The quasar M_bh - M_host relation through Cosmic Time I - Dataset and black hole masses

We study the M_bh - M_host relation as a function of Cosmic Time in a sample of 96 quasars from z=3 to the present epoch. In this paper we describe the sample, the data sources and the new spectroscopic observations. We then illustrate how we derive M_bh from single-epoch spectra, pointing out the uncertainties in the procedure. In a companion paper, we address the dependence of the ratio between the black hole mass and the host galaxy luminosity and mass on Cosmic Time.