Protoclusters at z=5.7: A view from the MultiDark galaxies

Protoclusters, which will yield galaxy clusters at lower redshift, can provide valuable information on the formation of galaxy clusters. However, identifying progenitors of galaxy clusters in observations is not an easy task, especially at high redshift. Different priors have been used to estimate the overdense regions that are thought to mark the locations of protoclusters. In this paper, we use mimicked Ly$\alpha$-emitting galaxies at $z=5.7$ to identify protoclusters in the MultiDark galaxies, which are populated by applying three different semi-analytic models to the 1 $Gpc h^{-1}$ MultiDark Planck2 simulation. To compare with observational results, we extend the criterion 1 (a Ly$\alpha$ luminosity limited sample), to criterion 2 (a match to the observed mean galaxy number density). To further statistically study the finding efficiency of this method, we enlarge the identified protocluster sample (criterion 3) to about 3500 at $z=5.7$ and study their final mass distribution. The number of overdense regions and their selection probability depends on the semi-analytic models and strongly on the three selection criteria (partly by design). The protoclusters identified with criterion 1 are associated with a typical final cluster mass of $2.82\pm0.92 \times 10^{15} M_\odot$ which is in agreement with the prediction (within $\pm 1 \sigma$) of an observed massive protocluster at $z=5.7$. Identifying more protoclusters allows us to investigate the efficiency of this method, which is more suitable for identifying the most massive clusters: completeness ($\mathbb{C}$) drops rapidly with decreasing halo mass. We further find that it is hard to have a high purity ($\mathbb{P}$) and completeness simultaneously.Comment: 10 pages, 4 figures, 2 tables, version matched to the publication in MNRA

The phase-diagram of cosmological baryons

We investigate the behaviour of cosmological baryons at low redshifts $z<5$ after reionization through analytic means. In particular, we study the density-temperature phase-diagram which describes the history of the gas. We show how the location of the matter in this $(\rho,T)$ diagram expresses the various constraints implied by usual hierarchical scenarios. This yields robust model-independent results which agree with numerical simulations. The IGM is seen to be formed via two phases: a ``cool'' photo-ionized component and a ``warm'' component governed by shock-heating. We also briefly describe how the remainder of the matter is distributed over galaxies, groups and clusters. We recover the fraction of matter and the spatial clustering computed by numerical simulations. We also check that the soft X-ray background due to the ``warm'' IGM component is consistent with observations. We find in the present universe a baryon fraction of 7% in hot gas, 24% in the warm IGM, 38% in the cool IGM, 9% within star-like objects and, as a still un-observed component, 22% of dark baryons associated with collapsed structures, with a relative uncertainty no larger than 30% on these numbers.Comment: 17 pages, accepted by A&A. This final version contains a more detailed discussion of the physics of the IGM and of the properties of the Warm IG

Mid-IR heterogeneous silicon photonics

In this paper we discuss silicon-based photonic integrated circuit technology for applications beyond the telecommunication wavelength range. Silicon-on-insulator and germanium-on-silicon passive waveguide circuits are described, as well as the integration of III-V semiconductors, IV-VI colloidal nanoparticle films and GeSn alloys on these circuits for increasing the functionality. The strong nonlinearity of silicon combined with the low nonlinear absorption in the mid-infrared is exploited to generate picosecond pulse based supercontinuum sources and optical parametric oscillators that can be used as spectroscopic sensor sources

HILT : High-Level Thesaurus Project M2M Feasibility Study : [Final Report]

The project was asked to investigate the feasibility of developing SOAP-based interfaces between JISC IE services and Wordmap APIs and non-Wordmap versions of the HILT pilot demonstrator created under HILT Phase II and to determine the scope and cost of the provision of an actual demonstrator based on each of these approaches. In doing so it was to take into account the possibility of a future Zthes1-based solution using Z39.50 or OAI-PMH and syntax and data-exchange protocol implications of eScience and semantic-web developments. It was agreed that the primary concerns of the study should be an assessment of the feasibility, scope, and cost of a follow-up M2M pilot that considered the best options in respect of: o Query protocols (SOAP, Z39.50, SRW, OAI) and associated data profiles (e.g. Zthes for Z39.50 and for SRW); o Standards for structuring thesauri and thesauri-type information (e.g. the Zthes XML DTD and SRW version of it and SKOS-Core2); The study was carried out within the allotted timescale, with this Final Report submitted to JISC on 31st March 2005 as scheduled. The detailed proposal for a follow-up project is currently under discussion and will be finalised – as agreed with JISC – by mid-April. It was concluded that an M2M pilot was feasible. A proposal for a follow-up M2M pilot project has been scoped, and is currently being costed

The three hundred project: The stellar and gas profiles

Using the catalogues of galaxy clusters from The Three Hundred project, modelled with both hydrodynamic simulations (GADGET-X and GADGET-MUSIC), and semi-analytical models (SAMs), we study the scatter and self-similarity of the profiles and distributions of the baryonic components of the clusters: the stellar and gas mass, metallicity, the stellar age, gas temperature, and the (specific) star formation rate. Through comparisons with observational results, we find that the shape and the scatter of the gas density profiles matches well the observed trends including the reduced scatter at large radii which is a signature of self-similarity suggested in previous studies. One of our simulated sets, GADGET-X, reproduces well the shape of the observed temperature profile, while GADGET-MUSIC has a higher and flatter profile in the cluster centre and a lower and steeper profile at large radii. The gas metallicity profiles from both simulation sets, despite following the observed trend, have a relatively lower normalization

Resolving the Cosmological Missing Energy Problem

Some form of missing energy may account for the difference between the observed cosmic matter density and the critical density. Two leading candidates are a cosmological constant and quintessence (a time-varying, inhomogenous component with negative pressure). We show that an ideal, full-sky cosmic background anisotropy experiment may not be able to distinguish the two, even when non-linear effects due to gravitational lensing are included. Due to this ambiguity, microwave background experiments alone may not determine the matter density or Hubble constant very precisely. We further show that degeneracy may remain even after considering classical cosmological tests and measurements of large scale structure.Comment: 6 pages, Latex, 4 postscript figures; revised analysis to include gravitational lensin

Quintessence with a constant equation of state in hyperbolic universes

Quintessence models leading to a constant equation of state are studied in hyperbolic universes. General properties of the quintessence potentials V(phi) are discussed, and for some special cases also the exact analytic expressions for these potentials are derived. It is shown that the observed angular power spectrum of the cosmic microwave background (CMB) is in excellent agreement with some of the quintessence models even in cases with negative curvature. It is emphasized that due to a (w_phi, Omega_phi, Omega_c)-degeneracy a universe with negative spatial curvature cannot be excluded.Comment: 15 pages, a version with figures in color can be obtained at http://www.physik.uni-ulm.de/theo/qc/ulm-tp/tp02-13.ps.g

Imprints of Dark Energy on Cosmic Structure Formation I) Realistic Quintessence Models and the Non-Linear Matter Power Spectrum

Dark energy as a quintessence component causes a typical modification of the background cosmic expansion, which in addition to its clustering properties, can leave a potentially distinctive signature on large scale structures. Many previous studies have investigated this topic, particularly in relation to the non-linear regime of structure formation. However, no careful pre-selection of viable quintessence models with high precision cosmological data was performed. Here we show that this has led to a misinterpretation (and underestimation) of the imprint of quintessence on the distribution of large scale structures. To this purpose we perform a likelihood analysis of the combined Supernova Ia UNION dataset and WMAP5-years data to identify realistic quintessence models. Differences from the vanilla LambdaCDM are especially manifest in the predicted amplitude and shape of the linear matter power spectrum, though these remain within the uncertainties of the SDSS data. We use these models as benchmark for studying the clustering properties of dark matter halos by performing a series of high resolution N-body simulations. We find that realistic quintessence models allow for relevant differences of the dark matter distribution with the respect to the LambdaCDM scenario well into the non-linear regime, with deviations up to 40% in the non-linear power spectrum. Such differences are shown to depend on the nature of DE, as well as the scale and epoch considered. At small scales (k~1-5 h Mpc^{-1}, depending on the redshift) the structure formation process is about 20% more efficient than in LambdaCDM. We show that these imprints are a specific record of the cosmic structure formation history in DE cosmologies and therefore cannot be accounted in standard fitting functions of the non-linear matter power spectrum.Comment: 24 pages, 11 figures. Higher resolution paper available at http://cp3.phys.ucl.ac.be/upload/papers/astro-ph-0903.5490.ps (ps) and http://cp3.phys.ucl.ac.be/upload/papers/astro-ph-0903.5490.pdf (pdf). v2: New discussion on the non-linear power spectrum at small scales. v3: same as v2 with corrected references. Matches version to appear in MNRA