B15 - Mapping the Hubble flow with supernovae
Principal Investigators: B. Leibundgut, W. Hillebrandt (Garching)
The quality of supernovae as cosmic distance indicators remains unique. Over the past years the diversity of Type Ia supernovae has become apparent and the characterisation of the extreme objects promises to shed light on the progenitor systems and the different explosion mechanisms. This will provide a better physical description of the Type Ia class and objective criteria to select the best objects for distance determinations. One of the biggest obstacles remains the accurate photometric calibration which we plan to improved through physical methods independent of standard star measurements.
Ongoing surveys for variable objects (SNFactory, PanSTARRS
, Palomar Transient Factory) find more supernovae than ever before. We are members of several of these collaborations and are organised in massive follow-up surveys (PESSTO). Deviations from a universal expansion (Hubble) flow can now be detected with these extensive data sets. These are signatures of (Dark) Matter concentrations and provide a measurement of the local mass distribution, e.g. needed for a comparison of the Hubble constant determined using distant probes, such as the CMB, with that obtained in the nearby Universe using SNe.
The expanding photosphere method (EPM) for massive stellar explosions provides a completely independent way to measure absolute distances and the Hubble parameter out to a redshift of about 0.3 with current 10m-class telescopes. This method requires a good physical model of the explosion calculated by a dedicated photospheric code adapted from the existing codes developed at the MPA and observational spectral and photometric series. The latter are provided by the ongoing observational surveys. These distances are derived independently of SNe Ia. Decreasing the uncertainty on the Hubble constant directly decreases the uncertainty in the equation of state parameter of Dark Energy, w, when combined with the accurate geometric measure of space as provided by the Planck satellite.