2025/10/27 by Dunne, D. A., Cleary, K. A., Lunde, J. G. S. +16 · 2 citations
#Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2510.23568
We present a stack of data from the second season of the CO Mapping Array Project (COMAP) Pathfinder 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∼3. COMAP's Season 2 represents a 3× increase in map-level sensitivity over the previous Early Science data release. We do not detect any CO emission in the stack, instead finding an upper limit of 10.0× 1010 \mathrmK km s-1 pc2 at 95% confidence within an ∼ 18 cMpc 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).