Exhaustion of the gas next to M31's supermassive black hole

TL;DR

This study uses IRAM observations to show a lack of molecular gas near M31's supermassive black hole, explaining the absence of star formation and suggesting gas either was accreted or expelled, with a small gas clump detected nearby.

Contribution

First direct measurement constrains molecular gas presence near M31's black hole, revealing gas depletion and providing insights into black hole feeding and feedback mechanisms.

Findings

No significant molecular gas detected near the black hole.

A small, unusual gas clump detected 2.4" from the black hole.

Absence of star formation consistent with gas depletion.

Abstract

New observations performed at IRAM Plateau de Bure reveal the absence of molecular gas next to Andromeda's black hole. We derived a 3 sigma upper limit on the molecular gas mass of 4300 Msol for the linewidth of 1000 km/s. This is compatible with infra-red observations which reveal a hole in dust emission next to the black hole. Some gas from stellar feedback is expected from the old eccentric stellar disc population, but it is not accreted close to the black hole. This absence of gas explains the absence of stellar formation observed in this region contrary to what is observed next to Sgr A* in the Milky Way. Either the gas has been swallowed by the black hole, or a feedback mechanism has pushed the gas outside the central 1 pc. Nevertheless, we detect a small clump of gas with a very small velocity dispersion at 2.4" from the black hole. It is probable that this clumpy gas is seen in projection, as it does not follow the rotation of the disk surrounding the black hole, its velocity dispersion is ten times smaller than the expected velocity gradient and the tidal shear from the black hole requires a gas density for this clump that is not compatible with our observations.