3,779 research outputs found
Globular Clusters in NGC 4365: New K-band Imaging and a Reassessment of the Case for Intermediate-age Clusters
We study the globular cluster (GC) system of the Virgo giant elliptical
galaxy NGC 4365, using new wide-field VIK imaging. The GC colour distribution
has (at least) two peaks, but the colours of the red GCs appear more strongly
weighted towards intermediate colours compared to most other large ellipticals
and the integrated galaxy light. The intermediate-color/red peak may itself be
composed of two sub-populations, with clusters of intermediate colours more
concentrated towards the centre of the galaxy than both the blue and red GCs.
Nearly all intermediate-colour and red GCs in our sample show an offset towards
red V-K and/or blue V-I colours compared to SSP models for old ages in a
(V-K,V-I) diagram. This has in the past been interpreted as evidence for
intermediate ages. We also combine our VIK data with previously published
spectroscopy. The differences between observed and model colour-metallicity
relations are consistent with the offsets observed in the two-colour diagram,
with the metal-rich GCs being too red (by about 0.2 mag) in V-K and too blue
(by about 0.05 mag) in V-I compared to the models at a given metallicity. These
offsets cannot easily be explained as an effect of younger ages. We conclude
that, while intermediate GC ages cannot be definitively ruled out, an
alternative scenario is more likely whereby all the GCs are old but the
relative number of intermediate-metallicity GCs is greater than typical for
giant ellipticals. The main obstacle to reaching a definitive conclusion is the
lack of robust calibrations of integrated spectral and photometric properties
for stellar populations with near-solar metallicity. In any case, it is
puzzling that the intermediate-colour GCs in NGC 4365 are not accompanied by a
corresponding shift of the integrated galaxy light towards bluer colours.Comment: 23 pages, including 20 figures and 5 tables. Accepted for publication
in A&
Detailed abundances from integrated-light spectroscopy: Milky Way globular clusters
We test the performance of our analysis technique for integrated-light
spectra by applying it to seven well-studied Galactic GCs that span a wide
range of metallicities. Integrated-light spectra were obtained by scanning the
slit of the UVES spectrograph on the ESO Very Large Telescope across the
half-light diameters of the clusters. We modelled the spectra using resolved
HST colour-magnitude diagrams (CMDs), as well as theoretical isochrones, in
combination with standard stellar atmosphere and spectral synthesis codes. The
abundances of Fe, Na, Mg, Ca, Ti, Cr, and Ba were compared with literature data
for individual stars in the clusters. The typical differences between iron
abundances derived from our integrated-light spectra and those compiled from
the literature are less than 0.1 dex. A larger difference is found for one
cluster (NGC 6752), and is most likely caused primarily by stochastic
fluctuations in the numbers of bright red giants within the scanned area. As
expected, the alpha-elements (Ca, Ti) are enhanced by about 0.3 dex compared to
the Solar-scaled composition, while the [Cr/Fe] ratios are close to Solar. When
using up-to-date line lists, our [Mg/Fe] ratios also agree well with literature
data. Our [Na/Fe] ratios are, on average, 0.08-0.14 dex lower than average
values quoted in the literature, and our [Ba/Fe] ratios may be overestimated by
0.20-0.35 dex at the lowest metallicities. We find that analyses based on
theoretical isochrones give very similar results to those based on resolved
CMDs. Overall, the agreement between our integrated-light abundance
measurements and the literature data is satisfactory. Refinements of the
modelling procedure, such as corrections for stellar evolutionary and non-LTE
effects, might further reduce some of the remaining offsets.Comment: 35 pages, 16 figures, accepted for A&
Nitrogen abundances and multiple stellar populations in the globular clusters of the Fornax dSph
We use measurements of nitrogen abundances in red giants to search for
multiple stellar populations in the four most metal-poor globular clusters
(GCs) in the Fornax dwarf spheroidal galaxy (Fornax 1, 2, 3, and 5). New
imaging in the F343N filter, obtained with the Wide Field Camera 3 on the
Hubble Space Telescope, is combined with archival F555W and F814W observations
to determine the strength of the NH band near 3370 AA. After accounting for
observational errors, the spread in the F343N-F555W colors of red giants in the
Fornax GCs is similar to that in M15 and corresponds to an abundance range of
Delta([N/Fe])=2 dex, as observed also in several Galactic GCs. The spread in
F555W-F814W is, instead, fully accounted for by observational errors. The stars
with the reddest F343N-F555W colors (indicative of N-enhanced composition) have
more centrally concentrated radial distributions in all four clusters, although
the difference is not highly statistically significant within any individual
cluster. From double-Gaussian fits to the color distributions we find roughly
equal numbers of "N-normal" and "N-enhanced" stars (formally about 40% N-normal
stars in Fornax 1, 3, and 5 and 60% in Fornax 2). We conclude that GC
formation, in particular regarding the processes responsible for the origin of
multiple stellar populations, appears to have operated similarly in the Milky
Way and in the Fornax dSph. Combined with the high ratio of metal-poor GCs to
field stars in the Fornax dSph, this places an important constraint on
scenarios for the origin of multiple stellar populations in GCs.Comment: 16 pages, 7 figures, accepted for publication in Ap
Mortality post inpatient alcohol detoxification: a descriptive case series
<br>Background: Individuals with alcohol dependence often die prematurely. Scotland in particular has high rates of alcohol misuse compared to the rest of the UK and Europe. Although there is some evidence that rates of alcoholrelated harm and alcohol-related deaths are reducing in Europe, there is little evidence of this trend occurring in Scotland. Inpatient detoxification is an important, but expensive, option in the management of alcohol dependence. Little work has been done with regard possible clinical characteristics associated with mortality post discharge in this cohort of patients.</br>
<br>Methods: Retrospective electronic records were used to identify patients admitted electively for alcohol detoxification into a psychiatric ward in a district general hospital under the care of a single consultant addiction psychiatrist between 1/1/05 and 31/12/07 inclusively. Demographic and clinical factors were recorded. 5-year mortality data was obtained by linkage to the National Records of Scotland.</br>
<br>Results: 25.2% of patients admitted for elective alcohol detoxification died during the 5-year follow up period. 42.9% of deaths (n=12) were due to alcoholic liver disease, one death (3.6%) was of undetermined intent. A higher proportion of the deceased cohort was likely to have continued disulfiram (93% vs. 80%) and acamprosate (81% vs. 60%) than those surviving. There was no statistically significant difference in survival between individuals on medication and those not on medications in our cohort. The average consumption of units of alcohol per week in the deceased cohort was significantly higher than that calculated for the surviving cohort (298.8 units vs. 233.3 units p=0.0137).</br>
<br>Conclusion: Inpatient detoxification was associated with significant mortality at 5-year follow up post- discharge. The majority of deaths were due to liver disease while deaths due to accidents and of undetermined intent were relatively infrequent. Increased education and practical strategies such as “space and pace” aimed both at an individual and societal level to reduce alcohol consumption may help to reduce mortality associated with alcohol dependence post inpatient detoxification.</br>
Near-IR Spectroscopy of a Young Super-Star Cluster in NGC 6946: Chemical Abundances and Abundance Patterns
Using the NIRSPEC spectrograph at Keck II, we have obtained H and K-band
echelle spectra for a young (10-15 Myr), luminous (MV=-13.2) super-star cluster
in the nearby spiral galaxy NGC 6946. From spectral synthesis and equivalent
width measurements we obtain for the first time accurate abundances and
abundance patterns in an extragalactic super-star cluster. We find
[Fe/H]=-0.45+/-0.08 dex, an average alpha-enhancement of +0.22+/-0.1 dex, and a
relatively low 12C/13C~ 8+/-2 isotopic ratio. We also measure a velocity
dispersion of ~9.1 km/s, in agreement with previous estimates. We conclude that
integrated high-dispersion spectroscopy of massive star clusters is a promising
alternative to other methods for abundance analysis in extragalactic young
stellar populations.Comment: 5 pages, incl. 2 figures. Accepted for publication in MNRAS Letters.
The definitive version will be available at http://www.blackwell-synergy.co
Dynamical Models of Elliptical Galaxies -- II. M87 and its Globular Clusters
We study the Globular Cluster (GC) system of the nearby elliptical galaxy M87
using the newly available dataset with accurate kinematics (Strader et
al.2011). We find evidence for three distinct sub-populations of GCs in terms
of colours, kinematics and radial profiles. We show that a decomposition into
three populations (blue, intermediate and red GCs) is statistically preferred
to one with two or four populations, and relate them to the stellar profile. We
exploit the sub-populations to derive dynamical constraints on the mass and
Dark Matter (DM) content of M87 out to kpc. We use a class of global
mass-estimators (from Paper I), obtaining mass measurements at different
locations. M87's DM fraction changes from 0.2 at the starlight's
effective radius (6 kpc) to 0.95 at the distance probed by the most
extended, blue GCs (135 kpc). We supplement this with \textit{virial
decompositions}, exploiting the dynamical model to produce a separation into
multiple components. These yield the luminous mass as and the DM within 135 kpc as The inner DM density behaves as with
. This is steeper than the cosmologically preferred cusp
providing evidence of DM contraction. Finally, we combine
the GC separation into three sub-populations and the Jeans equations, obtaining
information on the orbits of the GC system. The centrally concentrated red GCs
exhibit tangential anisotropy, consistent with radial-orbit depletion by tidal
shredding. The most extended blue GCs have an isotropic velocity dispersion
tensor in the central parts, which becomes more tangential moving outwards,
consistent with adiabatic contraction of the DM halo.Comment: MNRAS (submitted), 16 pages, 10 figure
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