Dark Energy and Dark Energy and Cosmic SoundCosmic Sound

Daniel EisensteinDaniel Eisenstein(University of Arizona)(University of Arizona)

Michael Blanton, David Hogg, Bob Nichol, Nikhil Michael Blanton, David Hogg, Bob Nichol, Nikhil Padmanabhan, Will Percival, David Schlegel, Padmanabhan, Will Percival, David Schlegel,

Roman Scoccimarro, Ryan Scranton, Hee-Jong Roman Scoccimarro, Ryan Scranton, Hee-Jong Seo, Ed Sirko, David Spergel, Max Tegmark, Seo, Ed Sirko, David Spergel, Max Tegmark,

Martin White, Idit Zehavi, and the SDSS.Martin White, Idit Zehavi, and the SDSS.

SummarySummary Sound waves that propagate in the first 400,000 years after Sound waves that propagate in the first 400,000 years after

the Big Bang imprint a signature that we can measure in the the Big Bang imprint a signature that we can measure in the clustering of galaxies today: baryon acoustic oscillations.clustering of galaxies today: baryon acoustic oscillations.

This signature has a size that we can calculate accurately. This signature has a size that we can calculate accurately. Measuring this as an angle allows us to infer the distance to Measuring this as an angle allows us to infer the distance to a sample of galaxies.a sample of galaxies.

Measuring accurate distances is a key way to study the Measuring accurate distances is a key way to study the acceleration of the Universe and the properties of dark acceleration of the Universe and the properties of dark energy.energy.

In the last 4 years, astronomers have detected this acoustic In the last 4 years, astronomers have detected this acoustic signature in the clustering of galaxies. Important tool to signature in the clustering of galaxies. Important tool to study cosmological composition.study cosmological composition.

Several new surveys being initiated to push the Several new surveys being initiated to push the measurements to 1% and below.measurements to 1% and below.

Acoustic Oscillations in the CMBAcoustic Oscillations in the CMB

Although there are fluctuations on all scales, there is a characteristic Although there are fluctuations on all scales, there is a characteristic angular scale. Hot and cold spots tend to be about 1 degree in size.angular scale. Hot and cold spots tend to be about 1 degree in size.

Acoustic Oscillations in the CMBAcoustic Oscillations in the CMB

WMAP team (Bennett et al. 2003)WMAP team (Bennett et al. 2003)

Acoustic Peaks followa harmonic pattern.

Sound Waves in the Early UniverseSound Waves in the Early Universe

Before recombination:Before recombination: Universe is ionized. Universe is ionized. Photons provide enormous Photons provide enormous

pressure and restoring force. pressure and restoring force. Perturbations oscillate as Perturbations oscillate as

acoustic waves.acoustic waves.

After recombination:After recombination: Universe is neutral.Universe is neutral. Photons can travel freely Photons can travel freely

past the baryons.past the baryons. Peturbations collapse due Peturbations collapse due

to gravity.to gravity.

Big

Ban

gTod

ay

Recombinationz ~ 1000

~400,000 yearsIonized Neutral

Time

Sound WavesSound Waves Each initial overdensity (in DM & Each initial overdensity (in DM &

gas) is an overpressure that gas) is an overpressure that launches a spherical sound wave.launches a spherical sound wave.

This wave travels outwards at This wave travels outwards at 57% of the speed of light.57% of the speed of light.

Pressure-providing photons Pressure-providing photons decouple at recombination. CMB decouple at recombination. CMB travels to us from these spheres.travels to us from these spheres.

Sound speed plummets. Wave Sound speed plummets. Wave stalls at a radius of 150 Mpc.stalls at a radius of 150 Mpc.

Overdensity in shell (gas) and in the Overdensity in shell (gas) and in the original center (DM) both seed the original center (DM) both seed the formation of galaxies. Preferred formation of galaxies. Preferred separation of 150 Mpc.separation of 150 Mpc.

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150 Mpc150 Mpc(500 Mlyr)(500 Mlyr)

Looking back in time in the Universe

CREDIT: WMAP & SDSS websites

CM

B

Looking back in time; angles imply distance

GA

LAX

IES

SDSS SDSS Galaxy Galaxy

Redshift Redshift SurveySurvey

200 kpc

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Correlations of GalaxiesCorrelations of Galaxies

CDM with baryons is a good fit: 2 = 16.1 with 17 dof.Pure CDM rejected at 2 = 11.7

Horizontal match of peak positions allows us to

measure distance to 4%.

Chasing Sound Across RedshiftChasing Sound Across Redshift

Distance Errors versus RedshiftDistance Errors versus Redshift

SDSS-IIISDSS-III SDSS-III will be the next phase of the SDSS project, SDSS-III will be the next phase of the SDSS project,

operating from summer 2008 to summer 2014.operating from summer 2008 to summer 2014. SDSS-III has 4 surveys on 3 major themes.SDSS-III has 4 surveys on 3 major themes.

BOSS: Largest yet redshift survey for large-scale structure. BOSS: Largest yet redshift survey for large-scale structure. Definitive study of the low-redshift acoustic oscillations using Definitive study of the low-redshift acoustic oscillations using 1.5 million galaxy redshifts. 1.5 million galaxy redshifts. Goal: 1% measurement of cosmological distance.Goal: 1% measurement of cosmological distance.

SEGUE-2: Optical spectroscopic survey of stars, aimed at structure SEGUE-2: Optical spectroscopic survey of stars, aimed at structure and nucleosynthetic enrichment of the outer Milky Way.and nucleosynthetic enrichment of the outer Milky Way.

APOGEE: Infrared spectroscopic survey of stars, to study the APOGEE: Infrared spectroscopic survey of stars, to study the enrichment and dynamics of the whole Milky Way.enrichment and dynamics of the whole Milky Way.

MARVELS: Multi-object radial velocity planet search.MARVELS: Multi-object radial velocity planet search. Using SDSS telescope, facilities, software.Using SDSS telescope, facilities, software. Strong commitment to public data releases.Strong commitment to public data releases. Collaboration is now forming. Seeking support from Sloan Collaboration is now forming. Seeking support from Sloan

Foundation, DOE, NSF, and over 20 member institutions.Foundation, DOE, NSF, and over 20 member institutions.

ConclusionsConclusions

Acoustic oscillations provide a robust way to Acoustic oscillations provide a robust way to measure cosmological distance and hence measure cosmological distance and hence probe dark energy.probe dark energy.

SDSS LRG sample uses the acoustic signature SDSS LRG sample uses the acoustic signature to measure distance to 4% at one redshift.to measure distance to 4% at one redshift.

New galaxy surveys in the coming decade will New galaxy surveys in the coming decade will push to 1% and below over a range of redshift.push to 1% and below over a range of redshift.

More information:More information: http://cmb.as.arizona.edu/~eisenste/acousticpeakhttp://cmb.as.arizona.edu/~eisenste/acousticpeak Physics Today article by Daniel Eisenstein & Chuck Physics Today article by Daniel Eisenstein & Chuck

Bennett, April 2008.Bennett, April 2008. http://www.sdss3.org/http://www.sdss3.org/

Response of a point perturbationResponse of a point perturbation

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Based on CMBfast outputs (Seljak & Based on CMBfast outputs (Seljak & Zaldarriaga). Green’s function view Zaldarriaga). Green’s function view from Bashinsky & Bertschinger 2001.from Bashinsky & Bertschinger 2001.

Remember: This is a tiny ripple on a big background.