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 $z=1-3$.
Categories: astro-ph.GA astro-ph.CO