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Ben Wandelt Flatiron Institute
Cosmology Ben Wandelt Flatiron Institute Institut d’Astrophysique, Paris (IAP) Lagrange Institute, Paris (ILP) Sorbonne University
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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?
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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
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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
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Matter, galaxies, voids in simulation
Hamaus et al. 2014
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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:
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Void-galaxy correlation function in redshift space
Benjamin Wandelt See month of June on 2017 APS calender!
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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: ) Preliminary Euclid forecasts => 30 times higher Figure of merit than standard BAO Hamaus et al. arXiv: Benjamin Wandelt
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Joint constraint on growth f/b and on matter density
for wDE = -1 3457 voids from SDSS Hamaus et al. arXiv: Benjamin Wandelt
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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
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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
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Non-Gaussianity with SphereX and Euclid
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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
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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
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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!
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