Circumgalactic Lyα Nebulae in Overdense Quasar Pair Regions Observed with the Palomar Cosmic Web Imager

Abstract

The recent discovery of enormous Ly α nebulae (ELANe), characterized by physical extents >200 kpc and Ly α luminosities >10 ^44 erg s ^−1 , provides a unique opportunity to study the intergalactic medium and circumgalactic medium 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. 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 α detections, but only one of the four targets meets the classification criteria of an ELANe associated with a QSO pair region ( z ∼ 2.87). The other three sample detections of Ly α 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 α regions shows that the Ly α emission around z ∼ 2 QSO pairs is consistent with emission around individual QSOs at z ∼ 2, which is fainter than that around z ∼ 3 QSOs. A larger sample of Ly α at z ∼ 2 will be needed to determine if there is evidence of redshift evolution when compared to nebular emissions at z ∼ 3 from other studies.

Keywords

• Quasars
• Galaxy evolution
• Emission nebulae
• Lyman-alpha galaxies
• Quasar-galaxy pairs
• Galaxy spectroscopy