624 research outputs found
Early-type galaxies at large galactocentric radii - I. Stellar kinematics and photometric properties
We present the results of a combined analysis of the kinematic and
photometric properties at large galactocentric radii of a sample of 14
low-luminosity early-type galaxies in the Fornax and Virgo clusters. From
Gemini South GMOS long-slit spectroscopic data we measure radial profiles of
the kinematic parameters v_{rot}, sigma, h_{3}, and h_{4} out to ~ 1 - 3
effective radii. Multi-band imaging data from the HST/ACS are employed to
evaluate surface brightness profiles and isophotal shape parameters of
ellipticity, position angle and discyness/boxiness. The galaxies are found to
host a cold and old stellar component which extend to the largest observed
radii and that is the dominant source of their dynamical support. The
prevalence of discy-shaped isophotes and the radial variation of their
ellipticity are signatures of a gradual gas dissipation. An early star-forming
collapse appears to be the main mechanism acting in the formation of these
objects. Major mergers are unlikely to have occurred in these galaxies. We can
not rule out a minor merging origin for these galaxies, but a comparison of our
results with model predictions of different merger categories places some
constraints on the possible merger progenitors. These merger events are
required to happen at high-redshift (i.e., z > 1), between progenitors of
different mass ratio (at least 3:1) and containing a significant amount of gas
(i.e., > 10 percent). A further scenario is that the low-luminosity galaxies
were originally late-type galaxies, whose star formation has been truncated by
removal of gas and subsequently the disc has been dynamically heated by high
speed encounters in the cluster environment.Comment: 19 pages, 16 figures (Contact author for high resolution version of
figures 1,2,3), MNRAS, accepted. The second paper of the series "Early-type
galaxies at large galactocentric radii - II. Metallicity gradients and the
[Z/H]-mass, [alpha/Fe] mass relations" can be found at arXiv:1006.169
A high Eddington-ratio, true Seyfert 2 galaxy candidate: implications for broad-line-region models
A bright, soft X-ray source was detected on 2010 July 14 during an
XMM--Newton slew at a position consistent with the galaxy GSN 069 (z=0.018).
Previous ROSAT observations failed to detect the source and imply that GSN 069
is now >240 times brighter than it was in 1994 in the soft X-ray band. We
report here results from a ~1 yr monitoring with Swift and XMM-Newton, as well
as from optical spectroscopy. GSN 069 is an unabsorbed, ultra-soft source in
X-rays, with no flux detected above ~1 keV. The soft X-rays exhibit significant
variability down to timescales of hundreds of seconds. The UV-to-X-ray spectrum
of GSN 069 is consistent with a pure accretion disc model which implies an
Eddington ratio of ~0.5 and a black hole mass of ~ 1.2 million solar masses. A
new optical spectrum, obtained ~3.5 months after the XMM-Newton slew detection,
is consistent with earlier spectra and lacks any broad line component,
classifying the source as a Seyfert 2 galaxy. The lack of cold X-ray absorption
and the short timescale variability in the soft X-rays rule out a standard
Seyfert 2 interpretation of the X-ray data. We discuss our results within the
framework of two possible scenarios for the broad-line-region (BLR) in AGN,
namely the two-phase model (cold BLR clouds in pressure equilibrium with a
hotter medium), and models in which the BLR is part of an outflow, or
disc-wind. Finally, we point out that GSN 069 may be a member of a population
of super-soft AGN whose SED is completely dominated by accretion disc emission,
as it is the case in some black hole X-ray binary transients during their
outburst evolution. The disc emission for a typical AGN with larger black hole
mass than GSN 069 does not enters the soft X-ray band, so that GSN 069-like
objects would likely be missed by current X-ray surveys, or mis-classified as
Compton-thick candidates. (ABRIDGED)Comment: Accepted for publication in MNRA
A year-round measurement of water-soluble trace and rare earth elements in arctic aerosol: Possible inorganic tracers of specific events
This study presents the year-round variability of the water-soluble fraction of trace elements (wsTE) and rare earth elements (wsREE) among size segregated airborne particulate matter samples collected at Ny-Ă… lesund in the Svalbard Archipelago from 26 February 2018 to 26 February 2019. Six different aerosol dimensional fractions were collected using a multi-stage Andersen impactor to better understand local and global circulation with the aim of disentangling the source of inorganic tracers from specific natural or anthropogenic sources. The wsTE and wsREE content, especially in the finest fractions in remote areas, is primarily related to long-range transport and it gives valuable information on (1) the global circulation, (2) the natural sources and (3) the contribution of human activities to aerosol composition. A Factor Analysis was applied to the dataset, including levoglucosan and methanesulfonic acid (MSA), to assess the possibility of using certain inorganic tracers as indicators of specific transport events or circulation regimes. We also investigate back-trajectories to determine potential source areas
Continuous flow analysis method for determination of soluble iron and aluminium in ice cores
n/
Towards the Use of Neuromusculoskeletal Modeling in Clinical Practice:A Feasibility Study in Parkinson Disease Patients
A model for nulling and mode changing in pulsars
We propose that in some pulsars the magnetosphere has different states with
different geometries or/and different distributions of currents, it
occasionally switches between them. These states have different spindown rates
and emission beams, in some of the states no radioemission is produced at all.
Switching into a different state manifests as a mode change when we see
different parts of the emission beam or the beams in different states have
significantly different geometries, it manifests as nulling when we either miss
the new beam or no radioemission is generated in the new state. We show that
modest variations in the beam shape can be accompanied by large variations in
the pulsar spindown rate W - the dependence of W on the opening angle of the
emission beam can be as strong as W\propto\alpha^4. We speculate about
physical mechanisms which may cause reconfiguration of the magnetosphere.Comment: 5 pages, 1 figure; MNRAS, in pres
A Millisecond Interferometric Search for Fast Radio Bursts with the Very Large Array
We report on the first millisecond timescale radio interferometric search for
the new class of transient known as fast radio bursts (FRBs). We used the Very
Large Array (VLA) for a 166-hour, millisecond imaging campaign to detect and
precisely localize an FRB. We observed at 1.4 GHz and produced visibilities
with 5 ms time resolution over 256 MHz of bandwidth. Dedispersed images were
searched for transients with dispersion measures from 0 to 3000 pc/cm3. No
transients were detected in observations of high Galactic latitude fields taken
from September 2013 though October 2014. Observations of a known pulsar show
that images typically had a thermal-noise limited sensitivity of 120 mJy/beam
(8 sigma; Stokes I) in 5 ms and could detect and localize transients over a
wide field of view. Our nondetection limits the FRB rate to less than
7e4/sky/day (95% confidence) above a fluence limit of 1.2 Jy-ms. Assuming a
Euclidean flux distribution, the VLA rate limit is inconsistent with the
published rate of Thornton et al. We recalculate previously published rates
with a homogeneous consideration of the effects of primary beam attenuation,
dispersion, pulse width, and sky brightness. This revises the FRB rate downward
and shows that the VLA observations had a roughly 60% chance of detecting a
typical FRB and that a 95% confidence constraint would require roughly 500
hours of similar VLA observing. Our survey also limits the repetition rate of
an FRB to 2 times less than any known repeating millisecond radio transient.Comment: Submitted to ApJ. 13 pages, 9 figure
- …