Simulating the formation of a proto-cluster at z~2

We present results from two high-resolution hydrodynamical simulations of proto-cluster regions at z~2.1. The simulations have been compared to observational results for the socalled Spiderweb galaxy system, the core of a putative proto-cluster region at z = 2.16, found around a radio galaxy. The simulated regions have been chosen so as to form a poor cluster with M200~10^14 h-1 Msun (C1) and a rich cluster with M200~2x10^15 h-1 Msun (C2) at z = 0. The simulated proto-clusters show evidence of ongoing assembly of a dominating central galaxy. The stellar mass of the brightest cluster galaxy (BCG) of the C2 system is in excess with respect to observational estimates for the Spiderweb galaxy, with a total star formation rate which is also larger than indicated by observations. We find that the projected velocities of galaxies in the C2 cluster are consistent with observations, while those measured for the poorer cluster C1 are too low compared to the observed velocities. We argue that the Spiderweb complex resemble the high-redshift progenitor of a rich galaxy cluster. Our results indicate that the included supernovae feedback is not enough to suppress star formation in these systems, supporting the need of introducing AGN feedback. According to our simulations, a diffuse atmosphere of hot gas in hydrostatic equilibrium should already be present at this redshift, and enriched at a level comparable to that of nearby galaxy clusters. The presence of this gas should be detectable with future deep X-ray observations.Comment: 6 pages, 4 figures, accepted for publication in MNRAS (Letters

A numerical method for the approximation of stable and unstable manifolds of microscopic simulators

We address a numerical methodology for the approximation of coarse-grained stable and unstable manifolds of saddle equilibria/stationary states of multiscale/stochastic systems for which a macroscopic description does not exist analytically in a closed form. Thus, the underlying hypothesis is that we have a detailed microscopic simulator (Monte Carlo, molecular dynamics, agent-based model etc.) that describes the dynamics of the subunits of a complex system (or a black-box large-scale simulator) but we do not have explicitly available a dynamical model in a closed form that describes the emergent coarse-grained/macroscopic dynamics. Our numerical scheme is based on the equation-free multiscale framework, and it is a three-tier procedure including (a) the convergence on the coarse-grained saddle equilibrium, (b) its coarse-grained stability analysis, and (c) the approximation of the local invariant stable and unstable manifolds; the later task is achieved by the numerical solution of a set of homological/functional equations for the coefficients of a polynomial approximation of the manifolds

On the influence of environment on star forming galaxies

We use our state-of-the-art semi analytic model for GAlaxy Evolution and Assembly (GAEA), and observational measurements of nearby galaxies to study the influence of the environment on the gas content and gaseous/stellar disc sizes of star-forming galaxies. We analyse the origin of differences between physical properties of satellites and those of their central counterparts, identified by matching the Vmax of their host haloes at the accretion time of the satellites. Our model reproduces nicely the differences between centrals and satellites measured for the HI mass, size of the star-forming region, and stellar radii. In contrast, our model predicts larger differences with respect to data for the molecular gas mass and star formation rate. By analysing the progenitors of central and satellite model galaxies, we find that differences in the gas content arise after accretion, and can be entirely ascribed to the instantaneous stripping of the hot gas reservoir. The suppression of cold gas replenishment via cooling and star formation leads to a reduction of the cold gas and of its density. Therefore, more molecular gas is lost than lower density HI gas, and model satellites have less molecular gas and lower star formation rates than observed satellites. We argue that these disagreements could be largely resolved with the inclusion of a proper treatment for ram-pressure stripping of cold gas and a more gradual stripping of the hot gas reservoir. A more sophisticated treatment of angular momentum exchanges, accounting for the multi-phase nature of the gaseous disc is also required.Comment: 15 pages, 9 figures, accepted for publication in MNRA

Anomalous Angular Dependence of the Dynamic Structure Factor near Bragg Reflections: Graphite

The electron energy-loss function of graphite is studied for momentum transfers q beyond the first Brillouin zone. We find that near Bragg reflections the spectra can change drastically for very small variations in q. The effect is investigated by means of first principle calculations in the random phase approximation and confirmed by inelastic x-ray scattering measurements of the dynamic structure factor S(q,\omega). We demonstrate that this effect is governed by crystal local field effects and the stacking of graphite. It is traced back to a strong coupling between excitations at small and large momentum transfers

Gas cooling in semi-analytic models and SPH simulations: are results consistent?

We present a detailed comparison between the galaxy populations within a massive cluster, as predicted by hydrodynamical SPH simulations and by a semi-analytic model (SAM) of galaxy formation. Both models include gas cooling and a simple prescription of star formation, which consists in transforming instantaneously any cold gas available into stars, while neglecting any source of energy feedback. We find that, in general, galaxy populations from SAMs and SPH have similar statistical properties, in agreement with previous studies. However, when comparing galaxies on an object-by-object basis, we find a number of interesting differences: a) the star formation histories of the brightest cluster galaxies (BCGs) from SAM and SPH models differ significantly, with the SPH BCG exhibiting a lower level of star formation activity at low redshift, and a more intense and shorter initial burst of star formation with respect to its SAM counterpart; b) while all stars associated with the BCG were formed in its progenitors in the semi-analytic model used here, this holds true only for half of the final BCG stellar mass in the SPH simulation, the remaining half being contributed by tidal stripping of stars from the diffuse stellar component associated with galaxies accreted on the cluster halo; c) SPH satellites can loose up to 90 per cent of their stellar mass at the time of accretion, due to tidal stripping, a process not included in the semi-analytic model used in this study; d) in the SPH simulation, significant cooling occurs on the most massive satellite galaxies and this lasts for up to 1 Gyr after accretion. This physical process is not included in the semi-analytic model used in our study, as well as in most of the models discussed in the recent literature.Comment: Revised version submitted to MNRAS, 15 pages, 9 figures. A High-resolution version of the paper and figures can be found at this http://adlibitum.oats.inaf.it/saro/SAM2/paper.pd

Imaging fractional incompressible stripes in integer quantum Hall systems

Transport experiments provide conflicting evidence on the possible existence of fractional order within integer quantum Hall systems. In fact integer edge states sometimes behave as monolithic objects with no inner structure, while other experiments clearly highlight the role of fractional substructures. Recently developed low-temperature scanning probe techniques offer today an opportunity for a deeper-than-ever investigation of spatial features of such edge systems. Here we use scanning gate microscopy and demonstrate that fractional features were unambiguously observed in every integer quantum Hall constriction studied. We present also an experimental estimate of the width of the fractional incompressible stripes corresponding to filling factors 1/3, 2/5, 3/5, and 2/3. Our results compare well with predictions of the edge-reconstruction theory

A Right to Choose: A Multi-Modal Approach to Improve Advance Directive Completion Rates

ABSTRACT Purpose: Advance Directives (AD) ensure that patients receive care consistent with their individual values, while also minimizing the decisional burden often placed on families when a patient’s wishes are not documented at the end of their life. This quality improvement (QI) project was intended to improve patients’ overall understanding of Advance directives (AD) and improve completion rates in a primary care setting for patients eighty years and above using a multimodal system. Methods: This QI project occurred in a primary care setting from March 2016 through March 2017. The multi-modal approach used included contacting patients by telephone, mailing AD informational packets prior to scheduled visit, in office AD discussions and follow-up phone calls. Collected data included patients’ age, provider, status of AD completion, multi-modal approach used and patients’ availability for discussion. Patients included were eighty and above and did not have a documented AD. Results: Pre-implementation, two participating providers had a 23.81% & 20.0% AD completion rate for patients eighty and above. Post-implementation, participating providers increased to 60.71% and 38.71% respectively. Conclusions: A multi-modal approach with structured education on the topic of ADs and providers’ recognition of patients in need of ADs, resulted in improved rates of AD completion, while also facilitating patient centered care. Keywords: Advance Care Planning, Advance Directives, End-of-life discussio

Characterizing Diffused Stellar Light in simulated galaxy clusters

[Abridged] In this paper, we carry out a detailed analysis of the performance of two different methods to identify the diffuse stellar light in cosmological hydrodynamical simulations of galaxy clusters. One method is based on a dynamical analysis of the stellar component. The second method is closer to techniques commonly employed in observational studies. Both the dynamical method and the method based on the surface brightness limit criterion are applied to the same set of hydrodynamical simulations for a large sample about 80 galaxy clusters. We find significant differences between the ICL and DSC fractions computed with the two corresponding methods, which amounts to about a factor of two for the AGN simulations, and a factor of four for the CSF set. We also find that the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of 1.5-2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to decrease from ~80 per cent in galaxy groups to ~60 per cent in rich clusters, thus in excess of what found from observational analysis. We identify the average surface brightness limits that yields the ICL fraction from the SBL method close to the DSC fraction from the dynamical method. These surface brightness limits turn out to be brighter in the CSF than in the AGN simulations. This is consistent with the finding that AGN feedback makes BCGs to be less massive and with shallower density profiles than in the CSF simulations. The BCG stellar component, as identified by both methods, are slightly older and more metal-rich than the stars in the diffuse component.Comment: 18 Pages, 15 figures. Matches to MNRAS published versio