Baryon Acoustic Oscillations - uwyo.edublyke/bao_present.pdfBAO – Baryon Acoustic Oscillation Enveloping term for fluctuations in mass density due to pressure fluctuations in the

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.


THE BIG PICTURE

We’re doing Theory!


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)


BICEP2 Visual Media

CMB AND TEMPERATURE VARIATIONS

“ACOUSTIC OSCILLATIONS”


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


Wayne Hu visual media

BARYON ACOUSTIC OSCILLATIONS 2


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


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


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


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


Huterer, D., Shafer, D., RPPh, 81, 6907 (2018)

CURRENT AND FUTURE PROJECTS

Looking at the future looking back in time


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.


Anderson, L., et al., MNRAS, 441, 24 (2014).

FUTURE PROJECTS


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.


ALL THE QUESTIONS

Documents

Baryon Acoustic Oscillations - uwyo.edublyke/bao_present.pdfBAO – Baryon Acoustic Oscillation Enveloping term for fluctuations in mass density due to pressure fluctuations in the