Cosmology: Cosmic Structure & content Tarun Souradeep I.U.C.A.A, Pune, India 1 st Asian Winter School Pheonix Park, Korea (Jan 15, 2007)

India I.U.C.A.A., Pune, India

Andromeda Galaxy The Realm of Cosmology Basic unit: Galaxy Size : kilo parsec (kpc.) Mass : 100 billion Stars Measure distances in light travel time 1 pc. (parsec) = 200,000 AU = 3.26 light yr. Measure Mass in Solar mass

Coma cluster The Realm of Cosmology Galaxy Clusters Size : Mega parsecs (Mpc.) Mass : 100 –1000 Galaxies (5% luminous, 15% hot gas, 80%dark matter !)

Perseus super cluster The Realm of Cosmology Super Clusters Size : 10 Mega parsecs Mass : few 1000 Galaxies

The Realm of Cosmology Distant galaxies beyond a cluster ….

The Realm of Cosmology …… most distant galaxies Hubble deep field

The Realm of Cosmology 100 million Light years

The Realm of Cosmology 100 million Light years

The Realm of Cosmology 500 million Light years

SLOAN DIGITAL SKY SURVEY (SDSS) Few billion parsecs The Realm of Cosmology

How can we even hope to comprehend this immensely large & complex Universe !?! Look for an appropriate simple model

Lick Observatory survey North South The Isotropic Universe Distribution of galaxies on the sky is broadly isotropic Isotropy around every point implies Homogeneity  Cosmological principle

Einstein’s General relativity applied to an uniform distribution of matter on cosmic scales leads to a smooth expanding universe The Expanding Universe

Leads to the Hubble’s law Recession velocity is Proportional to the distance

Flat Universe Hyperbolic Universe Constant negative curvature Spherical Universe Constant positive curvature Geometry of the Universe

Geometry, Expansion & Matter

The Isotropic Universe T 0 =2.725 (+/-0.002)K. Serendipitous discovery of the dominant Radiation content of the universe as an extremely isotropic, Black-body bath at temperature T 0 =2.725 (+/-0.002)K. “Clinching support for Hot Big Bang model” Nobel prize 1978

The dominant radiation component in the universe (D. Scott ’99) ~ 400 CMB photons per cubic cm.

The most perfect Black-Body spectrum in nature COBE website COBE –FIRAS The CMB temperature – A single number characterizes the radiation content of the universe!!

(figs: Bond, 1996) COBE-FIRAS results strongly constrain any Energy input into the CMB in the not-so-early universe (z<10 5 ) 10 Ghz30Ghz 60 Ghz600 Ghz ARCADE 2004 Next future: 3-90 GHz 10 GHz 30 GHz

The Expanding Universe Wavelength of light is stretched by expansion  Redshift, z=v/c Redshift is related to distance Expansion implies Hot early universe Smaller => hotter

MEASUREMENT of CMB temperature at higher-z 6.0<T<14.0K at z= (Srianand, Petitjean, Ledoux in Nature 2000) Smaller Universe is Hotter !

CMB isotropy strongly constrains Anisotropic Universe models (Fig: Amir Hajian)

Fingerprints of anisotropic cosmology (Fig: Amir Hajian, PhD thesis)

Post-recombination :Freely propagating through (weakly perturbed) homogeneous & isotropic cosmos. Pre-recombination : Tightly coupled to, and in thermal equilibrium with, ionized matter. Pristine relic of a hot, dense & smooth early universe - Hot Big Bang model (text background: W. Hu) Cosmic Microwave Background

Cosmic “Super–IMAX” theater Transparent universe Opaque universe 14 GPc Here & Now (14 Gyr) 0.5 Myr

How much do we now know about this model Universe ? lots !!!

Fig:NASA/WMAP science team Matter budget of the Universe Ordinary (baryonic) matter

Ordinary matter is sprinkled on the Cold Dark matter distribution Galaxies light up at the densest points

Where is the Cold Dark matter ? 6 times more in dark matter than ‘baryonic’ matter Zwicky 1935

Rotation of Spiral Galaxies !!!

Dark matter in Galaxies ! R

Dark matter in our own backyard !?!

Dark matter in the Milky way

Dark matter in other galaxies too !!

Dark matter in clusters !?!

Marbles in a glass bowl !!! Velocity dispersion of galaxies in a cluster Measures the depth of its gravitational potential Speeding galaxies in a cluster

Hot gas in clusters Coma cluster

Hot gas in clusters Virgo cluster

Gravitational lensing Distant galaxies beyond a cluster are lensed….

Bullet cluster

movie

Evidence for Dark Energy? Is it the Cosmological constant? The Cosmic repulsive force Einstein once proposed and later denounced as his ‘biggest blunder” ?

Geometry, Expansion & Matter Dark energy causes accelerated expansion

Correction to the Hubble’s Law …. measures the acceleration in the expansion of the universe Measure distances independent of redshift v/c till v/c=z~1

10 m Flux 5 m Measuring distance using standard candles 4 Flux

Supernova in a galaxy: standard candle

Supernova can be seen in distant galaxies

Supernova in a very distant galaxy

Starlight from Galaxies Stuff we are made of!! Light elements from early hot universe Low CMB temperature fluctuations Accelerated expansion of the universe (High redshift SN) Structure formation scenario compatible with observations Rotation of galaxies Speeding galaxies in clusters Gravitational lensing Hot gas in clusters Matter budget of the cosmos Fig:NASA/WMAP science team

NASA/WMAP science team Total energy density Baryonic matter density Age of the universe Dawn of Precision cosmology !! Dark energy density Dark matter density Expansion rate of the universe

How much do we now know about this model Universe ? How do we know so much now about this model Universe ?

Music of the Cosmic Drum Thank you !!!