535 research outputs found
The Scale Height of NGC 1058 Measured from its HI Power Spectrum
We have measured the HI power spectrum of the nearly face-on spiral galaxy
NGC 1058 from radio-interferometric observations using a visibility based
estimator. The power spectrum is well fitted by two different power laws
, one with at small length-scales
and another with
at large length-scales . We interpret this change in the slope of the power spectrum as a
transition from 3D turbulence at small length-scales to 2D turbulence in the
plane of the galaxy's disk at large length-scales. We use the observed break in
the power spectrum to estimate the galaxy's scale-height, which we find to be pc.Comment: Accepted for publication in Mon. Not. of Royal Astron. Soc. Letter
Turbulence in the Harassed Galaxy NGC 4254
Galaxy harassment is an important mechanism for the morphological evolution
of galaxies in clusters. The spiral galaxy NGC 4254 in the Virgo cluster is
believed to be a harassed galaxy. We have analyzed the power spectrum of HI
emission fluctuations from NGC 4254 to investigate whether it carries any
imprint of galaxy harassment. The power spectrum, as determined using the 16
central channels which contain most of the HI emission, is found to be well
fitted by a power law with at
length-scales to . This is similar to
other normal spiral galaxies which have a slope of and is
interpreted as arising from two dimensional turbulence at length-scales larger
than the galaxy's scale-height. NGC 4254 is hence yet another example of a
spiral galaxy that exhibits scale-invariant density fluctuations out to
length-scales comparable to the diameter of the HI disk. While a large variety
of possible energy sources like proto-stellar winds, supernovae, shocks, etc.
have been proposed to produce turbulence, it is still to be seen whether these
are effective on length-scales comparable to that of the entire HI disk. On
separately analyzing the HI power spectrum in different parts of NGC 4254, we
find that the outer parts have a different slope ()
compared to the central part of the galaxy (). Such a
change in slope is not seen in other, undisturbed galaxies. We suggest that, in
addition to changing the overall morphology, galaxy harassment also effects the
fine scale structure of the ISM, causing the power spectrum to have a steeper
slope in the outer parts.Comment: 6 figures, 1 table, accepted for publication in MNRAS letter
A slow bar in the dwarf irregular galaxy NGC 3741
Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen
in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an
{H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is
also highly dark matter-dominated. Our calculated value of the pattern speed
is 17.1 3.4 km . We also
find the ratio of the co-rotation radius to the bar semi-major axis to be (1.6
0.3), indicating a slow bar. This is consistent with bar models in which
dynamical friction results in a slow bar in dark matter dominated galaxies.Comment: 7 pages, 4 figures, 2 tables Accepted for publlication in MNRA
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