2016ApJ...823..162L

Radial velocity and transit surveys have found that the fraction of FGKM stars with close-in super-Earth(s) (η_⊕) is around 30%-50%, independent of the stellar mass M_* and metallicity Z_*. In contrast, the fraction of solar-type stars harboring one or more gas giants (η_J) with masses M_p > 100 M_⊕ is nearly 10%-15%, and it appears to increase with both M_* and Z_*. Regardless of the properties of their host stars, the total mass of some multiple super-Earths systems exceeds the core mass of Jupiter and Saturn. We suggest that both super-Earths and supercritical cores of gas giants were assembled from a population of embryos that underwent convergent type I migration from their birthplaces to a transition location between viscously heated and irradiation-heated disk regions. We attribute the cause for the η_⊕-η_J dichotomy to conditions required for embryos to merge and to acquire supercritical core mass ( {M}_{
c}∼10 {M}_⊕ ) for the onset of efficient gaseous envelope accretion. We translate this condition into a critical disk accretion rate, and our analysis and simulation results show that it weakly depends on M_* and decreases with metallicity of disk gas Z_d. We find that embryos are more likely to merge into supercritical cores around relatively massive and metal-rich stars. This dependence accounts for the observed η_J-M_*. We also consider the {Z}_{°}–{Z}{*} dispersed relationship and reproduce the observed η_J-Z_* correlation.