Misc,
Characterizing Quasar CIV Emission-line Measurements from Time-resolved Spectroscopy
(2020)cite arxiv:2007.15120Comment: Submitted to ApJ June 19, 2020, Accepted July 13, 2020.
Abstract
We use multi-epoch quasar spectroscopy to determine how accurately
single-epoch spectroscopy can locate quasars in emission-line parameter space
in order to inform investigations where time-resolved spectroscopy is not
available. We explore the improvements in emission-line characterization that
result from using non-parametric information from many lines as opposed to a
small number of parameters for a single line, utilizing reconstructions based
on an independent component analysis applied to the data from the Sloan Digital
Sky Survey Reverberation Mapping project. We find that most of the quasars are
well described by just two components, while more components signal a quasar
likely to yield a successful reverberation mapping analysis. In single-epoch
spectroscopy the apparent variability of equivalent width is exaggerated
because it is dependent on the continuum. Multi-epoch spectroscopy reveals that
single-epoch results do not significantly change where quasars are located in
CIV parameter space and do not have a significant impact on investigations of
the global Baldwin Effect. Quasars with emission line properties indicative of
higher $L/L_Edd$ are less variable, consistent with models with enhanced
accretion disk density. Narrow absorption features at the systemic redshift may
be indicative of orientation (including radio-quiet quasars) and may appear in
as much as 20% of the quasar sample. Future work applying these techniques to
lower luminosity quasars will be important for understanding the nature of
accretion disk winds.
