896 research outputs found
Distinguishing Dark Matter Cusps from Cores using Globular Clusters
Globular Clusters (GCs) provide valuable insight into the properties of their
host galaxies' dark matter halos. Using N-body simulations incorporating
semianalytic dynamical friction and GC-GC merger prescriptions, we study the
evolution of GC radial distributions and mass functions in cuspy and cored dark
matter halos. Modeling the dynamics of the GC-rich system in the dwarf galaxy
UGC7369, we find that friction-induced inspiral and subsequent mergers of
massive GCs can naturally and robustly explain the mass segregation of the GCs
and the existence of a nuclear star cluster (NSC). However, the multiple
mergers required to form the NSC only take place when the dark matter halo is
cuspy. In a cored halo, stalling of the dynamical friction within the core
halts the inspiral of the GCs, and so the GC merger rate falls significantly,
precluding the formation of an NSC. We therefore argue that the presence of an
NSC requires a cusp in UGC7369. More generally, we propose that the presence of
an NSC and the corresponding alteration of the GC mass function due to mergers
may be used as an indicator of a cuspy halo for galaxies in which we expect NSC
formation to be merger-dominated. These observables represent a simple,
powerful complement to other inner halo density profile constraint techniques,
and should allow for straightforward extension to larger samples.Comment: 19 pages, 11 figures. Main results in figures 7 and 8. Submitted to
ApJ, comments are welcome
Non-Markovian decay beyond the Fermi Golden Rule: Survival Collapse of the polarization in spin chains
The decay of a local spin excitation in an inhomogeneous spin chain is
evaluated exactly: I) It starts quadratically up to a spreading time t_{S}. II)
It follows an exponential behavior governed by a self-consistent Fermi Golden
Rule. III) At longer times, the exponential is overrun by an inverse power law
describing return processes governed by quantum diffusion. At this last
transition time t_{R} a survival collapse becomes possible, bringing the
polarization down by several orders of magnitude. We identify this strongly
destructive interference as an antiresonance in the time domain. These general
phenomena are suitable for observation through an NMR experiment.Comment: corrected versio
Risk Assessment and Health, Safety, and Environmental Management of Carbon Nanomaterials
The management of health, safety, and environmental (HSE) aspects during production, manipulation, storage, incorporation, and disposal of carbon nanomaterials is the key factor for the development of a safe-by-design work based on nanotechnology. The almost endless possibility of functionalization, chemical interaction, and addition of nanomaterials into new products implies a new management approach of HSE. Low amount of reliable toxicity and ecotoxicity data of nanomaterials and nanomaterial composites is available. As complete exposure/release assessments are a challenging task, recommendation for control measurements is still based on the precautionary point of view. There is an incomplete understanding of environmental fate- and time-related exposure, and of consumer- and worker-related risks and hazards. Control banding and risk evaluation matrix tools can be used to mitigate labor and environment impacts of carbon nanomaterials. This chapter presents new tools and methodologies for exposure assessment and risk evaluation of hazards used on HSE management system of carbon nanomaterials
Towards a time-reversal mirror for quantum systems
The reversion of the time evolution of a quantum state can be achieved by
changing the sign of the Hamiltonian as in the polarization echo experiment in
NMR. In this work we describe an alternative mechanism inspired by the acoustic
time reversal mirror. By solving the inverse time problem in a discrete space
we develop a new procedure, the perfect inverse filter. It achieves the exact
time reversion in a given region by reinjecting a prescribed wave function at
its periphery.Comment: 6 pages, 4 figures. Introduction modified, references added, one
figure added to improve the discussio
ELVES III: Environmental Quenching by Milky Way-Mass Hosts
Isolated dwarf galaxies usually exhibit robust star formation but satellite
dwarf galaxies are often devoid of young stars, even in Milky Way-mass groups.
Dwarf galaxies thus offer an important laboratory of the environmental
processes that cease star formation. We explore the balance of quiescent and
star-forming galaxies (quenched fractions) for a sample of ~400 satellite
galaxies around 30 Local Volume hosts from the Exploration of Local VolumE
Satellites (ELVES) Survey. We present quenched fractions as a function of
satellite stellar mass, projected radius, and host halo mass, to conclude that
overall, the quenched fractions are similar to the Milky Way, dropping below
50% at satellite M* ~ 10^8 M_sun. We may see hints that quenching is less
efficient at larger radius. Through comparison with the semi-analytic modeling
code satgen, we are also able to infer average quenching times as a function of
satellite mass in host halo-mass bins. There is a gradual increase in quenching
time with satellite stellar mass rather than the abrupt change from rapid to
slow quenching that has been inferred for the Milky Way. We also generally
infer longer average quenching times than recent hydrodynamical simulations.
Our results are consistent with models that suggest a wide range of quenching
times are possible via ram-pressure stripping, depending on the clumpiness of
the circumgalactic medium, the orbits of the satellites, and the degree of
earlier preprocessing.Comment: 18 pages, 12 figures, replaced post-refereeing, no major change
ELVES IV: The Satellite Stellar-to-Halo Mass Relation Beyond the Milky-Way
Quantifying the connection between galaxies and their host dark matter halos
has been key for testing cosmological models on various scales. Below , such studies have primarily relied on the satellite galaxy
population orbiting the Milky Way. Here we present new constraints on the
connection between satellite galaxies and their host dark matter subhalos using
the largest sample of satellite galaxies in the Local Volume () to date. We use confirmed and candidate dwarf
satellites around 27 Milky Way (MW)-like hosts from the Exploration of Local
VolumE Satellites (ELVES) Survey and use the semi-analytical SatGen model for
predicting the population of dark matter subhalos expected in the same volume.
Through a Bayesian model comparison of the observed and the forward-modeled
satellite stellar mass functions (SSMF), we infer the satellite stellar-to-halo
mass relation. We find that the observed SSMF is best reproduced when subhalos
at the low mass end are populated by a relation of the form , with a moderate slope of and a low scatter, constant as a function of the peak halo mass, of
. A model with a steeper slope
() and a scatter that grows with decreasing
is also consistent with the observed SSMF but is not
required. Our new model for the satellite-subhalo connection, based on hundreds
of Local Volume satellite galaxies, is in line with what was previously derived
using only the Milky Way satellites.Comment: Accepted for publication in ApJ. Figure 8 shows the key result -- the
Satellite Stellar to Halo Mass relation obtained in this work, in comparison
to previous studie
Medical imaging in the diagnosis of schistosomiasis: a review
Schistosomiasis is one of the most important parasitic diseases and it is endemic in tropical and subtropical areas. Clinical and laboratory data are fundamental for the diagnosis of schistosomiasis, but diagnostic imaging techniques such as x-rays, ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography/computed tomography (PET/CT) may be helpful in the evaluation of disease severity and complications. In this context, the aim of this review is to explore the actual role of diagnostic imaging in the diagnosis of schistosomiasis, underlining advantages and drawbacks providing information about the utilization of diagnostic imaging techniques in this context. Furthermore, we aim to provide a useful guide regarding imaging features of schistosomiasis for radiology and nuclear medicine physicians of non-endemic countries: in fact, in the last years non-endemic countries have experienced important flows of migrants from endemic areas, therefore it is not uncommon to face cases of this disease in daily practice
A Tip of the Red Giant Branch Distance to the Dark Matter Deficient Galaxy NGC1052-DF4 from Deep Hubble Space Telescope Data
Previous studies have shown that the large, diffuse galaxies NGC1052-DF2 and
NGC1052-DF4 both have populations of unusually luminous globular clusters as
well as a very low dark matter content. Here we present newly-obtained deep
Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging of one
of these galaxies, NGC1052-DF4. We use these data to measure the distance of
the galaxy from the location of the tip of the red giant branch (TRGB). We find
a rapid increase in the number of detected stars fainter than , which we identify as the onset of the red giant branch. Using a forward
modeling approach that takes the photometric uncertainties into account, we
find a TRGB magnitude of . The inferred
distance, including the uncertainty in the absolute calibration, is Mpc. The TRGB distance of NGC1052-DF4 is consistent with
the previously-determined surface brightness fluctuation distance of Mpc to NGC1052-DF2 and is consistent with the distance of the
bright elliptical galaxy NGC1052. We conclude that the unusual properties of
these galaxies cannot be explained by distance errors.Comment: Accepted for publication in ApJ Letters, in press. Figure 1 shows the
color image of the galaxy. The main result is shown in Figure
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