The Luminosity–Area Relation of z > 2 Quasars’ Lyα Nebulae

Cool ( T ∼ 10 4 K) gas is commonly observed around z > 2 quasars as traced by extended Ly α 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 α nebulae around 78 z ∼ 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 Ly α Neb ) = a 1 log ( Area Neb ) + a 0 . Most nebulae are symmetric and bright, the most lopsided ones being the faintest and less extended. The enormous Ly α nebulae, asymmetric due to the presence of active companions, are the exceptions to this trend. By using simulations able to reproduce z ∼ 6 quasars’ 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.