Circumgalactic Ly$\alpha$ Nebulae in Overdense Quasar Pair Regions Observed with the Palomar Cosmic Web Imager

TL;DR

This study investigates the presence and properties of enormous Ly$ ext{α}$ nebulae (ELANe) around quasar pairs at high redshift, finding one confirmed ELAN and analyzing Ly$ ext{α}$ emission characteristics in overdense regions.

Contribution

First observational analysis of Ly$ ext{α}$ nebulae around QSO pairs at z~2, identifying one ELAN and examining its kinematics and surface brightness profiles.

Findings

One confirmed ELAN associated with a QSO pair at z~2.87.

Ly$ ext{α}$ emission around z~2 QSO pairs is fainter than at z~3.

Evidence suggests some ELANs are powered by AGN outflows.

Abstract

The recent discovery of enormous Ly$\alpha$ nebulae (ELANe), characterized by physical extents $>200$ kpc and Ly$\alpha$ luminosities $>10^{44}$ erg s$^{-1}$, provide a unique opportunity to study the intergalactic and circumgalactic medium (IGM/CGM) in distant galaxies. Many existing ELANe detections are associated with local overdensities of active galactic nuclei (AGN). We have initiated a search for ELANe around regions containing pairs of quasi-stellar objects (QSOs) using the Palomar Cosmic Web Imager (PCWI). The first study of this search, Cai et al., presented results of ELAN0101+0201 which was associated with a QSO pair at $z=2.45$. In this study, all targets residing in QSO pair environments analyzed have Ly$\alpha$ detections, but only one of the four targets meets the classification criteria of an ELANe associated with a QSO pair region (z$\sim2.87$). The other three sample detections of Ly$\alpha$ nebulae do not meet the size and luminosity criteria to be classified as ELANe. We find kinematic evidence that the ELANe J1613, is possibly powered {mostly by AGN outflows.} The analysis of circularly-averaged surface brightness profiles of emission from the Ly$\alpha$ regions show that the {Ly$\alpha$ emission around $z\sim2$ QSO pairs is consistent with emission around individual QSOs at $z\sim2$, which is fainter than that around $z\sim3$ QSOs. A larger sample of Ly$\alpha$ at z$\sim$2 will be needed to determine if there is evidence of redshift evolution when compared to nebular emissions at z$\sim$3 from other studies.