14 March 2019
Europe/Warsaw timezone

Can reverberation-measured quasars be used for cosmology?

14 Mar 2019, 12:40


Dr Mary Loli Martínez-Aldama (CFT)


Quasars have been proposed as a new class of standard candles such as
Supernovae, their large redshift range and high luminosities make them
excellent candidates. Reverberation mapping (RM) method offers to
estimate the distance to the source from the time delay measurement of
the emission lines with respect to the continuum, since the time delay
depends on the absolute luminosity of the source. This radius-luminosity
(RL) relation showed a low scatter and was proposed to use for the
cosmological purposes. However, in the recent years the increase of the
studied sample, and in particular the inclusion of highly accreting QSO
has increased the dispersion in the RL relation, with many objects
showing time delays shorter than the expected. Using Hb RM
measurements for 117 sources with a 0.2<z<0.9 and
41.5<L5100<45.9, we find a correction for the time
delay based on the dimensionless accretion rate. With this correction we
are able to build a Hubble diagram, which is in a good agreement with
the standard cosmological model.On the other hand, using the excess of
variability, we find that departure from the RL relation is associated
with the variability. Therefore variability is anti-correlated with the
accretion rate, indicating that accretion rate is one of main drivers of
QSO properties. Large multi-epoch surveys like LSST will be provide
variability features, which can be used as a tool in order to derive
other AGN physical properties.

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