117 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 non-universality of the low-mass end of the IMF is robust against the choice of SSP model
We perform a direct comparison of two state-of-the art single stellar
population (SSP) models that have been used to demonstrate the non-universality
of the low-mass end of the Initial Mass Function (IMF) slope. The two public
versions of the SSP models are restricted to either solar abundance patterns or
solar metallicity, too restrictive if one aims to disentangle elemental
enhancements, metallicity changes and IMF variations in massive early-type
galaxies (ETGs) with star formation histories different from the solar
neighborhood. We define response functions (to metallicity and
\alpha-abundance) to extend the parameter space of each set of models. We
compare these extended models with a sample of Sloan Digital Sky Survey (SDSS)
ETGs spectra with varying velocity dispersions. We measure equivalent widths of
optical IMF-sensitive stellar features to examine the effect of the underlying
model assumptions and ingredients, such as stellar libraries or isochrones, on
the inference of the IMF slope down to ~0.1 solar masses. We demonstrate that
the steepening of the low-mass end of the Initial Mass Function (IMF) based on
a non-degenerate set of spectroscopic optical indicators is robust against the
choice of the stellar population model. Although the models agree in a relative
sense (i.e. both imply more bottom-heavy IMFs for more massive systems), we
find non-negligible differences on the absolute values of the IMF slope
inferred at each velocity dispersion by using the two different models. In
particular, we find large inconsistency in the quantitative predictions of IMF
slope variations and abundance patterns when sodium lines are used. We
investigate the possible reasons for these inconsistencies.Comment: 16 pages, 9 figures, 2 tables, accepted for publication on Ap
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
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
Antioxidant and UV-Blocking Functionalized Poly(Butylene Succinate) Films
The introduction of a limited number of functional groups on poly(butylene succinate) (PBS) chains by covalent bonding can impart new properties to the polymer without modifying its thermal and mechanical properties. In pursuit of a viable approach to obtain light- and heat-stabilized PBS samples, the nitroxide radical coupling (NRC) reaction between PBS macroradicals and the 3,5-di-tert-butyl-4-hydroxybenzoyl-2,2,6,6-tetramethylpiperidine-1-oxyl radical (BHB-TEMPO), a functionalizing agent bearing a sterically-hindered antioxidant phenol moiety, is here proposed. The reaction was initiated by peroxide and carried out in solution and in a melt. The functionalized materials were characterized by UV-visible spectroscopy (UV-Vis), proton nuclear magnetic resonance (1H-NMR), and size exclusion chromatography (SEC) analysis to gain structural information and by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) to investigate the thermal properties. In addition, films of the samples were subjected to thermal and photo-oxidative aging to assess their resistance to degradative processes. Finally, the PBS film with the highest degree of functionalization showed the ability to protect β-carotene, a molecule found in food and drugs and that is very sensitive to UV light, from degradation. This result suggests the use of this material (either alone or blended with other biopolyesters) for biodegradable and compostable active packaging
What does (not) drive the variation of the low-mass end of the stellar initial mass function of early-type galaxies
The stellar initial mass function (IMF) seems to be variable and not
universal, as argued in the literature in the last three decades. Several
relations among the low-mass end of the IMF slope and other stellar population,
photometric or kinematic parameters of massive early-type galaxies (ETGs) have
been proposed, but a consolidated agreement on a factual cause of the observed
variations has not been reached yet. We investigate the relations between the
IMF and other stellar population parameters in NGC 3311, the central galaxy of
the Hydra I cluster. NGC 3311 is characterized by old and metal-rich stars,
like other massive ETGs, but has unusual increasing stellar velocity dispersion
and [Fe] profiles. We use spatially resolved MUSE observations to
obtain stellar population properties using Bayesian full-spectrum fitting in
the central part of NGC 3311 to compare the IMF slope against other stellar
parameters with the goal of assessing their relations/dependencies. For NGC
3311, we unambiguously invalidate the previously observed direct correlation
between the IMF slope and the local stellar velocity dispersion, confirming
some doubts already raised in the literature. This relation may arise as a
spatial coincidence only, between the region with the largest stellar velocity
dispersion, with that where the oldest, population is found
and dominates. We also show robust evidence that the proposed IMF-metallicity
relation is contaminated by the degeneracy between these two parameters. The
tightest correlations we found are those between stellar age and IMF and
between galactocentric radius and IMF. The variation of the IMF is not due to
kinematical, dynamical, or global properties in NGC 3311. We speculate that IMF
might be dwarf-dominated in the "red-nuggets" formed at high redshifts that
ended up being the central cores of today's giant ellipticals. [Abridged]Comment: 5 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
KiDS-SQuaD: The KiDS Strongly lensed Quasar Detection project
New methods have been recently developed to search for strong gravitational
lenses, in particular lensed quasars, in wide-field imaging surveys. Here, we
compare the performance of three different, morphology- and photometry- based
methods to find lens candidates over the Kilo-Degree Survey (KiDS) DR3
footprint (440 deg). The three methods are: i) a multiplet detection in
KiDS-DR3 and/or Gaia-DR1, ii) direct modeling of KiDS cutouts and iii)
positional offsets between different surveys (KiDS-vs-Gaia, Gaia-vs-2MASS),
with purpose-built astrometric recalibrations. The first benchmark for the
methods has been set by the recovery of known lenses. We are able to recover
seven out of ten known lenses and pairs of quasars observed in the KiDS DR3
footprint, or eight out of ten with improved selection criteria and looser
colour pre-selection. This success rate reflects the combination of all methods
together, which, taken individually, performed significantly worse (four lenses
each). One movelty of our analysis is that the comparison of the performances
of the different methods has revealed the pros and cons of the approaches and,
most of all, the complementarities. We finally provide a list of high-grade
candidates found by one or more methods, awaiting spectroscopic follow-up for
confirmation. Of these, KiDS 1042+0023 is to our knowledge the first confirmed
lensed quasar from KiDS, exhibiting two quasar spectra at the same source
redshift at either sides of a red galaxy, with uniform flux-ratio
over the wavelength range
Comment: 12 pages, 4 figures, 4 tables, accepted for publication in MNRA
Galaxy evolution within the Kilo-Degree Survey
The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging
survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS
will scan 1500 square degrees in four optical filters (u, g, r, i). Designed to
be a weak lensing survey, it is ideal for galaxy evolution studies, thanks to
the high spatial resolution of VST, the good seeing and the photometric depth.
The surface photometry have provided with structural parameters (e.g. size and
S\'ersic index), aperture and total magnitudes have been used to derive
photometric redshifts from Machine learning methods and stellar
masses/luminositites from stellar population synthesis. Our project aimed at
investigating the evolution of the colour and structural properties of galaxies
with mass and environment up to redshift and more, to put
constraints on galaxy evolution processes, as galaxy mergers.Comment: 4 pages, 2 figures, to appear on the refereed Proceeding of the "The
Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on
25th-28th november 2014, to be published on Astrophysics and Space Science
Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic
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