Supernovae and Dark Energy Pierre Astier LPNHE / IN2P3 / CNRS , - - PowerPoint PPT Presentation
Supernovae and Dark Energy Pierre Astier LPNHE / IN2P3 / CNRS , Universits Paris 6&7. Frontiers of Fundamental Physics - July 2014. P. Astier (FFP14 15/07/14) The expansion of the universe Lematre (1927), Hubble (1929) The
LPNHE / IN2P3 / CNRS , Universités Paris 6&7.
Frontiers of Fundamental Physics - July 2014.
From redshift From apparent flux This “Hubble diagram” uses “nebulae” as tracers
“The farther, the fainter”
Us
If distant galaxies are moving away from us, their escape velocity can only depend on distance
Us
Us Them
(at least not too far from us)
e.g: different hypotheses for matter density
the universe
→ Friedman equation(s) Expansion rate Energy densities Cosmological constant Curvature
Calan-Tololo Survey (Hamuy et al, 1996)
Distances to ~ 7% Excellent distances ! but redshift range too short to go beyond The Hubble law
luminosity : 40 %
~14 %
Thermonuclear explosions of stars which appear to be reproducible
peak flux multi-band photometry => distance
z
Matter density, today (in some unit)
Riess et al, 1998 [High-z team] Perlmutter et al, 1999 [SCP]
DE density varies slowly (or not at all) with time
Perlmutter et al (99)
Static density(i..e Λ) Free curvature Zero curvature DE density variation : ρx ~ (1+z)3(1+wx) (P x = wxρx
)
Because distant supernovae are fainter than in a matter-dominated universe ==> Postulate a two-component universe : matter & dark energy
a c c e l e r a t e d e c e l l e r a t e
The Nobel Prize in Physics 2011 was divided,
jointly to Brian P. Schmidt and Adam G. Riess "for the discovery of the accelerating expansion
Scale factor R Density m a t t e r dark energy now ??
Matter
Λ
w tells how the density evolves with expansion
Constraints from SNe (Perlmutter et al 1999)
Betoule et al (2014)
Rolling searches on large CCD mosaics Observing steps:
From the same images ! Implemented on 3 major surveys … with “classical spectroscopy”
The SDSS SN Survey The SNLS survey @ CFHT 300 deg2 x 3 years 0.1<z<0.45 ~2000 SNe ~500 spectra 4 deg2 x 5 years 0.3<z<1 ~1000 SNe ~500 spectra
Low-z supernovae (z<0.1) : dominated by 2 samples:
Rolling surveys at 0.1<z<1
High z events with the HST:
~200 SNLS events still unpublished...
>700 SNe
Related to SN intrinsic luminosity and distance scale: → No cosmological information
Ratio of distances across redshifts: → This is what constrains dark energy
We are interested in the ratio of SN luminosities at different redshifts … for similar restframe wavelengths
Each SN is measured relative to surrounding stars
Field stars are measured Relative to “calibrators” ...derived from stellar models
Vega: historical foundation of photometric System (too bright and … variable...)
~10-3 ~ 4 10-3 Blue vs red known to ~ 4 10-3
Distant vs nearby SN brightnesses are typically measured to ~ 6 10-3
(Betoule et al, 2013)
– Direct cross-calibration (of field stars) – Redundant paths to standard stars
740 events in total Betoule et al (2014)
Ωm measurement independent of CMB and compatible with Planck
Planck + BAO: w = −1.01 ± 0.08 Planck + SN: w = −1.018 ± 0.057 Best EoS constraint. Improvements w.r.t previous results :
Betoule et al (2014)
– LSST (could cover the whole range to z=1) – Euclid and WFIRST could target the z>1 régime
Perlmutter et al (1999) Guy et al (2010), Conley et al (2011), Sullivan et al (2011)
(Betoule et al, 2013) Uncertainties validated through redundancy