470 research outputs found
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
Properties of the galaxy population in hydrodynamical simulations of clusters
We present a study of the galaxy population predicted by hydrodynamical
simulations for a set of 19 galaxy clusters based on the GADGET-2 Tree+SPH
code. These simulations include gas cooling, star formation, a detailed
treatment of stellar evolution and chemical enrichment, as well as SN energy
feedback in the form of galactic winds. We compute the spectro-photometric
properties of the simulated galaxies. All simulations have been performed for
two choices of the stellar initial mass function: a standard Salpeter IMF, and
a top-heavier IMF. Several of the observational properties of the galaxy
population in nearby clusters are reproduced fairly well by simulations. A
Salpeter IMF is successful in accounting for the slope and the normalization of
the color-magnitude relation for the bulk of the galaxy population. Simulated
clusters have a relation between mass and optical luminosity which generally
agrees with observations, both in normalization and slope. We find that
galaxies are generally bluer, younger and more star forming in the cluster
outskirts, thus reproducing the observational trends. However, simulated
clusters have a total number of galaxies which is significantly smaller than
the observed one, falling short by about a factor 2-3. Finally, the brightest
cluster galaxies are always predicted to be too massive and too blue, when
compared to observations, due to gas overcooling in the core cluster regions,
even in the presence of a rather efficient SN feedback.Comment: 15 pages, 17 figures, to appear in MNRA
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
Evolution of the metal content of the intra-cluster medium with hydrodynamical simulations
We present a comparison between simulation results and X-ray observational
data on the evolution of the metallicity of the intra-cluster medium (ICM). The
simulations of galaxy clusters were performed with the Tree-SPH Gadget2 code
that includes a detailed model of chemical evolution, by assuming three
different shapes for the stellar initial mass function (IMF), namely the
Salpeter (1955), Kroupa (2001) and Arimoto-Yoshii (1987) IMF. Our simulations
predict significant radial gradients of the Iron abundance, which extend over
the whole cluster virialized region. At larger radii, we do not detect any
flattening of the metallicity profiles. As for the evolution of the ICM metal
(Iron) abundance out to z=1, we find that it is determined by the combined
action of (i) the sinking of already enriched gas, (ii) the ongoing metal
production in galaxies and (iii) the locking of ICM metals in newborn stars. As
a result, rather than suppressing the metallicity evolution, stopping star
formation at z=1 has the effect of producing an even too fast evolution of the
emission-weighted ICM metallicity with too high values at low redshift.
Finally, we compare simulations with the observed rate of type-Ia supernovae
per unit B-band luminosity (SnU_B). We find that our simulated clusters do not
reproduce the decreasing trend of SnU_B at low redshift, unless star formation
is truncated at z=1.Comment: 9 pages, 7 figures, to appear in MNRA
Heat Transfer in Horizontal Copper Tube Heated by Electric Heating Process
Heat transfer from electrical and electronics component is essential for better performance of that electrical system, The maximum heat transfer from that system results long period durability. In most of the system base provided for equipments are very small and placed in a very complicated position. so heat transfer by forced convection is not easy for that purpose.The heat transfer by natural convection is the familiar technique used in electronics cooling; there is huge group of apparatus that lends itself to natural convection .This category consist of stand-alone correspondence such as modems and small computers having an array of printed circuit boards (PCB) accumulate within an area. Natural convection heat transfer in heated horizontal duct drive away heat from the interior surface is offered. The duct is open-ended and round in cross section. The test section is heated by provision of heating coils, where constant wall heat flux mentioned. Heat transfer experiment is carried out for channel of 50 mm. internal diameter and 4 mm thickness with length 600 mm. Ratios of length to diameter of the channel are taken as L/D = 12. Wall heat fluxes maintained at q// = 300 W/m2 to 3150 W/m2 . A methodical investigational record for the localsteady state natural convection heat transfer activities is obtained. The wall heating condition on local steady-state heat transfer phenomena are studied.The present experimental data is compared with the existing theoretical and experimental results for the cases of vertical smooth tubes.
On the impact of baryons on the halo mass function, bias, and cluster cosmology
Luminous matter produces very energetic events, such as active galactic nuclei and supernova explosions, that significantly affect the internal regions of galaxy clusters. Although the current uncertainty in the effect of baryonic physics on cluster statistics is subdominant as compared to other systematics, the picture is likely to change soon as the amount of high-quality data is growing fast, urging the community to keep theoretical systematic uncertainties below the ever-growing statistical precision. In this paper, we study the effect of baryons on galaxy clusters, and their impact on the cosmological applications of clusters, using the magneticum suite of cosmological hydrodynamical simulations. We show that the impact of baryons on the halo mass function can be recast in terms on a variation of the mass of the haloes simulated with pure N-body, when baryonic effects are included. The halo mass function and halo bias are only indirectly affected. Finally, we demonstrate that neglecting baryonic effects on haloes mass function and bias would significantly alter the inference of cosmological parameters from high-sensitivity next-generations surveys of galaxy clusters
Land subsidence susceptibility mapping in South Korea using machine learning algorithms
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. In this study, land subsidence susceptibility was assessed for a study area in South Korea by using four machine learning models including Bayesian Logistic Regression (BLR), Support Vector Machine (SVM), Logistic Model Tree (LMT) and Alternate Decision Tree (ADTree). Eight conditioning factors were distinguished as the most important affecting factors on land subsidence of Jeong-am area, including slope angle, distance to drift, drift density, geology, distance to lineament, lineament density, land use and rock-mass rating (RMR) were applied to modelling. About 24 previously occurred land subsidence were surveyed and used as training dataset (70% of data) and validation dataset (30% of data) in the modelling process. Each studied model generated a land subsidence susceptibility map (LSSM). The maps were verified using several appropriate tools including statistical indices, the area under the receiver operating characteristic (AUROC) and success rate (SR) and prediction rate (PR) curves. The results of this study indicated that the BLR model produced LSSM with higher acceptable accuracy and reliability compared to the other applied models, even though the other models also had reasonable results
The growth and assembly of a massive galaxy at z ~ 2
We study the stellar mass assembly of the Spiderweb Galaxy (MRC 1138-262), a
massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a
brightest cluster galaxy. Nearby protocluster galaxies are identified and their
properties are determined by fitting stellar population models to their
rest-frame ultraviolet to optical spectral energy distributions. We find that
within 150 kpc of the radio galaxy the stellar mass is centrally concentrated
in the radio galaxy, yet most of the dust-uncorrected, instantaneous star
formation occurs in the surrounding low-mass satellite galaxies. We predict
that most of the galaxies within 150 kpc of the radio galaxy will merge with
the central radio galaxy by z = 0, increasing its stellar mass by up to a
factor of ~ 2. However, it will take several hundred Myr for the first mergers
to occur, by which time the large star formation rates are likely to have
exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the
satellite galaxies are small, suggesting that stars and gas are being stripped
and deposited at distances of tens of kpc from the central radio galaxy. These
stripped stars may become intracluster stars or form an extended stellar halo
around the radio galaxy, such as those observed around cD galaxies in cluster
cores.Comment: 12 pages, accepted for publication in MNRA
Strategies to Prevent Anthracycline-Related Congestive Heart Failure in Survivors of Childhood Cancer
Cardiovascular complications are a leading cause of therapy-related morbidity and mortality in long-term survivors of childhood malignancy. In fact, childhood cancer survivors are at a 15-fold risk of developing CHF compared to age-matched controls. There is a strong dose-dependent association between anthracycline exposure and risk of CHF, and the incidence increases with longer followup. Outcome following diagnosis of CHF is generally poor, with overall survival less than 50% at 5 years. The growing number of childhood cancer survivors makes it imperative that strategies be developed to prevent symptomatic heart disease in this vulnerable population. We present here an overview of the current state of knowledge regarding primary, secondary, and tertiary prevention strategies for childhood cancer survivors at high risk for CHF, drawing on lessons learned from prevention studies in nononcology populations as well as from the more limited experience in cancer survivors
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