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

Abstract

Cool (T ∼ 104 K) gas is commonly observed around z > 2 quasars as traced by extended Lyα emission. These large-scale nebulae are usually studied using circularly averaged surface-brightness profiles, which suppress information on morphological differences. Here, we revisit the Lyα 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(LLyαNeb)=a1log(AreaNeb)+a0 . Most nebulae are symmetric and bright, the most lopsided ones being the faintest and less extended. The enormous Lyα 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.