Discovery of a protocluster core associated with an enormous Ly$\hat{I}\pm$ Nebula at $z=2.3$

Abstract

The MAMMOTH-1 nebula at $z=2.317$ is an enormous Ly$\hat{I}\pm$ nebula (ELAN) extending to a $\sim$440 kpc scale at the center of the extreme galaxy overdensity BOSS 1441. In this paper, we present observations of the $\mathrm{CO}(3-2)$ and 250 GHz dust-continuum emission from the MAMMOTH-1 using the IRAM NOrthern Extended Millimeter Array. Our observations show that $\mathrm{CO}(3-2)$ emission in this ELAN has not extended widespread emission into the circum- and inter-galactic media. We also find a remarkable concentration of six massive galaxies in $\mathrm{CO}(3-2)$ emission in the central $\sim$100 kpc region of the ELAN. Their velocity dispersions suggest a total halo mass of $M_{200c}\sim 10^{13.1}{M}_{\odot }$, marking a possible protocluster core associated with the ELAN. The peak position of the $\mathrm{CO}(3-2)$ line emission from the obscured AGN is consistent with the location of the intensity peak of MAMMOTH-1 in the rest-frame UV band. Its luminosity line ratio between the $\mathrm{CO}(3-2)$ and $\mathrm{CO}(1-0)$ $r_{3,1}$ is 0.61$\pm$0.17. The other five galaxies have $\mathrm{CO}(3-2)$ luminosities in the range of (2.1-7.1)$\times 10^9$ K $\mathrm{km}{\mathrm{s}}^{-1}$ pc${}^2$, with the star-formation rates derived from the 250GHz continuum of ($<$36)-224 $M_{\odot }$yr${}^{-1}$. Follow-up spectroscopic observations will further confirm more member galaxies and improve the accuracy of the halo mass estimation.

14 pages, 5 figures, 2 tables, accepted for publication in ApJ