12,770 research outputs found
Signatures of Galaxy-Cluster Interactions: Spiral Galaxy Rotation Curve Asymmetry, Shape, and Extent
The environmental dependencies of the characteristics of spiral galaxy
rotation curves are studied in this work. We use our large, homogeneously
collected sample of 510 cluster spiral galaxy rotation curves to test the claim
that the shape of a galaxy's rotation curve strongly depends on its location
within the cluster, and thus presumably on the strength of the local
intracluster medium and on the frequency and strength of tidal interactions
with the cluster and cluster galaxies. Our data do not corroborate such a
scenario, consistent with the fact that Tully-Fisher residuals are independent
of galaxy location within the cluster; while the average late-type spiral
galaxy shows more rise in the outer parts of its rotation curve than does the
typical early-type spiral galaxy, there is no apparent trend for either subset
with cluster environment. We also investigate as a function of cluster
environment rotation curve asymmetry and the radial distribution of H II region
tracers within galactic disks. Mild trends with projected cluster-centric
distance are observed: (i) the (normalized) radial extent of optical line
emission averaged over all spiral galaxy types shows a 4%+/-2% increase per Mpc
of galaxy-cluster core separation, and (ii) rotation curve asymmetry falls by a
factor of two between the inner and outer cluster for early-type spirals (a
negligible decrease is found for late-type spirals). Such trends are consistent
with spiral disk perturbations or even the stripping of the diffuse, outermost
gaseous regions within the disks as galaxies pass through the dense cluster
cores.Comment: 17 pages; to appear in the April 2001 Astronomical Journa
Diffusion of passive scalar in a finite-scale random flow
We consider a solvable model of the decay of scalar variance in a
single-scale random velocity field. We show that if there is a separation
between the flow scale k_flow^{-1} and the box size k_box^{-1}, the decay rate
lambda ~ (k_box/k_flow)^2 is determined by the turbulent diffusion of the
box-scale mode. Exponential decay at the rate lambda is preceded by a transient
powerlike decay (the total scalar variance ~ t^{-5/2} if the Corrsin invariant
is zero, t^{-3/2} otherwise) that lasts a time t~1/\lambda. Spectra are sharply
peaked at k=k_box. The box-scale peak acts as a slowly decaying source to a
secondary peak at the flow scale. The variance spectrum at scales intermediate
between the two peaks (k_box0). The mixing
of the flow-scale modes by the random flow produces, for the case of large
Peclet number, a k^{-1+delta} spectrum at k>>k_flow, where delta ~ lambda is a
small correction. Our solution thus elucidates the spectral make up of the
``strange mode,'' combining small-scale structure and a decay law set by the
largest scales.Comment: revtex4, 8 pages, 4 figures; final published versio
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