CIfAR Stanford 2008 SN Ia Rates: Theory, Progenitors, and Implications

CIfAR Stanford 2008 SN Ia progenitors  Why important?  Among the most powerful explosions in the Universe (next to GRBs)  SNe Ia and cosmology  Role in chemical evolution and gas dynamics  Scenario: exploding CO white dwarf near 1.4 M sun.  Energy released (~0.5M sun CO --> 56 Ni)  No H in spectrum  Light curve shape (radioactive decay)  Presence in old stellar pops (what else could they be?)

CIfAR Stanford 2008 SN Ia Progenitors - 2 Broad Classes Single Degenerate - white dwarf + evolving secondary (M ~ 1.4 M sun at explosion) Double Degenerate - 2 white dwarfs (M tot >= 1.4 M sun at explosion) Key point: white dwarf max mass = 1.4 M sun (Chandra- sekhar mass)

CIfAR Stanford 2008 Two Basic Questions  What is the “delay time distribution” of SNe Ia? What is the main sequence mass of SNe Ia progenitors?  By what evolutionary path(s) do white dwarfs become SNe Ia? Basic questions, but no clear answers …

CIfAR Stanford 2008 SN Ia rate depends on SFR Mannucci et al 2006 SNLS - Sullivan et al 2006

CIfAR Stanford 2008 Scannapieco and Bildsten 2005 Sullivan et al 2006 SNR/M M SFR

CIfAR Stanford different B values Scannapieco & Bildsten 2005 Sullivan et al 2006 passive active

CIfAR Stanford 2008 SN Ia rate depends on SFR SFR ½

CIfAR Stanford 2008 SNR = A٠M + B٠SFR SNR/M = A + B (SFR/M)  Does this imply two paths to SNeIa? …  … or is there a simple unifying picture that can be used to understand the A+B prescription for the SNIa rate?  Continuum of delay times – more natural?  Why do the A and B values have the values that are observed?  Why ~√SFR dependence rather than ~SFR?  Why is fit so poor in the SNR/M -- SFR/M plane?

CIfAR Stanford 2008  Single degenerate scenario  Delay time depends on evolutionary timescale of secondary Model

CIfAR Stanford 2008 “Rate” vs time  Rate at which stars leave main sequence  white dwarf formation rate  distribution of delay times for a burst  rate from a starburst decreases with time as ~ √t  Factor of ~100x in mean stellar age (100Myr – 10Gyr) gives factor of ~10x in SN Ia rate, as observed starburst rate~√t

CIfAR Stanford 2008 Rate vs time  Simple SFR(t) ~ t -η to allow for range of ages +1 +1

CIfAR Stanford different  values

CIfAR Stanford 2008 Models vs Observations  Locus of WD formation rates independent of SFR(t) - includes passive galaxies  1% of WD’s become SNeIa  1% agrees with models (roughly)  1% agrees with MW (roughly)  [Disagrees with clusters (10-20%)]  Note that 1% eff is constant from active to passive galaxies! age

CIfAR Stanford 2008 Meaning  Single component model – not A+B  Single free parameter normalization - f SNIa  Continuous distribution of delay times  Rate in active and passive galaxies both explained naturally  Only physics is evol- utionary timescales

CIfAR Stanford 2008 Normalization Fraction 0.01 of all stars in the mass range 1-9 Msun become SNeIa. “cum grano salis” (1e10 M sun ) =-0.5 1e10 M sun Salpeter mass fcn 1-9 M sun for SNIa 0.6 M sun Ni56 per SNIa X f SNIa 6 x 10 6 M sun Fe peak

CIfAR Stanford 2008 Efficiency vs mass (SD)  1 M sun main sequence stars find it very difficult to get to the Chandra mass and make a Type Ia SN Close binaries with primary < 2M sun make a He WD, not a C+O WD Mass arguments: 1 M sun on the m.s. makes a 0.5 M sun WD, hard to imagine 2 x 1 M sun making a 1.4 M sun WD Most of companions to 1 M sun stars haven’t evolved yet binary frequency lower for low mass objects (?) Therefore fraction of WD’s that make SNeIa should be much lower at low masses (>10x).

CIfAR Stanford 2008 Effects of efficiency  Normalized at high mass (short timescale) end  Assume efficiency drops by 10x from M=3 to 1 Msun (conservative) Single degenerate model cannot explain all SNeIa. Some other mechanism must be involved for at least some SNeIa.

CIfAR Stanford 2008 Han & Podsiadlowski 2004 DD Scenario

CIfAR Stanford 2008 SNLS-03D3bb (Howell et al. 2006)  z=0.24, star-forming host  Most luminous SNIa ever discovered (M V =-20.0, 10 billion Lsun)  Lies off the stretch-L relation - too bright for its stretch s=1.13 by 4.4 sigma

CIfAR Stanford D3bb  Requires 1.3 Msun of 56 Ni to power light curve, 2Msun total mass  “normal” SNIa – 0.6 Msun of 56 Ni  03D3bb is 2.2x brighter, therefore has 2.2x Ni mass  Detailed calculation using Arnett models agrees well  Mass > Chandra mass of 1.4 Msun!

CIfAR Stanford 2008 Cosmic SFR(z) Hopkins and Beacom 2006

CIfAR Stanford 2008 SNR predictions from SFR(z)  SFR(z) gives SFR(t) per Mpc^3  Normalization somewhat arbitrary  SN rate very sensitive to exact SFR(z)

CIfAR Stanford 2008 SNR predictions from SFR(z)  Solid=model, dashed=A+B (Sullivan 2006) Kuznetsova et al 2008 Dilday et al 2008

CIfAR Stanford 2008 Conclusions  SNIa rate depends on SFR  “natural” explanation in terms of evolutionary timescales  1% of white dwarfs become SNeIa  Single degenerate model cannot explain all SNeIa  one parameter model fits active and passive excellent fit to data – better than A + B SFR/M A and B naturally explained Based on stellar evolutionary timescales Continuous delay time distribution  Predictions: SNIa rate will correlate with mean age from population models SNII/SNIa z distributions Chem evol …

CIfAR Stanford 2008