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arXiv · 1704.01595

AGN with discordant optical and X-ray classification are not a physical family: Diverse origin in two AGN

I. Ordovás-Pascual·S. Mateos·F. J. Carrera·K. Wiersema·X. Barcons·V. Braito·A. Caccianiga·A. Del Moro·R. Della Ceca·P. Severgnini
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Abstract

Approximately 3-17 percent of Active Galactic Nuclei (AGN) without detected rest-frame UV/optical broad emission lines (type-2 AGN) do not show absorption in X-rays. The physical origin behind the apparently discordant optical/X-ray properties is not fully understood. Our study aims at providing insight into this issue by conducting a detailed analysis of the nuclear dust extinction and X-ray absorption properties of two AGN with low X-ray absorption and with high optical extinction, for which a rich set of high quality spectroscopic data is available from XMM-Newton archive data in X-rays and XSHOOTER proprietary data at UV-to-NIR wavelengths. In order to unveil the apparent mismatch, we have determined the A$_{\rm V}$/N$_{\rm H}$ and both the Super Massive Black Hole (SMBH) and the host galaxy masses. We find that the mismatch is caused in one case by an abnormally high dust-to-gas ratio that makes the UV/optical emission to appear more obscured than in the X-rays. For the other object we find that the dust-to-gas ratio is similar to the Galactic one but the AGN is hosted by a very massive galaxy so that the broad emission lines and the nuclear continuum are swamped by the star-light and difficult to detect.

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I. Ordovás-Pascual, S. Mateos, F. J. Carrera, K. Wiersema, X. Barcons, V. Braito, A. Caccianiga, A. Del Moro, R. Della Ceca, P. Severgnini. 2017-04-05. AGN with discordant optical and X-ray classification are not a physical family: Diverse origin in two AGN. https://doi.org/10.1093/mnras/stx862

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