The Design and Science Goals of LWCam, the CCAT Long-Wavelength Imager

We present the design of LWCam, the prospective facility long-wavelength imaging camera for CCAT. LWCam will provide a diffraction-limited 20' field-of-view with background-limited sensitivity in up to six bands: 750 um, 850 um, 1 mm, 1.3 mm, 2.0 mm, and 3.0 mm. It will use multi-scale phased-array antennas or multiband, corrugated platelet feedhorn arrays coupled via microstrip to titanium nitride MKIDs with an overall detector count exceeding 50,000. Photolithographic bandpass filters and microstrip channelizers will define spectral bands. LWCam will be able to map hundreds of square degrees per year to the confusion limit in these multiple bands, enabling the exhaustive study of continuum sources in the trans-mm wavelength region, including dusty, star-forming galaxies (DSFGs), galaxy clusters via the Sunyaev-Zeldovich (SZ) effect, and star-forming regions in our own and nearby galaxies. The multiple spectral bands and excellent angular resolution of LWCam will enable spectral separation of DSFGs and the thermal and kinetic Sunyaev-Zeldovich effects, including even relativistic corrections in the most massive galaxy clusters. LWCam will be ideally suited to survey for galaxy clusters via the thermal SZ effect and measure their peculiar velocities via the kinetic SZ effect as well as to study the intracluster medium of galaxy clusters from the core to the virial radius, including searches for substructure, internal bulk flows, turbulent pressure, and accretion shocks. With LWCam, it will be possible to detect the highest redshift galaxies via their mm/submm flux ratio (which peaks at mm wavelengths for DSFGs) and construct the auto- and frequency cross-power spectra of the cosmic infrared background to constrain models of their formation and evolution. LWCam's surveys will constrain the gas distribution in high-redshift groups and clusters by measuring the thermal SZ power spectum and will measure the duration of the epoch of reionization via the kinetic SZ power spectrum. LWCam will complement CCAT's short-wavelength imager SWCam and extragalactic multi object spectrometer X-Spec as well as numerous expected surveys over a range of wavelengths including DES, LSST, and eROSITA.