HST unveils a compact mildly relativistic broad-line region in the candidate true type 2 NGC 3147

NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad-line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the...

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Detalles Bibliográficos
Autores: Bianchi, Stefano, Antonucci, Robert, Capetti, Alessandro, Chiaberge, Marco, Laor, Ari, Bassani, Loredana, Carrera, Francisco J., La Franca, Fabio, Marinucci, Andrea, Matt, Giorgio, Middei, Riccardo, Panessa, Francesca
Tipo de recurso: artículo
Estado:Versión publicada
Fecha de publicación:2019
País:España
Institución:Consejo Superior de Investigaciones Científicas (CSIC)
Repositorio:DIGITAL.CSIC. Repositorio Institucional del CSIC
OAI Identifier:oai:digital.csic.es:10261/213182
Acceso en línea:http://hdl.handle.net/10261/213182
Access Level:acceso abierto
Palabra clave:Galaxies: active
Galaxies: individual: NGC3147
Galaxies: Seyfert
Descripción
Sumario:NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad-line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the dominant background host galaxy. Narrow (0.1 arcsec × 0.1 arcsec) slit HST spectroscopy allowed us to exclude most of the host galaxy light, and revealed an H α line with an extremely broad base (FWZI∼27000 km s−1). The line profile shows a steep cut-off blue wing and an extended red wing, which match the signature of a mildly relativistic thin accretion disc line profile. It is indeed well fit with a nearly face on thin disc, at i ∼ 23°, with an inner radius at 77 ± 15 rg, which matches the prediction of 62+18−14rg from the RBLR–L1/2 relation. This result questions the very existence of true type 2 AGN. Moreover, the detection of a thin disc, which extends below 100 rg in an L/LEdd ∼ 10−4 system, contradicts the current view of the accretion flow configuration at extremely low accretion rates.

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