CO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular
  Gas Reservoirs
  We report the detection of CO(1-0) emission in the strongly lensed
high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX
J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200),
using the Expanded Very Large Array and the Green Bank Telescope. We report
lensing-corrected CO(1-0) line luminosities of L'(CO) = 0.34-18.4 x 10^10 K
km/s pc^2 and total molecular gas masses of M(H2) = 0.27-14.7 x 10^10 Msun for
the sources in our sample. Based on CO line ratios relative to previously
reported observations in J>=3 rotational transitions and line excitation
modeling, we find that the CO(1-0) line strengths in our targets are consistent
with single, highly-excited gas components with constant brightness temperature
up to mid-J levels. We thus do not find any evidence for luminous extended, low
excitation, low surface brightness molecular gas components. These properties
are comparable to those found in z>4 quasars with existing CO(1-0)
observations. These findings stand in contrast to recent CO(1-0) observations
of z~2-4 submillimeter galaxies (SMGs), which have lower CO excitation and show
evidence for multiple excitation components, including some low-excitation gas.
These findings are consistent with the picture that gas-rich quasars and SMGs
represent different stages in the early evolution of massive galaxies.
