Oxygen Pumping. II. Probing the Inhomogeneous Metal Enrichment at the Epoch of Reionization with High‐Frequency CMB Observations

Abstract

At the epoch of reionization, when the high-redshift intergalactic medium (IGM) is being enriched with metals, the 63.2 μm fine-structure line of O I is pumped by the ~1300 A soft UV background and introduces a spectral distortion in the cosmic microwave background (CMB). Here we use a toy model for the spatial distribution of neutral oxygen in which metal bubbles surround dark matter halos, and compute the fluctuations of this distortion and the angular power spectrum it imprints on the CMB. We discuss the dependence of the power spectrum on the velocity of the winds polluting the IGM with metals, the minimum mass of the halos producing these winds, and the cosmic epoch when the O I pumping occurs. We find that, although the clustering signal of the CMB distortion is weak [(δy)rms 10−7; roughly corresponding to a temperature anisotropy of ~1 nK], it may be reachable in deep integrations with high-sensitivity infrared detectors. Even without a detection, these instruments should be able to set useful constraints on the heavy-element enrichment history of the IGM.