596 research outputs found
A non-ideal MHD Gadget: Simulating massive galaxy clusters
No full textMagnetic fields in the intra-cluster medium (ICM) of galaxy clusters have been studied in the past through different methods. So far, our understanding of the origin of these magnetic fields, as well as their role in the process of structure formation and their interplay with the other constituents of the ICM, is still limited. In the coming years, the up-coming generation of radio telescopes is going to provide new data that will have the potential of setting constraints on the properties of magnetic fields in galaxy clusters.
Here, we present zoomed-in simulations for a set of massive galaxy clusters (Mv ≥ 1015 h-1 M⊙). This is an ideal sample to study the evolution of the magnetic field during the process of structure formation in detail. Turbulent motions of the gas within the ICM will manifest themselves in a macroscopic magnetic resistivity ηm, which has to be taken explicitly into account, especially at scales below the resolution limit. We have adapted the magnetohydrodynamic (MHD) GADGET code by Dolag & Stasyszyn to include the treatment of the magnetic resistivity, and for the first time we have included non-ideal MHD equations to better follow the evolution of the magnetic field within the galaxy clusters. We investigate which value of the magnetic resistivity ηm is required to match the magnetic field profile derived from radio observations. We find that a value of ηm ̃ 6 × 1027 cm2 s-1 is necessary to recover the shape of the magnetic field profile inferred from radio observations of the Coma cluster. This value agrees well with the expected level of turbulent motions within the ICM at our resolution limit. The magnetic field profiles of the simulated clusters can be fitted by a β-model-like profile, with small dispersion of the parameters. We also find that the temperature, density and entropy profiles of the clusters depend on the magnetic resistivity constant, having flatter profiles in the inner regions when the magnetic resistivity increases
The Sunyaev–Zel'dovich effects from a cosmological hydrodynamical simulation: large-scale properties and correlation with the soft X-ray signal
No full textEvolution of massive haloes in non-Gaussian scenarios
No full textWe have performed high-resolution cosmological N-body simulations of a concordance ΛCDM model to study the evolution of virialized, dark matter haloes in the presence of primordial non-Gaussianity. Following a standard procedure, departures from Gaussianity are modelled through a quadratic Gaussian term in the primordial gravitational potential, characterized by a dimensionless non-linearity strength parameter fNL. We find that the halo mass function and its redshift evolution closely follow the analytic predictions of Matarrese, Verde & Jimenez. The existence of precise analytic predictions makes the observation of rare, massive objects at large redshift an even more attractive test to detect primordial non-Gaussian features in the large-scale structure of the Universe
The UV continua and inferred stellar populations of galaxies at z ≃ 7-9 revealed by the Hubble Ultra-Deep Field 2012 campaign
No full textJSD, PD, VW, RAAB and TAT acknowledge the support of the European Research Council via the award of an Advanced Grant. JSD and RJM acknowledge the support of the Royal Society via a Wolfson Research Merit Award, and a University Research Fellowship respectively. ABR and EFCL acknowledge the support of the UK Science & Technology Facilities Council. US authors acknowledge financial support from the Space Telescope Science Institute under award HST-GO-12498.01-A. SRF is partially supported by the David and Lucile Packard Foundation. SC acknowledges the support of the European Commission through the Marie Curie Initial Training Network ELIXIR.We use the new ultra-deep, near-infrared imaging of the Hubble Ultra-Deep Field (HUDF) provided by our UDF12 Hubble Space Telescope (HST) Wide Field Camera 3/IR campaign to explore the rest-frame ultraviolet (UV) properties of galaxies at redshifts z > 6.5. We present the first unbiased measurement of the average UV power-law index, ⟨β⟩, (fλ α λβ) for faint galaxies at z ≃ 7, the first meaningful measurements of at z ≃ 8, and tentative estimates for a new sample of galaxies at z ≃ 9. Utilizing galaxy selection in the new F140W (J140) imaging to minimize colour bias, and applying both colour and power-law estimators of β, we find ⟨β⟩= -2.1 ± 0.2 at z ≃ 7 for galaxies with MUV ≃ -18. This means that the faintest galaxies uncovered at this epoch have, on average, UV colours no more extreme than those displayed by the bluest star-forming galaxies at low redshift. At z ≃ 8 we find a similar value, ⟨β⟩ = -1.9 ± 0.3. At z ≃ 9, we find ⟨β⟩ = -1.8 ± 0.6, essentially unchanged from z ≃ 6 to 7 (albeit highly uncertain). Finally, we show that there is as yet no evidence for a significant intrinsic scatter in β within our new, robust z ≃ 7 galaxy sample. Our results are most easily explained by a population of steadily star-forming galaxies with either ≃ solar metallicity and zero dust, or moderately sub-solar (≃ 10-20 per cent) metallicity with modest dust obscuration (AV ≃ 0.1-0.2). This latter interpretation is consistent with the predictions of a state-of-the-art galaxy-formation simulation, which also suggests that a significant population of very-low metallicity, dust-free galaxies with β ≃ -2.5 may not emerge until MUV > -16, a regime likely to remain inaccessible until the James Webb Space Telescope.Peer reviewe
Hydrodynamical simulations of galaxy clusters in dark energy cosmologies – II. c–M relation
No full textWe use hydrodynamical simulations of different dark energy cosmologies to investigate the concentration-mass (c-M) relation in galaxy clusters. In particular, we consider a reference Lambda cold dark matter (Lambda CDM) model, two quintessence models with inverse power-law potentials (RP and SUGRA) and two extended quintessence (EQ) models, one with positive and one with negative coupling with gravity (EQp and EQn, respectively). All the models are normalized in order to match cosmic microwave background data from Wilkinson Microwave Anisotropy Probe 3. We fit both the dark matter only and the total mass profiles with an NFW profile, and recover the concentration of each halo from the fit using different definition. We consider both the complete catalogue of clusters and groups and subsamples of objects at different level of relaxation. We find that the definition itself of the concentration can lead to differences up to 20 per cent in its value and that these differences are smaller when more relaxed objects are considered. The c-M relation of our reference Lambda CDM model is in good agreement with the results in the literature, and relaxed objects have a higher normalization and a shallower slope with respect to the complete sample. The inclusion of baryon physics is found to influence high-mass systems more than low-mass ones, due to a higher concentration of baryons in the inner regions of massive haloes. For the different dark energy models, we find that for Lambda CDM, RP and SUGRA the normalization of the c-M relation is linked to the growth factor, with models having a higher value of sigma D-8(+) having also a higher normalization. This simple scheme is no longer valid for EQp and EQn because in these models a time-dependent effective gravitational interaction, whose redshift evolution depends on the sign of the coupling, is present. This leads to a decrease (increase) of the expected normalization in the EQp (EQn) model. This result shows a direct manifestation of the coupling between gravity and the quintessence scalar field characterizing EQ models that can be in principle investigated through the analysis of the relation
The complex galaxy cluster Abell 514: New results obtained with the XMM-Newton satellite
No full textAims: We study the X-ray morphology and dynamics of the galaxy cluster Abell 514. Also, the relation between the X-ray properties and Faraday Rotation measures of this cluster are investigated in order to study the connection of magnetic fields and the intra-cluster medium.
Methods: We use two combined XMM-Newton pointings that are split into three distinct observations.
Results: The data allow us to evaluate the overall cluster properties like temperature and metallicity with high accuracy. The cluster has a temperature of 3.8±0.2 keV and a metallicity of 0.22±0.07 in solar units. Additionally, a temperature map and the metallicity distribution are computed, which are used to study the dynamical state of the cluster in detail. Abell 514 represents an interesting merger cluster with many substructures visible in the X-ray image and in the temperature and abundance distributions. These results are used to investigate the connection between the ICM properties and the magnetic field of the cluster by comparing results from radio measurements. The new XMM-Newton data of Abell 514 confirm the relation between the X-ray brightness and the sigma of the Rotation Measure (S_X-σ_RM relation).
Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA
Angular diameter distance estimates from the Sunyaev-Zel'dovich effect in hydrodynamical cluster
No full textSimulated X-ray galaxy clusters at the virial radius: slopes of the gas density, temperature and surface brightness profiles
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