Deep VLBI Observations Challenge Previous Evidence of a Binary Supermassive Black Hole Residing in the Seyfert Galaxy NGC 7674

TL;DR

Deep VLBI observations of NGC 7674 refute previous claims of a binary supermassive black hole, setting strict upper limits on radio core flux densities and challenging earlier interpretations based on VLBA data.

Contribution

This study reanalyzes VLBI data to disprove the existence of a binary SMBH in NGC 7674, providing more stringent flux limits and discussing implications for future observations.

Findings

No evidence of binary SMBH from multi-epoch VLBI data

Stringent upper limits on sub-pc-scale radio core flux densities

Challenges previous VLBA-based binary SMBH detection claims

Abstract

Previous Ku-band (15 GHz) imaging with data obtained from the Very Long Baseline Array (VLBA) had shown two compact, sub-pc components at the location of a presumed kpc-scale radio core in the Seyfert galaxy NGC 7674. It was then presumed that these two unresolved and compact components were dual radio cores corresponding to two supermassive black holes (SMBHs) accreting surrounding gas and launching radio-bright relativistic jets. However, utilizing the original VLBA dataset used to claim the detection of a binary SMBH, in addition to later multi-epoch/multi-frequency datatsets obtained from both the VLBA and the European VLBI Network, we find no evidence to support the presence of a binary SMBH. We place stringent upper limits to the flux densities of any sub-pc-scale radio cores which are at least an order of magnitude lower than the original VLBI radio-core detections, directly challenging the original binary SMBH detection claim. With this in mind, we discuss the possible reasons for the non-detection of any VLBI radio cores in our imaging, the possibility of a binary SMBH still residing in NGC 7674, and the prospect of future observations shedding further light on the true nature of this active galactic nucleus.