Molecular gas properties of Q1700-MD94: a massive, main-sequence galaxy
  at $z\approx2$
  We use a combination of new NOrthern Extended Millimeter Array (NOEMA)
observations of the pair of [CI] transitions, the CO(7-6) line, and the dust
continuum, in addition to ancillary CO(1-0) and CO(3-2) data, to study the
molecular gas properties of Q1700-MD94, a massive, main-sequence galaxy at
$z\approx2$. We find that for a reasonable set of assumptions for a typical
massive star-forming galaxy, the CO(1-0), the [CI](1-0) and the dust continuum
yield molecular gas masses that are consistent within a factor of $\sim2$. The
global excitation properties of the molecular gas as traced by the [CI] and CO
transitions are similar to those observed in other massive, star-forming
galaxies at $z\sim2$. Our large velocity gradient (LVG) modeling using RADEX of
the CO and [CI] spectral line energy distributions (SLEDs) suggests the
presence of relatively warm ($T_{\rm kin}=41$K), dense ($n_{\rm
H_2}=8\times10^{3}~{\rm cm}^{-3}$) molecular gas, comparable to the
high-excitation molecular gas component observed in main-sequence, star-forming
galaxies at $z\sim1$. The galaxy size in the CO(1-0) and CO(7-6) line emission
are comparable, which suggests that the highly-excited molecular gas is
distributed throughout the disk powered by intense star formation activity. To
confirm this scenario will require spatially resolved observations of the CO
and [CI] lines which can now be obtained with NOEMA upgraded capabilities.
