Mapping the Epoch of Reionization with C+ Line Tomography
Creators: name: Bock, J. J.
name: Bradford, Charles M.
Publisher: name: Keck Institute for Space Studies
Year: 2016

description: Our KISS program has laid the theoretical foundations for probing the epoch of reionization with C+
tomography measurements, developed unique lithographed millimeter-wave spectrometer technology,
and initiated a first-light C+ experiment named TIME-Pilot. With KISS support we have carried out the
following investigations:
1) Developed the case for line intensity mapping methods to study the epoch of reionization
using singly ionized carbon (C+), typically the most luminous emission line in galaxies. The
theoretical studies not only explored the amplitude of the signal, and the usefulness in
determining physical properties of the partially ionized intergalactic medium, but also the
effects of foreground confusion from low-redshift galaxies. Our team made the first
calculations of C+ clustering fluctuations from the reionization epoch, and estimated the
effect of foreground galaxy confusion, largely from CO line emission at z ~ 1. We also
authored the first papers on tomographic measurements with the Ly emission line, which
shows great promise for near-infrared intensity mapping measurements with the SPHEREx
SMEX mission concept.
2) Developed a complete design for a first-detection instrument of [CII] large-scale clustering
emission named TIME-Pilot, based on an array of 32 novel waveguide spectrometers. The
spectrometers are mounted in a linear array in two polarizations, and observations are
carried out by scanning the detectors in a 1-deg linear strip, which maximizes depth (small
survey area) while preserving sensitivity on large scales (long scan length).
3) Demonstrated the key waveguide spectrometer technology, which confines radiation in 2
dimensions and the power propagates between parallel plates and is dispersed and
collimated by a curved grating. The waveguide spectrometers greatly reduce the mass and
volume that would otherwise be required with a conventional 3-d grating spectrometer.
4) Demonstrated a prototype superconducting detector array. These high-sensitivity
superconducting bolometers are mounted on the focal surface across multiple
spectrometers, and read out by superconducting current amplifiers. The devices present
unique micro-machining challenges to produce edge-butted sub-arrays that do not leave
spectral gaps between channels.
5) Completed the full cryogenic system for the instrument. We commandeered an existing 4
K cryostat from another project, and added cooling stages to an ultimate temperature of
220 mK to meet the TIME-Pilot cooling requirements. The system is fully tested and
operational.
6) Formed a partnership with ASIAA in Taiwan, led by Tzu-Ching Chang who attended the
original KISS study. ASIAA is providing major hardware components for the TIME-Pilot
instrument, and in the past year have developed a prototype of the spectrometer, and
procured cables and cryogenic coolers. ASIAA has also become the managing institution
for the James Clerk Maxwell Telescope (JCMT) in Hawaii, and ideal facility for carrying out
observations with the instrument.