Discovery of an Enormous Lyα Nebula in a Massive Galaxy Overdensity at z = 2.3

Abstract

Enormous Ly α nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys or have targeted known sources such as ultraluminous quasi-stellar objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Ly α absorptions, we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at . In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Ly α nebular luminosity of erg s −1 . Above the 2 σ surface brightness limit of SB erg s −1 cm −2 arcsec −2 , this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended C iv and He ii emission on scales. Note that the Ly α , He ii , and C iv emissions all have double-peaked line profiles. Each velocity component has an FWHM of ≈700–1000 km s −1 . We argue that this Ly α nebula could be powered by shocks due to an active galactic nucleus–driven outflow or photoionization by a strongly obscured source.