An Intensity Mapping Constraint on the CO-Galaxy Cross Power Spectrum at Redshift ~ 3

Abstract

The abundance of cold molecular gas plays a crucial role in models of galaxy evolution. While deep spectroscopic surveys of CO emission lines have been a primary tool for measuring this abundance, the difficulty of these observations has motivated alternative approaches to studying molecular gas content. One technique, line intensity mapping, seeks to constrain the average molecular gas properties of large samples of individually undetectable galaxies through the CO brightness power spectrum.Here we present constraints on the cross-power spectrum between CO intensity maps and optical galaxy catalogs. This cross-measurement allows us to check for systematic problems in CO intensity mapping data, and validate the data analysis used the auto-power spectrum measurement of the CO Power Spectrum Survey. We place a 2σ upper limit on the band-averaged CO-galaxy cross-power of P × < 540 µK h −3 Mpc 3 . Our measurement favors a non-zero T CO at around 90% confidence and gives an upper limit on the mean molecular gas density at z ∼ 2.6 of 7.7 × 10 8 M Mpc −3 . We forecast the expected cross-power spectrum by applying a number of literature prescriptions for the CO luminosity to halo mass relation to a suite of mock light cones. Under the most optimistic forecasts the cross-spectrum could be detected with only moderate extensions of the data used here, while more conservative models could be detected with a factor of 10 increase in sensitivity. Ongoing CO intensity mapping experiments will target fields allowing extensive cross correlation analysis and should reach the sensitivity required to detect the cross-spectrum signal.

A Beginner's Guide to Line Intensity Mapping Power Spectra

“…The HI intensity has been detected through cross-correlations between radio telescopes and existing galaxy redshift surveys (Chang et al, 2010;Masui et al, 2013;Switzer et al, 2013;Anderson et al, 2018;Wolz et al, 2021). Similar studies were then performed with other lines, and preliminary detections have been made of [CII] (Pullen et al, 2018;Yang et al, 2019), CO (Keating et al, 2020;Keenan et al, 2021), and Lyα (Croft et al, 2018). These first-generation detections have inspired confidence in our ability to overcome challenging systematics, while also providing novel information constraining galaxy evolution models.…”

Precision tests of CO and [CII] power spectra models against simulated intensity maps

“…Several recent works highlighted the potential of LIM for cosmology, including forecasts of its constraining power for probing nature of dark matter [18,19] and dark energy [20], primordial non-Gaussianity [21][22][23][24], and properties of neutrinos [16,25,26]. Tentative recent detections of CO intensity shot power spectrum by COPSS [27][28][29] and mmIME [30] surveys, and [CII] emission via crosscorrelation between Planck and SDSS quasars [12] have further amplified the growing observational and theoretical interest in LIM. Looking ahead, in addition to several 21 cm surveys, a wide range of ground-and space-based experiments (e.g., COMAP [10], TIME [31], CON-CERTO [32], CCAT-prime [33] EXCLAIM [34], SPHEREx [3] and CDIM [35]) will provide higher-fidelity detection of line intensity fluctuations at different redshifts from several emission lines.…”

Analytical covariance between voxel intensity distributions and line-intensity mapping power spectra

“…In addition, several other line transitions at higher frequencies have garnered attention as probes of the different phases of the interstellar medium, such as the rotational lines of carbon monoxide (CO) [12][13][14][15][16], the fine structure line of ionized carbon ([CII]) [17,18], Hα and Hβ [19,20], Lyman-α [21,22], and oxygen lines [19]. A vast number of experiments that target these spectral lines are already observing or currently under development (see e.g., [23][24][25][26][27][28]), with some initial constraints and tentative power spectrum detections [18,[29][30][31][32][33][34].…”