Supernova Legacy Survey Cosmology, Spectroscopy, and Progenitors T. Justin Bronder, DPhil Candidate Oxford University Isobel Hook, Supervisor

Supernova Legacy Survey

Cosmology, Spectroscopy, and Progenitors

T. Justin Bronder, DPhil Candidate Oxford University

Isobel Hook, Supervisor

Overview• Background on ‘Type Ia Cosmology’• Supernovae Legacy Survey Overview

– Goals– Methods

• Photometry and Spectroscopy

– Year 1 Cosmology Results

• Quantitative Spectroscopy of Hi-z SNe Ia– Goals / Methods / Results

• Brief intro to other SNLS Science – Ex) SNe Ia Hosts and Delay Times– Future work: Quantify evolution? Constrain progenitors?

Background

Hydrogen? No H2 present: H2 present:

General group? Type I supernovae Type II supernovae

Other properties? Si He neither Photometry/spectral properties

Specific type? Ia Ib Ic IIp IIn II...

- defining Type Ia Supernovae

Background

Hydrogen? No H2 present: H2 present:

General group? Type I supernovae Type II supernovae

Other properties? Si He neither Photometry/spectral properties

Specific type? Ia Ib Ic IIp IIn II...

- defining Type Ia Supernovae

Background (cont)

• Cosmological utility as ‘standardizeable candle’– Variance in B’ peak magnitude – Peak mag. correlates w/

decline rate of light curve – empirical correction reduces peak magnitude deviations enough for cosmological use

– Chart SNe Ia with z to determine matter / dark matter content in the Universe

‘s’ parameter – Goldhaber et al 2001

Cosmological constraints come from many sources

Combine with Type Ia supernova surveys = ‘Cosmological Concordance Model’

Results inconsistent with M=1 spatially flat cosmology

(SNe too faint)

SN data favor >0

What is dark energy?

Differentiate via the equation of state

<w = p

Background (cont)

• Issues / Concerns / Criticisms– Understanding of SNe Ia physics

• Extensive agreement (theory / observation / models) on basic model:– C/O White Dwarf exceeds MCh

– Thermonuclear runaway disrupts WD, late time – radioactive decay of unstable nuclear burning products

• Many questions follow:– Progenitor scenario – Single or Double Degenerate

– Burning front – Detonation / Deflagration / Both

– ‘homogeneity’? Case of 1991T, 1991bg

– Host dependence? Early galaxies host dimmer SNe Ia

– Type Ia Cosmology Statistics and Systematics• Luminosity calibration• Evolution• Extinction

SNLS collaboration http://cfht.hawaii.edu/SNLS/

Chris Pritchet: U. VictoriaRay Carlberg: U. Toronto Andy Howell: U. TorontoMark Sullivan: U. TorontoArif Babul: U. VictoriaDavid Balam: U. Victoria Sara Ellison: U. Victoria F.D.A. Hartwick: U. Victoria Henk Hoekstra: CITADon Neill: U. TorontoJulio Navarro: U. Victoria Kathy Perrett: U. Toronto David Schade: HIAPierre Astier : CNRS-IN2P3, Paris Eric Aubourg Christophe Balland

Luc Simard: HIA Peter Stetson: HIA Sidney van den Bergh: HIA Jon Willis: U. Victoria Isobel Hook: U. Oxford Justin Bronder: U. OxfordRichard McMahon: U. CambridgeReynald Pain: CNRS-IN2P3, Paris Saul Perlmutter:LBNLRobert Knop: U. VanderbiltJames Rich: CEA-Saclay Nic Walton: U. CambridgeEric Smith: Vanderbilt UniversityGreg Aldering: LBNL Lifan Wang: LBNL Rachel Gibbons: LBNL Vitaly Fadayev: LBNL

Stephane Basa Sylvain Baumont Sebastien Fabbro Melanie Filliol Ariel Goobar: StockholmDelphine Guide Julien Guy Delphine Hardin Nicolas Regnault Tony Spadafora: LBNLMax Scherzer: LBNL Harish Agarwal: LBNLHerve Lafoux Vincent Lebrun Martine Mouchet Ana Mourao Nathalie Palanques Gregory Sainton

Canada, France, UK, US, Sweden, Portugal

I – SNLS Overview• Populate Hubble Diagram with over ~700 Type Ia SNe (.2 <z<

1.0) to estimate w to + 0.1• CFHT ‘Megacam’ used to acquire multiple (~5 epochs monthly)

points in g’r’i’z’ for 1- potential candidate ID and 2-luminosity calibration (‘stretch factor’)

• Candidates verified w/ 8m-class telescopes – Gemini, VLT, and Keck

• Publications:– astro-ph/0509195 - Gemini spectroscopy, Howell et al– astro-ph/0510447 - Measurements for Cosmology, Astier et al– ‘Photometric Selection of high-z Type Ia Candidates’ – Sullivan et al– VLT Spectroscopy summary – in prep– Much more on Hi-z SNe science in the works

-Possible Type Ia candidates followed up with 8m spectroscopy main purpose is candidate ID and redshift confirmation

-GMOS: 0.75’’ slit range = 465-930 nm 1.34 A/binned pixel disp. 45-90 min exposure time

-FORS1: 0.7’’-1.3’’ slit range = 445-1100 nm 2.69 A/binned pixel disp. 25-62.5 min exposure time

Example Gemini/GMOS Nod & Shuffle spectrum2 hr exposure

SNi=24.0

Wavelength

Host Galaxy spectrum

Smoothed spectrum allowing for:• template host galaxy subtraction• Reddening

Extracted spectrum

SiII

- latest LSS / CMB / Baryon Acoustic Peak Oscillations results added to concordance model

(Allen, Schmidt, & Fabian 2002 / Spergel et al 2003 / Eisenstein et al 2005)

- SNLS Hubble diagram – Astier et al (accepted by A&A)

- M = .263 + .042 (stat) + .032 (sys) (flat CDM model)

- w = -1.023 + .090 (stat) + .054 (sys)

I – SNLS Overview• Spectroscopy implications

– Only 1 epoch• Velocity gradients, etc. not viable

– SNR to maximize number of candidates observed + identified• No synthetic spectra/detailed line analysis• SNR-driven error bars on any results

• Well suited for SNLS purposes– Candidate ID via template-matching

• ‘Superfit’ (Howell et al. 2002, Lidman et al. 2005)• Results in Gemini/VLT data papers• 72 observations - 47 confirmed Ia (Gemini, 12 months)• 108 observations – 67 confirmed Ia (VLT, 18 months

II – SNLS Spectroscopic Science• Main purpose of spectra is ID/z

– More thorough analysis a necessity for• Object clarification / independent identification

• Physical insight – Evolution / systematic checks / progenitors

– Needs + survey constraints imply data set is best suited for:• Quantify the distribution of spectral properties (check for evolution w/ z, environment)

– Specific comparison to low-z Ia SNe population

– Type Ia sub-types ?

• Object clarification independent of 2 fits

• Another parameter space to explore the systematics of this large sample for cosmology

II – Science w/ SNLS spectroscopy - background

- expansion velocity of CaII H&K feature

-May also probe for Z effects (Hoflich et al 1998, Lentz et al 2000) if measured on a high-z population


-R{CaII} and R{SiII} – spectral feature ratios from Nugent et al.1995

-Utilized in other empirical treatments of Type Ia spectra


- Velocity gradients / spectral feature ratios explored empirically in Benetti et al 2004

- continuum of Type Ia properties? Two different populations?

II – Science with SNLS spectroscopy

-Equivalent Widths (EW)

-Shape independent method of spectral feature strength

-Folatelli 2004 – EW measurements for

Type Ia – specific features

-Folatelli found this measurement useful for quantifying SNe Ia spectral -homogeneity – subtype ID, correlations w/ lightcurve-shape params

II- EW Results – Low z• Distribution of spectral properties

» EW {CaII} - Check of overluminous SNe Ia


» EW {SiII} - smaller epoch evolution than other features

- correlates to Lightcurve parameters


» EW {SiII} - smaller epoch evolution than other features

- correlates to Lightcurve parameters


» EW {MgII} - clear check of underluminous objects

- additional correlation to

luminosity params

II – Methods – EW (cont)



III – Equivalent Width results

• Quantitative analysis– Extensive low-z data employed to generate a mean trend

for branch normal SNe Ia– Comparison ‘model’ for high-z objects

• Ejection velocities of CaII H&K feature also measured– Gaussian fit to feature – minima of fit = blueshift

velocity– Low redshift branch normal ‘model’ computed for

quantitative comparison

III - Results• Distribution of spectral properties :

» EW {CaII} - SNLS 1st Year - reduced chi squared: .511


» EW {CaII} - epoch and sampling ‘free’ comparison via residuals – compare SNe populations w/ K-S Test – no significant difference


» EW {SiII} - SNLS 1st Year - reduced chi squared: .471


» EW {SiII} - KS test results show a difference (not significant) – identifies outliers independently of photometry / typing


» EW {SiII} - recall light curve – spectra correlation


» EW {SiII} - most objects follow Low-z trend… shift in distribution? Significant outliers?


» EW {MgII} - SNLS 1st Year - reduced chi squared: .421


» EW {MgII} - K-S test results similar to EW{CaII} – note possible overluminous outliers


» Vej {CaII} - SNLS 1st Year - reduced chi squared: .372


» Vej {CaII} - Residuals – outliers noted – trend or small numbers? Possible

metallicity indication – epoch not quite early enough to match predictions

III - Results• Quantitative look at distribution of these spectral properties shows ‘no

significant difference’ at high-z– Caveat – large error bars test for broad consistency

– K-S tests on residuals support 2 results – no major / systematic shift in Ia properties at high-z– Definite differences

• Are these expected?• Implications for SNe Ia cosmology?

• Object sub-typing / systematic checks / PG’s – Spectroscopic outliers noted for i) follow up investigation ii)

‘spectroscopic’ SNLS Hubble diagram to check cosmology systematics– Host Galaxy – Luminosity/sub-type correlation at low z

• Quantitative spectroscopy + high-z host/environment data will enable exploration of this observation test age/metallicity and progenitor dependencies

IV – SNLS science [brief intro]- Sullivan et al (2003) – ‘morphological’ SNe Ia Hubble diagram

- Residuals for objects in E/S0 hosts were smaller than other host types

- results w/in each type still supported dark matter model

- extrapolate to higher redshift – unveil population / age / evolutionary differences clues to progenitors?

… delay times?

IV – SNLS science [brief intro]- delay times useful in constraining PG scenarios (SD v DD)

- Previous work (Madau et al 1998, Dahlen & Fransson 1999, Gal-Yam & Maoz 2004, Strolger et al

2004) gave delay times from ~ 1.0 to 4.0 Gyr

- heavily dependent on SFR assumptions

- no results quite explained Fe / O (Ia / CC SNe) ratio in galaxy clusters

- Scannapieco & Bildsten 2005 – 2-component Type Ia formationScannapieco & Bildsten 2005 – 2-component Type Ia formation

i) ‘prompt’ – proportional to SFR ii) extended – proportional to mass

- quantifies simple observation that SNe Ia are seen in all galaxy types

- SNLS data: Host spectra can be used to quantify local SFR and mass = specific star-formation rate test this model

- initial results ‘agree’ – two Type Ia channels or one channel with a large range in PG system age

1

o10

o10 Gyr 10

.10

.SNRateM

SFRB

M

MAt

IV – SNLS science [brief intro]- other evidence for two-channel/extended PG time Ia channels?

- distribution of light-curve properties (here presented by star-formation rate rather than morphology courtesy of M. Sullivan) corroborates previous observations

- evidence for two PG channels or populations?

IV – SNLS science [brief intro]- evidence for two PG channels or populations?

- additional physical insight with spectroscopy?

IV – SNLS science [brief intro]- evidence for two PG channels or populations?

- additional physical insight with spectroscopy?

Conclusion• Brief summary of ‘Type Ia Cosmology’

– Earlier results (Riess et al 1998, Perlmutter et al 1999) supported by SNLS– Will also constrain w for additional cosmological insight

• SNLS Science and Spectroscopy– Successful at main goal – object ID / redshift– Quantified analysis can also i – check for broad consistency to low-z

population ii – id sub-types and outliers exert an additional systematic control on large SNLS data set iii – combine with other SNLS science to provide insight into Type Ia physics / pg’s

Documents

Supernova Legacy Survey Cosmology, Spectroscopy, and Progenitors T. Justin Bronder, DPhil Candidate Oxford University Isobel Hook, Supervisor