Title: N-body simulations of planet formation via pebble accretion I: First Results,
Abstract: Context. Planet formation with pebbles has been proposed to solve a couple of
long-standing issues in the classical formation model. Some sophisticated
simulations have been done to confirm the efficiency of pebble accretion.
However, there has not been any global N-body simulations that compare the
outcomes of planet formation via pebble accretion with observed extrasolar
planetary systems. Aims. In this paper, we study the effects of a range of
initial parameters of planet formation via pebble accretion, and present the
first results of our simulations. Methods. We incorporate the pebble accretion
model by Ida et al. (2016) in the N-body code SyMBA (Duncan et al. 1998), along
with the effects of gas accretion, eccentricity and inclination damping and
planet migration in the disc. Results. We confirm that pebble accretion leads
to a variety of planetary systems, but have difficulty in reproducing observed
properties of exoplanetary systems, such as planetary mass, semimajor axis, and
eccentricity distributions. The main reason behind this is a too-efficient type
I migration, which sensitively depends on the disc model. However, our
simulations also lead to a few interesting predictions. First, we find that
formation efficiencies of planets depend on the stellar metallicities, not only
for giant planets, but also for Earths (Es) and Super-Earths (SEs). The
dependency for Es/SEs is subtle. Although higher metallicity environments lead
to faster formation of a larger number of Es/SEs, they also tend to be lost
later via dynamical instability. Second, our results indicate that a wide range
of bulk densities observed for Es and SEs is a natural consequence of dynamical
evolution of planetary systems. Third, the ejection trend of our simulations
suggest that one free-floating E/SE may be expected for two smaller-mass
planets.