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

Our deep survey in the COSMOS field approaches the sensitivity required to test the presence of CO fluctuations in the redshift range 0.3 < z < 2 (see the figure below). While this is a foreground signal for [CII] (figure below, right), 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).