There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

WMAP precision data enable accurate testing of cosmological models. We find that the emerging standard model of cosmology, a flat � -dominated universe seeded by a nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP data. For the WMAP data only, the best-fit parameters are h ¼ 0:72 � 0:05, � bh 2 ¼ 0:024 � 0:001, � mh 2 ¼ 0:14 � 0:02, � ¼ 0:166 þ0:076 � 0:071 , ns ¼ 0:99 � 0:04, and � 8 ¼ 0:9 � 0:1. With parameters fixed only by WMAP data, we can fit finer scale cosmic microwave background (CMB) measure- ments and measurements of large-scale structure (galaxy surveys and the Lyforest). This simple model is also consistent with a host of other astronomical measurements: its inferred age of the universe is consistent with stellar ages, the baryon/photon ratio is consistent with measurements of the (D/H) ratio, and the inferred Hubble constant is consistent with local observations of the expansion rate. We then fit the model parameters to a combination of WMAP data with other finer scale CMB experiments (ACBAR and CBI), 2dFGRS measurements, and Lyforest data to find the model's best-fit cosmological parameters: h ¼ 0:71 þ0:04 � 0:03 , � bh 2 ¼ 0:0224 � 0:0009, � mh 2 ¼ 0:135 þ0:008 � 0:009 , � ¼ 0:17 � 0:06, ns(0.05 Mpc � 1 )=0 :93 � 0:03, and � 8 ¼ 0:84 � 0:04. WMAP's best determination of � ¼ 0:17 � 0:04 arises directly from the temperature- polarization (TE) data and not from this model fit, but they are consistent. These parameters imply that the age of the universe is 13:7 � 0:2 Gyr. With the Lyforest data, the model favors but does not require a slowly varying spectral index. The significance of this running index is sensitive to the uncertainties in the Ly� forest. By combining WMAP data with other astronomical data, we constrain the geometry of the universe, � tot ¼ 1:02 � 0:02, and the equation of state of the dark energy, w < � 0:78 (95% confidence limit assuming w �� 1). The combination of WMAP and 2dFGRS data constrains the energy density in stable neutrinos: � � h 2 < 0:0072 (95% confidence limit). For three degenerate neutrino species, this limit implies that their mass is less than 0.23 eV (95% confidence limit). The WMAP detection of early reionization rules out warm dark matter. Subject headings: cosmic microwave background — cosmological parameters — cosmology: observations — early universe On-line material: color figure

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First year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Determination of cosmological parameters

We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].

https://hal.archives-ouvertes.fr/hal-00012948/document

Stellar population synthesis at the resolution of 2003

This paper presents the first cosmological results based on Planck measurements of the cosmic microwave background (CMB) temperature and lensing-potential power spectra. We find that the Planck spectra at high multipoles (l ≳ 40) are extremely well described by the standard spatially-flat six-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations. Within the context of this cosmology, the Planck data determine the cosmological parameters to high precision: the angular size of the sound horizon at recombination, the physical densities of baryons and cold dark matter, and the scalar spectral index are estimated to be θ∗ = (1.04147 ± 0.00062) × 10-2, Ωbh2 = 0.02205 ± 0.00028, Ωch2 = 0.1199 ± 0.0027, and ns = 0.9603 ± 0.0073, respectively(note that in this abstract we quote 68% errors on measured parameters and 95% upper limits on other parameters). For this cosmology, we find a low value of the Hubble constant, H0 = (67.3 ± 1.2) km s-1 Mpc-1, and a high value of the matter density parameter, Ωm = 0.315 ± 0.017. These values are in tension with recent direct measurements of H0 and the magnitude-redshift relation for Type Ia supernovae, but are in excellent agreement with geometrical constraints from baryon acoustic oscillation (BAO) surveys. Including curvature, we find that the Universe is consistent with spatial flatness to percent level precision using Planck CMB data alone. We use high-resolution CMB data together with Planck to provide greater control on extragalactic foreground components in an investigation of extensions to the six-parameter ΛCDM model. We present selected results from a large grid of cosmological models, using a range of additional astrophysical data sets in addition to Planck and high-resolution CMB data. None of these models are favoured over the standard six-parameter ΛCDM cosmology. The deviation of the scalar spectral index from unity isinsensitive to the addition of tensor modes and to changes in the matter content of the Universe. We find an upper limit of r0.002< 0.11 on the tensor-to-scalar ratio. There is no evidence for additional neutrino-like relativistic particles beyond the three families of neutrinos in the standard model. Using BAO and CMB data, we find Neff = 3.30 ± 0.27 for the effective number of relativistic degrees of freedom, and an upper limit of 0.23 eV for the sum of neutrino masses. Our results are in excellent agreement with big bang nucleosynthesis and the standard value of Neff = 3.046. We find no evidence for dynamical dark energy; using BAO and CMB data, the dark energy equation of state parameter is constrained to be w = -1.13-0.10+0.13. We also use the Planck data to set limits on a possible variation of the fine-structure constant, dark matter annihilation and primordial magnetic fields. Despite the success of the six-parameter ΛCDM model in describing the Planck data at high multipoles, we note that this cosmology does not provide a good fit to the temperature power spectrum at low multipoles. The unusual shape of the spectrum in the multipole range 20 ≲ l ≲ 40 was seen previously in the WMAP data and is a real feature of the primordial CMB anisotropies. The poor fit to the spectrum at low multipoles is not of decisive significance, but is an “anomaly” in an otherwise self-consistent analysis of the Planck temperature data.

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Planck 2013 results. XVI. Cosmological parameters

Statistics for Spatial Data.

The null hypothesis that the three-dimensional power spectrum measured from the APM Survey is consistent with the one-dimensional power spectrum measured from the pencil-beams surveys of Broadhurst et al. and of Szalay et al. is tested. The external estimates of the mean power that we make are sensitive to details of the model for the survey geometry and to the assumed level of the distortion of the pattern of galaxy clustering caused by peculiar motions. We find that the measured 3D clustering of galaxies can account for the presence of peaks in the one­ dimensional power spectrum but is less successful in recovering the detailed appearance of the observations. We find no strong evidence for any additional large­ scale structure in the deep pencil beams beyond that recovered from the APM Survey. We conclude that it is unlikely that large-scale structure can be responsible for the steep local number counts of bright galaxies.

Large-scale fluctuations in the distribution of galaxies

We present the basic features and preliminary results of the interface between our spectro-photometric model GRASIL (that calculates galactic SED from the UV to the sub-mm with a detailed computation of dust extinction and thermal reemission) with the semi-analytical galaxy formation model GALFORM (that computes galaxy formation and evolution in the hierarchical scenario, providing the star formation history as an input to our model). With these two models we are able to synthetize simulated samples of a few thousands galaxies suited for statistical studies of galaxy properties to investigate on galaxy formation and evolution. We find good agreement with the available data of SED and luminosity functions.

Modeling Dust on Galactic SED: Application to Semi-Analytical Galaxy Formation Models

We propose a new filter, a smooth-$k$ space filter, to use in the Press-Schechter approach to model the dark matter halo mass function which overcomes shortcomings of other filters. We test this against the mass function measured in N-body simulations. We find that the commonly used sharp-$k$ filter fails to reproduce the behaviour of the halo mass function at low masses measured from simulations of models with a sharp truncation in the linear power spectrum. We show that the predictions with our new filter agree with the simulation results over a wider range of halo masses for both damped and undamped power spectra than is the case with the sharp-$k$ and real-space top-hat filters.

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A new smooth-$k$ space filter approach to calculate halo abundances

Advances in extragalactic astronomy have prompted the development of increasingly realistic models which aim to describe the formation and evolution of galaxies. We review the philosophy behind one such technique, called semi-analytic modelling, and explain the relation between this approach and direct simulations of gas dynamics. Finally, we present model predictions for the evolution of the stellar mass of galaxies in a universe in which structure formation is hierarchical.

The evolution of galaxy mass in hierarchical models

Advances in extragalactic astronomy have prompted the development of increasingly realistic models which aim to describe the formation and evolution of galaxies. We review the philosophy behind one such technique, called semi-analytic modelling, and explain the relation between this approach and direct simulations of gas dynamics. Finally, we present model predictions for the evolution of the stellar mass of galaxies in a universe in which structure formation is hierarchical. 1 Modelling the formation and evolution of galaxies An incredibly wide range of physical processes are believed to be influential in the formation of galaxies. Some of these processes are well understood, for example, the build up of dark matter haloes through mergers or the accretion of smaller units; the formation of haloes has been studied extensively using N-body simulations and can be described analytically with a reasonable degree of success (e.g. Lacey & Cole 1993, 1994). On the other hand, we are still some distance away from being able to simulate the formation of stars. An impressive initial step in this direction has been taken by Abel et al . (2002) with a simulation that leads up to the formation of the first star in the universe. However, the conditions in this calculation are much simpler than would be typical for the formation of the bulk of the stars in the universe and the simulation is stopped once additional physics not currently included in the calculation, such as radiative transfer, become important. The absence of a complete theory of star formation need not be an obstacle to the development of a theory of galaxy formation. One can take a phenomenological approach in which a physically motivated recipe is adopted to describe star formation within a galaxy. The recipe will inevitably contain one or more uncertain parameters but these can be fixed by comparing model predictions with observational data. Adopting this pragmatic approach, two techniques have been developed to model the formation and evolution of galaxies. The first of these is the direct simulation of gravitational instability and gas dynamics. The second class of technique is semi-analytic modelling (Kauffmann et al . 1993; Cole et al . 1994). In such models, the merger trees of dark matter haloes can either be grown using a Monte-Carlo algorithm or they can be extracted from an N-body simulation. The gas physics, namely shock heating, radiative cooling, star formation

Carlton M. Baugh

Papers

Large-scale fluctuations in the distribution of galaxies

Modeling Dust on Galactic SED: Application to Semi-Analytical Galaxy Formation Models

A new smooth-$k$ space filter approach to calculate halo abundances

The evolution of galaxy mass in hierarchical models

The evolution of galaxy mass in hierarchical models