141 research outputs found
Magnetorotational instability in cool cores of galaxy clusters
Clusters of galaxies are embedded in halos of optically thin, gravitationally
stratified, weakly magnetized plasma at the system's virial temperature. Due to
radiative cooling and anisotropic heat conduction, such intracluster medium
(ICM) is subject to local instabilities, which are combinations of the thermal,
magnetothermal and heat-flux-driven buoyancy instabilities. If the ICM rotates
significantly, its stability properties are substantially modified and, in
particular, also the magnetorotational instability (MRI) can play an important
role. We study simple models of rotating cool-core clusters and we demonstrate
that the MRI can be the dominant instability over significant portions of the
clusters, with possible implications for the dynamics and evolution of the cool
cores. Our results give further motivation for measuring the rotation of the
ICM with future X-ray missions such as ASTRO-H and ATHENA.Comment: 17 pages, 10 figures, accepted for publication in Journal of Plasma
Physics, Special Issue "Complex Plasma Phenomena in the Laboratory and in the
Universe
A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation
We present a new discrete chemo-dynamical axisymmetric modeling technique,
which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement
over previous Jeans models is that realistic chemical distributions are
included directly in the dynamical modelling of the discrete data. This avoids
loss of information due to spatial binning and eliminates the need for hard
cuts to remove contaminants and to separate stars based on their chemical
properties. Using a combined likelihood in position, metallicity and
kinematics, we find that our models naturally separate Sculptor stars into a
metal-rich and a metal-poor population. Allowing for non-spherical symmetry,
our approach provides a central slope of the dark matter density of . The metal-rich population is nearly isotropic (with
) while the metal-poor population is tangentially
anisotropic (with ) around the half light radius
of kpc. A weak internal rotation of the metal-rich population is
revealed with . We run tests using mock data
to show that a discrete dataset with stars is required to
distinguish between a core () and cusp (), and to
constrain the possible internal rotation to better than confidence
with our model. We conclude that our discrete chemo-dynamical modelling
technique provides a flexible and powerful tool to robustly constrain the
internal dynamics of multiple populations, and the total mass distribution in a
stellar system.Comment: Accepted by MNRA
Unveiling the stellar halo with TGAS
The detailed study of the Galactic stellar halo may hold the key to unlocking the assembly history of the Milky Way. Here, we present a machine learning model for selecting metal poor stars from the TGAS catalogue using 5 dimensional phase-space information, coupled with optical and near-IR photometry. We characterise the degree of substructure in our halo sample in the Solar neighbourhood by measuring the velocity correlation function.<br/
The power of teaming up HST and Gaia:The first proper motion measurement of the distant cluster NGC 2419
Aims: We present the first measurement of the proper motion and orbit of the
very distant and intriguing globular cluster NCG 2419. Methods: We have
combined data from HST and Gaia DR1 to derive the relative proper motions of
stars in the direction to the cluster. To tie to an absolute reference frame we
have used a background galaxy located in the field. Results: We find the
absolute proper motion of NGC 2419 to be ,
)=() mas/yr. We have integrated the
orbit of the cluster in a Galactic potential and found it to oscillate between
53 kpc and 98 kpc on a nearly polar orbit. This makes it very
likely that NGC 2419 is a former cluster of the Sagittarius dwarf spheroidal
galaxy, also because it shares the same sense of rotation around the Milky Way.Comment: 5 pages, 4 figures, accepted for publication by A&A Letter
Gaia DR2 orbital properties for field stars with globular cluster-like CN band strenghts
Context. Large spectroscopic surveys of the Milky Way have revealed that a small population of stars in the halo have light element abundances comparable to those found in globular clusters. The favoured explanation for the peculiar abundances of these stars is that they originated inside a globular cluster and were subsequently lost. Aims. Using orbit calculations we assess the likelihood that an existing sample of 57 field stars with globular cluster-like CN band strength originated in any of the currently known Milky Way globular clusters. Methods. Using Sloan Digital Sky Survey and Gaia data, we determine orbits and integrals of motion of our sample of field stars, and use these values and metallicity to identify likely matches to globular clusters. The pivot hypothesis is that had these stars been stripped from such objects, they would have remained on very similar orbits. Results. We find that similar to 70% of the sample of field stars have orbital properties consistent with the halo of the Milky Way; however, only 20 stars have likely orbital associations with an existing globular cluster. The remaining similar to 30% of the sample have orbits that place them in the outer Galactic disc. No cluster of similar metallicity is known on analogous disc orbits. Conclusions. The orbital properties of the halo stars seem to be compatible with the globular cluster escapee scenario. The stars in the outer disc are particularly surprising and deserve further investigation to establish their nature
The angular momentum of disc galaxies at z=1
We investigate the relation between stellar mass and specific stellar angular
momentum, or `Fall relation', for a sample of 17 isolated, regularly rotating
disc galaxies at z=1. All galaxies have a) rotation curves determined from
Halpha emission-line data; b) HST imaging in optical and infrared filters; c)
robust determinations of their stellar masses. We use HST images in f814w and
f160w filters, roughly corresponding to rest-frames B and I bands, to extract
surface brightness profiles for our systems. We robustly bracket the specific
angular momentum by assuming that rotation curves beyond the outermost Halpha
rotation point stay either flat or follow a Keplerian fall-off. By comparing
our measurements with those determined for disc galaxies in the local Universe,
we find no evolution in the Fall relation in the redshift range 0<z<1,
regardless of the band used and despite the uncertainties in the stellar
rotation curves at large radii. This result holds unless stellar masses at z=1
are systematically underestimated by more than 50%. Our findings are compatible
with expectations based on a LCDM cosmological framework and support a scenario
where both the stellar Tully-Fisher and mass-size relations for spirals do not
evolve significantly in this redshift range.Comment: 11 pages, 4 figures, 1 table. Accepted by A&
Risk for intracranial hemorrhage in individuals after mild traumatic brain injury who are taking serotonergic antidepressants
BackgroundSerotonergic antidepressants may predispose to bleeding, but little is known of the risk for traumatic intracranial bleeding. MethodsThis was a prospective case-control study of 218 patients with mild traumatic brain injuries (TBI) who were treated at a Finnish tertiary trauma hospital. Injury-related information and clinical findings were prospectively collected in the emergency department. Detailed pre-injury health history was collected from electronic medical records. Information on the use of serotonergic antidepressants was attained from the Finnish national prescription registry. All head CT scans were reviewed by a neuroradiologist based on the Common Data Elements. Cases were patients with traumatic intracranial hemorrhage on head CT. Controls were patients from the same cohort, but without traumatic intracranial lesions on CT. The proportion with traumatic intracranial bleeding for patients on serotonergic antidepressant medication was compared to the proportion for patients not on serotonergic medication. ResultsThe study cohort consisted of 24 cases with traumatic intracranial bleeding and 194 injured controls. The median age of the sample was 70 years (interquartile range = 50-83). One fifth (21.6%) of all the patients were taking a serotonergic antidepressant. Of the patients on an antidepressant, 10.6% (5/47) had an acute hemorrhagic lesion compared to 11.1% (19/171) of those who were not on an antidepressant (p = 0.927). In the regression analysis, traumatic intracranial hemorrhage was not associated with antidepressant use. ConclusionSerotonergic antidepressant use was not associated with an increased risk of traumatic intracranial hemorrhage after a mild TBI. The patients in this relatively small cohort were mostly middle-aged and older adults. These factors limit the generalizability of the results in younger patients with mild TBI.Peer reviewe
Potential of heart fatty-acid binding protein, neurofilament light, interleukin-10 and S100 calcium-binding protein B in the acute diagnostics and severity assessment of traumatic brain injury
Background: There is substantial interest in blood biomarkers as fast and objective diagnostic tools for traumatic brain injury (TBI) in the acute setting.
Methods: Adult patients (≥18) with TBI of any severity and indications for CT scanning and orthopaedic injury controls were prospectively recruited during 2011–2013 at Turku University Hospital, Finland. The severity of TBI was classified with GCS: GCS 13–15 was classified as mild (mTBI); GCS 9–12 as moderate (moTBI) and GCS 3–8 as severe (sTBI). Serum samples were collected within 24 hours of admission and biomarker levels analysed with high-performance kits. The ability of biomarkers to distinguish between severity of TBI and CT-positive and CT-negative patients was assessed.
Results: Among 189 patients recruited, neurofilament light (NF-L) was obtained from 175 patients with TBI and 40 controls. S100 calcium-binding protein B (S100B), heart fatty-acid binding protein (H-FABP) and interleukin-10 (IL-10) were analysed for 184 patients with TBI and 39 controls. There were statistically significant differences between levels of all biomarkers between the severity classes, but none of the biomarkers distinguished patients with moTBI from patients with sTBI. Patients with mTBI discharged from the ED had lower levels of IL-10 (0.26, IQR=0.21, 0.39 pg/mL), H-FABP (4.15, IQR=2.72, 5.83 ng/mL) and NF-L (8.6, IQR=6.35, 15.98 pg/mL) compared with those admitted to the neurosurgical ward, IL-10 (0.55, IQR=0.31, 1.42 pg/mL), H-FABP (6.022, IQR=4.19, 20.72 ng/mL) and NF-L (13.95, IQR=8.33, 19.93 pg/mL). We observed higher levels of H-FABP and NF-L in older patients with mTBI. None of the biomarkers or their combinations was able to distinguish CT-positive (n=36) or CT-negative (n=58) patients with mTBI from controls.
Conclusions: S100B, H-FABP, NF-L and IL-10 levels in patients with mTBI were significantly lower than in patients with moTBI and sTBI but alone or in combination, were unable to distinguish patients with mTBI from orthopaedic controls. This suggests these biomarkers cannot be used alone to diagnose mTBI in trauma patients in the acute setting.
Data availability statement:
Data are available on reasonable request. De-identified clinical, imaging and biochemical data not published within the article can be shared with a qualified investigator by request
Admission Levels of Interleukin 10 and Amyloid β 1–40 Improve the Outcome Prediction Performance of the Helsinki Computed Tomography Score in Traumatic Brain Injury
BACKGROUND: Blood biomarkers may enhance outcome prediction performance of head computed tomography scores in traumatic brain injury (TBI). OBJECTIVE: To investigate whether admission levels of eight different protein biomarkers can improve the outcome prediction performance of the Helsinki computed tomography score (HCTS) without clinical covariates in TBI. MATERIALS AND METHODS: ighty-two patients with computed tomography positive TBIs were included in this study. Plasma levels of β-amyloid isoforms 1–40 (Aβ40) and 1–42 (Aβ42), glial fibrillary acidic protein, heart fatty acid-binding protein, interleukin 10 (IL-10), neurofilament light, S100 calcium-binding protein B, and total tau were measured within 24 h from admission. The patients were divided into favorable (Glasgow Outcome Scale—Extended 5–8, n = 49) and unfavorable (Glasgow Outcome Scale—Extended 1–4, n = 33) groups. The outcome was assessed 6–12 months after injury. An optimal predictive panel was investigated with the sensitivity set at 90–100%. RESULTS: The HCTS alone yielded a sensitivity of 97.0% (95% CI: 90.9–100) and specificity of 22.4% (95% CI: 10.2–32.7) and partial area under the curve of the receiver operating characteristic of 2.5% (95% CI: 1.1–4.7), in discriminating patients with favorable and unfavorable outcomes. The threshold to detect a patient with unfavorable outcome was an HCTS > 1. The three best individually performing biomarkers in outcome prediction were Aβ40, Aβ42, and neurofilament light. The optimal panel included IL-10, Aβ40, and the HCTS reaching a partial area under the curve of the receiver operating characteristic of 3.4% (95% CI: 1.7–6.2) with a sensitivity of 90.9% (95% CI: 81.8–100) and specificity of 59.2% (95% CI: 40.8–69.4). CONCLUSION: Admission plasma levels of IL-10 and Aβ40 significantly improve the prognostication ability of the HCTS after TBI
The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
The assembly process of our Galaxy can be retrieved using the motions and
chemistry of individual stars. Chemo-dynamical studies of the nearby halo have
long hinted at the presence of multiple components such as streams, clumps,
duality and correlations between the stars' chemical abundances and orbital
parameters. More recently, the analysis of two large stellar surveys have
revealed the presence of a well-populated chemical elemental abundance
sequence, of two distinct sequences in the colour-magnitude diagram, and of a
prominent slightly retrograde kinematic structure all in the nearby halo, which
may trace an important accretion event experienced by the Galaxy. Here report
an analysis of the kinematics, chemistry, age and spatial distribution of stars
in a relatively large volume around the Sun that are mainly linked to two major
Galactic components, the thick disk and the stellar halo. We demonstrate that
the inner halo is dominated by debris from an object which at infall was
slightly more massive than the Small Magellanic Cloud, and which we refer to as
Gaia-Enceladus. The stars originating in Gaia-Enceladus cover nearly the full
sky, their motions reveal the presence of streams and slightly retrograde and
elongated trajectories. Hundreds of RR Lyrae stars and thirteen globular
clusters following a consistent age-metallicity relation can be associated to
Gaia-Enceladus on the basis of their orbits. With an estimated 4:1 mass-ratio,
the merger with Gaia-Enceladus must have led to the dynamical heating of the
precursor of the Galactic thick disk and therefore contributed to the formation
of this component approximately 10 Gyr ago. These findings are in line with
simulations of galaxy formation, which predict that the inner stellar halo
should be dominated by debris from just a few massive progenitors.Comment: 19 pages, 8 figures. Published in Nature in the issue of Nov. 1st,
2018. This is the authors' version before final edit
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