5,206 research outputs found
Testing Verlinde's emergent gravity in early-type galaxies
Verlinde derived gravity as an emergent force from the information flow,
through two-dimensional surfaces and recently, by a priori postulating the
entanglement of information in 3D space, he derived the effect of the
gravitational potential from dark matter (DM) as the entropy displacement of
dark energy by baryonic matter. In Emergent Gravity (EG) this apparent DM
depends only on the baryonic mass distribution and the present-day value of the
Hubble parameter. In this paper we test the EG proposition, formalized by
Verlinde for a spherical and isolated mass distribution, using the central
velocity dispersion, and the light distribution in a sample of 4260
massive and local early-type galaxies (ETGs) from the SPIDER sample. Our
results remain unaltered if we consider the sample of 807 roundest field
galaxies. We derive the predictions by EG for the stellar mass-to-light ratio
(M/L) and the Initial Mass Function (IMF), and compare them with the same
inferences derived from a) DM-based models, b) MOND and c) stellar population
models. We demonstrate that, consistently with a classical Newtonian framework
with a DM halo component, or alternative theories of gravity as MOND, the
central dynamics can be fitted if the IMF is assumed non-universal. The results
can be interpreted with a IMF lighter than a standard Chabrier at low-,
and bottom-heavier IMFs at larger . We find lower, but still
acceptable, stellar M/L in EG theory, if compared with the DM-based NFW model
and with MOND. The results from EG are comparable to what is found if the DM
haloes are adiabatically contracted and with expectations from spectral
gravity-sensitive features. If the strain caused by the entropy displacement
would be not maximal, as adopted in the current formulation, then the dynamics
of ETGs could be reproduced with larger M/L. (abridged)Comment: 12 pages, 2 figures, submitted to MNRAS. The updated manuscript
presents significantly altered conclusions, after discovering an internal bug
in an older version of the Mathematica package, leading to incorrect
numerical results when calculating the derivatives of Gamma function
Effect of information about organic production on beef liking and consumer willingness to pay
The present study was aimed to assess the effect of information about organic production on beef liking and consumer willingness to pay. Mean scores of perceived liking were higher for organic beef (OB) as
compared to conventional beef (CB). Expected liking scores were higher for OB than for CB. For OB the expected liking was significantly higher than the perceived liking expressed in blind conditions (negative disconfirmation), whereas for CB no difference was observed. Consumers completely assimilated their liking for OB in the direction of expectations. Consumers showed a willingness to pay for OB higher than the suggested price (P < 0.001), the latter corresponding to the local commercial value for organic beef.
We conclude that the information about organic farming can be a major determinant of beef liking, thus providing a potential tool for meat differentiation to traditional farms
Results from the LSND Neutrino Oscillation Search
The Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos Meson
Physics Facility sets bounds on neutrino oscillations in the appearance channel
nu_mu_bar --> nu_e_bar by searching for the signature of the reaction nu_e_bar
p --> e^+ n: an e followed by a 2.2MeV gamma ray from neutron capture. Five
e^{+/-} -- gamma coincidences are observed in time with the LAMPF beam, with an
estimated background of 6.2 events. The 90\% confidence limits obtained are:
Delta (m^2) < 0.07eV^2 for sin^2 (2theta) = 1, and sin^2(2theta) < 6 10^{-3}
for Delta (m^2) > 20 eV^2.Comment: 10 pages, uses REVTeX and epsf macro
A study on the multicolour evolution of Red Sequence galaxy populations: insights from hydrodynamical simulations and semi-analytical models
By means of our own cosmological-hydrodynamical simulation and
semi-analytical model we studied galaxy population properties in clusters and
groups, spanning over 10 different bands from UV to NIR, and their evolution
since redshift z=2. We compare our results in terms of galaxy red/blue
fractions and luminous-to-faint ratio (LFR) on the Red Sequence (RS) with
recent observational data reaching beyond z=1.5. Different selection criteria
were tested in order to retrieve galaxies belonging to the RS: either by their
quiescence degree measured from their specific SFR ("Dead Sequence"), or by
their position in a colour-colour plane which is also a function of sSFR. In
both cases, the colour cut and the limiting magnitude threshold were let
evolving with redshift, in order to follow the natural shift of the
characteristic luminosity in the LF.
We find that the Butcher-Oemler effect is wavelength-dependent, with the
fraction of blue galaxies increasing steeper in optical colours than in NIR.
Besides, only when applying a lower limit in terms of fixed absolute magnitude,
a steep BO effect can be reproduced, while the blue fraction results less
evolving when selecting samples by stellar mass or an evolving magnitude limit.
We then find that also the RS-LFR behaviour, highly debated in the literature,
is strongly dependent on the galaxy selection function: in particular its very
mild evolution recovered when measured in terms of stellar mass, is in
agreement with values reported for some of the highest redshift confirmed
(proto)clusters. As to differences through environments, we find that normal
groups and (to a lesser extent) cluster outskirts present the highest values of
both star forming fraction and LFR at low z, while fossil groups and cluster
cores the lowest: this separation among groups begins after z~0.5, while
earlier all group star forming properties are undistinguishable.Comment: revised version, A&A accepted (11 pages, 6 figures
KiDS0239-3211: A new gravitational quadruple lens candidate
We report the discovery of a candidate to quadrupole gravitationally lensed
system KiDS0239-3211 based on the public data release 3 of the KiDS survey and
machine learning techniques
Testing Convolutional Neural Networks for finding strong gravitational lenses in KiDS
Convolutional Neural Networks (ConvNets) are one of the most promising
methods for identifying strong gravitational lens candidates in survey data. We
present two ConvNet lens-finders which we have trained with a dataset composed
of real galaxies from the Kilo Degree Survey (KiDS) and simulated lensed
sources. One ConvNet is trained with single \textit{r}-band galaxy images,
hence basing the classification mostly on the morphology. While the other
ConvNet is trained on \textit{g-r-i} composite images, relying mostly on
colours and morphology. We have tested the ConvNet lens-finders on a sample of
21789 Luminous Red Galaxies (LRGs) selected from KiDS and we have analyzed and
compared the results with our previous ConvNet lens-finder on the same sample.
The new lens-finders achieve a higher accuracy and completeness in identifying
gravitational lens candidates, especially the single-band ConvNet. Our analysis
indicates that this is mainly due to improved simulations of the lensed
sources. In particular, the single-band ConvNet can select a sample of lens
candidates with purity, retrieving 3 out of 4 of the confirmed
gravitational lenses in the LRG sample. With this particular setup and limited
human intervention, it will be possible to retrieve, in future surveys such as
Euclid, a sample of lenses exceeding in size the total number of currently
known gravitational lenses.Comment: 16 pages, 10 figures. Accepted for publication in MNRA
Finding Strong Gravitational Lenses in the Kilo Degree Survey with Convolutional Neural Networks
The volume of data that will be produced by new-generation surveys requires
automatic classification methods to select and analyze sources. Indeed, this is
the case for the search for strong gravitational lenses, where the population
of the detectable lensed sources is only a very small fraction of the full
source population. We apply for the first time a morphological classification
method based on a Convolutional Neural Network (CNN) for recognizing strong
gravitational lenses in square degrees of the Kilo Degree Survey (KiDS),
one of the current-generation optical wide surveys. The CNN is currently
optimized to recognize lenses with Einstein radii arcsec, about
twice the -band seeing in KiDS. In a sample of colour-magnitude
selected Luminous Red Galaxies (LRG), of which three are known lenses, the CNN
retrieves 761 strong-lens candidates and correctly classifies two out of three
of the known lenses. The misclassified lens has an Einstein radius below the
range on which the algorithm is trained. We down-select the most reliable 56
candidates by a joint visual inspection. This final sample is presented and
discussed. A conservative estimate based on our results shows that with our
proposed method it should be possible to find massive LRG-galaxy
lenses at z\lsim 0.4 in KiDS when completed. In the most optimistic scenario
this number can grow considerably (to maximally 2400 lenses), when
widening the colour-magnitude selection and training the CNN to recognize
smaller image-separation lens systems.Comment: 24 pages, 17 figures. Published in MNRA
Improving keratoconus management with central corneal regularization and corneal collagen cross-linking protocol treatment
Purpose. To evaluate safety and efficacy of customized central corneal regularization (CCR), together with simultaneous accelerated corneal collagen cross-linking (A-CXL) - CCR-CXL protocol, to treat keratoconus-related corneal ectasia. Design. Retrospective, comparative observational case series. Methods. Patients that had undergone combined CCR-CXL protocol. Main inclusion criteria were keratoconus visual acuity deterioration and contact lens intolerance. All patients underwent complete ophthalmological evaluation, corrected distance visual acuity (CDVA) and Scheimpflug-corneal tomography. Central corneal regularization was performed by ablation using flying spot laser. Subsequently, the stroma was saturated with 0.17% riboflavin-5-phosphate added every 2 minutes, followed by A-CXL 9 mW/cm2 for 10 minutes. CDVA, medium keratometry value (Kmed), and total corneal morphological irregularity index (CMI) of patients were analyzed before surgery and after 1, 3 and 12 months. A P value of.05 or less was considered statistically significant. Results. 46 eyes of 39 keratoconus patients were treated. At 1 month, the mean CDVA (LogMar) increased from 0.19 ± 0.02 to 0.12 ± 0.02 (P < .05), and the difference remained stable at month 12. Kmax decrease was statistically significant from 57.02 ± 5.65 to 50.21 ± 4.48 (P < .05). CMI decreased significantly from 47.8 ± 2.84 to 30.1 ± 2.4 (P < .01). Conclusions. CCR-CXL protocol is safe and effective in arresting keratectasia progression and increasing corneal optic regularity in keratoconus. These findings showed a significant improvement in CDVA, keratometry values and corneal optical aberrations after being treated with the CCR-CXL protocol. Copyright © Società Editrice Universo (SEU
Intracluster stars in the Virgo cluster core
We have investigated the properties of the diffuse light in the Virgo cluster
core region, based on the detection of intracluster planetary nebulae (PNe) in
four fields. We eliminate the bias from misclassified faint continuum objects,
using improved Monte Carlo simulations, and the contaminations by high redshift
Ly galaxies, using the Ly luminosity function in blank fields.
Recent spectroscopic observations confirm that our photometric PN samples are
well-understood. We find that the diffuse stellar population in the Virgo core
region is inhomogeneous on scales of 30'-90': there exist significant
field-to-field variations in the number density of PNe and the inferred amount
of intracluster light, with some empty fields, some fields dominated by
extended Virgo galaxy halos, and some fields dominated by the true intracluster
component. There is no clear trend with distance from M87. The mean surface
luminosity density, its rms variation, and the mean surface brightness of
diffuse light in our 4 fields are L
arcmin, L arcmin, and
mag arcsec respectively. Our results indicate that
the Virgo cluster is a dynamically young environment, and that the intracluster
component is associated at least partially with local physical processes like
galaxy interactions or harassment. We also argue, based on kinematic evidence,
that the so-called 'over-luminous' PNe in the halo of M84 are dynamically
associated with this galaxy, and must thus be brighter than and part of a
different stellar population from the normal PN population in elliptical
galaxies.Comment: 31 pages, 6 figure. In press on the Astronomical Journa
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