Revealing the Gas Recycling in the Circumgalactic Medium (CGM) Utilizing a Luminous Ly$\alpha$ Nebula Around a Type-II Quasar at z=2.6 with the Keck Cosmic Web Imager (KCWI)

• 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: 26-07-2023
• Subjects: Physics - Astrophysics of Galaxies; Physics - Cosmology and Nongalactic Astrophysics
• DOI: 10.48550/arxiv.2307.14224

How galaxies acquire material from the circumgalactic medium (CGM) 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 (KCWI) integral field unit spectroscopic observations on
a type-II quasar, Q1517+0055 at z = 2.65, a pilot study of our Ly${\alpha}$
nebulae sample at $z\approx 2$. We revealed diffuse emission of the Ly$\alpha$
1216, HeII 1640, and CIV 1549 on the projected physical scale of 122 kpc, 45
kpc, and 79 kpc, respectively. The total Ly$\alpha$ luminosity is L$_{\rm
Ly\alpha}$ = $3.04\pm 0.02 \times 10^{44}$ erg s$^{-1}$. The line ratio
diagnostics shows that HeII/Ly$\alpha$ $\approx$0.08 and CIV/Ly$\alpha$
$\approx$0.28, consistent with the photoionization including recombination and
photon pumping. We also identify the associated HI and CIV 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
HeII 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 $\geq Z_{\odot}$. From detailed
modeling and estimation, gas recycling might be a more plausible interpretation
compared with the scenario of a powerful outflow.