474 research outputs found
The evolution of the galactic morphological types in clusters
The morphological types of galaxies in nine clusters in the redshift range
0.1<z<0.25 are derived from very good seeing images taken at the NOT and the La
Silla Danish telescopes. With the purpose of investigating the evolution of the
fraction of different morphological types with redshift, we compare our results
with the morphological content of nine distant clusters studied by the MORPHS
group, five clusters observed with HST-WFPC2 at redshift z = 0.2-0.3, and
Dressler's (1980) large sample of nearby clusters. After having checked the
reliability of our morphological classification both in an absolute sense and
relative to the MORPHS scheme, we analyze the relative occurrence of
elliptical, S0 and spiral galaxies as a function of the cluster properties and
redshift. We find a large intrinsic scatter in the S0/E ratio, mostly related
to the cluster morphology. In particular, in our cluster sample, clusters with
a high concentration of ellipticals display a low S0/E ratio and, vice-versa,
low concentration clusters have a high S0/E. At the same time, the trend of the
morphological fractions and ratios with redshift clearly points to a
morphological evolution: as the redshift decreases, the S0 population tends to
grow at the expense of the spiral population, whereas the frequency of Es
remains almost constant. We also analyze the morphology-density (MD) relation
in our clusters and find that -similarly to higher redshift clusters- a good MD
relation exists in the high-concentration clusters, while it is absent in the
less concentrated clusters. Finally, the comparison of the MD relation in our
clusters with that of the D97 sample suggests that the transformation of
spirals into S0 galaxies becomes more efficient with decreasing local density.Comment: 24 pages including 11 figures and 4 tables, accepted for publication
in Ap
The WINGS Survey: a progress report
A two-band (B and V) wide-field imaging survey of a complete, all-sky X-ray
selected sample of 78 clusters in the redshift range z=0.04-0.07 is presented.
The aim of this survey is to provide the astronomical community with a complete
set of homogeneous, CCD-based surface photometry and morphological data of
nearby cluster galaxies located within 1.5 Mpc from the cluster center. The
data collection has been completed in seven observing runs at the INT and
ESO-2.2m telescopes. For each cluster, photometric data of about 2500 galaxies
(down to V~23) and detailed morphological information of about 600 galaxies
(down to V~21) are obtained by using specially designed automatic tools.
As a natural follow up of the photometric survey, we also illustrate a long
term spectroscopic program we are carrying out with the WHT-WYFFOS and AAT-2dF
multifiber spectrographs. Star formation rates and histories, as well as
metallicity estimates will be derived for about 350 galaxies per cluster from
the line indices and equivalent widths measurements, allowing us to explore the
link between the spectral properties and the morphological evolution in high-
to low-density environments, and across a wide range in cluster X-ray
luminosities and optical properties.Comment: 12 pages, 10 eps figures, Proceedings of the SAIt Conference 200
The hybrid solution for the Fundamental Plane
By exploiting the database of early-type galaxies (ETGs) members of the WINGS
survey of nearby clusters, we address here the long debated question of the
origin and shape of the Fundamental Plane (FP). Our data suggest that different
physical mechanisms concur in shaping and tilting the FP with respect to the
virial plane (VP) expectation. In particular, an hybrid solution in which the
structure of galaxies and their stellar population are the main contributors to
the FP tilt seems to be favoured. We find that the bulk of the tilt should be
attributed to structural non-homology, while stellar population effects play an
important but less crucial role. Our data indicate that the differential FP
tilt between the V and K-band is due to a sort of entanglement between
structural and stellar population effects, for which the inward steepening of
color profiles (V-K) tends to increase at increasing the stellar mass of ETGs.
The same analysis applied to the ATLAS3D and SDSS data in common with WINGS
(WSDSS throughout the paper) confirms our results, the only remarkable
difference being the less important role of the stellar mass-to-light-ratio in
determining the FP tilt. The ATLAS3D data also suggest that the tilt depends as
well on the dark matter (DM) fraction and on the rotational contribution to the
kinetic energy (Vrot/sigma). We show that the global properties of the FP can
be understood in terms of the underlying correlation among mass, structure and
stellar population of ETGs, for which, at increasing the stellar mass, ETGs
become (on average) older and more centrally concentrated. Finally, we show
that a Malmquist-like selection effect may mimic a differential evolution of
the mass-to-light ratio for galaxies of different masses. This should be taken
into account in the studies investigating the amount of the so called
downsizing phenomenon.Comment: 22 pages, 17 figure
Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
We present a homogeneous photometric and spectroscopic analysis of 18 stars
along the evolutionary sequence of the metal-poor globular cluster NGC 6397
([Fe/H] = -2), from the main-sequence turnoff point to red giants below the
bump. The spectroscopic stellar parameters, in particular stellar-parameter
differences between groups of stars, are in good agreement with broad-band and
Stroemgren photometry calibrated on the infrared-flux method. The spectroscopic
abundance analysis reveals, for the first time, systematic trends of iron
abundance with evolutionary stage. Iron is found to be 31% less abundant in the
turnoff-point stars than in the red giants. An abundance difference in lithium
is seen between the turnoff-point and warm subgiant stars. The impact of
potential systematic errors on these abundance trends (stellar parameters, the
hydrostatic and LTE approximations) is quantitatively evaluated and found not
to alter our conclusions significantly. Trends for various elements (Li, Mg,
Ca, Ti and Fe) are compared with stellar-structure models including the effects
of atomic diffusion and radiative acceleration. Such models are found to
describe the observed element-specific trends well, if extra (turbulent) mixing
just below the convection zone is introduced. It is concluded that atomic
diffusion and turbulent mixing are largely responsible for the sub-primordial
stellar lithium abundances of warm halo stars. Other consequences of atomic
diffusion in old metal-poor stars are also discussed.Comment: 20 pages (emulateapj), 11 figures, accepted for publication in Ap
Apneic Oxygenation in Diagnosis and Treatment of Lung Tumours in an Experimental Porcine Model
Objectives: Respiratory movements may complicate diagnostic and therapeutic procedures such as biopsies and stereotactic irradiation therapy in lung cancer patients. An attempt to avoid respiratory movements, up to 30 minutes, long enough for procedures was performed in an animal study.Methods: Ten anaesthetized minipigs ~30 kg were intubated in the trachea and small NiTi-stents were placed in various parts of the lungs. Using a muscle relaxing drug, the pigs were deprived of the ability to breathe for 30 minutes, a longer time than normally used for positioning and irradiation or for biopsies. No attempt to hyperventilate the animals was made prior to the apneic period. After a lung recruitment manoeuvre, a constant oxygen pressure of 20 cm water was applied to the airways. Using X-ray fluoroscopy, the position of the stents and thereby the movements of the lung, were monitored. Arterial gas analyses were performed every 5 minutes during the apneic period.Results: All animals survived 30 minutes of apneic oxygenation. The median arterial oxygen partial pressure actually rose from 11.8 to 54.3 kPa and there were no changes in oxygen saturation. The median arterial carbon dioxide partial pressure rose from 6.9 to 18.7 kPa and the median pH fell from 7.41 to 7.04 during 30 minutes of apneic oxygenation. Our setup, or our strategy of anaesthesia, did not immobilise the internal parts of the lungs satisfactorily, and must be improved before it can be used in a clinical situation. Conclusion: Physiologically, it is possible to stop respiration using apneic oxygenation for periods long enough to perform biopsies or stereotactic radiation therapy
Structure and deformation of the Kermadec forearc in response to subduction of the Pacific oceanic plate
The Tonga-Kermadec forearc is deforming in response to on-going subduction of the Pacific Plate beneath the Indo-Australian Plate. Previous research has focussed on the structural development of the forearc where large bathymetric features such as the Hikurangi Plateau and Louisville Ridge seamount chain are being subducted. Consequently, knowledge of the ‘background’ forearc in regions of normal plate convergence is limited. We report on an ∼250-km-long multichannel seismic reflection profile that was shot perpendicular to the Tonga-Kermadec trench at ∼28°S to determine the lateral and temporal variations in the structure, stratigraphy and deformation of the Kermadec forearc resulting solely from Pacific Plate subduction.
Interpretation of the seismic profile, in conjunction with regional swath bathymetry data, shows that the Pacific Plate exhibits horst and graben structures that accommodate bending-induced extensional stresses, generated as the trenchward dip of the crust increases. Trench infill is also much thicker than expected at 1 km which, we propose, results from increased sediment flux into and along the trench. Pervasive normal faulting of the mid-trench slope most likely accommodates the majority of the observed forearc extension in response to basal subduction erosion, and a structural high is located between the mid- and upper-trench slopes. We interpret this high as representing a dense and most likely structurally robust region of crust lying beneath this region.
Sediment of the upper-trench slope documents depositional hiatuses and on-going uplift of the arc. Strong along-arc currents appear to erode the Kermadec volcanic arc and distribute this sediment to the surrounding basins, while currents over the forearc redistribute deposits as sediment waves. Minor uplift of the transitional Kermadec forearc, observed just to the north of the profile, appears to relate to an underlying structural trend as well as subduction of the Louisville Ridge seamount chain 250 km to the north. Relative uplift of the Kermadec arc is observed from changes in the tilt of upper-trench slope deposits and extensional faulting of the basement immediately surrounding the Louisville Ridge
WINGS-SPE Spectroscopy in the WIde-field Nearby Galaxy-cluster Survey
Aims. We present the results from a comprehensive spectroscopic survey of the
WINGS (WIde-field Nearby Galaxy-cluster Survey) clusters, a program called
WINGS-SPE. The WINGS-SPE sample consists of 48 clusters, 22 of which are in the
southern sky and 26 in the north. The main goals of this spectroscopic survey
are: (1) to study the dynamics and kinematics of the WINGS clusters and their
constituent galaxies, (2) to explore the link between the spectral properties
and the morphological evolution in different density environments and across a
wide range in cluster X-ray luminosities and optical properties. Methods. Using
multi object fiber fed spectrographs, we observed our sample of WINGS cluster
galaxies at an intermediate resolu- tion of 6-9 A and, using a
cross-correlation technique, we measured redshifts with a mean accuracy of
about 45 km/s. Results. We present redshift measurements for 6137 galaxies and
their first analyses. Details of the spectroscopic observations are reported.
The WINGS-SPE has about 30% overlap with previously published data sets,
allowing us to do both a complete comparison with the literature and to extend
the catalogs. Conclusions. Using our redshifts, we calculate the velocity
dispersion for all the clusters in the WINGS-SPE sample. We almost trip- licate
the number of member galaxies known in each cluster with respect to previous
works. We also investigate the X-ray luminosity vs. velocity dispersion
relation for our WINGS-SPE clusters, and find it to be consistent with the form
Lx proportional to sigma^4.Comment: 16 pages, 10 Postscript figures, accepted for publication in
Astronomy and Astrophysic
Intravascular versus surface cooling for targeted temperature management after out-of-hospital cardiac arrest : an analysis of the TTH48 trial
BackgroundThe aim of this study was to explore the performance and outcomes for intravascular (IC) versus surface cooling devices (SFC) for targeted temperature management (TTM) after out-of-hospital cardiac arrest.MethodsA retrospective analysis of data from the Time-differentiated Therapeutic Hypothermia (TTH48) trial (NCT01689077), which compared whether TTM at 33 degrees C for 48h results in better neurologic outcomes compared with standard 24-h duration. Devices were assessed for the speed of cooling and rewarming rates. Precision was assessed by measuring temperature variability (TV), i.e., the standard deviation (SD) of all temperature measurements in the cooling phase. Main outcomes were overall mortality and poor neurological outcome, including death, severe disability, or vegetative status.ResultsA total of 352 patients had available data and were included in the analysis; of those, 218 (62%) were managed with IC. A total of 114/218 (53%) patients with IC and 61/134 (43%) with SFC were cooled for 48h (p=0.22). Time to target temperature (34 degrees C) was significantly shorter for patients treated with endovascular devices (2.2 [1.1-4.0] vs. 4.2 [2.7-6.0] h, pPeer reviewe
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