Impact of an Active Sgr A* on the Synthesis of Water and Organic Molecules throughout the Milky Way

Abstract

Sgr A*, the supermassive black hole (SMBH) in our Galaxy, is dormant today, but it should have gone through multiple gas-accretion episodes in the past billions of years to grow to its current mass of 4 × 10 6 M ⊙ . Each episode temporarily ignites the SMBH and turns the Galactic Center into an active galactic nucleus (AGN). Recently, we showed that the AGN could produce large amounts of hard X-rays that can penetrate the dense interstellar medium in the Galactic plane. Here we further study the impact of X-rays on the molecular chemistry in our Galaxy. We use a chemical-reaction network to simulate the evolution of several molecular species, including H 2 O, CH 3 OH, and H 2 CO, both in the gas phase and on the surface of dust grains. We find that X-ray irradiation could significantly enhance the abundances of these species. The effect is most significant in young, high-density molecular clouds and could be prominent at a Galactic distance of 8 kpc or smaller. The imprint in the chemical abundance is visible even several million years after the AGN turns off.