The SUPERCOLD-CGM survey: II. [\ion{C}{1}]$(1-0)$ emission and the physical conditions of cold gas in Enormous Ly$\alpha$ nebulae at $z\,\sim\,2$

TL;DR

This study uses ALMA and ACA observations to analyze atomic carbon and dust in 10 high-redshift Ly$ ext{alpha}$ nebulae with QSOs, revealing insights into the physical conditions and potential circum-galactic medium gas content.

Contribution

First comprehensive ALMA/ACA survey of [C I](1-0) emission in Enormous Ly$ ext{alpha}$ nebulae hosting QSOs at z~2.2-2.5, exploring molecular gas and CGM properties.

Findings

Detected [C I](1-0) and dust in all targets.

QSOs and companions have high gas densities and intense radiation fields.

Potential [C I](1-0) emission from the circum-galactic medium.

Abstract

We report ALMA and ACA observations of atomic carbon ([\ion{C}{1}]$(1-0)$) and dust continuum in 10 Enormous Ly$\alpha$ Nebulae hosting ultra-luminous Type-I QSOs at $z=2.2-2.5$, as part of the SUrvey of Protocluster ELANe Revealing CO/CI in the Ly$\alpha$ Detected CGM (SUPERCOLD-CGM). We detect [\ion{C}{1}]$(1-0)$ and dust in all ten QSOs and five companion galaxies. We find that the QSOs and companions have higher gas densities and more intense radiation fields than Luminous Infrared galaxies and high-$z$ main sequence galaxies, with the highest values found in the QSOs. By comparing molecular gas masses derived from [\ion{C}{1}]$(1-0)$, CO(4$-$3) and dust continuum, we find that the QSOs and companions display a similar low CO conversion factor of $\alpha_{\rm CO}$\,$\sim$\,0.8 $\rm M_{\sun}$${[\rm K\,km/s\,pc^2]}^{-1}$. After tapering our data to low resolution, the [\ion{C}{1}]$(1-0)$ flux increases for nine QSOs, hinting at the possibility of [\ion{C}{1}]$(1-0)$ in the circum-galactic medium (CGM) on a scale of 16$-$40 kpc. However, the [\ion{C}{1}]$(1-0)$ sensitivity is too low to confirm this for individual targets, except for a tentative (2.7$\sigma$) CGM detection in Q0050+0051{} with M$_{\rm H_2}$\,=\, ($1.0 - 2.8$)$\times 10^{10}$ $\rm M_{\sun}$. The 3$\sigma$ mass limits of molecular CGM for the remaining QSO fields are ($0.2-1.4$)\,$\times$\,10$^{10}$ $\rm M_{\sun}$. This translates into a baryon fraction of $<$0.4-3$\% $ in the molecular CGM relative to the total baryonic halo mass. Our sample also includes a radio-detected AGN, Q1416+2649{}, which shows [\ion{C}{1}]$(1-0)$ and CO(4$-$3) luminosities an order of magnitude fainter for its far-infrared luminosity than other QSOs in our sample, possibly due to a lower molecular gas mass.