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

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT NGC 1448 is one of the nearest luminous galaxies (L 8−1000µm > 10 9 L ⊙ ) 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 N H (los) 2.5 × 10 24 cm −2 . The best-fitting torus models measured an intrinsic 2-10 keV luminosity of L 2−10,int = (3.5-7.6) × 10 40 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/TReCS, 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]λ5007Å emission line and the MIR 12µm continuum, further supporting the CT nature of the AGN.

A Long Hard-X-Ray Look at the Dual Active Galactic Nuclei of M51 with NuSTAR

“…The luminosity and Eddington ratio regime of M51a is an extremely low one, being the lowest luminosity Compton-thick AGN known, slightly less luminous than the recently identified low-luminosity CTAGN in NGC 1448 (Annuar et al 2017). This allows us to test various models of torus formation in a regime where the torus is predicted to disappear or be diminished.…”

The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV

“…Although the difference is only weakly significant, a similar result has also been reported for CT AGNs selected with SwiftBAT (Koss et al 2016a). Other studies, however, find that edge-on galaxy inclinations are not clearly related to CT absorption (e.g., Annuar et al 2017;Buchner & Bauer 2017). .…”

“…The observed X-ray-to-MIR luminosity ratio of a source can therefore give an independent, albeit indirect, assessment of the degree of obscuration (e.g., see Alexander 2017, for a recent review); the observed X-ray luminosity for any significantly absorbed AGN will be suppressed with respect to the intrinsic luminosity, causing it to deviate from the X-ray-to-MIR luminosity relation. This diagnostic has been utilized for other NuSTAR studies of obscured AGNs (e.g., Baloković et al 2014;Lansbury et al 2014Lansbury et al , 2015Stern et al 2014;Annuar et al 2015Annuar et al , 2017Gandhi et al 2017;LaMassa et al 2016). Figure 6 shows the observed X-ray versus intrinsic 6μm luminosities for the eight extreme NuSTAR serendipitous survey sources.…”

BAT AGN Spectroscopic Survey. V. X-Ray Properties of the Swift /BAT 70-month AGN Catalog

“…NuSTAR (Harrison et al 2013), launched in 2012, is the first on-orbit focusing hard X-ray telescope, and its serendipitous survey has detected 497 sources in the first 40 months of observations (Lansbury et al 2017b; see also Chen et al 2017). Thanks to its revolutionary characteristics, NuSTAR has been very efficient in constraining the properties of heavily obscured AGNs (e.g., Baloković et al 2014;Gandhi et al 2014;Stern et al 2014;Annuar et al 2015Annuar et al , 2017Brightman et al 2015;Koss et al 2015Koss et al , 2016bLansbury et al 2015Lansbury et al , 2017aBoorman et al 2016;Ricci et al 2016aRicci et al , 2016bRicci et al , 2017aRicci et al , 2017b. The recently launched mission AstroSat (Singh et al 2014) carries on board two hard X-ray instruments: the Large Area Xenon Proportional Counters (LAXPC; 3-80 keV) and the cadmiumzinc-telluride coded-mask imager (CZTI, 10-150 keV).…”