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SDSS超新星サーベイで発見されたIa型超新星の多様性
Diversity of Supernova Type Ia Discovered by
SDSS Supernova Survey
Kohki Konishi1, Naoki Yasuda1, Mamoru Doi1, Tomoki Morokuma2, Naohiro
Takanashi1, Kouichi Tokita1, Yutaka Ihara1 and SDSS Collaboration
1 Univ. of Tokyo, 2 NAOJ
1. INTRODUCTION
4. EQUIVALENT WIDTH vs ⊿m15
• Supernovae Type Ia (SNeIa)
• Good candidate for standard candle to the high-z Universe
(redshift <1.7, at present)
• Prime source of chemical enrichment in the Universe
• We show the equivalent widths of “CaII3945” and “SiII4000” dependence on ⊿m15, which can
be used as new spectral luminosity indicators.
• Optical light curve and spectrum
1 “CaII 3945”
2 “SiII 4000”
3 “MgII 4300”
4 “FeII 4800”
5 “SII W”
6 “SiII 5972”
7 “SiII 6355”
8 “CaII IR”
(Garavini+ 2007)
• Diversity have been studied.
•
•
•
•
• EW(CaII3945) is found to be increasing monotonously with ⊿m15 at the “max” epoch for the
first time.
• EW(SiII4000) is found to be increasing monotonously with ⊿m15 not only at the “max” but
also at the “post-max” epoch for the first time.
• The point at the left edge of both figures are from SNIa that shows an unusually broad light
curve.
Lower luminosity SNeIa show faster decline rate ⊿m15. (e.g. Phillips 1993)
Some EW features are related to ⊿m15. (e.g. Nugent 1995)
EW dependence on epoch shows dispersion among SNeIa. (e.g. Folatelli 2004)
Vabs dependence on epoch shows dispersion among SNeIa. (e.g. Blondin+ 2006)
SN Epoch
• the elapsed time
from the maximum brightness
• epoch = (tobs - tmax)/(1+z)
Photometric property
• Decline rate of brightness
during 15 days from its peak
(⊿m15) [mag]
Absorption features
• Photons emitted from the photosphere
are absorbed by expanding atmospheric layers
of ejected materials (e.g. Ca, Si, Fe)
5. EQUIVALENT WIDTHS vs EPOCH
• We show the equivalent widths of “CaII3945” and “FeII4800” dependence on epoch, with
higher-z results (SNLS and SCP) overlapped. We discriminate the SNeIa appeared near the
center of its host (○) because the contamination of galaxy still may exist in their spectra.
• EW(CaII3945) is found to decrease with increasing epoch.
• EW(FeII4800) is found to increase with increasing epoch.
• These trends from the “early” to the “post-max” are consistent to the results from high-z SNLS
& SCP samples (Bronder+ 07, Garavini+ 07).
Spectroscopic property
• Absorption features
• Equivalent Width (EW)
Blueshift
• Line Velocity (Vabs)
from blueshifted wavelength of lines
Here we explore the correlations in the intermediate redshift range using SDSSSN Survey
data and compare our results with the Local (z<0.05) and the high-z (ESSENCE, SNLS and SCP)
data. We show interesting trends of all the lines shown above in Section 4-6.
2. DATA
6. LINE VELOCITY vs EPOCH
• Sloan Digital Sky Survey Supernova Survey (SDSSSN Survey)
• This survey observes more than 450 SNeIa at 0.1<z<0.4.
•
•
•
•
•
• We show the line velocities of “CaII3945” and “SiII6355” dependence on epoch, with higher-z
results (ESSENCE) overlapped.
SDSS 2.5m telescope
Sep-Nov 2005-2007
300 sq. deg. , every 2 night
5-band photometry (u,g,r,i,z)
Spectroscopic followup using telescopes around the world
• Vabs(CaII3945) and Vabs(SiII6355) both decrease gradually with increasing epoch, showing that
the kinematical energy becomes smaller with increasing epoch.
• These trends are consistent to the results from high-z ESSENCE samples (Blondin+ 2006).
• Our followup spectroscopy
• Subaru/FOCAS (71objects)
• wavelength range (R=500)
• 4000-9000 Ang (300B+L600 & 300R+Y47) for 2005yr
• 3600-9000 Ang (300B+L550 & 300R+Y47) for 2006yr
• The redshift distribution and epoch distribution are shown at the figures below.
7. SUMMARY
early: epoch < -3
max: -3 < epoch < 3
post-max: 3 < epoch < 10
3. TECHNIQUE
• Supernova Extraction
• Light contamination of the host galaxy on SNIa generally becomes larger at higer redshift.
• SN component should be extracted.
SN
host
(b) Separate SN/galaxy flux
by fitting each spatial
profile with Gaussians for
every wavelength.
Wavelength
• Overview of our Supernova Extraction Code
2D host
• We developed the Supernova Spectrum Extraction Code to eliminate the contamination of its
host galaxy accurately.
• We measured equivalent widths and line velocities of absorption lines to explore the diversity
of Supernova Type Ia.
• We found new spectral luminosity indicators for independent checks of the decline rate. The
equivalent width of “CaII3945” line at the “max” epoch is found to be positively correlated with
⊿m15. The equivalent widths of “SiII4000” lines at the “post-max” epoch also show positive
correlations with the decline rate.
• We found that absorption features overall do not change with redshift.
(a) Prepare
flux calibrated
2D spectrum.
Wavelength
8. FUTURE WORKS
SN
SN
host
SN
• How metallicity of host galaxy is related to SNIa spectroscopic properties?
• How maximum brightness and color are related to SNIa spectroscopic properties?
• How SNIa’s properties affect the determination of cosmological parameters?