  We report evidence for a bimodality in damped Ly systems (DLAs). Using [C II]
158 mu cooling rates, lc, we find a distribution with peaks at lc=10^-27.4 and
10^-26.6 ergs s^-1 H^-1 separated by a trough at lc^crit ~= lc < 10^-27.0 ergs
s^-1 H^-1. We divide the sample into low cool DLAs with lc < lc^crit and high
cool DLAs with lc > lc^crit and find the Kolmogorv-Smirnov probabilities that
velocity width, metallicity, dust-to-gas ratio, and Si II equivalent width in
the two subsamples are drawn from the same parent population are small. All
these quantities are significantly larger in the high cool population, while
the H I column densities are indistinguishable in the two populations. We find
that heating by X-ray and FUV background radiation is insufficient to balance
the cooling rates of either population. Rather, the DLA gas is heated by local
radiation fields. The rare appearance of faint, extended objects in the Hubble
Ultra Deep Field rules out in situ star formation as the dominant
star-formation mode for the high cool population, but is compatible with in
situ star formation as the dominant mode for the low cool population. Star
formation in the high cool DLAs likely arises in Lyman Break galaxies. We
investigate whether these properties of DLAs are analogous to the bimodal
properties of nearby galaxies. Using Si II equivalent width as a mass
indicator, we construct bivariate distributions of metallicity, lc, and areal
SFR versus the mass indicators. Tentative evidence is found for correlations
and parallel sequences, which suggest similarities between DLAs and nearby
galaxies. We suggest that the transition-mass model provides a plausible
scenario for the bimodality we have found. As a result, the bimodality in
current galaxies may have originated in DLAs.
