  Lenticular galaxies are generally thought to have descended from spirals via
morphological transformation, although recent numerical simulations have shown
that minor or even major merger can also lead to an S0-like remnant. These
mechanisms, however, are active in a dense environment such as a group or a
cluster of galaxies - making it harder to explain the remarkable fraction of
S0s found in the field. Here, we propose a new mechanism to form such
lenticular galaxies. We show that an isolated cold disk settled into rotational
equilibrium becomes violently unstable - leading to fragmentation and formation
of stellar clumps that, in turn, not only grow the bulge, but also increase the
stellar disk velocity dispersion optimally in less than a billion year.
Subsequently, the galaxy evolves passively without any conspicuous spiral
structure. The final galaxy models resemble remarkably well the morphology and
stellar kinematics of the present-day S0s observed by the Planetary Nebulae
spectrograph. Our findings suggest a natural link between the high-redshift
clumpy progenitors to the present-day S0 galaxies.
