Cosmology with dropout selection: strawman surveys & CMB lensing
Abstract
We seek to prove the means, motive and opportunity of 'dropout' selected 2 <= z <= 5 galaxies for largescale structure. Together with acquired lowz tracers, these samples would map practically every linear mode and facilitate a tomographic decomposition of the Cosmic Microwave Background (CMB) lensing kernel over an unprecedented volume. With this, one may infer (the time evolution of) matter density fluctuations and perform compelling tests of horizonscale General Relativity, neutrino masses and Inflation—viz., curvature, running of the spectral index and a scaledependent halo bias induced by (local) primordial nonGaussianity. This is facilitated by the orderofmagnitude increase in sensitivity achieved by planned CMB, opticaltonearinfrared imaging and spectroscopy. Focusing on traditional colorcolor—rather than photometric redshift—selection, we estimate the expected completeness, contamination, and spectroscopic survey speed of tailored Lymanbreak galaxy (LBG) samples. With these in hand, we forecast the potential of CMB lensing crosscorrelation, `clustering redshifts' and RedshiftSpace Distortions (RSD) analyses. In particular, we estimate: the depth dependence of interlopers based on CFHTLSArchiveResearch Survey (CARS) data and propagate this to biases in cosmology; a simple relation for the dependence of the linear galaxy bias on redshift and depth; new inferences of nonlinear halo bias at these redshifts using legacy data; detailed forecasts of LBG spectra as would be observed by the Dark Energy Spectroscopic Instrument, Prime Focus Spectrograph, and their successors. We further assess the relative competitiveness of these spectroscopic facilities based on an intuitive figureofmerit and define modern equivalents to traditional color selection criteria for the Large Synoptic Survey Telescope, where necessary. We confirm these science cases to be compelling for achievable facilities in the next decade by defining a LBG sample of increasing Lymanα equivalent width with redshift, which delivers both percentlevel RSD constraints on the growth rate at highz and measurements of CMB lensing crosscorrelation at z=3 and 4 with a significance measured in the hundreds, given sufficient area overlap. Finally, we discuss the limitations of this initial exploration and provide avenues for future investigation.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 October 2019
 DOI:
 10.1088/14757516/2019/10/015
 arXiv:
 arXiv:1904.13378
 Bibcode:
 2019JCAP...10..015W
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 59 pages, comments welcome