The flaring HI disk of the nearby spiral galaxy NGC 2683
  New deep VLA D array HI observations of the highly inclined nearby spiral
galaxy NGC 2683 are presented. Archival C array data were processed and added
to the new observations. To investigate the 3D structure of the atomic gas
disk, we made different 3D models for which we produced model HI data cubes.
The main ingredients of our best-fit model are (i) a thin disk inclined by 80
degrees; (ii) a crude approximation of a spiral and/or bar structure by an
elliptical surface density distribution of the gas disk; (iii) a slight warp in
inclination; (iv) an exponential flare; and (v) a low surface-density gas ring.
The slope of NGC 2683's flare is comparable, but somewhat steeper than those of
other spiral galaxies. NGC 2683's maximum height of the flare is also
comparable to those of other galaxies. On the other hand, a saturation of the
flare is only observed in NGC 2683. Based on the comparison between the high
resolution model and observations, we exclude the existence of an extended
atomic gas halo around the optical and thin gas disk. Under the assumption of
vertical hydrostatic equilibrium we derive the vertical velocity dispersion of
the gas. The high turbulent velocity dispersion in the flare can be explained
by energy injection by (i) supernovae, (ii) magneto-rotational instabilities,
(iii) ISM stirring by dark matter substructure, or (iv) external gas accretion.
The existence of the complex large-scale warping and asymmetries favors
external gas accretion as one of the major energy sources that drives
turbulence in the outer gas disk. We propose a scenario where this external
accretion leads to turbulent adiabatic compression that enhances the turbulent
velocity dispersion and might quench star formation in the outer gas disk of
NGC 2683.
