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

TL;DR

This study investigates the size and luminosity relationship of Lyα nebulae around high-redshift quasars, revealing a consistent luminosity-area relation and insights into their morphology and potential driving mechanisms.

Contribution

It introduces a novel method to estimate nebula area and asymmetry, establishing a luminosity-area relation and analyzing morphological trends across a large quasar sample.

Findings

Most nebulae are symmetric and bright.

Fainter nebulae tend to be more lopsided.

The luminosity-area relation is consistent across redshifts.

Abstract

Cool ($T\sim10^4$~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 $z\sim2-3$ 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 ${{\rm log}(L_{\rm Ly\alpha}^{\rm Neb})=a_1 log({\rm Area^{Neb})+a_0}}$. 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 $z\sim6$ 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.