Nearby Supernova Factory: Étalonnage des données de SNIFS et ...

tel-00372504, version 1 - 1 Apr 2009
CHAPTER 1. BIG BANG COSMOLOGY
We thus introduced a new observable, the received flux of a distant source. The astronomical
object for which we are able to infer its intrinsic luminosity independently of the observed flux
is called a standard candle. That’s the case of the Cepheids (used by Hubble for the distances
determination), which are variable stars who present a correlation between their period and
luminosity, as well of other standardizable objects like globular or galaxies clusters (cf. Roos
(2003)).
One important standard candle, observable up to distances where the cosmological redshift
effects dominates (and thus for which we can use (1.48) to study the composition of the universe),
are the type Ia supernovæ (SNe Ia). They are the main study object of this thesis, and thus the
luminosity distance will be our most important observable. The SNe Ia will be further presented
in § 2.3.
Angular-diameter distance
The usage of objects of known intrinsic size, the standard rulers, allows us to measure the
proper distance in a similar fashion of the luminosity distances, although now in a “orthogonal”
direction of the metric. The diameter of a source of light at comoving distance dP is defined by
(1.2) as
D ≡ a(t)θdP . (1.50)
We can then define the angular-diameter distance as
dA ≡ D
θ
= a(t)dP
= dP
1 + z
, (1.51)
where θ is the measured angular diameter. It relates to the luminosity distance (1.46) as
dA =
dL
.
(1 + z) 2
A key application of the angular-diameter distance is in the study of features in the cosmic
microwave background radiation (§ 2.1).
Other observables
Other observables which I will not detail, include the number of objects (galaxies, quasars)
within a comoving volume element, which relates d2 P and H(z); and the mass power spectrum
from the distribution of galaxies at very large scales, which depends on the initial spectrum of
inhomogeneities and their evolution with time. They are mainly used by redshift surveys of
large scale structure (§ 2.2).
1.4 The ΛCDM concordance model
We arrive thus at the consensus cosmological model, the so-called ΛCDM (cosmological
constant and cold dark matter) model. Considered as the nowadays “standard model” for
cosmology, it tells us that:
• the geometry and dynamics of the expanding universe are described by the general relativity
FLRW models (§ 1.2 and 1.3);
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