Ben Wandelt Flatiron Institute Cosmology Ben Wandelt Flatiron Institute Institut d’Astrophysique, Paris (IAP) Lagrange Institute, Paris (ILP) Sorbonne University

Dark energy and SPHEREx++ (or: beyond BAO with SPHEREx) BAO requires large volume to be effective High-density, high resolution, all-sky coverage at low z is unique to SPHEREx Cosmic acceleration (“dark energy”) is known to dominate at low z – so an interesting science target for SPHEREx But.. low-z structure is non-linear What to do?

The large scale structure challenge Problem: to access high-res, low-z information we need to deal with non-linearity and "bias" Possible approaches: Avoid: Observe at high redshift before density contrast became non-linear (CMB, 21cm, Ly-alpha?) Adapt: Focus on less complicated parts of the Universe, e.g. those that retain more memory of the initial conditions: cosmic voids Attack: Physical & statistical forward model of the survey, bias, etc. (perturbative or non-linear) Benjamin Wandelt

The power of cosmic voids Biggest "objects" in the Universe – fill most of the volume! Simpler dynamics and evolution than high density regions The first regions in the universe that are dominated by dark energy; most sensitive to modifications of General Relativity Sensitive to small scale DM structure A free, additional observational probe in current and future surveys: ~104 voids in Euclid! Contrast high at low-z Several active groups and a rapidly growing body of work Google “VIDE bitbucket” Benjamin Wandelt

Matter, galaxies, voids in simulation Hamaus et al. 2014

A universal profile for voids Scaling properties of voids allow reduction from 4 to 2 params Subsampled DM sims NL velocity profile matches this NL profile! Hamaus, Sutter & Wandelt PRL 2014, arxiv:1403.5499

Void-galaxy correlation function in redshift space Benjamin Wandelt See month of June on 2017 APS calender!

Joint measurement of growth of structure and of expansion geometry Using BOSS data. AP measurement is 4 times tighter than RSD from SDSS DR12 galaxy clustering analysis! (Gil-Marin et al. arXiv:1509.06386) Preliminary Euclid forecasts => 30 times higher Figure of merit than standard BAO Hamaus et al. arXiv:1602.01784 Benjamin Wandelt

Joint constraint on growth f/b and on matter density for wDE = -1 3457 voids from SDSS Hamaus et al. arXiv:1602.01784 Benjamin Wandelt

SPHEREx voids probe low-z universe Preliminary Old specs, Using dz~0.003 only 230,000 voids! Alice Pisani Complementarity: expect LH contours to be rotated wrt Euclid, WFIRST

SPHEREx will get higher number density of voids at low z; sensitive to cosmic acceleration Preliminary Old specs Using dz~0.003 only 230,000 voids! Alice Pisani Complementarity: expect LH contours to be rotated wrt Euclid, WFIRST

Non-Gaussianity with SphereX and Euclid

SPHEREx non-Gaussianity K<<k This is challenging: need to know selection function very well on large scales; expect large angle selection systematics to be the bottleneck Potential large angle systematics for SPHEREx: Confusion could lead to large angle systematics due to star-galaxy separation in galactic coordinates Zodiacal emission could lead to large angle systematics in ecliptic coordinates S S S

SPHEREx non-Gaussianity A potential solution: cross-correlations K<<k Take combinations EUCLID/SPHEREx combinations so the short scale variations due to selection systematics do not couple to long scale fluctuations Another strategy to explore: Using a Euclid-selected SPHEREx sample X Y Z

Conclusions SPHEREx’s unique strength lies in “low”-z high density pseudo-spectroscopic mapping This is well-matched to void cosmology Worth exploring Euclid/SPHEREx cross-correlation and cross-calibration especially for science that is sensitive to selection systematics Need to explore these issues in simulations!