Supernova Legacy Survey

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Supernova Legacy Survey

• Mark Sullivan
• University of Oxford
• http//legacy.astro.utoronto.ca/
• http//cfht.hawaii.edu/SNLS/

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Paris Group Reynald Pain, Pierre Astier, Julien
Guy, Nicolas Regnault, Christophe Balland,
Delphine Hardin, Jim Rich,
Toronto Group Ray Carlberg, Alex Conley, Andy
Howell, Kathy Perrett
Victoria Group Chris Pritchet, Dave Balam,
Marseille Group Stephane Basa, Dominique Fouchez
Oxford Isobel Hook (Gemini PI), Mark Sullivan,
Emma Walker
The SNLS collaboration
Full list of collaborators at http//cfht.hawaii.
edu/SNLS/
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SNLS Vital Statistics

• 5 year rolling SN survey
• Goal 500 high-z SNe to measure w
• Uses Megacam imager on the CFHT griz every 4
  nights in queue scheduled mode

• Survey running for 4 years
• 350 confirmed zgt0.1 SNe Ia
• gt1500 SN detections in total
• Largest single telescope sample
• 450-500 by survey end

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Cosmology with SNe Ia

• Distance estimator constructed in rest-frame
  B-band

Note for the cosmological fits is gtgt1
unless an intrinsic dispersion term is added
this parameterises our lack of knowledge about
SNe
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SNLS 1st year 71 high-z SNe Ia
Astier et al. 2006 470 citations (297 in refereed
journals)
OM 0.263 0.042 (stat) 0.032 (sys) ltwgt-1.02
0.09 (stat) 0.054 (sys) (with BAO Flat
Universe)
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SNLS 3rd year versus 1st year

• Increase in SN numbers 71 to 250
• Ability to test SN sub-samples ( astrophysical
  systematics)
• Optimised survey design and calibration
• Deeper/more frequent z exposures increases
  utility of zgt0.7 SNe
• 3-year monitoring of fields better understanding
  of Megacam array
• Improved understanding of SN Ia properties
• New k-correction template (Hsiao et al. 2007)
  incorporates Ellis et al. UV spectra reduction
  in potential source of systematics
• New light curve fitting techniques exploit better
  understanding of SN light curves at ?lt4000A (rms
  0.19 -gt 0.16mag)

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Hubble Diagram
240 distant SNe Ia
(error was 0.042 in A06)
Sullivan et al. in prep
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Cosmological Constraints (Preliminary)
SNe
WMAP-3
6-7 measure of ltwgt
SNe
BAO
BAO
SNLSBAO (No flatness)
SNLS BAO simple WMAP Flat
(relaxing flatness error in ltwgt goes from 0.065
to 0.115)
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Potential SN Systematics in measuring w(a)

• Experimental Systematics
• Calibration, photometry, Malmquist-type effects
• Contamination by other SNe or peculiar SNe Ia
• Minimized by spectroscopic confirmation
• Non-SNe systematics
• Peculiar velocities Hubble Bubble Weak lensing
• K-corrections and SN spectra
• UV uncertain golden redshifts spectral
  evolution?
• Extinction/Colour
• Effective RV Intrinsic colour versus dust
• Redshift evolution in the mix of SNe
• Population drift environment?
• Evolution in SN properties

Extinction
Increasing knowledge of SN physics
Population Evolution
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Colour correction
ß4.1

• Colourluminosity relationship inconsistent with
  MW-type dust
• Best-fit ß3
• MW-dust ßRB4.1

Residual without c-correction
SN Colour (c)
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SN colour-colour space
In colour colour space, MW-type extinction laws
also dont work
SN B-V
SN U-B
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Combination of dustintrinsic?
In colour colour space, MW-type extinction laws
also dont work
SN B-V
SN U-B
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Residuals by host type

• SNe in passive galaxies show a smaller scatter
• Intrinsic dispersion consistent with zero
• (Does intrinsic dispersion in SNe arise from
  dust?)
• Cleaner sample But SNe in passive galaxies are
  at high-z (20 two component model) very few
  locally

Star-forming hosts
Passive hosts
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• Colour correction required in all host types
  with a similar ß
• Either
• Passive hosts have dust
• An intrinsic relation dominates over dust

180 high-z SNe
Residual without c-correction
Star-forming hosts
Large local SN surveys covering a wide
wavelength range (inc. near-IR) urgently needed
to disentangle this Not clear what more of the
same will tell us
40 high-z SNe
Residual without c-correction
Passive hosts
SN Colour (c)
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SN Ia SFR dependencies potential evolution?
SN rate versus host SFR
SN stretch distributions split by galaxy
star-formation rate
SN Ia rate per unit mass
Star-forming hosts
SFR per unit mass
Passive hosts
170 SNLS SNe Ia (Update from Sullivan et al.
2006 better zeropoints, host photometry, more
SNe)
SN stretch (s)
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SN mix predicted to evolve with redshift

• Predicted mix of two components evolves strongly
  with redshift

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Redshift drift in stretch? Average stretch, and
thus average intrinsic brightness of SNe Ia
evolves with redshift if stretch correction
works perfectly, this will not affect cosmology
Full 1st year sample solid slt1 at zlt0.4 and sgt1
at zgt0.4 dashed
Howell et al. 2007
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Future SN Ia Prospects

• Short-term
• Current constraints on ltwgt ltwgt-1 to 6-7
  (stat)
• (inc. flat Universe, BAOWMAP-3)
• At SNLS survey end statistical uncertainty will
  be 4-5
• 500 SNLS 200 SDSS larger local samples
• Improved external constraints (BAO, WL)
• Longer term
• No evolutionary bias in cosmology detected (tests
  continue!)
• SNe in passive galaxies seem more powerful
  probes, but substantially rarer (esp. at high-z)
• Colour corrections are the dominant uncertainty
• Urgent need for zlt0.1 samples with wide
  wavelength coverage
• Not clear what the next step at high-z should
  be

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Paris Group Reynald Pain, Pierre Astier, Julien
Guy, Nicolas Regnault, Christophe Balland,
Delphine Hardin, Jim Rich,
Toronto Group Ray Carlberg, Alex Conley, Andy
Howell, Kathy Perrett
Victoria Group Chris Pritchet, Dave Balam,
Marseille Group Stephane Basa, Dominique Fouchez
Oxford Isobel Hook (Gemini PI), Mark Sullivan,
Emma Walker
The SNLS collaboration
Full list of collaborators at http//cfht.hawaii.
edu/SNLS/