77,445 research outputs found
A Physical Distance Indicator for Spiral Galaxies and the Determination of H0
No full textWe consider the effect of dark matter on the Tully-Fisher relation for spiral galaxies. We show that a significant fraction of the scatter in this relation could stem from a systematic dependence of the ratio of dark to luminous mass on luminosity. The dynamical effect of the dark matter can be accounted for once a mass decomposition procedure, based on photometry and rotation curve data, has been carried out. We show that the contribution to the circular velocity from the luminous disc alone correlates better with luminosity than does the total velocity, which contains an additional contribution from the dark halo. This correlation is closer to a linear law, has less scatter, and is subject to fewer biases than the conventional Tully-Fisher relation. As an illustration, we use two different sets of distance moduli for a sample of local galaxies to calibrate our relation. Applying Teerikorpi's prescription to correct for Malmquist bias, we then derive values of the Hubble constant of H0 = 61 +/- 5 and 66 +/- 6 km s-1 Mpc-1 for our two sets of calibrators respectively
The Impact of Simulations in Cosmology and Galaxy Formation A summary of the Workshop NOVICOSMO 2008
No full textIn the study of the process of cosmic structure formation numerical simulations are crucial tools to interface observational data to theoretical models and to investigate issues otherwise unexplored. Enormous advances have been achieved in the last years thanks to the availability of sophisticated codes, now allowing to tackle the problem of cosmic structure formation and subsequent evolution by covering larger and larger dynamical ranges. Moreover, computational cosmology is the ideal interpretative framework for the overwhelming amount of new data from extragalactic surveys and from large sample of individual objects. The Workshop Novicosmo 2008 "The Impact of Simulations in Cosmology and Galaxy Formation' held in SISSA was aimed at providing the state-of-the-art on the latest numerical simulations in Cosmology and in Galaxy Formation. Particular emphasis was given to the implementation of new physical processes in simulation codes, to the comparison between different codes and numerical schemes and how to use best supercomputing facilities of the next generation. Finally, the impact on our knowledge on the Physics of the Universe brought by this new channel of investigation has also been focused. The Workshop was divided in three sections corresponding (roughly) to three main areas of study: Reionization and Intergalactic medium; Dark and Luminous matter in galaxies; Clusters of galaxies and Large scale Structures. This paper will provide i) a short resume' of the scientific results of the Workshop ii) the complete list of the talks and the instructions on how to retrieve the .pdf of the related (powerpoint) presentations iii) a brief presentation of the associated Exhibition "Space Art
Modelling dust in galactic SEDs Application to semi-analytical galaxy formation models
No full textWe present the basic features and preliminary results of the interface between our spectrophotometric model GRASIL (which calculates galactic SEDs from the UV to the submm with a detailed computation of dust extinction and thermal reemission) with the semi-analytical galaxy formation model GALFORM (which computes galaxy formation and evolution in the hierarchical scenario, providing the star formation history as an input to our model). With these two models we are able to synthesize simulated samples of a few thousand galaxies for statistical studies of galaxy properties to investigate galaxy formation and evolution. There is good agreement with the available SED and luminosity function data
Measurement of the ratio of prompt χ c to J / ψ production in pp collisions at √s = 7 TeV
No full textThe prompt production of charmonium χ c and J / ψ states is studied in proton-proton collisions at a centre-of-mass energy of √s = 7 TeV at the Large Hadron Collider. The χ c and J / ψ mesons are identified through their decays χ c → J / ψ γ and J / ψ → μ + μ - using 36 pb - 1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for χ c and J / ψ, σ (χ c → J / ψ γ) / σ (J / ψ), is determined as a function of the J / ψ transverse momentum in the range 2 < p T J / ψ < 15 GeV / c. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low p T J / ψ region
Galaxy evolution in the infrared: comparison of a hierarchical galaxy formation model with Spitzer data
No full textWe present predictions for the evolution of the galaxy luminosity function, number counts and redshift distributions in the infrared (IR) based on the Lambda CDM cosmological model. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy spectral energy distributions including the reprocessing of radiation by dust. The model, which is the same as that given by Baugh et al., assumes two different initial mass functions (IMFs): a normal solar neighbourhood IMF for quiescent star formation in discs, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF seems to be necessary to explain the number counts of faint submillimetre galaxies. We compare the model with observational data from the Spitzer Space Telescope, with the model parameters fixed at values chosen before Spitzer data became available. We find that the model matches the observed evolution in the IR remarkably well over the whole range of wavelengths probed by Spitzer. In particular, the Spitzer data show that there is strong evolution in the mid-IR galaxy luminosity function over the redshift range z similar to 0-2, and this is reproduced by our model without requiring any adjustment of parameters. On the other hand, a model with a normal IMF in starbursts predicts far too little evolution in the mid-IR luminosity function, and is therefore excluded
Modelling the dusty universe - I. Introducing the artificial neural network and first applications to luminosity and colour distributions
No full textWe introduce a new technique based on artificial neural networks which enable us to make accurate predictions for the spectral energy distributions (SEDs) of large samples of galaxies, at wavelengths ranging from the far-ultraviolet (UV) to the submillimetre (sub-mm) and radio. The neural net is trained to reproduce the SEDs predicted by a hybrid code comprised of the galform semi-analytical model of galaxy formation, which predicts the full star formation and galaxy merger histories, and the grasil spectro-photometric code, which carries out a self-consistent calculation of the SED, including absorption and emission of radiation by dust. Using a small number of galaxy properties predicted by galform, the method reproduces the luminosities of galaxies in the majority of cases to within 10 per cent of those computed directly using grasil. The method performs best in the sub-mm and reasonably well in the mid-infrared (IR) and far-UV. The luminosity error introduced by the method has negligible impact on predicted statistical distributions, such as luminosity functions or colour distributions of galaxies. We use the neural net to predict the overlap between galaxies selected in the rest-frame UV and in the observer-frame sub-mm at z = 2. We find that around half of the galaxies with a 850 mu m flux above 5 mJy should have optical magnitudes brighter than R(AB) < 25 mag. However, only 1 per cent of the galaxies selected in the rest-frame UV down to R(AB) < 25 mag should have 850 mu m fluxes brighter than 5 mJy. Our technique will allow the generation of wide-angle mock catalogues of galaxies selected at rest-frame UV or mid- and far-IR wavelengths
Prompt charm production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
No full textCharm production at the LHC in pp collisions at s√=7 TeV is studied with the LHCb detector. The decays D0→K−π+, D+→K−π+π+, D⁎+→D0(K−π+)π+, D+s→ϕ(K−K+)π+, Λ+c→pK−π+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb−1. Differential cross-sections dσ/dpT are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0<pT<8 GeV/c and 2.0<y<4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above pT-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives
σ(cc¯)pT<8 GeV/c,2.0<y<4.5=1419±12(stat)±116(syst)±65(frag) μb,
where the uncertainties are statistical, systematic, and due to the fragmentation functions
The infrared side of galaxy formation. I. The local universe in the semianalytical framework
No full textWe present a new evolutionary model for predicting the far-uv-to-submillimeter properties of the galaxy population. This combines a semianalytic galaxy formation model based on hierarchical clustering (GALFORM) with a spectrophotometric code that includes dust reprocessing (GRASIL). The former provides the star formation and metal enrichment histories, together with the gas mass and various geometrical parameters, for a representative sample of galaxies formed in different density environments. These quantities, together with a few other assumptions concerning the spatial distribution of dust and its optical properties, allow us to model the spectral energy distributions (SEDs) of galaxies, taking into account stellar emission and also dust extinction (absorption plus scattering) and reemission. In the spectrophotometric code, dust is considered only in the disk, but the general radiation field is contributed by both the disk and the bulge components with their own distinct age and metallicity distributions. Two phases are considered for the dust: molecular cloud complexes, where stars are assumed to be born, and the diffuse interstellar medium. The model includes both galaxies forming stars quiescently in disks and starbursts triggered by galaxy mergers. We test our models against the observed spectrophotometric properties of galaxies in the local universe, assuming a cold dark matter cosmology with Omega (0) = 0.3 and Lambda (0) = 0.7. The models reproduce fairly well the SEDs of normal spirals and starbursts from the far-UV to the submillimeter and their internal extinction properties. The starbursts follow the observed relationship between the far-IR-to-UV luminosity ratio and the slope of the UV continuum. They also reproduce the observed starburst attenuation law. This result is remarkable because we use a dust mixture that reproduces the Milky Way extinction law. It suggests that the observed attenuation law is closely related to the geometry of the stars and dust. We compute galaxy luminosity functions over a wide range of wavelengths, which turn out to be in good agreement with observational data in the UV (2000 Angstrom), in the B and K bands, and in the IR (12-100 mum). Finally, we investigate the reliability of some star formation indicators that are based on the properties of the continuum SEDs of galaxies. The UV continuum turns out to be a poor star formation indicator for our models, while the infrared luminosity is much more reliable
Recursive Approximation of the High Dimensional max Function
No full textAn alternative smoothing method for the high dimensional max functionhas been studied. The proposed method is a recursive extension of thetwo dimensional smoothing functions. In order to analyze the proposedmethod, a theoretical framework related to smoothing methods has beendiscussed. Moreover, we support our discussion by considering someapplication areas. This is followed by a comparison with analternative well-known smoothing method.n dimensional max function;recursive approximation;smoothing methods;vertical linear complementarity (VLCP)
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