Discovery of an Enormous Ly$\hat{I}\pm$ nebula in a massive galaxy overdensity at $z=2.3$

Abstract

Enormous Ly$\hat{I}\pm$ 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$\hat{I}\pm$ 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$\hat{I}\pm$ nebular luminosity of $L_{\mathrm{nebula}}=5.1\pm 0.1\times 10^{44}$ erg s${}^{-1}$. Above the 2$\ddot{I}ƒ$ surface brightness limit of SB${}_{\mathrm{Ly}\hat{\mathrm{I}}\pm }=4.8\times 10^{-18}$ 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\ $\lambda 1549$ and \heii\ $\lambda 1640$ emission on $\gtrsim 30$ kpc scales. Note that the Ly$\hat{I}\pm$, \heii\ and \civ\ emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of $\approx 700-1000$ km s${}^{-1}$. We argue that this Ly$\hat{I}\pm$ nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.

corrected a typo of a coordinate in the last published version; and also updated Fig.2