MAMMOTH-Subaru. II. Diverse Populations of Circumgalactic Lyα Nebulae at Cosmic Noon

Circumgalactic Lyman-alpha (Lyα) nebulae are gaseous halos around galaxies exhibiting luminous extended Lyα emission. This work investigates Lyα nebulae from deep imaging of ∼12 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 Lyα nebula selections, including QSO nebulae, Lyα blobs, and radio galaxy nebulae down to typical 2σ Lyα surface brightness of (5-10)×10^-18 erg s^-1 cm^-2 arcsec^-2. The sample contains 117 nebulae with Lyα sizes of 40 - 400 kpc, and the most gigantic one spans about 365 kpc, referred to as the Ivory Nebula. Combining with multiwavelength data, we investigate diverse nebula populations and associated galaxies. We find a small fraction of Lyα nebulae have QSOs (∼7%), luminous infrared galaxies (∼1%), and radio galaxies (∼ 2%). Remarkably, among the 28 enormous Lyα nebulae (ELANe) exceeding 100 kpc, about 80% are associated with UV-faint galaxies (M_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 Lyα 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 Lyα nebula capture massive galaxies at different evolutionary stages undergoing violent assembling. Lyα nebulae provide critical insights into the formation and evolution of today's massive cluster galaxies at cosmic noon.