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

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...

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Detalles Bibliográficos
Autores: 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
Tipo de recurso: artículo
Estado:Versión publicada
Fecha de publicación:2015
País:Brasil
Institución:Universidade Federal do Rio Grande do Sul (UFRGS)
Repositorio:Repositório Institucional da UFRGS
Idioma:inglés
OAI Identifier:oai:www.lume.ufrgs.br:10183/116505
Acceso en línea:http://hdl.handle.net/10183/116505
Access Level:acceso abierto
Palabra clave:Galaxias seyfert
Galáxias ativas
Nucleo galatico
Astronomia infravermelha
Poeira cosmica
Espectros astronômicos
Galaxies: active
Galaxies: individual (NGC 6418)
Galaxies: nuclei
Galaxies: Seyfert
Descripción
Sumario: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.

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