MAPping the Universe ►Introduction: the birth of a new cosmology ►The cosmic microwave background ►Measuring the CMB ►Results from WMAP ►The future of cosmology Susan Cartwright University of Sheffield

The Birth of a New Cosmology ►Cosmology is the science of the whole universe  its origin  its structure and evolution ►Cosmological data must apply to the whole universe  large distances  faint sources  large uncertainties “Cosmology in the 1950s was a science of 2½ facts.”Cosmology in the 1950s was a science of 2½ facts 1980s: maybe 8 facts, but all with factor ~2 uncertainty!

Precision Cosmology ►Aim: determine cosmological parameters to a few percent  H 0 : the expansion rate of the universe and how it changes over time  k: its geometrygeometry  Ω: its density Ω b : the density of ordinary matter Ω m : the density of all matter Ω Λ : the “dark energy” (or “cosmological constant”)  t 0 : its age

Steps towards precision abundances of light elements: measuring Ω b h 2 type Ia supernovae: measuring Ω Λ − Ω m

More steps… ►HST Key Project on Extragalactic Distance Scale  H 0 using variety of methods  result: 72 ± 4 ± 7 km/s/Mpc 10% accuracy dominated by systematics need an independent technique: the Cosmic Microwave Background

What is it? ►Look at the sky at wavelengths of a few mm (microwaves)  very uniform faint glow  spectrum is thermal, temperature ~3 K  discovered accidentally by Penzias and Wilson in 1965  predicted years earlier by Gamow et al. as consequence of Big Bang

Where did it come from? ►Early universe was hot, dense and ionised  photons repeatedly interacted with protons and electrons: universe opaque  result: thermal (blackbody) spectrum ►Universe expands and cools  at ~3000 K neutral atoms form: universe transparent  photons no longer interact with matter  thermal spectrum cools as expansion continues

What does it tell us? ►The Big Bang happened!  no other way to generate a uniform thermal spectrum ►The universe was very uniform when it was emitted  about years after the Big Bang ►So how did galaxies form then?  well…it’s not exactly uniform

Anisotropies ►Our rest frame ≠ CMB rest frame  dipole anisotropy of ~0.1% ►Foreground sources  most obviously our own Galaxy ►Density fluctuations in early universe  anisotropies of ~10 -5  seeds of galaxy formation COBE data

Generation of anisotropies ►Density fluctuations in early universe  series of potential wells  oscillations in and out of wells ►characteristic size = horizon radius  present size of horizon radius depends on geometry of universe Pictures by Wayne Hu

Measuring a map ►Need to quantify anisotropies  express as sum of increasingly high-frequency components (similar to sythesiser)  plot amplitudes of successive components

CMB Power Spectrum

Cosmological parameter dependence Movies from Martin White’s website Hubble parameter Cosmological constant Baryon density Spectral index

Making a map COBE satellite: discovered the fluctuations BOOMERanG balloon: first of the new generation

More Mappers the Cosmic Background Imager the Very Small Array

WMAP the Wilkinson Microwave Anisotropy Probe orbiting the Sun/Earth L2 point better view, less background

WMAP results ►Map covers whole sky  resolution ~0.2° good power spectrum to 3 rd peak  also measuring polarisation

WMAP Cosmology ►h = 0.72  0.05 ►Ω b h 2 =  ►Ω m h 2 =  ►Ω tot h 2 = 1.02  0.02 ►Ω h 2 < (95%) ►n = 0.99  0.04 ►age of universe = 13.7  0.2 Gyr (WMAP only) (also uses 2dF and Ly α) first stars born 200 Myr after Big Bang

Conclusion ►The Universe is dominated by dark energy  why? how? what? ►About 85% of the matter in the universe is non- baryonic cold dark matter  not atoms  not neutrinos ►The Universe is about 14 billion years old, and will expand forever ►Cosmology is no longer a science of 2½ facts!