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The Kilo-Degree Survey (KiDS) is an optical wide-field survey designed to map the matter distribution in the Universe using weak gravitational lensing. In this paper, we use these data to measure the density profiles and masses of a sample of $\sim \mathrm{1400}$ spectroscopically identified galaxy groups and clusters from the Galaxy And Mass Assembly (GAMA) survey. We detect a highly significant signal (signal-to-noise-ratio $\sim$ 120), allowing us to study the properties of dark matter haloes over one and a half order of magnitude in mass, from $M \sim 10^{13}-10^{14.5} h^{-1}\mathrm{M_{\odot}}$. We interpret the results for various subsamples of groups using a halo model framework which accounts for the mis-centring of the Brightest Cluster Galaxy (used as the tracer of the group centre) with respect to the centre of the group's dark matter halo. We find that the density profiles of the haloes are well described by an NFW profile with concentrations that agree with predictions from numerical simulations. In addition, we constrain scaling relations between the mass and a number of observable group properties. We find that the mass scales with the total r-band luminosity as a power-law with slope $1.16 \pm 0.13$ (1-sigma) and with the group velocity dispersion as a power-law with slope $1.89 \pm 0.27$ (1-sigma). Finally, we demonstrate the potential of weak lensing studies of groups to discriminate between models of baryonic feedback at group scales by comparing our results with the predictions from the Cosmo-OverWhelmingly Large Simulations (Cosmo-OWLS) project, ruling out models without AGN feedback., 23 pages, 17 figures, MNRAS accepted, cross-references to other KiDS/GAMA papers fixed in v2; Weak lensing catalogues are available at http://kids.strw.leidenuniv.nl

The alignments between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe. We provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience. The development of the field over the past one hundred years is briefly reviewed. We also discuss the impact of galaxy alignments on measurements of weak gravitational lensing, and discuss avenues for making theoretical and observational progress over the coming decade., Comment: 43 pages excl. references, 16 figures; minor changes to match version published in Space Science Reviews; part of a topical volume on galaxy alignments, with companion papers at arXiv:1504.05546 and arXiv:1504.05465

Masses of clusters of galaxies from weak gravitational lensing analyses of ever larger samples are increasingly used as the reference to which baryonic scaling relations are compared. In this paper we revisit the analysis of a sample of 50 clusters studied as part of the Canadian Cluster Comparison Project. We examine the key sources of systematic error in cluster masses. We quantify the robustness of our shape measurements and calibrate our algorithm empirically using extensive image simulations. The source redshift distribution is revised using the latest state-of-the-art photometric redshift catalogs that include new deep near-infrared observations. Nonetheless we find that the uncertainty in the determination of photometric redshifts is the largest source of systematic error for our mass estimates. We use our updated masses to determine b, the bias in the hydrostatic mass, for the clusters detected by Planck. Our results suggest 1-b=0.76+-0.05(stat)}+-0.06(syst)}, which does not resolve the tension with the measurements from the primary cosmic microwave background., resubmitted to MNRAS after review by referee

We present predictions for the galaxy-galaxy lensing (GGL) profile from the EAGLE hydrodynamical cosmological simulation at redshift z = 0.18, in the spatial range 0.02

We investigate possible signatures of halo assembly bias for spectroscopically selected galaxy groups from the GAMA survey using weak lensing measurements from the spatially overlapping regions of the deeper, high-imaging-quality photometric KiDS survey. We use GAMA groups with an apparent richness larger than 4 to identify samples with comparable mean host halo masses but with a different radial distribution of satellite galaxies, which is a proxy for the formation time of the haloes. We measure the weak lensing signal for groups with a steeper than average and with a shallower than average satellite distribution and find no sign of halo assembly bias, with the bias ratio of $0.85^{+0.37}_{-0.25}$, which is consistent with the $\Lambda$CDM prediction. Our galaxy groups have typical masses of $10^{13} M_{\odot}/h$, naturally complementing previous studies of halo assembly bias on galaxy cluster scales., Comment: 16 pages, 18 figures, accepted to MNRAS

We use cosmological hydrodynamical simulations to investigate how the inclusion of physical processes relevant to galaxy formation (star formation, metal-line cooling, stellar winds, supernovae and feedback from Active Galactic Nuclei, AGN) change the properties of haloes, over four orders of magnitude in mass. We find that gas expulsion and the associated dark matter (DM) expansion induced by supernova-driven winds are important for haloes with masses M200 < 10^13 Msun, lowering their masses by up to 20% relative to a DM-only model. AGN feedback, which is required to prevent overcooling, has a significant impact on halo masses all the way up to cluster scales (M200 ~ 10^15 Msun). Baryonic physics changes the total mass profiles of haloes out to several times the virial radius, a modification that cannot be captured by a change in the halo concentration. The decrease in the total halo mass causes a decrease in the halo mass function of about 20%. This effect can have important consequences for abundance matching technique as well as for most semi-analytic models of galaxy formation. We provide analytic fitting formulae, derived from simulations that reproduce the observed baryon fractions, to correct halo masses and mass functions from DM-only simulations. The effect of baryonic physics (AGN feedback in particular) on cluster number counts is about as large as changing the cosmology from WMAP7 to Planck, even when a moderately high mass limit of M500 ~ 10^14 Msun is adopted. Thus, for precision cosmology the effects of baryons must be accounted for., 21 pages, 15 figures. Accepted for publication in MNRAS after minor revisions

The clustering of galaxies and the matter distribution around them can be described using the halo model complemented with a realistic description of the way galaxies populate dark matter haloes. This has been used successfully to describe statistical properties of samples of galaxies at z, Comment: 15 pages, 8 figures, submitted to MNRAS

We present a new method that simultaneously solves for cosmology and galaxy bias on non-linear scales. The method uses the halo model to analytically describe the (non-linear) matter distribution, and the conditional luminosity function (CLF) to specify the halo occupation statistics. For a given choice of cosmological parameters, this model can be used to predict the galaxy luminosity function, as well as the two-point correlation functions of galaxies, and the galaxy-galaxy lensing signal, both as a function of scale and luminosity. These observables have been reliably measured from the Sloan Digital Sky Survey. In this paper, the first in a series, we present the detailed, analytical model, which we test against mock galaxy redshift surveys constructed from high-resolution numerical N-body simulations. We demonstrate that our model, which includes scale dependence of the halo bias and a proper treatment of halo exclusion, reproduces the three-dimensional galaxy-galaxy correlation and the galaxy-matter cross-correlation (which can be projected to predict the observables) with an accuracy better than 10 (in most cases 5) per cent. Ignoring either of these effects, as is often done, results in systematic errors that easily exceed 40 per cent on scales of similar to 1 h(-1) Mpc, where the data are typically most accurate. Finally, since the projected correlation functions of galaxies are never obtained by integrating the redshift-space correlation function along the line of sight out to infinity, simply because the data only cover a finite volume, they are still affected by residual redshift-space distortions (RRSDs). Ignoring these, as done in numerous studies in the past, results in systematic errors that easily exceed 20 per cent on large scales (r(p) greater than or similar to 10 h(-1) Mpc). We show that it is fairly straightforward to correct for these RRSDs, to an accuracy better than similar to 2 per cent, using a mildly modified version of the linear Kaiser formalism.

CH, MV, MC, HHo, CS and AC acknowledge support from the European Research Council under FP7 grant number 279396 (MV, MC, CS, HHo), grant number 240185 (AC and CH) and grant number G47112 (CH). MV acknowledges support from the Netherlands Organisation for Scientific Research (NWO) through grants 614.001.103. HHi is supported by an Emmy Noether grant (No. Hi 1495/2-1) of the Deutsche Forschungsgemeinschaft. RN acknowledges support from the German Federal Ministry for Economic Affairs and Energy (BMWi) provided via DLR under project no. 50QE1103. TM-R and PN acknowledge support from an European Research Council Starting Grant (DEGAS-259586). This work is supported by the Deutsche Forschungsgemeinschaft in the framework of the TR33 ‘The Dark Universe’. GVK acknowledges financial support from the Netherlands Research School for Astronomy (NOVA) and Target. Target is supported by Samenwerkingsverband Noord Nederland, European fund for regional development, Dutch Ministry of economic affairs, Pieken in de Delta, Provinces of Groningen and Drenthe. EvU acknowledges support from an STFC Ernest Rutherford Research Grant, grant reference ST/L00285X/1. Galaxies and their dark matter haloes are part of a complex network of mass structures, collectively called the cosmic web. Using the tidal tensor prescription these structures can be classified into four cosmic environments: voids, sheets, filaments and knots. As the cosmic web may influence the formation and evolution of dark matter haloes and the galaxies they host, we aim to study the effect of these cosmic environments on the average mass of galactic haloes. To this end we measure the galaxy-galaxy lensing profile of 91 195 galaxies, within 0.039 < z

We formulate the concept of non-linear and stochastic galaxy biasing in the framework of halo occupation statistics. Using two-point statistics in projection, we define the galaxy bias function, b_g(r_p), and the galaxy-dark matter cross-correlation function, R_{gm}(r_p), where r_p is the projected distance. We use the analytical halo model to predict how the scale dependence of b_g and R_{gm}, over the range 0.1 Mpc/h 1 - 5 Mpc/h, depending on luminosity. However, galaxy bias is scale-dependent out to much larger radii when one uses the projected quantities defined in this paper. These projected bias functions have the advantage that they are more easily accessible observationally and that their scale dependence carries a wealth of information regarding the properties of galaxy biasing. To observationally constrain the parameters of the halo occupation statistics and to unveil the origin of galaxy biasing we propose the use of the bias function Gamma_{gm}(r_p)=b_g(r_p)/R_{gm}(r_p). This function is obtained via a combination of weak gravitational lensing and galaxy clustering, and it can be measured using existing and forthcoming imaging and spectroscopic galaxy surveys.

We analyse the evolution of turbulence and gravitational instability of a galactic disc in a quasi-steady state governed by cosmological inflow. We focus on the possibility that the coupling between the in-streaming gas and the disc is maximal, e.g., via dense clumps, and ask whether the streams could be the driver of turbulence in an unstable disc with a Toomre parameter Q~1. Our fiducial model assumes an efficiency of ~0.5 per dynamical time for the decay of turbulence energy, and ~0.02 for each of the processes that deplete the disc gas, i.e., star formation, outflow, and inflow within the disc into a central bulge. In this case, the in-streaming drives a ratio of turbulent to rotation velocity sigma/V~0.2-0.3, which at z~2 induces an instability with Q~1, both as observed. However, in conflict with observations, this model predicts that sigma/V remains constant with time, independent of the cosmological accretion rate, because mass and turbulence have the same external source. Such strongly coupled cosmological inflow tends to stabilize the disc at low z, with Q ~ a few, which may be consistent with observations. The instability could instead be maintained for longer, with a properly declining sigma/V, if it is self-regulated to oscillations about Q~1 by a duty cycle for disc depletion. However, the 'off' phases of this duty cycle become long at low z, which may be hard to reconcile with observations. Alternatively, the coupling between the in-streaming gas and the disc may weaken in time, reflecting an evolving nature of the accretion. If, instead, that coupling is weak at all times, the likely energy source for self-regulated stirring up of the turbulence is the inflow within the disc down the potential gradient (studied in a companion paper).

We use the kinematics of satellite galaxies that orbit around the central galaxy in a dark matter halo to infer the scaling relations between halo mass and central galaxy properties. Using galaxies from the Sloan Digital Sky Survey, we investigate the halo mass-luminosity relation (MLR) and the halo mass-stellar mass relation (MSR) of central galaxies. In particular, we focus on the dependence of these scaling relations on the colour of the central galaxy. We find that red central galaxies on average occupy more massive haloes than blue central galaxies of the same luminosity. However, at fixed stellar mass there is no appreciable difference in the average halo mass of red and blue centrals, especially for M* $\lsim$ 10^{10.5} h^{-2} Msun. This indicates that stellar mass is a better indicator of halo mass than luminosity. Nevertheless, we find that the scatter in halo masses at fixed stellar mass is non-negligible for both red and blue centrals. It increases as a function of stellar mass for red centrals but shows a fairly constant behaviour for blue centrals. We compare the scaling relations obtained in this paper with results from other independent studies of satellite kinematics, with results from a SDSS galaxy group catalog, from galaxy-galaxy weak lensing measurements, and from subhalo abundance matching studies. Overall, these different techniques yield MLRs and MSRs in fairly good agreement with each other (typically within a factor of two), indicating that we are converging on an accurate and reliable description of the galaxy-dark matter connection. We briefly discuss some of the remaining discrepancies among the various methods.

Accurate knowledge of the non-linear dark-matter power spectrum is important for understanding the large-scale structure of the Universe, the statistics of dark-matter haloes and their evolution, and cosmological gravitational lensing. We analytically model the dark-matter power spectrum and its cross-power spectrum with dark-matter haloes. Our model extends the halo-model formalism, including realistic substructure population within individual dark-matter haloes and the scatter of the concentration parameter at fixed halo mass. We consider three prescriptions for the mass-concentration relation and two for the substructure distribution in dark-matter haloes. We show that this extension of the halo model mainly increases the predicted power on the small scales, and is crucial for proper modeling the cosmological weak-lensing signal due to low-mass haloes. Our extended formalism shows how the halo model approach can be improved in accuracy as one increases the number of ingredients that are calibrated from n-body simulations.

We use galaxy groups selected from the Sloan Digital Sky Survey (SDSS) together with mass models for individual groups to study the galaxy-galaxy lensing signals expected from galaxies of different luminosities and morphological types. We compare our model predictions with the observational results obtained from the SDSS by Mandelbaum et al. (2006) for the same samples of galaxies. The observational results are well reproduced in a $\Lambda$CDM model based on the WMAP 3-year data, but a $\Lambda$CDM model with higher $\sigma_8$, such as the one based on the WMAP 1-year data,significantly over-predicts the galaxy-galaxy lensing signal. We model, separately, the contributions to the galaxy-galaxy lensing signals from different galaxies: central versus satellite, early-type versus late-type, and galaxies in halos of different masses. We also examine how the predicted galaxy-galaxy lensing signal depends on the shape, density profile, and the location of the central galaxy with respect to its host halo.

Galaxy clustering and galaxy-galaxy lensing probe the connection between galaxies and their dark matter haloes in complementary ways. On one hand, the halo occupation statistics inferred from the observed clustering properties of galaxies are degenerate with the adopted cosmology. Consequently, different cosmologies imply different mass-to-light ratios for dark matter haloes. On the other hand, galaxy-galaxy lensing yields direct constraints on the actual mass-to-light ratios and it can be used to break this degeneracy, and thus to constrain cosmological parameters. In this paper we establish the link between galaxy luminosity and dark matter halo mass using the conditional luminosity function (CLF). We constrain the CLF parameters using the galaxy luminosity function and the luminosity dependence of the correlation lengths of galaxies. The resulting CLF models are used to predict the galaxy-galaxy lensing signal. For a cosmology with $(\Omega_{\rm m},\sigma_8)=(0.238,0.734)$, the model accurately fits the galaxy-galaxy lensing data obtained from the SDSS. For a comparison cosmology with $(\Omega_{\rm m},\sigma_8)=(0.3,0.9)$, however, we can accurately fit the luminosity function and clustering properties of the galaxy population, but the model predicts mass-to-light ratios that are too high, resulting in a strong overprediction of the galaxy-galaxy lensing signal. We conclude that the combination of galaxy clustering and galaxy-galaxy lensing is a powerful probe of the galaxy-dark matter connection, with the potential to yield tight constraints on cosmological parameters. Since this method mainly probes the mass distribution on non-linear scales, it is complementary to constraints obtained from the galaxy power-spectrum, which mainly probes the large-scale (linear) matter distribution., Comment: 20 pages, 11 figures, submitted to MNRAS

Satellite kinematics can be used to probe the masses of dark matter haloes of central galaxies. In order to measure the kinematics with sufficient signal-to-noise, one uses the satellite galaxies of a large number of central galaxies stacked according to similar properties (e.g., luminosity). However, in general the relation between the luminosity of a central galaxy and the mass of its host halo will have non-zero scatter. Consequently, this stacking results in combining the kinematics of satellite galaxies in haloes of different masses, which complicates the interpretation of the data. In this paper we present an analytical framework to model satellite kinematics, properly accounting for this scatter and for various selection effects. We show that in the presence of scatter in the halo mass-luminosity relation, the commonly used velocity dispersion of satellite galaxies can not be used to infer a unique halo mass-luminosity relation. In particular, we demonstrate that there is a degeneracy between the mean and the scatter of the halo mass-luminosity relation. We present a new technique that can break this degeneracy, and which involves measuring the velocity dispersions using two different weighting schemes: host-weighting (each central galaxy gets the same weight) and satellite-weighting (each central galaxy gets a weight proportional to its number of satellites). The ratio between the velocity dispersions obtained using these two weighting schemes is a strong function of the scatter in the halo mass-luminosity relation, and can thus be used to infer a unique relation between light and mass from the kinematics of satellite galaxies., 8 pages, 3 figures, MNRAS submitted

We study the stellar-to-halo mass relation of central galaxies in the range 9.7 < log 10(M*/h- 2 M☉) < 11.7 and z < 0.4, obtained from a combined analysis of the Kilo Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. We use ∼100 deg2 of KiDS data to study the lensing signal around galaxies for which spectroscopic redshifts and stellar masses were determined by GAMA. We show that lensing alone results in poor constraints on the stellar-to-halo mass relation due to a degeneracy between the satellite fraction and the halo mass, which is lifted when we simultaneously fit the stellar mass function. At M* > 5 × 1010 h- 2 M☉, the stellar mass increases with halo mass as {∼ }M_h^{0.25}. The ratio of dark matter to stellar mass has a minimum at a halo mass of 8 × 1011 h-1 M☉ with a value of M_h/M_{*}=56_{-10}^{+16} [h]. We also use the GAMA group catalogue to select centrals and satellites in groups with five or more members, which trace regions in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. We find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, we find that the stellar-to-halo mass relation of central galaxies can also be obtained by modelling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-to-halo mass relation. Finally, we show that the combination of weak lensing with the stellar mass function can be used to test the purity of group catalogues.

The shapes of galaxies are not randomly oriented on the sky. During the galaxy formation and evolution process, environment has a strong influence, as tidal gravitational fields in the large-scale structure tend to align nearby galaxies. Additionally, events such as galaxy mergers affect the relative alignments of both the shapes and angular momenta of galaxies throughout their history. These "intrinsic galaxy alignments" are known to exist, but are still poorly understood. This review will offer a pedagogical introduction to the current theories that describe intrinsic galaxy alignments, including the apparent difference in intrinsic alignment between early- and late-type galaxies and the latest efforts to model them analytically. It will then describe the ongoing efforts to simulate intrinsic alignments using both N-body and hydrodynamic simulations. Due to the relative youth of this field, there is still much to be done to understand intrinsic galaxy alignments and this review summarises the current state of the field, providing a solid basis for future work., 53 pages excl references, 17 figures; changes to match version published in Space Science Reviews; part of a topical volume on galaxy alignments, with companion papers arXiv:1504.05456 and arXiv:1504.05465

We report the alignment and shape of dark matter, stellar, and hot gas distributions in the EAGLE and cosmo-OWLS simulations. The combination of these state-of-the-art hydro-cosmological simulations enables us to span four orders of magnitude in halo mass ($11 < log_{10}(M_{200}/ [h^{-1}M_\odot]) < 15$), a wide radial range ($-2.3 < log_{10}(r/[h^{-1}Mpc ]) < 1.3$) and redshifts $0 < z < 1$. The shape parameters of the dark matter, stellar and hot gas distributions follow qualitatively similar trends: they become more aspherical (and triaxial) with increasing halo mass, radius and redshift. We measure the misalignment of the baryonic components (hot gas and stars) of galaxies with their host halo as a function of halo mass, radius, redshift, and galaxy type (centrals vs satellites and early- vs late-type). Overall, galaxies align well with the local distribution of the total (mostly dark) matter. However, the stellar distributions on galactic scales exhibit a median misalignment of about 45-50 degrees with respect to their host haloes. This misalignment is reduced to 25-30 degrees in the most massive haloes ($13 < log_{10}(M_{200}/ [h^{-1}M_\odot ]) < 15$). Half of the disc galaxies in the EAGLE simulations have a misalignment angle with respect to their host haloes larger than 40 degrees. We present fitting functions and tabulated values for the probability distribution of galaxy-halo misalignment to enable a straightforward inclusion of our results into models of galaxy formations based on purely collisionless N-body simulations., 19 pages, 16 figures. Accepted for publication in MNRAS. New figure added, e_rms values corrected, no changes to the conclusions

Accurate knowledge of the non-linear dark matter power spectrum is important for understanding the large-scale structure of the Universe, the statistics of dark matter haloes and their evolution, and cosmological gravitational lensing. We analytically model the dark matter power spectrum and its cross-power spectrum with dark matter haloes. Our model extends the halo model formalism, including realistic substructure population within individual dark matter haloes and the scatter of the concentration parameter at fixed halo mass. We consider three prescriptions for the mass-concentration relation and two for the substructure distribution in dark matter haloes. We show that this extension of the halo model mainly increases the predicted power on the small scales and is crucial for properly modelling the cosmological weak-lensing signal due to low-mass haloes. Our extended formalism shows how the halo model approach can be improved in accuracy as one increases the number of ingredients that are calibrated from N-body simulations.

Galaxy shapes are not randomly oriented, rather they are statistically aligned in a way that can depend on formation environment, history and galaxy type. Studying the alignment of galaxies can therefore deliver important information about the physics of galaxy formation and evolution as well as the growth of structure in the Universe. In this review paper we summarise key measurements of galaxy alignments, divided by galaxy type, scale and environment. We also cover the statistics and formalism necessary to understand the observations in the literature. With the emergence of weak gravitational lensing as a precision probe of cosmology, galaxy alignments have taken on an added importance because they can mimic cosmic shear, the effect of gravitational lensing by large-scale structure on observed galaxy shapes. This makes galaxy alignments, commonly referred to as intrinsic alignments, an important systematic effect in weak lensing studies. We quantify the impact of intrinsic alignments on cosmic shear surveys and finish by reviewing practical mitigation techniques which attempt to remove contamination by intrinsic alignments., 52 pages excl. references, 16 figures; minor changes to match version published in Space Science Reviews; part of a topical volume on galaxy alignments, with companion papers arXiv:1504.05456 and arXiv:1504.05546

We report results for the alignments of galaxies in the EAGLE and cosmo-OWLS simulations as a function of galaxy separation and halo mass. The combination of these hydro-cosmological simulations enables us to span four orders of magnitude in halo mass ($10.7, Comment: 13 pages, 12 figures. Accepted for publication in MNRAS

We use the first 100 sq. deg. of overlap between the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey to determine the galaxy halo mass of ~10,000 spectroscopically-confirmed satellite galaxies in massive ($M > 10^{13}h^{-1}{\rm M}_\odot$) galaxy groups. Separating the sample as a function of projected distance to the group centre, we jointly model the satellites and their host groups with Navarro-Frenk-White (NFW) density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses $\log M_{\rm sub} /(h^{-1}{\rm M}_\odot) \approx 11.7 - 12.2$ consistent across group-centric distance within the errorbars. Given their typical stellar masses, $\log M_{\rm \star,sat}/(h^{-2}{\rm M}_\odot) \sim 10.5$, such total masses imply stellar mass fractions of $M_{\rm \star,sat} /M_{\rm sub} \approx 0.04 h^{-1}$ . The average subhalo hosting these satellite galaxies has a mass $M_{\rm sub} \sim 0.015M_{\rm host}$ independent of host halo mass, in broad agreement with the expectations of structure formation in a $\Lambda$CDM universe., Comment: Accepted for publication in MNRAS. 14 pages; 9 figures, 2 tables. New subsection discussing sensitivity to contamination added during the refereeing process

Torques acting on galaxies lead to physical alignments, but the resulting ellipticity correlations are difficult to predict. As they constitute a major contaminant for cosmic shear studies, it is important to constrain the intrinsic alignment signal observationally. We measured the alignments of satellite galaxies within 90 massive galaxy clusters in the redshift range 0.05, Comment: 18 pages, 13 figures and 4 tables; accepted for publication in A&A

We describe simple useful toy models for key processes of galaxy formation in its most active phase, at z > 1, and test the approximate expressions against the typical behaviour in a suite of high-resolution hydro-cosmological simulations of massive galaxies at z = 4-1. We address in particular the evolution of (a) the total mass inflow rate from the cosmic web into galactic haloes based on the EPS approximation, (b) the penetration of baryonic streams into the inner galaxy, (c) the disc size, (d) the implied steady-state gas content and star-formation rate (SFR) in the galaxy subject to mass conservation and a universal star-formation law, (e) the inflow rate within the disc to a central bulge and black hole as derived using energy conservation and self-regulated Q ~ 1 violent disc instability (VDI), and (f) the implied steady state in the disc and bulge. The toy models provide useful approximations for the behaviour of the simulated galaxies. We find that (a) the inflow rate is proportional to mass and to (1+z)^5/2, (b) the penetration to the inner halo is ~50% at z = 4-2, (c) the disc radius is ~5% of the virial radius, (d) the galaxies reach a steady state with the SFR following the accretion rate into the galaxy, (e) there is an intense gas inflow through the disc, comparable to the SFR, following the predictions of VDI, and (f) the galaxies approach a steady state with the bulge mass comparable to the disc mass, where the draining of gas by SFR, outflows and disc inflows is replenished by fresh accretion. Given the agreement with simulations, these toy models are useful for understanding the complex phenomena in simple terms and for back-of-the-envelope predictions., Resubmitted to MNRAS after responding to referee's comments; Revised figures

We present a method that uses observations of galaxies to simultaneously constrain cosmological parameters and the galaxy-dark matter connection (aka halo occupation statistics). The latter describes how galaxies are distributed over dark matter haloes, and is an imprint of the poorly understood physics of galaxy formation. A generic problem of using galaxies to constrain cosmology is that galaxies are a biased tracer of the mass distribution, and this bias is generally unknown. The great advantage of simultaneously constraining cosmology and halo occupation statistics is that this effectively allows cosmological constraints marginalized over the uncertainties regarding galaxy bias. Not only that, it also yields constraints on the galaxy-dark matter connection, this time properly marginalized over cosmology, which is of great value to inform theoretical models of galaxy formation. We use a combination of the analytical halo model and the conditional luminosity function to describe the galaxy-dark matter connection, which we use to model the abundance, clustering and galaxy-galaxy lensing properties of the galaxy population. We use a Fisher matrix analysis to gauge the complementarity of these different observables, and present some preliminary results from an analysis based on data from the Sloan Digital Sky Survey. Our results are complementary to and perfectly consistent with the results from the 7 year data release of the WMAP mission, strengthening the case for a true 'concordance' cosmology., 8 Pages, 2 figures, A shorter version will be submitted to the proceedings of the International Conference on Gravitation and Cosmology, Goa

We simultaneously constrain cosmology and galaxy bias using measurements of galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the Sloan Digital Sky Survey. We use the conditional luminosity function (which describes the halo occupation statistics as function of galaxy luminosity) combined with the halo model (which describes the non-linear matter field in terms of its halo building blocks) to describe the galaxy-dark matter connection. We explicitly account for residual redshift space distortions in the projected galaxy-galaxy correlation functions, and marginalize over uncertainties in the scale dependence of the halo bias and the detailed structure of dark matter haloes. Under the assumption of a spatially flat, vanilla {\Lambda}CDM cosmology, we focus on constraining the matter density, {\Omega}m, and the normalization of the matter power spectrum, {\sigma}8, and we adopt WMAP7 priors for the spectral index, the Hubble parameter, and the baryon density. We obtain that \Omegam = 0.278_{-0.026}^{+0.023} and {\sigma}8 = 0.763_{-0.049}^{+0.064} (95% CL). These results are robust to uncertainties in the radial number density distribution of satellite galaxies, while allowing for non-Poisson satellite occupation distributions results in a slightly lower value for {\sigma}8 (0.744_{-0.047}^{+0.056}). These constraints are in excellent agreement (at the 1{\sigma} level) with the cosmic microwave background constraints from WMAP. This demonstrates that the use of a realistic and accurate model for galaxy bias, down to the smallest non-linear scales currently observed in galaxy surveys, leads to results perfectly consistent with the vanilla {\Lambda}CDM cosmology., Comment: 21 pages, 9 figures, 5 tables, submitted to MNRAS

We address the cosmological evolution of violent gravitational instability in high-redshift, massive, star-forming galactic discs. To this aim, we integrate in time the equations of mass and energy conservation under self-regulated instability of a two-component disc of gas and stars. The disc is assumed to be continuously fed by cold gas at the average cosmological rate. The gas forms stars and is partly driven away by stellar feedback. The gas and stars flow inward through the disc to a central bulge due to torques that drive angular momentum outwards. The gravitational energy released by the mass inflow down the gravitational potential gradient drives the disc turbulence that maintains the disc unstable with a Toomre instability parameter Q~1, compensating for the dissipative losses of the gas turbulence and raising the stellar velocity dispersion. We follow the velocity dispersion of stars and gas as they heat and cool respectively and search for disc `stabilization', to be marked by a low gas velocity dispersion comparable to the speed of sound ~10 km/s. We vary the model parameters that characterize the accreted gas fraction, turbulence dissipation rate, star-formation rate, and stellar feedback. We find that as long as the gas input roughly follows the average cosmological rate, the disc instability is a robust phenomenon at high redshift till z~1, driven by the high surface density and high gas fraction due to the intense cosmological accretion. For a broad range of model parameter values, the discs tend to `stabilize' at z~0-0.5 as they become dominated by hot stars. When the model parameters are pushed to extreme values, the discs may stabilize as early as z~2, with the gas loss by strong outflows serving as the dominant stabilizing factor.

International audience; Disk galaxies at high redshift have been predicted to maintain high gas surface densities due to continuous feeding by intense cold streams leading to violent gravitational instability, transient features, and giant clumps. Gravitational torques between the perturbations drive angular momentum out and mass in, and the inflow provides the energy for keeping strong turbulence. We use analytic estimates of the inflow for a self-regulated unstable disk at a Toomre stability parameter Q ~ 1, and isolated galaxy simulations capable of resolving the nuclear inflow down to the central parsec. We predict an average inflow rate ~10 M ☉ yr-1 through the disk of a 1011 M ☉ galaxy, with conditions representative of z ~ 2 stream-fed disks. The inflow rate scales with disk mass and (1 + z)3/2. It includes clump migration and inflow of the smoother component, valid even if clumps disrupt. This inflow grows the bulge, while only a fraction of gsim 10-3 of it needs to accrete onto a central black hole (BH), in order to obey the observed BH-bulge relation. A galaxy of 1011 M ☉ at z ~ 2 is expected to host a BH of ~108 M ☉, accreting on average with moderate sub-Eddington luminosity L X ~ 1042-1043 erg s-1, accompanied by brighter episodes when dense clumps coalesce. We note that in rare massive galaxies at z ~ 6, the same process may feed ~109 M ☉ BH at the Eddington rate. High central gas column densities can severely obscure active galactic nuclei in high-redshift disks, possibly hindering their detection in deep X-ray surveys.

The kinematics of satellite galaxies reflect the masses of the extended dark matter haloes in which they orbit, and thus shed light on the mass-luminosity relation (MLR) of their corresponding central galaxies. In this paper we select a large sample of centrals and satellites from the Sloan Digital Sky Survey (SDSS) and measure the kinematics (velocity dispersions) of the satellite galaxies as a function of the $r$-band luminosity of the central galaxies. Using the analytical framework presented in Paper I, we use these data to infer {\it both} the mean and the scatter of the MLR of central galaxies, carefully taking account of selection effects and biases introduced by the stacking procedure. As expected, brighter centrals on average reside in more massive haloes. In addition, we find that the scatter in halo masses for centrals of a given luminosity, $\sigma_{\log M}$, also increases with increasing luminosity. As we demonstrate, this is consistent with $\sigma_{\log L}$, which reflects the scatter in the conditional probability function $P(L_c|M)$, being independent of halo mass. Our analysis of the satellite kinematics yields $\sigma_{\log L}=0.16\pm0.04$, in excellent agreement with constraints from clustering and group catalogues, and with predictions from a semi-analytical model of galaxy formation. We thus conclude that the amount of stochasticity in galaxy formation, which is characterized by $\sigma_{\log L}$, is well constrained, is independent of halo mass, and is in good agreement with current models of galaxy formation., Comment: 17 pages, 12 figures, MNRAS submitted

Reference EPFL-ARTICLE-216742doi:10.1007/s11214-015-0222-3Afficher la publication dans Web of Science Notice creee le 2016-02-16, modifiee le 2017-12-03

We study the evolution of the luminosity-to-halo mass relation of luminous red galaxies (LRGs). We selected a sample of 52 000 LOWZ and CMASS LRGs from the Baryon Oscillation Spectroscopic Survey (BOSS) SDSS-DR10 in the ∼450 deg2 that overlaps with imaging data from the second Red-sequence Cluster Survey (RCS2), grouped them into bins of absolute magnitude and redshift and measured their weak-lensing signals. The source redshift distribution has a median of 0.7, which allowed us to study the lensing signal as a function of lens redshift. We interpreted the lensing signal using a halo model, from which we obtained the halo masses as well as the normalisations of the mass-concentration relations. The concentration of haloes that host LRGs is consistent with dark-matter-only simulations once we allow for miscentering or satellites in the modelling. The slope of the luminosity-to-halo mass relation has a typical value of 1.4 and does not change with redshift, but we find evidence for a change in amplitude: the average halo mass of LOWZ galaxies increases by 25+16 −14% between z = 0.36 and 0.22 to an average value of (6.43 ± 0.52) × 1013 h−1 70 M . If we extend the redshift range using the CMASS galaxies and assume that they are the progenitors of the LOWZ sample, the average mass of LRGs increases by 80+39 −28% between z = 0.6 and 0.2.

We use the conditional luminosity function (CLF) and data from the 2dFGRS to constrain the average relation between light and mass in a LCDM cosmology with Omega_m=0.23 and sigma_8=0.74 (hereafter WMAP3 cosmology). Reproducing the observed luminosity dependence of the galaxy two-point correlation function results in average mass-to-light ratios that are about 35 percent lower than in a LCDM cosmology with Omega_m=0.3 and sigma_8=0.9 (hereafter WMAP1 cosmology). This removes an important problem with previous halo occupation models which had a tendency to predict cluster mass-to-light ratios that were too high. For the WMAP3 cosmology our model yields average mass-to-light ratios, central galaxy luminosities, halo occupation numbers, satellite fractions, and luminosity-gap statistics, that are all in excellent agreement with those obtained from a 2dFGRS group catalogue and from other independent studies. We also use our CLF model to compute the probability distribution P(M|L_cen), that a central galaxy of luminosity L_cen resides in a halo of mass M. We find this distribution to be much broader than what is typically assumed in HOD models, which has important implications for the interpretation of galaxy-galaxy lensing data. Finally, reproducing the luminosity dependence of the pairwise velocity dispersions in the 2dFGRS requires relatively low mass-to-light ratios for clusters and a satellite fraction that decreases strongly with increasing luminosity. This is only marginally consistent with our CLF constraints. We argue that a cosmology with parameters between those of the WMAP1 and WMAP3 cosmologies is likely to yield results with a higher level of consistency., 23 pages, 11 figures. Submitted for publication in MNRAS