Abstract:
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 ≈ 2. 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 ∼ 2. 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 ∼ 2. Our large velocity gradient (LVG)
modeling using RADEX of the CO and [CI] spectral line energy distributions (SLEDs) suggests the presence of low-excitation (Tkin = 34 K, nH2 = 3.1 × 103
cm−3
) and high-excitation
(Tkin = 137 K, nH2 = 1.6 × 104
cm−3
) molecular gas components. While the former is re sponsible for the bulk of the [CI](1-0) and [CI](2-1) line emission, the later dominates the
CO line emission at J & 4. 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.
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