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Search Results: 1 - 10 of 9884 matches for " Violeta Gonzalez-Perez "
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Predictions for the intrinsic UV continuum properties of star forming galaxies and the implications for inferring dust extinction
Stephen M. Wilkins,Violeta Gonzalez-Perez,Cedric G. Lacey,Carlton M. Baugh
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21344.x
Abstract: The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function (IMF) and to the recent star formation and metal enrichment histories of a galaxy. Using the galform semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z=0, parameterised by the power law index beta, has a standard deviation of sigma_beta=0.30. This suggests an uncertainty on the inferred UV attenuation of A_fuv=0.7$ (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quantities irrespective of the sample size or quality of the photometry. Our results suggest that in some cases the attenuation by dust has been incorrectly estimated.
The accuracy of the UV continuum as an indicator of the star formation rate in galaxies
Stephen M. Wilkins,Violeta Gonzalez-Perez,Cedric G. Lacey,Carlton M. Baugh
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.22092.x
Abstract: The rest-frame intrinsic UV luminosity is often used as an indicator of the instantaneous star formation rate (SFR) in a galaxy. While it is in general a robust indicator of the ongoing star formation activity, the precise value of the calibration relating the UV luminosity to the SFR ($B_{\nu}$), is sensitive to various physical properties, such as the recent star formation and metal enrichment histories, along with the choice of stellar initial mass function. The distribution of these properties for the star-forming galaxy population then suggests that the adoption of a single calibration is not appropriate unless properly qualified with the uncertainties on the calibration. We investigate, with the aid of the {\sc galform} semi-analytic model of galaxy formation, the distribution of UV-SFR calibrations obtained using realistic star formation and metal enrichment histories. At $z=0$, we find that when the initial mass function is fixed (to the Kennicutt IMF), the median calibration is $B_{\rm fuv}=0.9$ where ${\rm SFR}/[{\rm M_{\odot}\,yr^{-1}}]=B_{\nu}\times 10^{-28}\times L_{\nu}/[{\rm ergs\,s^{-1}\,Hz^{-1}}]$. However, the width of the distribution $B_{\rm fuv}$ suggests that for a single object there is around a 20% {\em intrinsic} uncertainty (at $z=0$, rising to $\simeq 30%$ at $z=6$) on the star formation rate inferred from the FUV luminosity without additional constraints on the star formation history or metallicity. We also find that the median value of the calibration $B_{\rm fuv}$ is correlated with the star formation rate and redshift (at $z>3$) raising implications for the correct determination of the star formation rate from the UV.
Single Colour Diagnostics of the Mass-to-light Ratio: Predictions from Galaxy Formation Models
Stephen M. Wilkins,Violeta Gonzalez-Perez,Carlton M. Baugh,Cedric G. Lacey,Joe Zuntz
Physics , 2013, DOI: 10.1093/mnras/stt192
Abstract: Accurate galaxy stellar masses are crucial to better understand the physical mechanisms driving the galaxy formation process. We use synthetic star formation and metal enrichment histories predicted by the {\sc galform} galaxy formation model to investigate the precision with which various colours $(m_{a}-m_{b})$ can alone be used as diagnostics of the stellar mass-to-light ratio. As an example, we find that, at $z=0$, the {\em intrinsic} (B$_{f435w}-$V$_{f606w}$) colour can be used to determine the intrinsic rest-frame $V$-band stellar mass-to-light ratio ($\log_{10}\Gamma_{V}=\log_{10}[(M/M_{\odot})/(L_{V}/L_{V\odot})]$) with a precision of $\sigma_{lg\Gamma}\simeq 0.06$ when the initial mass function and redshift are known beforehand. While the presence of dust, assuming a universal attenuation curve, can have a systematic effect on the inferred mass-to-light ratio using a single-colour relation, this is typically small as it is often possible to choose a colour for which the dust reddening vector is approximately aligned with the $(m_{a}-m_{b})-\log_{10}\Gamma_{V}$ relation. The precision with which the stellar mass-to-light ratio can be recovered using a single colour diagnostic rivals implementations of SED fitting using more information but in which simple parameterisations of the star formation and metal enrichment histories are assumed. To facilitate the wide use of these relations, we provide the optimal observer frame colour to estimate the stellar mass-to-light ratio, along with the associated parameters, as a function of redshift ($0
Predictions for the abundance and colours of galaxies in high redshift clusters in hierarchical models
Alexander I. Merson,Carlton M. Baugh,Filipe B. Abdalla,Violeta Gonzalez-Perez,Claudia del P. Lagos,Simona Mei
Physics , 2015,
Abstract: High redshift galaxy clusters allow us to examine galaxy formation in extreme environments. Here we compile data for $z>1$ galaxy clusters to test the predictions from one of the latest semi-analytical models of galaxy formation. The model gives a good match to the slope and zero-point of the cluster red sequence. The model is able to match the cluster galaxy luminosity function at faint and bright magnitudes, but under-estimates the number of galaxies around the break in the luminosity function. We find that simply assuming a weaker dust attenuation improves the model predictions for the cluster galaxy luminosity function, but worsens the predictions for the red sequence at bright magnitudes. Examination of the properties of the bright cluster galaxies suggests that the default dust attenuation is very large due to these galaxies having large reservoirs of cold gas as well as small radii. We find that matching the luminosity function and colours of high redshift cluster galaxies, whilst remaining consistent with local observations, poses a challenge for galaxy formation models. Our results highlight the need to consider observations beyond the local Universe, as well as for different environments, when calibrating the parameters of galaxy formation models.
Social Responsibility Networks (SRN): The Role of the International Civil Society in Redressing the Negative Effects of Globalization at the Local Level Social Responsibility Networks (SRN): The Role of the International Civil Society in Redressing the Negative Effects of Globalization at the Local Level
Maria Alejandra Gonzalez-Perez
AD-minister , 2008,
Abstract: Evidencias, tanto teóricas como empíricas, indican que la globalización de laeconomía ha intensificado la exclusión social, los problemas medio ambientales y haexacerbado desigualdades en materia social y laboral. Para revertir estas situacionesse requiere de sistemas transnacionales de gobernabilidad legítimos y transparentes,que cuenten con la participación activa y reconocida de los trabajadores.Este documento se basa en una investigación empírica en la cual se presentaun modelo de participación transnacional de los actores de la sociedad civil(incluyendo los sindicatos y otras organizaciones de trabajadores), así como tambiénlas corporaciones privadas y las agencias gubernamentales. De esta manera se desarrolla una plataforma que opera como un sistema de responsabilidad socialcuyo alcance sobrepasa a la responsabilidad social empresarial (RSE). There is both theoretical and empirical evidence which indicates that the processes of globalization have intensified the onset of social exclusion and environmental problems. Globalized processes may also exacerbate inequalities that, in order to be readdressed, require transnational, transparent, accountable and participative governance systems, with an active and recognised contribution by the local community in the amelioration of these problems. This paper focuses on transnational participation of civil society actors as well as private corporations and state agencies, which together provide a platform for the development of a broader scope for corporate social responsibility (CSR).
Satellite galaxies in semi-analytic models of galaxy formation with sterile neutrino dark matter
Mark R. Lovell,Sownak Bose,Alexey Boyarsky,Shaun Cole,Carlos S. Frenk,Violeta Gonzalez-Perez,Rachel Kennedy,Oleg Ruchayskiy,Alex Smith
Physics , 2015,
Abstract: The sterile neutrino is a viable dark matter candidate that can be produced in the early Universe via non-equilibrium processes, and would therefore possess a highly non-thermal spectrum of primordial velocities. In this paper we analyse the process of structure formation with this class of dark matter particles. To this end we construct primordial dark matter power spectra as a function of the lepton asymmetry, $L_6$, that is present in the primordial plasma and leads to resonant sterile neutrino production. We compare these power spectra with those of thermally produced dark matter particles and show that resonantly produced sterile neutrinos are much colder than their thermal relic counterparts. We also demonstrate that the shape of these power spectra are not determined by the free-streaming scale alone. We then use the power spectra as an input for semi-analytic models of galaxy formation in order to predict the number of luminous satellite galaxies in a Milky Way-like halo. By assuming that the mass of the Milky Way halo must be no more than $2\times10^{12}M_{\odot}$ (the adopted upper bound based on current astronomical observations) we are able to constrain the value of $L_6$ for $M_{s}\le 5$keV. We also show that the range of $L_6$ that is in best agreement with the 3.5keV line (if produced by decays of 7keV sterile neutrino) requires that the Milky Way halo has a mass no smaller than $1.2\times10^{12}M_{\odot}$. Finally, we compare the power spectra obtained by direct integration of the Boltzmann equations for a non-resonantly produced sterile neutrino with the fitting formula of Viel et al. and find that the latter significantly underestimates the power amplitude on scales relevant to satellite galaxies.
Notch, IL-1 and Leptin Crosstalk Outcome (NILCO) Is Critical for Leptin-Induced Proliferation, Migration and VEGF/VEGFR-2 Expression in Breast Cancer
Shanchun Guo, Ruben R. Gonzalez-Perez
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0021467
Abstract: High levels of pro-angiogenic factors, leptin, IL-1, Notch and VEGF (ligands and receptors), are found in breast cancer, which is commonly correlated with metastasis and lower survival of patients. We have previously reported that leptin induces the growth of breast cancer and the expression of VEGF/VEGFR-2 and IL-1 system. We hypothesized that Notch, IL-1 and leptin crosstalk outcome (NILCO) plays an essential role in the regulation of leptin-mediated induction of proliferation/migration and expression of pro-angiogenic molecules in breast cancer. To test this hypothesis, leptin's effects on the expression and activation of Notch signaling pathway and VEGF/VEGFR-2/IL-1 were determined in mouse (4T1, EMT6 and MMT) breast cancer cells. Remarkably, leptin up-regulated Notch1-4/JAG1/Dll-4, Notch target genes: Hey2 and survivin, together with IL-1 and VEGF/VEGFR-2. RNA knockdown and pharmacological inhibitors of leptin signaling significantly abrogated activity of reporter gene-luciferase CSL (RBP-Jk) promoter, showing that it was linked to leptin-activated JAK2/STAT3, MAPK, PI-3K/mTOR, p38 and JNK signaling pathways. Interestingly, leptin upregulatory effects on cell proliferation/migration and pro-angiogenic factors Notch, IL-1 and VEGF/VEGFR-2 were abrogated by a γ-secretase inhibitor, DAPT, as well as siRNA against CSL. In addition, blockade of IL-1R tI inhibited leptin-induced Notch, Hey2 and survivin as well as VEGF/VEGFR-2 expression. These data suggest leptin is an inducer of Notch (expression/activation) and IL-1 signaling modulates leptin effects on Notch and VEGF/VEGFR-2. We show for the first time that a novel unveiled crosstalk between Notch, IL-1 and leptin (NILCO) occurs in breast cancer. Leptin induction of proliferation/migration and upregulation of VEGF/VEGFR-2 in breast cancer cells were related to an intact Notch signaling axis. NILCO could represent the integration of developmental, pro-inflammatory and pro-angiogenic signals critical for leptin-induced cell proliferation/migration and regulation of VEGF/VEGFR-2 in breast cancer. Targeting NILCO might help to design new pharmacological strategies aimed at controlling breast cancer growth and angiogenesis.
The information content in a volatility index for Spain
Maria T. Gonzalez-Perez,Alfonso Novales
SERIEs , 2011, DOI: 10.1007/s13209-010-0031-6
Abstract: A model-free methodology is used for the first time to estimate a daily volatility index (VIBEX-NEW) for the Spanish financial market. We use a public data set of daily option prices to compute this index and show that daily changes in VIBEX-NEW display a negative, tight contemporaneous relationship with IBEX daily returns, contrary to other common volatility indicators, as an implied volatility indicator or a GARCH(1,1) conditional volatility model. This relationship is approximately symmetric to the sign on VIBEX-NEW changes and asymmetric to the IBEX-35 returns sign, which make it clearly a suitable volatility index for the Spanish stock market. We also examine the relationship between current VIBEX-NEW and future IBEX-35 volatility. Our results suggest that VIBEX-NEW can be used to produce IBEX-35 volatility forecasts at least as good as historical and conditional volatility measures. A feasible volatility correction methodology is proposed to achieve it.
Lightcone mock catalogues from semi-analytic models of galaxy formation - I. Construction and application to the BzK colour selection
Alexander I. Merson,Carlton M. Baugh,John C. Helly,Violeta Gonzalez-Perez,Shaun Cole,Richard Bielby,Peder Norberg,Carlos S. Frenk,Andrew J. Benson,Richard G. Bower,Cedric G. Lacey,Claudia del P. Lagos
Physics , 2012, DOI: 10.1093/mnras/sts355
Abstract: We introduce a method for constructing end-to-end mock galaxy catalogues using a semi-analytical model of galaxy formation, applied to the halo merger trees extracted from a cosmological N-body simulation. The mocks that we construct are lightcone catalogues, in which a galaxy is placed according to the epoch at which it first enters the past lightcone of the observer, and incorporate the evolution of galaxy properties with cosmic time. We determine the position between the snapshot outputs at which a galaxy enters the observer's lightcone by interpolation. As an application, we consider the effectiveness of the BzK colour selection technique, which was designed to isolate galaxies in the redshift interval 1.4
Clustering of Extremely Red Objects in Elais-N1 from the UKIDSS DXS with optical photometry from Pan-STARRS1 and Subaru
Jae-Woo Kim,Alastair C. Edge,David A. Wake,Violeta Gonzalez-Perez,Carlton M. Baugh,Cedric G. Lacey,Toru Yamada,Yasunori Sato,William S. Burgett,Kenneth C. Chambers,Paul A. Price,Sebastien Foucaud,Peter Draper,Nick Kaiser
Physics , 2013, DOI: 10.1093/mnras/stt2245
Abstract: We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg$^{2}$, which cover the redshift range $z=0.8$ to $2$. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and Pan-STARRS PS1 datasets. We confirm the existence of a clear break in the angular correlation function at $\sim 0.02^{\circ}$ corresponding to $1 h^{-1}$ Mpc at $z\sim1$. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo Occupation Distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over $10^{13} h^{-1} M_{\odot}$ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at $z\sim1.1$, at $z\sim1.5$ EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host $10^{11.0} M_{\odot}
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