The soft X-ray counterpart of Hanny's Voorwerp near IC 2497

TL;DR

This study reports the detection of a soft X-ray feature associated with Hanny's Voorwerp near IC 2497, suggesting it is an ionization cone emission from a nearby active galactic nucleus, with implications for understanding AGN activity history.

Contribution

First detection of a soft X-ray counterpart to Hanny's Voorwerp, linking it to AGN ionization cones and providing insights into AGN activity timescales.

Findings

Soft X-ray feature has luminosity ~1.2x10^40 erg/s.

X-ray to [OIII] ratio is consistent with AGN ionization cones.

Extended soft X-ray components trace long-term AGN activity.

Abstract

We report the detection in Chandra ACIS archival data of an elongated soft (<3 keV) X-ray feature tp the south of the Compton Thick Active Galactic Nucleus (CT AGN) galaxy IC 2497, coincident with the emission feature known as Hanny's Voorwerp (HV). The data are consistent with the spatial correspondence between X-ray, optical emission line, and radio features detected in nearby obscured AGNs (e.g., ESO 428-G014). The X-ray luminosity of the (0.3-3.0 keV) soft feature is ~1.2x10^40 erg/s. We infer an [OIII]/Soft-X-ray ratio in the range of ~200, consistent with the highest values measured in some of the clouds of NGC 4151. Overall, given the uncertainties, Hanny's Voorwerp appears to be a feature consistent with the ionization cone emission of nearby AGNs. We estimate an X-ray recombination time of 2x10^7 yr, longer than the [OIII] recombination time (~8000 yr). This suggests that extended soft X-ray components may be a better diagnostic of overall long-term activity, while detection of an [OIII] HV would point to a time-limited activity burst.