A Kinematic Study of Spirals with Counter-Rotating Gas:
HI Synthesis Imaging of the Host Galaxies and their
Companions
Aeree Chung,
Baerbel Koribalski, Jacqueline van Gorkom, Martin Bureau
In a kinematical study of 30 edge-on
galaxies (Chung and Bureau 2004), we found compact central
ionized-gas disks rotating opposite to the stars in 3 galaxies:
NGC 128, NGC 1596, and NGC 3203. It is commonly suggested that gas-stellar
counter-rotation can form if the gas is rapidly acquired from outside, for
example from a gas-rich companion. Our three sample galaixes do have nearby
companions at a similar redshift, consistent with this scenario. If gas
transfer between galaxies indeed causes the counter-rotation, HI imaging
will uniquely allow us not only to constrain the galaxies' interaction, but
also to probe their kinematics. Thus we proposed to obtain the HI images of
those three galaxies and their companions using the ATCA and the VLA. We
also selected another galaxy NGC 7332 from the work of Falcon-Barroso
et al. (2003), which shows counter-rotating between the gas and stars and has
a nearby companion in the same redshift range. All our sample galaxies are
barred, and the observations will also help us further understand how
interactions can excite the bar instability in disks.
NGC 1596 has been observed with the
ATCA
in three configurations, EW 352 (Oct 2003), 1.5D
(Nov 2003) and 750A (Feb 2004). NGC 7332 has time scheduled
with the VLA C and D arrays (2004), and a D-array proposal
has been recently submitted to the VLA for NGC 128 and NGC 3203.
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Fig. The (derived) stellar rotation curve
is overplotted on different regions of the optical spectrum,
showing that the central gas emission rotates in the opposite direction
to the stars.
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We have been observing NGC
1596 and its gas-rich companion NGC 1602 since October 2003 using
the ATCA. For a good uv-coverage, the observations have done in
a series of different configurations: EW352, 1.5D, and 750A.
Our observations reveal that the gas acquisition from its companion
explains well the counter-rotation between the gas and the stars
in NGC 1596. Check our results on the right side. |
Preliminary Results of NGC 1596 |
