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We investigate the clustering of Lyman-break galaxies (LBGs) at z ~ 4. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within 3s with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field, central LBGs at z ~ 4 predominantly reside in haloes of mass ~1011-1012 h-1 M⊙ and that satellites reside in larger haloes of mass ~1012-1013 h-1 M⊙. The model predicts fewer bright satellite LBGs at z ~ 4 than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs, this uncertainty must be considered. [ABSTRACT FROM AUTHOR]

Redshifted 21-cm measurements of the structure of ionized regions that grow during reionization promise to provide a new probe of early galaxy and structure formation. One of the challenges of modelling reionization is to account both for the subhalo scale physics of galaxy formation and the regions of ionization on scales that are many orders of magnitude larger. To bridge this gap we first calculate the statistical relationship between ionizing luminosity and Mpc-scale overdensity using detailed models of galaxy formation computed using relatively small volume - (~100 Mpc h-1)3, high-resolution dark matter simulations. We then use a Monte Carlo technique to apply this relationship to reionization of the intergalactic medium within large volume dark matter simulations - (>1 Gpc h-1)3. The resulting simulations can be used to address the contribution of very large scale clustering of galaxies to the structure of reionization, and show that volumes larger than 500 Mpc h-1 are required to probe the largest reionization features mid-way through reionization. As an example application of our technique, we demonstrate that the predicted 21-cm power spectrum amplitude and gradient could be used to determine the importance of supernovae feedback for early galaxy formation. [ABSTRACT FROM AUTHOR]

Using galform, a semi-analytical model of galaxy formation in the Λ cold dark matter cosmology, we study the rest-frame ultraviolet (UV) colours of Lyman-break galaxies (LBGs) in the redshift range 2.5 ≤ z ≤ 10. As the impact of dust on UV luminosity can be dramatic, our model includes a self-consistent computation of dust attenuation based on a radiative transfer model. We find that intrinsically brighter galaxies suffer stronger dust attenuation than fainter ones, though the relation has a large scatter. The model predicts galaxies with UV colours consistent with the colour selection regions designed to select LBGs in observational surveys. We find that the drop-out technique that selects LBGs based on two rest-frame UV colours is robust and effective, selecting more than 70 per cent of UV bright galaxies at a given redshift. We investigate the impact on the predicted UV colours of varying selected model parameters. We find that the UV colours are most sensitive to the modelling of dust attenuation and, in particular, to the extinction curve used in the radiative transfer calculation. If we assume a Milky Way dust extinction curve, the predicted UV continuum slopes are, in general, bluer than observed. However, we find that the opposite is true when using the Small Magellanic Cloud dust extinction curve. This demonstrates the strong dependence of UV colours on dust properties and highlights the inadequacy of using the UV continuum slope as a tracer of dust attenuation without any further knowledge of the galaxy inclination or dust characteristics in high-redshift galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We predict the formation histories, properties and descendants of Lyman-break galaxies (LBGs) in the Λ cold dark matter cosmology. In our model, which incorporates a top-heavy initial mass function in starbursts, we find that most LBGs are starbursts triggered by minor mergers of galaxies. The duration of the LBG phase is predicted to be quite short, ∼ 20-60 Myr. We investigate the distributions of stellar and halo masses and morphologies for bright () and faint () LBGs at z= 3, 6 and 10 [where we classify LBGs according to their rest-frame ultraviolet (UV) luminosities relative the observed characteristic luminosity at z≈ 3]. Bright LBGs at z= 3 are predicted to have median stellar masses ∼ 1 × 109 h−1 M⊙ and host halo masses ∼ 3 × 1011 h−1 M⊙, and be typically mildly disc dominated in stellar mass. On the other hand, faint LBGs at z= 10 are predicted to have median stellar masses of only ∼ 1 × 107 h−1 M⊙ and host halo masses ∼ 2 × 1010 h−1 M⊙, and be generally bulge dominated. Bright LBGs at z= 3 evolve to present-day galaxies with median stellar mass ∼ 5 × 1010 h−1 M⊙ (comparable to the Milky Way), consisting of roughly equal numbers of disc- and bulge-dominated systems, and hosted by haloes with median mass ∼ 2 × 1013 h−1 M⊙ (corresponding to medium-size galaxy groups). The model predicts that 40 per cent of Milky Way mass galaxies at the present day have a bright LBG progenitor in the redshift range 3 < z < 4, while 95 per cent have a faint LBG progenitor in the same redshift range and 7 per cent have a faint LBG progenitor at 10 < z < 11. With our multiwavelength model, we also investigate the overlap between the LBG population and that of selected submillimetre galaxies (SMGs); at z= 3, only ∼ 1 per cent of bright LBGs are also predicted to be bright SMGs (with an m flux in excess of 5 mJy). [ABSTRACT FROM AUTHOR]

Future galaxy surveys will map the galaxy distribution in the redshift interval using near-infrared cameras and spectrographs. The primary scientific goal of such surveys is to constrain the nature of the dark energy by measuring the large-scale structure of the Universe. This requires a tracer of the underlying dark matter which maximizes the useful volume of the survey. We investigate two potential survey selection methods: an emission-line sample based on the line and a sample selected in the H band. We present predictions for the abundance and clustering of such galaxies, using two published versions of thegalform galaxy formation model. Our models predict that selected galaxies tend to avoid massive dark matter haloes and instead trace the surrounding filamentary structure; H-band selected galaxies, on the other hand, are found in the highest mass haloes. This has implications for the measurement of the rate at which fluctuations grow due to gravitational instability. We use mock catalogues to compare the effective volumes sampled by a range of survey configurations. To give just two examples: a redshift survey down to samples an effective volume that is approximately five to 10 times larger than that probed by an survey with and a flux limit of at least is required for an sample to become competitive in effective volume. [ABSTRACT FROM AUTHOR]

We use a model for the evolution of galaxies in the far-infrared (far-IR) based on the Λ-cold dark matter cosmology to make detailed predictions for the upcoming cosmological surveys with the Herschel Space Observatory. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy spectral energy distribution (SEDs) including the reprocessing of radiation by dust. The model, which is the same as that in Baugh et al., assumes two different initial mass functions (IMFs): a normal solar neighbourhood IMF for quiescent star formation in discs, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF appears necessary to explain the number counts and redshifts of faint submillimetre galaxies. In this paper, we present predictions for galaxy luminosity functions, number counts and redshift distributions in the Herschel imaging bands. We find that source confusion will be a serious problem in the deepest planned surveys. We also show predictions for physical properties such as star formation rates and stellar, gas and halo masses, together with fluxes at other wavelengths (from the far-ultraviolet to the radio) relevant for multi-wavelength follow-up observations. We investigate what fraction of the total IR emission from dust and of the high-mass star formation over the history of the Universe should be resolved by planned surveys with Herschel, and find a fraction ∼30–50 per cent, depending on confusion. Finally, we show that galaxies in Herschel surveys should be significantly clustered. [ABSTRACT FROM AUTHOR]

Future galaxy redshift surveys aim to measure cosmological quantities from the galaxy power spectrum. A prime example is the detection of baryonic acoustic oscillations, providing a standard ruler to measure the dark energy equation of state, , to high precision. The strongest practical limitation for these experiments is how quickly accurate redshifts can be measured for sufficient galaxies to map the large-scale structure. A promising strategy is to target emission-line (i.e. star-forming) galaxies at high redshift ; not only is the space density of this population increasing out to , but also emission lines provide an efficient method of redshift determination. Motivated by the prospect of future dark energy surveys targeting Hα emitters at near-infrared wavelengths (i.e. ), we use the latest empirical data to model the evolution of the Hα luminosity function out to and thus provide predictions for the abundance of Hα emitters for practical limiting fluxes. We caution that the estimates presented in this work must be tempered by an efficiency factor, ε, giving the redshift success rate from these potential targets. For a range of practical efficiencies and limiting fluxes, we provide an estimate of , where is the 3D galaxy number density and P0.2 is the galaxy power spectrum evaluated at . Ideal surveys must provide in order to balance shot-noise and cosmic variance errors. We show that a realistic emission-line survey could achieve out to with a limiting flux of 10−16 erg s−1 cm−2. If the limiting flux is a factor of 5 brighter, then this goal can only be achieved out to , highlighting the importance of survey depth and efficiency in cosmological redshift surveys. [ABSTRACT FROM AUTHOR]

We present predictions for the abundance and nature of extremely red objects (EROs) in the Λ cold dark matter model. EROs are red, massive galaxies observed at and their numbers and properties pose a challenge to hierarchical galaxy formation models. We compare the predictions from two published models, one of which invokes a ‘superwind’ to regulate star formation in massive haloes and the other which suppresses gas cooling in haloes through ‘radio-mode’ active galactic nucleus (AGN) feedback. The superwind model underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN feedback model gives excellent agreement with the number counts and redshift distribution of EROs. In the AGN feedback model the ERO population is dominated by old, passively evolving galaxies, whereas observations favour an equal split between old galaxies and dusty starbursts. Also, the model predicts a more extended redshift distribution of passive galaxies than is observed. These comparisons suggest that star formation may be quenched too efficiently in this model. [ABSTRACT FROM AUTHOR]

We use the combinedgalform semi-analytical model of galaxy formation andgrasil spectrophotometric code to investigate the properties of galaxies selected via their submillimetre (submm) emission. The fiducial model we use has previously been shown to fit the properties of local Ultra-Luminous Infrared Galaxies, as well as the number counts of faint submm galaxies. Here, we test the model in more detail by comparing the SEDs and stellar, dynamical, gas and halo masses of submm galaxies against observational data. We precisely mimic the submm and radio selection function of the observations and show that the predicted far-infrared properties of model galaxies with and are in good agreement with observations. Although the dust emission model does not assume a single dust temperature, the far-infrared SEDs are well described by single component modified blackbody spectrum with characteristic temperature , in good agreement with observations. We also find evidence that the observations may have uncovered evolution in the far-infrared–radio relation in ULIRGs out to . We show that the predicted redshift distribution of submm galaxies provides a reasonable fit to the observational data with a median redshift . The radio-selected subset of submm galaxies are predicted to make up approximately 75 per cent of the population and peak at , in a reasonable agreement with the observed radio detected fraction and redshift distribution. However, the predicted K band and mid-infrared (3–8 μm) flux densities of the submm galaxies [and Lyman-Break Galaxies (LBGs)] are up to a factor of 10× fainter than observed. We show that including the stellar thermally pulsating asymptotic giant branch phase in the stellar population models does not make up for this deficit. This discrepancy may indicate that the stellar masses of the submm galaxies in the model are too low: , while observations suggest more massive systems, . However, if the predicted K- and 3–8-μm extinctions in the model could be dramatically reduced, then this would reduce, but not eliminate, this discrepancy. Finally, we discuss the potential modifications to the models which may improve the fit to the observational data, as well as the new observational tests which will be made possible with the arrival of new facilities, such as Submillimetre Common-User Bolometer Array2. [ABSTRACT FROM AUTHOR]

We present predictions for the evolution of the galaxy luminosity function, number counts and redshift distributions in the infrared (IR) based on the ΛCDM cosmological model. We use the combinedgalform semi-analytical galaxy formation model andgrasil spectrophotometric code to compute galaxy spectral energy distributions including the reprocessing of radiation by dust. The model, which is the same as that given by Baugh et al., assumes two different initial mass functions (IMFs): a normal solar neighbourhood IMF for quiescent star formation in discs, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF seems to be necessary to explain the number counts of faint submillimetre galaxies. We compare the model with observational data from the Spitzer Space Telescope, with the model parameters fixed at values chosen before Spitzer data became available. We find that the model matches the observed evolution in the IR remarkably well over the whole range of wavelengths probed by Spitzer. In particular, the Spitzer data show that there is strong evolution in the mid-IR galaxy luminosity function over the redshift range , and this is reproduced by our model without requiring any adjustment of parameters. On the other hand, a model with a normal IMF in starbursts predicts far too little evolution in the mid-IR luminosity function, and is therefore excluded. [ABSTRACT FROM AUTHOR]

We present detailed predictions for the properties of Lyα-emitting galaxies in the framework of the Λ cold dark matter cosmology, calculated using the semi-analytical galaxy formation modelgalform. We explore a model that assumes a top-heavy initial mass function in starbursts and that has previously been shown to explain the sub-millimetre number counts and the luminosity function of Lyman-break galaxies at high redshift. We show that this model, with the simple assumption that a fixed fraction of Lyα photons escape from each galaxy, is remarkably successful at explaining the observed luminosity function of Lyα emitters (LAEs) over the redshift range . We also examine the distribution of Lyα equivalent widths and the broad-band continuum magnitudes of emitters, which are in good agreement with the available observations. We look more deeply into the nature of LAEs, presenting predictions for fundamental properties such as the stellar mass and radius of the emitting galaxy and the mass of the host dark matter halo. The model predicts that the clustering of LAEs at high redshifts should be strongly biased relative to the dark matter, in agreement with observational estimates. We also present predictions for the luminosity function of LAEs at , a redshift range that is starting to be be probed by near-infrared surveys and using new instruments such as the Dark Ages Z Lyman Explorer (DAzLE). [ABSTRACT FROM AUTHOR]

We present predictions for the abundance of submillimetre galaxies (SMGs) and Lyman-break galaxies (LBGs) in theΛ cold dark matter cosmology. A key feature of our model is the self-consistent calculation of the absorption and emission of radiation by dust. The new model successfully matches the LBG luminosity function, as well as reproducing the properties of the local galaxy population in the optical and infrared. The model can also explain the observed galaxy number counts at 850μm, but only if we assume a top-heavy initial mass function for the stars formed in bursts. The predicted redshift distribution of SMGs depends relatively little on their flux over the range 1–10 mJy, with a median value ofat a flux of 5 mJy, in good agreement with the recent measurement by Chapman et al. The counts of SMGs are predicted to be dominated by ongoing starbursts. However, in the model these bursts are responsible for making only a few per cent of the stellar mass locked up in massive ellipticals at the present day. [ABSTRACT FROM AUTHOR]