Disclosing the properties of low-redshift dual AGN through XMM-Newton and SDSS spectroscopy

TL;DR

This study combines optical and X-ray observations to analyze four dual AGN systems at low redshift, revealing high obscuration levels likely driven by galaxy interactions, and compares these properties with larger AGN samples.

Contribution

It provides new insights into the obscuration properties of dual AGN at low redshift using combined SDSS and XMM data, highlighting the role of galaxy encounters in increasing obscuration.

Findings

All sources detected in X-ray band; seven are Seyfert, one LINER likely powered by accretion.

Majority of dual AGN are obscured in X-rays, with some likely Compton-thick.

Obscured AGN fraction in dual systems is higher than in isolated galaxies, suggesting interaction-driven obscuration.

Abstract

We report on an optical (SDSS) and X-ray (XMM) study of an optically selected sample of four dual AGN systems at projected separations of 30--60~kpc. All sources are detected in the X-ray band (0.3-10 keV); seven objects are optically identified as Seyfert, while one source, optically classified as a LINER, is likely powered by accretion in virtue of its relatively high X-ray luminosity (1.2$\times10^{41}$ erg/s). Six of the eight objects are obscured in X-rays with N$_{\rm H} \geq$ 10$^{23}$ cm$^{-2}$; three of these, whose X-ray spectrum is dominated by a reflection component, are likely Compton-thick (N$_{\rm H} \geq$ 10$^{24}$ cm$^{-2}$). This finding is in agreement with the hypothesis that galaxy encounters are effective in driving gas inflow toward the nuclear region, thus increasing the obscuration. We compare the absorption properties in our dual AGN with those in larger samples observed in X-rays but selected in different ways (optical, IR and hard X-rays). We find that the obscured (N$_{\rm H} \geq$ 10$^{22}$ cm$^{-2}$) AGN fraction within the larger sample is 84$\pm$4 per cent (taking into account the 90 per cent error on the N$_{\rm H}$ measure) up to large pair separations ($\sim$100~kpc). This is statistically higher than the fraction of obscured AGN in isolated galaxies found in X-ray surveys.