COSMIC RATE OF SNIa

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COSMIC RATE OF SNIa

• Laura Greggio
• INAF, Padova Astronomical Observatory

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SNIa are relevant to the study of

• Chemical evolution of galaxies
• Chemical evolution of the ICM and IGM
• Gas flows in Ellipticals
• The determination of cosmological parameters

To study 1,2 and 3 we need the SNIa rate
following a burst of SF To address 4 we need
to understand the nature of the SNIa progenitor
The cosmic evolution of the SNIa rate helps
constraining both
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Dahlen et al. 2004
SNII trace the recent SF ? use the rate of type
II to
trace the cosmic SFR
SNIa come from longer lived progenitors At a
cosmic epoch t the SNIa rate is

• t is the delay time (interval between the birth
• of the stellar system and its explosion)
• fIa is the distribution function of the delay
• times
• AIa is the realization probability of the
• SNIa event out of one stellar generation
• ka is the number of stars per unit Mass of
• one stellar generation

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Close Binary Evolution
provides two main cathegories of SNIa
precursors Single Degenerate Systems a CO WD
accretes from a living companion Double
Degenerate Systems the companion is another WD

• Explosion may occur when
• the WD mass reaches the
• Chandrasekhar limit
• (Ch-exploders)
• a Helium layer of 0.1 MO, accumulated
• on top of the WD, detonates
• (Sub-Ch exploders)

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Pros and Cons
Single Degenerates
Candidate precursors observed (SSXRS,
Symbiotic, CV) Fine tuning of
accretion rate is needed to avoid
nova and/or CE (small volume in the
phase space) Absence of H in the
spectra
Double Degenerates Absence
of H in the spectra Theoretical
likelyhood accounts for current
rate in the MW Theoretical
explosion leads to neutron star
Observed DDs are not massive
enough
CHANDRA exploders uniform light curves and
better spectra
BUT few of them SUB-CHANDRA many
of them BUT
variety of Ni56 produced and
high velocity of ejected Ni
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Population Synthesis of Binaries
Monte Carlo simulations of a population of
binaries with n(m1), n(q), n(A0), following the
evolution of each system through the RLOs and
determining the outcome (CVs, RCBor, sdO,all
varieties of DD.., sometimes SNIa) Tutukov
Yungelson , Ruiz-Lapuente,Burket Canal, Han et
al., Nelemans et al.
Yungelson and Livio 2000
The results are (highly) model
dependent ( aCE, mass loss, criterion for mass
transfer stability ) hard to implement in
other computations (for galaxy evolution, cosmic
evolution)
BUT the distribution function of the delay times
can be characterized on general grounds
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Single DegeneratesClock is the nuclear
timescale of the secondary
limits on primary mass
Evolutionary clock and Distribution of the
secondaries in systems which give rise to a SNIa
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Double Degenerates
Double CO WDs m1, m2 ? 2 then tn 1Gyr
Clock is the nuclear timescale of the secondary
the gravitational delay
The distribution function of the separations of
the DD systems is crucial for the distribution of
the gravitational delays
MDD2 ?tgw ranges in 5Myr 15 Gyr
A ranges from 0.5 to 3.8 Ro

• Shrinkage at RLO
• Start from
• 100 R0 ltA0 lt 1000 R0
• Go through RLO
• standard CE (A/AO)few 10-3
• heavier systems have smaller A/AO shorter tgw
  
• Nelemans et al.
• large range of (A/AO)
• no correlation between mass and tgw

WIDE DDs
CLOSE DDs
A small dispersion in DD masses and/or final
separations yield a wide distribution of delay
times
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The distribution function of the delay times for
DDs
mainly controlled by maximum nuclear
delay (minimum m2 of a successful
system) whether evolution leads to WIDE or CLOSE
DD distribution function of the separations of
the DD whether favouring larger or smaller A
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The distribution function of the delay times
All models normalized at 12 Gyr
Main Parameters SD minimum mass of the
primary for a successful SNIa
(distribution of mass ratios) DD 1) minimum
mass of the secondary (fix maximum
nuclear delay) 2) distribution function of the
separations after II RLO 3) whether
WIDE or CLOSE

• Different models have
• different
• different Fe production

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The Cosmic SNIa rate
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Results of the convolution
The results of the convolution are rather
sensitive to the adopted cosmic SFR A steep
increase from z0 to 1 favors a steep increase of
the cosmic SNIa rate A decrease from z1
upward Could explain the low SNIa rate at z1.6
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SNIa rate in different galaxy types
Another way to constrain the distribution
function of the delay times

• Younger stellar populations sample the peak of
• the distribution function of the delay times
• Younger stellar populations are bluer
• ? Bluer galaxies have larger SPECIFIC SNIa rates

Data from Mannucci et al. 2005
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CONCLUSIONS

• I illustrated how the SFR and the distribution
  function of the delay times compose to determine
  the SNIa rate in galaxies
• The current SNIa rate in Spirals mostly
  constrains the realization probability of the
  SNIa scenario
• in
  Ellipticals it scales as the fIa function
• The ratio between the current SNIa rates in
  Spirals and Ellipticals constrains the shape of
  the function
• I presented analytic expressions, describing the
  distribution function of the delay times for
  Single and Double Degenerate progenitors
• These expressions are based on general stellar
  evolution arguments, which result into a
• fIa function controlled by a few main
  parameters
• Representing Es as instantaneous burst of SF,
  and using their current rate to calibrate the fIa
  function, I showed that
• SD models greatly overproduce Fe in
  Galaxy Clusters
• and overpredict the current
  rate in Spiral galaxies
• The data are met with
• either CLOSE DDs
  with flat n(A)
• or WIDE DDs
  with steep n(A)

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NORMALIZATION
Horizontal levels derived from rate in
galaxies Points derived from cosmic rate