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A new Compton-thick AGN in our cosmic backyard : unveiling the buried nucleus in NGC 1448 with NuSTAR.

Annuar, A. and Alexander, D.M. and Gandhi, P. and Lansbury, G.B. and Asmus, D. and Ballantyne, D.R. and Bauer, F.E. and Boggs, S.E. and Boorman, P.G. and Brandt, W.N. and Brightman, M. and Christensen, F.E. and Craig, W.W. and Farrah, D. and Goulding, A.D. and Hailey, C.J. and Harrison, F.A. and Koss, M.J. and LaMassa, S.M. and Murray, S.S. and Ricci, C. and Rosario, D.J. and Stanley, F. and Stern, D. and Zhang, W. (2017) 'A new Compton-thick AGN in our cosmic backyard : unveiling the buried nucleus in NGC 1448 with NuSTAR.', Astrophysical journal., 836 (2). p. 165.


NGC 1448 is one of the nearest luminous galaxies (L8−1000μm> 109L⊙) to ours (z = 0.00390), and yet the active galactic nucleus (AGN) it hosts was only recently discovered, in 2009. In this paper, we present an analysis of the nuclear source across three wavebands: mid-infrared (MIR) continuum, optical, and X-rays. We observed the source with the Nuclear Spectroscopic Telescope Array (NuSTAR), and combined this data with archival Chandra data to perform broadband X-ray spectral fitting (≈0.5-40 keV) of the AGN for the first time. Our X-ray spectral analysis reveals that the AGN is buried under a Compton-thick (CT) column of obscuring gas along our line-of-sight, with a column density of NH(los) ≳ 2.5 × 1024 cm−2. The best-fitting torus models measured an intrinsic 2-10 keV luminosity of L2−10,int = (3.5-7.6) × 1040 erg s−1, making NGC 1448 one of the lowest luminosity CTAGNs known. In addition to the NuSTAR observation, we also performed optical spectroscopy for the nucleus in this edge-on galaxy using the European Southern Observatory New Technology Telescope. We re-classify the optical nuclear spectrum as a Seyfert on the basis of the Baldwin-Philips-Terlevich diagnostic diagrams, thus identifying the AGN at optical wavelengths for the first time. We also present high spatial resolution MIR observations of NGC 1448 with Gemini/T-ReCS, in which a compact nucleus is clearly detected. The absorption-corrected 2-10 keV luminosity measured from our X-ray spectral analysis agrees with that predicted from the optical [OIII]λ5007\AA\ emission line and the MIR 12μm continuum, further supporting the CT nature of the AGN.

Item Type:Article
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Publisher statement:© 2017. The American Astronomical Society. All rights reserved.
Date accepted:27 December 2016
Date deposited:26 January 2017
Date of first online publication:17 February 2017
Date first made open access:No date available

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