An Intensity Mapping Detection of Aggregate CO Line Emission at 3 mm

TL;DR

This paper reports a significant detection of aggregate CO line emission at redshifts 1-5 using line intensity mapping with ALMA and ACA data, providing new insights into cosmic molecular gas density.

Contribution

First detection of molecular gas emission at high redshift via line intensity mapping, combining multiple datasets to measure shot power and estimate cosmic molecular gas density.

Findings

Detected non-zero power at 97.8% and 99.9% confidence levels.

Estimated cosmic molecular gas density of ~10^8 M_sun Mpc^-3 between z=1-3.

Results consistent with previous CO Power Spectrum Survey (COPSS).

Abstract

We present a detection of molecular gas emission at $z\sim1-5$ using the technique of line intensity mapping. We make use of a pair of 3 mm interferometric data sets, the first from the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS), and the second from a series of Atacama Compact Array (ACA) observations conducted between 2016 and 2018, targeting the COSMOS field. At 100 GHz, we measure non-zero power at 97.8% and 99.9% confidence in the ACA and ALMA data sets, respectively. In the joint result, we reject the zero-power hypothesis at 99.99% confidence, finding $\tilde{I}^{2}_{s}(\nu)=770\pm210\ \mu\textrm{K}^2\ \textrm{Hz}\ \textrm{sr}$. After accounting for sample variance effects, the estimated spectral shot power is $\tilde{I}^{2}_{s}(\nu)=1010_{-390}^{+550}\ \mu\textrm{K}^2\ \textrm{Hz}\ \textrm{sr}$. We derive a model for the various line species our measurement is expected to be sensitive to, and estimate the shot power to be $120_{-40}^{+80}\ \mu\textrm{K}^2\ h^{-3}\,\textrm{Mpc}^{3}$, $200^{+120}_{-70}\ \mu\textrm{K}^2\ h^{-3}\,\textrm{Mpc}^{3}$, and $90^{+70}_{-40}\ \mu\textrm{K}^2\ h^{-3}\,\textrm{Mpc}^{3}$ for CO(2-1) at $z=1.3$, CO(3-2) at $z=2.5$, and CO(4-3) at $z=3.6$, respectively. Using line ratios appropriate for high-redshift galaxies, we find these results to be in good agreement with those from the CO Power Spectrum Survey (COPSS). Adopting $\alpha_{\rm CO}=3.6\ M_{\odot}\ (\textrm{K}\ \textrm{km}\ \textrm{s}^{-1}\ \textrm{pc}^{2})^{-1}$, we estimate a cosmic molecular gas density of $\rho_{\textrm{H}_2}(z)\sim 10^{8}\ M_{\odot}\ \textrm{Mpc}^{-3}$ between $z=1-3$.