COMAP Early Science: VIII. A Joint Stacking Analysis with eBOSS Quasars

Kavli Affiliate: Sarah E. Church

| First 5 Authors: Delaney A. Dunne, Kieran A. Cleary, Patrick C. Breysse, Dongwoo T. Chung, Havard T. Ihle

| Summary:

We present a new upper limit on the cosmic molecular gas density at
$z=2.4-3.4$ obtained using the first year of observations from the CO Mapping
Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 282
quasars selected from the Extended Baryon Oscillation Spectroscopic Survey
(eBOSS) catalog, yielding a 95% upper limit for flux from CO(1-0) line emission
of 0.210 Jy km/s. Depending on the assumptions made, this value can be
interpreted as either an average CO line luminosity $L’_mathrm{CO}$ of eBOSS
quasars of $leq 7.30times10^{10}$ K km pc$^2$ s$^{-1}$, or an average
molecular gas density $rho_mathrm{H_2}$ in regions of the universe containing
a quasar of $leq 2.02times10^8$ M$_odot$ cMpc$^{-3}$. The $L’_mathrm{CO}$
upper limit falls among CO line luminosities obtained from
individually-targeted quasars in the COMAP redshift range, and the
$rho_mathrm{H_2}$ value is comparable to upper limits obtained from other
Line Intensity Mapping (LIM) surveys and their joint analyses. Further, we
forecast the values obtainable with the COMAP/eBOSS stack after the full 5-year
COMAP Pathfinder survey. We predict that a detection is probable with this
method, depending on the CO properties of the quasar sample. Based on these
achieved sensitivities, we believe that this technique of stacking LIM data on
the positions of traditional galaxy or quasar catalogs is extremely promising,
both as a technique for investigating large galaxy catalogs efficiently at high
redshift and as a technique for bolstering the sensitivity of LIM experiments,
even with a fraction of their total expected survey data.

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