Characterizing the Circumgalactic Medium of Quasars at z $\sim$ 2.2 through H$\alpha$ and Ly$\alpha$ Emission

Abstract

The discovery of giant quasar Ly$\alpha$ nebulae at $z>2$ has opened up the possibility to directly study in emission the Circumgalactic and Intergalactic Medium (CGM/IGM). However, the resonant nature of the Ly$\alpha$ line and its different emission mechanisms hamper the ability to constrain both the kinematics and physical properties of the CGM/IGM. Here, we present results of a pilot project aiming at the detection of CGM H$\alpha$ emission, a line which does not suffer from these limitations. To this end, we first used KCWI to detect Ly$\alpha$ emission around three bright quasars with $2.25<z<2.27$, a range which is free from bright IR sky lines for H$\alpha$, and then selected the most extended nebula for H$\alpha$ follow-up with MOSFIRE. Within the MOSFIRE slit, we detected H$\alpha$ emission extending up to 20 physical kpc with a total H$\alpha$ flux of F${}_{\text{H}\alpha }$=(9.5 $\pm$ 0.9) $\times$ 10${}^{-18}$ erg s${}^{-1}$ cm${}^{-2}$. Considering the Ly$\alpha$ flux in the same region, we found F${}_{\text{Ly}\alpha }$/F${}_{\text{H}\alpha }$=3.7 $\pm$ 0.3 consistent with that obtained for the Slug Nebula at z$=2.275$ and with recombination radiation. This implies high densities or a very broad density distribution within the CGM of high-redshift quasars. Moreover, the H$\alpha$ line profile suggests the presence of multiple emitting components overlapping along our line-of-sight and relatively quiescent kinematics, which seems incompatible with either quasar outflows capable of escaping the potential well of the host halo or disk-like rotation in a massive halo ($>10^{12}$M${}_{\odot }$).

15 pages, 12 figures, 2 tables

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Cited by in corpus (2)

• KBSS-InCLOSE I: Design and First Results from the Inner CGM of QSO Line Of Sight Emitting Galaxies at z~2-3
• ODIN: A New Lyman Alpha Blob Selection Method, Sample, and Statistical Analysis at $z\sim 3.1$