Introduction to the modern observational cosmology

03.03.2011 Introduction/Overview

Observational cosmology: what can we observe?

Electromagnetic waves Radio, submillimeter, IR, optical, UV, X, gamma

Particles Neutrinos, cosmic rays

Gravitational waves? .....

Observational cosmology: where can we observe?

From Earth (radio & optical: almost everywhere; close IR, sub-mm: some high places like Atakama desert)

From satellites (microwaves, IR, UV, X, gamma)

Observational cosmology: what kind of objects do we observe?

galaxies individual surveys

Clusters of galaxies CMBR IGM AGNs Lensing effects Transient phenomena:

GRBs SNIa

Cosmic Microwave Background Radiation

Temperature maps Polarisation maps 5-year WMAP data Measurements:

Temperature fluctuations (2.7 K +/- 10^(-5))

Power spectrum Photon polarization

Galaxies: individual

Many types of galaxies in a local and distant Universe

Investigating individual galaxies we can understand their evolution, the relation between their properties and their position in the LSS and so on

Galaxies: individual

An example of a “cosmologically interesting” local galaxy: NGC 1705

Low-metallicity local irregular dwarf galaxy with a recent outburst of star formation: a model of the first galaxies?

Galaxies: surveys

Angular (only positions on the sky) 3-dimensional (with a redshift measurement)

Different wavelengths

Sky looks differently in different wavelengths

+ identification problems

Galaxies: local surveys In optical: local: 2dFGRS: spectra for 245 591

objects (mainly galaxies) in 1500 square degrees

Galaxies: local surveys

In optical: local: SDSS

230 million celestial objects detected in 8,400 square degrees of imaging and spectra of 930,000 galaxies, 120,000 quasars, and 225,000 stars.

Galaxies: local surveys

In total, the local Universe in ~2 billion light year radius is pretty well known in the optical light

More than 1M galaxies LSS “special” objects (quasars, satellites of Milky

Way)

Galaxies: deep imaging surveys

CFHTLS:

Galaxies: deep imaging surveys

Hubble Ultra Deep Field: 10 000 galaxies in 11 square arc minutes

Galaxies: deep redshift surveys

DEEP2, VVDS, zCOSMOS

In total ~a few tens of thousands of galaxies at z>0.5

Galaxies: next generation of deep redshift surveys

VIPERS >100 000 galaxies at z~1 at 24 square degrees Statistical counterpart of SDSS or 2dF but at z~1 Volume (comoving) ~ 5 x 107 h-3 Mpc3

Galaxies: dedicated surveys to search for particular objects

If we want to increase the chance that our survey contains “interesting” (e.g. EROs) objects, we make a preselection, most often based on color-color diagrams

Galaxies: surveys in other wavelengths (IR)

IR: IRAS, 2MASS, Spitzer, AKARI...

350 000 objects, many of them still not identified!

Low resolution: 30”-2'

Galaxies: surveys in other wavelengths (UV)

GALEX: all-sky map in FUV and NUV

Unlike in IR, almost every UV source has an optical counterpart

Also a poor resolution

(Credit: Mark Seibert, OCIW)

Surveys: basic tools

For all the objects: Redshifts: how to measure and recognize Colors/morphological types/sizes Luminosities: apparent and absolute Stellar masses...

Statistics: Number/magnitude counts (how many objects brighter

than...) Luminosity function Angular/spatial distribution Correlation function(s) ...

Clusters of galaxies

The largest gravitationally bound structures in the Universe

Their distribution is “the closest” to the primordial matter distribution

Observed in X-rays, because they are filled with hot intergalactic gas (10 – 100 mln K)

Often with a massive central elliptical galaxy

Virgo: the closest massive cluster of galaxies in optical

light and X-rays (1 Mpc)

Credit: Ray White, University of Alabama

Intergalactic medium

Diffuse intergalactic gas in clusters (in some cases of a mass ~ mass of stars in galaxies)

Between clusters: Ly-alpha absorption systems

A powerful tool to study Metal production and feedback processes in the

history of galaxy formation Thermal and ionization history of the Universe

during and after the epoch of reionisation

Lensing

An effect of the change of the direction of photons in the gravitational field, due to the bending of the spacetime (relativistic effect) Strong (multiple images of the same object,

typically a quasar or an “Einstein ring”) Weak (distorted images of objects e.g. behind a

rich cluster) Microlensing (change of luminosity, in case of

lensing on small objects like planets or small stars)

Gravitational lensing is used to “map” mass distribution in galaxy clusters

Cosmological lensing:

An example of lensing on a rich galaxy cluster – fragments of Einstein rings, distorted images...

Transient sources: SN Ia

Thought to be white dwarfs from binary systems which collected too much matter from a companion through accretion processes and exceeded the Chandrasekhar mass

All ~ of the same mass -> the same absolute luminosity -> standard candles

Visible until z~1.3-1.4 Supernova Cosmology Project, Supernova

Legacy Survey (SNLS)

Transient sources: SN Ia

Hubble diagram from SN Ia led to “rediscovery” of the cosmological constant

Transient sources: GRBs

Short (from a few ms to several minutes) and very energetic events, occurring ~ 1/day in the sky

In 1997 connected with an optical outburst in a distant galaxy and thus finally proved to be of an extragalactic origin