Discovery of intergalactic bridges connecting two faint $z\sim3$ quasars

TL;DR

This study uses MUSE/VLT to discover and analyze filamentary Lyα intergalactic bridges connecting a close pair of faint $z\sim3$ quasars, revealing large-scale structures and their properties.

Contribution

First detection and detailed analysis of intergalactic Lyα bridges between faint $z\sim3$ quasars using MUSE, combining observational data with photoionization models.

Findings

Filamentary Lyα structures extend between quasars with surface brightness of 1.8×10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}.

Bridges span from 89 to 600 kpc, but not up to 2.9 Mpc as previously hypothesized.

Absorption features indicate presence of metal-enriched, ionized gas in the circumgalactic and intergalactic medium.

Abstract

We use MUSE/VLT to conduct a survey of $z\sim3$ physical quasar pairs at close separation with a fast observation strategy. Our aim is twofold: (i) explore the Ly$\alpha$ glow around the faint-end of the quasar population; (ii) take advantage of the combined illumination of a quasar pair to unveil large-scale intergalactic structures extending between the two quasars. Here, we report the results for a quasar pair ($z=3.020,3.008$; $i=21.84,22.15$), separated by 11.6 arcsec (or 89 projected kpc). MUSE reveals filamentary Ly$\alpha$ structures extending between the two quasars with an average surface brightness of SB$_{\rm Ly\alpha}=1.8\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Photoionization models of the constraints in the Ly$\alpha$, HeII, and CIV line emissions show that the emitting structures are intergalactic bridges with an extent between $\sim89$ and up to $\sim600$ kpc. Our models rule out the possibility that the structure extends for $\sim 2.9$ Mpc, i.e., the separation inferred from the uncertain systemic redshift difference of the quasars if the difference was only due to the Hubble flow. At the current spatial resolution and surface brightness limit, the average projected width of an individual bridge is about 35 kpc. We also detect a strong absorption in HI, NV, and CIV along the background sight-line at higher $z$, which we interpret as due to at least two components of cool, metal enriched, and relatively ionized CGM or IGM surrounding the quasar pair. Two additional HI absorbers are detected along both quasar sight-lines at $\sim -900$ and $-2800$ km s$^{-1}$ from the system, with the latter having associated CIV absorption only along the foreground quasar sight-line. The absence of galaxies in the MUSE field of view at the redshifts of these two absorbers suggests that they trace large-scale structures or expanding shells in front of the quasar pair.