1. Searching High-z Supernovae with HSC and WFMOS
Yutaka Ihara (U. Tokyo/IOA)
Mamoru Doi, Naoki Yasuda,
Tomoki Morokuma, Kohki Konishi, Kouich Tokita
Subaru User’s Meeting Mitaka

2. Abstract We will search Type Ia supernovae with HSC and WFMOS.
HSC (Imaging observations)
Detect variable objects in high-z galaxies
(5-10 nights (epochs) observations give SN light curves. )
→~1000 SNe Ia will be obtained for one year (two terms) survey.
(2) WFMOS
・ ~500 spectra of SNe Ia will be obtained for one year.
・ ~1000 spectra of host galaxies of the detected SNe Ia
Our Goal
(1) For SN Ia properties
① SN rate study → Progenitor of SNe Ia
② SN Ia spectra → Diversity
(2) For Cosmology
・Resolve the time variation of “Dark Energy”
・Obtain more accurate cosmological parameters (ΩM, ΩΛ, w)

3. Classification of SNe × × ○ ○ ○ Binary (WD) Ia Si line Core CollapseIb ×
He line
H line Ic × ○
Line shape
IIn
Narrow
Plateau
IIP
Light curve
Linear
IIL

4. How to detect SNe ?
(1) Detect variable objects with repeat imaging observations
Example of a SN Ia at z=0.606 (Morokuma+2008)
Reference
Another Image
Subtracted Image
(2) Classify SNe
① From Spectra (Confirmed method)
② From Light Curves (with Uncertainty) II Ia
Filippenko 1997

5. Why do SNe Ia are important?
　　　　　　　　　↓
Standard candle in the universe
・ Constant Maximum brightness
・ Uniform Light curves and spectra
Very bright (MV~-19.3 mag)
・ Observable at cosmological distances (z~1.5)
SN1994D
© NASA / HST
Measure the expansion of the universe
using SNe Ia.
On the contrary…
Large systematic errors still exist on the cosmological parameter fit.
Diversity of SNe Ia
caused by Progenitors?, Metallicity of Host Galaxies?, Time evolution? or…
→ Need more spectra of SNe Ia from low-z to high-z

6. SN Ia survey Mid-z survey High-z survey
・ SNLS (0.2<z<0.9)
~700 SNe Ia obtained in
Imaging: CFHT 4m
・ SDSS-II SN survey (0.1<z<0.4)
~500 SNe Ia obtained in
Imaging: SDSS 2.5m
・ ESSENCE (0.2<z<0.9)
~200 SNe Ia obtained in
Imaging: CTIO 4m
High-z survey
・ SCP (0.3<z<1.4)
~30 SNe Ia obtained in 2002 and 2005,6.
Imaging: Subaru 8m and HST
・ High-z Team (0.2<z<1.6)
~30 SNe Ia obtained in
Imaging: HST
HSC+WFMOS
If using HSC (imaging) + WFMOS (spectroscopy),
We will get ~1000 SNe Ia for one year survey.
Out of them, ~500 SNe Ia are high-z SNe (z>1.0).

7. Science with SNe Ia

8. SN Ia rate study → Many SNe Ia samples are very useful. Motivation
SN Ia rate is the clue of progenitors of SNe Ia
Recently, large delay time distribution of SNe Ia are shown by rate studies.
( “Delay time” → time interval between star formation and SN explosion )
★ Two populations of SNe Ia ?
(Mannucci+2005, 2006)
Sullivan+06
Nearby results
(e.g. Cappellaro+99)
“Prompt” : Short delay time (~0.1-1Gyr)
“Tardy” : Long delay time (~1-10Gyr)
High-z rate is important!!
It is difficult to measure that
from current SN surveys
→ HSC+WFMOS survey
Neill+06
(SNLS work)
Prompt
Tardy

9. Results of our work and the others
( Detailed results will be shown in
Joint Subaru/Gemini Science Conference)
At highest-z (z>1.4),
very large errors
due to small statistics
Ihara+09
(SXDS)
Dahlen+08
(GOODS)
Poznanski+07
(SDF)
Neill+06 (73)
(SNLS) z=0.47
Dilday+08 (17)
(SDSS) z=0.12
Ihara+09 shows
increasing rates toward z~1.2

10. Expecting Results ? ? If a major fraction of SNe Ia is “prompt”,
SN Ia rates increase toward z~2 (SFR peak),
else SN Ia rates decrease.
HSC+WFMOS resolve SN Ia population!! ? ?

11. Diversity of SNe
Though SNe Ia should have uniformed property,
diversities of colors, light curves, or spectra are found by large surveys.
→ These diversities affect measuring cosmological parameters.
Ex.1) Color-Color diagram of mid-z SNe Ia
Ex.2) Diversity of Light curves
U-B
B-V
Conley et al. 2008
Kim et al.

12. Diversity of SNe
Corrected diversities with stretch factor, epoch, and MW extinction
→ But the diversities still remain…
→ Extinction of host galaxies? Metallicity of hosts? Other unknown reasons?
→ Resolve that by large statistic samples of SN Ia spectra
( Need large amounts of SNe at each epoch and stretch factor)
Red　sample
Blue sample
Tokita 2009 PhD thesis

13. Diversity of SNe
Correlation of EW(FeII) and Color of SNe Ia (?) (see detail on Konishi’s Poster)
→ SN spectra may be useful to decide color terms of SNe
SALT2 (Light curve fitting method) (Guy+2007)
Color term
A few spectra of SNe…
Large statistical samples with WFMOS
will find distinct correlations.
● Subaru(SDSS)
● Suspect
At max
Konishi+09 in prep

14. Cosmology Small statistics at z>1 Need more samples
Kowalski’s work → Using all SNe Ia obtained by SN surveys or the other works
→ 307 SNe Ia (after selection cuts)
Small statistics at z>1
Need more samples
Enough statistics
Errors depend on systematic

15. Cosmology ★ Need spectroscopic information Using WFMOS,
Redshift should be determined well below 1% level
Difficult only with photometric information
★ Need spectroscopic information
Combine with photo-z of host galaxies?
Different error properties are expected
Spectroscopy of host galaxies
Need large observing time
Using WFMOS,
Get ~50 SNe Ia spectra at once!!
And, get spectra of their host galaxies at the same time.

16. Cosmology ○ Errors on ΩM and w ○ The time variation of Dark Energy
reduce by a factor of 2
○ The time variation of Dark Energy
will be constrained
Kowalski et al. 2008
HSC+WFMOS
Contour : 1σ

17. Summary WFMOS → Spectra of ~500 SNe Ia and
HSC → Detect ~1000 SNe Ia at z<1.5
WFMOS → Spectra of ~500 SNe Ia and
all of the ~1000 host galaxies
This survey will be the largest and the deepest SN survey
for the next five years.
① Nature of SNe Ia and their evolution can be
explored with large sample.
→ SN Ia rate study ( for progenitors)
→ Diversities
② Measure cosmological parameters
→ ΩM, ΩΛ, w
→ The time variation of Dark Energy (?)

18. ~ Fin ~