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

The Supernova Legacy Survey (SNLS): New Results on Cosmology and the Nature of Type Ia Supernovae. Victoria Group Chris Pritchet, (Don Neill), Dave Balam, Eric Hsiao, Melissa Graham. French Group

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

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  1. The Supernova Legacy Survey (SNLS): New Results on Cosmology and the Nature of Type Ia Supernovae www.astro.uvic.ca/~pritchet

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

  3. Special Mention … Kathy Perrett – PDF U Toronto, Ms. Data Andy Howell – PDF U.Toronto Alex Conley – PDF U Toronto Mark Sullivan – PDF U Toronto Melissa Graham U Victoria Eric Hsiao U Victoria Dave Balam, RA, U Victoria www.astro.uvic.ca/~pritchet

  4. Historical Background • Supernova Cosmology • SNLS Overview • SNLS Results • Other SN Science • Conclusions/Future www.astro.uvic.ca/~pritchet

  5. Golden Moments in Cosmology repulsive force, vacuum energy, 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) www.astro.uvic.ca/~pritchet

  6. (what Hubble actually did to demonstrate the expansion of the Universe) Hubble Diagram (ℓ vs z) distant V [km/s] bright faint nearby Assumptions: Inverse square law ℓ=L/4πd² Euclidean space Standard candle www.astro.uvic.ca/~pritchet

  7. Ω<1 Ω=1 Ω>1 log apparent brightness z = v/c = Δλ/λ 1+z = Ro/R log d or log z flat Hubble Diagram and Cosmology Low ρ High ρ Curvature of space causes deviations from linear Hubble diagram. Ω<1 means expansion forever. Standard candle! www.astro.uvic.ca/~pritchet

  8. Cosmology – A Search for 2 Numbers? Ho– rate of expansion (v=Hod) Ωo – deceleration - matter density Hubble 1953 www.astro.uvic.ca/~pritchet

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

  10. Historical Background • Supernova Cosmology • SNLS Overview • SNLS Results • Other SN Science • Conclusions/Future www.astro.uvic.ca/~pritchet

  11. SNe Ia vs SNe II – a Primer www.astro.uvic.ca/~pritchet

  12. Making a standard candle Phillips 1993 www.astro.uvic.ca/~pritchet

  13. Making a standard candle www.astro.uvic.ca/~pritchet

  14. 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 www.astro.uvic.ca/~pritchet

  15. Supernovae and Dark Energy Cosmological constant Λ Universe is accel-erating. Λ exists! • Not: • i/s abs (hi z) • evolution • selection effects Riess et al. 1998 Perlmutter et al. 1999 www.astro.uvic.ca/~pritchet

  16. Dark Energy - a Strange Brew … • Expansion is accelerating • Vacuum energy, ρ≈ const • Einstein was right! • Ωtot=ΩM+ΩDE=1 • ρΛ≈ 10-8 eV cm-3≈ 10-120 x “theoretical value” • ρΛ≈ρM – why?? www.astro.uvic.ca/~pritchet

  17. Rocky Horror Show – Tucson 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 “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 www.astro.uvic.ca/~pritchet

  18. What is it ?? What is the Dark Energy? Copeland et al astro-ph/ 0603057 www.astro.uvic.ca/~pritchet

  19. What is it ?? 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 “Raffiniert is der Herrgott, aber boshaft ist er nicht.” (Einstein) (Einstein’s translation: “God is slick, but he ain’t mean.”) www.astro.uvic.ca/~pritchet

  20. Equation of State Parameter “w” P = wr, 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. www.astro.uvic.ca/~pritchet

  21. Background • Supernova Cosmology • SNLS Overview • SNLS • Other SN Science • Conclusions www.astro.uvic.ca/~pritchet

  22. 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. www.astro.uvic.ca/~pritchet

  23. Hoekstra et al 2006 astro-ph/0511089 CFHT Legacy Survey 470 nights (dark-grey) over 5 years (2003-2008) • 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 www.astro.uvic.ca/~pritchet

  24. SNLS in a nutshell • 202 nights over 5 years (part of CFHTLS) • four 1 deg² fields • queue scheduled obs, 3-4 day temporal sampling • grizfilters (450-950nm) • spectroscopic followup (VLT, Gemini, Keck, Magellan) • 2 independent search, photometry, cosmology pipelines • >500 SNeIa over 5 yrs with spectroscopic type www.astro.uvic.ca/~pritchet

  25. 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 0.2-0.9 • 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 www.astro.uvic.ca/~pritchet

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

  27. Detections >1700 since Aug 2003! 04D2ca z=0.83 Mar 10 ~10-4 of total Megacam area ACS www.astro.uvic.ca/~pritchet

  28. D2 • Cosmos • ACS imaging • ~7 x 7 arcsec +- • Note diversity www.astro.uvic.ca/~pritchet

  29. Rolling Search • griz (redshift 0.2-0.9) • 2-3 day sampling restframe • 12 month observing www.astro.uvic.ca/~pritchet

  30. Typical light-curves z=0.36 z=0.91 www.astro.uvic.ca/~pritchet

  31. Spectroscopy CFHT Gemini-N www.astro.uvic.ca/~pritchet

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

  33. N(z) to 2006 (N ~ 300) www.astro.uvic.ca/~pritchet

  34. SNLS: Current and projected numbers Currently >350 spec confirmed SNe Ia 400-500 spec confirmed SNeIa by survey end (>1000 total) www.astro.uvic.ca/~pritchet

  35. Historical Background • Supernova Cosmology • SNLS Overview • SNLS Results • Other SN Science • Conclusions/Future www.astro.uvic.ca/~pritchet

  36. 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 www.astro.uvic.ca/~pritchet

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

  38. w = -1.02 ± 0.09 Astier et al 2006 • N=71, one year, SNLS+low z only • w to ~±0.05 by 2008 (why not +-0.03?) www.astro.uvic.ca/~pritchet

  39. WMAP3 constraints • Spergel et al 2007 Assumptions: flat universe, perturbations in dark energy www.astro.uvic.ca/~pritchet

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

  41. Residuals vs. SFR Green=moderate star formation Blue=active star formation Passive galaxies www.astro.uvic.ca/~pritchet

  42. 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: www.astro.uvic.ca/~pritchet

  43. 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) www.astro.uvic.ca/~pritchet

  44. Systematics … • k-corrections (Hsiao et al 2007) • Based on 800 individual spectra (Suspect, etc) • Ellis et al 2007 UV www.astro.uvic.ca/~pritchet

  45. Systematics … • Malmquist Bias ±0.025 in w (Perrett 2007) www.astro.uvic.ca/~pritchet

  46. 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 2005 • 1000 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. www.astro.uvic.ca/~pritchet

  47. Historical Background • Supernova Cosmology • SNLS Overview • SNLS Results • Other SN Science • Conclusions/Future www.astro.uvic.ca/~pritchet

  48. 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 2007 - 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 Other SN science www.astro.uvic.ca/~pritchet

  49. SN Ia Progenitors Key point: white dwarf max mass = 1.4 Msun (Chandrasekhar mass) Double Degenerate - 2 white dwarfs (M >= 1.4 Msun at explosion) Single Degenerate - white dwarf + evolving secondary (M=1.4 Msun at explosion) www.astro.uvic.ca/~pritchet

  50. z=0.24, star-forming host Most luminous SNIa ever discovered (MV=-20.0, 10 billion Lsun) Lies off the stretch-L relation - too bright for its stretch s=1.13 by 4.4 sigma SNLS-03D3bb(Howell et al. 2006) www.astro.uvic.ca/~pritchet

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