Type Ia Supernovae andDark Energy

Bruno Leibundgut

European Southern Observatory

Outline

The Hubble diagram of Type Ia Supernovae• evidence for accelerated expansion

• evidence for/against dust and evolution

Systematics of Type Ia Supernovae

Measuring the equation of state parameter

Riess et al. (2003)

Higher-z SN team (GOODS/HST)

Distant supernovae

The principle

Establish a cosmological distance indicatorin the local universe (z<0.05)e.g. Cepheids, SNe II, Tully-Fisher relation,fundamental plane relation, surfacebrightness fluctuations, SNe Ia)

Measure objects at cosmological distances establish identity of distance indicator control measurement errors

evolution (primary and secondary)interstellar and intergalactic dustgravitational lensing

Type Ia Supernovae

Establish a cosmological distance indicatorin the local universe (z<0.05)Type Ia Supernovae can be normalisedthrough their light curve shapes (102 objects)Ëexcellent relative distances (Phillips 1993, Hamuy et al.

1996, Riess et al. 1996, 1998, 1999, Perlmutter et al. 1997, Phillipset al. 1999, Suntzeff et al. 1999, Jha et al. 1999, 2003)

Measure objects at cosmological distances 77 distant SNe Ia (0.3<z<1.0) published

(Garnavich et al. 1998, Riess et al. 1998, Perlmutter et al. 1997,1999, Tonry et al. 2003, Suntzeff et al. 2004, Barris et al. 2004,Leibundgut et al. 2004)

evolution Ë light curve shapes, colours, spectroscopy

dust Ë colours, spectroscopy

gravitational lensing Ë difficult, need mapping oflight beam

The nearby SN Ia sample

Evidence for gooddistances

Starting from Einstein’s Fieldequation

Friedmann cosmologyAssumption:homogeneous and isotropic universe

Null geodesic in a Friedmann-Robertson-Walker metric:

[ ]Ô

Ô˝¸

ÔÓ

ÔÌÏ

¢W+¢+W+¢+WWW

+=

-

LÚ zdzzSH

czD

z

ML

21

0

32

0

)1()1()1(

kk

k

MM H

Gr

p203

8=W

20

2

2

HR

kck -=W

20

2

3H

cL=WL

Cosmology inthe Hubble

diagram

Assumption:Lambda is constantNo time-dependence inthe equation of state

Tonry et al. 2003

Supernovacosmology

Mean distancebetween galaxies

today

fainter

redshift

WM = 1

Time

Closed WM > 1

Open WM < 1

WM = 0

- 14 - 9 - 7

billion years

Perlmutter 2003

Distant SNe IaDistant objects appearfainter than theirnearby counterpartsThis is a 3.5s result(High-z SN Team andSupernova CosmologyProject)

• evolution

• dust

• cosmology

Checks:

Dust• observations over many

filters

Evolution• spectroscopy

Cosmology• more distant SNe Ia

Is dust a problem?

Falco et al. 1999

Leibundgut 2001

SNe Ia in elliptical galaxiesDetermination of host galaxy morphologies

• 38 SNe Ia from the SCP sample

Sullivan et al. 2003

Elliptical galaxiesare dust-free

Modified Hubble diagram

Supernova Cosmology Project Sample

Sullivan et al. (2003)

WM=0.28; WL=0.72

Sullivan et al. 2003

Leibundgut and Sollerman 2001

Evolution?Spectroscopy ofdistant SNe Ia

Coil et al. 2000

Evolution? - Colours

Leibundgut 2001

209 SNe Ia inone diagram

Tonry et al. 2003

209 SN Ia and mediansTonry et al. 2003

79 SNe Ia

Cosmology

Leibundgut 2001

H0=63 km s-1 Mpc-1

Tonry et al. 2003

155 SNe Ia

SN Ia and 2dF constraints

KP:h = 0.72 ± 0.08

2dF:WM=0.2±0.03

Tonry et al. 2003

2dF:WM=0.2±0.03

KP:h = 0.72 ± 0.08

Tonry et al. 2003

Supernovae

Extremely bright stellar explosions

SN Ia Systematics?

Explosions not fully understood• many possible models

– Chandrasekhar-mass models

– deflagrations vs. detonations

Progenitor systems not known• white dwarfs yes, but …

– double degenerate vs. single degenerate binaries

Ë Evolution very difficult to control

B

V

I

The SN Ia luminositycan be normalised

Bright = slow Dim = fast

Nature of the Dark Energy?

Currently two proposals:• cosmological constant

Nature of the Dark Energy?

Currently two proposals:• cosmological constant

• quintessence– decaying particle field

– signature:– equation of state parameter with

2c

p

rw =1-≠w

On to new physics?

Both quintessence and the cosmologicalconstant would require additions beyondthe current standard model of physics.

Type Ia Supernovae (together withadditional information on _M) candistinguish between those twopossibilities• required is a large homogeneous set (about

200) of distant (0.2 < z < 0.8) supernovae

General luminosity distance

• with and

wM= 0 (matter)

wR= _ (radiation)

wL= -1 (cosmological constant)

Ô

Ô˝¸

ÔÓ

ÔÌÏ

¢˙˚

˘ÍÎ

È¢+W+¢+WW

W

+=

-

+Ú Â zdzzSH

czD

z

iiL

i

21

0

)1(32

0

)1()1()1( w

kk

k

 W-=i

i1k2c

p

i

ii r

w =

The equation of state parameter w

w

Garnavich et al. 1998

SN Ia and 2dF constraints

KP:h = 0.72 ± 0.08

Quintessence

Cosmic strings

Cosmological constant

2dF:W M h = 0.2 ± 0.03

Tonry et al. 2003

%)95(73.0-<w

Tonry et al. 2003

ResultsSupernovae measure distances over a large

cosmological rangeThey are complementary to the CMB

measurements in that they can measurethe dynamics of the cosmic expansion

Ë map the cosmological expansion• SNe Ia indicate accelerated expansion for the

last 6 Gyr• There are indications that the accelerations

turns into a deceleration at z>1 (>8 Gyr)• dynamic age of the universe H0t0=0.95±0.04

(13 Gyr for H0=72 km s-1Mpc-1; 15 Gyr for H0=64 km s-1Mpc-1)

It’s not all doneyet …

Tonry et al. 2003

GOODS (Higher-z) Supernovae

Find supernovae atz>1.2 from the GOODSACS observations

Riess et al. (2003)

GOODS SupernovaeVLT spectrumFORS2 - 300I - 3.5h integration (6. Nov ‘02)

Ca II H&Kz=1.31

Summary (Problems)

Supernova systematics• unknown explosion mechanism

• unknown progenitor systems

• light curve shape correction methods for theluminosity normalisation (SCP vs. HZT)

• signatures of evolution in the colours?

• spectroscopy?

The Future

Future experiments will distinguishbetween a cosmological constant orquintessence• ESSENCE, CFHT Legacy Survey, VST,

VISTA, NGST, LSST, SNAP

The Future

Future experiments will distinguishbetween a cosmological constant orquintessence• ESSENCE, CFHT Legacy Survey, VST,

VISTA, NGST, LSST, SNAP

Systematic uncertainties depend on ourunderstanding of the supernovae• nearby samples, explosion models, radiation

hydrodynamics

Einstein’s cosmological constantCan not be explained within the currentparticle physics models

QuintessenceSignatures of higher dimensions

some theories of gravity work in higherdimensions - leakage from there into the 4-dimensional world would effect theFriedmann equation

Phantom energieDark energy will tear the universe apart(Big Rip)

Interpretations/Speculations

Summary

Only Type Ia supernovae can currentlyprovide a possible answer to what theDark Energy is:• what is _?

• what is d_/dt?

• what is the future of the universe?