Ensemble power spectral density of SDSS quasars in UV/optical bands
arxiv(2024)
摘要
Context: Quasar variability has proven to be a powerful tool to constrain the
properties of their inner engine and the accretion process onto supermassive
black holes. Correlations between UV/optical variability and physical
properties have been long studied with a plethora of different approaches and
time-domain surveys, although the detailed picture is not yet clear. Aims: We
analysed archival data from the SDSS Stripe-82 region to study how the quasar
power spectral density (PSD) depends on the black hole mass, bolometric
luminosity, accretion rate, redshift, and rest-frame wavelength. We developed a
model-independent analysis framework that could be easily applied to upcoming
large surveys such as the Legacy Survey of Space and Time (LSST). Methods: We
used light curves of 8042 spectroscopically confirmed quasars, observed in at
least six yearly seasons in five filters ugriz. We split the sample into bins
of similar physical properties containing at least 50 sources, and we measured
the ensemble PSD in each of them. Results: We find that a simple power law is a
good fit to the power spectra in the frequency range explored. Variability does
not depend on redshift at a fixed wavelength. Instead, both PSD amplitude and
slope depend on the black hole mass, accretion rate, and rest-frame wavelength.
We provide scaling relations to model the observed variability as a function of
the physical properties, and discuss the possibility of a universal PSD shape
for all quasars, where frequencies scale with the black hole mass, while
normalization and slope(s) are fixed (at any given wavelength and accretion
rate).
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