295 research outputs found
Small-scale systems of galaxies. IV. Searching for the faint galaxy population associated with X-ray detected isolated E+S pairs
In hierarchical evolutionary scenarios, isolated, physical pairs may
represent an intermediate phase, or "way station", between collapsing groups
and isolated elliptical (E) galaxies (or fossil groups). We started a
comprehensive study of a sample of galaxy pairs composed of a giant E and a
spiral (S) with the aim of investigating their formation/evolutionary history
from observed optical and X-ray properties. Here we present VLT-VIMOS
observations designed to identify faint galaxies associated with the E+S
systems from candidate lists generated using photometric criteria on WFI images
covering an area of ~ 0.2 h^{-1} Mpc radius around the pairs.
The results are discussed in the context of the evolution of poor galaxy
group associations. A comparison between the Optical Luminosity Functions
(OLFs) of our E+S systems and a sample of X-ray bright poor groups suggest that
the OLF of X-ray detected poor galaxy systems is not universal. The OLF of our
X-ray bright systems suggests that they are more dynamically evolved than our
X-ray faint sample and some X-ray bright groups in the literature. However, we
suggest that the X-ray faint E+S pairs represent a phase in the dynamical
evolution of some X-ray bright poor galaxy groups. The recent or ongoing
interaction in which the E member of the X-ray faint pairs is involved could
have decreased the luminosity of any surrounding X-ray emitting gas.Comment: accepted for publication in Astronomy and Astrophysic
Moving constraints as stabilizing controls in classical mechanics
The paper analyzes a Lagrangian system which is controlled by directly
assigning some of the coordinates as functions of time, by means of
frictionless constraints. In a natural system of coordinates, the equations of
motions contain terms which are linear or quadratic w.r.t.time derivatives of
the control functions. After reviewing the basic equations, we explain the
significance of the quadratic terms, related to geodesics orthogonal to a given
foliation. We then study the problem of stabilization of the system to a given
point, by means of oscillating controls. This problem is first reduced to the
weak stability for a related convex-valued differential inclusion, then studied
by Lyapunov functions methods. In the last sections, we illustrate the results
by means of various mechanical examples.Comment: 52 pages, 4 figure
VEGAS: a VST Early-type GAlaxy Survey. IV. NGC 1533, IC 2038 and IC 2039: an interacting triplet in the Dorado group
This paper focuses on NGC 1533 and the pair IC 2038 and IC 2039 in Dorado a
nearby, clumpy, still un-virialized group. We obtained their surface photometry
from deep OmegaCAM@ESO-VST images in g and r bands. For NGC 1533, we map the
surface brightness down to mag/arcsec and mag/arcsec and out to about . At such faint levels
the structure of NGC 1533 appear amazingly disturbed with clear structural
asymmetry between inner and outer isophotes in the North-East direction. We
detect new spiral arm-like tails in the outskirts, which might likely be the
signature of a past interaction/merging event. Similarly, IC 2038 and IC 2039
show tails and distortions indicative of their ongoing interaction. Taking
advantages of deep images, we are able to detect the optical counterpart to the
HI gas. The analysis of the new deep data suggests that NGC 1533 had a complex
history made of several interactions with low-mass satellites that generated
the star-forming spiral-like structure in the inner regions and are shaping the
stellar envelope. In addition, the VST observations show that also the two less
luminous galaxies, IC 2038 and IC 2039, are probably interacting each-other
and, in the past, IC 2038 could have also interacted with NGC 1533, which
stripped away gas and stars from its outskirts. The new picture emerging from
this study is of an interacting triplet, where the brightest galaxy NGC 1533
has ongoing mass assembly in the outskirts.Comment: Accepted for publication in The Astronomical Journal. High-resolution
version of paper is available at the following link:
https://www.dropbox.com/preview/VEGAS_IV.pdf?role=persona
Small Scale Systems of Galaxies. III. X-ray detected E+S galaxy pairs in low density environments
We present a comprehensive study of the local environments of four E+S galaxy
pairs with the main goal to investigate their formation/evolution histories.
New XMM-Newton data were obtained for two pairs (RR 143 and RR 242) that
complements existing ROSAT data for the other two (RR 210 and RR 216). The new
observations reveal diffuse X-ray emission in both pairs. The emission is
asymmetric in both cases and extends out to 120 kpc and 160 kpc in RR 143 and
RR 242 respectively. The nucleus of RR 242 hosts a low luminosity mildly
absorbed AGN. We find that the early-type components of pairs with diffuse hot
gas appear to be relaxed objects while those in RR 210 and RR 216, where no
diffuse emission has been found, display unambiguous signatures of ongoing
interaction. Wide-field V and R-band data are used to study the photometric
properties of the early-type components and to search for a candidate faint
galaxy populations around each of the pairs. While no diffuse optical light is
found for any of the pairs, all of the early-type members show very extended
and concentric luminous envelopes. We identify a faint galaxy sample in each
field and we consider whether they could be physically associated with the
luminous pairs based upon (V-R) colors and photometric properties. We find that
the distribution of r_e and M_R for the candidates are similar in three of the
fields (RR 143, 216 and 242). The same selection criteria applied to the field
of RR 210 suggest a fainter and more compact population possibly suggesting a
larger background fraction than in the other fields.Comment: 47 pages, 18 figures, Astron. J. in pres
PA6 and halloysite nanotubes composites with improved hydrothermal ageing resistance : role of filler physicochemical properties, functionalization and dispersion technique
Polyamide 6 (PA6) suffers from fast degradation in humid conditions due to hydrolysis of amide bonds, which limits its durability. The addition of nanotubular fillers represents a viable strategy for overcoming this issue, although the additive/polymer interface at high filler content can become privileged site for moisture accumulation. As a cost-effective and versatile material, halloysite nanotubes (HNT) were investigated to prepare PA6 nanocomposites with very low loadings (1-45% w/w). The roles of the physicochemical properties of two differently sourced HNT, of filler functionalization with (3-aminopropyl)triethoxysilane and of dispersion techniques (in situ polymerization vs. melt blending) were investigated. The aspect ratio (5 vs. 15) and surface charge (-31 vs.-59 mV) of the two HNT proved crucial in determining their distribution within the polymer matrix. In situ polymerization of functionalized HNT leads to enclosed and well-penetrated filler within the polymer matrix. PA6 nanocomposites crystal growth and nucleation type were studied according to Avrami theory, as well as the formation of different crystalline structures (\u3b1 and \u3b3 forms). After 1680 h of ageing, functionalized HNT reduced the diffusion of water into polymer, lowering water uptake after 600 h up to 90%, increasing the materials durability also regarding molecular weights and rheological behavior
A selective ratiometric fluorescent probe for no‐wash detection of PVC microplastic
Microplastics (MP) are micrometric plastic particles present in drinking water, food and the environment that constitute an emerging pollutant and pose a menace to human health. Novel methods for the fast detection of these new contaminants are needed. Fluorescence‐based detection exploits the use of specific probes to label the MP particles. This method can be environmentally friendly, low‐cost, easily scalable but also very sensitive and specific. Here, we present the synthesis and application of a new probe based on perylene‐diimide (PDI), which can be prepared in a few minutes by a one‐pot reaction using a conventional microwave oven and can be used for the direct detection of MP in water without any further treatment of the sample. The green fluorescence is strongly quenched in water at neutral pH because of the formation dimers. The ability of the probe to label MP was tested for polyvinyl chloride (PVC), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), poly methyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE). The probe showed considerable selectivity to PVC MP, which presented an intense red emission after staining. Interestingly, the fluorescence of the MP after labeling could be detected, under excitation with a blue diode, with a conventional CMOS color camera. Good selectivity was achieved analyzing the red to green fluorescence intensity ratio. UV– Vis absorption, steady‐state and time‐resolved fluorescence spectroscopy, fluorescence anisotropy, fluorescence wide‐field and confocal laser scanning microscopy allowed elucidating the mechanism of the staining in detail
Ongoing Star Formation in the BL Lacertae object PKS 2005-489
We present VLT long slit optical spectroscopy of the luminous BL Lacertae
object PKS 2005-489. The high signal-to-noise ratio and the good spatial
resolution of the data allow us to detect the signatures of ongoing star
formation in an extended rotating ring, at ~4 kpc from the nucleus. We find
that the ring is almost perpendicular to the radio axis and its total star
formation rate is ~1 MSol/yr. We briefly discuss the concomitant presence of
recent star formation and nuclear activity.Comment: Accepted for publication by ApJ
Controle de qualidade da digitalização de cartas de solo 1: 1.000.000 da bacia do alto rio Paraguai.
O controle de qualidade de produtos cartográficos é uma fase extremamente importante no processo de mapeamento, sendo poucas vezes realizado no Brasil. A exatidão de um mapa pode ser estabelecida por parâmetros estatísticos que relacionam as posições de um conjunto de pontos encontrados no mapa, com as respectivas posições levantadas em campo, que nesse caso são consideradas como verdadeiras. O trabalho teve como objetivo fazer o controle de qualidade de cartas de solo 1: 1.000.000 da bacia do alto rio Paraguai utilizando os padrões de exatidão cartográfica estabelecidos pelo Decreto n° 89817/84. O método utilizado para verificar a exatidão e a precisão cartográfica das cartas foi baseado em uma análise das discrepâncias entre as coordenadas de um conjunto de pontos medidos nas cartas com as coordenadas de referência, uma grade de pontos (quadrícula) bem definidos, dos pontos homólogos. A partir desses valores, foram calculadas as demais estatísticas para proceder à realização do teste. Em seguida, foram empregados os testes para verificar a exatidão e a precisão das cartas geradas. Foi possível verificar por estes resultados que as cartas não apresentaram tendências em nenhuma das coordenadas testadas. No teste de precisão, as cartas atingiram o padrão estabelecido para as classes A e B.Geopantanal 2006
- …