Download - Review of SNLS results
Blois 2008 21 May 2008 1
Vanina Ruhlmann-KleiderCEA/Irfu/SPPSaclay
Review of SNLS results
1) The Supernova Legacy Survey2) Cosmology results3) SNe Ia : usable for precision
cosmology ?4) Conclusions
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o The survey (2003-08): - four 1°x1° fields - each field observed every
3-4 nights during 6 monthso MegaCam : - 1°x1° CCD imager - 340 millions of pixels - pixel resolution: 0.18“ - four filters (400-1000nm) o Spectroscopy: time allocated
on 8-10 meter class telescopes ~500 confirmed SNe Ia in 5 years with redshifts in 0.1 – 1.2
SNLS at CFHT
04D1dc
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SNLS "rolling search"
large and homogeneous sample of high-z spectroscopically confirmed SNe Ia, measured with
good photometric accuracy
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a SNIa lightcurve
spectroscopy triggered type Ia confirmed, z=0.627
multi-band LC’s :
test compatibility with SNIa model (trained on SNIa lightcurves and
spectra)
i’, r’, z’, g’ filters
apparent B flux : mB*, (B-V) colour c and stretch s
see e.g J.Guy et al., A&A 466 (2007) 11
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Cosmology with SNe Iao SNe Ia are (assumed to be) standard candles :
mB* from B* L(c,s) /4πdL2 with
dL(z,H0,ΩM,ΩΛ,w,..)
B = mB* - MB + (s-1) - c
apparent rest-frame maximum light
magnitude
reference absolute B-
band magnitudelightcurve shape
variability
(B-V) colour variability(intrinsic variation and
extinction)
known luminosity
o Distance estimator :
+ intrinsic dispersion term, int allowed in cosmological fits to account for our lack of knowledge about SNe
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1st year resultsP.Astier et al., A&A 447 (2006) 31
residuals to (0.26,0.74):
older
fain
ter
First year result (71 SNe) consistent with an accelerating Universe
int: 0.13± 0.02Low-z: 0.15±0.02High-z: 0.12±0.02
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if ΩM+ΩΛ=1:
ΩM=0.263±0.043±0.032 (SNLS,w=-1)
w=-1.023±0.090±0.054 (SNLS+BAO)
w=-1
M+=1
Cosmological parameters
wpde
de
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Preliminary 3rd year result
SNLS3 result (~250 SNe) agrees with SNLS1 result, w consistent with -1 within 6% (SNLS+BAO+WMAP5)
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SNe Ia : usable for precision cosmology ?
Distance estimator :
MB, , assumed
to be z-independent
Is that so ?
compare properties of SN sub-samples split by redshift, host activity…
B = mB* - (MB - (s-1) + c)
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resi
dual
s w
ithou
t s-t
erm
resi
dual
s w
ithou
t c-t
erm
mB* - MB + (s-1) - c – 5 log10(dLfit c-1 H0)
‘’brighter-slower relationship’’ ‘’brighter-bluer relationship’’
consistent behaviour for nearby and distant SNe Ia (1st year data)
P.Astier et al., A&A 447 (2006) 31
blue: z<0.15 / black: z>0.15
bri
ghte
r
slower bluer
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stretch-corrected lightcurves
SN Ia rise-times consistent at 1σ
o low-z vs high-z SNe Iao passive/active host galaxies
A.Conley et al., AJ 132 (2006) 1707
73 SNe z<0.9 – 2 years of data
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SN Ia rate is a function of the
host stellar mass and SFR
Passive
hosts
Active hosts
SN
Ia r
ate
per
unit
mass
per
year
Star formation rate per unit mass
SN stretch depends on host activity
M.Sullivan et al., ApJ 648 (2006) 868
SN Ia environment
Brighter, slower SNe occur mostly in star-forming
galaxies(2 years of data)
10 10 10 10 10
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Two-component rate modelisation1
SNRIa(t) = A Mtot + B dM/dt(t)
galactic stellar mass SFR old stars prompt SNe
evolved galaxies star-forming galaxies
1. Fit A and B from SNLS data2. Use fitted A, B values and a model2 for SFR(z) to
predict rates vs redshift3. Compare predicted rate with measurements
1Scannapieco, Bildsten (2005) 2 Cosmic SFH from Hopkins & Beacom (2006)
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Average SN stretch will evolve
with z
Predicted mix of two SN
populations evolves with z
Implication:
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SNLS
D.Howell et al., ApJ 667 (2007) 37
Stay tuned !
stretch evolution with z: predictions agree with data
<stretch> + 8% for z=0.03-1.12
<intrinsic brigthness> +12%
If is the same for old/prompt SNe, this will
not affect cosmology
Need more data to test , values from sub-samples
split by stretch or host type
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Conclusions
o SNLS: efficient high-z SN Ia detection, optimised temporal sampling, very good photometric accuracy.
o Cosmology: ~250 SNe in SNLS3. Constraints on m, w consistent with SNLS1 results, accuracy on w from 9 to 6% (stat).
o Are SNe Ia good cosmological probes ? • Average SN Ia properties evolve with redshift. So far,
no bias in cosmology detected. • Larger samples needed to test if the empirical
luminosity-shape or color relations need to be refined.
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BACK-UP SLIDES
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A possible type Ia explosion mechanism
reproducible intrinsic luminosity : SNe Ia ~ standard candles
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Spectroscopic time allocated on 8-10 meter class telescopes
more 8-10m time than CFHT time !
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September 06:>350 spec confirmed Ia
>500 spec confirmed Ia by end of June 08
More than 1000 Ia in total
SNLS SNIa data sample
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SNLS data analysis
An example of raw image:
entire 4x9 CCD mosaicone exposure of 300secfilter r (<>=620nm)size: 1.4 Gb
2004/10/21
whole survey: 15 Tb
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SN detections
Reference image Current image Subtraction
SN Ia events found by CCD image subtraction:
Many steps: image cleaning and alignment, photometric calibration, match reference and current image qualities…
SN
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if ΩM+ΩΛ=1:
ΩM=0.271±0.021±0.007
w=-1.023±0.090±0.054
DE equation of state
M+=1
(SNLS+BAO)
wpde
de
1de
dde
dt 3H1w
w=1/3 radiationw=0 matterw>-1 quintessencew=-1 cosmological constant
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Systematics, 1st year paper
photometric accuracy
selectionbias
SN Ia model
SN Ib/Ic contamination: 0.5 in the 1st year sample
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Comparison with previous SN results
Knop et al, 2003 (HST+SCP) : 52 SNe,dotted contours
SNLS 1st year:71 SNe, solid countours
SNLS projected end of surveyshaded area
the superior color and time sampling leads to tighter constraints
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Intrinsic colour vs dust extinction
Colour—luminosity relationship
inconsistent with MW-type dust
Best-fit: β~3
MW-dust: β≡RB=4.1
SN Colour (c)
Resid
ual w
ith
ou
t c-c
orr
ecti
on
β=4.1
Preliminary SNLS3
M.Sullivan, STScI, may 2008
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Colour correction required in all host
types
SN Colour (c)
Resid
ual w
ith
ou
t c-
corr
ecti
on
Resid
ual w
ith
ou
t c-
corr
ecti
on
Passive hosts
Star-forming hosts
40 high-z SNe
180 high-z SNe
Large “local” SN surveys Large “local” SN surveys covering a wide wavelength covering a wide wavelength range (inc. near-IR) urgently range (inc. near-IR) urgently needed to disentangle thisneeded to disentangle this
M.Sullivan, STScI, may 2008
Preliminary SNLS3
Either:Passive hosts have dust?An intrinsic relation dominates over dust?
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Determine (luminosity correction), (color
correction), from subsamples split by…
spiral
elliptical
low s
high s
Early days… larger samples will be definitive
Tension?s<1
s>1
Preliminary SNLS3
M.Sullivan, STScI, may 2008
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Spectroscopic corollaries
T.J.Bronder et al., A&A 477 (2008) 717
SiII equivalent width distributions (residuals / low-z
beahviour)□ E/S0 ■ Spirals
Lower EWs in late-type galaxies, whatever the redshift
SNe Ia in late-type (star-forming) galaxies are brighter (more 56Ni)
and thus hotter more ionisation less intermediate
mass elements (Ca, Si).
(87 SN Ia spectra from Gemini – 3 years of data)
Lower EWs in late-type galaxies, whatever the redshift
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SNe Ia as standard candles
o 1990s: a simple temporal stretch correction aligns the light-curves in a sample of nearby SNe Ia
o Study cosmology with distant SNe Ia• The High-Z project (95-97):
10 SNe Ia in 0.3<z<0.97• The SuperNova Cosmology
Project (93-98): 42 SNe Ia in 0.18<z<0.83
days
days
~flux
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SNLS vs 1st generation experiments
Ex: the High-Z experiment:
o Small CCD camera few nights of observation
only 10 high z SNe Ia
poor light-curve sampling
o Only two filters
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the Universe expansion is accelerating
0.01 0.1
1z~ apparent fluxB
= L /4πdL2
withdL(z,H0,ΩM,ΩΛ,w)
fain
ter
furt
her
back
in t
ime
more redshift more expansion
Cosmology from SNe Ia : 1997-98