TIME is a new mm-wavelength grating spectrometer array designed to study the Epoch of Reionization - the period of time when the first stars and galaxies ionized the intergalactic medium - by mapping the fluctuations of the redshifted 157.7 μm emission line of singly ionized carbon ([CII]) from redshift z ~ 5 to 9. As a tracer of star formation, the [CII] power spectrum can provide information on the sources driving reionization and complements 21 cm data, which traces neutral hydrogen in the intergalactic medium. Intensity mapping provides a measure of the mean [CII] intensity without the need to resolve and detect faint sources individually. TIME is also sensitive to CO emission from galaxies at intermediate redshifts, producing a rich dataset of neutral gas intensity fluctuations during the peak of cosmic star formation. We plan to target a 1 degree by 0.35 arcminute field on the sky and a spectral range of 199-305 GHz, producing a thin spatial-spectral data slab. With careful separation of the [CII] and CO signals (using low-redshift galaxy tracers and differences in k-space projections), we anticipate a detection of the halo-halo clustering term in the [CII] power spectrum consistent with current models for star formation history.
The TIME instrument will use two stacks of 16 parallel-plate waveguide spectrometers (one stack per polarization) with a resolving power R ~ 100 and a spectral range of 183 to 326 GHz. The range is divided into 60 spectral channels, of which 16 at the band edges on each spectrometer serve as atmospheric monitors. The diffraction gratings are curved to produce a compact instrument, each focusing the diffracted light onto an output arc sampled by the 60 bolometers. The bolometers are built in buttable dies of 8 (low freqeuency) or 12 (high frequency) spectral channels by 4 spatial channels and are mated to the spectrometer stacks. Each detector consists of a gold micro-mesh absorber and a titanium transition edge sensor (TES). The detectors (1920 total) are designed to operate from a 250 mK base temperature in an existing cryostat with a photon-noise-dominated NEP of ~2e-17 W/sqrt(Hz).