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Matter Content of the Universe David Spergel March 2006 Valencia, Spain.

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Presentation on theme: "Matter Content of the Universe David Spergel March 2006 Valencia, Spain."— Presentation transcript:

1 Matter Content of the Universe David Spergel March 2006 Valencia, Spain

2 Overview What is the composition of the universe? What is the composition of the universe? 4.5% Baryons 22.4% Dark Matter 73% Dark Energy <0.1% Neutrinos, Radiation

3 Baryon Density Nucleosynthesis [D]/[H] Nucleosynthesis [D]/[H] CMB Power Spectrum CMB Power Spectrum Lyman  forest Lyman  forest Local Universe Local Universe –Where are the missing baryons? –Fukugita, Hogan & Peebles, ApJ, 503, 518

4 Baryon Abundance from Nucleosynthesis Deuterium abundance is sensitive to the ratio of baryons/photons Deuterium abundance is sensitive to the ratio of baryons/photons  b h 2 = \pm 0.02  b h 2 = \pm 0.02

5 CMB & Baryon Abundance Baryon abundance determines sound speed of baryon/photon fluid Baryon abundance determines sound speed of baryon/photon fluid Peak positions and peak heights are sensitive to baryon abundance. Peak positions and peak heights are sensitive to baryon abundance.

6 Lyman  Forest Gas along the line of sight to a distant quasar absorbs light at the Lyman transition. Gas at different redshifts produces lines at different positions. The line strength is a measure of the gas column density at each position Gas along the line of sight to a distant quasar absorbs light at the Lyman transition. Gas at different redshifts produces lines at different positions. The line strength is a measure of the gas column density at each position

7 Local Universe: Galaxies Stars in disks Stars in spheroids Neutral atomic gas Molecular gas Plasma in clusters Plasma in groups “Missing” Warm Plasma TOTAL

8 Using the CMB to Find the Missing Baryons Kinetic Sunyaev Zel’dovich Effect Kinetic Sunyaev Zel’dovich Effect Sensitive to electron density. Since we can use the local density field to predict velocity, this is a tool to find the missing baryons CMB is not just a tool for studying the high redshift universe but also the growth of structure

9 Atacama Cosmology Telescope Operations start November Operations start November Full science operations in November 2007 Full science operations in November 2007 Studies both high redshift and low redshift universe Studies both high redshift and low redshift universe

10 Evidence for Dark Matter Galaxy Motions in Clusters Galaxy Motions in Clusters Dynamical Measurements Dynamical Measurements Gravitational Lensing Gravitational Lensing CMB Observations CMB Observations

11 A2142: A Rich Cluster Images are 7’ on each side (moon is 30’) Images are 7’ on each side (moon is 30’) X-ray temperature X-ray temperature (5-10 keV) Contains 100’s of galaxies and enough gas for thousands more

12 Weighing a Cluster Galaxy velocity dispersion Galaxy velocity dispersion Hydrostatic Equlibrium of Gas Hydrostatic Equlibrium of Gas Gravitational Lensing Gravitational Lensing

13 Weighing Galaxies: Rotation Curves Galaxies contain more than just stars and gas. Roughly 10% of their mass is in non- visible matter Galaxies contain more than just stars and gas. Roughly 10% of their mass is in non- visible matter

14 Strong Gravitational Lensing

15 Gravitational Lensing:A2218

16 CMB Observations Measure Dark Matter Density at z = 1000 CMB observations imply the existence of significant amount of NON-BARYONIC dark matter Observations provide an accurate determination of dark matter density (More accurate soon!)

17 Data will improve very soon…..

18 Dwarf Spheroidals and 3 Myths about Dark Matter Myth #1: MOND can fit all galactic observations Myth #1: MOND can fit all galactic observations Myth #2: Observations imply the existence of light neutrinos Myth #2: Observations imply the existence of light neutrinos Myth #3: Locally dark matter is associated with tidal streams Myth #3: Locally dark matter is associated with tidal streams

19 What is a dwarf spheroidal? Dwarf spheroidal is a small galaxy composed of roughly a million old stars, dark matter and trace amounts of gas Dwarf spheroidal is a small galaxy composed of roughly a million old stars, dark matter and trace amounts of gas Our Galaxy has ~10 satellite dwarf galaxies Our Galaxy has ~10 satellite dwarf galaxies Dwarf spheroidals are close enough that we can observe the motions of individual stars Dwarf spheroidals are close enough that we can observe the motions of individual stars

20 Dwarf Galaxies and MOND MOND is an alternative to dark matter based on modifications on Newton’s equations MOND is an alternative to dark matter based on modifications on Newton’s equations MOND fails dramatically in explaining dwarf spheroidals MOND fails dramatically in explaining dwarf spheroidals

21 Dwarf Galaxies and the Nature of Dark Matter Recent analysis claim that the dwarf galaxy observations imply a characteristic mass for the dark matter Recent analysis claim that the dwarf galaxy observations imply a characteristic mass for the dark matter

22 Dwarf Spheroidals have a minimum velocity disperson Over a wide range of luminosity, dwarf spheroidals all have about the same velocity dispersion: Over a wide range of luminosity, dwarf spheroidals all have about the same velocity dispersion: 9 km/s Recent claim interpret this as a signature of dark matter properties m p v 2 = 10 4 K = binding energy of Hydrogen

23 Sagittarius Dwarf spheroidal currently being torn apart by our Galaxy Dwarf spheroidal currently being torn apart by our Galaxy Tidal stream goes through galactic neighborhood Tidal stream goes through galactic neighborhood

24 Sagittarius Dwarf

25 Tidal Debris Model Law, Johnston & Majewski 2005

26 Does the tidal debris affect the dark matter searches? Freese et al: could be up to 20% of local dark matter density. Argue for important local contribution Freese et al: could be up to 20% of local dark matter density. Argue for important local contribution PROBLEM: PROBLEM: –Assumes copious amounts of dark matter –However, the width of the tidal stream depends on the dark matter density. –Can place upper limit on local density < 1% of the local dark matter density

27 Conclusions We have not yet identified most of the mass in the local universe - dark baryons (hot gas?) - dark matter (SUSY particles??) Astronomical observations constrain dark matter properties: - CMB observations require non-baryonic dark matter - Be wary of strong claims based on dwarf spheroidals!


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