B12 Next Generation Supernova Surveys

Marek Kowalski1 and Bruno Leibundgut2

1Physikalisches Institut, Universität Bonn 2European Southern Observatory

Ωm = 0.284 ± 0.020(stat) ± 0.01(sys)

Ωk= 1-Ωm -ΩΛ

Ωk = 0.008 ± 0.013(stat) ± 0.005(sys)

SNe + BAO + CMB

Krümmung:

w =−1.00 ±0.07(stat) ±0.07(sys)

SNe + BAO + CMB

Supernova Cosmology today

• Some large surveys (SNLS, ESSENCE, SDSS II, SNfactory) and many smaller ones.

• Union2 compilation (Amanullah et al., submitted, Kowalski et al, 2008) consists of 555 SNe Ia from 19 surveys.

• Constraints on dark energy from combining SNe with BAO (Percival, 2009) and WMAP05:

• Systematic uncertainties now dominate the measurement! Limiting systematic errors are the absolute flux calibration (particularly in the U-band) and the reddening correction for interstellar dust..

universität

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w = −0.974 ± 0.051(stat) ± 0.059(sys)

Supernova Cosmology tomorrow

Project z range # SNe Pan-STARRS 0.1–0.5 ~104

DES (2011) 0.2–0.7 ~2x103 GAIA (2013) 0.0–0.1 ~6x103 LSST (2015) 0.1–0.9 ~106

Euclid (2017) 0.2–0.8 ~103

Huge increase in SN statistics becoming available:

Goal 1: Reduce systematic uncertainty

The dominating uncertainty lies in the flux calibration (see e.g. Kessler et al., 2009). In particular: to compare the flux of SNe at different redshifts, as well as the color measurements requires relative flux calibration between different wavelengths.

Method: Perform in situ calibration of the SNIFS spectrograph, operated on the 2.2m telescope of the University of Hawaii, and provide color-calibrated spectra of SNe and stars that - for the first time - do not rely on the calibration of standard stars.

Goal 2: Optimal analysis of SN spectra

Spectroscopy is needed for classification and redshift determination. It can also be used for improved standardization (e.g. Bailey et al. 2009). However, spectroscopy of high-z SNe is observationally expensive and it will be the limiting bottleneck for future surveys. Hence, optimal tools for analysis of SN spectra of poor quality need to be developed.

Figure: Implementation of the flux/color calibrationTunable laser/LED light reflected from a uniform screen and a calibrated photo-diode to measure the flux F(

SNIFS

screen

Light

source

Calibrated Photo-Diode

Primary Mirror

3000 4000 5000 6000

Rest-Frame Wavelength (Å)

Rel

ativ

e F

lux

(Fλ)

+ C

onst

.

Nearby SN spectra from the SNfactory

High redshift (z=1.12) SN spectrum (Amanullah et al, 2009)

Figure: SNIFS - a custom made 3D spectrograph for SN follow-up - is part of the SNfactory project, that will deliver spectral time series of ~200 nearby SNe Ia with 0.03>z>0.08.

The proposed bottom-up calibration can reduce or even eliminate the largest uncertainty that haunts current and future SN surveys.

Method:Adoption of statistical methods to deal with unevenly sampled and noisy data sets. Mathematical methods for the comparison of

such data beyond a simple will be explored to provide information on

spectral type, phase, redshift and peculiar spectral features. Having access spectroscopic

data from ESSENCE, SNLS and

SNfactory, the algorithms will be systematically tested for efficiency and reliability.

Optimized tools for the efficient analysis of current and future spectroscopic data will be developed.

Goal 3: Next generation SN spectroscopy

The large SN statistics produced by next generation imaging surveys requires dedicated spectroscopic follow-up capabilities far beyond what has been available in the past. To optimally prepare for the upcoming shortage, we will perform the following tasks:

• Development of a generic exposure time calculator (ETC) for spectroscopy, utilizing the experience with the ESO instruments as well as SNIFS.

• Application of analysis tools that have been developed for Goal #2 as well as the above ETC to develop optimal spectroscopic observing strategies for the various surveys that maximize the cosmological impact.

• Investigate concepts for development of a dedicated spectrograph optimized for SN observations.

The SN constraints on Dark Energy can improve by more then one order of magnitude. The bottleneck to utilizing the increase in statistics will be the understanding of systematic uncertainties and the significant spectroscopic follow-up capabilities needed for redshift and classification of the SNe Ia. Correspondingly, the three goals of this proposal focus on these issues.

Development of optimal observing strategies (e.g. which SN to observe for how long) for the upcoming surveys. Planning for a dedicated SN spectrograph.

References – Amanullah et al., submitted to Astrophys. J. (2009), Bailey et al. A&A 500, 17 (2009) Kessler et al. 2009, Astrophys.J.Suppl.185, 32 (2009), Kowalski et al. Astrophys.J.686, 749 (2008)

Figure: Expected redshift distribution of SNe Ia from the GAIA satellit. The generic survey simulation toolhas been developed as part of the preliminary work.