EXPLOSION RATE OF TYPE IA SUPERNOVAE AS FUNCTION

EXPLOSION RATE OF TYPE IA SUPERNOVAE AS FUNCTION OF REDSHIFT FROM SUPERNOVA LEGACY SURVEY Tuesday lone supernovae presentation Moriond 2008 – La Thuile - Italy Pascal Ripoche – LPNHE - Paris Moriond 2008 - Pascal Ripoche 1

Outline The SNLS Measuring Rate in the SNLS Photometric selection of type Ia supernovae Type Ia Detection/Identification efficiency The rate measurement Moriond 2008 - Pascal Ripoche 2

Super. Nova Legacy Survey Moriond 2008 - Pascal Ripoche 3

The Super. Nova Legacy Survey Main goal : measurement of cosmological parameters using type Ia supernovae. Method : 5 years on 4 one square degree fields at CFHT (megacam + 4 filters) Spectroscopic follow-up (VLT, Keck, Gemini) Results : about 300 type Ia supernovae up to z = 1. 0 with spectroscopic identification during the 3 first years. Opportunity to accurately measure SN Ia rate vs z Moriond 2008 - Pascal Ripoche 4

Real time detection Pipeline • • 4 fields observed every 3 -4 days in 4 bands (“rolling search”) Variable object detection method : PSF matched image subtraction new sub detection ref Increasing Sn Ia color Off-centered Good weather Spec time available spectroscopy Day Spectroscopy: z = 0. 81 Type : Sn Ia Moriond 2008 - Pascal Ripoche 5

Measurement of the Rate Moriond 2008 - Pascal Ripoche 6

How to measure supernovae explosion rate in the SNLS ? A simple division : Observed type Ia supernovae sample Detection/Identification efficiency but Real Time spectroscopic identification efficiency is almost impossible to model due to spectroscopic selection (human selection, weather, available time, host luminosity, …). pure photometric detection/identification Moriond 2008 - Pascal Ripoche 7

Variable object detection Dataset : 2. 5 years of SNLS images reprocessed First level selection : Variables objects ◦ Images subtraction ◦ Each detection is scored with a neural network and shapelet to remove artifacts ◦ At least 5 good detections with S/N greater than 5. Spurious subtraction residuals ◦ Cut on field area and date to avoid edge effects. Selected objects are mostly physical objects : AGNs, variable stars, supernovae (all types). Moriond 2008 - Pascal Ripoche 8

Selected objects 3051 variable objects Host galaxy photometric redshift : Ilbert et al. 2006 289 objects with spectroscopic data from real-time operations: redshift and type (not always) Used as control sample Redshift accuracy : 0. 001 Sn. Ia Sn? Sn. II Sn. I b/c AGN 196 53 24 7 9 Moriond 2008 - Pascal Ripoche 9

SN Ia photometric selection Level II Selection : Type Ia supernovae Cut I : multi-color Lightcurve fit (SALT 2) ◦ Redshift fixed (spectroscopic or photometric) ◦ Fitted parameters : stretch, color and brightness ◦ Χ 2 selection Cut II : loose cut on brightness ◦ gets rid of catastrophic redshift ◦ minimize contamination Moriond 2008 - Pascal Ripoche 10

Test on control sample The control sample is used to test cuts (with host photometric redshift) • Blue : cut with chi 2 • Red : cut on brightness • Selected objects Moriond 2008 - Pascal Ripoche 11

Results : Snia sample 435/3051 selected objects SNIa spec SN no spec No contamination with spectroscopic redshift 2% Contamination with photometric redshift Photometric redshift accuracy improved Spec type Detected Selected Sn Ia 196 182 Sn 53 32 Sn II 24 0 Sn Ib/c 7 0 AGN/Var 9 0 No Spec 2762 221 Moriond 2008 - Pascal Ripoche 12

Detection and selection efficiency Moriond 2008 - Pascal Ripoche 13

On image SN Ia simulation Main parameters: ◦ ◦ ◦ ◦ Ra/Dec: coordinates z : Redshift (from photo. Z catalogue) D 0: Date of maximum s : Stretch c : Color (extinction) disp : intrinsic dispersion (α, β, Rv, …) Filter g’ Lightcurves simulated with SALT 2 Filter r’ Filter i’ Filter z’ Simulated supernovae added on all images (before subtraction) Simulated images processed with the photometric detection pipeline Moriond 2008 - Pascal Ripoche 14

Detection/Selection Efficency 2. 5 years of data processed (15 To) 720000 simulated supernovae MC distributions tuned to match observed distributions: • Color • Stretch • Intrinsic dispersion • S/N • position on host I’ mag vega Moriond 2008 - Pascal Ripoche 15

SN Ia Rate measurement Moriond 2008 - Pascal Ripoche 16

Rate calculation Time dilatation correction Comoving volume Moriond 2008 - Pascal Ripoche 17

Corrections and Systematic Errors Corrections Photometric Redshift dispersion Photometric Redshift inefficiency Contamination Systematic uncertainties Efficiency calculation : distribution (stretch/dispersion/color) Photometric Redshift dispersion Contamination Moriond 2008 - Pascal Ripoche 18

Type Ia SN rate Photometric selection Spectroscopic selection Rest frame Rate (z) assumed cosmology : LCDM (0. 3, 0. 7) Moriond 2008 - Pascal Ripoche 19

Comparison with previous measurements Selection method Spectro mixed Photo Réf Nb Spec Ia Hardin et al. 4 100% Pain et al. 38 97% Blanc et al. 16 100% Barris & Tonry 98 23% Niell et al. 77 75% Dilday et al. 17 94% Kuznetsova et al. 57% Dahlen et al. 56 59% This study 435 42% Moriond 2008 - Pascal Ripoche 20

Rate and model Rate = star formation rate (SFR) (Hopkins et Beacom 2006]) ∗ delay time function Φ(t) σ/τ=0. 2 τ=3. 7± 0. 25 Gyr χ2=3. 75 Slope measurement α=2. 14± 0. 51 10 -5 Sn/Mpc 3/yr R 0=2. 0± 0. 54 χ2=4. 77 Moriond 2008 - Pascal Ripoche 21

Conclusion We have derived a photometric SN Ia rate vs z up to redshift 1. 2 Tested against a spectroscopic sample (40%) Rate increase with redshift. Possible flattening around z = 1 Good agreement with previously measured low and higher z rate (except with Barris and Tonry 2003) Moriond 2008 - Pascal Ripoche 22

The End Moriond 2008 - Pascal Ripoche 23

Taux spectroscopique (1) Nouvelles coupures : sélection spectroscopique SNIa spec SN no spec Moriond 2008 - Pascal Ripoche 24

Taux spectroscopique (2) On suppose que l’absence de spectroscopie est aléatoire (temps disponible, méteo) on estime l’efficacité spectroscopique : 69% ± 10% On n’utilise que les supernovae Ia identifiées • Pas d’erreur sur les redshifts • Pas de contamination • Nouvelle systématique d’efficacité spectro Pas de spectroscopie pour z >1 Moriond 2008 - Pascal Ripoche 25

Moriond 2008 - Pascal Ripoche 26

(Z >1) Moriond Pascal- Marseille Ripoche 18 octobre 2008 2007 - CPPM 27