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Xia J.-Q.,International School for Advanced Studies | Granett B.R.,National institute for astrophysics | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy | And 6 more authors.
Journal of Cosmology and Astroparticle Physics | Year: 2012

We use the galaxy angular power spectrum at z ∼ 0.5-1.2 from the Canada-France-Hawaii-Telescope Legacy Survey Wide fields (CFHTLS-Wide) to constrain separately the total neutrino mass ∑m ν and the effective number of neutrino species N eff. This survey has recently benefited from an accurate calibration of the redshift distribution, allowing new measurements of the (non-linear) matter power spectrum in a unique range of scales and redshifts sensitive to neutrino free streaming. Our analysis makes use of a recent model for the effect of neutrinos on the weakly non-linear matter power spectrum derived from accurate N-body simulations. We show that CFHTLS, combined with WMAP7 and a prior on the Hubble constant provides an upper limit of ∑m ν<0.29 eV and N eff=4.17 +1.62 -1.26 (2σ confidence levels). If we omit smaller scales which may be affected by non-linearities, these constraints become ∑m ν<0.41 eV and N eff=3.98 +2.02 -1.20 (2σ confidence levels). Finally we show that the addition of other large scale structures probes can further improve these constraints, demonstrating that high redshift large volumes surveys such as CFHTLS are complementary to other cosmological probes of the neutrino mass. © 2012 IOP Publishing Ltd and Sissa Medialab srl.


Bridle S.,University College London | Balan S.T.,University of Cambridge | Bethge M.,University of Tübingen | Gentile M.,Ecole Polytechnique Federale de Lausanne | And 30 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present the results of the Gravitational LEnsing Accuracy Testing 2008 (GREAT08) Challenge, a blind analysis challenge to infer weak gravitational lensing shear distortions from images. The primary goal was to stimulate new ideas by presenting the problem to researchers outside the shear measurement community. Six GREAT08 Team methods were presented at the launch of the Challenge and five additional groups submitted results during the 6-month competition. Participants analyzed 30 million simulated galaxies with a range in signal-to-noise ratio, point spread function ellipticity, galaxy size and galaxy type. The large quantity of simulations allowed shear measurement methods to be assessed at a level of accuracy suitable for currently planned future cosmic shear observations for the first time. Different methods perform well in different parts of simulation parameter space and come close to the target level of accuracy in several of these. A number of fresh ideas have emerged as a result of the Challenge including a re-examination of the process of combining information from different galaxies, which reduces the dependence on realistic galaxy modelling. The image simulations will become increasingly sophisticated in future GREAT Challenges, meanwhile the GREAT08 simulations remain as a benchmark for additional developments in shear measurement algorithms. © 2010 The Authors. Journal compilation © 2010 RAS. Re-use of this article is permitted in accordance with the Terms and Conditions set out at http://www3.interscience.wiley.com/authorresources/onlineopen.html.


Karl S.J.,Institute of Astronomy and Kavli Institute for Cosmology | Aarseth S.J.,University of Cambridge | Naab T.,Max Planck Institute for Astrophysics | Haehnelt M.G.,Institute of Astronomy and Kavli Institute for Cosmology | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present a hybrid code combining the OpenMP-parallel tree code VINE with an algorithmic chain regularization scheme. The new code, called 'rVINE', aims to significantly improve the accuracy of close encounters of massive bodies with supermassive black holes (SMBHs) in galaxy-scale numerical simulations. We demonstrate the capabilities of the code by studying two test problems, the sinking of a single massive black hole to the centre of a gas-free galaxy due to dynamical friction and the hardening of an SMBH binary due to close stellar encounters. We show that results obtained with rVINE compare well with NBODY7 for problems with particle numbers that can be simulated with NBODY7. In particular, in both NBODY7 and rVINE we find a clear N-dependence of the binary hardening rate, a low binary eccentricity and moderate eccentricity evolution, as well as the conversion of the galaxy's inner density profile from a cusp to a core via the ejection of stars at high velocity. The much larger number of particles that can be handled by rVINE will open up exciting opportunities to model stellar dynamics close to SMBHs much more accurately in a realistic galactic context. This will help to remedy the inherent limitations of commonly used tree solvers to follow the correct dynamical evolution of black holes in galaxy-scale simulations. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bird S.,Institute of Astronomy and Kavli Institute for Cosmology | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy | Haehnelt M.G.,Institute of Astronomy and Kavli Institute for Cosmology
Monthly Notices of the Royal Astronomical Society | Year: 2012

We perform an extensive suite of N-body simulations of the matter power spectrum, incorporating massive neutrinos in the range M ν= 0.15-0.6eV, probing the non-linear regime at scales k < 10hMpc -1 at z < 3. We extend the widely used halofit approximation to account for the effect of massive neutrinos on the power spectrum. In the strongly non-linear regime, halofit systematically overpredicts the suppression due to the free streaming of the neutrinos. The maximal discrepancy occurs at k∼ 1hMpc -1, and is at the level of 10 per cent of the total suppression. Most published constraints on neutrino masses based on halofit are not affected, as they rely on data probing the matter power spectrum in the linear or mildly non-linear regime. However, predictions for future galaxy, Lyman α forest and weak lensing surveys extending to more non-linear scales will benefit from the improved approximation to the non-linear matter power spectrum we provide. Our approximation reproduces the induced neutrino suppression over the targeted scales and redshifts significantly better. We test its robustness with regard to changing cosmological parameters and a variety of modelling effects. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Dubois Y.,CNRS Paris Institute of Astrophysics | Dubois Y.,University of Oxford | Pichon C.,CNRS Paris Institute of Astrophysics | Pichon C.,CEA Saclay Nuclear Research Center | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Supermassive black holes (BH) are powerful sources of energy that are already in place at very early epochs of the Universe (by z = 6). Using hydrodynamical simulations of the formation of a massive Mvir = 5 × 1011M⊙ halo by z = 6 (the most massive progenitor of a cluster of Mvir =2×1015M⊙ at z=0), we evaluate the impact of active galactic nuclei (AGN) on galaxy mass content, BH self-regulation and gas distribution inside this massive halo. We find that supernova feedback has a marginal influence on the stellar structure, and no influence on the mass distribution on large scales. In contrast, AGN feedback alone is able to significantly alter the stellar-bulge mass content by quenching star formation when the BH is self-regulating, and by depleting the cold gas reservoir in the centre of the galaxy. The growth of the BH proceeds first by a rapid Eddington-limited period fed by direct cold filamentary infall. When the energy delivered by the AGN is sufficiently large to unbind the cold gas of the bulge, the accretion of gas on to the BH is maintained by both smooth gas inflow and clump migration through the galactic disc triggered by merger-induced torques. The feedback from the AGN has also a severe consequence on the baryon mass content within the halo, producing large-scale hot superwinds, able to blow away some of the cold filamentary material from the centre and reduce the baryon fraction by more than 30 per cent within the halo's virial radius. Thus, in the very young universe, AGN feedback is likely to be a key process, shaping the properties of the most massive galaxies. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Karl S.J.,Institute of Astronomy and Kavli Institute for Cosmology | Karl S.J.,Max Planck Institute for Astrophysics | Lunttila T.,University of Helsinki | Naab T.,Max Planck Institute for Astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present a set of hydro-dynamical numerical simulations of the Antennae galaxies in order to understand the origin of the central overlap starburst. Our dynamical model provides a good match to the observed nuclear and overlap star formation, especially when using a range of rather inefficient stellar feedback efficiencies (0.01 ≲ qEoS ≲ 0.1). In this case a simple conversion of local star formation to molecular hydrogen surface density motivated by observations accounts well for the observed distribution of CO. Using radiative transfer post-processing we model synthetic far-infrared spectral energy distributions (SEDs) and two-dimensional emission maps for direct comparison with Herschel-PACS observations. For a gas-to-dust ratio of 62:1 and the best matching range of stellar feedback efficiencies the synthetic far-infrared SEDs of the central star-forming region peak at values of ̃65-81 Jy at 99-116 μm, similar to a three-component modified blackbody fit to infrared observations. Also the spatial distribution of the far-infrared emission at 70 μm, 100 μm and 160 μm compares well with the observations: ≳50 per cent (≳35 per cent) of the emission in each band is concentrated in the overlap region while only <30 per cent (<15 per cent) is distributed to the combined emission from the two galactic nuclei in the simulations (observations). As a proof of principle we show that parameter variations in the feedback model result in unambiguous changes both in the global and in the spatially resolved observable far-infrared properties of Antennae galaxy models. Our results strengthen the importance of direct, spatially resolved comparative studies of matched galaxy merger simulations as a valuable tool to constrain the fundamental star formation and feedback physics. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Dubois Y.,CNRS Paris Institute of Astrophysics | Dubois Y.,University of Oxford | Pichon C.,CNRS Paris Institute of Astrophysics | Haehnelt M.,Institute of Astronomy and Kavli Institute for Cosmology | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We use cosmological hydrodynamical simulations to show that a significant fraction of the gas in high redshift rare massive haloes falls nearly radially to their very centre on extremely short time-scales. This process results in the formation of very compact bulges with specific angular momentum a factor of 5-30 smaller than the average angular momentum of the baryons in the whole halo. Such low angular momentum originates from both segregation and effective cancellation when the gas flows to the centre of the halo along well-defined cold filamentary streams. These filaments penetrate deep inside the halo and connect to the bulge from multiple rapidly changing directions. Structures falling in along the filaments (satellite galaxies) or formed by gravitational instabilities triggered by the inflow (star clusters) further reduce the angular momentum of the gas in the bulge. Finally, the fraction of gas radially falling to the centre appears to increase with the mass of the halo; we argue that this is most likely due to an enhanced cancellation of angular momentum in rarer haloes which are fed by more isotropically distributed cold streams. Such an increasingly efficient funnelling of low angular momentum gas to the centre of very massive haloes at high redshift may account for the rapid pace at which the most massive supermassive black holes grow to reach observed masses around 10 9M ⊙ at an epoch when the Universe is barely 1 Gyr old. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Barnes L.A.,Institute of Astronomy and Kavli Institute for Cosmology | Haehnelt M.G.,Institute of Astronomy and Kavli Institute for Cosmology
Monthly Notices of the Royal Astronomical Society | Year: 2010

We use detailed Lyα radiative transfer calculations to further test the claim of Rauch et al. that they have detected spatially extended faint Lyα emission from the elusive host population of damped Lyα absorption systems (DLAs) in their recent ultra-deep spectroscopic survey. We investigate the spatial and spectral distribution of Lyα emission due to star formation at the centre of DLAs, and its dependence on the spatial and velocity structure of the gas. Our model simultaneously reproduces the observed properties of DLAs and the faint Lyα emitters, including the velocity width and column density distribution of DLAs and the large spatial extent of the emission of the faint emitters. Our modelling confirms previous suggestions that DLAs are predominately hosted by dark matter (DM) haloes in the mass range 109.5-1012 M⊙, and are thus of significantly lower mass than those inferred for L* Lyman Break Galaxies (LBGs). Our modelling suggests that DM haloes hosting DLAs retain up to 20 per cent of the cosmic baryon fraction in the form of neutral hydrogen, and that star formation at the centre of the haloes is responsible for the faint Lyα emission. The scattering of a significant fraction of the Lyα emission to the observed radii, which can be as large as 50 kpc or more, requires the amplitude of the bulk motions of the gas at the centre of the haloes to be moderate. The observed space density and size distribution of the emitters together with the incidence rate of DLAs suggests that the Lyα emission due to star formation has a duty cycle of ∼25 per cent. © 2010 The Authors. Journal compilation © 2010 RAS.


Barnes L.A.,University of Sydney | Haehnelt M.G.,Institute of Astronomy and Kavli Institute for Cosmology
Monthly Notices of the Royal Astronomical Society | Year: 2014

We discuss the recent Baryon Oscillation Spectroscopic Survey measurement of a rather high bias factor for the host galaxies/haloes of damped Lyman alpha absorbers (DLAs), in the context of our previous modelling of the physical properties of DLAs within the Λ cold dark matter paradigm. Joint modelling of the column density distribution, the velocity width distribution of associated low-ionization metal absorption, and the bias parameter suggests that DLAs are hosted by galaxies with dark matter halo masses in the range 10.5 < log Mv<13, with a rather sharp cutoff at the lower mass end, corresponding to virial velocities of ~90 km s-1. The observed properties of DLAs appear to suggest very efficient (stellar) feedback in haloes with masses/virial velocities below the cutoff and a large retained baryon fraction (≳35 per cent) in haloes above the cutoff. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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