The 2MIG isolated AGNs -- 2. X-ray general properties and peculiarities

TL;DR

This study analyzes the X-ray properties of isolated AGNs to determine if their nuclear activity differs from those in denser environments, finding no significant differences and discovering a new correlation between luminosity and SMBH mass.

Contribution

First comprehensive X-ray analysis of isolated AGNs, revealing a new luminosity-mass correlation and identifying potential Milky Way analogues.

Findings

Isolation does not significantly affect nuclear activity.

Diversity of accretion types observed among isolated AGNs.

A new linear correlation between X-ray luminosity and SMBH mass was identified.

Abstract

We have analyzed a sample of 2MIG isolated galaxies hosting AGNs (isolated AGNs) to assess whether their nuclear activity differs from that in a denser environment. The isolation criteria rule out interactions with other galaxies of similar size for at least $\sim$3 Gyr. We systemized the available Swift, NuSTAR, XMM-Newton, Chandra, and INTEGRAL X-ray data for isolated AGN at $z<0.05$, determining their general X-ray properties and peculiarities, spectral models, SMBH masses, and possible parameter correlations. We investigated the best spectral models of 25 isolated AGNs, including 10 recently fitted in this work. The intrinsic luminosities $\log L_{2-10,\mathrm{keV}}$ do not exceed $\sim43$. Our results indicate that the isolation of galaxies in the nearby Universe does not significantly affect nuclear activity. This is confirmed by the diversity of accretion types and the absence of any advantage of one particular basic/compound spectral model. We note an interesting case discovered for the ESO499-041 spectrum, where the data-to-model ratio shows significant changes after 6.4 keV. These deviations from the continuum may indicate the presence of a relativistic Iron line in the Chandra spectrum of ESO 499-041 compared to the Swift spectrum. Most isolated AGNs contain SMBH with $M_{\mathrm{SMBH}} \leq 10^7,M_{\odot}$. For the first time, we found a linear correlation between $L_{2-10,\mathrm{keV}}$ and $\log M_{\mathrm{SMBH}}$ that is not observed in other AGN samples. This trend may be affected by the limited sample size and requires further confirmation with larger datasets. Finally, we identified UGC10120, NG6300, and CGCG243-024 as promising candidates for Milky Way analogues.