197 research outputs found
Unusual magnetic fields in the interacting spiral NGC 3627
By observing the interacting galaxy NGC 3627 in radio polarization we try to
answer the question to which degree the magnetic field follows the galactic gas
flows. We obtained total power and polarized intensity maps at 8.46 GHz and
4.85 GHz using the VLA in its compact D-configuration. In order to overcome the
zero-spacing problems, the interferometric data were combined with single-dish
measurements obtained with the Effelsberg 100-m radio telescope. The observed
magnetic field structure in NGC 3627 suggests that two field components are
superposed. One component smoothly fills the interarm space and shows up also
in the outermost disk regions, the other component follows a symmetric S-shaped
structure. In the western disk the latter component is well aligned with an
optical dust lane, following a bend which is possibly caused by external
interactions. However, in the SE disk the magnetic field crosses a heavy dust
lane segment, apparently being insensitive to strong density-wave effects. We
suggest that the magnetic field is decoupled from the gas by high turbulent
diffusion, in agreement with the large \ion{H}{i} line width in this region. We
discuss in detail the possible influence of compression effects and
non-axisymmetric gas flows on the general magnetic field asymmetries in NGC
3627. On the basis of the Faraday rotation distribution we also suggest the
existence of a large ionized halo around this galaxy.Comment: 11 pages, 11 figure
The properties of Low Surface Brightness galaxies
A description is given of the samples of Low Surface Brightness galaxies
(LSBs) used for comparison with models of their chemical and
spectro-photometric evolution (Boissier et al., this Volume). These samples
show the large variation and scatter in observed global properties of LSBs,
some of which cannot be modeled without adding starbursts or truncations to
their star formation history.Comment: To appear in the Proceedings of the Euroconference on The Evolution
of Galaxies: III. From simple approaches to self-consistent models (Kluwer).
4 page
Can cluster environment modify the dynamical evolution of spiral galaxies?
Over the past decade many effects of the cluster environment on member galaxies have been established. These effects are manifest in the amount and distribution of gas in cluster spirals, the luminosity and light distributions within galaxies, and the segregation of morphological types. All these effects could indicate a specific dynamical evolution for galaxies in clusters. Nevertheless, a more direct evidence, such as a different mass distribution for spiral galaxies in clusters and in the field, is not yet clearly established. Indeed, Rubin, Whitmore, and Ford (1988) and Whitmore, Forbes, and Rubin (1988) (referred to as RWF) presented evidence that inner cluster spirals have falling rotation curves, unlike those of outer cluster spirals or the great majority of field spirals. If falling rotation curves exist in centers of clusters, as argued by RWF, it would suggest that dark matter halos were absent from cluster spirals, either because the halos had become stripped by interactions with other galaxies or with an intracluster medium, or because the halos had never formed in the first place. Even if they didn't disagree with RWF, other researchers pointed out that the behaviour of the slope of the rotation curves of spiral galaxies (in Virgo) is not so clear. Amram, using a different sample of spiral galaxies in clusters, found only 10% of declining rotation curves (2 declining vs 17 flat or rising) in opposition to RWF who find about 40% of declining rotation curves in their sample (6 declining vs 10 flat or rising), we will hereafter briefly discuss the Amram data paper and compare it to the results of RWF. We have measured the rotation curves for a sample of 21 spiral galaxies in 5 nearby clusters. These rotation curves have been constructed from detailed two-dimensional maps of each galaxy's velocity field as traced by emission from the Ha line. This complete mapping, combined with the sensitivity of our CFHT 3.60 m. + Perot-Fabry + CCD observations, allows the construction of high-quality rotation curves. Details concerning the acquisition and reduction procedures of the data are given in Amram. We present and discuss our preliminary analysis and compare them with RWF's results
Globular clusters and dwarf galaxies in Fornax - I. Kinematics in the cluster core from multi-object spectroscopy
We acquired radial velocities of a significant number of globular clusters
(GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies,
in order to derive their velocity dispersion radial profile and to probe the
dynamics of the cluster. We used FLAMES on the VLT to obtain accurate
velocities for 149 GCs, within a ~500x150 kpc strip centered on NGC 1399, the
Fornax central galaxy. These objects are at the very bright tail (M_V < -9.5)
of the GC luminosity function, overlapping the so-called ``ultra-compact
dwarfs'' magnitude range. Eight of the brightest FLAMES-confirmed members
indeed show hints of resolution in the subarcsecond pre-imaging data we used
for selecting the ~500 targets for FLAMES spectroscopy. Ignoring the GCs around
galaxies by applying 3d_25 diameter masks, we find 61 GCs of 20.0 < V < 22.2
lying in the intra-cluster (IC) medium. The velocity dispersion of the
population of ICGCs is 200 km/s at ~150 kpc from the central NGC 1399 and rises
to nearly 400 km/s at 200 kpc, a value which compares with the velocity
dispersion of the population of dwarf galaxies, thought to be infalling from
the surroundings of the cluster.Comment: To be published in A&A Letters. 4 pages, 3 figures, 3 table
Kinematics and morphology of ionized gas in Hickson Compact Group 18
We present new observations of emission in the Hickson Compact
Group 18 (HCG 18) obtained with a scanning Fabry-Perot interferometer. The
velocity field does not show motions of individual group members but, instead,
a complex common velocity field for the whole group. The gas distribution is
very asymmetric with clumps of maximum intensity coinciding with the optically
brightest knots. Comparing and HI data we conclude that HCG 18 is
not a compact group but instead a large irregular galaxy with several clumps of
star formation.Comment: Accepted for publication in Astronomical Journal (13p 6 figures
Large-Scale Structures Behind the Southern Milky Way from Observations of Partially Obscured Galaxies
We report here on extragalactic large-scale structures uncovered by a deep
optical survey for galaxies behind the southern Milky Way. Systematic visual
inspection of the ESO/SRC-survey revealed over 10000 previously unknown
galaxies in the region 265 < l < 340, |b| < 10. With subsequently obtained
redshifts of more than 10% of these galaxies, new structures across the Milky
Way are unveiled, such as a filament at ~ 2500 km/s connecting to the Hydra
and Antlia clusters, a shallow extended supercluster in Vela (~ 6000km/s), and
a nearby (4882 km/s), very massive (M ~ 2-5 10^15 Msun), rich Coma-like cluster
which seems to constitute the previously unidentified center of the Great
Attractor. The innermost part of the Milky Way where the foreground obscuration
in the blue is 5mag, respectively HI-column densities greater than 6 10^21 /
cm^2 remains fully opaque. In this approximately 8 degrees wide strip, the
forthcoming blind HI-survey with the multi-beam system at Parkes will provide
the only tool to unveil this part of the extragalactic sky.Comment: Presented at the Multibeam Workshop on ``HI in the Local Universe'',
Sydney, May 13-15 1996. Accepted 2.11.1996 for publication by PASA.
Latex-file with 4 encapsulated postscript files. Version with original
figures available at
http://www.atnf.csiro.au/~lstavele/13beam/proceedings/korteweg/korteweg.htm
H-alpha Kinematics of the SINGS Nearby Galaxies Survey. I
This is the first part of an Halpha kinematics follow-up survey of the SINGS
sample. The data for 28 galaxies are presented. The observations were done on
three different telescopes with FaNTOmM, an integral field photon counting
spectrometer, installed in the respective focal reducer of each telescope. The
data reduction was done through a newly built pipeline with the aim of
producing the most homogenous data set possible. Adaptive spatial binning was
applied to the data cubes in order to get a constant signal-to-noise ratio
across the field of view. Radial velocity and monochromatic maps were generated
using a new algorithm and the kinematical parameters were derived using
tilted-ring models.Comment: 47 pages, 37 figures, accepted for publication in MNRAS. All
high-res. figures are available at
http://www.astro.umontreal.ca/fantomm/sings . An high-res. version of the
article is available at http://www.astro.umontreal.ca/~odaigle/SINGS.pd
- âŠ