MAMMOTH-Subaru. II. Diverse Populations of Circumgalactic Ly$\alpha$ Nebulae at Cosmic Noon

TL;DR

This study presents a large, diverse sample of circumgalactic Lyα nebulae at cosmic noon, revealing their association with various galaxy types and evolutionary stages, and providing insights into galaxy formation and evolution.

Contribution

It offers one of the largest blind Lyα nebula samples, including diverse populations and their connection to galaxy evolution, using deep wide-field imaging from the MAMMOTH-Subaru survey.

Findings

117 Lyα nebulae detected with sizes 40-400 kpc.

Most enormous Lyα nebulae are linked to UV-faint galaxies.

Type II ELANe are the majority but often hidden in surveys.

Abstract

Circumgalactic Lyman-alpha (Ly$\alpha$) nebulae are gaseous halos around galaxies exhibiting luminous extended Ly$\alpha$ emission. This work investigates Ly$\alpha$ nebulae from deep imaging of $\sim12~\mathrm{deg}^2$ sky, targeted by the MAMMOTH-Subaru survey. Utilizing the wide-field capability of Hyper Suprime-Cam (HSC), we present one of the largest blind Ly$\alpha$ nebula selections, including QSO nebulae, Ly$\alpha$ blobs, and radio galaxy nebulae down to typical $2\sigma$ Ly$\alpha$ surface brightness of $(5-10)\times10^{-18}\mathrm{~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$. The sample contains 117 nebulae with Ly$\alpha$ sizes of 40 - 400 kpc, and the most gigantic one spans about 365 kpc, referred to as the Ivory Nebula. Combining multiwavelength data, we investigate diverse nebula populations and associated galaxies. We find a small fraction of Ly$\alpha$ nebulae have QSOs ($\sim7\%$), luminous infrared galaxies ($\sim1\%$), and radio galaxies ($\sim 2\%$). Remarkably, among the 28 enormous Ly$\alpha$ nebulae (ELANe) exceeding 100 kpc, about 80\% are associated with UV-faint galaxies ($M_\mathrm{UV} > -22$), categorized as Type II ELANe. We underscore that Type II ELANe constitute the majority but remain largely hidden in current galaxy and QSO surveys. Dusty starburst and obscured AGN activity are proposed to explain the nature of Type II ELANe. The SED of stacking all Ly$\alpha$ nebulae also reveals signs of massive dusty star-forming galaxies with obscured AGNs. We propose a model to explain the dusty nature where the diverse populations of Ly$\alpha$ nebulae capture massive galaxies at different evolutionary stages undergoing violent assembling. Ly$\alpha$ nebulae provide critical insights into the formation and evolution of today's massive cluster galaxies at cosmic noon.