2006/01/31 by M. Chiaberge, R. Gilli, F. Macchetto +2 · 3 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/508131
published as Astrophys.J.651:728-734,2006 · 7 pages, 6 figures, accepted for publication in the Astrophysical Journal
arxiv created 2006/07/26 · openalex publication_date 2006/11/02 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We derive the spectral energy distribution (SED) of the nucleus of the Seyfert galaxy NGC 4565. Despite its classification as a Seyfert 2, the nuclear source is substantially unabsorbed. The absorption we find from Chandra data ( N H = 2.5 × 10 21 cm -2 ) is consistent with that produced by material in the galactic disk of the host galaxy. HST images show a nuclear unresolved source in all of the available observations, from the near-IR H band to the optical U band. The SED is completely different from that of Seyfert galaxies and QSOs, as it appears basically "flat" in the IR-optical region, with a small drop-off in the U band. The location of the object in diagnostic planes for low-luminosity AGNs excludes a jet origin for the optical nucleus, and its extremely low Eddington ratio L o / L Edd indicates that the radiation we observe is most likely produced in a radiatively inefficient accretion flow. This would make NGC 4565 the first AGN in which an ADAF-like process is identified in the optical. We find that the relatively high [O III] flux observed from the ground cannot be all produced in the nucleus. Therefore, an extended NLR must exist in this object. This may be interpreted in the framework of two different scenarios: (1) the radiation from ADAFs is sufficient to give rise to high-ionization emission-line regions through photoionization, or (2) the nuclear source has recently "turned off," switching from a high-efficiency accretion regime to the present low-efficiency state.