dispersion of $<270$ km s$^-1$, which we interpret as a signature of the inspiraling accretion of substructures within the quasar's host halo. Future multiwavelength data will complement our MUSE observations, and are definitely needed to fully characterise such a complex system. None the less, our observations reveal the potential of new sensitive integral-field spectrographs to characterise the dynamical state of diffuse gas on large scales in the young Universe, and thereby witness the assembly of galaxies.

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