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| Halo Models of Large Scale Structure |
| We review the formalism and applications of the halo-based description of non-linear gravitational clustering. In this approach, all mass is associated with virialized dark matter halos; models of the number and spatial distribution of the halos, and the distribution of dark matter within each halo, are used to provide estimates of how the statistical properties of large scale density and velocity fields evolve as a result of non-linear gravitational clustering. We first describe the model, and demonstrate its accuracy by comparing its predictions with exact results from numerical simulations of non-linear gravitational clustering. We then present several astrophysical applications of the halo model: these include models of the spatial distribution of galaxies, the non-linear velocity, momentum and pressure fields, descriptions of weak gravitational lensing, and estimates of secondary contributions to temperature fluctuations in the cosmic microwave background. |
| Publication date: 16 Feb 2011 |
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| Submillimetre galaxies reside in dark matter haloes with masses greater than 3×10^11 solar masses |
| The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500 ¼m. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, Mmin, such that log10[Mmin/Msolar] = 11.5 (+0.7-0.2) at 350 µm, where Msolar is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation. |
| Publication date: 16 Feb 2011 |
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| On the origin of the energetic ion events measured upstream of the Earth's bow shock by STEREO, Cluster, and Geotail |
| In 2007 during the declining phase of the solar cycle the energetic upstream ion events occurred mainly after a corotating interaction region passed the Earth's magnetosphere. We study the relation between these upstream events observed from about 70 to 1750 RE away from the Earth and observations in the vicinity of the terrestrial bow shock (up to 30 RE). For this purpose, simultaneous measurements of energetic ions from STEREO A and STEREO B (far upstream region) and from Cluster and Geotail (near the bow shock) are used. In all cases the energetic ions far upstream are associated with the upstream ion events near the bow shock. The upstream events are observed simultaneously mainly when the magnetic field is pointing along the line joining those satellites in the far upstream region with those near the terrestrial bow shock. The upstream events near the bow shock often coincide with sunward directed electron bursts, increased AE index (>200 nT), nonexponential proton spectra, and most important the presence of O+ ions, all of which imply at least partly a magnetospheric origin. In ~57% of cases the upstream ion events near the bow shock are associated with electron bursts and/or with the presence of O+, and ~40% of the latter events are associated with electron bursts at STEREO A. Although we present strong evidence that the events are partially of magnetospheric origin, we do not exclude the presence of the ions accelerated at the bow shock. |
| Publication date: 11 Feb 2011 |
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| 'Crater' flux transfer events: Highroad to the X line? |
| We examine Cluster observations of a so-called magnetosphere crater FTE, employing data from five instruments (FGM, CIS, EDI, EFW, and WHISPER), some at the highest resolution. The aim of doing this is to deepen our understanding of the reconnection nature of these events by applying recent advances in the theory of collisionless reconnection and in detailed observational work. Our data support the hypothesis of a stratified structure with regions which we show to be spatial structures. We support the bulge-like topology of the core region (R3) made up of plasma jetting transverse to reconnected field lines. We document encounters with a magnetic separatrix as a thin layer embedded in the region (R2) just outside the bulge, where the speed of the protons flowing approximately parallel to the field maximizes: (1) short (fraction of a sec) bursts of enhanced electric field strengths (up to <30 mV/m) and (2) electrons flowing against the field toward the X line at approximately the same time as the bursts of intense electric fields. R2 also contains a density decrease concomitant with an enhanced magnetic field strength. At its interface with the core region, R3, electric field activity ceases abruptly. The accelerated plasma flow profile has a catenary shape consisting of beams parallel to the field in R2 close to the R2/R3 boundary and slower jets moving across the magnetic field within the bulge region. We detail commonalities our observations of crater FTEs have with reconnection structures in other scenarios. We suggest that in view of these properties and their frequency of occurrence, crater FTEs are ideal places to study processes at the separatrices, key regions in magnetic reconnection. This is a good preparation for the MMS mission. |
| Publication date: 08 Feb 2011 |
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| An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10 |
| Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids. |
| Publication date: 03 Feb 2011 |
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| EJSM-Laplace assessment study report (Yellow Book) |
| Reference: ESA/SRE(2011)1
This report, the so-called Yellow Book, contains the results of ESA's assessment study (Phase 0/A) of the candidate L-class Cosmic Vision mission EJSM-Laplace. |
| Publication date: 03 Feb 2011 |
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| IXO assessment study report (Yellow Book) |
| Reference: ESA/SRE(2011)2
This report, the so-called Yellow Book, contains the results of ESA's assessment study (Phase 0/A) of the candidate L-class Cosmic Vision mission IXO. |
| Publication date: 03 Feb 2011 |
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| LISA assessment study report (Yellow Book) |
| Reference: ESA/SRE(2011)3 This report, the so-called Yellow Book, contains the results of ESA's assessment study (Phase 0/A) of the candidate L-class Cosmic Vision mission LISA.
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| Publication date: 03 Feb 2011 |
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| Altitude distribution of the auroral acceleration potential determined from Cluster satellite data at different heights |
| Aurora, commonly seen in the polar sky, is a ubiquitous phenomenon occurring on Earth
and other solar system planets. The colorful emissions are caused by high-energy beams of
electrons hitting the upper atmosphere, after being accelerated by quasi-static electric
fields at altitudes around one Earth radius, or by wave electric fields. Although the aurora
was studied by many past satellite missions, Cluster is first to explore the acceleration
region with multi-probes, enabling open issues on its nature to be resolved. Here, Cluster
data from the upper and lower parts of this region are used to determine the altitude
distribution of the acceleration potential above the Aurora Borealis, and to address its
stability in space and time. The derived acceleration potential consists of two broad Ushaped
potentials in the upper parts of the acceleration region, and a narrower S-shaped
potential structure located below, and is stable on a five minute time scale. The results
demonstrate that the spatial scale of the electric field is much smaller than the current
width in the lower parts, but almost equal in the upper parts of the acceleration region
Revealing of these features was possible only by combining data from the two spacecraft. |
| Publication date: 01 Feb 2011 |
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| X-ray wind tomography of the highly absorbed HMXB IGR J17252–3616 |
Context. About ten persistently highly absorbed super-giant high-mass X-ray binaries (sgHMXB) have been discovered by INTEGRAL as bright hard X-ray sources lacking bright X-ray counterparts. Besides IGR J16318-4848, which has peculiar characteristics, the other members of this family share many properties with the classical wind-fed sgHMXB systems.
Aims. Our goal is to understand the characteristics of highly absorbed sgHMXB and in particular the companion stellar wind, which is thought to be responsible for the strong absorption.
Methods. We monitored IGR J17252-3616, a highly absorbed system featuring eclipses, with XMM-Newton to study the variability of the column density and the Fe K-alpha emission line along the orbit and during the eclipses. We also compiled a 3D model of the stellar wind to reproduce the observed variability.
Results. We first derive a refined orbital solution based on INTEGRAL, RXTE, and XMM-Newton data. We find that the XMM-Newton monitoring campaign reveals significant variations in the intrinsic absorbing column density along the orbit and the Fe K-alpha line equivalent width around the eclipse. The origin of the soft X-ray absorption is associated with a dense and extended hydrodynamical tail, trailing the neutron star. This structure extends along most of the orbit, indicating that the stellar wind has been strongly disrupted.
The remainder of the abstract is truncated. |
| Publication date: 01 Feb 2011 |
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| X-ray wind tomography of the highly absorbed HMXB IGR J17252–3616 |
Context. About ten persistently highly absorbed super-giant high-mass X-ray binaries (sgHMXB) have been discovered by INTEGRAL as bright hard X-ray sources lacking bright X-ray counterparts. Besides IGR J16318-4848, which has peculiar characteristics, the other members of this family share many properties with the classical wind-fed sgHMXB systems.
Aims. Our goal is to understand the characteristics of highly absorbed sgHMXB and in particular the companion stellar wind, which is thought to be responsible for the strong absorption.
Methods. We monitored IGR J17252-3616, a highly absorbed system featuring eclipses, with XMM-Newton to study the variability of the column density and the Fe K-alpha emission line along the orbit and during the eclipses. We also compiled a 3D model of the stellar wind to reproduce the observed variability.
Results. We first derive a refined orbital solution based on INTEGRAL, RXTE, and XMM-Newton data. We find that the XMM-Newton monitoring campaign reveals significant variations in the intrinsic absorbing column density along the orbit and the Fe K-alpha line equivalent width around the eclipse. The origin of the soft X-ray absorption is associated with a dense and extended hydrodynamical tail, trailing the neutron star. This structure extends along most of the orbit, indicating that the stellar wind has been strongly disrupted.
The remainder of the abstract is truncated. |
| Publication date: 01 Feb 2011 |
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