521 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
Lyman Alpha Emitter Evolution in the Reionization Epoch
Combining cosmological SPH simulations with a previously developed Lyman
Alpha production/transmission model and the Early Reionization Model (ERM,
reionization ends at redshift z~7), we obtain Lyman Alpha and UV Luminosity
Functions (LFs) for Lyman Alpha Emitters (LAEs) for redshifts between 5.7 and
7.6. Matching model results to observations at z~5.7 requires escape fractions
of Lyman Alpha, f_alpha=0.3, and UV (non-ionizing) continuum photons, f_c=0.22,
corresponding to a color excess, E(B-V)=0.15. We find that (i) f_c increases
towards higher redshifts, due the decreasing mean dust content of galaxies,
(ii) the evolution of f_alpha/f_c hints at the dust content of the ISM becoming
progressively inhomogeneous/clumped with decreasing redshift. The clustering
photoionization boost is important during the initial reionization phases but
has little effect on the Lyman Alpha LF for a highly ionized IGM. Halo
(stellar) masses are in the range 10.0 < \log M_h < 11.8 (8.1 < \log M_* <
10.4) with M_h \propto M_*^{0.64}. The star formation rates are between 3-120
solar masses per year, mass-weighted mean ages are greater than 20 Myr at all
redshifts, while the mean stellar metallicity increases from Z=0.12 to 0.22
solar metallicity from z~7.6 to z~5.7; both age and metallicity positively
correlate with stellar mass. The brightest LAEs are all characterized by large
star formation rates and intermediate ages (~200 Myr), while objects in the
faint end of the Lyman Alpha LF show large age and star formation rate spreads.
With no more free parameters, the Spectral Energy Distributions of three LAE at
z~5.7 observed by Lai et al. (2007) are well reproduced by an intermediate age
(182-220 Myr) stellar population and the above E(B-V) value.Comment: 13 pages, 9 figures, accepted to MNRA
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
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
Utilización de enzimas fibrolÃticas para mejorar la digestión de forrajes tropicales. I. Influencia del método de aplciacion en la producción de gas in vitro y la composición quÃmica
Los forrajes tropicales presentan, en general, un menor valor nutritivo que los forrajes de zonas templadas. Sin embargo, su disponibilidad suele ser elevada y en numerosas
ocasiones son el único recurso alimenticio disponible para los animales rumiantes. Esta situación limita la productividad de estos animales y por ello se han investigado diferentes estrategias para aumentar el valor nutritivo de los forrajes tropicales. Una de las
metodologÃas propuestas para incrementar la utilización digestiva de los forrajes es el tratamiento de los mismos con enzimas fibrolÃticas (Carro y Ranilla, 2001), pero todavÃa son escasos los estudios realizados con forrajes tropicales. El objetivo de este trabajo fue evaluar el efecto de tres preparados enzimáticos en la fermentación ruminal in vitro y la degradabilidad de tres forrajes tropicales
Utilización de enzimas fibrolÃticas para mejorar la digestión de forrajes tropicales. II. Efectos en la fermetación ruminal in vitro y la degradabilidad
En muchos paÃses tropicales los sistemas productivos de animales rumiantes se basan en una amplia utilización de recursos forrajeros. Sin embargo, estos recursos suelen tener una baja calidad, por lo que cualquier mejora de su valor nutritivo tendrá una repercusión positiva en la productividad de los animales. En los últimos años se han realizado numerosos estudios para evaluar diferentes enzimas fibrolÃticas como aditivos para mejorar el valor
nutritivo de forrajes, pero la mayorÃa de ellos han utilizado forrajes de elevada calidad y apenas existen estudios con forrajes de baja calidad. Por otra parte, los resultados han sido muy variables, ya que la efectividad de las enzimas se ve afectada por numerosos factores, siendo el tipo de forraje y el método de aplicación de las enzimas dos de los más importantes (Giraldo et al., 2008). El objetivo del presente estudio fue evaluar el efecto de
tres enzimas fibrolÃticas exógenas en la fermentación ruminal in vitro de tres forrajes tropicales cuando las enzimas se aplicaron 24 h antes o en el momento de la incubación
High Frequency Cluster Radio Galaxies: Luminosity Functions and Implications for SZE Selected Cluster Samples
We study the overdensity of point sources in the direction of X-ray-selected
galaxy clusters from the Meta-Catalog of X-ray detected Clusters of galaxies
(MCXC; ) at South Pole Telescope (SPT) and Sydney
University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150
and 220 GHz are extracted from the 2500 deg SPT-SZ survey maps at the
locations of SUMSS sources, producing a multi-frequency catalog of radio
galaxies. In the direction of massive galaxy clusters, the radio galaxy flux
densities at 95 and 150 GHz are biased low by the cluster Sunyaev-Zel'dovich
Effect (SZE) signal, which is negative at these frequencies. We employ a
cluster SZE model to remove the expected flux bias and then study these
corrected source catalogs. We find that the high frequency radio galaxies are
centrally concentrated within the clusters and that their luminosity functions
(LFs) exhibit amplitudes that are characteristically an order of magnitude
lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the
impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy
flux typically produces a small bias on the SZE signal and has negligible
impact on the observed scatter in the SZE mass-observable relation. If we
assume there is no redshift evolution in the radio galaxy LF then
percent of the clusters would be lost from the sample. Allowing for redshift
evolution of the form increases the incompleteness to
percent. Improved constraints on the evolution of the cluster radio galaxy LF
require a larger cluster sample extending to higher redshift.Comment: Submitted to MNRA
The influence of diet on the effectiveness of garlic oil and cinnamaldehyde to manipulate in vitro ruminal fermentation and methane production.
The objective of this study was to evaluate the effects of increasing doses [0 (control: CON), 20, 60, 180 and 540 mg/L incubation medium] of garlic oil (GO) and cinnamaldehyde (CIN) on in vitro ruminal fermentation of two diets. Batch cultures of mixed ruminal microorganisms were inoculated with ruminal fluid from four sheep fed a medium-concentrate diet (MC; 50 : 50 alfalfa hay : concentrate) or four sheep fed a high-concentrate diet (HC; 15 : 85 barley straw : concentrate). Diets MC and HC were representative of those fed to dairy and fattening ruminants, respectively. Samples of each diet were used as incubation substrates for the corresponding inoculum, and the incubation was repeated on 4 different days (four replicates per experimental treatment). There were GO × diet-type and CIN × diet-type interactions (P 0.05) total volatile fatty acid (VFA) production at any dose. For MC diet, GO at 60, 180 and 540 mg/L decreased (P 0.05) on butyrate proportion were detected. Methane/VFA ratio was reduced (P < 0.05) by GO at 60, 180 and 540 mg/L for MC diet (0.23, 0.16 and 0.10 mol/mol, respectively), and by GO at 20, 60, 180 and 540 mg/L for HC diet (0.19, 0.19, 0.16 and 0.08 mol/mol, respectively), compared with CON (0.26 and 0.21 mol/mol for MC and HC diets, respectively). No effects (P = 0.16–0.85) of GO on final pH and concentrations of NH3-N and lactate were detected. For both diet types, the highest CIN dose decreased (P < 0.05) production of total VFA, gas and methane, which would indicate an inhibition of fermentation. Compared with CON, CIN at 180 mg/L increased (P < 0.05) acetate proportion for the MC (629 and 644 mmol/mol total VFA for CON and CIN, respectively) and HC (525 and 540 mmol/mol total VFA, respectively) diets, without affecting the proportions of any other VFA or total VFA production. Whereas for MC diet CIN at 60 and 180 mg/L decreased (P < 0.05) NH3-N concentrations compared with CON, only a trend (P < 0.10) was observed for CIN at 180 mg/L with the HC diet. Supplementation of CIN up to 180 mg/L did not affect (P = 0.18–0.99) lactate concentrations and production of gas and methane for any diet. The results show that effectiveness of GO and CIN to modify ruminal fermentation may depend on diet type, which would have practical implications if they are confirmed in vivo
Machine learning to identify ICL and BCG in simulated galaxy clusters
Nowadays, Machine Learning techniques offer fast and efficient solutions for classification problems that would require intensive computational resources via traditional methods. We examine the use of a supervised Random Forest to classify stars in simulated galaxy clusters after subtracting the member galaxies. These dynamically different components are interpreted as the individual properties of the stars in the Brightest Cluster Galaxy (BCG) and IntraCluster Light (ICL). We employ matched stellar catalogues (built from the different dynamical properties of BCG and ICL) of 29 simulated clusters from the DIANOGA set to train and test the classifier. The input features are cluster mass, normalized particle cluster-centric distance, and rest-frame velocity. The model is found to correctly identify most of the stars, while the larger errors are exhibited at the BCG outskirts, where the differences between the physical properties of the two components are less obvious. We investigate the robustness of the classifier to numerical resolution, redshift dependence (up to z = 1), and included astrophysical models. We claim that our classifier provides consistent results in simulations for z 0.1 R-200) is significantly affected by uncertainties in the classification process. In conclusion, this work suggests the importance of employing Machine Learning to speed up a computationally expensive classification in simulations
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