22,579 research outputs found
The galaxy counterpart of the high-metallicity and 16 kpc impact parameter DLA towards Q0918+1636 - a challenge to galaxy formation models?
The quasar Q0918+1636 (z=3.07) has an intervening high-metallicity Damped
Lyman-alpha Absorber (DLA) along the line of sight, at a redshift of z=2.58.
The DLA is located at a large impact parameter of 16.2 kpc, and has an almost
solar metallicity. It is shown, that a novel type of cosmological galaxy
formation models, invoking a new SNII feedback prescription, the Haardt & Madau
(2012) UVB field and explicit treatment of UVB self-shielding, can reproduce
the observed characteristics of the DLA. UV radiation from young stellar
populations in the galaxy, in particular in the photon energy range 10.36-13.61
eV (relating to Sulfur II abundance), are also considered in the analysis. It
is found that a) for L~L* galaxies (at z=2.58), about 10% of the sight-lines
through the galaxies at impact parameter 16.2 kpc will display a Sulfur II
column density N(SII) 10 cm (the observed value for the
DLA), and b) considering only cases where a near-solar metallicity will be
detected at 16.2 kpc impact parameter, the probability distribution of galaxy
SFR peaks near the value observed for the DLA galaxy counterpart of ~27
Msun/yr. It is argued, that the bulk of the alpha-elements, like Sulfur, traced
by the high metal column density, b=16.2 kpc absorption lines, were produced by
evolving young stars in the inner galaxy, and later transported outward by
galactic winds.Comment: 22 pages, 24 figures, MNRAS in pres
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&
CDM, Feedback and the Hubble Sequence
We have performed TreeSPH simulations of galaxy formation in a standard LCDM
cosmology, including effects of star formation, energetic stellar feedback
processes and a meta-galactic UV field, and obtain a mix of disk, lenticular
and elliptical galaxies. The disk galaxies are deficient in angular momentum by
only about a factor of two compared to observed disk galaxies. The stellar
disks have approximately exponential surface density profiles, and those of the
bulges range from exponential to r^{1/4}, as observed. The bulge-to-disk ratios
of the disk galaxies are consistent with observations and likewise are their
integrated B-V colours, which have been calculated using stellar population
synthesis techniques. Furthermore, we can match the observed I-band
Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk
galaxies, (M/L_I), is about 0.8. The ellipticals and lenticulars have
approximately r^{1/4} stellar surface density profiles, are dominated by
non-disklike kinematics and flattened due to non-isotropic stellar velocity
distributions, again consistent with observations.Comment: 6 pages, incl. 4 figs. To appear in the proceedings of the
EuroConference "The Evolution of Galaxies: II - Basic Building Blocks", Ile
de La Reunion (France), 16-21 October 2001 (Slightly updated version). A much
more comprehensive paper about this work with links to pictures of some of
the galaxies can be found at http://babbage.sissa.it/abs/astro-ph/020436
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
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
Low-background temperature sensors fabricated on parylene substrates
Temperature sensors fabricated from ultra-low radioactivity materials have
been developed for low-background experiments searching for neutrinoless
double-beta decay and the interactions of WIMP dark matter. The sensors consist
of electrical traces photolithographically-patterned onto substrates of
vapor-deposited parylene. They are demonstrated to function as expected, to do
so reliably and robustly, and to be highly radio-pure. This work is a
proof-of-concept study of a technology that can be applied to broad class of
electronic circuits used in low-background experiments
Lyman alpha Resonant Scattering in Young Galaxies - Predictions from Cosmological Simulations
We present results obtained with a 3D, Ly alpha radiative transfer code,
applied to a fully cosmological galaxy formation simulation. The developed
Monte Carlo code is capable of treating an arbitrary distribution of source Ly
alpha emission, neutral hydrogen density, temperature, and peculiar velocity of
the interstellar medium. We investigate the influence of resonant scattering on
the appearance and properties of young galaxies by applying the code to a
simulated "Lyman Break Galaxy" at redshift z = 3.6, and of star formation rate
22 M_sun/yr and total Ly alpha luminosity 2.0 X 10^43 erg/s. It is found that
resonant scattering of Ly alpha radiation can explain that young galaxies
frequently are observed to be more extended on the sky in Ly alpha than in the
optical. Moreover, it is shown that, for the system investigated, due to the
anisotropic escape of the photons, the appearent maximum surface brightness can
differ by a factor of ~15, and the total derived luminosity by a factor of ~4,
depending on the orientation of the system relative to the observer.Comment: Letter updated to match version published in Ap
Effect of short-term probiotic Enterococcus faecium SF68 dietary supplementation in overweight and obese cats without comorbidities
Obesity in cats is associated with metabolic abnormalities and increased susceptibility to diseases such as diabetes mellitus. Studies in mouse models and human beings have shown that probiotics can reduce food intake, promote weight loss and improve metabolic profile. Studies assessing the effects of probiotics on these same parameters are absent in cats. Therefore, the aim of this study was to determine if probiotic Enterococcus faecium strain SF68 dietary supplementation reduces food intake, promotes weight loss and improves metabolic profile in overweight and obese cats without comorbidities. Twenty overweight and obese specific pathogen-free cats without comorbidities were acclimatised to a dry diet for four weeks. After exclusion of four cats for unrelated reasons, eight cats received a daily oral probiotic for eight weeks and eight control cats received no probiotic. All cats were fed ad libitum with food intake measured daily and bodyweight weekly. Blood was collected at three time points: after four weeks of acclimatisation to the diet, after eight weeks of intervention and after six weeks of washout for measurement of glucose, triglyceride, cholesterol, fructosamine, insulin, leptin, total adiponectin and deuterium oxide for body composition. There were no differences in food intake, metabolic parameters and body composition between the probiotic and control groups after eight weeks of intervention and six weeks of washout (Pâ„0.050). Short-term use of E faecium SF68 dietary supplementation had no significant effect on food intake, bodyweight, body composition or metabolic parameters in overweight and obese specific pathogen-free cats without comorbidities
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