Metal Enrichment in the Circumgalactic Medium and Lyα Halos around Quasars at z ∼ 3

• Published in: The Astrophysical journal 2020-07, Vol.898 (1), p.26
• Main Authors: Guo, Yucheng, Maiolino, Roberto, Jiang, Linhua, Matsuoka, Kenta, Nagao, Tohru, Dors, Oli Luiz, Ginolfi, Michele, Henden, Nick, Bennett, Jake, Sijacki, Debora, Puchwein, Ewald
• Format: Article
• Language: English
• Subjects: Astrophysics; Cubes; Emission; Emission lines; Enrichment; Galactic halos; Halos; Intergalactic media; Metallicity; Nebulae; Object recognition; Quasars; Red shift
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab9b7f

Deep observations have detected extended Ly α emission nebulae surrounding tens of quasars at redshift 2–6. However, the metallicity of such extended halos is still poorly understood. We perform a detailed analysis on a large sample of 80 quasars at z  ∼ 3 based on MUSE-VLT data. We find clear evidence of extended emission of the UV nebular lines such as  C iv   λ 1549 or  He ii   λ 1640 for about 20% of the sample, while  C iii ]  λ 1909 is only marginally detected in a few objects. By stacking the cubes, we detect emission of C iv , He ii , and C iii ] out to a radius of about 45 kpc. C iv and He ii  show a radial decline much steeper than Ly α , while C iii ] shows a shallower profile similar to Ly α in the inner 45 kpc. We infer that the average metallicity of the circumgalactic gas within the central 30–50 kpc is ∼0.5 solar, or even higher. However, we also find evidence of a component of the Ly α halos, which has much weaker metal emission lines relative to Ly α . We suggest that the high metallicity of the circumgalactic medium within the central 30–50 kpc is associated with chemical pre-enrichment by past quasar-driven outflows and that there is a more extended component of the circumgalactic medium that has much lower metallicity and is likely associated with near-pristine gas accreted from the intergalactic medium. We show that our observational results are in good agreement with the expectations of the FABLE zoom-in cosmological simulations.