Kavli Affiliate: Claudio Ricci
| First 5 Authors: Kriti K. Gupta, Claudio Ricci, Matthew J. Temple, Alessia Tortosa, Michael J. Koss
| Summary:
We present one of the largest multiwavelength studies of simultaneous
optical-to-X-ray spectral energy distributions (SEDs) of unobscured active
galactic nuclei (AGN) in the local Universe. Using a representative sample of
hard-X-ray-selected AGN from the 70-month Swift/BAT catalog, with optical/UV
photometric data from Swift/UVOT and X-ray spectral data from Swift/XRT, we
constructed broadband SEDs of 236 nearby AGN (0.001<z<0.3). We employed GALFIT
to estimate host galaxy contamination in the optical/UV and determine the
intrinsic AGN fluxes. We used an absorbed power law with a reflection component
to model the X-ray spectra and a dust-reddened multi-temperature blackbody to
fit the optical/UV SED. We calculated total bolometric luminosities
($L_{bol}$), optical-to-X-ray spectral indices ($alpha_{ox}$), and multiple
bolometric corrections (BCs) in the optical, UV, and X-rays. We used black hole
masses obtained by reverberation mapping and the virial method to estimate
Eddington ratios ($lambda_{Edd}$) for all our AGN. We confirm the tight
correlation between UV and X-ray luminosity for our sample. We observe a
significant decrease in $alpha_{ox}$ with $L_{bol}$ and $lambda_{Edd}$,
suggesting that brighter sources emit more UV photons per X-rays. We report a
second-order regression relation between the 2-10 keV BC and $alpha_{ox}$,
which is useful to compute $L_{bol}$ in the absence of multiband SEDs. We also
investigate the dependence of optical/UV BCs on the physical properties of AGN
and obtain a significant increase in the UV BCs with $L_{bol}$ and
$lambda_{Edd}$, unlike those in the optical, which are constant across five
orders of $L_{bol}$ and $lambda_{Edd}$. We obtain significant dispersions
(~0.1-1 dex) in all BCs, and hence recommend using appropriate relations with
observed quantities while including the reported scatter, instead of their
median values.
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