1,721,828 research outputs found
The evolution of a pre-heated Intergalactic Medium
Get PDFWe analyse the evolution of the intergalactic medium by means of an extended set of large box size hydrodynamical simulations which include pre-heating. We focus on the properties of the z similar to 2 Lyman alpha forest and the population of clusters and groups of galaxies at z = 0. We investigate the distribution of voids in the Lyman alpha flux and the entropy-temperature relation of galaxy groups, comparing the simulation results to recent data from high-resolution quasar spectra and X-ray observations. Pre-heating is included through a simple phenomenological prescription, in which at z = 4 the entropy of all gas particles, whose overdensity exceeds a threshold value delta(h), is increased to a minimum value K-fl. While the entropy level observed in the central regions of galaxy groups requires a fairly strong pre-heating, with K-fl > 100 keV cm(2), the void statistics of the Lyman alpha forest impose that this pre-heating should take place only in relatively high-density regions, delta(h) greater than or similar to 30, in order not to destroy the cold filaments that give rise to the forest. We conclude that any injection of non-gravitational energy in the diffuse baryons should avoid low-density regions at high redshift and/or take place at relatively low redshift z less than or similar to 1
A measurement of Omega(0) from the internal dynamics of spiral galaxies
No full textThe mean mass density of the universe is a primary target of observational cosmology. We devise a method to estimate this quantity by extending to spiral disks the argument that the peculiar motions of galaxies are generated by the overdensities of matter related to galaxy clustering. We obtain the density excess associated with the dark halos of spiral galaxies by considering, rather than the motion of a companion galaxy bound in an unknown orbit (as in earlier work of Davis & Peebles), the motion of test bodies rotating in the disk plane of spiral galaxies. This is done by means of a proper visible/dark mass decomposition of galaxy rotation curves. On scales R approximately 3-50 kpc (for a Hubble constant value of 50 km s-1 Mpc-1), we find that the mass excess around galaxies scales with R like the excess in number of spiral galaxies. On the assumption that light traces mass, we estimate the value of the cosmological density parameter to be OMEGA0 = 0.35 +/- 0.15. If the universe is flat, galaxy clustering is enhanced over matter clustering by a biasing factor of about 3
Turbulence driven by structure formation in the circumgalactic medium
No full textThe injection of turbulence in the circumgalactic medium at redshift z = 2 is investigated using the mesh-based hydrodynamic code ENZO and a sub-grid-scale (SGS) model for unresolved turbulence. Radiative cooling and heating by a uniform Ultraviolet (UV) background are included in our runs and compared with the effect of turbulence modelling. Mechanisms of gas exchange between galaxies and the surrounding medium, as well as metal enrichment, are not taken into account, and turbulence is here driven solely by structure formation (mergers and shocks). We find that turbulence, both at resolved and SGS scales, impacts mostly the warm-hot intergalactic medium (WHIM), with temperature between 105 and 107 K, mainly located around collapsed and shock-heated structures, and in filaments. Typical values of the ratio of turbulent to thermal pressure is 0.1 in the WHIM, corresponding to a volume-weighted average of the SGS turbulent to thermal Doppler broadening bt/btherm = 0.26, on length scales below the grid resolution of 25 kpc h- 1. In the diffuse intergalactic medium, defined in a range of baryon overdensity δ between 1 and 50, the importance of turbulence is smaller, but grows as a function of gas density, and the Doppler broadening ratio is fitted by the function bt/btherm = 0.023 × δ0.58
The Epoch of Structure Formation in Blue Mixed Dark Matter Models
No full textRecent data on the high-redshift abundance of damped Lyalpha systems are compared with theoretical predictions for `blue' (i.e. n1) mixed dark matter (MDM) models. The results show that decreasing the hot component fraction Omega_nu and/or increasing the primordial spectral index n leads to an earlier epoch of cosmic structure formation. We also show, however, that varying Omega_nu and n in these ways makes the models barely consistent with the observed abundance of galaxy clusters. Therefore, requiring both the observational constraints on damped Lyalpha systems and the cluster abundance to be satisfied simultaneously represents a challenge for the MDM class of models
Cosmological constraints from the ROSAT Deep Cluster Survey
No full textThe ROSAT Deep Cluster Survey (RDCS) has provided a new large deep sample of X-ray selected galaxy clusters. Observables such as the nux number counts n(S), the redshift distribution n(z), and the X-ray luminosity function (XLF) over a large redshift baseline (,z less than or similar to 0.8) are used here in order to constrain cosmological models. Our analysis is based on the Press-Schechter approach, whose reliability is tested against N-body simulations. Following a phenomenological approach, no assumption is made a priori on the relation between cluster masses and observed X-ray luminosities. As a first step, we use the local XLF from RDCS, along with the high-luminosity extension provided by the XLF from the Brightest Cluster Survey, in order to constrain the amplitude of the power spectrum, a,, and the shape of the local luminosity-temperature, L-bol-T, relation. We obtain sigma(8) = (0.58 +/- 0.06) x Omega(0)(-0.47+0.16 Ohm 0) for flat models (Omega(Lambda) = 1 - Omega(0)) and sigma(8) = (0.58 +/- 0.06) x Omega(0)(-0.53+0.27 Ohm 0) for open models (Omega(Lambda) = 0) at a 90% confidence level, almost independent of the L-bol-T shape. The density parameter Omega(0) and the evolution of the L-bol-T relation are constrained by the RDCS XLF at z > 0 and the EMSS XLF at (z) over bar = 0.33, and by the RDCS n(S) and n(z) distributions. By modeling the evolution for the amplitude of the L-bol-T relation as (1 + z)(A), an Omega(0) = 1 model can be accommodated for the evolution of the XLF with 1 less than or equal to A less than or equal to 3 at a 90% confidence level, while Omega(0) = 0.4(-0.2)(+0.3) and Omega(0) less than or similar to 0.6 are implied by a nonevolving L-bol-T (A = 0) for open and flat models, respectively
Cosmological constraints from the abundance, weak lensing, and clustering of galaxy clusters: Application to the SDSS
Get PDFAims. The clustering of galaxy clusters is a powerful cosmological tool. When it is combined with other cosmological observables, it can help to resolve parameter degeneracies and improve constraints, especially on Ωm and Ï8. We aim to demonstrate its potential in constraining cosmological parameters and scaling relations when combined with cluster counts and weak-lensing mass information. As a case study, we use the redMaPPer cluster catalog derived from the Sloan Digital Sky Survey (SDSS). Methods. We extended a previous analysis of the number counts and weak-lensing signal by the two-point correlation function. We derived cosmological and scaling relation posteriors for all possible combinations of the three observables to assess their constraining power, parameter degeneracies, and possible internal tensions. Results. We find no evidence for tensions between the three data sets we analyzed. We demonstrate that the constraining power of the sample can be greatly improved by including the clustering statistics because this can break the Ωmâ â â Ï8 degeneracy that is characteristic of cluster abundance studies. In particular, for a flat Î CDM model with massive neutrinos, we obtain Ωmâ =â 0.28â ±â 0.03 and Ï 8â =â 0.82â ±â 0.05, which is an improvement of 33% and 50% compared to the posteriors derived by combining cluster abundance and weak-lensing analyses. Our results are consistent with cosmological posteriors from other cluster surveys, and also with Planck results for the cosmic microwave background (CMB) and DES-Y3 galaxy clustering and weak-lensing analysis
The Wide Field X-ray Telescope
No full textProceedings of the "Wide Field X-ray Telescope" conference held in Bologna, Italy on 25-26 Nov 2009. The conference highlighted the scientific potential and discovery space provided by an X-ray mission concept characterized by a wide field-of-view (1 sq.deg.), large effective area (1 sq.mt.) and approximately constant PSF (~5 arcsec HEW) across the whole FOV
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
Kinetic or thermal AGN feedback in simulations of isolated and merging disc galaxies calibrated by the M-sigma relation
No full textWe investigate two modes of coupling the feedback energy from a central active galactic nucleus (AGN) to the neighbouring gas in galaxy simulations: kinetic - velocity boost and thermal - heating. We formulate kinetic feedback models for energy-driven wind (EDW) and momentum-driven wind (MDW), using two free parameters: feedback efficiency ∊f and AGN wind velocity vw. A novel numerical algorithm is implemented in the smoothed particle hydrodynamics code GADGET-3, to prevent the expansion of a hole in the gas distribution around the black hole (BH). We perform simulations of isolated evolution and merger of disc galaxies, of Milky Way mass as well as lower and higher masses. We find that in the isolated galaxy BH kinetic feedback generates intermittent bipolar jet-like gas outflows. We infer that current prescriptions for BH subgrid physics in galaxy simulations can grow the BH to observed values even in an isolated disc galaxy. The BH growth is enhanced in a galaxy merger, which consequently requires different model parameters to fit the observations than an isolated case. Comparing the [MBH-σ⋆] relation obtained in our simulations with observational data, we conclude that it is possible to find parameter sets for a fit in all the models (e.g. vw = 10 000 km s-1 and ∊f = 0.25 for BH kinetic EDW), except for the case with MDW feedback in a galaxy merger, in which the BH is always too massive. The BH thermal feedback implementation of Springel et al. within the multiphase star formation model is found to have negligible impact on gas properties, and the effect claimed in all previous studies is attributed to gas depletion around the BH by the creation of an artificial hole. The BH mass accretion rate in our simulations exhibit heavy fluctuations. The star formation rate is quenched with feedback by removal of gas. The circumgalactic medium gas at galactocentric distances (20-100) h-1 kpc is found to give the best metallicity observational diagnostic to distinguish between BH models
From Vlasov-Poisson to Schrödinger-Poisson: Dark matter simulation with a quantum variational time evolution algorithm
Get PDFCosmological simulations describing the evolution of density perturbations of a self-gravitating collisionless dark matter (DM) fluid in an expanding background provide a powerful tool to follow the formation of cosmic structures over wide dynamic ranges. The most widely adopted approach, based on the N-body discretization of the collisionless Vlasov-Poisson (VP) equations, is hampered by an unfavorable scaling when simulating the wide range of scales needed to cover at the same time the formation of single galaxies and of the largest cosmic structures. On the other hand, the dynamics described by the VP equations is limited by the rapid increase of the number of resolution elements (grid points and/or particles) which is required to simulate an ever growing range of scales. Recent studies showed an interesting mapping of the six-dimensional + 1 (6D+1) VP problem into a more amenable 3D+1 nonlinear Schrödinger-Poisson (SP) problem for simulating the evolution of DM perturbations. This opens up the possibility of improving the scaling of time propagation simulations using quantum computing. In this paper, we introduce a quantum algorithm for simulating the Schrödinger-Poisson (SP) equation by adapting a variational real-time evolution approach to a self-consistent, nonlinear, problem. To achieve this, we designed a novel set of quantum circuits that establish connections between the solution of the original Poisson equation and the solution of the corresponding time-dependent Schrödinger equation. We also analyzed how nonlinearity impacts the variance of observables. Furthermore, we explored how the spatial resolution behaves as the SP dynamics approaches the classical limit (h/m→0) and discovered an empirical logarithmic relationship between the required number of qubits and the scale of the SP equation (h/m). This entire approach holds the potential to serve as an efficient alternative for solving the Vlasov-Poisson (VP) equation by means of classical algorithms
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