Mickael Rigault (HU Berlin)

Environmental dependencies in Type Ia supernova luminosity, and their consequences on cosmological measurements
When Dec 16, 2014 from 11:00 AM to 12:00 PM
What
  • Special Seminar
  • Colloquium
Where SH, Lecture Hall
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Use of Type Ia supernovae (SNe Ia) as distance indicators has proven to be a powerful technique for measuring the dark energy equation of state and the Hubble Constant. However, their progenitor remains largely unknown and bias may arise from unaccounted for stellar variation that could impact the way the progenitor-star evolves in SN Ia.

In this talk I will present the results of a study of host galaxy regions in close proximity to SNe Ia. We find a significant offset in SNe~Ia standardized magnitude between these from locally star-forming regions and those from passive regions. (Rigault et al 2013) Since the fraction of SNe Ia from passive region is expected to decrease with redshift and/or to vary between samples, such a magnitude bias, introduces a bias in distance measurements using these standardizable candles.

We discover that this effect impacts the measurement of the Hubble by 3%, which explains the current tension between the indirect- (from CMB) and direct-measurements of this constant. (Rigault et al submitted)

Systematic errors are today dominating the error budget of cosmological constant measurement (such as w). In this context, local host informations of SNe~Ia are precious to better understand this probe. In the near future, these informations will enable us to improve their use as standardisable candles. As an example, I will show that a simple environmental selection of SNe Ia allow to significantly reduce the dispersion of the Hubble diagram by 30%.