1,594 research outputs found
The Westerbork HI Survey of Spiral and Irregular Galaxies I. HI Imaging of Late-type Dwarf Galaxies
Neutral hydrogen observations with the Westerbork Synthesis Radio Telescope
are presented for a sample of 73 late-type dwarf galaxies. These observations
are part of the WHISP project (Westerbork HI Survey of Spiral and Irregular
Galaxies). Here we present HI maps, velocity fields, global profiles and radial
surface density profiles of HI, as well as HI masses, HI radii and line widths.
For the late-type galaxies in our sample, we find that the ratio of HI extent
to optical diameter, defined as 6.4 disk scale lengths, is on average 1.8+-0.8,
similar to that seen in spiral galaxies. Most of the dwarf galaxies in this
sample are rich in HI, with a typical M_HI/L_B of 1.5. The relative HI content
M_HI/L_R increases towards fainter absolute magnitudes and towards fainter
surface brightnesses. Dwarf galaxies with lower average HI column densities
also have lower average optical surface brightnesses. We find that lopsidedness
is as common among dwarf galaxies as it is in spiral galaxies. About half of
the dwarf galaxies in our sample have asymmetric global profiles, a third has a
lopsided HI distribution, and about half shows signs of kinematic lopsidedness.Comment: Accepted for publication in A&A. 18 pages. 39 MB version with all
figures is available http://www.robswork.net/publications/WHISPI.ps.g
IC 4200: a gas-rich early-type galaxy formed via a major merger
We present the result of radio and optical observations of the S0 galaxy IC
4200. We find that the galaxy hosts 8.5 billion solar masses of HI rotating on
a ~90 deg warped disk extended out to 60 kpc from the centre of the galaxy.
Optical spectroscopy reveals a simple-stellar-population-equivalent age of 1.5
Gyr in the centre of the galaxy and V- and R-band images show stellar shells.
Ionised gas is observed within the stellar body and is kinematically decoupled
from the stars and characterised by LINER-like line ratios.We interpret these
observational results as evidence for a major merger origin of IC 4200, and
date the merger back to 1-3 Gyr ago.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 13
figures; the tables of Appendix C can be downloaded at
http://www.astro.rug.nl/~pserra/IC420
Tidal Remnants and Intergalactic HII Regions
We report the discovery of two small intergalactic HII regions in the loose
group of galaxies around the field elliptical NGC 1490. The HII regions are
located at least 100 kpc from any optical galaxy but are associated with a
number of large HI clouds that are lying along an arc 500 kpc in length and
that have no optical counterpart on the Digital Sky Survey. The sum of the HI
masses of the clouds is almost 10^10 M_sun and the largest HI cloud is about
100 kpc in size. Deep optical imaging reveals a very low surface brightness
counterpart to this largest HI cloud, making this one of the HI richest optical
galaxies known (M_HI/L_V~200). Spectroscopy of the HII regions indicates that
the abundance in these HII regions is only slightly sub-solar, excluding a
primordial origin of the HI clouds. The HI clouds are perhaps remnants
resulting from the tidal disruption of a reasonably sized galaxy, probably
quite some time ago, by the loose group to which NGC1490 belongs.
Alternatively, they are remnants of the merger that created the field
elliptical NGC1490. The isolated HII regions show that star formation on a very
small scale can occur in intergalactic space in gas drawn from galaxies by
tidal interactions. Many such intergalactic small star formation regions may
exist near tidally interacting galaxies.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling
Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E.
Brinks, 6 pages with low resolution figures. The full paper with high
resolution images can be downloaded from
http://www.astron.nl/~morganti/Papers/cloud.ps.g
Large-scale HI in nearby radio galaxies: segregation in neutral gas content with radio source size
We present results of a study of neutral hydrogen (HI) in a complete sample
of nearby non-cluster radio galaxies. We find that radio galaxies with large
amounts of extended HI (M_HI >= 10^9 M_solar) all have a compact radio source.
The host galaxies of the more extended radio sources, all of Fanaroff & Riley
type-I, do not contain these amounts of HI. We discuss several possible
explanations for this segregation. The large-scale HI is mainly distributed in
disk- and ring-like structures with sizes up to 190 kpc and masses up to 2 x
10^10 M_solar. The formation of these structures could be related to past
merger events, although in some cases it may also be consistent with a
cold-accretion scenario.Comment: 4 pages, 2 figures. Accepted for publication in A&A Letters. A
version with full resolution figures can be found at
http://www.astro.rug.nl/~emonts/emonts_HIletter_jan07.pd
The Kinematic Properties of the Extended Disks of Spiral Galaxies: A Sample of Edge-On Galaxies
We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17
edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a
few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search for H-alpha emission, which
must be emitted at these flux levels by any accumulation of hydrogen due to the
presence of the extragalactic UV background and any other, local source of UV
flux. We present results from the individual galaxy spectra and a stacked
composite. We detect H-alpha in many cases well beyond R_25 and sometimes as
far as 2 R_25. The combination of sensitivity, spatial resolution, and
kinematic resolution of this technique thus provides a powerful complement to
21-cm observations. Kinematics in the outer disk are generally disk-like (flat
rotation curves, small velocity dispersions) at all radii, and there is no
evidence for a change in the velocity dispersion with radius. We place strong
limits, few percent, on the existence of counter-rotating gas out to 1.5 R_25.
These results suggest that thin disks extend well beyond R_25; however, we also
find a few puzzling anomalies. In ESO 323-G033 we find two emission regions
that have velocities close to the systemic velocity rather than the expected
rotation velocity. These low relative velocities are unlikely to be simply due
to projection effects and so suggest that these regions are not on disk-plane,
circular orbits. In MCG-01-31-002 we find emission from gas with a large
velocity dispersion that is co-rotating with the inner disk.Comment: 18 pages, 14 figures, accepted for publication in Ap
The Effect of Statins and Other Cardiovascular Medication on Ischemia-Reperfusion Damage in a Human DIEP Flap Model: Theoretical and Epidemiological Considerations
Background. Statins and other cardiovascular medication possess antioxidant capacity. It was examined whether chronic use of these medications protects from the development of ischemia-reperfusion (I/R) related complications after DIEP (Deep Inferior Epigastric Perforator Free Flap) surgery. This paper contains a literature study on the antioxidant working mechanisms of these drugs. Methods. Medical information of 134 DIEP patients (173 flaps) was studied from their medical files. Patient and operative characteristics were registered, as well as I/R related complications. Results. Of the group that didnot use statins, 16.3% developed complications versus 30.8% amongst patients that did use these drugs (P = 0.29). Amongst patients that chronically use other cardiovascular medication, 26.8% developed I/R related complications versus 14.4% of the patients without medication (P = 0.10). Conclusions. Chronic use of statins or other cardiovascular medication didnot decrease the occurrence of I/R related complications after DIEP surgery. Therefore, research should be aimed at evaluating short-term pre-treatment with statins
Modelling of laboratory data of bi-directional reflectance of regolith surface containing Alumina
Bidirectional reflectance of a surface is defined as the ratio of the
scattered radiation at the detector to the incident irradiance as a function of
geometry. The accurate knowledge of the bidirectional reflection function (BRF)
of layers composed of discrete, randomly positioned scattering particles is
very essential for many remote sensing, engineering, biophysical applications
and in different areas of Astrophysics. The computations of BRF's for plane
parallel particulate layers are usually reduced to solve the radiative transfer
equation (RTE) by the existing techniques. In this work we present our
laboratory data on bidirectional reflectance versus phase angle for two sample
sizes of 0.3 and 1 of Alumina for the He-Ne laser at 632.8 nm (red) and
543.5nm(green) wavelength. The nature of the phase curves of the asteroids
depends on the parameters like- particle size, composition, porosity, roughness
etc. In our present work we analyse the data which are being generated using
single scattering phase function i.e. Mie theory considering particles to be
compact sphere. The well known Hapke formula will be considered along with
different particle phase function such as Mie and Henyey Greenstein etc to
model the laboratory data obtained at the asteroid laboratory of Assam
University.Comment: 5 pages, 5 figures [accepted for publication in Publications of the
Astronomical Society of Australia (PASA) on 8 June, 2011
- …