Probing Reionization with Intensity Mapping of Molecular and Fine Structure Lines

We propose observations of the molecular gas distribution during the era of reionization. At z ∼ 6 to 8, 12CO(J = 1 − 0) line intensity results in a mean brightness temperature of about 0.5 μK with rms fluctuations of 0.1 μK at 1 to 10 Mpc spatial scales, corresponding to 30 arcminute angular scales. This intensity fluctuations can be mapped with an interferometer, similar to existing and planned 21-cm background experiments, but operating at ∼ 12 to 17 GHz. We discuss the feasibility of detecting the cross-correlation between HI and CO molecular gas since such a cross-correlation has the advantage that it will be independent of systematics and most foregrounds in each of the 21-cm and CO(1 − 0) line experiments. Additional instruments tuned to higher-order transitions of the CO molecule or an instrument operating with high spectral resolution at mmwavelengths targeting 158 μm CII could further improve the reionization studies with molecular gas. The combined 21-cm and CO line observations has the potential to establish the relative distribution of gas in the inter-galactic medium and molecular gas that are clumped in individual first-light galaxies that are closely connected to the formation of massive stars in these galaxies. Subject headings: cosmology: theory — diffuse radiation