60 research outputs found
Assessing the impact of tourism on hospitals’ performance in a coastal destination
Tourism represents one the most relevant industries in promoting the development of a destination, but tourism and its seasonality can produce negative outcomes. The additional demand caused by tourism can strongly affect public service providers which cannot adapt their supply to seasonal variations as a result of organisational, financial and institutional limitations. This work focuses on hospital services in an Italian coastal destination and it aims to explain the impact tourism and its related seasonality have on the performance of hospitals in a coastal destination. The activity of three hospitals located in Gallura, a region in the north-east of Sardinia, Italy, has been analysed. The analysis has been carried out using data on hospitals admission from 2014 and 2015.The study highlights the critical impact tourism can have on the activity of healthcare providers in a coastal destination, identifying the reduction of hospital performance and a potential cause of bed crises
The velocity function of gas-rich galaxies
We measure the distribution function of rotational velocities phi(V_c) of
late-type galaxies from the HIPASS galaxy catalogue. Previous measurements of
the late-type velocity function are indirect, derived by converting the galaxy
luminosity function using the relation between galaxy luminosity and rotation
velocity (the Tully-Fisher relation). The advantage of HIPASS is that space
densities and velocity widths are both derived from the same survey data. We
find good agreement with earlier inferred measurements of phi(V_c), but we are
able to define the space density of objects with V_c as low as 30 km/s. The
measured velocity function is `flat' (power-law slope alpha ~ -1.0) below V_c =
100 km/s. We compare our results with predictions based on LCDM simulations and
find good agreement for rotational velocities in excess of 100 km/s, but at
lower velocities current models over-predict the space density of objects. At
V_c=30 km/s this discrepancy is approximately a factor 20.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics
We present new medium resolution kinematic data for a sample of 21 dwarf
early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT
and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain).
These data are used to study the origin of the dwarf elliptical galaxy
population inhabiting clusters. We confirm that dEs are not dark matter
dominated galaxies, at least up to the half-light radius. We also find that the
observed galaxies in the outer parts of the cluster are mostly rotationally
supported systems with disky morphological shapes. Rotationally supported dEs
have rotation curves similar to those of star forming galaxies of similar
luminosity and follow the Tully-Fisher relation. This is expected if dE
galaxies are the descendant of low luminosity star forming systems which
recently entered the cluster environment and lost their gas due to a ram
pressure stripping event, quenching their star formation activity and
transforming into quiescent systems, but conserving their angular momentum.Comment: 24 pages, 15 figures and 7 tables. Replaced to match the journal
versio
The hierarchical build-up of the Tully-Fisher relation
We use the semi-analytic model GalICS to predict the Tully-Fisher relation in
the B, I and for the first time, in the K band, and its evolution with
redshift, up to z~1. We refined the determination of the disk galaxies rotation
velocity, with a dynamical recipe for the rotation curve, rather than a simple
conversion from the total mass to maximum velocity. The new recipe takes into
account the disk shape factor, and the angular momentum transfer occurring
during secular evolution leading to the formation of bulges. This produces
model rotation velocities that are lower by ~20-25% for the majority of the
spirals. We implemented stellar population models with a complete treatment of
the TP-AGB, which leads to a revision of the mass-to-light ratio in the
near-IR. I/K band luminosities increase by ~0.3/0.5 mags at redshift z=0 and by
~0.5/1 mags at z=3. With these two new recipes in place, the comparison between
the predicted Tully-Fisher relation with a series of datasets in the optical
and near-IR, at redshifts between 0 and 1, is used as a diagnostics of the
assembly and evolution of spiral galaxies in the model. At 0.4<z<1.2 the match
between the new model and data is remarkably good, especially for later-type
spirals (Sb/Sc). At z=0 the new model shows a net improvement in comparison
with its original version of 2003, and in accord with recent observations in
the K band, the model Tully-Fisher also shows a morphological differentiation.
However, in all bands the z=0 model Tully-Fisher is too bright. We argue that
this behaviour is caused by inadequate star formation histories in the model
galaxies at low redshifts. The star-formation rate declines too slowly, due to
continuous gas infall that is not efficiently suppressed. An analysis of the
model disk scale lengths, at odds with observations, hints to some missing
physics in the modeling of disk formation inside dark matter halos.Comment: Accepted for publication on MNRAS. 2 new plots, 1 new section, and
extended discussion. 21 pages, 11 figures in tota
GALICS -- VI. Modelling Hierarchical Galaxy Formation in Clusters
High-resolution N-body re-simulations of 15 massive (10^{14}-10^{15} Msun)
dark matter haloes have been combined with the hybrid galaxy formation model
GalICS (Hatton et al. 2003), to study the formation and evolution of galaxies
in clusters, within the framework of the hierarchical merging scenario. New
features in GalICS include a better description of galaxy positioning within
dark matter haloes, a more reliable computation of the temperature of the
inter-galactic medium as a function of redshift, and a description of the ram
pressure stripping process. We focus on the luminosity functions, morphological
fractions and colour distributions of galaxies in clusters and in cluster
outskirts, at z=0. No systematic dependency on cluster richness is found either
for the galaxy luminosity functions, morphological mixes, or colour
distributions. Moving from higher density (cluster cores), to lower density
environments (cluster outskirts), we detect a progressive flattening of the
luminosity functions, an increase of the fraction of spirals and a decrease of
that of ellipticals and S0s, and the progressive emergence of a bluer tail in
the distributions of galaxy colours, especially for spirals. As compared to
cluster spirals, early-type galaxies show a flatter luminosity function, and
more homogeneous and redder colours. An overall good agreement is found between
our results and the observations, particularly in terms of the cluster
luminosity functions and morphological mixes. However, some discrepancies are
also apparent, with too faint magnitudes of the brightest cluster members,
especially in the B band, and galaxy colours tendentially too red (or not blue
enough) in the model, with respect to the observations. Finally, ram pressure
stripping appears to affect very little our results.Comment: Accepted for publication in MNRAS. 17 pages, 11 figures.
High-resolution Figure 1 available in the on-line version of the pape
The clustering of galaxies as a function of their photometrically-estimated atomic gas content
We introduce a new photometric estimator of the HI mass fraction (M_HI/M_*)
in local galaxies, which is a linear combination of four parameters: stellar
mass, stellar surface mass density, NUV-r colour, and g-i colour gradient. It
is calibrated using samples of nearby galaxies (0.025<z<0.05) with HI line
detections from the GASS and ALFALFA surveys, and it is demonstrated to provide
unbiased M_HI/M_* estimates even for HI-rich galaxies. We apply this estimator
to a sample of ~24,000 galaxies from the SDSS/DR7 in the same redshift range.
We then bin these galaxies by stellar mass and HI mass fraction and compute
projected two point cross-correlation functions with respect to a reference
galaxy sample. Results are compared with predictions from current semi-analytic
models of galaxy formation. The agreement is good for galaxies with stellar
masses larger than 10^10 M_sun, but not for lower mass systems. We then extend
the analysis by studying the bias in the clustering of HI-poor or HI-rich
galaxies with respect to galaxies with normal HI content on scales between 100
kpc and ~5 Mpc. For the HI-deficient population, the strongest bias effects
arise when the HI-deficiency is defined in comparison to galaxies of the same
stellar mass and size. This is not reproduced by the semi-analytic models,
where the quenching of star formation in satellites occurs by "starvation" and
does not depend on their internal structure. HI-rich galaxies with masses
greater than 10^10 M_sun are found to be anti-biased compared to galaxies with
"normal" HI content. Interestingly, no such effect is found for lower mass
galaxies.Comment: 14 pages, 10 figures, accepted for publication in MNRAS, slightly
revised in the tex
Dwarf galaxy populations in present-day galaxy clusters: I. Abundances and red fractions
We compare the galaxy population in the Virgo, Fornax, Coma and Perseus
cluster to a state-of-the-art semi-analytic model, focusing on the regime of
dwarf galaxies with luminosities from approximately 10^8 L_sun to 10^9 L_sun.
We find that the number density profiles of dwarfs in observed clusters are
reproduced reasonably well, and that the red fractions of model clusters
provide a good match to Coma and Perseus. On the other hand, the red fraction
among dwarf galaxies in Virgo is clearly lower than in model clusters. We argue
that this is mainly caused by the treatment of environmental effects in the
model. This explanation is supported by our finding that the colours of central
("field") dwarf galaxies are reproduced well, in contrast to previous claims.
Finally, we find that the dwarf-to-giant ratio in model clusters is too high.
This may indicate that the current model prescription for tidal disruption of
faint galaxies is still not efficient enough.Comment: 20 pages, 10 figures. Accepted by MNRAS. Includes the modifications
after referee report. Main results unchanged, interpretation slightly change
Galaxy Zoo and ALFALFA: Atomic Gas and the Regulation of Star Formation in Barred Disc Galaxies
We study the observed correlation between atomic gas content and the
likelihood of hosting a large scale bar in a sample of 2090 disc galaxies. Such
a test has never been done before on this scale. We use data on morphologies
from the Galaxy Zoo project and information on the galaxies' HI content from
the ALFALFA blind HI survey. Our main result is that the bar fraction is
significantly lower among gas rich disc galaxies than gas poor ones. This is
not explained by known trends for more massive (stellar) and redder disc
galaxies to host more bars and have lower gas fractions: we still see at fixed
stellar mass a residual correlation between gas content and bar fraction. We
discuss three possible causal explanations: (1) bars in disc galaxies cause
atomic gas to be used up more quickly, (2) increasing the atomic gas content in
a disc galaxy inhibits bar formation, and (3) bar fraction and gas content are
both driven by correlation with environmental effects (e.g. tidal triggering of
bars, combined with strangulation removing gas). All three explanations are
consistent with the observed correlations. In addition our observations suggest
bars may reduce or halt star formation in the outer parts of discs by holding
back the infall of external gas beyond bar co-rotation, reddening the global
colours of barred disc galaxies. This suggests that secular evolution driven by
the exchange of angular momentum between stars in the bar, and gas in the disc,
acts as a feedback mechanism to regulate star formation in intermediate mass
disc galaxies.Comment: 16 pages, 10 figures. In press at MNRAS. v2 contains corrections
found in proof
Evolution of the infrared Tully-Fisher relation up to z=1.4
The Tully-Fisher relation (TFR) represents a connection between fundamental
galaxy parameters, such as its total mass and the mass locked in stars.
Therefore, the study of the evolution of this relation in the optical and
infrared bands can provide valuable information about the evolution of the
individual galaxies through the changes found in each band. This work aims to
study the TFR at high redshift in the B, V, R, I, and K-bands by comparison
with the local relations derived from a large sample of galaxies in the
redshift range 0.1<z<0.3, processed in the same way, and with the same
instrumental constraints that the high-redshift sample. Using the large
photometric information available in the AEGIS database, we have studied the
best procedure to obtain reliable k-corrections. Instrumental magnitudes are
then k and extinction corrected and the absolute magnitudes derived, using the
concordance cosmological model. The rotational velocities have been obtained
from the widths of optical lines using DEEP2 spectra. Finally, morphology has
been determined via visual classification of the HST images. We detect
evolution in the B, V and R-band TFRs in the sense that galaxies were brighter
in the past for the same rotation velocity. The change in luminosity is more
noticeable in the bluer bands. This colour evolution, unnoticed in our previous
work (Fern\'andez Lorenzo et al. 2009) has been detected thanks to the more
reliable k-corrections carried out in this paper, which included photometry
from B to IRAC bands. The change in the (V-K) and (R-I) colours (for a fixed
velocity) could be interpreted as an ageing of the stellar populations as
consequence of the star formation decrease since z=1.25. In addition, we
conclude that spiral galaxies could have doubled their stellar masses in the
last 8.6 Gyr.Comment: 14 pages, 10 figures; accepted in A&
Local Gravity versus Local Velocity: Solutions for and nonlinear bias
(abridged) We perform a reconstruction of the cosmological large scale flows
in the nearby Universe using two complementary observational sets. The first,
the SFI++ sample of Tully-Fisher (TF) measurements of galaxies, provides a
direct probe of the flows. The second, the whole sky distribution of galaxies
in the 2MASS redshift survey (2MRS), yields a prediction of the flows given the
cosmological density parameter, , and a biasing relation between mass
and galaxies. We aim at an unbiased comparison between the peculiar velocity
fields extracted from the two data sets and its implication on the cosmological
parameters and the biasing relation. We expand the fields in a set of
orthonormal basis functions, each representing a plausible realization of a
cosmological velocity field. Our analysis completely avoids the strong error
covariance in the smoothed TF velocities by the use of orthonormal basis
functions and employs elaborate realistic mock data sets to extensively
calibrate the errors in 2MRS predicted velocities. We relate the 2MRS galaxy
distribution to the mass density field by a linear bias factor, , and
include a luminosity dependent, , galaxy weighting. We assess
the agreement between the fields as a function of and
, where is the growth factor of linear perturbations.
The agreement is excellent with a reasonable per degree of freedom.
For , we derive and ,
respectively, at the 68.3% and 95.4% confidence levels (CLs). For ,
we get and , respectively, at the 68.3% and 95.4%
CLs. We set a constraint on the fluctuation normalization, finding , in very good agreement with the latest WMAP results.Comment: MNRAS accepted versio
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