256 research outputs found
Statistics of mass substructure from strong gravitational lensing: quantifying the mass fraction and mass function
A Bayesian statistical formalism is developed to quantify the level at which
the mass function slope (alpha) and the projected cumulative mass fraction (f)
of (CDM) substructure in strong gravitational-lens galaxies, with arcs or
Einstein rings, can be recovered as function of the lens-survey parameters and
the detection threshold of the substructure mass. The method is applied to
different sets of mock data to explore a range of observational limits: (i) the
number of lens galaxies in the survey, (ii) the mass threshold, Mlow, for the
detection of substructures and (iii) the uncertainty of the measured
substructure masses. We explore two different priors on the mass function
slope: a uniform prior and a Gaussian prior with alpha = 1.90+-0.1. With a
substructure detection threshold Mlow=3x10^8 Msun, the number of lenses
available now (n_l=30), a true dark-matter mass fraction in (CDM) substructure
<=1.0% and a prior of alpha = 1.90+-0.1, we find that the upper limit of f can
be constrained down to a level <=1.0% (95% CL). In the case of a Gaussian prior
on alpha, it is always possible to set stringent constraints on both
parameters. We also find that lowering the detection threshold has the largest
impact on the ability to recover alpha, because of the (expected) steep
mass-function slope. In the future, thanks to new surveys with telescopes, such
as SKA, LSST and JDEM and follow-up telescopes with high-fidelity data, a
significant increase in the number of known lenses will allow us to recover the
satellite population in its completeness. For example, a sample of 200 lenses,
equivalent in data-quality to the Sloan Lens ACS Survey and a detection
threshold of 10^8 Msun, allows one to determine f=0.5+-0.1% (68% CL) and
alpha=1.90+-0.2 (68% CL).Comment: MNRAS (in press
Semi-Automated Ontology Generation Process from Industrial Product Data Standards
Ontology development has become an important research area for manufacture industries. Ontologies are one of the most popular methods to achieve semantic interoperability between information systems. In previous works, an ontology network that reuses ontological and non-ontological re-sources have been proposed in order to reach semantic interoperability. Howev-er, processing non-ontological resources to build an ontology is a great time-consuming task. Therefore, this work presents a framework and a prototype tool to support the reuse of the non-ontological resources involved in the develop-ment of the ontology network.Sociedad Argentina de Informática e Investigación Operativa (SADIO
Semi-Automated Ontology Generation Process from Industrial Product Data Standards
Ontology development has become an important research area for manufacture industries. Ontologies are one of the most popular methods to achieve semantic interoperability between information systems. In previous works, an ontology network that reuses ontological and non-ontological re-sources have been proposed in order to reach semantic interoperability. Howev-er, processing non-ontological resources to build an ontology is a great time-consuming task. Therefore, this work presents a framework and a prototype tool to support the reuse of the non-ontological resources involved in the develop-ment of the ontology network.Sociedad Argentina de Informática e Investigación Operativa (SADIO
SHARP - I. A high-resolution multi-band view of the infra-red Einstein ring of JVAS B1938+666
We present new mass models for the gravitational lens system B1938+666, using
multi-wavelength data acquired from Keck adaptive optics (AO) and Hubble Space
Telescope (HST) observations. These models are the first results from the
Strong-lensing at High Angular Resolution Program (SHARP), a project designed
to study known quadruple-image and Einstein ring lenses using high-resolution
imaging, in order to probe their mass distributions in unprecedented detail.
Here, we specifically highlight differences between AO- and HST-derived lens
models, finding that -- at least when the lens and source galaxies are both
bright and red, and the system has a high degree of circular symmetry --
AO-derived models place significantly tighter constraints on model parameters.
Using this improved precision, we infer important physical properties about the
B1938+666 system, including the mass density slope of the lensing galaxy (gamma
= 2.045), the projected dark matter mass fraction within the Einstein radius
(M_dark/M_lens = 0.55), and the total magnification factor of the source galaxy
(~ 13). Additionally, we measure an upper-limit constraint on luminous
substructure (M_V > 16.2), based on the non-detection of bright satellite
galaxies in all data sets. Finally, we utilize the improved image resolution of
the AO data to reveal the presence of faint arcs outside of the primary
Einstein ring. The positions and orientations of these arcs raise the
intriguing possibility that B1938+666 has a second source galaxy, located at a
more distant redshift. However, future work is needed to verify this
hypothesis.Comment: 12 pages, 7 figures; Accepted for publication in MNRA
Inference of the Cold Dark Matter substructure mass function at z=0.2 using strong gravitational lenses
We present the results of a search for galaxy substructures in a sample of 11
gravitational lens galaxies from the Sloan Lens ACS Survey. We find no
significant detection of mass clumps, except for a luminous satellite in the
system SDSS J0956+5110. We use these non-detections, in combination with a
previous detection in the system SDSS J0946+1006, to derive constraints on the
substructure mass function in massive early-type host galaxies with an average
redshift z ~ 0.2 and an average velocity dispersion of 270 km/s. We perform a
Bayesian inference on the substructure mass function, within a median region of
about 32 kpc squared around the Einstein radius (~4.2 kpc). We infer a mean
projected substructure mass fraction at the 68
percent confidence level and a substructure mass function slope < 2.93
at the 95 percent confidence level for a uniform prior probability density on
alpha. For a Gaussian prior based on Cold Dark Matter (CDM) simulations, we
infer and a slope of =
1.90 at the 68 percent confidence level. Since only one
substructure was detected in the full sample, we have little information on the
mass function slope, which is therefore poorly constrained (i.e. the Bayes
factor shows no positive preference for any of the two models).The inferred
fraction is consistent with the expectations from CDM simulations and with
inference from flux ratio anomalies at the 68 percent confidence level.Comment: Accepted for publication on MNRAS, some typos corrected and some
important references adde
The X-shooter Lens Survey - II. Sample presentation and spatially resolved kinematics
We present the X-shooter Lens Survey (XLENS) data. The main goal of XLENS is
to disentangle the stellar and dark matter content of massive early-type
galaxies (ETGs), through combined strong gravitational lensing, dynamics and
spectroscopic stellar population studies. The sample consists of 11 lens
galaxies covering the redshift range from to and having stellar
velocity dispersions between and . All
galaxies have multi-band, high-quality HST imaging. We have obtained long-slit
spectra of the lens galaxies with X-shooter on the VLT. We are able to
disentangle the dark and luminous mass components by combining lensing and
extended kinematics data-sets, and we are also able to precisely constrain
stellar mass-to-light ratios and infer the value of the low-mass cut-off of the
IMF, by adding spectroscopic stellar population information. Our goal is to
correlate these IMF parameters with ETG masses and investigate the relation
between baryonic and non-baryonic matter during the mass assembly and structure
formation processes. In this paper we provide an overview of the survey,
highlighting its scientific motivations, main goals and techniques. We present
the current sample, briefly describing the data reduction and analysis process,
and we present the first results on spatially resolved kinematics.Comment: Accepted for publication in MNRA
Gravitational detection of a low-mass dark satellite at cosmological distance
The mass-function of dwarf satellite galaxies that are observed around Local
Group galaxies substantially differs from simulations based on cold dark
matter: the simulations predict many more dwarf galaxies than are seen. The
Local Group, however, may be anomalous in this regard. A massive dark satellite
in an early-type lens galaxy at z = 0.222 was recently found using a new method
based on gravitational lensing, suggesting that the mass fraction contained in
substructure could be higher than is predicted from simulations. The lack of
very low mass detections, however, prohibited any constraint on their mass
function. Here we report the presence of a 1.9 +/- 0.1 x 10^8 M_sun dark
satellite in the Einstein-ring system JVAS B1938+666 at z = 0.881, where M_sun
denotes solar mass. This satellite galaxy has a mass similar to the Sagittarius
galaxy, which is a satellite of the Milky Way. We determine the logarithmic
slope of the mass function for substructure beyond the local Universe to be
alpha = 1.1^+0.6_-0.4, with an average mass-fraction of f = 3.3^+3.6_-1.8 %, by
combining data on both of these recently discovered galaxies. Our results are
consistent with the predictions from cold dark matter simulations at the 95 per
cent confidence level, and therefore agree with the view that galaxies formed
hierarchically in a Universe composed of cold dark matter.Comment: 25 pages, 7 figures, accepted for publication in Nature (19 January
2012
The fundamental plane of evolving red nuggets
We present an exploration of the mass structure of a sample of 12 strongly
lensed massive, compact early-type galaxies at redshifts to provide
further possible evidence for their inside-out growth. We obtain new ESI/Keck
spectroscopy and infer the kinematics of both lens and source galaxies, and
combine these with existing photometry to construct (a) the fundamental plane
(FP) of the source galaxies and (b) physical models for their dark and luminous
mass structure. We find their FP to be tilted towards the virial plane relative
to the local FP, and attribute this to their unusual compactness, which causes
their kinematics to be totally dominated by the stellar mass as opposed to
their dark matter; that their FP is nevertheless still inconsistent with the
virial plane implies that both the stellar and dark structure of early-type
galaxies is non-homologous. We also find the intrinsic scatter of their FP to
be comparable to the local value, indicating that variations in the stellar
mass structure outweight variations in the dark halo in the central regions of
early-type galaxies. Finally, we show that inference on the dark halo structure
-- and, in turn, the underlying physics -- is sensitive to assumptions about
the stellar initial mass function (IMF), but that physically-motivated
assumptions about the IMF imply haloes with sub-NFW inner density slopes, and
may present further evidence for the inside-out growth of compact early-type
galaxies via minor mergers and accretion.Comment: 10 pages, 3 figures, 3 tables; submitted to MNRA
Dataset of Electoral Volatility in the European Parliament elections since 1979
This dataset provides data on electoral volatility and its internal components in the elections for the European Parliament (EP) in all European Union (EU) countries since 1979 or the date of their accession to the Union. It also provides data about electoral volatility for both the class bloc and the demarcation bloc. This dataset will be regularly updated so as to include the next rounds of the European Parliament elections.
How to cite this dataset?
Emanuele, V., Angelucci, D., Marino, B., Puleo, L., and Vegetti, F. (2019), Dataset of Electoral Volatility in the European Parliament elections since 1979, Rome: Italian Center for Electoral Studies, http://dx.doi.org/10.7802/1905
Red nuggets grow inside-out: evidence from gravitational lensing
We present a new sample of strong gravitational lens systems where both the
foreground lenses and background sources are early-type galaxies. Using imaging
from HST/ACS and Keck/NIRC2, we model the surface brightness distributions and
show that the sources form a distinct population of massive, compact galaxies
at redshifts , lying systematically below the
size-mass relation of the global elliptical galaxy population at those
redshifts. These may therefore represent relics of high-redshift red nuggets or
their partly-evolved descendants. We exploit the magnifying effect of lensing
to investigate the structural properties, stellar masses and stellar
populations of these objects with a view to understanding their evolution. We
model these objects parametrically and find that they generally require two
S\'ersic components to properly describe their light profiles, with one more
spheroidal component alongside a more envelope-like component, which is
slightly more extended though still compact. This is consistent with the
hypothesis of the inside-out growth of these objects via minor mergers. We also
find that the sources can be characterised by red-to-blue colour gradients as a
function of radius which are stronger at low redshift -- indicative of ongoing
accretion -- but that their environments generally appear consistent with that
of the general elliptical galaxy population, contrary to recent suggestions
that these objects are predominantly associated with clusters.Comment: 21 pages; accepted for publication in MNRA
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