Nearby Supernova Factory: Étalonnage des données de SNIFS et ...
Nearby Supernova Factory: Étalonnage des données de SNIFS et ...
Nearby Supernova Factory: Étalonnage des données de SNIFS et ...
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tel-00372504, version 1 - 1 Apr 2009<br />
CHAPTER 1. BIG BANG COSMOLOGY<br />
We thus introduced a new observable, the received flux of a distant source. The astronomical<br />
object for which we are able to infer its intrinsic luminosity in<strong>de</strong>pen<strong>de</strong>ntly of the observed flux<br />
is called a standard candle. That’s the case of the Cepheids (used by Hubble for the distances<br />
<strong>de</strong>termination), which are variable stars who present a correlation b<strong>et</strong>ween their period and<br />
luminosity, as well of other standardizable objects like globular or galaxies clusters (cf. Roos<br />
(2003)).<br />
One important standard candle, observable up to distances where the cosmological redshift<br />
effects dominates (and thus for which we can use (1.48) to study the composition of the universe),<br />
are the type Ia supernovæ (SNe Ia). They are the main study object of this thesis, and thus the<br />
luminosity distance will be our most important observable. The SNe Ia will be further presented<br />
in § 2.3.<br />
Angular-diam<strong>et</strong>er distance<br />
The usage of objects of known intrinsic size, the standard rulers, allows us to measure the<br />
proper distance in a similar fashion of the luminosity distances, although now in a “orthogonal”<br />
direction of the m<strong>et</strong>ric. The diam<strong>et</strong>er of a source of light at comoving distance dP is <strong>de</strong>fined by<br />
(1.2) as<br />
D ≡ a(t)θdP . (1.50)<br />
We can then <strong>de</strong>fine the angular-diam<strong>et</strong>er distance as<br />
dA ≡ D<br />
θ<br />
= a(t)dP<br />
= dP<br />
1 + z<br />
, (1.51)<br />
where θ is the measured angular diam<strong>et</strong>er. It relates to the luminosity distance (1.46) as<br />
dA =<br />
dL<br />
.<br />
(1 + z) 2<br />
A key application of the angular-diam<strong>et</strong>er distance is in the study of features in the cosmic<br />
microwave background radiation (§ 2.1).<br />
Other observables<br />
Other observables which I will not <strong>de</strong>tail, inclu<strong>de</strong> the number of objects (galaxies, quasars)<br />
within a comoving volume element, which relates d2 P and H(z); and the mass power spectrum<br />
from the distribution of galaxies at very large scales, which <strong>de</strong>pends on the initial spectrum of<br />
inhomogeneities and their evolution with time. They are mainly used by redshift surveys of<br />
large scale structure (§ 2.2).<br />
1.4 The ΛCDM concordance mo<strong>de</strong>l<br />
We arrive thus at the consensus cosmological mo<strong>de</strong>l, the so-called ΛCDM (cosmological<br />
constant and cold dark matter) mo<strong>de</strong>l. Consi<strong>de</strong>red as the nowadays “standard mo<strong>de</strong>l” for<br />
cosmology, it tells us that:<br />
• the geom<strong>et</strong>ry and dynamics of the expanding universe are <strong><strong>de</strong>s</strong>cribed by the general relativity<br />
FLRW mo<strong>de</strong>ls (§ 1.2 and 1.3);<br />
18