Cosmological Hydrodynamic Simulations of Preferential Accretion in the
  SMBH of Milky Way Size Galaxies
  Using a new, high-resolution cosmological hydrodynamic simulation of a Milky
Way-type (MW-type) galaxy, we explore how a merger-rich assembly history
affects the mass budget of the central supermassive black hole (SMBH). We
examine a MW-mass halo at the present epoch whose evolution is characterized by
several major mergers to isolate the importance of merger history on black hole
accretion. This study is an extension of Bellovary et. al. 2013, which analyzed
the accretion of high mass, high redshift galaxies and their central black
holes, and found that the gas content of the central black hole reflects what
is accreted by the host galaxy halo. In this study, we find that a merger-rich
galaxy will have a central SMBH preferentially fed by merger gas. Moreover, we
find that nearly 30$\%$ of the accreted mass budget of the SMBH enters the
galaxy through the two major mergers in its history, which may account for the
increase of merger-gas fueling the SMBH. Through an investigation of the
angular momentum of the gas entering the host and its SMBH, we determine that
merger gas enters the galaxy with lower angular momentum compared to smooth
accretion, partially accounting for the preferential fueling witnessed in the
SMBH. In addition, the presence of mergers, particularly major mergers, also
helps funnel low angular momentum gas more readily to the center of the galaxy.
Our results imply that galaxy mergers play an important role in feeding the
SMBH in MW-type galaxies with merger-rich histories. Our results imply that
galaxy mergers play an important role in feeding the SMBH in MW-type galaxies
with merger-rich histories.
