Stacked reverberation lags at high redshift
  Over the past 20years reverberation mapping has proved one of the most
successful techniques for studying the local (<1pc) environment of
super-massive black holes that drive active galactic nuclei. Key successes of
reverberation mapping have been direct black hole mass estimates, the
radius-luminosity relation for the Hbeta line and the calibration of
single-epoch mass estimators commonly employed up to z~7. However, observing
constraints mean that few studies have been successful at z>0.1, or for the
more-luminous quasars that make up the majority of current spectroscopic
samples, or for the rest-frame ultra-violet emission lines available in optical
spectra of z>0.5 objects.
  Previously we described a technique for stacking cross correlations to obtain
reverberation mapping results at high z. Here we present the first results from
a campaign designed for this purpose. We construct stacked cross-correlation
functions for the CIV and MgII lines and find a clear peak in both. We find the
peak in the MgII correlation is at longer lags than CIV consistent with
previous results at low redshift. For the CIV sample we are able to bin by
luminosity and find evidence for increasing lags for more-luminous objects.
This CIV radius-luminosity relation is consistent with previous studies but
with a fraction of the observational cost.
