6 research outputs found
The Structure of Rapidly Rotating Late-Type Spiral Galaxies: I. Photometry, HI and Optical Kinematics
We present I-band photometry, long-slit optical spectroscopy, and new
aperture synthesis HI observations for eight late-type spirals with rotation
velocities in the range 243 km/s < V_{rot} < 308 km/s. The sample will be used
to study the structure and angular momentum of disks at the high-mass end of
the spiral galaxy population; here we discuss the basic properties of these
``fast rotators'', and derive hybrid optical/HI rotation curves for each.
Despite the presence of HI warps and low-mass companions in many systems, their
kinematics are regular and there is excellent agreement between optical and HI
tracers near the optical radius r_{opt}. At high inclinations at which
projection effects are negligible, the sample galaxies exhibit flat,
featureless rotation curves out to their last measured points at
1.7r_{opt}--3.5 r_{opt}. The intermediate inclination systems are also
consistent with a constant rotation amplitude for r > 0.5 r_{opt}. We therefore
find no evidence for declining rotation curves at the high-mass end of the
late-type spiral galaxy population. Combining our data with the compilation of
spirals with reliable outer HI kinematics from the work of Casertano & van
Gorkom, we find no convincing trends between logarithmic outer rotation curve
slopes and rotation amplitudes or surface brightnesses for galaxies with
V_{rot} > 220 km/s. Correlations between these slopes and morphological types
or disk scale lengths are also marginal in this regime.Comment: v2: minor changes to match proofs. 23 pages, 15 figures, AJ in press.
For version with high resolution figures, see
http://www.physics.rutgers.edu/~spekkens/papers/fast1.pd
Extensive spiral structure and corotation resonance
Spiral density wave theories demand that grand design spiral structure be
bounded, at most, between the inner and outer Lindblad resonances of the spiral
pattern. The corotation resonance lies between the outer and inner Lindblad
resonances. The locations of the resonances are at radii whose ratios to each
other are rather independent of the shape of the rotation curve. The measured
ratio of outer to inner extent of spiral structure for a given spiral galaxy
can be compared to the standard ratio of corotation to inner Lindblad resonance
radius. In the case that the measured ratio far exceeds the standard ratio, it
is likely that the corotation resonance is within the bright optical disk.
Studying such galaxies can teach us how the action of resonances sculpts the
appearance of spiral disks. This paper reports observations of 140 disk
galaxies, leading to resonance ratio tests for 109 qualified spirals. It lists
candidates that have a good chance of having the corotation resonance radius
within the bright optical disk.Comment: 29 pages, 7 figure files, AAS late
Rotation Curves of Spiral Galaxies
Rotation curves of spiral galaxies are the major tool for determining the
distribution of mass in spiral galaxies. They provide fundamental information
for understanding the dynamics, evolution and formation of spiral galaxies. We
describe various methods to derive rotation curves, and review the results
obtained. We discuss the basic characteristics of observed rotation curves in
relation to various galaxy properties, such as Hubble type, structure,
activity, and environment.Comment: 40 pages, 6 gif figures; Ann. Rev. Astron. Astrophys. Vol. 39, p.137,
200
Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4 spiral
galaxies which are characterized by a zero-velocity plateau along the major
axis and a velocity gradient along the minor axis, respectively. By combining
these new kinematical data with those available in the literature for the
ionized-gas component of the S0s and spirals listed in the Revised Shapley-Ames
Catalog of Bright Galaxies we realized that about 50% of unbarred galaxies show
a remarkable gas velocity gradient along the optical minor axis. This fraction
rises to about 60% if we include unbarred galaxies with an irregular velocity
profile along the minor axis. This phenomenon is observed all along the Hubble
sequence of disk galaxies, and it is particularly frequent in early-type
spirals. Since minor-axis velocity gradients are unexpected if the gas is
moving onto circular orbits in a disk coplanar to the stellar one, we conclude
that non-circular and off-plane gas motions are not rare in the inner regions
of disk galaxies.Comment: 12 pages, 4 postscript figures. Accepted for publication in A&