329 research outputs found
MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines
Optical changing-look Active Galactic Nuclei (AGN) are a class of sources
that change type within a short timescale of years or decades. This change is
characterised by the appearance or disappearance of broad emission lines, often
associated with dramatic AGN continuum flux changes that are orders of
magnitude larger than those expected from typical AGN variability. In this work
we study for the first time the host galaxy of a changing-look AGN, Mrk 590,
using high spatial resolution optical and near-infrared observations. We
discover that after ~ 10 yr absence, the optical broad emission lines of Mrk
590 have reappeared. The AGN optical continuum flux however, is still ~ 10
times lower than that observed during the most luminous state in the 1990s. The
host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionised and
cold molecular gas emission. Extended ionised and warm molecular gas emission
are detected in the nucleus, indicating that there is a reservoir of gas as
close as 60 pc from the black hole. We observe a nuclear gas spiral between
radii r ~ 0.5 - 2 kpc, which has been suggested as a dynamical mechanism able
to drive the necessary gas to fuel AGN. We also discover blue-shifted and high
velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a
nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance
between gas inflow and outflow in the nucleus of the galaxy.Comment: Accepted for publication in MNRA
Condições de trabalho e a saúde do professor de educação física escolar
O objetivo desta pesquisa bibliográfica descritiva foi analisar quais os fatores, associados à condição de trabalho, que interferem na saúde do professor de educação física escolar. Para tal, buscou-se respaldo em autores que tratam da temática da saúde ocupacional docente (BENEVIDES-PEREIRA, 2002, 2004; FREUDENBERGER, 1974; FRIEDMAN, 1991; KRAFT, 2006; MASLACH, JACKSON, 1986; REINHOLD, 2002). Entende-se que as condições de trabalho mostram-se hoje como uma das causas que acomete à saúde de profissionais de diversas áreas, levando até mesmo a um quadro de esgotamento profissional. Nesse sentido, a dedicação excessiva ao trabalho, associada a uma jornada além da proposta pela legislação, levam o sujeito ao depauperamento e, em contraposição, o mesmo deixa de praticar outras atividades que poderiam ter ações compensatórias. No caso do professor de educação física, o cotidiano escolar, ambiente no qual atua, exige uma práxis docente fundamentada por um diálogo constante entre teoria e prática. Esse tipo de intervenção docente requer habilidades que abrangem os aspectos físicos e intelectuais. Assim sendo, após análise contatou-se como principais fatores que precarizam a saúde do professor de educação física associados às condições de trabalho: i) O desgaste devido horas excessivas de aulas a serem cumpridas; ii) O número demasiado de alunos de uma turma; iii) A falta de recursos didáticos; iv) A má remuneração; v) A falta de reconhecimento profissional, comum no que tange à disciplina de educação física; vi) A necessidade de efetuar a prática profissional além dos limites da sala de aula, como por exemplo, quadra, pátio etc; vii) A proximidade corporal exigida pela decorrência das atividades desenvolvidas pelo docente e alunos. Dentre os setes fatores encontrados, os quatro primeiros são considerados como comuns a todos os professores. Entretanto, os três últimos fatores são particularmente agressores à saúde do professor de educação física
Evaluation of the effect of polymorphism on G-quadruplex-ligand interaction by means of spectroscopic and chromatographic techniques
Guanine-rich sequences may fold into highly ordered structures known as G-quadruplexes. Apart from the monomeric G-quadruplex, these sequences may form multimeric structures that are not usually considered when studying interaction with ligands. This work studies the interaction of a ligand, crystal violet, with three guanine-rich DNA sequences with the capacity to form multimeric structures. These sequences correspond to short stretches found near the promoter regions of c-kit and SMARCA4 genes. Instrumental techniques (circular dichroism, molecular fluorescence, size-exclusion chromatography and electrospray ionization mass spectrometry) and multivariate data analysis were used for this purpose. The polymorphism of G-quadruplexes was characterized prior to the interaction studies. The ligand was shown to interact preferentially with the monomeric G-quadruplex; the binding stoichiometry was 1:1 and the binding constant was in the order of 105 M-1 for all three sequences. The results highlight the importance of DNA treatment prior to interaction studie
Eddington ratio and accretion efficiency in AGN evolution
The cosmological evolution of Active Galactic Nuclei (AGN) is important for
understanding the mechanism of accretion onto supermassive black holes, and the
related evolution of the host galaxy. In this work, we include objects with
very low Eddington ratio (10^{-3} - 10^{-2}) in an evolution scenario, and
compare the results with the observed local distribution of black holes. We
test several possibilities for the AGN population, considering obscuration and
dependence with luminosity, and investigate the role of the Eddington ratio and
radiative accretion efficiency on the shape of the evolved mass function. We
find that three distinct populations of AGN can evolve with a wider parameter
range than is usually considered, and still be consistent with the local mass
function. In general, the black holes in our solutions are spinning rapidly.
Taking fixed values for accretion efficiency and Eddington ratio neither
provides a full knowledge of the evolution mechanism nor is consistent with the
existence of low Eddington ratio objects.Comment: Accepted for publication in MNRAS, 5 page
The broad-line type Ic SN 2020bvc: signatures of an off-axis gamma-ray burst afterglow
Long-duration gamma-ray bursts (GRBs) are almost unequivocally associated
with very energetic, broad-lined supernovae (SNe) of Type Ic-BL. While the
gamma-ray emission is emitted in narrow jets, the SN emits radiation
isotropically. Therefore, some SN Ic-BL not associated with GRBs have been
hypothesized to arise from events with inner engines such as off-axis GRBs or
choked jets. Here we present observations of the nearby ( Mpc) SN
2020bvc (ASAS-SN 20bs) which support this scenario. \textit{Swift} UVOT
observations reveal an early decline (up to two days after explosion) while
optical spectra classify it as a SN Ic-BL with very high expansion velocities
( 70,000 km/s), similar to that found for the jet-cocoon emission in
SN 2017iuk associated with GRB 171205A. Moreover, \textit{Swift} X-Ray
Telescope and \textit{CXO} X-ray Observatory detected X-ray emission only three
days after the SN and decaying onwards, which can be ascribed to an afterglow
component. Cocoon and X-ray emission are both signatures of jet-powered GRBs.
In the case of SN 2020bvc, we find that the jet is off axis (by 23
degrees), as also indicated by the lack of early ( day) X-ray
emission which explains why no coincident GRB was detected promptly or in
archival data. These observations suggest that SN 2020bvc is the first orphan
GRB detected through its associated SN emission.Comment: 9 pages, 6 figures, 5 tables. Accepted for publication in A&
Can we measure the accretion efficiency of Active Galactic Nuclei?
The accretion efficiency for individual black holes is very difficult to
determine accurately. There are many factors that can influence each step of
the calculation, such as the dust and host galaxy contribution to the observed
luminosity, the black hole mass and more importantly, the uncertainties on the
bolometric luminosity measurement. Ideally, we would measure the AGN emission
at every wavelength, remove the host galaxy and dust, reconstruct the AGN
spectral energy distribution and integrate to determine the intrinsic emission
and the accretion rate. In reality, this is not possible due to observational
limitations and our own galaxy line of sight obscuration. We have then to infer
the bolometric luminosity from spectral measurements made in discontinuous
wavebands and at different epochs. In this paper we tackle this issue by
exploring different methods to determine the bolometric luminosity. We first
explore the trend of accretion efficiency with black hole mass (efficiency
proportional to M^{\sim 0.5}) found in recent work by Davis & Laor and discuss
why this is most likely an artefact of the parameter space covered by their PG
quasar sample. We then target small samples of AGN at different redshifts,
luminosities and black hole masses to investigate the possible methods to
calculate the accretion efficiency. For these sources we are able to determine
the mass accretion rate and, with some assumptions, the accretion efficiency
distributions. Even though we select the sources for which we are able to
determine the parameters more accurately, there are still factors affecting the
measurements that are hard to constrain. We suggest methods to overcome these
problems based on contemporaneous multi-wavelength data measurements and
specifically targeted observations for AGN in different black hole mass ranges.Comment: 16 pages, 20 figures, accepted for publication in MNRA
Riding the wake of a merging galaxy cluster
Using WHT OASIS integral field unit observations, we report the discovery of
a thin plume of ionised gas extending from the brightest cluster galaxy in
Abell 2146 to the sub-cluster X-ray cool core which is offset from the BCG by
~37 kpc. The plume is greater than 15 kpc long and less than 3 kpc wide. This
plume is unique in that the cluster it is situated in is currently undergoing a
major galaxy cluster merger. The brightest cluster galaxy is unusually located
behind the X-ray shock front and in the wake of the ram pressure stripped X-ray
cool core and evidence for recent disruption to the BCG is observed. We examine
the gas and stellar morphology, the gas kinematics of the BCG and their
relation to the X-ray gas. We propose that a causal link between the ionised
gas plume and the offset X-ray cool core provides the simplest explanation for
the formation of the plume. An interaction or merger between the BCG and
another cluster galaxy is probably the cause of the offset.Comment: 14 pages, 18 figures, accepted for publication in MNRA
Balancing WNT signalling in early forebrain development: The role of LRP4 as a modulator of LRP6 function
The specification of the forebrain relies on the precise regulation of WNT/ß-catenin signalling to support neuronal progenitor cell expansion, patterning, and morphogenesis. Imbalances in WNT signalling activity in the early neuroepithelium lead to congenital disorders, such as neural tube defects (NTDs). LDL receptor-related protein (LRP) family members, including the well-studied receptors LRP5 and LRP6, play critical roles in modulating WNT signalling capacity through tightly regulated interactions with their co-receptor Frizzled, WNT ligands, inhibitors and intracellular WNT pathway components. However, little is known about the function of LRP4 as a potential modulator of WNT signalling in the central nervous system. In this study, we investigated the role of LRP4 in the regulation of WNT signalling during early mouse forebrain development. Our results demonstrate that LRP4 can modulate LRP5- and LRP6-mediated WNT signalling in the developing forebrain prior to the onset of neurogenesis at embryonic stage 9.5 and is therefore essential for accurate neural tube morphogenesis. Specifically, LRP4 functions as a genetic modifier for impaired mitotic activity and forebrain hypoplasia, but not for NTDs in LRP6-deficient mutants. In vivo and in vitro data provide evidence that LRP4 is a key player in fine-tuning WNT signalling capacity and mitotic activity of mouse neuronal progenitors and of human retinal pigment epithelial (hTERT RPE-1) cells. Our data demonstrate the crucial roles of LRP4 and LRP6 in regulating WNT signalling and forebrain development and highlight the need to consider the interaction between different signalling pathways to understand the underlying mechanisms of disease. The findings have significant implications for our mechanistic understanding of how LRPs participate in controlling WNT signalling
A layering model for superconductivity in the borocarbides
We propose a superlattice model to describe superconductivity in layered
materials, such as the borocarbide families with the chemical formul\ae\
BC and BC, with being (essentially) a rare earth, and a
transition metal. We assume a single band in which electrons feel a local
attractive interaction (negative Hubbard-) on sites representing the B
layers, while U=0 on sites representing the C layers; the multi-band
structure is taken into account minimally through a band offset . The
one-dimensional model is studied numerically through the calculation of the
charge gap, the Drude weight, and of the pairing correlation function. A
comparison with the available information on the nature of the electronic
ground state (metallic or superconducting) indicates that the model provides a
systematic parametrization of the whole borocarbide family.Comment: 4 figure
On weak vs. strong universality in the two-dimensional random-bond Ising ferromagnet
We address the issue of universality in two-dimensional disordered Ising
systems, by considering long, finite-width strips of ferromagnetic Ising spins
with randomly distributed couplings. We calculate the free energy and spin-spin
correlation functions (from which averaged correlation lengths, ,
are computed) by transfer-matrix methods. An {\it ansatz} for the
size-dependence of logarithmic corrections to is proposed. Data for
both random-bond and site-diluted systems show that pure system behaviour (with
) is recovered if these corrections are incorporated, discarding the
weak--universality scenario.Comment: RevTeX code, 4 pages plus 2 Postscript figures; to appear in Physical
Review B Rapid Communication
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