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

Abstract

We present a detection of molecular gas emission at $z\sim 1-5$ 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 ${\tilde{I}}_s^2(\nu )=770\pm 210\mu {\text{K}}^2\text{Hz}\text{sr}$. After accounting for sample variance effects, the estimated spectral shot power is ${\tilde{I}}_s^2(\nu )=1010_{-390}^{+550}\mu {\text{K}}^2\text{Hz}\text{sr}$. We derive a model for the various line species our measurement is expected to be sensitive to, and estimate the shot power to be $120_{-40}^{+80}\mu {\text{K}}^2{h}^{-3}{\text{Mpc}}^3$, $200_{-70}^{+120}\mu {\text{K}}^2{h}^{-3}{\text{Mpc}}^3$, and $90_{-40}^{+70}\mu {\text{K}}^2{h}^{-3}{\text{Mpc}}^3$ 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 ${\alpha }_{\mathrm{CO}}=3.6M_{\odot }(\text{K}\text{km}{\text{s}}^{-1}{\text{pc}}^2{)}^{-1}$, we estimate a cosmic molecular gas density of ${\rho }_{{\text{H}}_2}(z)\sim 10^8{M}_{\odot }{\text{Mpc}}^{-3}$ between $z=1-3$.

25 pages, 12 figures, 6 tables, 2 appendices. Accepted for publication in ApJ

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