We have imaged the 2.6 mm CO(1-0) emission in three
optically selected ``Toomre Sequence" mergers
(NGC 520,
NGC 3921,
NGC 4676).
The molecular gas distributions are well
resolved by the observations, and they are as compact as in IR
selected mergers (R<2 kpc). For NGC 520 and NGC 4676A, the nuclear gas
concentrations form a disk- or a ring-like structure, and
the gas kinematics are regular and are consistent with
simple rotation. Discrete molecular gas complexes are found
along the stellar bar in NGC4676B, and the gas kinematics is
consistent with the disk rotation traced in Halpha. The
molecular gas distribution in NGC3921 is asymmetric about the stellar
remnant, and both the distribution and kinematics suggest that the
molecular gas has not settled into the center of the remnant.
Molecular gas clouds are detected outside the central regions of
NGC3921 and NGC4676, and they may be associated with the tidal tails
and bridges mapped in HI. Departures from the canonical scenario for
a merger involving two large spiral galaxies are found in all three
Toomre Sequence mergers studied. Our data suggest that one of the
progentor disks in NGC520 and NGC3921 were relatively gas-poor.
A detailed comparison of these
optically selected mergers and more luminous IR selected mergers is
deferred to a companion paper
(Paper II).
Halpha (red and blue), and HI clean components (grey))
(the HST image is from
Scweizer et al., 1996, AJ, 112, 1839
Back to home
Maintained by
jhibbard
@ nrao.edu