The recoiling black hole candidate 3C 186: spatially-resolved quasar feedback and further evidence of a blue-shifted broad line region

TL;DR

This study uses integral field spectroscopy to analyze the complex kinematics of the quasar 3C 186, providing evidence supporting its classification as a gravitational wave recoiling black hole with spatially-resolved feedback effects.

Contribution

It offers the first spatially-resolved analysis of the NLR and broad line region in 3C 186, revealing velocity offsets consistent with black hole recoil and outflows driven by radiation pressure.

Findings

Multiple velocity components in the NLR indicate complex gas kinematics.

The broad Hbeta component is significantly blue-shifted, supporting recoil hypothesis.

Outflows are likely caused by radiation pressure on interstellar gas.

Abstract

We present the results of integral field spectroscopy of the gravitational wave (GW) recoiling black hole candidate 3C 186. The goal of the observations is to study the kinematics of the [OIII]5007 narrow emission line region (NLR) of the quasar, and investigate the origin of the velocity offsets originally measured for different UV lines. The results show that i) the spatial structure of the NLR is complex. The [OIII]5007 line shows significant velocity offsets with respect to the systemic redshift of the source. Different components at different velocities (-670, -100, + 75 km s^-1) are produced in different regions of the source. ii) we detect both the narrow and the broad components of the Hbeta line. The narrow component generally follows the kinematics of the [OIII] line, while the broad component is significantly blue-shifted. The peak of the broad line is near the blue end, or possibly outside of the sensitivity band of the instrument, implying a velocity offset of >~1800 km s^-1. This result is in agreement with the interpretation of the QSO as a GW recoiling black hole. The properties of the NLR show that the observed outflows are most likely the effect of radiation pressure on the (photoionized) gas in the interstellar medium of the host galaxy.