Is IRAS 01072+4954 a True-Seyfert 2?

Hints from near-infrared integral field spectroscopy

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: mvalencias@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh EH9 3HJ, UK

Received: 14 March 2012
Accepted: 31 May 2012

Abstract

In contrast to the predictions of the unified model, some X-ray unobscured Seyfert 2 galaxies have been discovered in the last decade. One of them, the starburst/Seyfert composite galaxy IRAS 01072+4954 (z = 0.0236), has a typical Type-1 X-ray emission, while its optical spectrum resembles an H ii galaxy and lacks the expected broad lines. We performed near-infrared integral-field observations of this object with the aim to determine the nature of its nuclear emission and to find indications for the existence or absence of a broad-line region. Several reasons have been proposed to explain this peculiar emission. We studied the validity of these hypotheses, including the possibility for this galaxy to be a True-Seyfert 2. We found little obscuration toward the nucleus A_V = 2.5   mag, and a nuclear star-formation rate Σ_SFR < 11.6   M_⊙   yr^-1   kpc^-2, which is below the average in Seyferts. Unresolved hot-dust emission with T ~ 1150   K seems to indicate the presence of a torus with its axis close to the line of sight. We found that IRAS 01072+4954 hosts a low-mass black hole with an estimated mass of M_BH ~ 10⁵   M_⊙. Its bolometric luminosity is L_bol ≃ 2.5 × 10⁴²   erg   s^-1, which yields a high accretion rate with an Eddington ratio λ_Edd ≃ 0.2. If the relations found in more massive systems also apply to this case, then IRAS 01072+4954 should show broad emission lines with a FWHM_broad ~ (400−600)   km   s^-1. Indeed, some indications for such narrow broad-line components are seen in our data, but the evidence is not yet conclusive. This source therefore does not seem to be a True-Seyfert 2, but an extreme case of a narrow-line Seyfert 1, which, due to the faintness of the active nucleus, does not have strong Fe ii emission in the optical.