The luminosity-area relation of $z>2$ quasars' Ly$\alpha$ nebulae

Abstract

Cool ($T\sim 10^4$~K) gas is commonly observed around $z>2$ quasars as traced by extended Ly$\alpha$ emission. These large-scale nebulae are usually studied using circularly averaged surface brightness profiles, which suppress information on morphological differences. Here, we revisit the Ly$\alpha$ nebulae around 78 $z\sim 2-3$ quasars to obtain a novel estimate of their area and asymmetry using a common redshift-corrected surface-brightness threshold. We find a luminosity-area relation of the form $\log (L_{\mathrm{Ly}\alpha }^{\mathrm{Neb}})=a_{1}log(\mathrm{Are}{\mathrm{a}}^{\mathrm{Neb}})+{\mathrm{a}}_0$. Most nebulae are symmetric and bright, the most lopsided ones being the faintest and the less extended. The Enormous Lyman-Alpha Nebulae, asymmetric due to the presence of active companions, are the exceptions to this trend. By using simulations able to reproduce $z\sim 6$ quasar's nebulae, we show that the observed relation should not vary with redshift. Finally, we discuss possible mechanisms that drive the relation and future work needed to constrain them.

7 pages, accepted for publication in ApJ Letters

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• Circumgalactic Ly$\alpha$ emission around submillimeter-bright galaxies with different quasar contributions
• QSO MUSEUM II: Search for extended Ly$\alpha$ emission around eight $z\sim 3$ quasar pairs
• QSO MUSEUM III: the circumgalactic medium in Ly$\alpha$ emission around 120 $z\sim 3$ quasars covering the SDSS parameter space. Witnessing the instantaneous AGN feedback on halo scales
• J-PAS: Discovery of RaJav, a bright spatially extended Ly$\alpha$ Nebula at z=2.25