406 research outputs found
Density profiles of dark matter haloes on Galactic and Cluster scales
In the present paper, we improve the "Extended Secondary Infall Model" (ESIM)
of Williams et al. (2004) to obtain further insights on the cusp/core problem.
The model takes into account the effect of ordered and random angular momentum,
dynamical friction and baryon adiabatic contraction in order to obtain a
secondary infall model more close to the collapse reality. The model is applied
to structures on galactic scales (normal and dwarf spiral galaxies) and on
cluster of galaxies scales. The results obtained suggest that angular momentum
and dynamical friction are able, on galactic scales, to overcome the competing
effect of adiabatic contraction eliminating the cusp. The NFW profile can be
reobtained, in our model only if the system is constituted just by dark matter
and the magnitude of angular momentum and dynamical friction are reduced with
respect to the values predicted by the model itself. The rotation curves of
four LSB galaxies from de Blok & Bosma (2002) are compared to the rotation
curves obtained by the model in the present paper obtaining a good fit to the
observational data. On scales smaller than
the slope and on cluster scales we observe a similar
evolution of the dark matter density profile but in this case the density
profile slope flattens to for a cluster of . The total mass profile, differently from that of dark
matter, shows a central cusp well fitted by a NFW model.Comment: 26 pages; 4 figures A&A Accepte
Density profile slope in Dwarfs and environment
In the present paper, we study how the dark matter density profiles of dwarfs
galaxies in the mass range are modified by the
interaction of the dwarf in study with the neighboring structures, and by
changing baryon fraction in dwarfs. As already shown in Del Popolo (2009), the
slope of density profile of inner halos flattens with decreasing halo mass and
the profile is well approximated by a Burkert's profile. The analysis shows
that dwarfs who suffered a smaller tidal torquing (consequently having smaller
angular momentum) are characterized by steeper profiles with respect to dwarfs
subject to higher torque, and similarly dwarfs having a smaller baryons
fraction have also steeper profiles than those having a larger baryon fraction.
In the case tidal torquing is shut down and baryons are not present, the
density profile is very well approximated by an Einasto profile, similarly to
dwarfs obtained in dissipationless N-body simulations. We then apply the result
of the previous analysis to the dark matter halo rotation curves of three
different dwarfs, namely NGC 2976, known to have a flat inner core, NGC 5949
having a profile intermediate between a cored and a cuspy one, and NGC 5963
having a cuspy profile. After calculating baryon fraction, which is for the three galaxies, we fitted the rotation curves changing the value
of angular momentum. NGC 2976, has an higher value of ordered angular momentum
() with respect to NGC 5949 () and
in the case of NGC 5963 the very steep profile can be obtained with a low value
of () and also decreasing the value of the
random angular momentum. In the case of NGC 2976 tidal interaction with M81
could have also influenced the inner part of the density profile.Comment: 15 pages; 5 figures; 1 tabl
In vivo testing of novel vaccine prototypes against Actinobacillus pleuropneumoniae
Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is a Gram-negative bacterium that represents the main cause of porcine pleuropneumonia in pigs, causing significant economic losses to the livestock industry worldwide. A. pleuropneumoniae, as the majority of Gram-negative bacteria, excrete vesicles from its outer membrane (OM), accordingly defined as outer membrane vesicles (OMVs). Thanks to their antigenic similarity to the OM, OMVs have emerged as a promising tool in vaccinology. In this study we describe the in vivo testing of several vaccine prototypes for the prevention of infection by all known A. pleuropneumoniae serotypes. Previously identified vaccine candidates, the recombinant proteins ApfA and VacJ, administered individually or in various combinations with the OMVs, were employed as vaccination strategies. Our data show that the addition of the OMVs in the vaccine formulations significantly increased the specific IgG titer against both ApfA and VacJ in the immunized animals, confirming the previously postulated potential of the OMVs as adjuvant. Unfortunately, the antibody response raised did not translate into an effective protection against A. pleuropneumoniae infection, as none of the immunized groups following challenge showed a significantly lower degree of lesions than the controls. Interestingly, quite the opposite was true, as the animals with the highest IgG titers were also the ones bearing the most extensive lesions in their lungs. These results shed new light on A. pleuropneumoniae pathogenicity, suggesting that antibody-mediated cytotoxicity from the host immune response may play a central role in the development of the lesions typically associated with A. pleuropneumoniae infections
On the reliability of merger-trees and the mass growth histories of dark matter haloes
We have used merger trees realizations to study the formation of dark matter
haloes. The construction of merger-trees is based on three different pictures
about the formation of structures in the Universe. These pictures include: the
spherical collapse (SC), the ellipsoidal collapse (EC) and the non-radial
collapse (NR). The reliability of merger-trees has been examined comparing
their predictions related to the distribution of the number of progenitors, as
well as the distribution of formation times, with the predictions of analytical
relations. The comparison yields a very satisfactory agreement. Subsequently,
>.........Comment: A&SS Accepte
On the universality of density profiles
We use the secondary infall model described in Del Popolo (2009), which takes
into account the effect of dynamical friction, ordered and random angular
momentum, baryons adiabatic contraction and dark matter baryons interplay, to
study how in- ner slopes of relaxed LCDM dark matter (DM) halos with and
without baryons (baryons+DM, and pure DM) depend on redshift and on halo mass.
We apply the quoted method to structures on galactic scales and clusters of
galaxies scales. We find that the inner logarithmic density slope, of dark
matter halos with baryons has a significant dependence on halo mass and
redshift with slopes ranging from 0 for dwarf galaxies to 0.4 for objects of M
= 10^13M_solar and 0.94 for M = 10^15M_solar clusters of galaxies. Structures
slopes increase with increasing redshift and this trend reduces going from
galaxies to clusters. In the case of density profiles constituted just of dark
matter the mass and redshift dependence of slope is very slight. In this last
case, we used the Merrit et al. (2006) analysis who compared N-body density
profiles with various parametric models finding systematic variation in profile
shape with halo mass. This last analysis suggests that the galaxy-sized halos
obtained with our model have a different shape parameter, i.e. a different mass
distribution, than the cluster-sized halos, obtained with the same model. The
results of the present paper argue against universality of density profiles
constituted by dark matter and baryons and confirm claims of a systematic
variation in profile shape with halo mass, for dark matter halos.Comment: 11 pages, 5 figure
Large scale inhomogeneity and local dynamical friction
We investigate the effect of a density gradient on Chandrasekhar's dynamical
friction formula based on the method of 2-body encounters in the local
approximation. We apply these generalizations to the orbit evolution of
satellite galaxies in Dark Matter haloes. We find from the analysis that the
main influence occurs through a position-dependent maximum impact parameter in
the Coulomb logarithm, which is determined by the local scale-length of the
density distribution. We also show that for eccentric orbits the explicit
dependence of the Coulomb logarithm on position yields significant differences
for the standard homogeneous force. Including the velocity dependence of the
Coulomb logarithm yields ambigous results. The orbital fits in the first few
periods are further improved, but the deviations at later times are much
larger. The additional force induced by the density gradient, the inhomogeneous
force, is not antiparallel to the satellite motion and can exceed 10% of the
homogeneous friction force in magnitude. However, due to the symmetry
properties of the inhomogeneous force, there is a deformation and no secular
effect on the orbit at the first order. Therefore the inhomogeneous force can
be safely neglected for the orbital evolution of satellite galaxies. For the
homogeneous force we compare numerical N-body calculations with semi-analytical
orbits to determine quantitatively the accuracy of the generalized formulae of
the Coulomb logarithm in the Chandresekhar approach. With the local
scale-length as the maximum impact parameter we find a significant improvement
of the orbital fits and a better interpretation of the quantitative value of
the Coulomb logarithm.Comment: 17 pages, 16 figures, accepted for publication by Astronomy and
Astrophysics 19.10.200
The star forming region Monoceros R2 as a gamma-ray source
After the release of the gamma-ray source catalog produced by the Fermi satellite during its first two years of operation, a significant fraction of sources still remain unassociated at lower energies. In addition to well-known high-energy emitters (pulsars, blazars, supernova remnants, etc.), theoretical expectations predict new classes of gamma-ray sources. In particular, gamma-ray emission could be associated with some of the early phases of stellar evolution, but this interesting possibility is still poorly understood. Aims: The aim of this paper is to assess the possibility of the Fermi gamma-ray source 2FGL J0607.5-0618c being associated with the massive star forming region Monoceros R2. Methods: A multi-wavelength analysis of the Monoceros R2 region is carried out using archival data at radio, infrared, X-ray, and gamma-ray wavelengths. The resulting observational properties are used to estimate the physical parameters needed to test the different physical scenarios. Results: We confirm the 2FGL J0607.5-0618c detection with improved confidence over the Fermi two-year catalog. We find that a combined effect of the multiple young stellar objects in Monoceros R2 is a viable picture for the nature of the source
Cuspy No More: How Outflows Affect the Central Dark Matter and Baryon Distribution in Lambda CDM Galaxies
We examine the evolution of the inner dark matter (DM) and baryonic density
profile of a new sample of simulated field galaxies using fully cosmological,
Lambda CDM, high resolution SPH + N-Body simulations. These simulations include
explicit H2 and metal cooling, star formation (SF) and supernovae (SNe) driven
gas outflows. Starting at high redshift, rapid, repeated gas outflows following
bursty SF transfer energy to the DM component and significantly flatten the
originally `cuspy' central DM mass profile of galaxies with present day stellar
masses in the 10^4.5 -- 10^9.8 Msolar range. At z=0, the central slope of the
DM density profile of our galaxies (measured between 0.3 and 0.7 kpc from their
centre) is well fitted by rhoDM propto r^alpha with alpha \simeq -0.5 + 0.35
log_10(Mstar/10^8Msolar) where Mstar is the stellar mass of the galaxy and 4 <
log_10 Mstar < 9.4. These values imply DM profiles flatter than those obtained
in DM--only simulations and in close agreement with those inferred in galaxies
from the THINGS and LITTLE THINGS survey. Only in very small halos, where by
z=0 star formation has converted less than ~ 0.03% of the original baryon
abundance into stars, outflows do not flatten the original cuspy DM profile out
to radii resolved by our simulations. The mass (DM and baryonic) measured
within the inner 500 pc of each simulated galaxy remains nearly constant over
four orders of magnitudes in stellar mass for Mstar 10^9 Msolar. This finding
is consistent with estimates for faint Local Group dwarfs and field galaxies.
These results address one of the outstanding problems faced by the CDM model,
namely the strong discrepancy between the original predictions of cuspy DM
profiles and the shallower central DM distribution observed in galaxies.Comment: MNRAS in press. Accepted version, a few references added. 12 pages.
Animation at http://youtu.be/FbcgEovabDI?hd=
Research activity and capability in the European reference network MetabERN
BACKGROUND: MetabERN is one of the 24 European Reference Networks created according to the European Union directive 2011/24/EU on patient's rights in cross border healthcare. MetabERN associates 69 centres in 18 countries, which provide care for patients with Hereditary Metabolic Diseases, and have the mission to reinforce research and provide training for health professionals in this field. MetabERN performed a survey in December 2017 with the aim to produce an overview documenting research activities and potentials within the network. As the centres are multidisciplinary, separated questionnaires were sent to the clinical, university and laboratory teams. Answers were received from 52 out of the 69 centres of the network, covering 16 countries. A descriptive analysis of the information collected is presented. RESULTS: The answers indicate a marked interest of the respondents for research, who expressed high motivation and commitment, and estimated that the conditions to do research in their institution were mostly satisfactory. They are active in research, which according to several indicators, is competitive and satisfies standards of excellence, as well as the education programs offered in the respondent's universities. Research in the centres is primarily performed in genetics, pathophysiology, and epidemiology, and focuses on issues related to diagnosis. Few respondents declared having activity in human and social sciences, including research on patient's quality of life, patient's awareness, or methods for social support. Infrastructures offering services for medical research were rarely known and used by respondents, including national and international biobanking platforms. In contrast, respondents often participate to patient registries, even beyond their specific field of interest. CONCLUSIONS: Taken as a whole, these results provide an encouraging picture of the research capacities and activities in the MetabERN network, which, with respect to the number and representativeness of the investigated centres, gives a comprehensive picture of research on Hereditary Metabolic Diseases in Europe, as well as the priorities for future actions. Marginal activity in human and social sciences points out the limited multidisciplinary constitution of the responding teams with possible consequences on their current capability to participate to patient's empowerment programs and efficiently collaborate with patient's advocacy groups
Soft gamma-ray sources detected by INTEGRAL
We aim to exploit the available INTEGRAL/SPI data to provide time-averaged
spectra of the brightest soft gamma-ray sources.
Employing a maximum-likelihood fit technique for our SPI data analysis, we
take as input to our source model the source catalog derived by Bouchet et al.
(2008) from a SPI all-sky study. We use the first four years of public SPI data
and extract spectra between 25 keV and 1 MeV for the 20 catalog sources
detected by Bouchet et al. at 200 - 600 keV with >= 2.5 sigma. In order to
verify our analysis, we also extract spectra for the same sources from the
corresponding INTEGRAL/ISGRI data. We fit adequate spectral models to the
energy range 25-1000 keV for SPI and 25-600 keV for ISGRI. We use our spectra
from the Crab (which is among the 20 sources studied here) and an empty
location in a crowded field to derive an estimation of the systematic errors.
The agreement between our SPI and ISGRI measurements is good if we normalise
them on the Crab spectrum. Our SPI flux measurements also agree well with those
by Bouchet et al. (2008). All 20 sources in our sample are detected
independently in the bands 25-100 keV and 100-200 keV. At 200-600 keV we detect
eight sources, at 600-1000 keV we detect two sources. Our spectra agree well
with the results from previous publications where available. For six of the 14
XRBs in our sample we find evidence for a hard powerlaw-component which becomes
dominant above the cutoff energy of the thermal Comptonization component. In
two of these cases, our study provides the first indication of such emission.
For the others, our results confirm previous studies. Our Crab spectrum (from
1.3 Ms exposure), shows a significant flux in all points and is well described
by a powerlaw with a break near 100 keV and spectral indices 2.11 and 2.20.Comment: 24 pages, 44 figures, accepted for publication by A&
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