# Baryon Acoustic Oscillations: A standard ruler method for determining the expansion rate of the Universe. Martin White UC Berkeley/LBNL

Save this PDF as:

Size: px
Start display at page:

Download "Baryon Acoustic Oscillations: A standard ruler method for determining the expansion rate of the Universe. Martin White UC Berkeley/LBNL"

## Transcription

1 Baryon Acoustic Oscillations: A standard ruler method for determining the expansion rate of the Universe. Martin White UC Berkeley/LBNL

2 Outline Dark energy and standard rulers. Cosmic sound: baryon acoustic oscillations. Current state-of-the-art Future experiments. More on theoretical issues. More on modeling issues. Prospects and conclusions. Eisenstein, New Astronomy Reviews, 49, 360,

3 Beyond Einstein? Our theories of the Universe are based upon General Relativity which, like Newton s theory, predicts that gravity is an attractive force which would act to slow any existing expansion The discovery that the expansion of the Universe is currently accelerating was heralded as the Breakthrough of the year by Science in 1998.

4 Dark energy There are now several independent ways to show that the expansion of the Universe is accelerating. This indicates that: a) Our theory of gravity (General Relativity) is wrong. b) The universe is dominated by a material which violates the strong energy condition: ρ+3p>0. If (b) then it cannot be any fluid we are familiar with, but some weird stuff which dominates the energy density of the Universe (today). We refer to it as dark energy. The most prosaic explanation is Einstein s cosmological constant, which can be interpreted as the energy of empty space.

5 Dark energy equation of state The amount of dark energy is actually quite well constrained by present data: ρ DE = (1.43±0.09)x10-29 g/cm 3 What distinguishes models is the time-evolution of ρ DE This is usually described by the equation of state: w=p/ρ. A cosmological constant, vacuum energy, has w=-1. Many (most) dark energy models have w>-1, and time evolving. So the holy grail of DE research is to demonstrate that w -1 at any epoch.

6 Probing DE via cosmology We see dark energy through its effects on the expansion of the universe: Three (3) main approaches Standard candles measure d L (integral of H -1 ) Standard rulers measure d A (integral of H -1 ) and H(z) Growth of fluctuations. Crucial for testing extra ρ components vs modified gravity.

7 Standard rulers Suppose we had an object whose length (in meters) we knew as a function of cosmic epoch. By measuring the angle (Δθ) subtended by this ruler (Δχ) as a function of redshift we map out the angular diameter distance d A By measuring the redshift interval (Δz) associated with this distance we map out the Hubble parameter H(z)

8 Ideal properties of the ruler? To get competitive constraints on dark energy we need to be able to see changes in H(z) at the 1% level -- this would give us statistical errors in DE equation of state (w=p/ρ) of ~10%. We need to be able to calibrate the ruler accurately over most of the age of the universe. We need to be able to measure the ruler over much of the volume of the universe. We need to be able to make ultra-precise measurements of the ruler.

9 Where do we find such a ruler? Cosmological objects can probably never be uniform enough. We believe that the laws of physics haven t changed over the relevant time scales. Use features arising from physical processes in the early Universe. Use statistics of the large-scale distribution of matter and radiation. If we work on large scales or early times perturbative treatment is valid and calculations under control. Sunyaev & Zel dovich (1970); Peebles & Yu (1970); Doroshkevitch, Sunyaev & Zel dovich (1978); ; Hu & White (1996); Cooray, Hu, Huterer & Joffre (2001); Eisenstein (2003); Seo & Eisenstein (2003); Blake & Glazebrook (2003); Hu & Haiman (2003); Back to the beginning

10 The CMB power spectrum Anisotropy power Angular scale The current CMB data are in excellent agreement with the theoretical predictions of a ΛCDM model. Hinshaw et al. (2008)

11 The cartoon At early times the universe was hot, dense and ionized. Photons and matter were tightly coupled by Thomson scattering. Short m.f.p. allows fluid approximation. Initial fluctuations in density and gravitational potential drive acoustic waves in the fluid: compressions and rarefactions with δ γ δ b. Consider a (standing) plane wave perturbation of comoving wavenumber k. If we expand the Euler equation to first order in the Compton mean free path over the wavelength we obtain

12 The cartoon These perturbations show up as temperature fluctuations in the CMB. Since ρ~t 4 for a relativistic fluid the temperature perturbations look like: [harmonic wave] plus a component due to the velocity of the fluid (the Doppler effect).

13 The cartoon A sudden recombination decouples the radiation and matter, giving us a snapshot of the fluid at last scattering. These fluctuations are then projected on the sky with λ~r ls θ or l~k r ls

14 Acoustic oscillations seen! First compression, at kcstls=π. Density maxm, velocity null. Velocity maximum First rarefaction peak at kcstls=2π Acoustic scale is set by the sound horizon at last scattering: s = cstls

15 CMB calibration Not coincidentally the sound horizon is extremely well determined by the structure of the acoustic peaks in the CMB. WMAP 5 th yr data Dominated by uncertainty in ρ m from poor constraints near 3 rd peak in CMB spectrum. (Planck will nail this!)

16 Baryon oscillations in P(k) Since the baryons contribute ~15% of the total matter density, the total gravitational potential is affected by the acoustic oscillations with scale set by s. This leads to small oscillations in the matter power spectrum P(k). No longer order unity, like in the CMB, now suppressed by Ω b /Ω m ~ 0.1 Note: all of the matter sees the acoustic oscillations, not just the baryons.

17 Baryon (acoustic) oscillations RMS fluctuation Wavenumber

18 Divide out the gross trend A damped, almost harmonic sequence of wiggles in the power spectrum of the mass perturbations of amplitude O(10%).

19 In configuration space The configuration space picture offers some important insights,and will be useful when we consider non-linearities and bias. In configuration space we measure not power spectra but correlation functions: ξ(r )= Δ 2 (k)j 0 (kr) dlnk. A harmonic sequence would be a δ-function in r, the shift in frequency and diffusion damping broaden the feature. Acoustic feature at ~100 Mpc/h with width ~10Mpc/h (Silk scale)

20 Configuration space In configuration space on uses a Green s function method to solve the equations, rather than expanding k-mode by k- mode. (Bashinsky & Bertschinger 2000) To linear order Einstein s equations look similar to Poisson s equation relating φ and δ, but upon closer inspection one finds that the equations are hyperbolic: they describe traveling waves. [effects of local stress-energy conservation, causality, ] In general the solutions are unenlightening, but in some very simple cases you can see the main physical processes by eye, e.g. a pure radiation dominated Universe:

21 The acoustic wave Start with a single perturbation. The plasma is totally uniform except for an excess of matter at the origin. High pressure drives the gas+photon fluid outward at speeds approaching the speed of light. Baryons Photons Mass profile Eisenstein, Seo & White (2006)

22 The acoustic wave Initially both the photons and the baryons move outward together, the radius of the shell moving at over half the speed of light. Baryons Photons

23 The acoustic wave This expansion continues for 10 5 years

24 The acoustic wave After 10 5 years the universe has cooled enough the protons capture the electrons to form neutral Hydrogen. This decouples the photons from the baryons. The former quickly stream away, leaving the baryon peak stalled. Baryons Photons

25 The acoustic wave The photons continue to stream away while the baryons, having lost their motive pressure, remain in place.

26 The acoustic wave

27 The acoustic wave The photons have become almost completely uniform, but the baryons remain overdense in a shell 100Mpc in radius. In addition, the large gravitational potential well which we started with starts to draw material back into it.

28 The acoustic wave As the perturbation grows by ~10 3 the baryons and DM reach equilibrium densities in the ratio Ω b /Ω m. The final configuration is our original peak at the center (which we put in by hand) and an echo in a shell roughly 100Mpc in radius. Further (non-linear) processing of the density field acts to broaden and very slightly shift the peak -- but galaxy formation is a local phenomenon with a length scale ~10Mpc, so the action at r=0 and r~100mpc are essentially decoupled. We will return to this

29 Features of baryon oscillations Firm prediction of models with Ω b >0 Positions well predicted once (physical) matter and baryon density known - calibrated by the CMB. Oscillations are sharp, unlike other features of the power spectrum. Internal cross-check: d A should be the integral of H -1 (z). Since have d(z) for several z s can check spatial flatness: d(z 1 +z 2 ) = d(z 1 )+d(z 2 )+O(Ω K ) Ties low-z distance measures (e.g. SNe) to absolute scale defined by the CMB (in Mpc, not h -1 Mpc). Allows ~1% measurement of h using trigonometry!

30 Aside:broad-band shape of P(k) This picture also allows us a new way of seeing why the DM power spectrum has a peak at the scale of M-R equality. Initially our DM distribution is a δ-function. As the baryon-photon shell moves outwards during radiation domination, its gravity drags the DM, causing it to spread. The spreading stops once the energy in the photonbaryon shell no longer dominates: after M-R equality. The spreading of the δ-function ρ(r) is a smoothing, or suppression of high-k power.

31 Shape of P(k) in pictures Eisenstein, Seo & White (2007)

32 The program Find a tracer of the mass density field and compute its 2-point function. Locate the features in the above corresponding to the sound horizon, s. Measure the Δθ and Δz subtended by the sound horizon, s, at a variety of redshifts, z. Compare to the value at z~10 3 to get d A and H(z) Infer expansion history, DE properties, modified gravity. But ruler inconveniently large

33 Early surveys too small BAO scale CfA2 redshift survey (Geller & Huchra 1989) Formally, this could measure BAO with a ~0.05σ detection

34 Finally technically possible SDSS and 2dF surveys allow detection of BAO signal

35 Another prediction verified!! Eisenstein et al. (2005) detect oscillations in the SDSS LRG ξ(r) at z~0.35! Knowing s determines D(z=0.35). About 10% of the way to the surface of last scattering! Constraints argue for the existence of DE, but do not strongly constrain its properties.

36 Current state of the art 1. Eisenstein et al 2005 o 3D map from SDSS o 46,000 galaxies, 0.72 (h -1 Gpc) 3 2. Cole et al 2005 o 3D map from 2dFGRS at AAO o 221,000 galaxies in 0.2 (h -1 Gpc) 3 3. Hutsi (2005ab) o Same data as (1). 4. Padmanabhan et al 2007 o Set of 2D maps from SDSS o 600,000 galaxies in 1.5 (h -1 Gpc) 3 5. Blake et al 2007 o (Same data as above) 6. Percival et al 2007 o (Combination of SDSS+2dF) 7. Okumura et al 2007 o (Anisotropic fits) 8. Gaztanaga et al. 2008a o (3pt function) 9. Gaztanaga et al. 2008b o (measure of H) (spectro-z) 4% distance measure (spectro-z) 5% distance measure (photo-z) 6% distance measure (spectro-z) Detection

37 Current combined constraints P(k)/P smooth (k) Percival et al. (2007); Dunkley et al. (2008)

38 on cosmological parameters Equation of state (p/ρ) SNe only SNe + BAO Mass density From Percival et al. (2007)

39 The next step? We need a much more precise measurement of s at more redshifts to constrain DE. To measure P(k) or ξ(r) well enough to see such subtle features requires many well defined modes More than a Gpc 3 volume. Million(s) of galaxies. Systematic errors need to be controlled to high precision.

40 The next generation There are now proposals for several next-generation BAO surveys, both spectroscopic and photometric. Photometric surveys generally deeper and wider. Not a requirements driver if already doing weak lensing. More susceptible to systematic errors in z determination. Generally takes 3-10x as much sky for same constraints as a spectro survey (# modes in 2D vs 3D). Cannot make use of reconstruction. Future surveys should be able to measure d A and H to ~1%, giving competitive constraints on DE Eventually a space-based, all-sky BAO survey could measure distances to ~0.1% over most of the redshift range of interest for DE.

41 The landscape It s difficult to do BAO at very low z, because you can t get enough volume. BAO surveys turn on around z~0.3 and can go as high as z~3. A point at high z constrains Ω K Allowing focus on w 0 and w a at lower z. Lower z very complementary to SNe. Completes distance triangle, constrains curvature. Ground BAO+Stage IV SNe (opt), FoM ~6x. Tests of GR? Can do lensing from BAO, but weak constraint. Assuming GR, distances give δ(z~1)/δ(z~10 3 ) to <1%. A spectroscopic survey that does BAO can use redshift space distortions to measure the temporal metric perturbations (c.f. WL which measures sum of temporal and spatial) and hence constrain dd/dln(a).

42 Distances In the standard parameterization the effects of DE are confined to low z, and are (partially) degenerate with curvature. A high z measurement can nail down the curvature, removing the degeneracy. Distance from last scattering Ω Κ w 0 w a

43 Not-so-next-generation surveys While the final round of data (DR7) from SDSS-I & II hasn t been analyzed yet the next generation of surveys is already underway. Project Redshift Area (sq. deg.) n (10-4 ) WiggleZ , HETDEX SDSS-III (BOSS) , , Pan-STARRS * , With more waiting in the wings

44 BOSS in a nutshell BOSS is part of SDSS-III which started July 2008 Image additional 2000 deg 2 in Fall by end of 2008 BOSS will then have: 8500 deg 2 footprint in Spring 2500 deg 2 footprint in Fall Upgrade spectrographs in summer 2008 or 2009 Replace 640x 3-arcsec fibres with 1000x 2-arcsec fibers in cartridges Replace CCDs with (larger/better) Fairchild & LBNL CCDs Increase wavelength range to A (R=2400) Replace ruled gratings with VPH grisms Only spectroscopy from million LRGs i<20, z<0.8, over 10,000 deg 2 (dark+grey time) 160,000 QSOs g<22, 2.3<z<3, over 8,000 deg 2 (dark time)

45 Tracing large-scale structure The cosmic web at z~0.5, as traced by luminous red galaxies SDSS BOSS A slice 500h -1 Mpc across and 10 h -1 Mpc thick

46 DE constraints A 1% H 0 measurement A 0.2% Ω K measurement BOSS science Like SDSS-I and II, BOSS will provide a rich scientific return including: Strong constraints on primordial non-gaussianity (f NL ~10) Large scale structure constraints (250,000 modes at k<0.2) A S/N=44 measurement of fσ 8 from redshift space distortions. A S/N=200 measurement of ξ gm from galaxy-galaxy lensing Constraints on galaxy formation: evolution of massive galaxies QSO science (piggy-back program approx. doubles N QSO with z>3.6) Galactic structure (C stars) Loads of other stuff

47 BOSS science II Dark energy Large-scale structure δh 0.008, δw p (z~0.2)~0.03, δw a ~0.3 x1/2 if can model broad-band power!

48 Growth of structure Modeling of redshift space distortions allows us to constrain the growth rate of structure, fσ 8 ~dd/dln(a). BOSS forecast 2dF VVDS DEEP2

49 Findings of the Dark Energy Task Force (Reporting to DOE, NASA & NSF; chair Rocky Kolb) Four observational techniques for studying DE with baryon oscillations: Less affected by astrophysical uncertainties than other techniques. BUT We need Theoretical investigations of how far into the non-linear regime the data can be modeled with sufficient reliability and further understanding of galaxy bias on the galaxy power spectrum.

50 Those pesky details Unfortunately we don t measure the linear theory matter power spectrum in real space. We measure: the non-linear galaxy power spectrum in redshift space How do we handle this?

51 Numerical simulations Our ability to simulate structure formation has increased tremendously in the last decade. Simulating the dark matter for BAO: Meiksin, White & Peacock (1999) 10 6 particles, 10 2 dynamic range, ~1Gpc 3 Springel et al. (2005) particles, 10 4 dynamic range, 0.1Gpc 3 Our understanding of -- or at least our ability to describe -- galaxy formation has also increased dramatically.

52 Effects of non-linearity As large-scale structure grows, neighboring objects pull on the baryon shell around any point. This superclustering causes a broadening of the peak [and additional non-linear power on small scales]. From simulations or PT (of various flavors) find: This does a reasonable job of providing a template low-z spectrum, and it allows us to understand where the information lives in Fourier space [forecasting]. Eisenstein, Seo & White (2007) Smith, Scoccimarro & Sheth (2007) Eisenstein et al. (2007) Matsubara (2007, 2008) Padmanabhan et al. (2008)

53 Non-linearities smear the peak Loss of contrast and excess power from non-linear collapse. Broadening of feature due to Gaussian smoothing and ~0.5% shift due to mode coupling.

54 Information on the acoustic scale For a Gaussian random field Var[x 2 ]=2Var[x] 2, so our power spectrum errors are go as the square of the (total) power measured. Measured power is P+1/n For a simple 1D model the error on the sound horizon, s, is: Note that δp/δlns depends only on the wiggles while P+1/n depends on the whole spectrum. The wiggles are (exponentially) damped at high k. So an optimal survey has a large V, and sets 1/n such that it is less than P for k<σ -1 Seo & Eisenstein (2006)

55 Reconstruction The broadening of the peak comes from the tugging of largescale structure on the baryon shell. We measure the large-scale structure and hence the gravity that tugged. Half of the displacement in the shell comes from tugs on scales > 100 Mpc/h Use the observations to undo non-linearity Measure δ(x), infer φ(x), hence displacement. Move the galaxies back to their original positions. Putting information from the phases back into P(k). Reconstruction effectively reduces Σ, recovering high k information. There were many ideas about this for measuring velocities in the 80 s and 90 s; but not much of it has been revisited for reconstruction (yet). Eisenstein et al. (2007) Huff et al. (2007) Seo et al. (2008)

56 Reconstruction: simplest idea z=49 Reconstructed z=0.3 From Eisenstein et al. (2007)

57 Mode coupling BAO may be one of the few places where perturbation theory really helps. In perturbation theory I can expand δ=δ 1 +δ 2 +δ 3 + where δ n is n th order in δ 1. Under some (not completely justified) assumptions, it is straightforward to write δ n as integrals over n δ 1 s: δ n (k) = dp j δ(d) (k p) F n (p 1 p n ) δ 1 (p 1 ) δ n (p n ) The F n are simply ratios of dot products of the p n, and can be derived by a simple recurrence relation. The power spectrum looks like: P(k)=P 11 (k)+p 13 (k)+p 22 (k)+ Juszkiewicz (1981); Vishniac (1983); Fry (1984); Goroff et al. (1986); Makino et al. (1992); Jain & Bertschinger (1994); etc.

58 Mode coupling The term P 13 looks like P 11 times an integral over P 11 with a broad kernel. Terms of the form P 1n give the exponential damping, though standard PT over-estimates the strength of the damping. This is essentially the random Zel dovich displacement of particles from their initial positions. rms Zel dovich displacement at 100Mpc that for infinite displacement. The term P 22 is a true convolution-like integral of P 11, times the square of F 2. Since F 2 has a strong peak for p 1 =p 2, the mode coupling term P 22 has wiggles out of phase with P 11 and gives a shift in the acoustic scale. Reconstruction appears to remove this shift. These arguments can be generalized to halos & galaxies.

59 Redshift space distortions Anisotropic correlation function 2dFGRS, Peacock et al. Inhomogeneities in Φ lead to motion, so the observed v is not directly proportional to distance: These effects are still difficult to describe with high accuracy analytically, but they can be simulated.

60 Redshift space distortions II The distortions depend on non-linear density and velocity fields, which are correlated. Velocities enhance power on large scales and suppress power on small scales. Coherent infall Random (thermal) motion The transition from enhancement to suppression occurs on the scale of the baryon oscillations but does not introduce a feature.

61 Galaxy bias The hardest issue is galaxy bias. Galaxies don t faithfully trace the mass... but galaxy formation scale is << 100Mpc so effects are smooth. In P(k) effect of bias can be approximated as a smooth multiplicative function and a smooth additive function. Work is on-going to investigate these effects: Seo & Eisenstein (2005) White (2005) Schulz & White (2006) Eisenstein, Seo & White (2007) Percival et al. (2007) Huff et al. (2007) Angulo et al. (2007) Smith et al. (2007) Padmanabhan et al. (2008) Seo et al. (2008) Matsubara (2008) Δ 2 g(k)=b 2 (k) Δ 2 (k) + C(k) Rational functions or polynomials

62 Modeling red galaxies Recent advances in our ability to model (understand?) red galaxies as a function of luminosity in the range 0<z<1: SDSS LRGs NDWFS NDWFS Padmanabhan et al. (2008); Brown et al. (2008); This small-scale understanding aids our models of large-scale effects.

63 Ongoing work Templates for fitting data, able to account for nonlinearity, redshift space distortions and galaxy bias. New estimators optimized for large-scale signals calibrated by numerical simulations. Models for the covariance matrices, calibrated by simulations. More sophisticated reconstruction algorithms. Some new ideas, and experimental approaches

64 Statistics Extracting science from surveys always involves a comparison of some statistic measured from the data which can be computed reliably from theory. Theory probably means simulations. Significant advances in statistical estimators in the last decade (CMB and SDSS) Open questions: Which space should we work in? Fourier or configuration space? What is the best estimator to use? P(k), ξ(r ), Δξ(r ), ω l (r s ),? How do we estimate errors? Assume Gaussian, mock catalogs,

65 Lensing Hui, Gaztanaga & LoVerde have analyzed the effects of lensing on the correlation function. For next-generation experiments the effect is small, but it may eventually be measurable. Template is known: For normal galaxy parameters fractional peak shift on isotropic spectrum is below 0.1% out to z~2 or so.

66 A new way of doing BAO at z~2-3 One requires less sky area per unit volume at high z, but it becomes increasingly expensive to obtain spectra (and imaging) of high z galaxies. Quasars can be seen to high z easily. Their light is filtered by the IGM along the line-of-sight The fluctuations in the IGM can be seen in QSO spectra. The fluctuations contain the BAO signature. Thus a dense grid of QSO spectra can (in principle) be used to measure BAO at high z. This has little impact on instrument design, but could dramatically alter survey optimization. A very promising idea which needs to be further investigated (theoretically & observationally). White (2003) McDonald & Eisenstein (2006)

67 QSO constraints BOSS (an example): 8000 sq. deg. to g=22 1.5% measure of both d A and H Comparable to other high z measurements, but with a 2.5m telescope! QSO+LRG QSO only McDonald & Eisenstein (2006)

68 DE or early universe weirdness? Key to computing s is our ability to model CMB anisotropies. Want to be sure that we don t mistake an error in our understanding of z~10 3 for a property of the DE! What could go wrong in the early universe? Recombination. Misestimating c s or ρ B /ρ γ. Misestimating H(z>>1) (e.g. missing radiation). Strange thermal history (e.g. decaying ν). Isocurvature perturbations. It seems that future measurements of CMB anisotropies (e.g. with Planck) constrain s well enough for this measurement even in the presence of odd high-z physics. Eisenstein & White (2004); White (2006)

69 Conclusions Baryon oscillations are a firm prediction of CDM models. Method is simple geometry, with few systematics. The acoustic signature has been detected in the SDSS! With enough samples of the density field, we can measure d A (z) and H -1 (z) to the percent level and thus constrain DE. Was Einstein right? Require only a large redshift survey - we have >20 years of experience with redshift surveys. Exciting possibility of doing high z portion with QSO absorption lines, rather than galaxies. It may be possible to undo non-linearity. Much work remains to be done to understand structure and galaxy formation to the level required to maximize our return on investment!

70 The End

### Probing Dark Energy with Baryon Acoustic Oscillations from Future Large Galaxy Redshift Surveys

Probing Dark Energy with Baryon Acoustic Oscillations from Future Large Galaxy Redshift Surveys Hee-Jong Seo (Steward Observatory) Daniel J. Eisenstein (Steward Observatory) Martin White, Edwin Sirko,

### Galaxy Survey data analysis using SDSS-III as an example

Galaxy Survey data analysis using SDSS-III as an example Will Percival (University of Portsmouth) showing work by the BOSS galaxy clustering working group" Cosmology from Spectroscopic Galaxy Surveys"

### Testing gravity at large scales.

Testing gravity at large scales. Outline: How to test gravity at large scales with Cosmology What can we expect from different experiments in the next decade. F. B. Abdalla Cosmology: Concordance Model

### Pillars of Standard Model. Homogeneity and Isotropy Night Sky is Dark

Pillars of Standard Model Homogeneity and Isotropy Night Sky is Dark Linear Expansion Light Element Abundances Microwave Background Radiation [+other large scale structures] Wilkinson Microwave Anisotropy

### World of Particles Big Bang Thomas Gajdosik. Big Bang (model)

Big Bang (model) What can be seen / measured? basically only light (and a few particles: e ±, p, p, ν x ) in different wave lengths: microwave to γ-rays in different intensities (measured in magnitudes)

### Malcolm S. Longair. Galaxy Formation. With 141 Figures and 12 Tables. Springer

Malcolm S. Longair Galaxy Formation With 141 Figures and 12 Tables Springer Contents Part I Preliminaries 1. Introduction, History and Outline 3 1.1 Prehistory 3 1.2 The Theory of the Expanding Universe

### Testing the laws of gravity with redshift-space distortions (RSDs) Chris Blake (Swinburne)

Testing the laws of gravity with redshift-space distortions (RSDs) Chris Blake (Swinburne) What observations can cosmologists make? How fast is the Universe expanding with time? How fast are structures

### Neutrino properties from Cosmology

Neutrino properties from Cosmology Anže Slosar, BNL Neutrino16, July 16 1 / 30 plan for the talk Pedagogical introduction to the role neutrinos play in Cosmology aimed at a non-cosmo community Neutrinos

### Testing the laws of gravity with cosmological data. Chris Blake (Swinburne)

Testing the laws of gravity with cosmological data Chris Blake (Swinburne) The Our dark current energy model puzzle of cosmology We have a superbly detailed picture of the early Universe [e.g. CMB, nucleosynthesis]

### Theoretical Astrophysics & Cosmology Spring 2015

Theoretical Astrophysics & Cosmology Spring 2015 Lectures: Lucio Mayer & Alexandre Refregier Problem sessions: Andrina Nicola & Aleksandra Sokolowska Lectures take place at: Wednesday at ETH: 13-15 room

### Big Bang Cosmology. Big Bang vs. Steady State

Big Bang vs. Steady State Big Bang Cosmology Perfect cosmological principle: universe is unchanging in space and time => Steady-State universe - Bondi, Hoyle, Gold. True? No! Hubble s Law => expansion

### Einstein's Cosmological Principle: the foundation of cosmology

Einstein's Cosmological Principle: the foundation of cosmology The Universe, on average, is homogeneous (equal density everywhere if averaged over a sufficiently large volume) and isotropic (it looks the

### SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems 1.

SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems 1 January 8, 2008 1 Abstracted from a proposal to the National Science Foundation,

### Cosmological and Solar System Tests of. f (R) Cosmic Acceleration

Cosmological and Solar System Tests of f (R) Cosmic Acceleration Wayne Hu Origins Institute, May 2007 Why Study f(r)? Cosmic acceleration, like the cosmological constant, can either be viewed as arising

### What was before the Big Bang?

1 / 68 Std. What was before the Big Bang? of the Very Robert Brandenberger McGill University February 21, 2013 2 / 68 Outline Std. 1 What is? 2 Standard Big Bang 3 ary 4 String 5 3 / 68 Plan Std. 1 What

### History of the universe!

Cosmology & the CMB - Cosmology: Overview - Cosmic Microwave Background - Large Scale Structure (Wed) - CMB Fluctuations (Wed) Wednesday: HW#8 presentations Nov 02, 2015 History of the universe Discovery

### Topic 3. Evidence for the Big Bang

Topic 3 Primordial nucleosynthesis Evidence for the Big Bang! Back in the 1920s it was generally thought that the Universe was infinite! However a number of experimental observations started to question

### Cosmic Structure Formation on Supercomputers (and laptops)

Cosmic Structure Formation on Supercomputers (and laptops) Lecture 1: Motivation and Initial Conditions Benjamin Moster! Ewald Puchwein 1 Outline of the lecture course Lecture 1: Motivation & Initial conditions!

### arxiv:1302.1640v2 [astro-ph.co] 11 Apr 2013

Draft version April, 03 Preprint typeset using L A TEX style emulateapj v. 5// MASS-DEPENDENT BARYON ACOUSTIC OSCILLATION SIGNAL AND HALO BIAS Qiao Wang and Hu Zhan Key Laboratory of Optical Astronomy,

### Galaxy Formation Carlos Frenk Institute of Computational Cosmology University of Durham. Books:

Galaxy Formation Carlos Frenk Institute of Computational Cosmology Goal: understand origin and evolution of cosmic structures Review of standard Big Bang model Growth of small fluctuations (linear theory)

### Experimental Astroparticle Physics

Experimental Astroparticle Physics WIMP Lecture UZH / ETH Zurich Spring Semester 2013 Organization Lectures: Fridays, 11:15 13:00 (this room) Exercises: Fridays, 14:00 15:45 (every 2nd Friday!) Slides,

### The Big Bang. working our way forward to Now

The Big Bang In the beginning the Universe was created. This has made a lot of people very angry and has been widely regarded as a bad move. - Hitchhiker s guide to the galaxy The Big Bang working our

### Cosmological Scale Tests of Gravity

Cosmological Scale Tests of Gravity Edmund Bertschinger MIT Department of Physics and Kavli Institute for Astrophysics and Space Research January 2011 References Caldwell & Kamionkowski 0903.0866 Silvestri

### Dark Matter and the Universe

Dark Matter and the Universe Topic 1 Dark Matter, Dark Energy and the Cosmology Revolution What is the real structure of our Universe and how do we know it is so? Contents of Topic 1 This first Topic provides

### arxiv:0805.0117v2 [astro-ph] 7 Aug 2008

Accepted for publication in the Astrophysical Journal Preprint typeset using L A TEX style emulateapj v. 2/4/05 NON-LINEAR STRUCTURE FORMATION AND THE ACOUSTIC SCALE Hee-Jong Seo,2, Ethan R. Siegel 2,

### Dark Energy, Modified Gravity and The Accelerating Universe

Dark Energy, Modified Gravity and The Accelerating Universe Dragan Huterer Kavli Institute for Cosmological Physics University of Chicago Makeup of universe today Dark Matter (suspected since 1930s established

### The Expanding Universe. Prof Jim Dunlop University of Edinburgh

The Expanding Universe Prof Jim Dunlop University of Edinburgh Cosmology: The Study of Structure & Evolution of the Universe Small & Hot Big & Cold Observational Evidence for the Expansion of the Universe

### Lecture I: Structure Formation in the Universe. Avi Loeb Harvard University

Lecture I: Structure Formation in the Universe Avi Loeb Harvard University we are here Cradle Mountain Lodge Tasmania, January 2008 The initial conditions of the Universe can be summarized on a single

### Modified Gravity and the CMB

Modified Gravity and the CMB Philippe Brax, IphT Saclay, France arxiv:1109.5862 PhB, A.C. Davis Work in progress PhB, ACD, B. Li Minneapolis October 2011 PLANCK will give us very precise information on

### Astro 102 Test 5 Review Spring 2016. See Old Test 4 #16-23, Test 5 #1-3, Old Final #1-14

Astro 102 Test 5 Review Spring 2016 See Old Test 4 #16-23, Test 5 #1-3, Old Final #1-14 Sec 14.5 Expanding Universe Know: Doppler shift, redshift, Hubble s Law, cosmic distance ladder, standard candles,

### Chapter 27: The Early Universe

Chapter 27: The Early Universe The plan: 1. A brief survey of the entire history of the big bang universe. 2. A more detailed discussion of each phase, or epoch, from the Planck era through particle production,

### Gravity slows down the expansion

Key Concepts: Lecture 33: The Big Bang! Age of the Universe and distances from H 0 Gravity slows down the expansion Closed, Flat and Open Universes Evidence for the Big Bang (Galactic Evolution; Microwave

### An algorithm for reconstructing gradient- and curl- type deflection angle from CMB maps

An algorithm for reconstructing gradient- and curl- type deflection angle from CMB maps Toshiya Namikawa (The University of Tokyo) Collaboration with Daisuke Yamauchi (ICRR) Atushi Taruya (RESCEU, IPMU)

### What Energy Drives the Universe? Andrei Linde

What Energy Drives the Universe? Andrei Linde Two major cosmological discoveries:! The new-born universe experienced rapid acceleration (inflation)! A new (slow) stage of acceleration started 5 billion

### Astro 321 Set 4: Inflation. Wayne Hu

Astro 321 Set 4: Inflation Wayne Hu Horizon Problem The horizon in a decelerating universe scales as η a (1+3w)/2, w > 1/3. For example in a matter dominated universe η a 1/2 CMB decoupled at a = 10 3

### AST Cosmology and extragalactic astronomy. Lecture 1. Introduction/Background

AST4320 - Cosmology and extragalactic astronomy Lecture 1 Introduction/Background 1 Relevant information Class times + day: Tuesday + Wednesday 12:15-14:00. Group sessions: Monday 14:15-16:00, led by Max

### DESI: The Dark Energy Spectroscopic Instrument Pat McDonald (LBL)

DESI: The Dark Energy Spectroscopic Instrument Pat McDonald (LBL) P. McDonald 10/02/2014 LBL 1 The Big Goals Answer the ancient questions: How did the Universe begin? What is it made of? What physical

### The Birth of Our Universe Today s Lecture:

The Birth of Our Universe Today s Lecture: (Chapter 19, pages 454-481) Cosmic Microwave Background (CMB) The first few minutes of the Universe Inflation! Cosmic Microwave Background (CMB) A. Penzias and

### Chapter 16. The Hubble Expansion

Chapter 16 The Hubble Expansion The observational characteristics of the Universe coupled with theoretical interpretation to be discussed further in subsequent chapters, allow us to formulate a standard

### 10 Things Everyone Should Know About the Universe

10 Things Everyone Should Know About the Universe Dragan Huterer KICP, University of Chicago 10 Things Everyone Should Know About the Universe p.1/12 1. What is Dark Matter? DM is the unseen matter that

### The Search for Dark Matter, Einstein s Cosmology and MOND. David B. Cline

The Search for Dark Matter, Einstein s Cosmology and MOND David B. Cline Astrophysics Division, Department of Physics & Astronomy University of California, Los Angeles, CA 90095 USA dcline@physics.ucla.edu

### Today. Course Evaluations Open. Modern Cosmology. The Hot Big Bang. Age & Fate. Density and Geometry. Microwave Background

Today Modern Cosmology The Hot Big Bang Age & Fate Density and Geometry Microwave Background Course Evaluations Open 1 Distances between faraway galaxies change while light travels. distance? 2 2007 Pearson

### T = m hc 2 k B = K

PHYSICS 43/53: Cosmology Midterm Exam Solution Key (06). [5 points] Short Answers (5 points each) (a) What are the two assumptions underlying the cosmological principle? i. The Universe is homogeneous

### Modern Ways of Dating the Universe. Martha P. Haynes Goldwin Smith Professor of Astronomy Cornell University. CAU Study Tour June 2014

Modern Ways of Dating the Universe Martha P. Haynes Goldwin Smith Professor of Astronomy Cornell University CAU Study Tour June 2014 What does the night sky look like? The disk of the Milky Way, our galaxy

### Milky Way Galaxy Determining the size/extent counting stars (doesn t work) Variable Stars Red Giants/Supergiants Instability Strip Hydrostatic

Milky Way Galaxy Determining the size/extent counting stars (doesn t work) Variable Stars Red Giants/Supergiants Instability Strip Hydrostatic Equilibrium Cepheids characteristics Type I, II differences

### Lecture III. CMB Polarization. Wayne Hu Tenerife, November 2007

Lecture III CMB Polarization Wayne Hu Tenerife, November 2007 Polarized Landscape 100 10 reionization ΘE (µk) 1 EE BB 0.1 0.01 Hu & Dodelson (2002) gravitational waves 10 100 1000 l (multipole) gravitational

### Dark Energy and the Accelerating Universe. Dragan Huterer Kavli Institute for Cosmological Physics University of Chicago

Dark Energy and the Accelerating Universe Dragan Huterer Kavli Institute for Cosmological Physics University of Chicago The universe today presents us with a grand puzzle: what is 95% of it made of!? Shockingly,

### Cosmic Surveys and the Composition of the Universe

2014 Shaw Lecture Essay in Astronomy Cosmic Surveys and the Composition of the Universe 1. Introduction Shaun Cole 1, Daniel J. Eisenstein 2, John A. Peacock 3 1: Institute for Computational Cosmology,

### Taking the Universe s Baby Picture. David Spergel Princeton

Taking the Universe s Baby Picture David Spergel Princeton Overview n Cosmology after WMAP: Standard Model n Last Two Years: n Improving Sensitivity and Resolution n ACT, SPT, and Planck n Looking to the

### phenomenological aspects of dark energy / mod. gravity

phenomenological aspects of dark energy / mod. gravity Martin Kunz University of Sussex MK & Domenico Sapone, PRL 98, 121301 (2007) MK, astro-ph/0702615 (2007) Luca Amendola, MK & Domenico Sapone, JCAP

### The Origin, Evolution, and Fate of the Universe

The Origin, Evolution, and Fate of the Universe Announcements n Homework # 8 is available as of this morning in OWL. Due date for is Friday Dec 9th n Exam # 3 will take place on Tuesday, December 6 th

### Lecture Outlines. Chapter 26. Astronomy Today 7th Edition Chaisson/McMillan Pearson Education, Inc.

Lecture Outlines Chapter 26 Astronomy Today 7th Edition Chaisson/McMillan Chapter 26 Cosmology Units of Chapter 26 26.1 The Universe on the Largest Scales 26.2 The Expanding Universe 26.3 The Fate of the

### II Jose Plinio Baptista School of Cosmology March CMB theory. David Wands. Institute of Cosmology and Gravitation University of Portsmouth

II Jose Plinio Baptista School of Cosmology March 014 CMB theory David Wands Institute of Cosmology and Gravitation University of Portsmouth Part 1: overview introduction cosmological parameters a brief

### The Birth of the Universe Newcomer Academy High School Visualization One

The Birth of the Universe Newcomer Academy High School Visualization One Chapter Topic Key Points of Discussion Notes & Vocabulary 1 Birth of The Big Bang Theory Activity 4A the How and when did the universe

### Institut für Kern- und Teilchenphysik Neutrinos & Cosmology

Neutrinos & Cosmology 1 Cosmology: WHY??? From laboratory experiment limits can be set ONLY in neutrino mass difference No information if neutrino masses are degenerated From kinematic experiment limits

### Astronomy & Physics Resources for Middle & High School Teachers

Astronomy & Physics Resources for Middle & High School Teachers Gillian Wilson http://www.faculty.ucr.edu/~gillianw/k12 A cosmologist is.... an astronomer who studies the formation and evolution of the

### Lecture 19 Big Bang Cosmology

The Nature of the Physical World Lecture 19 Big Bang Cosmology Arán García-Bellido 1 News Exam 2: you can do better! Presentations April 14: Great Physicist life, Controlled fusion April 19: Nuclear power,

### Structure formation in modified gravity models

Structure formation in modified gravity models Kazuya Koyama Institute of Cosmology and Gravitation University of Portsmouth Dark energy v modified gravity Is cosmology probing the breakdown of general

### Lecture 15 Fundamentals of Physics Phys 120, Fall 2015 Cosmology

Lecture 15 Fundamentals of Physics Phys 120, Fall 2015 Cosmology A. J. Wagner North Dakota State University, Fargo, ND 58108 Fargo, October 20, 2015 Overview A history of our view of the universe The Big

### 6. What is the approximate angular diameter of the Sun in arcseconds? (d) 1860

ASTR 1020 Stellar and Galactic Astronomy Professor Caillault Fall 2009 Semester Exam 1 Multiple Choice Answers (Each multiple choice question is worth 1.5 points) 1. The number of degrees in a full circle

### OUTLINE The Hubble parameter After these lectures, you should be able to: Define the Hubble parameter H Sketch a(t) for k>0, k=0, k<0 assuming Λ=0 Def

Observational cosmology: The Friedman equations 2 Filipe B. Abdalla Kathleen Lonsdale Building G.22 http://zuserver2.star.ucl.ac.uk/~hiranya/phas3136/phas3136 OUTLINE The Hubble parameter After these lectures,

### Mapping structure of the Universe. the very large scale. INAF IASF Milano

Mapping the large scale structure of the Universe the very large scale structure Marco Scodeggio INAF IASF Milano The large scale structure (100Mpc) Zero order approximation: the Universe is homegeneous

### Federation of Galaxy Explorers Space Science

Federation of Galaxy Explorers Space Science Once Upon A Big Bang Learning Objectives: 1. Explain how the universe was created using the Big Bang theory. 2. Understand how the existence of Cosmic Background

### The Early Universe. Lecture 27-1

The Early Universe Lecture 27-1 Back to the Big Bang The total energy of the universe consists of both radiation and matter. As the Universe cooled, it went from being radiation dominated to being matter

### Lecture Outlines. Chapter 27. Astronomy Today 7th Edition Chaisson/McMillan. 2011 Pearson Education, Inc.

Lecture Outlines Chapter 27 Astronomy Today 7th Edition Chaisson/McMillan Chapter 27 The Early Universe Units of Chapter 27 27.1 Back to the Big Bang 27.2 The Evolution of the Universe More on Fundamental

### FIRST LIGHT IN THE UNIVERSE

FIRST LIGHT IN THE UNIVERSE Richard Ellis, Caltech 1. Role of Observations in Cosmology & Galaxy Formation 2. Galaxies & the Hubble Sequence 3. Cosmic Star Formation Histories 4. Stellar Mass Assembly

### 1 Introduction. 1 There may, of course, in principle, exist other universes, but they are not accessible to our

1 1 Introduction Cosmology is the study of the universe as a whole, its structure, its origin, and its evolution. Cosmology is soundly based on observations, mostly astronomical, and laws of physics. These

### Data Management Plan Extended Baryon Oscillation Spectroscopic Survey

Data Management Plan Extended Baryon Oscillation Spectroscopic Survey Experiment description: eboss is the cosmological component of the fourth generation of the Sloan Digital Sky Survey (SDSS-IV) located

### Chapter 23 The Beginning of Time

Chapter 23 The Beginning of Time 23.1 The Big Bang Our goals for learning What were conditions like in the early universe? What is the history of the universe according to the Big Bang theory? What were

WIMP dark matter and the isotropic radio signal Roberto A. Lineros R. Instituto de Física Corpuscular - CSIC/U. Valencia @Roberto_Lineros Outline Introduction Cosmic ray propagation Synchrotron emission

### PLANCK'S VIEW OF THE UNIVERSE IN FRONT OF THE MICROWAVE BACKGROUND

PLANCK'S VIEW OF THE UNIVERSE IN FRONT OF THE MICROWAVE BACKGROUND Gravitational lensing and Sunyaev-Zeldovich signals The Planck Consortium (presented by Simon White) Paris 21/03/2013 PLANCK'S FIRST IMAGE

### PROLOGUE: THE BIG PICTURE

1 PROLOGUE: THE BIG PICTURE 1.1 In the Beginning As the Universe expands, galaxies get separated from one another, and the average density of matter over a large volume of space is reduced. If we imagine

### 8 Radiative Cooling and Heating

8 Radiative Cooling and Heating Reading: Katz et al. 1996, ApJ Supp, 105, 19, section 3 Thoul & Weinberg, 1995, ApJ, 442, 480 Optional reading: Thoul & Weinberg, 1996, ApJ, 465, 608 Weinberg et al., 1997,

### Why is the Night Sky Dark?

Why is the Night Sky Dark? Cosmology Studies of the universe as a whole Today Brief history of ideas (Early Greeks Big Bang) The expanding universe (Hubble, Relativity, density & destiny) An alternative

### arxiv:astro-ph/9604166 28 Apr 96

IASSNS-AST-96/30 THE PHYSICS OF MICROWAVE BACKGROUND ANISOTROPIES arxiv:astro-ph/9604166 28 Apr 96 Wayne Hu, 1 Naoshi Sugiyama, 2 & Joseph Silk 3 1 Institute for Advanced Study School of Natural Sciences

### Data Provided: A formula sheet and table of physical constants is attached to this paper. DARK MATTER AND THE UNIVERSE

Data Provided: A formula sheet and table of physical constants is attached to this paper. DEPARTMENT OF PHYSICS AND ASTRONOMY Autumn Semester (2014-2015) DARK MATTER AND THE UNIVERSE 2 HOURS Answer question

### Einstein Rings: Nature s Gravitational Lenses

National Aeronautics and Space Administration Einstein Rings: Nature s Gravitational Lenses Leonidas Moustakas and Adam Bolton Taken from: Hubble 2006 Science Year in Review The full contents of this book

### Cosmic sound waves rule

feature Cosmic sound waves rule Daniel J. Eisenstein and Charles L. Bennett In the microwave background and the distribution of galaxies, relic imprints of primordial sound waves have contributed to an

### Understanding the Cosmic Microwave Background Temperature Power Spectrum

Understanding the Cosmic Microwave Background Temperature Power Spectrum Rita Tojeiro March 16, 2006 The Cosmic Microwave Background The Cosmic Microwave Background (CMB) radiation field is an open window

### Origins of the Cosmos Summer 2016. Pre-course assessment

Origins of the Cosmos Summer 2016 Pre-course assessment In order to grant two graduate credits for the workshop, we do require you to spend some hours before arriving at Penn State. We encourage all of

### What Are Stars? continued. What Are Stars? How are stars formed? Stars are powered by nuclear fusion reactions.

What Are Stars? How are stars formed? Stars are formed from clouds of dust and gas, or nebulas, and go through different stages as they age. star: a large celestial body that is composed of gas and emits

### Specific Intensity. I ν =

Specific Intensity Initial question: A number of active galactic nuclei display jets, that is, long, nearly linear, structures that can extend for hundreds of kiloparsecs. Many have two oppositely-directed

### Dark Matter and the Universe

Dark Matter and the Universe Topic 3 Dark Matter in Galaxy Clusters and Superclusters How does Einstein s bending of light reveal the true picture of our Universe?! Contents of Topic 3 In this Topic we

### The Big Bang. The early universe must have. extremely hot and dense. Copyright 2012 Pearson Education, Inc. Copyright 2012 Pearson Education, Inc.

The Big Bang The early universe must have been extremely hot and dense. 1 Photons converted into particle antiparticle pairs and vice versa. E = mc 2 The early universe was full of particles and radiation

### CFHT STRIPE82 SURVEY (CS82)

CFHT STRIPE82 SURVEY (CS82) 160 degrees (130 effective) i=24.1, AB mag, 5σ, 2 aperture Seeing ~ 0.6 over full survey Pixel size : 0.187 Alexie Leauthaud. Jean-Paul Kneib. Martin Makler. Ludovic van Waerbeke.

### UNIVERSITY OF OSLO. Please make sure that your copy of the problem set is complete before you attempt to answer anything.

UNIVERSITY OF OSLO Faculty of mathematics and natural sciences Constituent exam in: AST4320 Cosmology and Extragalactic Astronomy Day of examination: Thursday 8. October 2015 Examination hours: 10.00 13.00

### Exploring dark energy models with linear perturbations: Fluid vs scalar field. Masaaki Morita (Okinawa Natl. College Tech., Japan)

Exploring dark energy models with linear perturbations: Fluid vs scalar field Masaaki Morita (Okinawa Natl. College Tech., Japan) September 11, 008 Seminar at IAP, 008 1 Beautiful ocean view from my laboratory

### Physical Self-Calibration of X-ray and SZ Surveys

Physical Self-Calibration of X-ray and SZ Surveys Greg L. Bryan, Zoltan Haiman (Columbia University) and Joshua D. Younger (CfA) 1. Cluster Surveys and Self-Calibration Clusters of galaxies form at the

### Evolution of the Universe from 13 to 4 Billion Years Ago

Evolution of the Universe from 13 to 4 Billion Years Ago Prof. Dr. Harold Geller hgeller@gmu.edu http://physics.gmu.edu/~hgeller/ Department of Physics and Astronomy George Mason University Unity in the

### Heating diagnostics with MHD waves

Heating diagnostics with MHD waves R. Erdélyi & Y. Taroyan Robertus@sheffield.ac.uk SP 2 RC, Department of Applied Mathematics, The University of Sheffield (UK) The solar corona 1860s coronium discovered

### The Cosmic Perspective Seventh Edition. Dark Matter, Dark Energy, and the Fate of the Universe. Chapter 23 Review Clickers

Review Clickers The Cosmic Perspective Seventh Edition Dark Matter, Dark Energy, and the Fate of the Universe Doppler shifts can be measured with a) visible light. b) radio waves. c) microwaves. d) all

### Our UNIVERSE: where it all came from.

Our UNIVERSE: where it all came from. QUESTIONS OF THE DAY. How did the Universe start? How did the Universe evolve up to the present day? What is the fate of our Universe? The theory of general relativity

### TMT/IRMS: the Science Case. Bahram Mobasher University of California, Riverside

TMT/IRMS: the Science Case Bahram Mobasher University of California, Riverside IRMS = MOSFIRE + TMT/NFIRAOS IRMS provides a relatively cheap near-ir multi-slit spectrograph and imager on TMT. With no significant

### The Development of Structure in the Universe: The Big Picture

The Development of Structure in the Universe: The Big Picture Ay21 Feb 19, 2010 Wilkinson Microwave Anisotropy Probe (WMAP) 2003 1 Growth of Perturbations After Recombination Pressure on baryons from its

### Measuring the mass of galaxies Luminous matter in a galaxy: stars (of different masses) gas (mostly hydrogen) Can detect these directly using optical

Measuring the mass of galaxies Luminous matter in a galaxy: stars (of different masses) gas (mostly hydrogen) Can detect these directly using optical and radio telescopes - get an estimate of how much

### The Milky Way Galaxy. Our Home Away From Home

The Milky Way Galaxy Our Home Away From Home Lecture 23-1 Galaxies Group of stars are called galaxies Our star, the Sun, belongs to a system called The Milky Way Galaxy The Milky Way can be seen as a band

### The High Redshift Universe Reprise

The High Redshift Universe Reprise Planck time Particle physics stuff Inflation Element creation All in first 1000 seconds Bit of a snooze for the next 400000 years Atoms form from the ions and electrons

### Chapter 5 Light and Matter: Reading Messages from the Cosmos

Chapter 5 Light and Matter: Reading Messages from the Cosmos Messages Interactions of Light and Matter The interactions determine everything we see, including what we observe in the Universe. What is light?