The Linear Point: a cleaner cosmological standard ruler in the galaxy correlation

  • June 11, 2018, 2:00 pm US/Central
  • Stefano Anselmi, Observatoire de Paris

Cosmology has made fundamental progress thanks to the role of standard rulers: objects of known size that are constant in redshift. The acoustic peak in the large scale structure clustering correlation function is one of them. However, in the era of precision cosmology, its power has been highly challenged by late time non-linear effects that shift its position in a redshift dependent way. To overcome this problem currently the distance measurements based on Baryon Acoustic Oscillations are realized at the price of highly increasing the difficult-to-quantify theoretical priors that may overestimate the precision and accuracy of the distance estimates.

Given the following limitations we propose a new way of looking at the Baryon Acoustic Oscillations! I will explain how we can evade non-linearities identifying a scale in the correlation function, called the “linear point”, that is an excellent cosmological standard ruler. Hence we measure the location of the linear point in the galaxy correlation function in the Twelfth Data Release (DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS) collaboration. We estimate cosmological distances without relying on the traditionally employed theoretical priors. Our remarkable result suggests that all the distance information contained in the Baryon Acoustic Oscillations can be conveniently compressed into the single length associated with the linear point.

Last but not least, the correlation function amplitude at the linear point is similarly insensitive to non-linear corrections to within a few percent. Therefore, exploiting the particular Baryon features in the correlation function, we propose three new estimators for growth measurements.