The Supernova Legacy Survey (SNLS): New Results on Cosmology and the Nature of Type Ia Supernovae

Toronto Group Ray Carlberg, Mark Sullivan, Andy Howell, Kathy Perrett, Alex Conley French Group Reynald Pain, Pierre Astier, Julien Guy, Nicolas Regnault, Jim Rich, Stephane Basa, Dominique Fouchez UK Gemini PI: Isobel Hook + Justin Bronder, Richard McMahon, Nic Walton Victoria Group Chris Pritchet, (Don Neill), Dave Balam, Eric Hsiao, Melissa Graham USA LBL: Saul Perlmutter CIT: Richard Ellis Plus: Many students and associate members throughout the world

Special Mention … Andy Howell – PDF U.Toronto Melissa Graham U Victoria Alex Conley – PDF U Toronto Eric Hsiao U Victoria Mark Sullivan – PDF U Toronto Kathy Perrett – PDF U Toronto, Ms. Data Dave Balam, RA, U Victoria

 Historical Background  Supernova Cosmology  SNLS Overview  SNLS Results  Other SN Science  Conclusions/Future

Golden Moments in Cosmology repulsive force repulsive force, vacuum energy, ρ=const ρ=const “Much later, when I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder of his life.” – G. Gamow, “My World Line” (1970)

Hubble Diagram (ℓ vs z) faintbright nearby distant V [km/s] Assumptions: Inverse square law ℓ =L/4πd² Euclidean space Standard candle (what Hubble actually did to demonstrate the expansion of the Universe)

Hubble Diagram and Cosmology log d or log z log apparent brightness Ω=1 Ω<1 Ω>1 Curvature of space causes deviations from linear Hubble diagram. Ω<1 means expansion forever. Standard candle! High ρ Low ρ z = v/c = Δλ/λ 1+z = R o /Rflat

Hubble 1953 Cosmology – A Search for 2 Numbers? H o – rate of expansion (v=H o d) Ω o – deceleration - matter density

Gunn and Oke 1975 “… although the heterogeneity of the sample makes conclusions about cosmology slightly suspect.” -2 < Ω <0 +2 < Ω < +4 Kristian, Sandage and Westphal 1978 >400 nights of Palomar 200” time! evolution (mass and age)

 Historical Background  Supernova Cosmology  SNLS Overview  SNLS Results  Other SN Science  Conclusions/Future

SNe Ia vs SNe II – a Primer SN Ia SN Ia SN II SN II brightness L sun ~10 9 L sun progenitor 1 or 2 white dwarfs (M>1.4Msun) massive star mechanism mass transfer or merger; thermonuclear disruption core collapse progenitor age ~10 10 yr~10 7 yr evolution with z Little?(1+z) 2-4 :

Making a standard candle Phillips 1993

More 56 Ni  Higher Temp  Higher Opacities  Brighter, Broader SNe Ia Higher opacities trap the radiation more effectively and release it later, making for broader light curves. (Nugent) (But Kasen & Woosley astro-ph/ ) s= stretch Log L Making a standard candle Peak brightness is a std candle. σ~ 0.15 mag

Making a standard candle

Supernovae as Cosmological Probes  Max brightness makes an excellent standard candle - ±6% distance errors  Bright - can be seen to cosmological distances  Standard candle has a physical basis SNeIa are “well-understood” - thermonuclear disruptions of C+O white dwarfs - std physics  “The supernova distance-redshift relation comes from the FRW metric. That’s it. Issues of DE sound speed, anisotropic stress, matter growth, etc, do not affect this probe.” (Linder 2006)  Systematics – possibly, but ample opportunity to study with potentially hundreds of objects

Supernovae and Dark Energy Not:  i/s abs (hi z)  evolution  selection effects Riess et al Perlmutter et al Cosmological constant Λ Universe is accel- erating. Λ exists!

Dark Energy - a Strange Brew …  Expansion is accelerating  Vacuum energy,  Vacuum energy, ρ ≈ const Einstein was right!  Ω tot =Ω M +Ω DE =1  ρ Λ ≈ eV cm -3 ≈ x “theoretical value”  ρ Λ ≈ ρ M – why??

“On a good day I can think of 3 or 4 plausible candidates for dark matter. The same cannot be said for dark energy.” “On a good day I can think of 3 or 4 plausible candidates for dark matter. The same cannot be said for dark energy.” - Rocky Kolb, Tucson, Mar 2004 “Our theoretical understanding is so limited right now …” - Rocky Kolb, Tucson, Mar 2004 “… DE is not understood sufficiently to answer the basic questions …” - Rocky Kolb, Tucson, Mar 2004 Rocky Horror Show – Tucson 2004

What is the Dark Energy? What is it ?? Copeland et al astro-ph/

What is the DE?  Cosmological Constant Λ  Pure vacuum energy  Some other new physical component  e.g. scalar field models, quintessence, Chaplygin gas models  A new physical law  e.g. modifications to GR What is it ?? “Raffiniert is der Herrgott, aber boshaft ist er nicht.” (Einstein) (Einstein’s translation: “God is slick, but he ain’t mean.”)

Equation of State Parameter “w” P = w  ρ(a) ~ a -3(1+w) w = 1/3 radiation w = 0 matter w > -1 “quintessence” w = -1 Λ  w is a measurable.  most sensitivity at z<1.  w,dw/dz constrain DE.

 Background  Supernova Cosmology  SNLS Overview  SNLS  Other SN Science  Conclusions

MegaCam at CFHT  Built by CEA  1 deg x 1 deg field  40 x (2048 x 4612) chips ~ 400Megapixels  good blue response “Size matters …” Anon.

CFHT Legacy Survey  SNLS - Deep (“SNe + galaxy evolution”)  4 deg², long time sequenced exposures  202 nights  Wide (“weak lensing”)  172 deg² in 3 patches  Very Wide (“KBO”)  1300 deg², +-2 deg from ecliptic,  short exposures 470 nights (dark-grey) over 5 years ( ) Hoekstra et al 2006 astro-ph/

 202 nights over 5 years  202 nights over 5 years (part of CFHTLS)  four 1 deg² fields  queue scheduled obs, 3-4 day temporal sampling  griz filters ( nm)  spectroscopic followup (VLT, Gemini, Keck, Magellan)  2 independent search, photometry, cosmology pipelines  >500 SNeIa over 5 yrs with spectroscopic type SNLS in a nutshell

SNLS – multiband  SNLS provides the definitive high-z SN dataset for the next 5+ years. Multi-band g’r’i’z’ photometry is the key:  Wide z range  Better control over systematics: SN colour evolution  Better control over dust: Extinction corrections using rest-frame U-B & B-V  Better control over k-corrections: wider wavelength coverage  Better estimates of rest-frame B-band luminosities

2 pipelines Data stays in Hawaii, remote real-time access 90% agreement i’~24 Short turnaround (6 hr to spec candidates) Two Search Pipelines (Ca, Fr) K. Perrett

>1700 since Aug 2003! Detections 04D2ca z=0.83 Mar 10 ACS ~10 -4 of total Megacam area

 D2  Cosmos  ACS imaging  ~7 x 7 arcsec +-  Note diversity

Rolling Search  griz (redshift )  2-3 day sampling restframe  12 month observing

Typical light-curves z=0.36 z=0.91

Spectroscopy CFHTGemini-N

Follow-up Spectroscopy (types and redshifts) Keck (~8 nights/yr) Ellis / Perlmutter VLT (120 hr/yr) France/UK: FORS1/2 to get types & redshifts for SNe (0.3 < z < 0.8) Gemini N & S (120 hr/yr) Canada/UK/US GMOS to get types/redshifts for SNe (0.6 < z < 0.9) More 8-10m time than CFHT time

N(z) to 2006 (N ~ 300)

SNLS: Current and projected numbers Currently >350 spec confirmed SNe Ia spec confirmed SNeIa by survey end (>1000 total)

 Historical Background  Supernova Cosmology  SNLS Overview  SNLS Results  Other SN Science  Conclusions/Future

Distance estimator: stretch and colour  Distance estimator used:  s, c terms dominate; no need for other terms s – “stretch” corrects for light-curve shape via α “c” – B-V colour corrects for extinction (and intrinsic variation) via β

First Year Cosmology (Astier et al. 2006) First year results (72 SNe Ia) consistent with an accelerating Universe: Ω M =0.263 in a flat universe Intrinsic disp.: 0.13 ± 0.02 Low-z: 0.15 ±0.02 SNLS: 0.12 ± 0.02 z’ errors – now observing 3x longer

w = ± 0.09 w = ± 0.09  N=71, one year, SNLS+low z only  w to ~±0.05 by 2008 (why not ?) Astier et al 2006

WMAP3 constraints  Spergel et al 2007 Assumptions: flat universe, perturbations in dark energy

 2007 – prelim!  ~230 out of 270 SNeIa, to Aug 2006  Fit - w=-1 SNLS 3 rd year analysis Preliminary Cuts: Stretch 0.75<s<1.25 Colour Light curve coverage Intrinsic scatter: SNLS ±0.09 Low z ±0.13

Residuals vs. SFR Passive galaxies Green=moderate star formation Blue=active star formation

Addressing systematics  The control of systematics will define how accurately w and especially dw/dz will be determined  Large sample size of SNLS will allow subsample tests to investigate role of systematics Largest systematics currently are:

Systematics …  ZP uncertainty ±0.04 in w  Improve mosaic uniformity to better than 1% (done)  Tie calibration to CALSPEC standards (precise flux standards)  Tie low and high z SNe together on uniform photometric system (SDSS-II)

Systematics …  k-corrections (Hsiao et al 2007)  Based on 800 individual spectra (Suspect, etc)  Ellis et al 2007 UV

Systematics …  Malmquist Bias ±0.025 in w (Perrett 2007)

Systematics …  Redshift dependent population changes Sullivan et al …  Redshift evolution in SN properties Conley et al, Bronder et al …  Selection by SN photo-z? Sullivan et al candidates – how to prioritize for followup? Defines success of survey. Photometric pre-selection. Fits early-time SN light- curves, returns probability of the candidate being a SN Ia.

 Historical Background  Supernova Cosmology  SNLS Overview  SNLS Results  Other SN Science  Conclusions/Future

Other SN science  Howell et al 2006 (Nature, Sep 2006) – SN 03D3bb – a super-Chandra mass SN Ia – evidence for double degenerate merger?  Sullivan et al 2006 – SNIa rate depends strongly on host SFR  Pritchet et al Interpretation of SNIa rate vs. SFR diagram, nature of SNIa Progenitors  Neill et al 2006 – best determination of absolute SN Ia rate  Conley et al 2006 – SN light curve shapes are identical at low and high z  Nugent et al 2006 – first ever SN II Hubble diagram

SN Ia Progenitors Single Degenerate - white dwarf + evolving secondary (M=1.4 Msun at explosion) Double Degenerate - 2 white dwarfs (M >= 1.4 Msun at explosion) Key point: white dwarf max mass = 1.4 Msun (Chandrasekhar mass)

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

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!

03D3bb  Low velocity of ejecta (8000 km/s)  Also implies super-Chandra mass  Conclusion: either (i) a rapidly rotating WD, or (ii) WD-WD merger  Implications for cosmology (this object was not used in Astier et al 2006)

Other SN science  Howell et al 2006 (Nature, Sep 2006) – SN 03D3bb – a super-Chandra mass SN Ia – evidence for double degenerate merger?  Sullivan et al 2006 – SNIa rate depends strongly on host SFR  Pritchet et al Interpretation of SNIa rate vs. SFR diagram, nature of SNIa Progenitors  Neill et al 2006 – best determination of absolute SN Ia rate  Conley et al 2006 – SN light curve shapes are identical at low and high z  Nugent et al 2006 – first ever SN II Hubble diagram

SNeIa in Star-Forming Galaxies Mannucci et al 2006 Scannapieco and Bildsten 2006

m = , n = A=5.1E-14 SNe/yr/Msun B=4.1E-4 SNe/yr/(Msun/yr) B needed at 99.99% confidence cf. Scannapieco and Bildsten 2005 (m=1, n=1) Bivariate fits give m,n close to 1 Sullivan et al 2006

SN Ia rate depends on SFR SFR ½

Meaning of A٠M + B٠SFR  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?  Why do the A and B values have the values that are observed?  Continuum of delay times – more natural?  Why ~√SFR dependence rather than ~SFR?

 Single degenerate scenario  Delay time depends on evolutionary timescale of secondary - T(evol) ≈ T(ms)  Simple SFR(t) ~ t -η to allow for range of ages Toy Model

Models vs Observations  Locus of WD formation rates independent of SFR(t)  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

Meaning  Single component model – not A+B  Continuous distribution of delay times  Rate in active and passive galaxies both explained  Only physics is evol timescales  Single free parameter normalization - f SNIa

Efficiency vs mass  1 Msun main sequence stars find it very difficult to get to the Chandra mass and make a Type Ia SN Close binaries M1 < 2Msun make a He WD, not a C+O WD Mass arguments: 1 Msun on the m.s. makes a 0.5 Msun WD, hard to imagine 2 x 1 Msun making a 1.4 Msun WD Most of companions to 1 Msun 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).

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.

Cosmic SFR(z) Hopkins 2006

SNR predictions from SFR(z)  Dot-dash=A+B  normalization arbitrary  Per Mpc^3

Poznanski 2007 Dahlen 2004 Neill 2006

 Historical Background  Supernova Cosmology  SNLS Overview  SNLS Results  Other SN Science  Conclusions/Future

Conclusions  w = -1 (preliminary) from 3 rd year data (N=230).  Dark energy resembles pure cosmological constant (vacuum energy).  Most accurate estimate of w yet  SNIa rate depends on SFR  progenitors found in young and old stellar populations  Natural explanation from evolutionary timescales  1% of white dwarfs become SNeIa  SNeIa not only from single degenerate progenitors  ~ SNeIa with spectroscopy by 2008, >1000 total  SNLS-2? ~60 deg^2, z<0.7, N=3000:  Stay tuned!

More SNLS information   - database (Perrett)   – people, papers, …

Special Mention … Andy Howell – PDF U.Toronto Melissa Graham U Victoria Alex Conley – PDF U Toronto Eric Hsiao U Victoria Mark Sullivan – PDF U Toronto Kathy Perrett – PDF U Toronto, Ms. Data Dave Balam, RA, U Victoria