Evidence from the Very Long Baseline Array that J1502SE/SW are Double Hotspots, not a Supermassive Binary Black Hole

TL;DR

High-resolution VLBA observations of SDSS J150243.09+111557.3 reveal a double-hotspot structure in the obscured AGN, challenging previous interpretations of a supermassive binary black hole system and suggesting alternative feedback mechanisms.

Contribution

The paper provides higher sensitivity VLBA imaging evidence supporting the double-hotspot scenario over the binary black hole interpretation for J1502SE/SW.

Findings

Evidence of edge-brightened double-hotspot structure in VLBA images.

Reconsideration of the binary black hole hypothesis for J1502SE/SW.

Detection of high-brightness emission from the unobscured AGN.

Abstract

SDSS J150243.09+111557.3 is a merging system at z = 0.39 that hosts two confirmed AGN, one unobscured and one dust-obscured, offset by several kiloparsecs. Deane et al. recently reported evidence from the European VLBI Network (EVN) that the dust-obscured AGN exhibits two flat-spectrum radio sources, J1502SE/SW, offset by 26 mas (140 pc), with each source being energized by its own supermassive black hole (BH). This intriguing interpretation of a close binary BH was reached after ruling out a double-hotspot scenario, wherein both hotspots are energized by a single, central BH, a configuration occuring in the well-studied Compact Symmetric Objects. When observed with sufficient sensitivity and resolution, an object with double hotspots should have an edge-brightened structure. We report evidence from the Very Long Baseline Array (VLBA) for just such a structure in an image of the obscured AGN with higher sensitivity and resolution than the EVN images. We thus conclude that a double-hotspot scenario should be reconsidered as a viable interpretation for J1502SE/SW, and suggest further VLBA tests of that scenario. A double-hotspot scenario could have broad implications for feedback in obscured AGNs. We also report a VLBA detection of high-brightness-temperature emssion from the unobscured AGN that is offset several kiloparsecs from J1502SE/SW.