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?
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 t 0 10-36 s to t f 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 SDSS-III BOSS Visual Media Shells of baryons, at z ls are moving at speed of sound, or v 0.5c At z ls perturbations are small, but Matthew Effect causes them to grow with time. At z ls, d s =0.145 Mpc
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) Eisenstein, D., et al., ApJ, 633, 560 (2005). DD( s) 2DR( s) RR( s) ( s) RR( s) DD survey galaxy sep. RR random galaxy sep. DR survey-random sep. Acoustic radius, r s, is dependent on z: r s = d s x (1+z ls -z obs ) Mpc r s (z obs =0.47) 150 Mpc
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 Ω Λ, H, Ω M, Ω k, or m ν 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 DESI 4m Telescope via desi.lbl.gov LSST Model Render via lsst.org
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