CO intensity fluctuations from galaxies at redshift z=0.3-2

Our deep survey in the COSMOS field approached the sensitivity required to test the presence of CO fluctuations in the redshift range 0.3 < z < 2. While this is a foreground signal for [CII], it is also a chance for investigating the star formation and gas content of galaxies at lower redshift, as CO is the most abundant molecular species (after H₂) tracing the metal-enriched, relatively dense, cool-to-warm molecular ISM phase where stars efficiently form. In particular, cross-power spectrum of two CO lines at the same redshift, within CONCERTO, could give a measure of the 3D clustering of undetected galaxies and the distribution of molecular gas in the cosmic web.

Left: Low-redshift CO lines observable in CONCERTO frequency range (shown by the two dashed lines). The high-J rotational levels are of low intensity, as illustrated on the right figure that gives the comoving power spectra of [CII] at z = 6 and CO interlopers at lower redshifts in the same observing frequency range (from Cheng et al. 2016).