A photometric method to classify high-z supernovae found with HSC

Institute of Astronomy, School of Science,

The University of Tokyo

Yutaka IharaMamoru Doi, Tomoki Morokuma,

Naohiro Takanashi, Naoki Yasuda, SCP collaborations, and SDSS Collaborations

Abstract

★ MethodClassification of SNe → SNe Ia or CC SNe (Ib/c or II)→Using only Light curves and colors

★ Our goalSN Ia rate at high redshift ( 0.8 < z < 1.4)

★ Previous Observations (Suprime-Cam/Doi et al. 2002)

More than 100 SNe in SXDF (Subaru/XXM-Newton Deep Field)

→ ~50 are SNe Ia ( SXDF = 5 fields of view of Suprime-Cam )

★ If we use Hyper Suprime-Cam…→ 1000 high-z SNe Ia in one observing mode.

Classification of SNe

H line

Si line

He line

Line shape

Light curve

Ia

Ib

Ic

IIn

IIP

IIL

○

Narrow

Plateau

Linear

Binary (WD)

Core Collapse○

×○

×

Motivation ★ Spectroscopy is the best method to identify SNe.

→ But, it is impossible to get all spectra of SNe.

★ Using only photometric information ( Light curves and colors )

The classification includes some incompleteness. (Some SNe Ia may regard as II, or SNe II may regard as Ia. )

SN Ia rate can be obtained by these samples with estimation of incompleteness.

SN Ia rateSN Ia rate is the clue of progenitors of SNe Ia

★ Two populations of SNe Ia ? (Mannucci+2005, 2006)・ “ Prompt” ・・・ Short delay time (~1Gyr)・ “ Tardy” 　　・・・ Long delay time (~10Gyr)

SNLS (Neil+2006, Sullivan+2006)73 mid-z SNe Ia → error is small

GOODS (Dahlen+2004)High-z, but ~1-10 SNe Ia → error is large

Prompt Tardy

We aim at accurate high-z SN Ia rate.

(Sullivan+2006)

※ Delay time is between star formation and SN explosion.

Method

① Select SN-like light curves

② Classify by LC fittings

Remove AGN, variable stars

Remove Type II supernovae

③ Classify by colors

Remove Type Ib/c supernovae

Type Ia supernovae are detected !

LC fitting Method ★ We classify SNe into SNe Ia and core collapse SNe

by fitting observed LCs with template LCs.

【 χ2 fitting 】　 Reduced χ2= ∑n

Observing date

Mag

nitu

de (

i’)

・ Observing data－ Best fitted template (Ia)

z=0.921, Spec-Ia (SXDF)

(3) (1+z)×sf

(2) Day of Maximum light

(1) Magnitude

Obs. – Temp.error / (n － 3)

( n :The number of observing days )

( )2

Template(1 of Ia and 12 of II)

Ia (Takanashi+2008) ※ With intrinsic diversity

IIL (1979C, 1980K)

IIP (1999em, 1999gi)II (SDSS-II)

※ LCs of SNe II at rising phase corrected by Nugent+2002 (model)

IIn (1998S)

Color information ★ We can classify SNe into SNe I and SNe II by light curves.

→ Light curves of SNe Ia and Ib/c are similar.

★ Excluding SNe Ib/c from SNe Ia by color (Rc – i’ vs i’ – z’)

At Max (epoch=-3~3)

Rc and z’-band observationsare also needed.

→ 1 epoch per month

※ This figure is made from spectral templates of Nugent+2002.

SNe in SXDF (preliminary)Field-1 (center) of SXDF = 1 field of view of S-cam ( 34’×27’ = 0.918deg2 )20 SNe are discovered in 2002. ( 8 epochs in 3 months )→ Out of 20 SNe, 12 are Ia, and 8 are CC.

Ex.1 1-175 (spec-Ia ) z=0.921 i’ max = 24.16

Fitting result = Iasf*(1+z)=2.04 i’ max=24.2

Ex.2 1-258 (spec-Ia* ) z=0.928 i’ max = 23.72

Fitting result = Iasf*(1+z)=1.76 i’ max=23.7

Fitted very well !!

SNe in SXDF (preliminary)○ Not identified by spectroscopy

Ex.3 1-242 ( ? ) z=0.823 i’ max = 24.01

Fitting result = Iasf*(1+z)=2.00 i’ max=24.0

○ No spectrum

Ex.4 1-018 ( ? ) z= ? i’ max = 24.47

Fitting result = Iasf*(1+z)=2.52 i’ max=24.7

They are possible Ia by LC !!

※

※ Their redshift will be estimated by phot-z of host-galaxies (Future work)

Simulation for HSC Obs. ★ Using i’-band of Hyper Suprime-Cam

・ High-z SNe Ia (z~1). → observed i’ = rest U - B ・ The limiting magnitude is 26.3 mag (Each exposure time = 3600 sec) ・ Peak magnitudes of SNe are 23.0~25.5 mag. → z=0.6~1.4

★ Make simulated ~1000 LCs of SNe Ia and II from the template LCs

★Check Completeness & Contamination

Simulation for HSC Obs.Test 2 observing mode for 3 months

(1) 2 epochs per month

-3 +3(2) 5 epochs per month

+3 +50-3-5

0 30 60

★ Various mag at peak & day of peak on observing days

-20 0 30 60 (Days)

24

26

28

Ex.) 2epoch modePeak mag = 24.0andDay of peak = 0 = 20 = 40 = 60

Completeness

Contamination

2epochs

2epochs 5epochs

5epochs

Great! >90%Great! >90%

Good >80%

Great! <10%

Good <20%

Great! <10%

Good <20%

Good >80%>1.4

1.2

1.0

0.8

0.7

0.6

>1.4

1.2

1.0

0.8

0.7

0.6

i’-mag

i’-mag

Red

shift

Red

shift

Observing date Observing date

Observing dateObserving date

Summary of Observations

(1) 5 epochs per month for 3 months +1 half night as reference

High-z SNe (z~1.2) with >90% completenessHighest SNe (z~1.4) with ~80% completeness

(2) 2 epochs per month for 3 months + 1 half nights as reference

High-z SNe (z~1.0) with >90% completeness

1000 SNe Ia will be identified in our HSC observations !

Expected resultsDelay time distribution of SNe Ia can be resolved by high-z SN Ia rate (z>1).

SNLS (z=0.47)73 spec-Ia samples (0.2<z<0.6)

HSC → 1000 SNe Ia(z=0.6~1.4 z=0.2)⊿~200 SNe Ia of each bin

?

Fin