Line Intensity Mapping

While the CMB provides a pristine view of the early Universe, it is only a 2D screen.  3D maps of large-scale structure (LSS) are emerging as a powerful cosmological observable, and could potentially offer much higher constraining power than the CMB.  Galaxy surveys are the standard probe of LSS, but at high redshift they are prohibitively expensive and individual galaxies become too faint to detect.

I am working on a new observational technique---line intensity mapping (IM)---which uses low angular resolution observations of a molecular or atomic emission line to trace the aggregate distribution of galaxies in 3D.  IM has the potential to measure large cosmological volumes very quickly, at high redshifts inaccessible to galaxy surveys, providing a unique handle on early-Universe cosmology.  But to fully realize the promise of IM cosmology, we require new instruments with large-format, spectroscopic focal planes performing large-angle CMB-like measurements.  With the SuperSpec Collaboration, I am developing an on-chip millimeter-wave spectrometer that shrinks the volume of traditional spectrometers by orders of magnitude.  In our initial 2019 deployment to the Large Millimeter Telescope, we will demonstrate on-sky performance with observations of individual high-redshift point source galaxies.  Future SuperSpec focal planes will enable extremely sensitive IM observations of LSS at high redshift.

These measurements will bear on fundamental cosmology.  In addition to constraining cosmological parameters with up to ~4x the volume of current galaxy surveys, high-redshift measurements of LSS can probe inflation by testing for primordial non-Gaussianity or oscillatory features in the matter power spectrum.  By measuring the distance-redshift relation using the baryon acoustic oscillations, which provide strong evidence for dark energy, we may uncover clues about its origin and dynamics at early times.  High-redshift IM data could also be used to delens degree-scale B-mode polarization maps.


At South Pole: The Dark Sector Laboratory (left) hosting BICEP1/2/3 and the South Pole Telescope, and the Martin A. Pomerantz Observatory (right) hosting the Keck Array.