NOEMA observations support a recoiling black hole in 3C186

TL;DR

This study uses NOEMA observations to confirm that the quasar 3C186 hosts a recoiling supermassive black hole, evidenced by spatial and spectral offsets of the galaxy's gas and the quasar itself.

Contribution

First high-resolution molecular gas observations of 3C186 confirm the recoiling black hole scenario through spatial and spectral offsets.

Findings

Detection of a large molecular gas reservoir aligned with the host galaxy.

Confirmed spatial offset between galaxy's gas and the quasar.

Spectral offset indicating the quasar's black hole is recoiling.

Abstract

3C186 is a powerful radio loud quasar (QSO) at the center of a cool-core cluster at z=1.06. Previous studies reported evidence for a projected spatial offset of ~1'' between the isophotal center of the galaxy and the point-source QSO as well as a spectral shift of ~2000 km/s between the narrow and broad line region of the system. In this work we report high-resolution molecular gas CO(4-3) observations of the system taken with NOEMA interferometer. We clearly detect a large reservoir of molecular gas, $M_{H_2}\sim8\times10^{10}~M_\odot$, that is cospatial with the host galaxy and likely associated with a rotating disk-like structure. We firmly confirm both the spatial offset of the galaxy's gas reservoir with respect to the continuum emission of the QSO and the spectral offset with respect to the redshift of the broad line region. Our morphological and kinematical analysis confirms that the most likely scenario to explain the 3C186 system is that the QSO is a kicked super-massive black hole (SMBH), which we believe may have resulted from a strong gravitational wave recoil as two SMBHs coalesced after the merger of their host galaxies.