1. Daniel Eisenstein – Univ. of Arizona Dark Energy and Cosmic Sound Bob Nichol on behalf of the SDSS Collaboration Copy of presentation to be given by Daniel Eisenstein at AAS meeting in San Diego at 9am PST today Bob Nichol - ICG, Portsmouth

2. Daniel Eisenstein – Univ. of Arizona Synopsis “Smoking gun” evidence that gravity played the major role in the growth of galaxies: the “Smoking gun” we have detected the “acoustic oscillations”, a sound wave created in the first minute of the Universe use “oscillation” as a “cosmic yardstick” to measure distances more accurately than before. the most precise measurement yet of the geometry of the Universe: it’s flat to 1%! Bob Nichol - ICG, Portsmouth

3. Daniel Eisenstein – Univ. of Arizona How did galaxies form? Local universe is full of galaxies: Where did they come from? How did they form they way they did? Our theory predicts they form via gravity from tiny quantum fluctuations in the early Universe Bob Nichol - ICG, Portsmouth

4. Daniel Eisenstein – Univ. of Arizona Sound Waves in Early Universe For 400,000 years after the Big Bang, the cosmic microwave background photons are trapped in the ionized cosmic gas. These photons provide an enormous restoring pressure, causing the gas to resist being squeezed by gravity sound waves Therefore, fluctuations in the gas propagate as sound waves. This ends abruptly when the Universe cools below 3000K and the gas becomes neutral: Universe suddenly becomes transparent Big Bang Today Recombination z ~ 1000 ~400,000 years Ionized Neutral Time Bob Nichol - ICG, Portsmouth

5. Daniel Eisenstein – Univ. of Arizona Cosmic Microwave Background Effect of this sound wave already discovered in relic light of the early universe i.e. the CMB! That was the Universe at 400,000 years. Can we see these sound waves today? Bob Nichol - ICG, Portsmouth

6. Daniel Eisenstein – Univ. of Arizona Theory of the sound wave At first, sound wave expands at 57% of the speed of light, then slows as the gas changes from ionized to neutral (red = ionized, green = neutral) 500 million light years Final size is reached after one million years. Today, that radius is 500 million light years. Both are seeds for the formation of galaxies Central peak is overdense in dark matter. Outer ring is overdense in gas. Both are seeds for the formation of galaxies. Our theory accurately predicts an excess of galaxy pairs separated by 500 million light-years: this would be the “SMOKING GUN” that only gravity was important to explain the rich structures of galaxies and clusters of galaxies we see today Bob Nichol - ICG, Portsmouth

7. Daniel Eisenstein – Univ. of Arizona The Sloan Digital Sky Survey The Sloan Digital Sky Survey is a survey of (one quarter) of the northern sky. Over 200 scientists from 14 institutions around the world. Here we report on a sample that covers 10% of the sky. Luminous red galaxy sample: special spectroscopic sample of 47,000 galaxies that extends to z = 0.47, 6 billion light years away. SDSS Telescope in Apache Point, New Mexico Bob Nichol - ICG, Portsmouth Largest volume ever surveyed with galaxies (This is why we can see this wave)

8. Daniel Eisenstein – Univ. of Arizona 700,000 light years 500 Million Light Years Credit: SDSS A slice of the SDSS Bob Nichol - ICG, Portsmouth

9. Daniel Eisenstein – Univ. of Arizona The Correlation Function The correlation function is the probability of finding pairs at a given separation, above that of a random distribution. Excess of galaxies separated by 500 million light years Bob Nichol - ICG, Portsmouth

10. Daniel Eisenstein – Univ. of Arizona What does it mean? SMOKING GUN” We have detected the sound wave in the Universe at two very different epochs (400,000 yrs after Big Bang and present-day). This is important because our theory of gravitational structure formation predicts that such features should have been preserved. Detecting the sound wave in the galaxies is the “SMOKING GUN” that our theory is correct. Better yet, the sound wave is an object of fixed size, a “standard ruler” or “cosmic yardstick”. This means that we can measure its apparent size anywhere in the Universe, and determine how far it is away because we know its true size. Bob Nichol - ICG, Portsmouth

11. Daniel Eisenstein – Univ. of Arizona Looking back in time in the Universe FLAT GEOMETRY CREDIT: WMAP & SDSS websites CMB Looking back in time in the Universe FLAT GEOMETRY SDSS GALAXIES

12. Daniel Eisenstein – Univ. of Arizona Looking back in time in the Universe FLAT GEOMETRY CREDIT: WMAP & SDSS websites SDSS GALAXIES CMB Looking back in time in the Universe OPEN GEOMETRY

13. Daniel Eisenstein – Univ. of Arizona Looking back in time in the Universe FLAT GEOMETRY CREDIT: WMAP & SDSS websites CMB Looking back in time in the Universe CLOSED GEOMETRY SDSS GALAXIES

14. Daniel Eisenstein – Univ. of Arizona UNIVERSE IS FLAT TO 1% PRECISION Bob Nichol - ICG, Portsmouth

15. Daniel Eisenstein – Univ. of Arizona Dark Energy In 1998, two groups used distant supernovae to discover the acceleration of the expansion history of the Universe. supernovae were fainter than expected, implying that they were further away. dark energy The cause of this is completely unknown but almost surely exotic new physics. It has been dubbed “dark energy”. Our detection requires dark energy to be correct! Now we can map the expansion of the Universe using our “cosmic yardstick”. This is a robust and innovative new method for cosmologists and will spawn future surveys of the Universe. Bob Nichol - ICG, Portsmouth

16. Daniel Eisenstein – Univ. of Arizona More Information http://cmb.as.arizona.edu/~eisenste/acousticpeak http://www.dsg.port.ac.uk/~nicholb/wiggles bob.nichol@port.ac.uk Bob Nichol - ICG, Portsmouth

17. Daniel Eisenstein – Univ. of Arizona Thanks to.... The science analysis team was supported by several grants from the National Science Foundation, as well as funds from the University of Arizona, the Sloan Foundation, and NASA. The SDSS is supported by the Alfred P. Sloan Foundation, NASA, the National Science Foundation, Dept of Energy, the Japanese Monbukagakusho, the Max Planck Society, and the Participating Institutions: University of Chicago, Fermilab, the Institute for Advanced Study, the Japanese Participation Group, the Johns Hopkins University, the Korean Scientist Group, the Max Planck Institute for Astronomy, the Max Planck Institute for Astrophysics, New Mexico State University, the University of Pittsburgh, the University of Portsmouth, Princeton University, the US Naval Observatory, and the University of Washington. Bob Nichol - ICG, Portsmouth

18. Daniel Eisenstein – Univ. of Arizona EXTRA SLIDES EXTRA SLIDES FOR Q&A Bob Nichol - ICG, Portsmouth

19. Daniel Eisenstein – Univ. of Arizona What is going on (part 2) ? Gravity squeezes the gas, pressure pushes back! They oscillate When the Universe cools below 3000K these sound waves are frozen in Bob Nichol - ICG, Portsmouth Courtesy of Wayne Hu

20. Daniel Eisenstein – Univ. of Arizona Cosmic Yardstick? Bob Nichol - ICG, Portsmouth If we know the true size of something, we can estimate how far it is away by it’s apparent size Satellite photos of Earth via Google can now be used to measure distances

21. Daniel Eisenstein – Univ. of Arizona Color SDSS Data (Hogg & Blanton) LRG

22. Daniel Eisenstein – Univ. of Arizona Life is more complicated Universe is composed of many perturbations, all superimposed. We do not expect to see bulls-eyes in the galaxy map. Indeed, the ring is only 1% of the height of the center. The whole analysis is statistical. Therefore need massive datasets like SDSS Bob Nichol - ICG, Portsmouth