Constraining Dark Energy with the Supernova Legacy Survey

1
Constraining Dark Energy with the Supernova
Legacy Survey

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

2
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, Mark Sullivan
Victoria Group Chris Pritchet, Dave Balam,
Marseille Group Stephane Basa, Dominique Fouchez,

UK Gemini PI Isobel Hook, Richard McMahon,
USA LBL Saul Perlmutter, CIT Don Neill
The SNLS collaboration
Full list of collaborators at http//cfht.hawaii.
edu/SNLS/
3
White Dwarf
SNe Ia are thermonuclear explosions of C-O white
dwarf stars Standard nuclear physics
Bright 10 billion suns Standardizable 7
calibration Brightness and homogeneity make them
the best measure of distance, and hence dark
energy, in the Universe
4
Supernova Legacy Survey (2003-2008)

• 5 year survey, goal 500 distant SNe Ia to
  measure w
• Uses CFHT/Megacam
• 36 CCDs, good blue response
• 4 filters for good k-corrections and color
  measurement

Megaprime
5
CFHT-LS Organisation

• SNLS collaboration
• Data-processing
• Major Spectroscopic Program
• Gemini (Canada/UK/USA)
• 120 hrs/yr (604020)
• VLT (France/Other Euros)
• 120 hrs/yr
• Keck (through LBL)
• 40 hrs/yr
• Cosmological analyses

• Magellan near-IR study (Freedman et al.)
• Rest-frame I-band Hubble diagram

• Keck SN Ia UV study (Ellis/Sullivan et al.)
• LRIS high-S/N - metallicity through UV lines
• Testing accuracy of k-corrections in the UV

• SN IIP study (Nugent/Sullivan/Ellis et al.)
• Using SNe IIP as standard candles
• Independent Hubble diagram to z0.5

6
Supernova Legacy Survey
Imaging Distances from light-curves
Spectroscopy Redshifts ? Distances from
cosmological model
Discoveries
Lightcurves
Gemini N S (120 hr/yr)
VLT (120 hr/yr)
griz every 4 days during dark time
Magellan (15 nights/yr)
Keck (8 nights/yr)
7
k-corrections in SNLS
8
k-corrections in SNLS
9
Making a standard candle
1. Phillips relation A correction to SN Ia
light-curves based on light-curve shape
drastically improves the quality of the standard
candle.
Brightness ?

• 56Ni ? 56Co ? 56Fe powers the SN Ia light-curve
• Conventional Wisdom
• SNe are a one-parameter family defined by amount
  of 56Ni synthesized in the explosion.
• More 56Ni ? greater luminosity ? higher
  Temperatures ? higher opacity ? broader LC

Time ?
Brightness ?
Time ?
10
Making a standard candle
1. Phillips relation A correction to SN Ia
light-curves based on light-curve shape
drastically improves the quality of the standard
candle.
2. SN colour A correction to the SN luminosity
based on the SN colour
Fainter ?
Blue
Red
Colour at peak
11
Making a standard candle
1. Phillips relation A correction to SN Ia
light-curves based on light-curve shape
drastically improves the quality of the standard
candle.
20
Brightness ?
2. SN colour A correction to the SN luminosity
based on the SN colour

• Many methods
• Stretch Perlmutter 97, 99
• (M)LCS(2k2) Riess, 95,96, Jha 07
• SALT(2) Guy 05, 07
• SiFTO Sullivan 07
• CMAGIC Wang et al. Conley 06
• ?m15 Phillips 93 Hamuy 95 Prieto 06

Brightness ?
7!
Time ?
12
Local SN Ia Hubble Diagrams
Most light-curve fitting techniques fare equally
well
Prieto et al. 2006
Jha et al. 2007
13
Light-curve fit parameters from different fitters
are tightly correlated
14
A Typical SNWhat we need to measure
Peak brightness
Colour (c)
Lightcurve width (stretch)
15
SNLS Current status

• Survey running for 3.5 years
• 310 confirmed distant SNe Ia ( 40-50 not yet
  processed)
• Largest single telescope sample of SNe
• On track for 500 spectroscopically confirmed
  SNe Ia by survey end (gt1000/gt2000 total SNIa/All
  SN light-curves)

16
Rolling light-curves
17
SNLS 1st year
Astier et al. 2006 349 citations (187 in refereed
journals)
OM 0.263 0.042 (stat) 0.032 (sys) ltwgt-1.02
0.09 (stat) 0.054 (sys)
18
Third year SNLS Hubble Diagram (preliminary)
3/5 years of SNLS 240 distant SNe Ia
Independent analysis to 1st year Different
calibration route Different photometric
methods Different SN light-curve analysis tools
Preliminary
Sullivan et al. 2007
19
Third year SNLS Hubble Diagram (preliminary)
Best-fit for SNLSflatness
Preliminary
(error was 0.042 in A06)
OM0.3, O?0
OM1.0, O?0
Sullivan et al. 2007
20
Cosmological Constraints (Preliminary)
SNe
WMAP-3
6-7 measure of ltwgt
SNe
BAO
BAO
SNLSBAO (No flatness)
SNLS BAO simple WMAP Flat
Sullivan et al. 2007
21
Future Prospects with SNLS

• Current constraints on ltwgt ltwgt-1 to 6-7
  (stat)
• ltwgt gt-0.8 excluded at 3-sigma level
• At survey end a 4-5 statistical measure will be
  achieved
• 500 SNLS 200(?) SDSS new local samples
• Improved external constraints (BAO, WMAP, WL)
• Systematic errors becoming ever more important

22
Potential SN Systematics in measuring w(a)

• Experimental Systematics
• Calibration, photometry, Malmquist-type effects
• Contamination by non-SNe Ia
• Minimized by spectroscopic confirmation
• K-corrections
• UV uncertain golden redshifts spectral
  evolution?
• Non-SNe systematics
• Peculiar velocities Hubble Bubble Weak lensing
• Extinction
• Effective RB Dust evolution
• Redshift evolution in the mix of SNe
• Population drift environment?
• Evolution in SN properties
• Light-curves/Colors/Luminosities

More mundane
More scientifically interesting
23
Hubble Bubble

• Latest MLCS2k2 paper (Jha 2007)
• MLCS2k2 attempts to separate intrinsic
  colour-luminosity and reddening
• 3s decrease in Hubble constant at 7400 km/sec
  local value of H0 high distant SNe too faint
• Local void in mass density?
• Could have significant effects on w measurement

SALT
MLCS2k2
No Bubble with other light-curve fitters!
Conley et al. (2007)
24
Light-curve fit parameters from different fitters
are tightly correlated
25
Handling colour in SN Ia

• Colour is the most important correction to SN Ia
  luminosities
• Underlying physics Redder SNe Ia are fainter due
  to
• Extinction along the line of sight
• Intrinsic luminosity/colour relationship of the
  SN population
• Two basic approaches
• Attempt to identify intrinsic relationship and
  assume standard dust dominates the rest (Jha et
  al.)
• Fit a luminosity/colour relationship empirically
  on the SN data

ß4.1
26
Bubble significance versus ß
Conley et al. (2007)
27
All fitters agree ßlt4.1
Conley et al. (2007)
28
What does ß2 (RV1) mean?

• Very strange dust? But RV1 is not seen anywhere
  in the Milky Way
• Dust around SNe is changed by the explosion?
• Most likely SNe have an (as yet) uncorrected-for
  intrinsic colour-luminosity relationship
• While fitting empirically for ß may be empirical,
  currently its the best way

29
Potential SN Systematics in measuring w(a)

• Experimental Systematics
• Calibration, photometry, Malmquist-type effects
• Contamination by non-SNe Ia
• Minimized by spectroscopic confirmation
• K-corrections
• UV uncertain golden redshifts spectral
  evolution?
• Non-SNe systematics
• Peculiar velocities Hubble Bubble Weak lensing
• Extinction
• Effective RB Dust evolution
• Redshift evolution in the mix of SNe
• Population drift environment?
• Evolution in SN properties
• Light-curves/Colors/Luminosities

More mundane
More scientifically interesting
30
Potential SN Systematics in measuring w(a)

• Experimental Systematics
• Calibration, photometry, Malmquist-type effects
• Contamination by non-SNe Ia
• Minimized by spectroscopic confirmation
• K-corrections
• UV uncertain golden redshifts spectral
  evolution?
• Non-SNe systematics
• Peculiar velocities Hubble Bubble Weak lensing
• Extinction
• Effective RB Dust evolution
• Redshift evolution in the mix of SNe
• Population drift environment?
• Evolution in SN properties
• Light-curves/Colors/Luminosities

Population Evolution
31
White Dwarf

• Many uncertainties
• Nature of progenitor system the second star
• Single versus double degenerate?
• Young versus old progenitor?
• Explosion mechanism?
• Effect of progenitor metallicity on luminosity?

?
32
Host galaxies impact SN properties
SN Ia Light-curve shape depends on morphology
e.g. Hamuy et al. (2000)
Low stretch
High stretch
Some evidence that SNe Ia in ellipticals show
smaller scatter
Sullivan et al. (2003)
33
Typing of SNLS SN Ia hosts

• Little morphological information available
• CFHT ugriz imaging via the Legacy program.
• PEGASE2 is used to fit SED templates to the
  optical data.
• Recent star-formation rate, total stellar mass,
  mean age are estimated.
• Hosts classified according to physical
  parameters instead of what they look like.

Passive
Star-forming
Starbursting
Sullivan et al. (2006)
34
SNLS SN rate as a function of sSFR
SN Ia hosts classified by star-formation
activity Per unit stellar mass, SNe are at least
an order of magnitude more common in more
vigorously star-forming galaxies
SNLS passive galaxies
35
SNLS selection of hosts

• D2 ACS imaging
• Plenty of irregular/late-type systems
• Few genuine ellipiticals

36
SN Ia Stretch dependencies
Stretch by galaxy star-formation activity
Stretch versus mean age
Star-forming
Passive
The majority of SN Ia come from young stellar
populations
170 SNe Ia (Update from Sullivan et al. 2006
better zeropoints, host photometry, more SNe)
37
Recent SNLS evidence for two components for SNe Ia
Older progenitor SNe Empirically, SN Rate is
proportional to galaxy mass Preferentially
found in old stellar environments Typically
fainter with faster light-curves (low stretch)
Younger progenitor SNe Empirically, SN rate is
proportional to galaxy star formation
rate Exclusively found in later type
star-forming galaxies Typically brighter with
slower light-curves (high stretch) (Extreme
example SNLS-03D3bb?)
38
Recent SNLS evidence for two components for SNe Ia
Older progenitor SNe Empirically, SN Rate is
proportional to galaxy mass Preferentially
found in old stellar environments Typically
fainter with faster light-curves (low stretch)
Younger progenitor SNe Empirically, SN rate is
proportional to galaxy star formation
rate Exclusively found in later type
star-forming galaxies Typically brighter with
slower light-curves (high stretch) (Extreme
example SNLS-03D3bb?)
Could evolution between the two components with
redshift distort the dark energy signal?
39
SN population drift?

• Relative mix of evolves with redshift
• AB predictions, but similar for any two
  component model

Sullivan et al. 2006
40
Stretch versus redshift (3rd year)
?
41
Evolution in Stretch? Gaussians predicted
evolution from AB model Average stretch, and
thus average intrinsic brightness of SNe Ia
evolves with redshift but if stretch correction
works perfectly, this should not affect cosmology
Nearby
zlt0.75
zgt1
Howell et al. 2007
42
Effect on cosmology Extreme case using SNLS 1st
year Use only slt1 SNe Ia at zlt0.4, only sgt1 SNe
at zgt0.4 Effects of evolution smaller than error
budget for determination of ltwgt, must be studied
closely to determine the effect on measuring w(a)
SNLS yr 1 N 115 ? 1.6 ? 1.8 w -1.05 ?
0.09 ?M 0.27 ? 0.02
Yr 1 s split N 56 ? 1.4 ? 1.8 w -0.92
? 0.15 ?M 0.28 ? 0.03
43
Split by s (preliminary)
44
Stretch correction across environments
Rest-frame B composite light-curve

• Conley et al. 2006

No evidence for gross differences between
light-curves in passive and active galaxies
45
Morphological Hubble diagram
46
Split by host galaxy
SN Subsets
Passive
a1.34 0.25 ß2.52 0.2 s0.10
mag ltwgt-0.880.11
Star-forming
a1.19 0.15 ß2.71 0.2 s0.140 mag
ltwgt-1.040.08
Preliminary
Problems Low-redshift sample very small,
Malmquist correction likely to be different
47
Do SNe Ia Evolve? UV Spectrum Probes Metallicity
Lentz et al. (2000)
48
High S/N spectra of SNLS SNe
Ellis, Sullivan et al. 2007
49
Light-curve width dependence
Implications for JDEM k-corrections must improve
in accuracy
50
Summary

• SNLS is a well-controlled, calibrated and
  understood experiment
• Current SN Ia measurement determine ltwgt to 6-7
• SNLS is the best cosmological SN Ia dataset
  available
• In 2-3 years, 4-5 will be achieved
• Colour is the critical correction to SN Ia
  distances currently can only be handled
  empirically
• SNe Ia have a range of progenitor ages
• Impacts on light-curve shape faster/older
  slower/younger
• SNe in passive galaxies are better standard
  candles?
• More homogeneous stellar population? Less dust?