A color-coded display of the HI velocity field of the inner 13.4 arcminutes
of NGC 4449. The optical galaxy sits in the inner 10 arcminutes or so.
Note the reversal of the velocity field between the gas in the inner
4 arcminutes and the gas beyond that (at an angle of roughly 45 degrees
counter-clockwise from up). This counter-rotation could be a signature of
a past encounter with another galaxy in which NGC 4449 swallowed some
gas.
(Funded in part by the Lowell Research Fund and by NSF through grant
AST-9616940).
Color-coded display of the velocity dispersion of the HI gas of NGC 4449,
superposed
with contours of the Halpha image of the galaxy. The Halpha image shows
where the current star formation is taking place. Surprisingly,
the regions where the neutral gas has a high velocity dispersion are
not coincident with the location of the
massive stars that could be the source of
energy input. Rather, the high velocity dispersion regions are in
the outskirts of the optical galaxy. This is consistent with the picture
in which the galaxy has suffered a disturbance from another galaxy sometime
in the past, and the gas has not yet settled back to equilibrium.
(Funded in part by the Lowell Research Fund and by NSF through grant
AST-9616940).