Type Ia Supernovae as Distance Indicators Philip A. Pinto Steward Observatory University of Arizona Type Ia SupernovaeasDistance Indicators – p.1/45 p.2/45 – " # ! Indicators ,.- ,.- , £ + 0 aeasDistance v ¦ ¦ ¦ Superno Ia ype T ¨$ / ¨$ ¨ © (*) (*) ¦ ' ' $ % %& is £ ¨$ distance ¨ © ¦ and luminosity © ¦ ¦ erse, parameter v ¨ © Connections ¦ uni ¤ ¥§¦ £ ature W £ ¦ FR curv ¢¡ an In with Cosmic ¢¡ Comparing expansion velocity ( ) with luminosity distance ( ) type Ia supernovae (SNe Ia) have provided best measurement of current expansion rate ¢£¢¤¢£¢ ¡ ¥ £ ¦ ¡ today gave the first hard evidence for an additional component (dark energy) ¥ £ ¦ © ¥ § ¤ ¨ ¦ allow measurement of the EOS of dark energy, and perhaps ¨ even ¦ ¥ £ Type Ia SupernovaeasDistance Indicators – p.3/45 Measuring redshift is easy by spectroscopy of known atomic transitions with laboratory wavelength calibration. Measuring distance is hard there is no easily-determined standard of length for calibration. This has always been a central problem in astronomy Type Ia SupernovaeasDistance Indicators – p.4/45 Standard Candles Favorite astronomical technique: Discover a class of bright objects Assert they all have the same luminosity – a “standard candle” Measure the flux from the object and assign a distance When possible, try to reduce dispersion in distance by correlating luminosity with an easily-measured surrogate parameter. Type Ia SupernovaeasDistance Indicators – p.5/45 The problems with this process have been understood for a long time... The distance to a light cannot be estimated from its apparent brightness. There are too many factors which can change the perceived intensity. (Bowditch, American Practical Navigator, 1802) Type Ia SupernovaeasDistance Indicators – p.6/45 How good are SNe Ia as standard candles? What systematic effects may be lurking in cosmological measurements made with them? measurement problems, e.g. K-corrections statistical problems, e.g. sample biases Intervening material: extinction, gravitational lensing Evolution of sample properties: , © £ are SNe Ia the same at £ as in the local sample at ? Type Ia SupernovaeasDistance Indicators – p.7/45 Type Ia Supernovae: observed £ ¡¢ © ¦¨§ © ¥ ¥ ¤ (w/ mag) © , Peak phase lasts ¥ days (in co-moving frame!) Unique lightcurve shape and colors. Unique spectrum: early: Si, S, Ca, He, (C?), Fe, no H late: Fe, Co, Ni, (Si?) after 100 or so Seen in all types of galaxies. Rate: ,¨§ © ¦ ,¨§ , ¦ SNU (Hamuy & Pinto 1999) ¤ ¦ ¦ ¦ © © , £ (1 SNU ) Type Ia SupernovaeasDistance Indicators – p.8/45 SNe Ia as Standard Candles A good standard candle has the smallest possible range in luminosity £ ¡¢ ¢ © © ¡ ¥ ¤ SNe Ia exhibit § ( in L) £ too large for precision cosmology Phillips (’93) discovered that the width of the lightcurve peak is correlated with the peak luminosity: Brighter ¤ Broader ¨ © ¥§¦ Larger smaller ∆ M Can use the 15 ¨ © relation to M “standardize” the candle B to mag d 15 20 time Type Ia SupernovaeasDistance Indicators – p.9/45 Three Techniques (same sample!) ¡ : initerpolate in among a set of fiducial lightcurves from nearby sample. (Hamuy et al.1996) MCLS: fit to one-parameter family of lightcurves derived from the same fiducial sample (Riess et al.1998) ¨£¢ ¢ § § ¤¥¦ Stretch Factor: use a relation beween ¤¥¦ and derived from the nearby sample (Perlmutter et al.1998) All three methods have similar statistical properties and all use virtually the same “training set” of nearby supernovae. Type Ia SupernovaeasDistance Indicators – p.10/45 The Luminosity-Width Relation Broader is Brighter In all three techniques, a width parameter is proportional to peak magnitude: can “correct” all SNe Ia to a fiducial width ¢¡ © © £ ( § ) Phillips et al.(1999) show that colors converge in nebular phase can do accurate de-reddening ¤ , Calán-Tololo survey provides a well-observed sample of ¥ SNe Ia for calibration SNe Ia are very good “standard candles” once calibrated: ,¨§ © ¥ ¤ mag dispersion in ,¨§ © © ¤£ ¥ mag Hubble diagram Type Ia SupernovaeasDistance Indicators – p.11/45 Reddening-Free Luminosity-Width Relation (Phillips et al.1999) Type Ia SupernovaeasDistance Indicators – p.12/45 In the stretch factor method a scaling of the time axis is correlated with an offset in luminosity Type Ia SupernovaeasDistance Indicators – p.13/45 Effects of reddening and corrections (Phillips et al.1999) Calan/Tololo "Low Extinction" Sample 39 Corrected for: Galactic Reddening 37 35 ± Ho = 57.7 3.5 σ = 0.24 mag 33 39 Corrected for: Galactic Reddening ∆ m15(B) vs. Mmax 37 (m−M) 35 ± Ho = 64.3 3.2 σ = 0.18 mag 33 39 Corrected for: Galactic Reddening Host Galaxy Reddening 37 ∆ m15(B) vs. Mmax 35 ± Ho = 64.1 2.8 σ = 0.14 mag 33 3.5 4 4.5 log(czCMB) Type Ia SupernovaeasDistance Indicators – p.14/45 © , Local Hubble diagram scatter ¥ %: (Perlmutter & Schmidt 2003) Type Ia SupernovaeasDistance Indicators – p.15/45 Questions: What are SNe Ia? Where do they come from? How do they work? The luminosity-width relation is the crux of the measurement. Where does it come from? How reliable is it? What systematic effects might it exhibit as we observe SNe at ever-higher redshift (i.e. longer look-back times) as we require ever-smaller systematic errors ¨ (e.g. to measure Type Ia SupernovaeasDistance Indicators – p.16/45 Type Ia Supernovae Thermonuclear incineration of a C/O white dwarf He dwarf £ too energetic an explosion Ne/Mg/O dwarf collapses to NS Mass probably near 1.35 M § , , , © , 0 + ¡ ¥ Kinetic energy ¥ erg km s “Burns” C/O into ¢ 0.05 - 0.9 M Ni (NSE) 0.2 - 0.9 M Si - Ca (incomplete burning) Luminous output powered entirely by the decay chain ¢ ¢ ¢ £ £ Ni £¥¤ £ Co Fe ¦ ¦§ ¦ § ¦ Type Ia SupernovaeasDistance Indicators – p.17/45 Significant uncertainty surround the details of these explosions Progenitor population accreting white dwarf or “double-degenerate” Evolution to explosion Ignition physics Nature of combustion turbulent burning large-scale instabilities deflagration/detonation transition Type Ia SupernovaeasDistance Indicators – p.18/45 Current evolution/explosion scenarios are not suf®ciently predictive to reliably assess evolutionary effects Given an explosion, what can we say about the luminosity-width relation? Type Ia SupernovaeasDistance Indicators – p.19/45 0 56 56 10 Ni Ni 56 Ni Si O Si S -1 Si S n 54 56 10 Fe 54 Si Mg o Ca Ar Ni i Fe t 52 S 52 Ca Ar c Fe Ca Ar Fe a -2 CaS r Si S f 10 Ar s 52 s Fe a -3 m 10 54Fe 54 Fe C 10-9 ρ -10 ρ × 9 10 ρ 2 10 ρ v e y t l i -11 ρ o s 10 c n v i t e 9 y d v 10 10-12 v v v 10-13 0 0 0.2 0.4 0.6 0.8 1.0 1.2 M/Msun Type Ia SupernovaeasDistance Indicators – p.20/45 Lightcurve Physics Three timescales: ¢ PdV ¥ : shortly after explosion, radiation energy is PdV’d away to kinetic energy. ¦£¢ © ¢ escape ¥ : as increases, an increasing fraction of deposited energy from decay diffuses out and escapes conversion to kinetic energy heat ¥ decay : energy deposition drops rapidly £ ¡ lightcurve peaks when escape ¢ Type Ia SupernovaeasDistance Indicators – p.21/45 10-9 10-10 10-11 -12 ] 10 1 - m -13 lines c 10 [ y -14 t i 10 c a -15 p 10 - o e -16 10 free-free 10-17 bound-free 10-18 103 104 wavelength [A] Type Ia SupernovaeasDistance Indicators – p.22/45 Opacity is dominated by spectral lines below critical density £ modified diffusion Time spent rattling about with small mfp in a line « time spent between lines: each line acts as a single interaction. ¡ ¥ - ¦ mfp £¢ dist. between lines ¡ optical depth ¥ # of lines traversed opacity ¥ spectral density of lines Type Ia SupernovaeasDistance Indicators – p.23/45 d e r o t 3 1 - 10 s m k 4 0 all lines 1 n 2 i 10 h t i w τ>2/3 10000 K s e τ>67 τ>6.7 n i l f 1 o 10 r e 20000 K b m 30000 K u n 1000 2000 3000 4000 5000 6000 7000 8000 wavelength [A] Type Ia SupernovaeasDistance Indicators – p.24/45 Optical depth in blue remains very high as the # of lines does not change rapidly Diffusion time would be hundreds of days, yet lightcurve peaks at ¥ 20 days. Optical depth in red is small, even at maximum light Type Ia SupernovaeasDistance Indicators – p.25/45 opacity aises in nearly-neutral iron-group ions with very complex spectra – thousands of optical transitions density of the supernova is low £ slow electron collision rate cannot couple radiation and matter distributions In an iron-group plasma, fluorescence most common result of radiative absorption: photon absorption is followed by raditive cascade, effectively “splitting” blue photons into many red photons Type Ia SupernovaeasDistance Indicators – p.26/45 Type Ia SupernovaeasDistance Indicators – p.27/45 10-3 30000 K σ = 0.25 20000 K ε = 0 10000 K y t -4 i 10 s o n i m u l 10-5 2000 4000 6000 8000 wavelength Type Ia SupernovaeasDistance Indicators – p.28/45 Supernova is less than a thermalization length thick (Lucy) 1041 40 ] 1 10 - A 2 - m c 39 1 - 10 s g r e [ λ L 1038 1037 103 104 wavelength [A] Type Ia SupernovaeasDistance Indicators – p.29/45 At peak (20 ) the interior of the SN is a radiation-dominated ¡ © © , , © , ¡ gas at K, w/ peak ¥ Å UV opacity is very large & evolves only slowly £ diffusion time in blue is ¥ 500 days Energy escapes where it can, as optical/IR flux where ¨ ¡ © ¥ . Transport in energy longward in wavelength is thus more important than outward in radius. Energy escape is mediated by ¯uorescence. Type Ia SupernovaeasDistance Indicators – p.30/45 Rate at which stored UV energy can be converted to low- wavelengths determines the bolometric lightcurve What transitions are available is set by the ionization state Less-ionized species have redder lines than more-ionized ones £ ionization determines the color evolution & the effective opacity ¢ £ £ More Ni £ higher ionization bluer transitions higher effective opacity £ BROADER LIGHTCURVE More heating £ BRIGHTER LIGHTCURVE M © is the ªhidden parameterº in the luminosity width relation Type Ia SupernovaeasDistance Indicators – p.31/45 Consequences for the luminosity-width relation: Because spatial transport is less important, how the composition of the explosion is distributed may not strongly affect the lightcurve.