193 research outputs found
Dissecting the 3D structure of elliptical galaxies with gravitational lensing and stellar kinematics
The combination of strong gravitational lensing and stellar kinematics
provides a powerful and robust method to investigate the mass and dynamical
structure of early-type galaxies. We demonstrate this approach by analysing two
massive ellipticals from the XLENS Survey for which both high-resolution HST
imaging and X-Shooter spectroscopic observations are available. We adopt a
flexible axisymmetric two-component mass model for the lens galaxies,
consisting of a generalised NFW dark halo and a realistic self-gravitating
stellar mass distribution. For both systems, we put constraints on the dark
halo inner structure and flattening, and we find that they are dominated by the
luminous component within one effective radius. By comparing the tight
inferences on the stellar mass from the combined lensing and dynamics analysis
with the values obtained from stellar population studies, we conclude that both
galaxies are characterised by a Salpeter-like stellar initial mass function.Comment: Proceedings of the IAU Symposium 309, Contributed Talk, Vienna, July
2014; 4 pages, 2 figure
The SWELLS survey. III. Disfavouring "heavy" initial mass functions for spiral lens galaxies
We present gravitational lens models for 20 strong gravitational lens systems
observed as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS)
project. Fifteen of the lenses are taken from paper I while five are newly
discovered systems. The systems are galaxy-galaxy lenses where the foreground
deflector has an inclined disc, with a wide range of morphological types, from
late-type spiral to lenticular. For each system, we compare the total mass
inside the critical curve inferred from gravitational lens modelling to the
stellar mass inferred from stellar population synthesis (SPS) models, computing
the stellar mass fraction f* = M(SPS)/M(lens). We find that, for the lower mass
SWELLS systems, adoption of a Salpeter stellar initial mass function (IMF)
leads to estimates of f* that exceed 1. This is unphysical, and provides strong
evidence against the Salpeter IMF being valid for these systems. Taking the
lower mass end of the SWELLS sample sigma(SIE) < 230 km/s, we find that the IMF
is lighter (in terms of stellar mass-to-light ratio) than Salpeter with 98%
probability, and consistent with the Chabrier IMF and IMFs between the two.
This result is consistent with previous studies of spiral galaxies based on
independent techniques. In combination with recent studies of massive
early-type galaxies that have favoured a heavier Salpeter-like IMF, this result
strengthens the evidence against a universal stellar IMF.Comment: Accepted for publication in MNRAS. Some changes (none major) to
address the referee's comments. 18 pages, 8 figure
The SWELLS Survey. VI. hierarchical inference of the initial mass functions of bulges and discs
The long-standing assumption that the stellar initial mass function (IMF) is
universal has recently been challenged by a number of observations. Several
studies have shown that a "heavy" IMF (e.g., with a Salpeter-like abundance of
low mass stars and thus normalisation) is preferred for massive early-type
galaxies, while this IMF is inconsistent with the properties of less massive,
later-type galaxies. These discoveries motivate the hypothesis that the IMF may
vary (possibly very slightly) across galaxies and across components of
individual galaxies (e.g. bulges vs discs). In this paper we use a sample of 19
late-type strong gravitational lenses from the SWELLS survey to investigate the
IMFs of the bulges and discs in late-type galaxies. We perform a joint analysis
of the galaxies' total masses (constrained by strong gravitational lensing) and
stellar masses (constrained by optical and near-infrared colours in the context
of a stellar population synthesis [SPS] model, up to an IMF normalisation
parameter). Using minimal assumptions apart from the physical constraint that
the total stellar mass within any aperture must be less than the total mass
within the aperture, we find that the bulges of the galaxies cannot have IMFs
heavier (i.e. implying high mass per unit luminosity) than Salpeter, while the
disc IMFs are not well constrained by this data set. We also discuss the
necessity for hierarchical modelling when combining incomplete information
about multiple astronomical objects. This modelling approach allows us to place
upper limits on the size of any departures from universality. More data,
including spatially resolved kinematics (as in paper V) and stellar population
diagnostics over a range of bulge and disc masses, are needed to robustly
quantify how the IMF varies within galaxies.Comment: Accepted for publication in MNRAS. 15 pages, 8 figures. Code
available at https://github.com/eggplantbren/SWELLS_Hierarchica
Lean Strategy e creazione di valore
Eliminazione degli sprechi, creazione di valore e miglioramento continuo sono gli obiettivi strategici del Lean Thinking.
Ideata ed applicata originariamente nel mondo manifatturiero e in realtĂ industriali come la Toyota, oggigiorno la âfilosofiaâ Lean si è successivamente
diffusa in numerosi contesti gestionali - compresi quelli delle pubbliche amministrazioni e dei servizi - e si è progressivamente trasformata in uno degli
approcci manageriali di maggiori potenzialitĂ e successo.
Nel dettaglio, sono le componenti manageriale e strategica che rendono questa filosofia quanto mai attuale e di interesse, soprattutto in un momento storico nel quale le risorse sono scarse e devono essere utilizzate con efficacia ed efficienza, e le richieste dei clienti e dei vari portatori di interesse aziendali sono pressanti.
Partendo da queste premesse, il lavoro presenta a tutti gli interessati le caratteristiche fondamentali della filosofia Lean, i suoi principi guida, le primarie
tecniche utilizzabili, nonchĂŠ gli strumenti di management, controllo e misurazione che ne accompagnano lâimplementazione ed il monitoraggio in azienda e guidano lâopera dei manager verso il miglioramento continuo e la perfezione.
In maggior dettaglio, il focus dellâopera è posto sulla dimensione strategica del Lean (da cui la denominazione di Lean Strategy), ovvero sulla definizione
dellâarchitettura strategica nella quale un sistema Lean può efficacemente essere implementato e prosperare in azienda, perseguendo e raggiungendo i suoi primari obiettivi, tra i quali innanzitutto la creazione di valore.
Da notare che nel lavoro sono presentati anche strumenti non strettamente convenzionali, nello specifico ponendo in risalto il ruolo che la simulazione ed i business games possono svolgere a supporto della Lean Strategy in azienda
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
The non-evolving internal structure of early-type galaxies: the case study SDSS J0728+3835 at z = 0.206
We study the internal dynamical structure of the early-type lens galaxy SDSS
J0728+3835 at z = 0.206. The analysis is based on two-dimensional kinematic
maps extending out to 1.7 effective radii obtained from Keck spectroscopy, on
lensing geometry and on stellar mass estimates obtained from multiband Hubble
Space Telescope imaging. The data are modelled under the assumptions of axial
symmetry supported by a two-integral distribution function (DF), by applying
the combined gravitational lensing and stellar dynamics code CAULDRON, and
yielding high-quality constraints for an early-type galaxy at cosmological
redshifts. Modelling the total density profile as a power-law of the form
rho_tot ~ 1/r^{gamma}, we find that it is nearly isothermal (logarithmic slope
gamma = 2.08^{+0.04}_{-0.02}), and quite flattened (axial ratio q =
0.60^{+0.08}_{-0.03}). The galaxy is mildly anisotropic (delta = 0.08 +/- 0.02)
and shows a fair amount of rotational support, in particular towards the outer
regions. We determine a dark matter fraction lower limit of 28 per cent within
the effective radius. The stellar contribution to the total mass distribution
is close to maximal for a Chabrier initial mass function (IMF), whereas for a
Salpeter IMF the stellar mass exceeds the total mass within the galaxy inner
regions. We find that the combination of a NFW dark matter halo with the
maximally rescaled luminous profile provides a remarkably good fit to the total
mass distribution over a broad radial range. Our results confirm and expand the
findings of the SLACS survey for early-type galaxies of comparable velocity
dispersion (sigma_SDSS = 214 +/- 11 km/s). The internal structure of J0728 is
consistent with that of local early-type galaxies of comparable velocity
dispersion as measured by the SAURON project, suggesting lack of evolution in
the past two billion years.Comment: 13 pages, 10 figures. MNRAS in press. Revised to match accepted
versio
Two-dimensional kinematics of SLACS lenses: III. Mass structure and dynamics of early-type lens galaxies beyond z ~ 0.1
We combine in a self-consistent way the constraints from both gravitational
lensing and stellar kinematics to perform a detailed investigation of the
internal mass distribution, amount of dark matter, and dynamical structure of
the 16 early-type lens galaxies from the SLACS Survey, at z = 0.08 - 0.33, for
which both HST/ACS and NICMOS high-resolution imaging and VLT VIMOS IFU
spectroscopy are available. Based on this data set, we analyze the inner
regions of the galaxies, i.e. typically within one (3D) effective radius r_e,
under the assumption of axial symmetry and by constructing dynamical models
supported by two-integral stellar DFs. For all systems, the total mass density
distribution is found to be well approximated by a simple power-law: this
profile is on average slightly super-isothermal, with a logarithmic slope
= 2.074^{+0.043}_{-0.041} (68% CL) and an intrinsic scatter
0.144^{+0.055}_{-0.014}, and is fairly round, with an average axial ratio =
0.77+/-0.04. The lower limit for the dark matter fraction (fDM) inside r_e
ranges, in individual systems, from nearly zero to almost a half, with a median
value of 12%. By including stellar masses derived from SPS models with a
Salpeter IMF, we obtain an average fDM = 31%. The fDM rises to 61% if, instead,
a Chabrier IMF is assumed. For both IMFs, the dark matter fraction increases
with the total mass of the galaxy (3-sigma correlation). Based on the intrinsic
angular momentum parameter calculated from our models, we find that the
galaxies can be divided into two dynamically distinct groups, which are shown
to correspond to the usual classes of the slow and fast rotators. Overall, the
SLACS systems are structurally and dynamically very similar to their nearby
counterparts, indicating that the inner regions of early-type galaxies have
undergone little, if any, evolution since redshift z ~ 0.35. (Abridged)Comment: 27 pages, 34 figures. MNRAS, in pres
Use of System Dynamics Models as Part of a Game-based, Urban Sustainability Course for Students in Higher Education (SUSTAIN Project)
The difficulty with sustainability arises from its abstract nature and the fact that these problems have long term horizons. The objective of the SUSTAIN course is to promote sustainability literacy among students of higher education through an innovative and student-centered education that makes use of system dynamics (SD) models embedded in game-based learning. In this project, as part of the SUSTAIN course, we try to develop small illustrative SD simulation models that will allow for experimentation in a consequence-free environment. These simulation models will then be translated to game elements, mechanics and potential playing scenarios for a table top / board game that deal with sustainability issues.
The purpose of this project under development is to help students of higher education achieve competences such as the ability of constantly assessing the environment, operating and adapting to it through continuous and iterative individual process of revision from their frames of reference, and to provide the material to comprehend systemic complexity. We expect these competences to allow them to deal with complex decisions and decision making processes in their future careers in private and public organizations, and provide insights into the complexity and the effort required to achieve the Sustainable Development Goals (SDGs)
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