159 research outputs found
How Dry Are Red Mergers?
The focus of current research in galaxy evolution has increasingly turned to
understanding the effect that mergers have on the evolution of systems on the
red sequence. For those interactions purported to occur dissipationlessly (so
called "dry mergers"), it would appear that the role of gas is minimal.
However, if these mergers are not completely dry, then even low levels of gas
may be detectable. The purpose of our study is to test whether early type
galaxies with HI in or around them, or "wet" ellipticals, would have been
selected as dry mergers by the criteria in van Dokkum (2005, AJ, 130, 2647). To
that end, we examine a sample of 20 early types from the HI Rogues Gallery with
neutral hydrogen in their immediate environs. Of these, the 15 brightest and
reddest galaxies match the optical dry merger criteria, but in each case, the
presence of HI means that they are not truly dry.Comment: 8 pages plus 1 table and 5 figures; accepted for publication in A
The Evolution of the ISM in the Mildly Disturbed Spiral Galaxy NGC 4647
We present matched-resolution maps of HI and CO emission in the Virgo Cluster
spiral NGC 4647. The galaxy shows a mild kinematic disturbance in which one
side of the rotation curve flattens but the other side continues to rise. This
kinematic asymmetry is coupled with a dramatic asymmetry in the molecular gas
distribution but not in the atomic gas. An analysis of the gas column densities
and the interstellar pressure suggests that the H2/HI surface density ratio on
the east side of the galaxy is three times higher than expected from the
hydrostatic pressure contributed by the mass of the stellar disk. We discuss
the probable effects of ram pressure, gravitational interactions, and
asymmetric potentials on the interstellar medium and suggest it is likely that
a m=1 perturbation in the gravitational potential could be responsible for all
of the galaxy's features. Kinematic disturbances of the type seen here are
common, but the curious thing about NGC 4647 is that the molecular distribution
appears more disturbed than the HI distribution. Thus it is the combination of
the two gas phases that provides such interesting insight into the galaxy's
history and into models of the interstellar medium.Comment: ApJ, accepte
Electrons in a ferromagnetic metal with a domain wall
We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.Comment: 10 pages with 4 figure
Ballistic and diffuse transport through a ferromagnetic domain wall
We study transport through ballistic and diffuse ferromagnetic domain walls
in a two-band Stoner model with a rotating magnetization direction. For a
ballistic domain wall, the change in the conductance due to the domain wall
scattering is obtained from an adiabatic approximation valid when the length of
the domain wall is much longer than the Fermi wavelength. In diffuse systems,
the change in the resistivity is calculated using a diagrammatic technique to
the lowest order in the domain wall scattering and taking into account
spin-dependent scattering lifetimes and screening of the domain wall potential.Comment: 9 pages, 3 figures, to appear in Phys. Rev.
The MeerKAT Fornax Survey
We present the science case and observations plan of the MeerKAT Fornax
Survey, an HI and radio continuum survey of the Fornax galaxy cluster to be
carried out with the SKA precursor MeerKAT. Fornax is the second most massive
cluster within 20 Mpc and the largest nearby cluster in the southern
hemisphere. Its low X-ray luminosity makes it representative of the environment
where most galaxies live and where substantial galaxy evolution takes place.
Fornax's ongoing growth makes it an excellent laboratory for studying the
assembly of clusters, the physics of gas accretion and stripping in galaxies
falling in the cluster, and the connection between these processes and the
neutral medium in the cosmic web.
We will observe a region of 12 deg reaching a projected distance of 1.5
Mpc from the cluster centre. This will cover a wide range of environment
density out to the outskirts of the cluster, where gas-rich in-falling groups
are found. We will: study the HI morphology of resolved galaxies down to a
column density of a few times 1e+19 cm at a resolution of 1 kpc; measure
the slope of the HI mass function down to M(HI) 5e+5 M(sun); and attempt to
detect HI in the cosmic web reaching a column density of 1e+18 cm at a
resolution of 10 kpc.Comment: Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA",
Stellenbosch, 25-27 May 201
Resistance of a domain wall in the quasiclassical approach
Starting from a simple microscopic model, we have derived a kinetic equation
for the matrix distribution function. We employed this equation to calculate
the conductance in a mesoscopic F'/F/F' structure with a domain wall (DW).
In the limit of a small exchange energy and an abrupt DW, the conductance
of the structure is equal to . Assuming that the scattering times
for electrons with up and down spins are close to each other we show that the
account for a finite width of the DW leads to an increase in this conductance.
We have also calculated the spatial distribution of the electric field in the F
wire. In the opposite limit of large (adiabatic variation of the
magnetization in the DW) the conductance coincides in the main approximation
with the conductance of a single domain structure . The account for rotation of
the magnetization in the DW leads to a negative correction to this conductance.
Our results differ from the results in papers published earlier.Comment: 11 pages; replaced with revised versio
Ram Pressure Stripping in the Low Luminosity Virgo Cluster Elliptical Galaxy NGC 4476
We present a deep VLA search for HI emission from the low-luminosity Virgo
Cluster elliptical galaxy NGC 4476, which contains 1.1 x 10^8 M_sun of
molecular gas in an undisturbed disk in regular rotation. No HI was detected.
The rms noise in the final image corresponds to a 3 sigma column density
sensitivity of 1.2 x 10^20 cm^{-2} at the position of NGC 4476, averaged over
the 4 kpc beam. The total HI mass is less than 1.5 x 10^7 M_sun. If we compare
our HI upper limit to the H_2 content, we find that NGC 4476 is extremely
deficient in HI compared to other galaxies detected in these two species. The
H_2/HI mass ratio for NGC 4476 is > 7, whereas typical H_2/HI ratios for
elliptical galaxies detected in both HI and H_2 are <~2. Based on this extreme
HI deficiency and the intra-cluster medium (ICM) density at the projected
distance from M87 we argue that either NGC 4476 has undergone ram-pressure
stripping while traveling through the Virgo cluster core or its average
molecular gas density is larger and its interstellar UV field is smaller than
in typical spiral galaxies. NGC 4476 is located 12' in projection from M87,
which causes extreme continuum confusion problems. We also discuss in detail
the techniques used for continuum subtraction. The spectral dynamic range of
our final image is 50,000 to 1.Comment: accepted by A
Major differences in clinical presentation, diagnosis and management of men and women with autosomal inherited bleeding disorders
Background: In recent years, more awareness is raised about sex-specific dilemmas in inherited bleeding disorders. However, no large studies have been performed to assess differences in diagnosis, bleeding phenotype and management of men and women with bleeding disorders. Therefore, we investigated sex differences in a large cohort of well-defined patients with autosomal inherited bleeding disorders (von Willebrand disease (VWD), rare bleeding disorders (RBDs) and congenital platelet defects (CPDs)).Methods: We included patients from three nationwide cross-sectional studies on VWD, RBDs and CPDs in the Netherlands, respectively the WiN, RBiN and TiN study. In all studies a bleeding score (BS) was obtained, and patients filled in an extensive questionnaire on the management and burden of their disorder.Findings: We included 1092 patients (834 VWD; 196 RBD; 62 CPD), of whom 665 (60.9%) were women. Women were more often referred because of a bleeding diathesis than men (47.9% vs 36.6%, p = 0.002). Age of first bleeding was similar between men and women, respectively 8.9 +/- 13.6 (mean +/- sd) years and 10.6 +/- 11.3 years (p = 0.075). However, the diagnostic delay, which was defined as time from first bleeding to diagnosis, was longer in women (11.6 +/- 16.4 years) than men (7.7 +/- 16.6 years, p = 0.002). Similar results were found when patients referred for bleeding were analyzed separately. Of women aging 12 years or older, 469 (77.1%) had received treatment because of sex-specific bleeding.Interpretation: Women with autosomal inherited bleeding disorders are more often referred for bleeding, have a longer diagnostic delay, and often require treatment because of sex-specific bleeding. (C) 2021 The Authors. Published by Elsevier Ltd.Clinical epidemiolog
Parsec-Scale Images of Flat-Spectrum Radio Sources in Seyfert Galaxies
We present high angular resolution (~2 mas) radio continuum observations of
five Seyfert galaxies with flat-spectrum radio nuclei, using the VLBA at 8.4
GHz. The goal of the project is to test whether these flat-spectrum cores
represent thermal emission from the accretion disk, as inferred previously by
Gallimore et al. for NGC 1068, or non-thermal, synchrotron self-absorbed
emission, which is believed to be responsible for more powerful, flat-spectrum
nuclear sources in radio galaxies and quasars. In four sources (T0109-383, NGC
2110, NGC 5252, Mrk 926), the nuclear source is detected but unresolved by the
VLBA, indicating brightness temperatures in excess of 10^8 K and sizes, on
average, less than 1 pc. We argue that the radio emission is non-thermal and
synchrotron self-absorbed in these galaxies, but Doppler boosting by
relativistic outflows is not required. Synchrotron self-absorption brightness
temperatures suggest intrinsic source sizes smaller than ~0.05-0.2 pc, for
these four galaxies, the smallest of which corresponds to a light-crossing time
of ~60 light days or 10^4 gravitational radii for a 10^8 M_sun black hole.
We also present MERLIN and VLA observations of NGC 4388, which was undetected
by the VLBA, and argue that the observed, flat-spectrum, nuclear radio emission
in this galaxy represents optically thin, free-free radiation from dense
thermal gas on scales ~0.4 to a few pc. It is notable that the two Seyfert
galaxies with detected thermal nuclear radio emission (NGC 1068 and NGC 4388)
both have large X-ray absorbing columns, suggesting that columns in excess of
\~10^{24} cm^{-2} are needed for such disks to be detectable. (Abridged)Comment: 36 pages including 5 tables and 4 figures; accepted for publication
in Ap
Spin dependent scattering of a domain-wall of controlled size
Magnetoresistance measurements in the CPP geometry have been performed on
single electrodeposited Co nanowires exchange biased on one side by a sputtered
amorphous GdCo layer. This geometry allows the stabilization of a single domain
wall in the Co wire, the thickness of which can be controlled by an external
magnetic field. Comparing magnetization, resistivity, and magnetoresistance
studies of single Co nanowires, of GdCo layers, and of the coupled system,
gives evidence for an additional contribution to the magnetoresistance when the
domain wall is compressed by a magnetic field. This contribution is interpreted
as the spin dependent scattering within the domain wall when the wall thickness
becomes smaller than the spin diffusion length.Comment: 9 pages, 13 figure
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