197 research outputs found
Detailed Chemical Evolution of Carina and Sagittarius Dwarf Spheroidal Galaxies
In order to verify the effects of the most recent data on the evolution of
Carina and Sagittarius Dwarf Spheroidal Galaxies (dSph) and to set tight
constraints on the main parameters of chemical evolution models, we study in
detail the chemical evolution of these galaxies through comparisons between the
new data and the predictions of a model, already tested to reproduce the main
observational constraints in dSphs. Several abundance ratios, such as
[/Fe], [Ba/Fe] and [Eu/Fe], and the metallicity distribution of stars
are compared to the predictions of our models adopting the observationally
derived star formation histories in these galaxies. These new comparisons
confirm our previously suggested scenario for the evolution of these galaxies,
and allow us to better fix the star formation and wind parameters. In
particular, for Carina the comparisons indicate that the best efficiency of
star formation is , that the best wind efficiency
parameter is = 5 (the wind rate is five times stronger than the star
formation rate), and that the star formation history, which produces the best
fit to the observed metallicity distribution of stars is characterized by
several episodes of activity. In the case of Sagittarius our results suggest
that and , again in agreement with our previous work.
Finally, we show new predictions for [N/Fe] and [C/Fe] ratios for the two
galaxies suggesting a scenario for Sagittarius very similar to the one of the
solar vicinity in the Milky Way, except for a slight decrease of [N/Fe] ratio
at high metallicities due to the galactic wind. For Carina we predict a larger
[N/Fe] ratio at low metallicities, reflecting the lower star formation
efficiency of this galaxy relative to Sagittarius and the Milky Way.Comment: 11 pages, 7 figures, accepted for publication in Asttronomy &
Astrophysic
Cosmic Star Formation: Constraints on the Galaxy Formation Models
We study the evolution of the cosmic star formation by computing the
luminosity density (LD) in the UV, B, J, and K bands, and the stellar mass
density (MD) of galaxies in two reference models of galaxy evolution: the pure
luminosity evolution (PLE) model developed by Calura & Matteucci (2003) and the
semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al.
(2002). The former includes a detailed description of the chemical evolution of
galaxies of different morphological types with no density evolution; the latter
includes the merging histories of the galactic DM haloes, as predicted by the
hierarchical clustering scenario, but it does not contain morphological
classification nor chemical evolution. We find that at z< 1.5 both models are
consistent with the available data on the LD of galaxies in all the considered
bands. At high z, the LDs predicted in the PLE model show a peak due to the
formation of ellipticals, whereas the SAM predicts a gradual decrease of the
star formation and of the LD for z> 2.5. At such redshifts the PLE predictions
tend to overestimate the present data in the B band whereas the SAM tends to
underestimate the observed UV LD. As for the stellar MD, the PLE picture
predicts that nearly 50% and 85% of the present stellar mass are in place at
z=4 and z=1, respectively. According to the SAM, 50% and 60% of the present
stellar mass are in place at z=1.2 and z=1, respectively. Both predictions fit
the observed MD up to z=1. At z>1, the PLE model and the SAM tend to
overestimate and underestimate the observed values, respectively. We discuss
the origin of the above model results, and the role of observational
uncertainties (such as dust extinction) in comparing models with observations.Comment: 14 pages, accepted for publication in MNRA
Effects of the integrated galactic IMF on the chemical evolution of the solar neighbourhood
The initial mass function determines the fraction of stars of different
intial mass born per stellar generation. In this paper, we test the effects of
the integrated galactic initial mass function (IGIMF) on the chemical evolution
of the solar neighbourhood. The IGIMF (Weidner & Kroupa 2005) is computed from
the combination of the stellar intial mass function (IMF), i.e. the mass
function of single star clusters, and the embedded cluster mass function, i.e.
a power law with index beta. By taking into account also the fact that the
maximum achievable stellar mass is a function of the total mass of the cluster,
the IGIMF becomes a time-varying IMF which depends on the star formation rate.
We applied this formalism to a chemical evolution model for the solar
neighbourhood and compared the results obtained by assuming three possible
values for beta with the results obtained by means of a standard, well-tested,
constant IMF. In general, a lower absolute value of beta implies a flatter
IGIMF, hence a larger number of massive stars and larger metal ejection rates.
This translates into higher type Ia and II supernova rates, higher mass
ejection rates from massive stars and a larger amount of gas available for star
formation, coupled with lower present-day stellar mass densities. (abridged) We
also discuss the importance of the present day stellar mass function (PDMF) in
providing a way to disentangle among various assumptions for beta. Our results
indicate that the model adopting the IGIMF computed with beta ~2 should be
considered the best since it allows us to reproduce the observed PDMF and to
account for most of the chemical evolution constraints considered in this work.Comment: 22 pages, 19 figure
The evolution of the photometric properties of Local Group dwarf spheroidal galaxies
We investigate the present-day photometric properties of the dwarf spheroidal
galaxies in the Local Group. From the analysis of their integrated colours, we
consider a possible link between dwarf spheroidals and giant ellipticals. From
the analysis of the V vs (B-V) plot, we search for a possible evolutionary link
between dwarf spheroidal galaxies (dSphs) and dwarf irregular galaxies (dIrrs).
By means of chemical evolution models combined with a spectro-photometric
model, we study the evolution of six Local Group dwarf spheroidal galaxies
(Carina, Draco, Sagittarius, Sculptor, Sextans and Ursa Minor). The chemical
evolution models, which adopt up-to-date nucleosynthesis from low and
intermediate mass stars as well as nucleosynthesis and energetic feedback from
supernovae type Ia and II, reproduce several observational constraints of these
galaxies, such as abundance ratios versus metallicity and the metallicity
distributions. The proposed scenario for the evolution of these galaxies is
characterised by low star formation rates and high galactic wind efficiencies.
Such a scenario allows us to predict integrated colours and magnitudes which
agree with observations. Our results strongly suggest that the first few Gyrs
of evolution, when the star formation is most active, are crucial to define the
luminosities, colours, and other photometric properties as observed today.
After the star formation epoch, the galactic wind sweeps away a large fraction
of the gas of each galaxy, which then evolves passively. Our results indicate
that it is likely that at a certain stage of their evolution, dSphs and dIrrs
presented similar photometric properties. However, after that phase, they
evolved along different paths, leading them to their currently disparate
properties.Comment: 13 pages, Astronomy & Astrophysics, accepte
A new comprehensive set of elemental abundances in DLAs III. Star formation histories
We obtained comprehensive sets of elemental abundances for eleven damped
Ly-alpha systems (DLAs) at z_DLA=1.7-2.5. In Paper I of this series, we showed
for three DLA galaxies that we can derive their star formation histories and
ages from a detailed comparison of their intrinsic abundance patterns with
chemical evolution models. We determine in this paper the star formation
properties of six additional DLA galaxies. The derived results confirm that no
single star formation history explains the diverse sets of abundance patterns
in DLAs. We demonstrate that the various star formation histories reproducing
the DLA abundance patterns are typical of local irregular, dwarf starburst and
quiescent spiral galaxies. Independent of the star formation history, the DLAs
have a common characteristic of being weak star forming galaxies; models with
high star formation efficiencies are ruled out. All the derived DLA star
formation rates per unit area are moderate or low, with values between -3.2 <
log SFR < -1.1 M_sol yr^{-1} kpc^{-2}. The DLA abundance patterns require a
large spread in ages ranging from 20 Myr up to 3 Gyr. The oldest DLA in our
sample is observed at z_DLA=1.864 with an age estimated to more than 3 Gyr; it
nicely indicates that galaxies were already forming at z_f>10. But, most of the
DLAs show ages much younger than that of the Universe at the epoch of
observation. Young galaxies thus seem to populate the high redshift Universe at
z>2, suggesting relatively low redshifts of formation (z~3) for most
high-redshift galaxies. The DLA star formation properties are compared with
those of other high-redshift galaxies identified in deep imaging surveys with
the aim of obtaining a global picture of high-redshift objects.Comment: 19 pages, 11 figures, Accepted for publication in A&
Disparities in dialysis treatment and outcomes for Dutch and Belgian children with immigrant parents
BACKGROUND: In Belgium and the Netherlands, up to 40% of the children on dialysis are children with immigrant parents of non-Western European origin (non-Western). Concerns exist regarding whether these non-Western patients receive the same quality of care as children with parents of Western European origin (Western). We compared initial dialysis, post-initial treatment, and outcomes between non-Western and Western patients on dialysis. METHODS: All children <19 years old on chronic dialysis in the Netherlands and Belgium between September 2007 and May 2011 were included in the study. Non-Western patients were defined as children of whom one or both parents were born in non-Western countries. RESULTS: Seventy-nine of the 179 included patients (44%) were non-Western children. Compared to Western patients, non-Western patients more often were treated with hemodialysis (HD) instead of peritoneal dialysis (PD) as first dialysis mode (52 vs. 37%, p = 0.046). Before renal transplantation, non-Western patients were on dialysis for a median (range) of 30 (5-99) months, vs. 15 (0-66) months in Western patients (p = 0.007). Renal osteodystrophy was diagnosed in 34% of non-Western vs. 18% of Western patients (p = 0.028). The incidence rate ratio [95% confidence interval] for acute peritonitis was 2.44 [1.43-4.17] (p = 0.032) for non-Western compared to Western patients. CONCLUSIONS: There are important disparities between children on chronic dialysis with parents from Western European origin and those from non-Western European origin in the choice of modality, duration, and outcomes of dialysis therapy
Diurnal Variation in Urodynamics of Rat
In humans, the storage and voiding functions of the urinary bladder have a characteristic diurnal variation, with increased voiding during the day and urine storage during the night. However, in animal models, the daily functional differences in urodynamics have not been well-studied. The goal of this study was to identify key urodynamic parameters that vary between day and night. Rats were chronically instrumented with an intravesical catheter, and bladder pressure, voided volumes, and micturition frequency were measured by continuous filling cystometry during the light (inactive) or dark (active) phases of the circadian cycle. Cage activity was recorded by video during the experiment. We hypothesized that nocturnal rats entrained to a standard 12:12 light:dark cycle would show greater ambulatory activity and more frequent, smaller volume micturitions in the dark compared to the light. Rats studied during the light phase had a bladder capacity of 1.44±0.21 mL and voided every 8.2±1.2 min. Ambulatory activity was lower in the light phase, and rats slept during the recording period, awakening only to urinate. In contrast, rats studied during the dark were more active, had a lower bladder capacities (0.65±0.18 mL), and urinated more often (every 3.7±0.9 min). Average bladder pressures were not significantly different between the light and dark (13.40±2.49 and 12.19±2.85 mmHg, respectively). These results identify a day-night difference in bladder capacity and micturition frequency in chronically-instrumented nocturnal rodents that is phase-locked to the normal circadian locomotor activity rhythm of the animal. Furthermore, since it has generally been assumed that the daily hormonal regulation of renal function is a major driver of the circadian rhythm in urination, and few studies have addressed the involvement of the lower urinary tract, these results establish the bladder itself as a target for circadian regulation
Adult Height in Patients with Advanced CKD Requiring Renal Replacement Therapy during Childhood.
BACKGROUND AND OBJECTIVES: Growth and final height are of major concern in children with ESRD. This study sought to describe the distribution of adult height of patients who started renal replacement therapy (RRT) during childhood and to identify determinants of final height in a large cohort of RRT children. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A total of 1612 patients from 20 European countries who started RRT before 19 years of age and reached final height between 1990 and 2011 were included. Linear regression analyses were performed to calculate adjusted mean final height SD score (SDS) and to investigate its potential determinants. RESULTS: The median final height SDS was -1.65 (median of 168 cm in boys and 155 cm in girls). Fifty-five percent of patients attained an adult height within the normal range. Adjusted for age at start of RRT and primary renal diseases, final height increased significantly over time from -2.06 SDS in children who reached adulthood in 1990-1995 to -1.33 SDS among those reaching adulthood in 2006-2011. Older age at start of RRT, more recent period of start of RRT, cumulative percentage time on a functioning graft, and greater height SDS at initiation of RRT were independently associated with a higher final height SDS. Patients with congenital anomalies of the kidney and urinary tract and metabolic disorders had a lower final height than those with other primary renal diseases. CONCLUSIONS: Although final height remains suboptimal in children with ESRD, it has consistently improved over time
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