# Active Galactic Nucleus Pairs from the Sloan Digital Sky Survey. III. Chandra X-ray Observations Unveil Obscured Double Nuclei

## TL;DR

This study uses Chandra X-ray observations to confirm and analyze dual active galactic nuclei in merging galaxies, revealing obscured nuclei and differences in luminosity ratios compared to single AGNs, thus advancing understanding of galaxy mergers.

## Contribution

First X-ray confirmation of obscured dual AGNs in a systematically selected sample from SDSS, providing insights into their properties and merger-induced gas inflows.

## Key findings

- Confirmed two dual AGNs with X-ray observations.
- Observed lower X-ray-to-[O III] luminosity ratios in dual AGNs.
- Identified high nuclear gas columns likely from merger inflows.

## Abstract

We present Chandra ACIS-S X-ray imaging spectroscopy for five dual active galactic nucleus (AGN) candidates. Our targets were drawn from a sample of 1286 [O III]-selected AGN pairs systematically selected from the Sloan Digital Sky Survey Seventh Data Release. Each of the targets contains two nuclei separated by $\sim$3-9 kpc in projection, both of which are optically classified as Type 2 (obscured) AGNs based on diagnostic ratios of the narrow emission lines. Combined with independent, empirical star formation rate estimates based on the host-galaxy stellar continua, the new Chandra X-ray observations allow us to evaluate the dual-AGN hypothesis for each merging system. We confirm two (SDSS J0907+5203 and SDSS J1544+0446) of the five targets as bona-fide dual AGNs. For the other three targets, the existing data are consistent with the dual-AGN scenario, but we cannot rule out the possibility of stellar/shock heating and/or one AGN ionizing both gaseous components in the merger. The average X-ray-to-[O III] luminosity ratio in our targets seems to be systematically smaller than that observed in single AGNs but is higher than that seen in dual AGNs selected from AGNs with double-peaked narrow emission lines. We suggest that the systematically smaller X-ray-to-[O III] luminosity ratio observed in dual AGNs than in single AGNs is due to a high nuclear gas column likely from strong merger-induced inflows. Unlike double-peaked-[O III]-selected dual AGNs, the new sample selected from resolved galaxy pairs are not subject to the orientation bias caused by the double-peak line-of-sight velocity splitting selection, which also contributes to lowering the X-ray-to-[O III] luminosity ratio.