NGC5252: a pair of radio-emitting active galactic nuclei?

TL;DR

This study uses high-resolution VLBI observations to reveal that NGC 5252 hosts a pair of active galactic nuclei, both emitting in radio, indicating a rare dual AGN system with compact, high-luminosity radio sources.

Contribution

First high-resolution VLBI imaging of NGC 5252's radio source, confirming it as a dual AGN system with both nuclei showing compact, radio-luminous emission.

Findings

Radio counterpart is remarkably compact and unresolved at milliarcsecond resolution.

Both nuclei exhibit similar radio properties, consistent with low-luminosity AGN.

The system is a rare example of a dual active galactic nuclei pair.

Abstract

The X-ray source CXO J133815.6+043255 has counterparts in the UV, optical, and radio bands. Based on the multi-band investigations, it has been recently proposed by Kim et al. (2015) as a rarely-seen off-nucleus ultraluminous X-ray (ULX) source with a black hole mass of >= 10^4 solar mass in the nearby Seyfert galaxy NGC 5252. To explore its radio properties at very high angular resolution, we performed very long-baseline interferometry (VLBI) observations with the European VLBI Network (EVN) at 1.7 GHz. We find that the radio counterpart is remarkably compact among the known ULXs. It does not show a resolved structure with a resolution of a few milliarcsecond (mas), and the total recovered flux density is comparable to that measured in earlier sub-arcsecond-resolution images. The compact radio structure, the relatively flat spectrum, and the high radio luminosity are consistent with a weakly accreting supermassive black hole in a low-luminosity active galactic nucleus. The nucleus of NGC 5252 itself has similar radio properties. We argue that the system represents a relatively rare pair of active galactic nuclei, where both components emit in the radio.