Download presentation
Presentation is loading. Please wait.
Published byAshlee Jennings Modified over 8 years ago
1
CIfAR Stanford 2008 SN Ia Rates: Theory, Progenitors, and Implications
2
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?)
3
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)
4
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 …
5
CIfAR Stanford 2008 SN Ia rate depends on SFR Mannucci et al 2006 SNLS - Sullivan et al 2006
6
CIfAR Stanford 2008 Scannapieco and Bildsten 2005 Sullivan et al 2006 SNR/M M SFR
7
CIfAR Stanford 2008 2 different B values Scannapieco & Bildsten 2005 Sullivan et al 2006 passive active
8
CIfAR Stanford 2008 SN Ia rate depends on SFR SFR ½
9
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?
10
CIfAR Stanford 2008 Single degenerate scenario Delay time depends on evolutionary timescale of secondary Model
11
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
12
CIfAR Stanford 2008 Rate vs time Simple SFR(t) ~ t -η to allow for range of ages +1 +1
13
CIfAR Stanford 2008 4 different values
14
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
15
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
16
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
17
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).
18
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.
19
CIfAR Stanford 2008 Han & Podsiadlowski 2004 DD Scenario
20
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
21
CIfAR Stanford 2008 03D3bb 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!
22
CIfAR Stanford 2008 Cosmic SFR(z) Hopkins and Beacom 2006
23
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)
24
CIfAR Stanford 2008 SNR predictions from SFR(z) Solid=model, dashed=A+B (Sullivan 2006) Kuznetsova et al 2008 Dilday et al 2008
25
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 …
26
CIfAR Stanford 2008
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.