Sub-percent calibration of the extragalactic distance scale in the era of big surveys

After detection of the accelerated expansion of the Universe (Nobel prize 2011) and the existence of an enigmatic “dark energy” component of the matter-energy content of the Universe the physical explanation of the nature of dark energy has become a major challenge for astronomers and physicists in recent years.

The recent empirical determinations of H0 complicated even more our understanding of the Universe since they differ by about 4σ from the value obtained from Planck data and the ΛCDM model, which suggest that new physics might be required in the models.We will calibrate two geometrical methods which will yield 1% distances a thousand times further out than Gaia parallaxes.

The great advantage of our approach is the full control on all potential errors affecting the distance determinations, including systematic errors elusive in most other methods.

In addition, we will provide mutual crosschecks at the sub-percent accuracy level with three completely independent geometrical methods.

This will allow for the first time to verify the accuracy (and not only precision) at this unprecedented level of precision. Applying these methods we will calibrate the extragalactic distance scale with an unprecedented precision and accuracy. This will allow for a 1% H0 determination with Cepheids and SN Ia.

Novel reverberation studies of AGN continua will allow us to determine H0 completely independently, and provide direct insight into the larger redshift Universe, including the H(z) dependence which will constrain other cosmological parameters.Our results will have strong impact on many fields of modern astrophysics.

In particular they will definitively answer the question if new physics beyond the standard cosmological model is required.

They will also be central to understand the physical nature of dark energy which constitutes about 72% of the matter-energy of the Universe.