5,553 research outputs found
The high mass end of the Tully-Fisher relation
We study the location of massive disk galaxies on the Tully-Fisher relation.
Using a combination of K-band photometry and high-quality rotation curves, we
show that in traditional formulations of the TF relation (using the width of
the global HI profile or the maximum rotation velocity), galaxies with rotation
velocities larger than 200 km/s lie systematically to the right of the relation
defined by less massive systems, causing a characteristic `kink' in the
relations. Massive, early-type disk galaxies in particular have a large offset,
up to 1.5 magnitudes, from the main relation defined by less massive and
later-type spirals.
The presence of a change in slope at the high-mass end of the Tully-Fisher
relation has important consequences for the use of the Tully-Fisher relation as
a tool for estimating distances to galaxies or for probing galaxy evolution. In
particular, the luminosity evolution of massive galaxies since z = 1 may have
been significantly larger than estimated in several recent studies.
We also show that many of the galaxies with the largest offsets have
declining rotation curves and that the change in slope largely disappears when
we use the asymptotic rotation velocity as kinematic parameter. The remaining
deviations from linearity can be removed when we simultaneously use the total
baryonic mass (stars + gas) instead of the optical or near-infrared luminosity.
Our results strengthen the view that the Tully-Fisher relation fundamentally
links the mass of dark matter haloes with the total baryonic mass embedded in
them.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
The triggering of starbursts in low-mass galaxies
Strong bursts of star formation in galaxies may be triggered either by
internal or external mechanisms. We study the distribution and kinematics of
the HI gas in the outer regions of 18 nearby starburst dwarf galaxies, that
have accurate star-formation histories from HST observations of resolved
stellar populations. We find that starburst dwarfs show a variety of HI
morphologies, ranging from heavily disturbed HI distributions with major
asymmetries, long filaments, and/or HI-stellar offsets, to lopsided HI
distributions with minor asymmetries. We quantify the outer HI asymmetry for
both our sample and a control sample of typical dwarf irregulars. Starburst
dwarfs have more asymmetric outer HI morphologies than typical irregulars,
suggesting that some external mechanism triggered the starburst. Moreover,
galaxies hosting an old burst (>100 Myr) have more symmetric HI morphologies
than galaxies hosting a young one (<100 Myr), indicating that the former ones
probably had enough time to regularize their outer HI distribution since the
onset of the burst. We also investigate the nearby environment of these
starburst dwarfs and find that most of them (80) have at least one
potential perturber at a projected distance <200 kpc. Our results suggest that
the starburst is triggered either by past interactions/mergers between gas-rich
dwarfs or by direct gas infall from the IGM.Comment: 21 pages, 8 figures, 6 tables, accepted for publication in MNRA
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
Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby objects
We investigate the dynamics of starbursting dwarf galaxies, using both new
and archival HI observations. We consider 18 nearby galaxies that have been
resolved into single stars by HST observations, providing their star formation
history and total stellar mass. We find that 9 objects have a
regularly-rotating HI disk, 7 have a kinematically disturbed HI disk, and 2
show unsettled HI distributions. Two galaxies (NGC 5253 and UGC 6456) show a
velocity gradient along the minor axis of the HI disk, that we interpret as
strong radial motions. For galaxies with a regularly rotating disk we derive
rotation curves, while for galaxies with a kinematically disturbed disk we
estimate the rotation velocities in their outer parts. We derive baryonic
fractions within about 3 optical scale lengths and find that, on average,
baryons constitute at least 30 of the total mass. Despite the star
formation having injected 10 ergs in the ISM in the last 500
Myr, these starbursting dwarfs have both baryonic and gas fractions similar to
those of typical dwarf irregulars, suggesting that they did not eject a large
amount of gas out of their potential wells.Comment: Published on A&A (23 pages, 9 tables, 12 figures, plus an optical-HI
atlas). Typos fixe
WIYN Integral-Field Kinematics of Disk Galaxies
We have completed a new fiber array, SparsePak, optimized for
low-surface-brightness studies of extended sources on the WIYN telescope. We
are now using this array as a measuring engine of velocity and
velocity-dispersion fields of stars and ionized gas in disk galaxies from high
to low surface-brightness. Here we present commissioning data on the velocity
ellipsoids, surface densities and mass-to-light ratios in two blue, high
surface-brightness, yet small disks. If our preliminary results survive further
observation and more sophisticated analysis, then NGC 3949 has sigma_z/sigma_R
>> 1, implying strong vertical heating, while NGC 3982's disk is substantially
sub-maximal. These galaxies are strikingly unlike the Milky Way, and yet would
be seen more easily at high redshift.Comment: to appear in Disk Galaxies: Kinematics, Dynamics and Perturbations,
eds. E. Athanassoula and A. Bosma, ASP Conference Series; 4 pages with 4
embedded figure
Hydrogen 21-Centimeter Emission from a Galaxy at Cosmological Distance
We have detected the neutral atomic hydrogen (HI) emission line at a
cosmologically significant distance (z=0.18) in the rich galaxy cluster Abell
2218 with the Westerbork Synthesis Radio Telescope. The HI emission originates
in a spiral galaxy 2.0 megaparsecs from the cluster core. No other significant
detections have been made in the cluster, suggesting that the mechanisms that
remove neutral gas from cluster galaxies are efficient. We infer that fewer
than three gas-rich galaxies were accreted by Abell 2218 over the past 10^9
years. This low accretion rate is qualitatively consistent with low-density
cosmological models in which clusters are largely assembled at z>1.Comment: 7 pages, 2 figures. Science 2001 September 7; 293, 1800 (in reports).
Also available from
http://www.sciencemag.org/cgi/content/abstract/293/5536/180
The latest on Apertif
We describe a Phased Array Feed (PAF) system, called Apertif, which will be
installed in the Westerbork Synthesis Radio Telescope (WSRT). The aim of
Apertif is, at frequencies from 1.0 to 1.7 GHz, to increase the instantaneous
field of view of the WSRT 8 deg^2 and its observing bandwidth to 300 MHz with
high spectral resolution. This system will turn the WSRT into an effective
survey telescope with scientific applications ranging from deep surveys of the
northern sky of HI and OH emission and polarised continuum to efficient
searches for pulsars and transients. We present results obtained with a
prototype PAF installed in one of the WSRT dishes. These results demonstrate
that at decimetre wavelengths PAFs have excellent performance and that even for
a single beam on the sky they outperform single feed radio dishes. PAFs turn
radio telescopes into very effective survey instruments. Apertif is now fully
funded and the community is invited to express their interest in using Apertif
(http://www.astron.nl/radio-observatory/call-expressions-interest-apertif-surveys
)Comment: Talk presented at 'A New Golden Age for Radio Astronomy',
International SKA Forum 2010, 10-14 June 2010, Hof van Saksen, N
Reversible electrowetting and trapping of charge: model and experiments
We derive a model for voltage-induced wetting, so-called electrowetting, from
the principle of virtual displacement. Our model includes the possibility that
charge is trapped in or on the wetted surface. Experimentally, we show
reversible electrowetting for an aqueous droplet on an insulating layer of 10
micrometer thickness. The insulator is coated with a highly fluorinated layer
impregnated with oil, providing a contact-angle hysteresis lower than 2
degrees. Analyzing the data with our model, we find that until a threshold
voltage of 240 V, the induced charge remains in the liquid and is not trapped.
For potentials beyond the threshold, the wetting force and the contact angle
saturate, in line with the occurrence of trapping of charge in or on the
insulating layer. The data are independent of the polarity of the applied
electric field, and of the ion type and molarity. We suggest possible
microscopic origins for charge trapping.Comment: 13 pages & 5 figures; the paper has been accepted for publication in
Langmui
- …