Partial alignment between jets and megamasers: Coherent versus selective accretion

TL;DR

This study analyzes the orientation of radio jets and megamaser disks in galaxies to understand black hole spin evolution, revealing partial alignment influenced by coherent or selective accretion processes, with implications for black hole growth models.

Contribution

It provides the first statistical analysis of jet and megamaser disk alignment, distinguishing between coherent and selective accretion as causes of partial alignment in black hole growth.

Findings

Strong partial alignment between jets and megamasers observed.

Alignment caused by anisotropic gas fueling or spin-dependent feedback.

Implications for black hole spin evolution and accretion models.

Abstract

Spins play a crucial role in the appearance, evolution, and occupation fraction of massive black holes (MBHs). To date, observational estimates of MBH spins are scarce, and the assumptions commonly made in such estimates have recently been questioned. Similarly, theoretical models for MBH spin evolution, while reproducing the few observational constraints, are based on possibly oversimplified assumptions. New independent constraints on MBH spins are therefore of primary importance. We present a rigorous statistical analysis of the relative orientation of radio jets and megamaser disks in ten low-redshift galaxies. We find a strong preference for (partial) alignment between jets and megamaser that can be attributed to two different causes: coherent accretion and selective accretion. In the first case the partial alignment is due to an anisotropy in the gas reservoir fueling the growth of MBHs. In the second case the spin-dependent anisotropic feedback allows long-lived accretion only if the orbits of the gas inflows are almost aligned to the MBH equatorial plane. A discussion of the implications of the two accretion scenarios regarding the evolution of MBHs is presented, together with an outlook on future observational tests aiming at discriminating between the two scenarios and checking whether either applies to different redshifts and black hole mass regimes.