One of the most standard technique for the determination of mass
profiles relies on the abundant HI content of disk galaxies and its
observed kinematics (see
[1]
and references therein). Some concerns were raised by the lack of spatial
resolution in the central region which impairs the application of
decomposition techniques to constrain the relative contribution of the
stars, gas and dark matter. The use of
H
mapping (via
Fabry-Perot interferometers) seems to properly address this issue,
although the complex dynamics expected in the central regions of spiral
(and barred) galaxies enters then as an extra complication. A remarkable
sample of 329 H rotation
curves of field spirals was obtained by Vogt et al.
[15].
I should also mention the unique
coverage of Virgo spirals conducted by Chemin et al.
[3],
which will permit a detailed study of the mass profiles as well as the
impact of environment on the gas content, distribution and kinematics.
Two-dimensional maps are certainly a requirement if we wish to disentangle
the global (circular?) motion from the effect of density waves. Via the
combined use of high resolution ionised
(H) and molecular (CO)
gas velocity fields, Simon et al.
[16]
constrained the mass variation with radius in the
dwarf spiral NGC 2976. The addition of multi-colour optical and
near-infrared images allowed the authors to suggest that the stellar
mass fraction is relatively high in the central region, with the dark
matter having then a profile shallower than
r-0.17, with the caveat that the obtained central M
/ LK may be
too low to be accounted by normal stellar populations.
A similar study, but this time of a flocculent isolated spiral NGC 4414, had
been conducted by Vallejo et al.
[17],
who combined high resolution CO data with extended HI rotation curve, to
conclude that the mass-to-light ratio cannot be constant throughout the
galaxy, but that dark matter has certainly a nearly negligible role in
the central 7 kpc.