  There are two planetary formation scenarios: core accretion and gravitational
disk instability. Based on the fact that gaseous objects are preferentially
observed around metal-rich host stars, most extra-solar gaseous objects
discovered to date are thought to have been formed by core accretion. Here, we
present 569 samples of gaseous planets and brown dwarfs found in 485 planetary
systems that span three mass regimes with boundary values at 4 and 25
Jupiter-mass masses through performing cluster analyses of these samples
regarding the host-star metallicity, after minimizing the impact of the
selection effect of radial-velocity measurement on the cluster analysis. The
larger mass is thought to be the upper mass limit of the objects that were
formed during the planetary formation processes. In contrast, the lower mass
limit appears to reflect the difference between planetary formation processes
around early-type and G-type stars; disk instability plays a greater role in
the planetary formation process around early-type stars than that around G-type
stars. Population with masses between 4 and 25 Jupiter masses that orbit
early-type stars comprise planets formed not only via the core-accretion
process but also via gravitational disk instability because the population
preferentially orbits metal-poor stars or is independent of the host-star
metallicity. Therefore, it is essential to have a hybrid scenario for the
planetary formation of the diverse systems.
