Revealing the Gas Recycling in the Circumgalactic Medium (CGM) Utilizing a Luminous Lya Nebula around a Type II Quasar at z = 2.6 with the Keck Cosmic Web Imager (KCWI)

• Published in: The Astrophysical journal Vol. 952; no. 2; pp. 124 - 137
• Main Authors: Zhang, Shiwu, Cai, Zheng, Xu, Dandan, Afruni, Andrea, Wu, Yunjing, Wang, Wuji, Battaia, Fabrizio Arrigoni, Li, Mingyu, Wang, Sen, Bi, Xianzhi
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-08-2023; IOP Publishing
• Subjects: Absorption; Astrophysics; Circumgalactic medium; Density ratio; Emissions; Galactic evolution; Galaxies; Galaxy accretion; High-redshift galaxies; Luminosity; Metallicity; Nebulae; Photoionization; Quasars; Recycling; Spectra; Spectroscopic observation; Star & galaxy formation; Star formation; Velocity; Velocity distribution; Webs
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/acd760

Abstract
How galaxies acquire material from the circumgalactic medium is a key question in galaxy evolution. Recent observations and simulations show that gas recycling could be an important avenue for star formation. This paper presents Keck Cosmic Web Imager integral field unit spectroscopic observations on a type II quasar, Q1517 + 0055 at
z
= 2.65, a pilot study of our Ly
α
nebulae sample at
z
≈ 2. We revealed diffuse emission of the Ly
α
1216, He
ii
1640, and C
iv
1549 on the projected physical scale of 122, 45, and 79 kpc, respectively. The total Ly
α
luminosity is
L
Ly
α
= 3.04 ± 0.02 × 10
44
erg s
−1
. The line ratio diagnostics shows that He II/Ly
α
≈ 0.08, and C IV/Ly
α
≈ 0.28, consistent with the photoionization including recombination and photon pumping. We also identify the associated H
i
and C
iv
absorption from the spectra. By fitting the spectra, we derive both the column density and the velocity. We find that the velocity profile from both the absorption and the He
ii
emission exhibit increasing trends. Moreover, both the line ratio diagnostic from the emission and the column density ratio from the absorption confirm that the cool gas metallicity is ≥
Z
⊙
. From detailed modeling and estimation, gas recycling might be a more plausible interpretation compared with the scenario of a powerful outflow.