Discovery of an Enormous Ly$\alpha$ nebula in a massive galaxy overdensity at $z=2.3$

TL;DR

This paper reports the discovery of an extremely luminous and large Ly$ extalpha$ nebula in a massive galaxy overdensity at redshift 2.3, revealing insights into galaxy formation and cosmic structure at high redshift.

Contribution

It introduces a new method using CoSLAs to identify high-redshift galaxy overdensities and reports the discovery of the most luminous Ly$ extalpha$ nebula associated with a galaxy overdensity.

Findings

The nebula has the highest diffuse Ly$ extalpha$ luminosity of 5.1×10^{44} erg s^{-1}.

The nebula extends over 442 kpc and shows extended emission in extciv\\ and extheii\\ lines.

The emission lines have double-peaked profiles with FWHM of 700-1000 km s^{-1}.

Abstract

Enormous Ly$\alpha$ 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$\alpha$ absorptions (CoSLAs), we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at $z=2-3$ (Cai et al. 2016a). 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$\alpha$ nebular luminosity of $L_{\rm{nebula}}=5.1\pm0.1\times10^{44}$ erg s$^{-1}$. Above the 2$\sigma$ surface brightness limit of SB$_{\rm{Ly\alpha}}= 4.8\times10^{-18}$ 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 \civ\ $\lambda1549$ and \heii\ $\lambda1640$ emission on $\gtrsim30$ kpc scales. Note that the Ly$\alpha$, \heii\ and \civ\ emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of $\approx700 - 1000$ km s$^{-1}$. We argue that this Ly$\alpha$ nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.