Precise Cosmology from SNe Ia Wang Xiao-feng Physics Department and Tsinghua Center for Astrophysics, Tsinghua University 2005, 9, 22, Sino-French Dark Universe Worshop(Marsellei)

Outlines Supernovae Observational Issues and SNe Ia correlations A Novel Color Parameter As SN Ia Calibrator The Hubble constant from SNe Ia Implications for Cosmology

What is supernova A Nearby Supernova in M51! (SN 2005cs) Stellar explosion with giant energy release Supernovae might be the brightest objects in the universe, and can outshine a whole galaxy (for a few weeks) One of the endpoints of stellar evolution Energy of the visible explosion~10 51 ergs Luminosity~ L ⊙

To measure the universe with supernovae Extremely bright stellar explosions Important for the production of the heavy elements Best distance indicators in the universe The only reliable way of determining extragalactic distances is through supernova investigations. F. Zwicky

Supernovae Big Bang Stars Supernovae

Type II (core-collapse) supernovae H He C O Si Fe Non- burning H Massive star: Fe is fusion endpoint electron capture  pressure drop collapse density increases core bounces back shockwave  heating  expansion

core collapse supernova mechanism Fe core inner core pre SN star 1. infalling outer core outgoing shock from rebounce proto neutron star 2. infalling outer core proto neutron star stalled shock 3. revived shock proto neutron star matter flow gets reversed - explosion 4. neutrinos neutrino heated layer

Type Ia supernovae white dwarf in binary stellar system high H accretion rates growing C/O white dwarf ~Chandrasekhar mass (1.4 M solar )  contraction high central density  C fusion thermonuclear explosion

The variety of SN light curves Patat et al. (2001)

Riess et al. 1999

SN Ia Differences SN Ia are not all the same. Variations are present in their light curves and spectra.

SN Ia correlations  m15 relation  BATM Phillips (1993), Hamuy et al. (1996), Phillips et al. (1999) MLCS  MLCS2k2 Riess et al. (1996, 1998), Jha et al. (2003) Stretch  SALT perlmutter et al. (1997), Goldhaber et al. (2001),Guy et al.(2005)

Luminosity vs. decline rate  m 15 relation Phillips et al. 1999

The SN Ia luminosity can be normalised Bright = slow Dim = fast BVIBVI Riess et al MLCS

Stretch factor method Goldhaber et al. 2001

Nearby SN Ia sample Evidence for good distances, but not good enough for precise cosmology –distance accuracy around 12%

Wang et al 2005a More precise cosmology- A Novel Color Parameter Wang et al 2005a

SN Luminosity vs.  C 12

Estimate of SN host galaxy reddening

The dust properties for distant host galaxy (Wang et al. 2005b) Smaller than the Galactic values of 5.5 in U, 4.3 in B, 3.3 in V, and 1.8 in I SN explosion may change the distribution of the size of dust grains

max M V vs.  m 15, B max - V max

Observational issues 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  color –explosion mechanism? What are the subluminous objects? a faint end of normal or distinct type ?

Distances in the local universe Assume a linear expansion Hubble law v=cz=H 0 ·D Use the distance modulus m-M=5log(D/10pc)-5 Distances of a ‘ standard candle ’ (M=const.) m=5log(z)+b b = M+25+5log(c)-5log(H 0 )

Raw Hubble diagram of SNe Ia

Precise SN Ia Hubble diagram (calibrated by  C 12 ) ~6% in distance Improved by ~50% than traditional methods

The Hubble constant Sets the absolute scale of cosmology –replaces these annoying h ’ s in all the theorists talks Measure redshifts and distances in the nearby universe –Supernovae can do this in two ways: Expanding photosphere method of core-collapse SNe accurate (relative) distances from SN Ia

Absolute Magnitudes of SNe Ia Wang et al. 2005b

H 0 from SNe Ia (wang et al. 2005b) A robust value of H 0 (UBVI) = 72.0±4.0(total) km s -1 Mpc -1

Implications for high-z SN Ia distances

Distant SNe Ia- dark energy Distant objects appear fainter than their nearby counterparts This is a 2.5  result (High-z SN Team and Supernova Cosmology Project) –evolution –dust –cosmology Checks: Dust –observations over many filters Evolution –spectroscopy Cosmology –more distant SNe Ia

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  Evolution very difficult to control

Over corrections by traditional calibration method Are there SNe Ia with broader light curves but normal and even lower peak luminosity? SN 2001ay, M V =-19.02mag; SN 1992al, M V =-19.30mag  m 15 =0.6  1.1 (fiducial SN 1992al), M V   C 12 =0.34  0.31(fiducial SN 1992al), M V  SN 1999aa-like events may also bear such properties

There is a trend that SNe with broader light curves increase with redshift whether from observational selection effect or evolution effect of age or metallicity. Essence Observations -Kriscunias et al. (2005) Eight of nine SNe Ia discovered have  m 15 < 0.92 If SNe Ia with broader light curves but normal luminosity are dominant in the high-z sample, the mean luminosity of SNe Ia at higher redshifts may be overcorrected. This may have significant impact on present cosmological results!