Speaker: Thomas de Jaeger (UC Berkeley)
Title: Type II supernova cosmology: past and future
Measuring accurate extragalactic distances is one of the most challenging tasks in Astronomy but remains one of the best observational probes to understand the Universe's content. For more than two decades, Type Ia supernovae (SNe Ia) have been used as standard candles to measure extragalactic distances with an accuracy of 5-6%. In 1998, SNe Ia led to the measurement of the Universe expansion history and revealed the surprising accelerated growth rate of the Universe driven by an unknown effect attributed to dark energy. However, even if SN Ia cosmology is one of the most mature methods, the nature of the dark energy remains unknown. The precise value of the Universe expansion rate H0 is also vigorously debated and a 3sigma discrepancy is seen between measurements from SNe Ia calibrated using Cepheid stars and the baryon acoustic oscillations calibrated using the cosmic microwave background radiation. Since truth will likely emerge from the combination of different independent approaches, it is essential to develop as many methods as possible.
Among the new techniques found in the literature, one of the most interesting for deriving accurate distances and measuring cosmological parameters is the use of Type II supernovae. Even though detecting SNe II at high redshift is challenging owing to their relatively low luminosity, their use as cosmic distance indicators is motivated by the fact that their progenitors and environments are better understood than those of SNe Ia. The SN II family displays a large range of peak luminosities; but as for SNe Ia, their extrinsic differences can be calibrated. In this talk, after giving an overview of all the techniques available in the literature I will present in details the Standard Candle Method which is the most used method. I will show our ability to extend the current SN II Hubble diagram beyond z = 0.3 and derive the cosmological parameters. As the coming era of large photometric wide-field surveys will increase the detection rate of supernovae by orders of magnitude, which will prohibit spectroscopic follow-up in the vast majority of cases, I will also present a new method to standardise SNe II based on photometric parameters.