BARYON ACOUSTIC OSCILLATIONS Cosmological Parameters and You
OUTLINE OF TOPICS
Definitions of Terms
Big Picture (Cosmology)
What is going on (History)
An Acoustic Ruler(CMB)
Measurements in Time and Space
Measurements of Galaxies
Galactic Correlation Function
The Big Why
Current and Future Projects
SDSS
LSST/DESI
Summary
SDSS-III visual media by Chris Blake
and Sam Moorfield
DEFINITION OF TERMS
What’s that mean?
Definitions Big Picture Measurements Projects Summary
BAO – Baryon Acoustic Oscillation
Enveloping term for fluctuations in mass density due to pressure fluctuations in the early universe.
2P(A)CF – Two-Point (Angular) Correlation Function
Measurement of “distance” between any two randomly selected objects in a given (area) volume.
Power Spectrum
The Fourier Transform of the 2PCF converting angular scales (rad) to multipoles (ℓ) or wave numbers (k).
Inflation
A period of rapid cosmic expansion from t0 ≈ 10-36 s to tf ≈ 10-33 s.
Definitions Big Picture Measurements Projects Summary
THE BIG PICTURE
We’re doing Theory!
Definitions Big Picture Measurements Projects Summary
WHAT HAPPENED
WHEN
Big Bang
Universe is tiny Quantum fluctuations in
energy density
Universe inflates Quantum fluctuations
are stretched to cosmic scales
Energy density fluctuations persist until Recombination (z~1089)
Definitions Big Picture Measurements Projects Summary
BICEP2 Visual Media
CMB AND TEMPERATURE VARIATIONS
“ACOUSTIC OSCILLATIONS”
Definitions Big Picture Measurements Projects Summary
Bobin, J., et al., A&A, 563, 105B (2014).
BARYON ACOUSTIC OSCILLATIONS 1
Acoustic Oscillations
occur in photons and
baryons, but not dark
matter
Dark matter perturbations
happen in place
Baryon perturbations
happen in expanding
shell
Definitions Big Picture Measurements Projects Summary
Wayne Hu visual media
BARYON ACOUSTIC OSCILLATIONS 2
Definitions Big Picture Measurements Projects Summary
Shells of baryons, at zls are moving at speed of sound, or v≈0.5c
At zls perturbations are small, but Matthew Effect causes them to grow with time.
At zls, ds=0.145 Mpc SDSS-III BOSS Visual Media
MEASUREMENTS IN TIME AND SPACE
Here comes the math
Definitions Big Picture Measurements Projects Summary
MEASUREMENTS OF GALAXIES
Need large survey of
galaxies
Redshift distortions
require they have a
small Δz
Also need large
survey of random
galaxies for the
2PCF
Definitions Big Picture Measurements Projects Summary
SDSS DR8 Press Release
GALACTIC CORRELATION FUNCTION (ξ)
DD – survey galaxy sep.
RR – random galaxy sep.
DR – survey-random sep.
Acoustic radius, rs, is dependent on z:
rs = ds x (1+zls-zobs) Mpc
rs(zobs=0.47) ≈ 150 Mpc
Definitions Big Picture Measurements Projects Summary
Eisenstein, D., et al., ApJ, 633, 560 (2005).
)(
)()(2)()(
sRR
sRRsDRsDDs
THE BIG WHY
Acoustic scale incredibly well constrained
2PACF is cosmology independent
Converting to 2PCF constrains distance ladder from SN Ia
Can survey different redshift epochs, to constrain ΩΛ, H, ΩM, Ωk, or mν
Definitions Big Picture Measurements Projects Summary
Huterer, D., Shafer, D., RPPh, 81, 6907 (2018)
CURRENT AND FUTURE PROJECTS
Looking at the future looking back in time
Definitions Big Picture Measurements Projects Summary
SDSS/BARYON OSCILLATION SPECTROSCOPIC
SURVEY (BOSS)
Acoustic features in
Galaxy survey detected
at 7σ
Ly α forest allow
measuring BAOs through
redshift distortions
Need galaxy surveys as
QSOs suffer from shot
noise.
Definitions Big Picture Measurements Projects Summary
Anderson, L., et al., MNRAS, 441, 24 (2014).
FUTURE PROJECTS
Definitions Big Picture Measurements Projects Summary
LSST Model Render via lsst.org
DESI 4m Telescope via desi.lbl.gov
SUMMARY
Cosmic Microwave Background allows <1% measurement of acoustic scale.
Baryons oscillate in potential wells before Recombination.
Baryon oscillation scale frozen at Recombination
Gravitational instabilities cause growing density fluctuations with time
Expanding universe makes increases baryon oscillation scale.
Angular correlation function is model-independent, but 2PCF allows for model testing.
Uncertainties in BAO-derived models are orthogonal to uncertainties from SN Ia distance ladder.
Definitions Big Picture Measurements Projects Summary
ALL THE QUESTIONS
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