Cross-correlations as a cosmological carbon monoxide detector

Abstract

We present a new procedure to measure the large-scale carbon monoxide (CO) emissions across cosmic history. As a tracer of the large-scale structure (LSS) itself, the CO gas content as a function of redshift can be quantified by its three-dimensional fluctuation power spectra. Furthermore, cross-correlating CO emission with other tracers of LSS offers a way to measure the emission as a function of scale and redshift. Here we introduce the formalism and model relevant for such a cross-correlation measurement between CO and other LSS tracers, and between different CO rotational lines. As an illustration, we propose a novel use of Cosmic Microwave Background (CMB) data and attempt to extract redshifted CO emissions embedded in the Wilkinson Microwave Anisotropy Probe (WMAP) dataset. We cross-correlate the all-sky WMAP7 data with LSS data sets, namely, the photometric quasar sample and the luminous red galaxy (LRG) sample from the Sloan Digital Sky Survey (SDSS) Data Release 6 and 7 respectively. We are not able to detect a cross-correlation signal with either CO(1-0) nor CO(2-1) lines at different redshifts, mainly due to the instrumental noise in the WMAP data. However, we are able to rule out models that are more than three times greater than our more optimistic model. We discuss the cross-correlation signal from the thermal Sunyaev-Zeldovich (tSZ) effect and dust as potential contaminants, and quantify their impact for our CO measurements. We discuss forecasts for current CMB experiments and a hypothetical future CO focused experiment, for which we propose to cross-correlate the CO temperature data with the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Lyα-emitter sample, for which a signal-to-noise ratio of 58 is possible.