1,081 research outputs found
The Ursa Major Cluster of Galaxies. IV ; HI synthesis observations
In this data paper we present the results of an extensive 21cm-line synthesis
imaging survey of 43 spiral galaxies in the nearby Ursa Major cluster using the
Westerbork Synthesis Radio Telescope. Detailed kinematic information in the
form of position-velocity diagrams and rotation curves is presented in an atlas
together with HI channel maps, 21cm continuum maps, global HI profiles, radial
HI surface density profiles, integrated HI column density maps, and HI velocity
fields. The relation between the corrected global HI linewidth and the
rotational velocities Vmax and Vflat as derived from the rotation curves is
investigated. Inclination angles obtained from the optical axis ratios are
compared to those derived from the inclined HI disks and the HI velocity
fields. The galaxies were not selected on the basis of their HI content but
solely on the basis of their cluster membership and inclination which should be
suitable for a kinematic analysis. The observed galaxies provide a
well-defined, volume limited and equidistant sample, useful to investigate in
detail the statistical properties of the Tully-Fisher relation and the dark
matter halos around them.Comment: 32 pages, including 2 sample pages of HI atlas. For full atlas (104
pages, 11 MB) see http://www.nrao.edu/library/preprints/00173.ps.gz .
Accepted for publication in Astronomy and Astrophysic
Gas accretion in galactic disks
Evidence for the accretion of material in spiral galaxies has grown over the
past years and clear signatures can be found in HI observations of galaxies.
We describe here new detailed and sensitive HI synthesis observations of a
few nearby galaxies (NGC 3359, NGC 4565 and NGC 6946) which show that indeed
accretion of small amounts of gas is taking place.
These should be regarded as examples illustrating a general phenomenon of gas
infall in galaxies. Such accretion may also be at the origin of the gaseous
halos which are being found around spirals. Probably it is the same kind of
phenomenon of material infall as observed in the stellar streams in the halo
and outer parts of our galaxy and M 31Comment: To appear in the proceedings of the symposium "Extraplanar Gas", ASP
Conference series, editor R. Braun, 8 pages + 5 figure
High velocity gas in external galaxies
Two nearby, nearly face-on spiral galaxies, M 101 and NGC 6946, observed in the HI with the Westerbork Synthesis Radio Telescope (WSRT) as part of a program to search for high velocity gas in other galaxies, are used to illustrate the range of properties of high velocity gas in other galaxies found thusfar
The vertical extent and kinematics of the HI in NGC 2403
The neutral hydrogen line profiles along the major axis of the nearby spiral
galaxy NGC 2403 show a wing towards the sytemic velocity. This asymmetry can be
explained with the presence of an abnormally thick HI disk (FWHM ~ 5 kpc) or
with a two-component structure: a thin disk and a slowly rotating, thicker (1-3
kpc) HI layer. The latter model gives a better representation of the
observations. These results throw a new light on the disk-halo connection. In
particular, the decrease of rotational velocity with height above the plane may
be the result of a galactic fountain flow. A vertically extended, slowly
rotating HI layer may be common among spiral galaxies with high levels of star
formation.Comment: 4 pages, 2 figures, accepted for publication in Astronomy and
Astrophysics Letter
Bose-Einstein Condensates in Strongly Disordered Traps
A Bose-Einstein condensate in an external potential consisting of a
superposition of a harmonic and a random potential is considered theoretically.
From a semi-quantitative analysis we find the size, shape and excitation
energy as a function of the disorder strength. For positive scattering length
and sufficiently strong disorder the condensate decays into fragments each of
the size of the Larkin length . This state is stable over a large
range of particle numbers. The frequency of the breathing mode scales as
. For negative scattering length a condensate of size
may exist as a metastable state. These finding are generalized to anisotropic
traps
High Velocity Gas in the Halos of Spiral Galaxies
Recent, high sensitivity, HI observations of nearby spiral galaxies show that
their thin `cold' disks are surrounded by thick layers (halos) of neutral gas
with anomalous kinematics. We present results for three galaxies viewed at
different inclination angles: NGC891 (edge-on), NGC2403 (i=60 deg), and NGC6946
(almost face-on). These studies show the presence of halo gas up to distances
of 10-15 kpc from the plane. Such gas has a mean rotation 25-50 km/s lower than
that of the gas in the plane, and some complexes are detected at very high
velocities, up to 200-300 km/s. The nature and origin of this halo gas are
poorly understood. It can either be the result of a galactic fountain or of
accretion from the intergalactic medium. It is probably the analogous of some
of the High Velocity Clouds (HVCs) of the Milky Way.Comment: 6 pages, 4 figures. To appear in the ASP proceedings of IAU Symposium
217, "Recycling intergalactic and interstellar matter", eds. Pierre-Alain
Duc, Jonathan Braine, Elias Brink
Neutral Hydrogen and Optical Observations of Edge-on Galaxies: Hunting for Warps
We present 21-cm HI line and optical R-band observations for a sample of 26
edge-on galaxies. The HI observations were obtained with the Westerbork
Synthesis Radio Telescope, and are part of the WHISP database (Westerbork HI
Survey of Spiral and Irregular Galaxies). We present HI maps, optical images,
and radial HI density profiles. We have also derived the rotation curves and
studied the warping and lopsidedness of the HI disks.
20 out of the 26 galaxies of our sample are warped, confirming that warping
of the HI disks is a very common phenomenon in disk galaxies. Indeed, we find
that all galaxies that have an extended HI disk with respect to the optical are
warped.
The warping usually starts around the edge of the optical disk. The degree of
warping varies considerably from galaxy to galaxy. Furthermore, many warps are
asymmetric, as they show up in only one side of the disk or exhibit large
differences in amplitude in the approaching and receding sides of the galaxy.
These asymmetries are more pronounced in rich environments, which may indicate
that tidal interactions are a source of warp asymmetry. A rich environment
tends to produce larger warps as well. The presence of lopsidedness seems to be
related to the presence of nearby companions.Comment: To appear in Astronomy & Astrophysic
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