SNe Ia and the effect of environment

Type Ia Supernovae as Probes of Dark EnergyMark Sullivan University of Oxford

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ParisReynald Pain, Pierre Astier, Julien Guy, Nicolas Regnault, Christophe Balland, Delphine Hardin,+ OxfordMark Sullivan, Isobel Hook, +

Full list of collaborators at: http://cfht.hawaii.edu/SNLS/ VictoriaChris Pritchet TorontoRay Carlberg, Kathy PerrettThe SNLS collaboration MarseilleStephane Basa, Dominique FouchezUSAAndy Howell, Alex Conley, Saul Perlmutter, +

2Deluge of astrophysical data show the expansion of the Universe is accelerating. What does this mean?

Gravity should act to slow the expansion

GR is wrong - modified gravity on large scales?

, >70% of the Universe in an unknown form dark energyCharacterised by an equation of state, w(z) or w(a)

Nearly a century after Einstein, the cosmological constant is back in vogue3The standard candleStandard candle:

Measure apparent flux and redshift can infer distance and cosmologyMeasurement of flux gives distanceGR:4The modern day Hubble Diagram

Nearby standard candlesUniverse was smallerFainter (Further)For a given redshiftBrighter Nearer Slower expansion Higher mass density Less cosmological constantFainter Further Faster expansion More cosmological constantDistance-redshift relationDifferent cosmological parameters make different predictions in the distance-redshift relation5

White DwarfSNe Ia: thermonuclear explosions of C-O white dwarf starsStandard nuclear physicsUniform triggering massBright: 10 billion suns, peak in optical56Ni 56Co 56Fe powers the SN Ia light-curve

Duration: a few weeksStandardizable: 6% calibration

Brightness and homogeneity make them the best known measure of distance, and hence dark energy6SNe are not good standard candles!Uncorrected dispersion is ~0.5mag or 25% in distance

Empirical linear relations exist which reduce this scatterBrighter SNe have wider light curvesBrighter SNe have a bluer optical colour

SNe Ia are standardised, not standard, candles:

Cosmology with SNe Iac optical colour estimator corrects for extinction and/or intrinsic variation via s stretch corrects for light-curve shape via Standard absolute magnitude and corrections reduce scatter from 25% to 6% in distance

Measured maximum light magnitude

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A Typical SN

What we need to measurePeak brightnessLightcurve width (stretch)Colour (c)

9SNLS: Vital Statistics2003-2008 SN survey with MegaCam on CFHTgriz every 4 nights in queue mode, densely sampled SN light curves

>400 high-z confirmed SNe Ia to measure w2000 SN detections in total

10SNLS3 Hubble Diagram (preliminary)~250 distant SNLS SNe Ia128 local SNe Ia86 SDSS-SN Ia17 from HST476 SNe totalSNLS+flatness+w=-1:M 0.2710.017

Sullivan et al. 200911

SNLS3 Cosmological Constraints (Preliminary)SNLS3 + BAO + WMAP5 shifts + FlatBAOSNeWMAP-5

Sullivan et al. 20094.5% statistical errors12Experimental SystematicsPhotometric calibration; contamination; Malmquist biasesNon-SN systematicsPeculiar velocities; Weak lensing

SN model and K-correctionsSED uncertainties; colour relations; light curve fitters

Extinction/ColourEffective RV; Mix of intrinsic colour and dust

Redshift evolution in the mix of SNePopulation drift environment?

Evolution in SN propertiesLight-curves/Colours/LuminositiesSNe Ia: Systematics and IssuesTractable, can be modelled13Systematic% errorExtraStatistical only4.3SNLS zero points4.51.3SNLS filters4.40.6External zero points4.71.9External filters4.50.8SN colour relation5.02.5BD+17 colours5.12.6BD+17 SED4.40.4Peculiar velocities4.40.5Malmquist bias4.40.7Nicmos non-linearity4.40.7Non-Ia contamination4.40.7All systematics6.85.0

Identified systematics in SNLS3 (preliminary)Conley et al. 200914

SNLS3 Cosmological Constraints (Preliminary)SNLS3 + BAO + WMAP5 shifts + FlatBAOSNeWMAP-54.5% statistical errors

Sullivan et al. 2009~5% systematic errors~7% stat + sys errorsNo evidence for departures from w=-115

SNLS3 Cosmological Constraints (Preliminary)SNLS3 + BAO + WMAP5 shifts + FlatBAOSNeWMAP-54.5% statistical errors

Sullivan et al. 2009~5% systematic errors~7% stat + sys errorsNo evidence for departures from w=-116Systematic% errorExtraStatistical only4.3SNLS zero points4.51.3SNLS filters4.40.6External zero points4.71.9External filters4.50.8SN colour relation5.02.5BD+17 colours5.12.6BD+17 SED4.40.4Peculiar velocities4.40.5Malmquist bias4.40.7Nicmos non-linearity4.40.7Non-Ia contamination4.40.7All systematics6.85.0

Identified systematics in SNLS3 (preliminary)Conley et al. 2009Most uncertainties arise from combining different SN samples17CalibrationThe single greatest challenge in SNLS3(and probably every current SN Ia survey)

All SNe must be placed on the same photometric system

Different SN samples are calibrated to different systems:Historical low-redshift samples: Observed in U,B,V,R (Landolt)High-z: Observed in g,r,i,z - calibrate to SDSS or Landolt?

Challenges:Zeropoints (colour terms)Filter (system) throughput

Goal: Replace low-z sample & remove dependence on Landolt system18Systematic% errorExtraStatistical only4.3SNLS zero points4.51.3SNLS filters4.40.6External zero points4.71.9External filters4.50.8SN colour relation5.02.5BD+17 colours5.12.6BD+17 SED4.40.4Peculiar velocities4.40.5Malmquist bias4.40.7Nicmos non-linearity4.40.7Non-Ia contamination4.40.7All systematics6.85.0

Identified systematics in SNLS3 (preliminary)When low-redshift sample is replaced, systematics should drop below 4%Need for a rolling low-z survey (e.g. PTF, Skymapper)19Experimental SystematicsPhotometric calibration; contamination; Malmquist biasesNon-SN systematicsPeculiar velocities; Weak lensing

SN model and K-correctionsSED uncertainties; colour relations; light curve fitters

Extinction/ColourEffective RV; Mix of intrinsic colour and dust

Redshift evolution in the mix of SNePopulation drift environment?

Evolution in SN propertiesLight-curves/Colours/LuminositiesSNe Ia: Systematics and IssuesPopulation EvolutionExtinctionTractable, can be modelledIncreasing knowledge of SN physics20Astrophysics I: Colour correction

Dust would give a linear relation in log/log space

But, slope, ,