What question did this study set out to answer?

This research aims to analyze CO emission in the vicinity of quasars using data from the COMAP project.

February 17, 2026

COMAP Pathfinder -- Season 2 results. IV. A stack on eBOSS/DESI quasars

Key Points

This research aims to analyze CO emission in the vicinity of quasars using data from the COMAP project.
Conducted a stack analysis of data from the second season of COMAP targeting eBOSS and DESI quasars.
Evaluated upper limits of CO emission against theoretical models while addressing multiple sources of uncertainty.
Measured CO luminosity in relation to environmental factors surrounding quasars.
No detection of CO emission was found in the stacked data.
An upper limit of CO luminosity was established at 10.0 with 95% confidence.
Indications of a ∼ 3 σ tension were observed when comparing limits to the brightest stack models.

Abstract

We present a stack of data from the second season of the CO Mapping Array Project (COMAP) on the positions of quasars from eBOSS and DESI. COMAP is a line intensity mapping (LIM) experiment targeting dense molecular gas via CO (1--0) emission at z box. We compare this upper limit to models of the CO emission stacked on quasars and find a tentative (∼ 3 σ) tension between the limit and the brightest stack models after accounting for a suite of additional sources of experimental attenuation and uncertainty, including quasar velocity uncertainty, pipeline signal loss, cosmic variance, and interloper emission in the LIM data. The COMAP-eBOSS/DESI stack is primarily a measurement of the CO luminosity in the quasars' wider environment, and is therefore potentially subject to environmental effects such as feedback. With our current simple models of the galaxy-halo connection, we are thus unable to confidently rule out any models of cosmic CO with the stack alone. Conversely, the stack's sensitivity to these large-scale environmental effects has the potential to make it a powerful tool for galaxy formation science, once we are able to constrain the average CO luminosity via the auto-power spectrum (a key goal of COMAP). Season 2 of COMAP represents a factor of three increase in map-level sensitivity over the previous early science data release. We do not detect any CO emission in the stack; instead, we find an upper limit of 10. 0 at 95% confidence within an ∼ 18 10^ 10 K km -1 pc² cMpc

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