362 research outputs found
Galaxy pre-processing in substructures around z0.4 galaxy clusters
We present a detailed analysis of galaxy colours in two galaxy clusters at
\mbox{z 0.4}, \mbox{MACS J0416.1-2403} and \mbox{MACS J1206.2-0847},
drawn from the CLASH-VLT survey, to investigate the role of pre-processing in
the quenching of star formation. We estimate the fractions of red and blue
galaxies within the main cluster and the detected substructures and study the
trends of the colour fractions as a function of the projected distance from the
cluster and substructure centres. Our results show that the colours of cluster
and substructure members have consistent spatial distributions. In particular,
the colour fractions of galaxies inside substructures follow the same spatial
trends observed in the main clusters. Additionally, we find that at large
cluster-centric distances \mbox{()} the fraction of blue
galaxies in both the main clusters and in the substructures is always lower
than the average fraction of UVJ-selected star-forming galaxies in the field as
measured in the COSMOS/UltraVista data set. We finally estimate environmental
quenching efficiencies in the clusters and in the substructures and find that
at large distances from the cluster centres, the quenching efficiency of
substructures becomes comparable to the quenching efficiency of clusters. Our
results suggest that pre-processing plays a significant role in the formation
and evolution of passive galaxies in clusters at low redshifts.Comment: Accepted for publication in MNRAS. 28 pages, 14 figures, 20 table
Single polymer dynamics in elongational flow and the confluent Heun equation
We investigate the non-equilibrium dynamics of an isolated polymer in a
stationary elongational flow. We compute the relaxation time to the
steady-state configuration as a function of the Weissenberg number. A strong
increase of the relaxation time is found around the coil-stretch transition,
which is attributed to the large number of polymer configurations. The
relaxation dynamics of the polymer is solved analytically in terms of a central
two-point connection problem for the singly confluent Heun equation.Comment: 9 pages, 6 figure
The Geometry of Mass Outflows and Fueling Flows in the Seyfert 2 Galaxy Mrk 3
We present a study of the resolved emission-line regions and an inner
dust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble Space Telescope
observations. We show that the extended narrow-line region (ENLR), spanning ~4
kpc, is defined by the intersection of the ionizing bicone of radiation from
the AGN and the inner disk, which is not coplanar with the large-scale stellar
disk. This intersection leads to different position and opening angles of the
ENLR compared to the narrow-line region (NLR). A number of emission-line arcs
in the ENLR appear to be continuations of dust lanes in the disk, supporting
this geometry. The NLR, which consists of outflowing emission-line knots
spanning the central ~650 pc, is in the shape of a backwards S. This shape may
arise from rotation of the gas, or it may trace the original fueling flow close
to the nucleus that was ionized after the AGN turned on.Comment: 22 page, 7 figures, accepted for publication in the Astronomical
Journa
Ram pressure feeding super-massive black holes
When supermassive black holes at the center of galaxies accrete matter
(usually gas), they give rise to highly energetic phenomena named Active
Galactic Nuclei (AGN). A number of physical processes have been proposed to
account for the funneling of gas towards the galaxy centers to feed the AGN.
There are also several physical processes that can strip gas from a galaxy, and
one of them is ram pressure stripping in galaxy clusters due to the hot and
dense gas filling the space between galaxies. We report the discovery of a
strong connection between severe ram pressure stripping and the presence of AGN
activity. Searching in galaxy clusters at low redshift, we have selected the
most extreme examples of jellyfish galaxies, which are galaxies with long
tentacles of material extending for dozens of kpc beyond the galaxy disk. Using
the MUSE spectrograph on the ESO Very Large Telescope, we find that 6 out of
the 7 galaxies of this sample host a central AGN, and two of them also have
galactic-scale AGN ionization cones. The high incidence of AGN among the most
striking jellyfishes may be due to ram pressure causing gas to flow towards the
center and triggering the AGN activity, or to an enhancement of the stripping
caused by AGN energy injection, or both. Our analysis of the galaxy position
and velocity relative to the cluster strongly supports the first hypothesis,
and puts forward ram pressure as another, yet unforeseen, possible mechanism
for feeding the central supermassive black hole with gas.Comment: published in Nature, Vol.548, Number 7667, pag.30
Non-Hermitian matrix description of the PT symmetric anharmonic oscillators
Schroedinger equation H \psi=E \psi with PT - symmetric differential operator
H=H(x) = p^2 + a x^4 + i \beta x^3 +c x^2+i \delta x = H^*(-x) on
L_2(-\infty,\infty) is re-arranged as a linear algebraic diagonalization at
a>0. The proof of this non-variational construction is given. Our Taylor series
form of \psi complements and completes the recent terminating solutions as
obtained for certain couplings \delta at the less common negative a.Comment: 18 pages, latex, no figures, thoroughly revised (incl. title), J.
Phys. A: Math. Gen., to appea
Diffuse-Charge Dynamics in Electrochemical Systems
The response of a model micro-electrochemical system to a time-dependent
applied voltage is analyzed. The article begins with a fresh historical review
including electrochemistry, colloidal science, and microfluidics. The model
problem consists of a symmetric binary electrolyte between parallel-plate,
blocking electrodes which suddenly apply a voltage. Compact Stern layers on the
electrodes are also taken into account. The Nernst-Planck-Poisson equations are
first linearized and solved by Laplace transforms for small voltages, and
numerical solutions are obtained for large voltages. The ``weakly nonlinear''
limit of thin double layers is then analyzed by matched asymptotic expansions
in the small parameter , where is the
screening length and the electrode separation. At leading order, the system
initially behaves like an RC circuit with a response time of
(not ), where is the ionic diffusivity, but nonlinearity
violates this common picture and introduce multiple time scales. The charging
process slows down, and neutral-salt adsorption by the diffuse part of the
double layer couples to bulk diffusion at the time scale, . In the
``strongly nonlinear'' regime (controlled by a dimensionless parameter
resembling the Dukhin number), this effect produces bulk concentration
gradients, and, at very large voltages, transient space charge. The article
concludes with an overview of more general situations involving surface
conduction, multi-component electrolytes, and Faradaic processes.Comment: 10 figs, 26 pages (double-column), 141 reference
Recent ecological change in ancient lakes
Ancient lakes are among the best archivists of past environmental change, having experienced more than one full glacial cycle, a wide range of climatic conditions, tectonic events, and long association with human settlements. These lakes not only record long histories of environmental variation and human activity in their sediments, but also harbor very high levels of biodiversity and endemism. Yet, ancient lakes are faced with a familiar suite of anthropogenic threats, which may degrade the unusual properties that make them especially valuable to science and society. In all ancient lakes for which data exist, significant warming of surface waters has occurred, with a broad range of consequences. Eutrophication threatens both native species assemblages and regional economies reliant on clean surface water, fisheries, and tourism. Where sewage contributes nutrients and heavy metals, one can anticipate the occurrence of less understood emerging contaminants, such as pharmaceuticals, personal care products, and microplastics that negatively affect lake biota and water quality. Human populations continue to increase in most of the ancient lakesâ watersheds, which will exacerbate these concerns. Further, human alterations of hydrology, including those produced through climate change, have altered lake levels. Coâoccurring with these impacts have been intentional and unintentional species introductions, altering biodiversity. Given that the distinctive character of each ancient lake is strongly linked to age, there may be few options to remediate losses of species or other ecosystem damage associated with modern ecological change, heightening the imperative for understanding these systems
Building a multisystemic understanding of societal resilience to the COVID-19 pandemic
The current global systemic crisis reveals how globalised societies are unprepared to face a pandemic. Beyond the dramatic loss of human life, the COVID-19 pandemic has triggered widespread disturbances in health, social, economic, environmental and governance systems in many countries across the world. Resilience describes the capacities of natural and human systems to prevent, react to and recover from shocks. Societal resilience to the current COVID-19 pandemic relates to the ability of societies in maintaining their core functions while minimising the impact of the pandemic and other societal effects. Drawing on the emerging evidence about resilience in health, social, economic, environmental and governance systems, this paper delineates a multisystemic understanding of societal resilience to COVID-19. Such an understanding provides the foundation for an integrated approach to build societal resilience to current and future pandemics
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