Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by the energetic photons emitted from the first galaxies. The [C II] 158µm fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star-formation activity. However, [C II] intensity maps at 6 z 8 are contaminated by interloping CO rotational line emission (3 ≤ J upp ≤ 6) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming [C II] intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at z < 3 and with stellar masses M * > 10 8 M selected in K-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment (TIME), we find that masking out the "voxels" (spectral-spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a z-dependent criterion m AB K 22 (or M * 10 9 M ) at z < 1 and makes a [C II]/CO tot power ratio of 10 at k = 0.1 h/Mpc achievable, at the cost of a moderate 8% loss of total survey volume.
TIME-Pilot is designed to make measurements from the Epoch of Reionization (EoR), when the first stars and galaxies formed and ionized the intergalactic medium. This will be done via measurements of the redshifted 157.7 um line of singly ionized carbon ([CII]). In particular, TIME-Pilot will produce the first detection of [CII] clustering fluctuations, a signal proportional to the integrated [CII] intensity, summed over all EoR galaxies. TIME-Pilot is thus sensitive to the emission from dwarf galaxies, thought to be responsible for the balance of ionizing UV photons, that will be difficult to detect individually with JWST and ALMA. A detection of [CII] clustering fluctuations would validate current theoretical estimates of the [CII] line as a new cosmological observable, opening the door for a new generation of instruments with advanced technology spectroscopic array focal planes that will map [CII] fluctuations to probe the EoR history of star formation, bubble size, and ionization state. Additionally, TIME-Pilot will produce high signal-to-noise measurements of CO clustering fluctuations, which trace the role of molecular gas in star-forming galaxies at redshifts 0 < z < 2. With its unique atmospheric noise mitigation, TIME-Pilot also significantly improves sensitivity for measuring the kinetic Sunyaev-Zel'dovich (kSZ) effect in galaxy clusters. TIME-Pilot will employ a linear array of spectrometers, each consisting of a parallel-plate diffraction grating. The spectrometer bandwidth covers 185-323 GHz to both probe the entire redshift range of interest and to include channels at the edges of the band for atmospheric noise mitigation. We illuminate the telescope with f/3 horns, which balances the desire to both couple to the sky with the best efficiency per beam, and to pack a large number of horns into the fixed field of view. Feedhorns couple radiation to the waveguide spectrometer gratings. Each spectrometer grating has 190 facets and provides resolving power above 100. At this resolution, the longest dimension of the grating is 31 cm, which allows us to stack gratings in two blocks (one for each polarization) of 16 within a single cryostat, providing a 1x16 array of beams in a 14 arcminute field of view. Direct absorber TES sensors sit at the output of the grating on six linear facets over the output arc, allowing us to package and read out the detectors as arrays in a modular manner. The 1840 detectors will be read out with the NIST time-domain-multiplexing (TDM) scheme and cooled to a base temperature of 250 mK with a 3He sorption refrigerator. We present preliminary designs for the TIME-Pilot cryogenics, spectrometers, bolometers, and optics.
Line intensity mapping (LIM) provides a unique and powerful means to probe cosmic structures by measuring the aggregate line emission from all galaxies across redshift. The method is complementary to conventional galaxy redshift surveys that are object-based and demand exquisite point-source sensitivity. The Tomographic Ionized-carbon Mapping Experiment (TIME) will measure the star formation rate (SFR) during cosmic reionization by observing the redshifted [C II] 158 µm line (6 z 9) in the LIM regime. TIME will simultaneously study the abundance of molecular gas during the era of peak star formation by observing the rotational CO lines emitted by galaxies at 0.5 z 2. We present the modeling framework that predicts the constraining power of TIME on a number of observables, including the line luminosity function, and the auto-and cross-correlation power spectra, including synergies with external galaxy tracers. Based on an optimized survey strategy and fiducial model parameters informed by existing observations, we forecast constraints on physical quantities relevant to reionization and galaxy evolution, such as the escape fraction of ionizing photons during reionization, the faint-end slope of the galaxy luminosity function at high redshift, and the cosmic molecular gas density at cosmic noon. We discuss how these constraints can advance our understanding of cosmological galaxy evolution at the two distinct cosmic epochs for TIME, starting in 2021, and how they could be improved in future phases of the experiment.
TIME is a mm-wavelength grating spectrometer array that will map fluctuations of the 157.7 µm emission line of singly ionized carbon ([CII]) during the Epoch of Reionization (redshift z ∼ 5 to 9). 60 transition-edge sensor (TES) bolometers populate the output arc of each of the 32 spectrometers, for a total of 1920 detectors. Each bolometer consists of gold absorber on a ∼ 3 x 3 mm silicon nitride micro-mesh suspended near the corners by 1 x 1 x 500 µm silicon nitride legs targeting a photon-noise-dominated NEP ∼ 1 × 10 −17 W/ √ Hz. Hafnium films are explored as a lower-T c alternative to Ti (500 mK) for TIME TESs, allowing thicker support legs for improved yield. Hf T c is shown to vary between 250 mK and 450 mK when varying the resident Ar pressure during deposition. Magnetic shielding designs and simulations are presented for the TIME first-stage SQUIDs. Total axial field suppression is predicted to be 5 × 10 7 .
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