MESMER: MeerKAT Search for Molecules in the Epoch of Reionization

Observations of molecular gas in galaxies at all redshifts are critical for measuring the cosmic evolution in molecular gas density (H2(z)) and understanding the star-formation history of the Universe. The 12 CO molecule (�rest for the J=1!0 rotational transition = 115.27 GHz) is the best proxy for extragalactic molecular hydrogen (H2), which is the gas reservoir from which star formation occurs. The detection of CO at high-redshift has been a growing industry over the last few years with successful molecular gas detections out to z�6. Typically, redshifted high-J transitions are observed using mm-wave instruments, with the most commonly targeted systems being those with high star formation rates such as submm galaxies, and far-infrared-bright quasars. While the most luminous objects are naturally the most readily observed, observations of the typical members of the galaxy population which exhibit modest star-formation rates are essential for completing the picture. The arrival of ALMA will be revolutionary in terms of increasing the detection rate and pushing the sensitivity limit down to include more normal star-forming galaxies, however the limited field-of-view when observing at such high frequencies makes it difficult to use ALMA for studies of the large-scale structure traced out by molecular gas in galaxies. This article introduces a strategy for a systematic search for molecular gas during the Epoch of Reionization (z�7 and above), capitalizing on the fact that the J=1!0 transition of 12 CO enters the upper frequency bands of cm-wave instruments at the appropriate redshift. The field-of-view advantage gained by observing at such frequencies, coupled with modern broadband correlators allows significant cosmological volumes to be surveyed on reasonable timescales. In this article we present an overview of our proposed observing programme which has been awarded 6,500 hours as one of the Large Survey Projects for MeerKAT, the forthcoming South African Square Kilometre Array pathfinder instrument. Its large field of view and correlator bandwidth, and high-sensitivity provide unprecedented survey speed for such work. An existing astrophysical simulation is coupled with instrumental considerations to demonstrate the feasibility of such observations and predict detection rates.