Extended Cold Molecular Gas Reservoirs in z~3.4 Submillimeter Galaxies
  We report the detection of spatially resolved CO(1-0) emission in the z~3.4
submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the
Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two
previously reported millimeter sources H6 and H7, separated by ~30kpc in
projection. We derive CO(1-0) line luminosities of L'(CO 1-0) = (2.49+/-0.86)
and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L'(CO 1-0) =
(23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x
higher than what is expected from simple excitation modeling of higher-J CO
lines, suggesting the presence of copious amounts of low-excitation gas. This
is supported by the finding that the CO(1-0) line in SMM J13120+4242, the
system with lowest CO excitation, appears to have a broader profile and more
extended spatial structure than seen in higher-J CO lines (which is less
prominently seen in SMM J09431+4700). Based on L'(CO 1-0) and excitation
modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and
M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0)
properties are consistent with the picture that SMM J09431+4700 represents an
early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a
system in an advanced stage. This study thus highlights the importance of
spatially and dynamically resolved CO(1-0) observations of SMGs to further
understand the gas physics that drive star formation in these distant galaxies,
which becomes possible only now that the EVLA rises to its full capabilities.
