A Step towards Precise Cosmology from Type Ia Supernovae

Wang Xiaofeng

Tsinghua University

IHEP, Beijing, 23/04, 2006

Outlines

• What is Supernova?• The light curve properties of SNe Ia • The empirical calibration methods for SNe Ia• New cosmological distances from SNe Ia and t

he implications for cosmology

Supernova Explosion!

SN 2005mf

Supernova Search 300-400/year since 1998

A New record: 365 in 2005!

SN classificationsTaxonomy Chart Spectroscopic classifications

Stellar evolution and supernova explosion

Type Iasupernovaewhite dwarf in binary stellar system

high H accretion rates

growing C/ O white dwarf

~Chandrasekhar mass (1.4 Msolar) contraction

high central density C f usion

thermonuclear explosion

Type I a: WD defl agration

Expanding, cooling optically-thick shell: 56Ni 56Co

cooling optically-thin: 56Co 56Fe

57Co, 44Ti, 22Na decay

Supernova Light curves

Riess et al. 1999

Raw Hubble diagram of SNe Ia

Luminosity Function of SNe Ia

(wang et al. 2005b)

The environmental effect on SN luminosity

SN Ia correlations m15 relation BATM

Phillips (1993), Hamuy et al. (1996), Phillips et al. (1999)

• MLCS MLCS2k2Riess et al. (1996, 1998), Jha et al. (2003)

• Stretch SALTPerlmutter et al. (1997), Goldhaber et al. (2001), Guy et al.

(2005)

• C12 method Wang et al. (2005a, b)

The template method (Phillips 1993, Hamuy et al. 1996)

The light curve fitting by template

Luminosity vs. decline rate Piskovski-Phllips relation

Phillips et al. 1999

The SN Ia luminosity can be normalised

Bright = slow Dim = fast

B

V

I

Riess et al. 1996

MLCS method

Stretch factor method

Goldhaber et al. 2001

stretch

The reasons underlying the light curve correlation

SN MB log(L) M(Ni)SN1989B -19.37 43.06 0.57SN1991T -19.76 43.23 0.84SN1991bg -16.78 42.32 0.11SN1992A -18.80 42.88 0.39SN1992bc -19.72 43.22 0.84SN1992bo -18.89 42.91 0.41SN1994D -18.91 42.91 0.41SN1994ae -19.24 43.04 0.55SN1995D -19.66 43.19 0.77

DeductionsSlower SNe Ia are more luminous

--more energy radiated

More luminous SNe Ia have slower declines at late phases (Phillips et al. 1999, Contardo et al. 2001)

-- slower release of the energy

Slower SNe Ia have larger expansion velocities (Mazzali et al. 1998)

--less efficient trapping of -rays

Contardo et al. 2000; data for SN 1991 from Strolger et al. 2002

The nearby SNe Ia

distance accuracy around 8-12%

Evidence for good distances, but not good enough for precise cosmology

Tonry et al. 2003

The post-maximum color calibration(Wang et al. 2005)

SN Peak Luminosity vs. C12

distance accuracy around 4-5%

Treatment of the host galaxy reddening

Non-standard dust in other galaxies (Wang et al. 2006a) Smaller than the standard

values of 5.5 in U, 4.3 in B, 3.3 in V, and 1.8 in I in the Milkyway

SN explosion may change the size of the dust grains or the distribution of the dust in CSM

Second parameter correlations

The residual correlations

The Most Precise Hubble diagram from SNe Ia

•Normalising Type Ia Supernovae–light curve and color curve shape corrections

•what is the determining parameter?–Ni mass trapped energy light curve shape (affected also by opacity?)

–temperature colour

–explosion mechanism?

•What are the subluminous objects? a faint end of normal or distinct type ?

Applications to SNLS data

Comparison between different methods: magnitudes at maximum

(TF Vs. SF)

C12 vs. Stretch factor

distribution of Color parameters and Extinction

Nearby vs. distant

C12: 0.44 vs. 0.33

E(B-V）host: 0.062vs.0.077

Calibration difference

Correcting relations

conditions bB RB bV RV

All(excl. 91bg-like) 1.69(10) , 3.45(11) 1.47(10), 2.43(12)If E(B – V) < 0.40 mag 1.64(09), 2.84(18) 1.43(10), 1.81(20)If E(B – V) < 0.30 mag 1.60(10), 2.93(22) 1.42(10), 1.86(22)

If E(B – V) < 0.20 mag 1.65(10), 2.90(27) 1.45(10), 2.06(28)

Hubble diagram from C12 calibration

Cosmological results (for 131 well-sampled SNe Ia)

N Fit parameters(C12) parameters(salt) 84 (m, (m,flat

(m, (m,flat

m- contour

m- w contour

New result