CIfAR Stanford 2008 SN Ia Rates: Theory, Progenitors, and Implications.
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Transcript of CIfAR Stanford 2008 SN Ia Rates: Theory, Progenitors, and Implications.
CIfAR Stanford 2008CIfAR Stanford 2008
SN Ia Rates: Theory, SN Ia Rates: Theory, Progenitors, and Progenitors, and
ImplicationsImplications
CIfAR Stanford 2008CIfAR 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 Msun. Energy released (~0.5Msun CO --> 56Ni) No H in spectrum Light curve shape (radioactive decay) Presence in old stellar pops (what else could they be?)
CIfAR Stanford 2008CIfAR Stanford 2008
SN Ia Progenitors - 2 Broad Classes
Single Degenerate - white dwarf + evolving secondary (M ~ 1.4 Msun at explosion)
Double Degenerate - 2 white dwarfs (Mtot >= 1.4 Msun at explosion)
Key point: white dwarf max mass = 1.4 Msun (Chandra- sekhar mass)
CIfAR Stanford 2008CIfAR 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 2008CIfAR Stanford 2008
SN Ia rate depends on SFR
Mannucci et al 2006SNLS - Sullivan et al 2006
CIfAR Stanford 2008CIfAR Stanford 2008
€
SN rate = A ⋅M + B ⋅SFRScannapieco and Bildsten 2005
Sullivan et al 2006
SN
R/M
SN
R/M
M SFR
CIfAR Stanford 2008CIfAR Stanford 2008
2 different B values
Scannapieco & Bildsten 2005
Sullivan et al 2006
passive
active
€
SNR /M = A + B(SFR /M)
CIfAR Stanford 2008CIfAR Stanford 2008
SN Ia rate depends on SFR
SFR½
€
cf . SNR /M = A + B(SFR /M)
CIfAR Stanford 2008CIfAR Stanford 2008
SNR = A٠M + B٠SFRSNR/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 2008CIfAR Stanford 2008
Single degenerate scenario
Delay time depends on evolutionary timescale of secondary
Model
±−
+−
−
∝
∝
⋅=
∝∝
−≅−≅∝
∝
5.0
/)1(
1/1/1 ,
5.2,35.2 timescaleevol
fcn mass
τ
τττ
ττ
τ
τ
bba
bb
b
a
ddM
dMdN
ddN
ddMM
baM
MdMdN
CIfAR Stanford 2008CIfAR 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 2008CIfAR Stanford 2008
Rate vs time Simple SFR(t) ~ t-η to allow for range of ages
+1
-1 -1
+1
CIfAR Stanford 2008CIfAR Stanford 2008
4 different values
CIfAR Stanford 2008CIfAR 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 2008CIfAR Stanford 2008
Meaning
Single component model – not A+B Single free parameter
normalization - fSNIa Continuous distribution of
delay times Rate in active and
passive galaxies both explained naturally
Only physics is evol-utionary timescales
CIfAR Stanford 2008CIfAR Stanford 2008
Normalization
Fraction 0.01 of all stars in the mass range 1-9 Msun become SNeIa.
“cum grano salis” (1e10 Msun) <[Fe/H]>=-0.5
1e10 Msun Salpeter mass fcn 1-9 Msun for SNIa 0.6 Msun Ni56 per SNIa
X fSNIa
6 x 106 Msun
Fe peak
CIfAR Stanford 2008CIfAR Stanford 2008
Efficiency vs mass (SD) 1 Msun main sequence stars find it very difficult to
get to the Chandra mass and make a Type Ia SN
• Close binaries with primary < 2Msun make a He WD, not a C+O WD
• Mass arguments: 1 Msun on the m.s. makes a 0.5 Msun WD, hard to imagine 2 x 1 Msun making a 1.4 Msun WD
• Most of companions to 1 Msun 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 2008CIfAR 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 2008CIfAR Stanford 2008
Han & Podsiadlowski2004
DD Scenario
CIfAR Stanford 2008CIfAR Stanford 2008
SNLS-03D3bb (Howell et al. 2006) z=0.24, star-forming host
Most luminous SNIa ever discovered (MV=-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 2008CIfAR Stanford 2008
03D3bb
Requires 1.3 Msun of 56Ni to power light curve, 2Msun total mass
“normal” SNIa – 0.6 Msun of 56Ni 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 2008CIfAR Stanford 2008
Cosmic SFR(z)
Hopkins and Beacom 2006
CIfAR Stanford 2008CIfAR 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 2008CIfAR Stanford 2008
SNR predictions from SFR(z) Solid=model, dashed=A+B (Sullivan 2006)
Kuznetsova et al 2008
Dilday et al 2008
CIfAR Stanford 2008CIfAR 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 2008CIfAR Stanford 2008