Intensity mapping of molecular gas during cosmic reionization

Abstract

I present a simple calculation of the expected mean CO brightness temperature from the large scale distribution of galaxies during cosmic reionization. The calculation is based on the cosmic star formation rate density required to reionize, and keep ionized, the intergalactic medium, and uses standard relationships between star formation rate, IR luminosity, and CO luminosity derived for star forming galaxies over a wide range in redshift. I find that the mean CO brightness temperature resulting from the galaxies that could reionize the Universe at $z = 8$ is $T_B \sim 1.1 (C/5) (f_{esc}/0.1)^{-1} \mu$K, where $f_{esc}$ is the escape fraction of ionizing photons from the first galaxies, and $C$ is the IGM clumping factor. Intensity mapping of the CO emission from the large scale structure of the star forming galaxies during cosmic reionization on scales of order $10^2$ to 10$^3$ deg$^2$, in combination with HI 21cm imaging of the neutral IGM, will provide a comprehensive study of the earliest epoch of galaxy formation.