www.astro.uvic.ca/~pritchet the supernova legacy survey (snls): new results on cosmology and the...

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

The Supernova Legacy The Supernova Legacy Survey (SNLS): Survey (SNLS):

New Results on Cosmology New Results on Cosmology and the Nature of Type Ia and the Nature of Type Ia

SupernovaeSupernovae


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 Golden Moments in Cosmology

μνμν πT

c

GG

4

8−= μνμνμν π

gTc

GG Λ−−=

4

8

repulsive forcerepulsive force, vacuum energy, ρρ=const =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)

faintbrightnearby

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

appa

rent

brig

htne

ss

Ω=1Ω<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 = Ro/R

flatflat


Hubble 1953Hubble 1953

Cosmology – A Search for 2 Numbers?Cosmology – A Search for 2 Numbers?

Ho– rate of expansion (v=Hod)Ωo – 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 >400 nights of Palomar of Palomar 200” time!200” time!

evolution (mass and age)

evolution (mass and age)


SNe Ia vs SNe II – a PrimerSNe Ia vs SNe II – a Primer

SN IaSN Ia SN IISN IIbrightness 1010 Lsun ~109 Lsun

progenitor 1 or 2 white dwarfs (M>1.4Msun)

massive star

mechanism mass transfer or merger; thermonuclear disruption

core collapse

progenitor age ~1010 yr ~107 yr

evolution with z Little? (1+z) 2-4 :


Making a standard candle Phillips 1993


Making a standard candle

csMMOBB βα −−+= )1(


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 EnergySupernovae and Dark Energy

Not:i/s abs (hi z)evolution selection effects

Riess et al. 1998Riess et al. 1998Perlmutter et al. 1999Perlmutter et al. 1999

Cosmological constant Λ

Universe is accel-erating. Λ exists!


Dark Energy - a Strange Brew …

Expansion is accelerating Vacuum energyVacuum energy, , ρ ≈ const

• Einstein was right! ΩΩtottot=Ω=ΩMM+Ω+ΩDEDE=1=1

ρΛ ≈ 10-8 eV cm-3 ≈ 10-120 x “theoretical value” ρΛ ≈ ρM – why??


““On a good day I can think of 3 or 4 On a good day I can think of 3 or 4 plausible candidates for dark plausible candidates for dark matter. The same cannot be said matter. The same cannot be said for dark energy.”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 What is the Dark the Dark Energy?Energy?

What is it ??What is it ??

Copeland et al astro-ph/ 0603057


What is the DE?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 ??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”Equation of State Parameter “w”

P = wρ(a) ~ a-3(1+w)

w = 1/3 radiation w = 0 matterw > -1 “quintessence”w = -1 w = -1 ΛΛ

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 Size matters …”…” Anon.


CFHT Legacy CFHT Legacy SurveySurvey

SNLS - Deep SNLS - Deep (“SNe + galaxy evolution”)(“SNe + galaxy evolution”) 4 deg², long time sequenced exposures 202 nights

Wide (“weak lensing”)Wide (“weak lensing”) 172 deg² in 3 patches

Very Wide Very Wide (“KBO”)(“KBO”) 1300 deg², +-2 deg from ecliptic, short exposures

470 nights (dark-grey) 470 nights (dark-grey) over 5 years (2003-2008)over 5 years (2003-2008)

Hoekstra et al 2006 astro-ph/0511089


202 nights over 5 years 202 nights over 5 years (part of CFHTLS) four 1 degfour 1 deg² ² fieldsfields queue scheduled obs, queue scheduled obs, 3-4 day temporal sampling3-4 day temporal sampling ggrriizz filters (450-950nm)filters (450-950nm) spectroscopic followup (VLT, Gemini, Keck, Magellan)spectroscopic followup (VLT, Gemini, Keck, Magellan) 2 independent search, photometry, cosmology pipelines >500 SNeIa>500 SNeIa over 5 yrs with spectroscopic type over 5 yrs with spectroscopic type

SNLS in a nutshellSNLS in a nutshell


SNLS SNLS – multiband– 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


•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!>1700 since Aug 2003!

Detections

04D2ca 04D2ca z=0.83 Mar 10z=0.83 Mar 10

ACSACS

~10-4 of total Megacam area


D2 Cosmos ACS

imaging ~7 x 7

arcsec +-

Note diversity


Rolling Search

griz (redshift 0.2-0.9) 2-3 day sampling restframe 12 month observing


Typical light-curves

z=0.36

z=0.91


Spectroscopy

CFHT Gemini-N


Follow-up Spectroscopy Follow-up Spectroscopy (types and redshifts)(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 timeMore 8-10m time than CFHT time


N(z) to 2006 (N ~ 300)


SNLS: Current and projected numbers

Currently >350 spec confirmed

SNe Ia

400-500 spec confirmed SNeIa by survey end

(>1000 total)


Distance estimator: stretch and colour

Distance estimator used:

s, c terms dominate; no need for other terms

s – “stretch” corrects s – “stretch” corrects for light-curve shape for light-curve shape

via via αα

““c” – B-V colour corrects c” – B-V colour corrects for extinction (and for extinction (and

intrinsic variation) via intrinsic variation) via ββ

csMm BBB ×−−+−= βαμ )1(


First YearFirst Year Cosmology Cosmology (Astier et al. 2006)(Astier et al. 2006)

First year results (72 SNe Ia) consistent with

an accelerating Universe: ΩM=0.263 in

a flat universe

Intrinsic disp.: 0.13 ± 0.02Low-z: 0.15 ±0.02

SNLS: 0.12 ± 0.02z’ errors – now observing 3x longer

csMmBB βαμ +−+−= )1(


w = -1.02 w = -1.02 ± 0.09± 0.09

N=71, one year, SNLS+low z only w to ~±0.05 by 2008 (why not +-0.03?)

Astier et al 2006


WMAP3 constraints

Spergel et al 2007

073.0072.0967.0w +

−−=

Assumptions: flat universe, perturbations in dark energy


2007 – prelim! ~230 out of 270

SNeIa, to Aug 2006

Fit - w=-1

SNLS 3rd year analysis

Preliminary

Cuts:Stretch 0.75<s<1.25ColourLight 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 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.


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 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


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 (MV=-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 56Ni to power light curve, 2Msun total mass

“normal” SNIa – 0.6 Msun of 56Ni 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 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


SNeIa in Star-Forming Galaxies

Mannucci et al 2006

SFRBMA ⋅+⋅=rateSNScannapieco and Bildsten 2006


m = 1.10+-0.12, n = 0.84+-0.09A=5.1E-14 SNe/yr/MsunB=4.1E-4 SNe/yr/(Msun/yr)B needed at 99.99% confidence

€

SN rate = A ⋅Mm + B ⋅SFR n

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

SFR½

€

cf . SNR /M = A + B(SFR /M)


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?

)/(/ MSFRBAMSNR +=


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 - fSNIa


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 2004Neill 2006


ConclusionsConclusions

w = -1 (preliminary) from 3rd 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

~400-500 SNeIa with spectroscopy by 2008, >1000 total

SNLS-2? ~60 deg^2, z<0.7, N=3000:

Stay tuned!


More SNLS information http://legacy.astro.utoronto.ca/ - database (Perrett) www.cfht.hawaii.SNLS – people, papers, …

http://legacy.astro.utoronto.ca/





http://www.cfht.hawaii.snls/






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

www.astro.uvic.ca/~pritchet the supernova legacy survey (snls): new results on cosmology and the...

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