2,490 research outputs found
HI distribution and kinematics of NGC 1569
We present WSRT observations of high sensitivity and resolution of the
neutral hydrogen in the starburst dwarf galaxy NGC 1569. Assuming a distance of
2.2 Mpc, we find a total HI mass of 1.3 * 10^8 M_sun to be distributed in the
form of a dense, clumpy ridge surrounded by more extended diffuse HI containing
a few additional discrete features, such as a Western HI Arm and an HI bridge
reaching out to a small counterrotating companion cloud. About 10% by mass of
all HI in NGC 1569 is at unusually high velocities. Some of this HI may be
associated with the mass outflow evident from H-alpha measurements, but some
may also be associated with NGC 1569's HI companion and intervening HI bridge,
in which case, infall rather than outflow might be the cause of the discrepant
velocities. No indication of a large bubble structure was found in
position-velocity maps of the high-velocity HI. The galaxy as a whole is in
modest overall rotation, but the HI gas lacks any sign of rotation within 60''
(0.6 kpc) from the center, i.e. over most of the optical galaxy. Here,
turbulent motions resulting from the starburst appear to dominate over
rotation. In the outer disk, the rotational velocities reach a maximum of 35
\pm 6 km/s, but turbulent motion remains significant. Thus, starburst effects
are still noticeable in the outer HI disk, although they are no longer dominant
beyond 0.6 kpc. Even excluding the most extreme high-velocity HI clouds, NGC
1569 still has an unusually high mean HI velocity dispersion of sigma_v=21.3
km/s, more than double that of other dwarf galaxies.Comment: Figure 11a,b and Figure 14 separately in jpg forma
Cut distance identifying graphon parameters over weak* limits
The theory of graphons comes with the so-called cut norm and the derived cut
distance. The cut norm is finer than the weak* topology. Dole\v{z}al and
Hladk\'y [Cut-norm and entropy minimization over weak* limits, J. Combin.
Theory Ser. B 137 (2019), 232-263] showed, that given a sequence of graphons, a
cut distance accumulation graphon can be pinpointed in the set of weak*
accumulation points as a minimizer of the entropy. Motivated by this, we study
graphon parameters with the property that their minimizers or maximizers
identify cut distance accumulation points over the set of weak* accumulation
points. We call such parameters cut distance identifying. Of particular
importance are cut distance identifying parameters coming from subgraph
densities, t(H,*). This concept is closely related to the emerging field of
graph norms, and the notions of the step Sidorenko property and the step
forcing property introduced by Kr\'al, Martins, Pach and Wrochna [The step
Sidorenko property and non-norming edge-transitive graphs, J. Combin. Theory
Ser. A 162 (2019), 34-54]. We prove that a connected graph is weakly norming if
and only if it is step Sidorenko, and that if a graph is norming then it is
step forcing. Further, we study convexity properties of cut distance
identifying graphon parameters, and find a way to identify cut distance limits
using spectra of graphons. We also show that continuous cut distance
identifying graphon parameters have the "pumping property", and thus can be
used in the proof of the the Frieze-Kannan regularity lemma.Comment: 48 pages, 3 figures. Correction when treating disconnected norming
graphs, and a new section 3.2 on index pumping in the regularity lemm
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