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Spitzer space telescope measurements of dust reverberation lags in the Seyfert 1 galaxy NGC 6418

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Spitzer space telescope measurements of dust reverberation lags in the Seyfert 1 galaxy NGC 6418

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Título Spitzer space telescope measurements of dust reverberation lags in the Seyfert 1 galaxy NGC 6418
Autor Vasquez, Billy
Galianni, Pasquale
Richmond, Michael
Robinson, Andrew
Axon, David J.
Horne, Keith
Almeyda, Triana
Fausnaugh, Michael
Peterson, Bradley M.
Bottorff, Mark
Gallimore, Jack F.
Elitzur, Moshe
Netzer, Hagai
Storchi-Bergmann, Thaisa
Marconi, A.
Capetti, A.
Batcheldor, Dan
Buchanan, Catherine
Stirpe, Giovanna M.
Kishimoto, Makoto
Packham, Christopher
Pérez Jiménez, Enrique
Tadhunter, Clive
Upton, John
Estrada-Carpenter, Vicente
Abstract We present results from a 15 month campaign of high-cadence (∼3 days) mid-infrared Spitzer and optical (B and V) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). We find that the 3.6 and 4.5 μm flux variations lag behind those of the optical continuum by - 37.2+2.2 2.4 days and - 47.1+3.1 3.1 days, respectively. We report a cross-correlation time lag between the 4.5 and 3.6 μm flux of - 13.9+0.1 0.5 days. The lags indicate that the dust emitting at 3.6 and 4.5 μm is located at a distance ≈1 light-month (≈0.03 pc) from the source of the AGN UV–optical continuum. The reverberation radii are consistent with the inferred lower limit to the sublimation radius for pure graphite grains at 1800 K, but smaller by a factor of ∼2 than the corresponding lower limit for silicate grains; this is similar to what has been found for near-infrared (K-band) lags in other AGNs. The 3.6 and 4.5 μm reverberation radii fall above the K-band t ∝ L0.5 size–luminosity relationship by factors <~2.7 and <~3.4, respectively, while the 4.5 μm reverberation radius is only 27% larger than the 3.6 μm radius. This is broadly consistent with clumpy torus models, in which individual optically thick clouds emit strongly over a broad wavelength range.
Contido em The astrophysical journal. Bristol. Vol. 801, no. 2 (Mar. 2015), 127, 11 p.
Assunto Astronomia infravermelha
Espectros astronômicos
Galáxias ativas
Galaxias seyfert
Nucleo galatico
Poeira cosmica
[en] Galaxies: active
[en] Galaxies: individual (NGC 6418)
[en] Galaxies: nuclei
[en] Galaxies: Seyfert
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/116505
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