Spatially resolved Fe K spectroscopy of NGC 4945

Abstract

We present the imaging and spectroscopic analysis of the combined Chandra ACIS-S observations of the Compton-thick Seyfert 2 galaxy NGC 4945. We performed a spatially-resolved spectroscopy of the circumnuclear environment of the source, picturing the innermost 200 parsecs around the highly absorbed nucleus. The additional 200 ks ACIS-S data with respect to the previous campaign allowed us to map with even greater detail the central structure of this source and to discover an enhanced iron emission in the innermost nuclear region, with respect to the associated Compton reflection continuum. We revealed that the Equivalent Width of the iron Kα line is spatially variable (ranging from 0.5 to 3 keV), on scales of tens of parsecs, likely due to the ionization state and orientation effects of the reprocessing material, with respect to the central X-ray illuminating source. A clump of highly ionized Fe xxv He-α is also detected, 40 parsecs east to the nucleus. When observations taken years apart are considered, the central unresolved reflected emission is found to remain constant.

Chandra Observations of Excess Fe Kα Line Emission in Galaxies with High Star Formation Rates: X-Ray Reflection on Galaxy Scales?

“…We interpret this relation as being due to reflection of nuclear emission by the star-forming gas that is typically distributed on galaxy scales. This observed relationship clearly indicates that nuclear emission from AGN can be strongly affected by gas and dust in the host galaxy (e.g., Hickox & Alexander 2018;Circosta et al 2019;D'Amato et al 2020) Considering this result in the context of previous discoveries of extended iron line limited in nearby CT AGNs (e.g., Bauer et al 2015;Gandhi et al 2015;Fabbiano et al 2017;Marinucci et al 2017), our analysis suggests that Fe line reflection on galaxy scales may be a widespread phenomenon in AGN at moderate to high redshifts. Furthermore, the presence of extended Fe Kα line emission in distant AGN presents a challenge in modeling of their X-ray spectra, which is often carried out assuming absorption and reflection as the result of a small (parsec-scale) torus rather than galaxy-scale material (e.g., Netzer 2015;Brightman et al 2017;Baloković et al 2018;Panagiotou & Walter 2019).…”

“…It is generally assumed that iron line photons are produced by reflection from obscuring material in a small-scale (∼1-100 pc) region by interacting with the dense circumnuclear "torus" (e.g., Shu et al 2010;Ricci et al 2014). However, recent Chandra X-ray Observatory studies of nearby obscured AGNs (e.g., Bauer et al 2015;Gandhi et al 2015;Fabbiano et al 2017;Marinucci et al 2017;Jones et al 2020;Yi et al 2021) also discovered kiloparsecscale diffuse emission of the iron line, suggesting additional reflection of the X-ray emission extending to galactic scales well beyond the parsec-scale "torus". These direct observations of the extended Fe Kα emission are limited to low-redshift obscured AGNs, for which the kiloparsec-scale structures can be resolved by Chandra.…”

Tracking the iron K α line and the ultra fast outflow in NGC 2992 at different accretion states

“…We produced a grid model for xspec using cloudy 17 (last described by Ferland et al 2017). It is an extension of the same model used in Bianchi et al (2010); Marinucci et al (2011Marinucci et al ( , 2017. Grid parameters are log U = [−2.00 : 4.00], step 0.25, log NH = [19.0 : 23.5], step 0.1.…”

Second Epoch ALMA Observations of 321 GHz Water Maser Emission in NGC 4945 and the Circinus Galaxy

“…(X-ray luminosity: L X ∼ 4 × 10 43 erg s −1 ) buried in the Compton-thick nucleus (e.g., Marinucci et al 2017). The X-ray luminosity is highly variable with a time scale of ∼1 day, suggesting that the size scale of X-ray emitting region is no more than ∼0.001 pc (Madejski et al 2000), however it is uncertain whether this compact X-ray region is responsible for the decreased maser intensities over the four years.…”