A New Compton-thick AGN in Our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR

NGC 1448 is one of the nearest luminous galaxies (L 8-1000μm >109 L o) 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 these 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 N H(los) ≥2.5 ×1024 cm-2.

The best-fitting torus models measured an intrinsic 2-10 keV luminosity of L (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 [O iii]λ5007 Å emission line and the MIR 12 μm continuum, further supporting the CT nature of the AGN.