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Supernova cosmology: legacy and future
Bruno Leibundgut ESO


Congratulations!

"for the discovery of the accelerating expansion of the Universe through observations of distant supernovae"


Supernova Cosmology
· Required observations
­ light curve ­ spectroscopic classification ­ redshift

· Required theory
­ cosmological model ­ (supernova explosions and light emission)

· Required phenomenology
­ calibrations (photometric systems) ­ normalisations (light curve fitters)


Required observations
· Light curves

SN 2007af Stritzinger et al., in2007 Miknaitis et al. prep


Required observations
· Spectroscopic classification
Matheson et al. 2007

Rodney et al. 2012

Blondin et al., in prep.


Required observations
· Redshifts

Blondin et al., in prep.

Courtesy: StÈphane Blondin


Supernova Cosmology
· Published data sets as of January 2011

Union2 data set (557 SNe Ia) Goobar & Leibundgut 2011


A more recent Hubble diagram

Rodney et al. 2012


Cosmological model
· Theory of Gravity


Cosmological model
· Assume isotropy and homology
Friedmann-LemaÍtre model

· for an example of a model-independent interpretation see Sandra BenitezHerrera's talk


et voilÞ ...
· 10 years of progress

Goobar & Leibundgut 2011


Required phenomenology
· photometric calibration
­ see Marek Kowalski's talk
Goobar & Leibundgut 2011 SNLS SN04D2gp z=0.732

· normalisation
­ ("standardisable candle"; "standard crayon") ­ different light curve fitters
· m15,SALT, SiFTO, MLCS


Required phenomenology
· Checks
­ selection effects? evolution?

Goobar & Leibundgut 2011


Systematics
· Current questions
­ calibration ­ restframe UV flux
· redshifted into the observable window · detect absorption

­ reddening and absorption
­ through colours or spectroscopic indicators ­ knowledge of absorption law

· correct for absorption

­ light curve fitters ­ selection bias

· sampling of different populations

­ gravitational lensing ­ brightness evolution


Supernova cosmology
· firmly established
­ general agreement between different experiments
Astier et al. 2006 Wood-Vasey et al. 2007 Kessler et al. 2009 Amanullah et al. 2010 Suzuki et al. 2011

580

0.271+0.014 - 0.014

0.068 - 1.013-+0.073

SALT2


What next?
· Already in hand
­ >1000 SNe Ia for cosmology ­ constant determined to 5% ­ accuracy dominated by systematic effects ­ good data at z>1
· light curves and spectra

· Missing

­ good infrared data at z>0.5

­ I-band Hubble diagram
· Freedman et al. · Nobili et al.

· cover the restframe B and V filters · move towards longer wavelengths to reduce absorption effects


I-band Hubble diagram
· Currently only 35 SNe Ia
Freedman et al. 2009

Union2 data set (557 SNe Ia) Goobar & Leibundgut 2011


Supernova Cosmology ­ do we need more?
· Test for variable
­ required accuracy ~2% in individual distances ­ can SNe Ia provide this?
· · · · can the systematics be reduced to this level? homogeneous photometry? further parameters (e.g. host galaxy metalicity) handle >100000 SNe Ia per year?

· Euclid

­ 3000 SNe Ia to z<1.2 with IR light curves (deep fields) I-band Hubble diagram ­ 16000 SNe discovered


Cosmology ­ more?

Goobar & Leibundgut 2011 (courtesy E. Linder and J. Johansson)


Distant SNe with CANDELS and CLASH
· Multi-cycle HST Treasury Programs

PIs: S. Faber/H. Fergusson

PI: M. Postman

HST MCT SN Survey
PI: A. Riess

SN discoveries and target-of-opportunity follow-up SNe Ia out to z2 Determine the SN rate at z>1 and constrain the progenitor systems


SN rates and what they can tell us

Graur et al. 2011


SNe at z>1
· First SN Ia at z=1.55 "Primo"

Rodney et al. 2012


Discovery
Rodney et al. 2012


Light curve
· WFC3 IR light curves

Rodney et al. 2012


Spectroscopy
· VLT spectrum of host galaxy
­ X-shooter (Frederiksen et al., in prep.)


Spectroscopy
· SN spectroscopy with ACS grism

Rodney et al. 2012


Predicting the future ...
· What will we know about supernovae 10 years from now?
­ ~5400 SNe reported until end of 2009 ­ expect up to 100000 SNe (?) for the coming decade
· PanSTARRS, PTF/PTF2, LSST


Summary
· Concentrate on not covered so far
­ particular IR is interesting
· reduced effect of reddening · better behaviour of SNe Ia(?)

· Understand the SN zoo
­ many (subtle?) differences observed in recent samples (PanSTARRS and PTF)
· subluminous and superluminous · see S. Taubenberger's poster for a prominent example (SN 2009dc)

­ understand potential evolutionary effects
· spectroscopy important PESSTO · DES?, LSST?, Euclid follow-up?