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We present a quantitative analysis of the properties of galaxies and structures evolving in universes dominated by different modified gravitational models, including two variants of the f (R)-gravity (F) and two of the Dvali–Gabdadze–Poratti (N) braneworld model, which respectively feature the chameleon and Vainshtein screening mechanisms. Using the Simulation HYdrodynamics BeyONd Einstein (shybone) cosmological hydrodynamical full-physics simulations suite, we study the departures in the properties of galaxies residing in different environments with respect to the standard model (GR). Using two different criteria to compare, we find that structures formed within modified gravity tend to show a denser gas density profile than their GR counterparts. Within the different modified gravity models, N1 and F5 gravity models show greater departures from the standard model, with gas density profiles |$\rho _{\rm IGM} \ge 30~{{\ \rm per\ cent}}$| denser in the outskirts for the N1 model, and in the inner parts for the F5 model. Additionally, we find that haloes evolving in MG universes show, in general, larger quenched fractions than GR, reaching up to 20 per cent larger quenching fractions in F5 regardless of the stellar mass of the galaxy. Concerning the other models, F6, N1, and N5 show slightly larger quenched fractions, but no strong differences can be found. These results directly impact the colour distribution of galaxies, making them in MG models redder and older than their GR counterparts. Like GR, once the environment starts to play a role, galaxies rapidly get quenched, and the differences between models vanish. [ABSTRACT FROM AUTHOR]

This study investigates the clustering and bias of Luminous Red Galaxies (LRG) in the BOSS-LOWZ, -CMASS, -COMB, and eBOSS samples, using two types of simulated lightcones: (i) high-fidelity lightcones from Uchuu N -body simulation, employing SHAM technique to assign LRG to (sub)haloes, and (ii) 16 000 covariance lightcones from GLAM-Uchuu N -body simulations, including LRG using HOD data from Uchuu. Our results indicate that Uchuu and glam lightcones closely replicate BOSS/eBOSS data, reproducing correlation function and power spectrum across scales from redshifts 0.2 to 1.0, from 2 to |$150 \,h^{-1}\,\mathrm{Mpc}$| in configuration space, from 0.005 to |$0.7\, h\,\mathrm{Mpc}^{-1}$| in Fourier space, and across different LRG stellar masses. Furthermore, comparing with existing MD-Patchy and EZmock BOSS/eBOSS lightcones based on approximate methods, our GLAM-Uchuu lightcones provide more precise clustering estimates. We identify significant deviations from observations within |$20 \,h^{-1}\,\mathrm{Mpc}$| scales in MD-Patchy and EZmock , with our covariance matrices indicating that these methods underestimate errors by between 10 per cent and 60 per cent. Lastly, we explore the impact of cosmology on galaxy clustering. Our findings suggest that, given the current level of uncertainties in BOSS/eBOSS data, distinguishing models with and without massive neutrino effects on large-scale structure (LSS) is challenging. This paper highlights the Uchuu and GLAM-Uchuu simulations' robustness in verifying the accuracy of Planck cosmological parameters, providing a strong foundation for enhancing lightcone construction in future LSS surveys. We also demonstrate that generating thousands of galaxy lightcones is feasible using N -body simulations with adequate mass and force resolution. [ABSTRACT FROM AUTHOR]

We apply the marked correlation function test proposed by Armijo et al. (Paper I) to samples of luminous red galaxies (LRGs) from the final data release of the Sloan Digital Sky Survey (SDSS) III. The test assigns a density-dependent mark to galaxies in the estimation of the projected marked correlation function. Two gravity models are compared: general relativity (GR) and |$f(R)$| gravity. We build mock catalogues which, by construction, reproduce the measured galaxy number density and two-point correlation function of the LRG samples, using the halo occupation distribution model (HOD). A range of HOD models give acceptable fits to the observational constraints, and this uncertainty is fed through to the error in the predicted marked correlation functions. The uncertainty from the HOD modelling is comparable to the sample variance for the SDSS-III LRG samples. Our analysis shows that current galaxy catalogues are too small for the test to distinguish a popular |$f(R)$| model from GR. However, upcoming surveys with a better measured galaxy number density and smaller errors on the two-point correlation function, or a better understanding of galaxy formation, may allow our method to distinguish between viable gravity models. [ABSTRACT FROM AUTHOR]

In this series of papers, we present an emulator-based halo model for the non-linear clustering of galaxies in modified gravity cosmologies. In the first paper, we present emulators for the following halo properties: the halo mass function, concentration–mass relation and halo-matter cross-correlation function. The emulators are trained on data extracted from the forge and bridge suites of N -body simulations, respectively, for two modified gravity (MG) theories: f (R) gravity, and the DGP model, varying three standard cosmological parameters Ωm0, H 0, σ8, and one MG parameter, either |$\bar{f}_{R0}$| or r c. Our halo property emulators achieve an accuracy of |${\lesssim}1\ \hbox{per cent}$| on independent test data sets. We demonstrate that the emulators can be combined with a galaxy–halo connection prescription to accurately predict the galaxy–galaxy and galaxy–matter correlation functions using the halo model framework. [ABSTRACT FROM AUTHOR]

In this series of papers, we present a simulation-based model for the non-linear clustering of galaxies based on separate modelling of clustering in real space and velocity statistics. In the first paper, we present an emulator for the real-space correlation function of galaxies, whereas the emulator of the real-to-redshift space mapping based on velocity statistics is presented in the second paper. Here, we show that a neural network emulator for real-space galaxy clustering trained on data extracted from the dark quest suite of N-body simulations achieves sub-per cent accuracies on scales 1 < r < 30 |$h^{-1} \, \mathrm{Mpc}$|⁠ , and better than 3 per cent on scales r < 1 |$h^{-1}\, \mathrm{Mpc}$| in predicting the clustering of dark-matter haloes with number density 10−3.5 |$(h^{-1}\, \mathrm{Mpc})^{-3}$|⁠ , close to that of SDSS LOWZ-like galaxies. The halo emulator can be combined with a galaxy–halo connection model to predict the galaxy correlation function through the halo model. We demonstrate that we accurately recover the cosmological and galaxy–halo connection parameters when galaxy clustering depends only on the mass of the galaxies' host halos. Furthermore, the constraining power in σ8 increases by about a factor of 2 when including scales smaller than 5 |$h^{-1} \, \mathrm{Mpc}$|⁠. However, when mass is not the only property responsible for galaxy clustering, as observed in hydrodynamical or semi-analytic models of galaxy formation, our emulator gives biased constraints on σ8. This bias disappears when small scales (r < 10 |$h^{-1}\, \mathrm{Mpc}$|⁠) are excluded from the analysis. This shows that a vanilla halo model could introduce biases into the analysis of future data sets. [ABSTRACT FROM AUTHOR]

We use the GALFORM semi-analytical model of galaxy formation and the Planck-Millennium simulation to investigate the origins of stellar mass in galaxies and their spheroids. We compare the importance of mergers and disc instabilities, as well as the starbursts that they trigger. We find that the fraction of galaxy stellar mass formed ex situ (i.e. through mergers; f ex) increases sharply from M * = 1011 M⊙ upwards, reaching 80 per cent at M * = 1011.3 M⊙. The massive end of the f ex– M * relation does not evolve with redshift, in disagreement with other models. For low-mass galaxies we find larger ex situ contributions at z  = 0 than in other models (7–12 per cent), with a decrease towards higher redshifts. Major mergers contribute roughly half of the ex situ mass, with minor mergers and smooth accretion of satellites both accounting for ≈25 per cent, almost independent of stellar mass and redshift. Mergers dominate in building up high-mass (M *, sph > 1011 M⊙) and low-mass (M *, sph < 108.5 M⊙) spheroids. Disc instabilities and their associated starbursts dominate for intermediate-mass spheroids (108.5 < M *, sph < 1011 M⊙) at z  = 0. The mass regime where pseudo-bulges dominate is in agreement with observed pseudo-bulge fractions, but the peak value in the pseudo-bulge fraction predicted by GALFORM is likely too high. Starbursts induced by disc instabilities are the dominant channel for spheroid growth at all redshifts, while merger-induced starbursts are relatively negligible, except at very high redshifts (z > 5). [ABSTRACT FROM AUTHOR]

The coming generation of galaxy surveys will provide measurements of galaxy clustering with unprecedented accuracy and data size, which will allow us to test cosmological models at much higher precision than achievable previously. This means that we must have more accurate theoretical predictions to compare with future observational data. As a first step towards more accurate modelling of the redshift space distortions (RSD) of small-scale galaxy clustering in modified gravity (MG) cosmologies, we investigate the validity of the so-called Skew-T (ST) probability distribution function (PDF) of halo pairwise peculiar velocities in these models. We show that, combined with the streaming model of RSD, the ST PDF substantially improves the small-scale predictions by incorporating skewness and kurtosis, for both Λ cold dark matter (ΛCDM) and two leading MG models: f (R) gravity and the DGP braneworld model. The ST model reproduces the velocity PDF and redshift-space halo clustering measured from MG N -body simulations very well down to |$\sim 5 \, h^{-1}\, \mathrm{Mpc}$|⁠. In particular, we investigate the enhancements of halo pairwise velocity moments with respect to ΛCDM for a larger range of MG variants than previous works, and present simple explanations to the behaviours observed. By performing a simple Fisher analysis, we find a significant increase in constraining power to detect modifications of General Relativity by introducing small-scale information in the RSD analyses. [ABSTRACT FROM AUTHOR]

Author(s): John A. Peacock (corresponding author) [1]; Shaun Cole [2]; Peder Norberg [2]; Carlton M. Baugh [2]; Joss Bland-Hawthorn [3]; Terry Bridges [3]; Russell D. Cannon [3]; Matthew Colless [4]; [...]

Conservative mass limits are often imposed on the dark matter halo catalogues extracted from N -body simulations. By comparing simulations with different mass resolutions, at z  = 0 we find that even for haloes resolved by 100 particles, the lower resolution simulation predicts a cumulative halo abundance that is 5 per cent lower than in the higher resolution simulation. We propose a simple weighting scheme to utilize the haloes that are usually regarded as being 'sub-resolution'. With the scheme, we are able to use haloes which contain only 11 particles to reproduce the clustering measured in the higher resolution simulation to within 5 per cent on scales down to 2  h −1 Mpc, thereby extending the useful halo resolution by a factor of 10 below the mass at which the mass functions in the two simulations first start to deviate. The performance of the method is slightly worse at higher redshift. Our method allows a simulation to be used to probe a wider parameter space in clustering studies, for example, in a halo occupation distribution analysis. This reduces the cost of generating many simulations to estimate the covariance matrix on measurements or using a larger volume simulation to make large-scale clustering predictions. [ABSTRACT FROM AUTHOR]

We characterize the selection cuts and clustering properties of a magnitude-limited sample of bright galaxies that is part of the Bright Galaxy Survey (BGS) of the Dark Energy Spectroscopic Instrument (DESI) using the ninth data release of the Legacy Imaging Surveys (DR9). We describe changes in the DR9 selection compared to the DR8 one and we also compare the DR9 selection in three distinct regions: BASS/MzLS in the north Galactic Cap (NGC), DECaLS in the NGC, and DECaLS in the south Galactic Cap (SGC). We investigate the systematics associated with the selection and assess its completeness by matching the BGS targets with the Galaxy and Mass Assembly (GAMA) survey. We measure the angular clustering for the overall bright sample (r mag ≤ 19.5) and as function of apparent magnitude and colour. This enables to determine the clustering strength r 0 and slope γ by fitting a power-law model that can be used to generate accurate mock catalogues for this tracer. We use a counts-in-cells technique to explore higher order statistics and cross-correlations with external spectroscopic data sets in order to check the evolution of the clustering with redshift and the redshift distribution of the BGS targets using clustering redshifts. While this work validates the properties of the BGS bright targets, the final target selection pipeline and clustering properties of the entire DESI BGS will be fully characterized and validated with the spectroscopic data of Survey Validation. [ABSTRACT FROM AUTHOR]

We implement a sample-efficient method for rapid and accurate emulation of semi-analytical galaxy formation models over a wide range of model outputs. We use ensembled deep learning algorithms to produce a fast emulator of an updated version of the galform model from a small number of training examples. We use the emulator to explore the model's parameter space, and apply sensitivity analysis techniques to better understand the relative importance of the model parameters. We uncover key tensions between observational data sets by applying a heuristic weighting scheme in a Markov chain Monte Carlo framework and exploring the effects of requiring improved fits to certain data sets relative to others. Furthermore, we demonstrate that this method can be used to successfully calibrate the model parameters to a comprehensive list of observational constraints. In doing so, we re-discover previous galform fits in an automatic and transparent way, and discover an improved fit by applying a heavier weighting to the fit to the metallicities of early-type galaxies. The deep learning emulator requires a fraction of the model evaluations needed in similar emulation approaches, achieving an out-of-sample mean absolute error at the knee of the K -band luminosity function of 0.06 dex with less than 1000 model evaluations. We demonstrate that this is an extremely efficient, inexpensive, and transparent way to explore multidimensional parameter spaces, and can be applied more widely beyond semi-analytical galaxy formation models. [ABSTRACT FROM AUTHOR]

The next generation of spectroscopic surveys will target emission-line galaxies (ELGs) to produce constraints on cosmological parameters. We study the large-scale structure traced by ELGs using a combination of a semi-analytical model of galaxy formation, a code that computes the nebular emission from H  ii regions using the properties of the interstellar medium, and a large-volume, high-resolution N -body simulation. We consider fixed number density samples where galaxies are selected by their H α, [O  iii ] λ5007, or [O  ii ] λλ3727–3729 emission-line luminosities. We investigate the assembly bias signatures of these samples, and compare them to those of stellar mass- and star formation rate-selected samples. Interestingly, we find that the [O  iii ]- and [O  ii ]-selected samples display scale-dependent bias on large scales and that their assembly bias signatures are also scale dependent. Both these effects are more pronounced for lower number density samples. The [O  iii ] and [O  ii ] emitters that contribute most to the scale dependence tend to have a low gas-phase metallicity and are preferentially found in low-density regions. We also measure the baryon acoustic oscillation (BAO) feature and the β parameter related to the growth rate of overdensities. We find that the scale of the BAO peak is roughly the same for all selections and that β is scale dependent at large scales. Our results suggest that ELG samples include environmental effects that should be modelled in order to remove potential systematic errors that could affect the estimation of cosmological parameters. [ABSTRACT FROM AUTHOR]

We carry out 'full-physics' hydrodynamical simulations of galaxy formation in the normal-branch Dvali–Gabadadze–Porrati (nDGP) braneworld model using a new modified version of the arepo code and the IllustrisTNG galaxy formation model. We simulate two nDGP models (N5 and N1) that represent, respectively, weak and moderate departures from general relativity (GR), in boxes of sizes |$62$| and |$25\, h^{-1}{\rm Mpc}$| using 2 × 5123 dark matter particles and initial gas cells. This allows us to explore, for the first time, the impact of baryonic physics on galactic scales in braneworld models of modified gravity and to make predictions on the stellar content of dark matter haloes and galaxy evolution through cosmic time in these models. We find significant differences between the GR and nDGP models in the power spectra and correlation functions of gas, stars and dark matter of up to ∼25 per cent on large scales. Similar to their impact in the standard cosmological model (Λ cold dark matter), baryonic effects can have a significant influence over the clustering of the overall matter distribution, with a sign that depends on scale. Studying the degeneracy between modified gravity and galactic feedback in these models, we find that these two physical effects on matter clustering can be cleanly disentangled, allowing for a method to accurately predict the matter power spectrum with baryonic effects included, without having to run hydrodynamical simulations. Depending on the braneworld model, we find differences compared with GR of up to ∼15 per cent in galaxy properties such as the stellar-to-halo-mass ratio, galaxy stellar mass function, gas fraction, and star formation rate density. The amplitude of the fifth force is reduced by the presence of baryons in the very inner part of haloes, but this reduction quickly becomes negligible above ∼0.1 times the halo radius. [ABSTRACT FROM AUTHOR]

Upcoming surveys will use a variety of galaxy selections to map the large-scale structure of the Universe. It is important to make accurate predictions for the properties and clustering of such galaxies, including the errors on these statistics. Here, we describe a novel technique which uses the semi-analytical model of galaxy formation galform , embedded in the high-resolution N -body Planck-Millennium simulation, to populate a thousand halo catalogues generated using the Parallel-PM N -body glam code. Our hybrid scheme allows us to make clustering predictions on scales that cannot be modelled in the original N -body simulation. We focus on luminous red galaxies (LRGs) selected in the redshift range z = 0.6 − 1 from the galform output using similar colour-magnitude cuts in the r, z , and W 1 bands to those that will be applied in the Dark Energy Spectroscopic Instrument (DESI) survey, and call this illustrative sample 'DESI-like' LRGs. We find that the LRG-halo connection is non-trivial, leading to the prediction of a non-standard halo occupation distribution; in particular, the occupation of central galaxies does not reach unity for the most massive haloes, and drops with increasing mass. The glam catalogues reproduce the abundance and clustering of the LRGs predicted by galform. We use the glam mocks to compute the covariance matrices for the two-point correlation function and power spectrum of the LRGs and their background dark matter density field, revealing important differences. We also make predictions for the linear-growth rate and the baryon acoustic oscillations distances at z = 0.6, 0.74, and 0.93. All 'DESI-like' LRG catalogues are made publicly available. [ABSTRACT FROM AUTHOR]

We present – and make publicly available – accurate and precise photometric redshifts in the ACS footprint from the COSMOS field for objects with i AB ≤ 23. The redshifts are computed using a combination of narrow-band photometry from PAUS, a survey with 40 narrow bands spaced at |$100\,\mathring{\rm A}$| intervals covering the range from 4500 to |$8500\,\mathring{\rm A}$|⁠ , and 26 broad, intermediate, and narrow bands covering the UV, visible and near-infrared spectrum from the COSMOS2015 catalogue. We introduce a new method that models the spectral energy distributions as a linear combination of continuum and emission-line templates and computes its Bayes evidence, integrating over the linear combinations. The correlation between the UV luminosity and the O  ii line is measured using the 66 available bands with the zCOSMOS spectroscopic sample, and used as a prior which constrains the relative flux between continuum and emission-line templates. The flux ratios between the O  ii line and H α , H β and |$\mathrm{O\,{\small III}}$| are similarly measured and used to generate the emission-line templates. Comparing to public spectroscopic surveys via the quantity Δ z ≡ (z photo − z spec)/(1 + z spec), we find the photometric redshifts to be more precise than previous estimates, with σ 68(Δ z ) ≈ (0.003, 0.009) for galaxies at magnitude i AB ∼ 18 and i AB ∼ 23, respectively, which is three times and 1.66 times tighter than COSMOS2015. Additionally, we find the redshifts to be very accurate on average, yielding a median of the Δ z distribution compatible with |median(Δ z )| ≤ 0.001 at all redshifts and magnitudes considered. Both the added PAUS data and new methodology contribute significantly to the improved results. The catalogue produced with the technique presented here is expected to provide a robust redshift calibration for current and future lensing surveys, and allows one to probe galaxy formation physics in an unexplored luminosity-redshift regime, thanks to its combination of depth, completeness, and excellent redshift precision and accuracy. [ABSTRACT FROM AUTHOR]

We explore how to mitigate the clustering distortions in Lyman α emitter (LAE) samples caused by the misidentification of the Lyman α (⁠|$\rm {Ly}\,\alpha$|⁠) wavelength in their |$\rm {Ly}\,\alpha$| line profiles. We use the |$\rm {Ly}\,\alpha$| line profiles from our previous LAE theoretical model that includes radiative transfer in the interstellar and intergalactic mediums. We introduce a novel approach to measure the systemic redshift of LAEs from their |$\rm {Ly}\,\alpha$| line using neural networks. In detail, we assume that for a fraction of the whole LAE population their systemic redshift is determined precisely through other spectral features. We then use this subset to train a neural network that predicts the |$\rm {Ly}\,\alpha$| wavelength given an |$\rm {Ly}\,\alpha$| line profile. We test two different training sets: (i) the LAEs are selected homogeneously and (ii) only the brightest LAE is selected. In comparison with previous approaches in the literature, our methodology improves significantly the accuracy in determining the |$\rm {Ly}\,\alpha$| wavelength. In fact, after applying our algorithm in ideal |$\rm {Ly}\,\alpha$| line profiles, we recover the clustering unperturbed down to |$1\, {\rm cMpc}\, h^{-1}$|⁠. Then, we test the performance of our methodology in realistic |$\rm {Ly}\,\alpha$| line profiles by downgrading their quality. The machine learning technique using the uniform sampling works well even if the |$\rm {Ly}\,\alpha$| line profile quality is decreased considerably. We conclude that LAE surveys such as HETDEX would benefit from determining with high accuracy the systemic redshift of a subpopulation and applying our methodology to estimate the systemic redshift of the rest of the galaxy sample. [ABSTRACT FROM AUTHOR]

The presence of neutral hydrogen in the interstellar medium (ISM) and intergalactic medium (IGM) induces radiative transfer (RT) effects on |$\rm {Ly}\,\alpha$| photons that affect the observability of Lyman alpha emitters (LAEs). We use the galform semi-analytic model of galaxy formation and evolution to analyse how these effects shape the spatial distribution of LAEs with respect to |$\rm {H}\,\alpha$| emitters (HAEs) around high-density regions at high redshift. We find that when a large sample of protoclusters is considered, HAEs showing also |$\rm {Ly}\,\alpha$| emission (HAEs + LAEs) populate the same regions as those that do not display the |$\rm {Ly}\,\alpha$| line at |$z$|  = 2.2. We compare against the protocluster USS1558-003, one of the most massive protoclusters located at |$z$|  = 2.53. Our results indicate that the strong depletion of HAEs + LAEs present in the high-density regions of USS1558-003 may be due to cosmic variance. We find that at |$z$|  = 2.2 and |$z$|  = 3.0, RT of the ISM produces a strong decline (30–50 per cent) of the clustering amplitude of HAEs + LAEs with respect to HAEs towards the protoclusters centre. At |$z$|  = 5.7, given the early evolutionary state of protoclusters and galaxies, the clustering of HAEs + LAEs has a smaller variation (10–20 per cent) towards the protoclusters centre. Depending on the equivalent width and luminosity criteria of the emission-line galaxy sample, the IGM can have a mild or a null effect on galaxy properties and clustering in high-density regions. [ABSTRACT FROM AUTHOR]

To understand the nature of the accelerated expansion of the Universe, we need to combine constraints on the expansion rate and growth of structure. The growth rate is usually extracted from 3D galaxy maps by exploiting the effects of peculiar motions on galaxy clustering. However, theoretical models of the probability distribution function (PDF) of galaxy pairwise peculiar velocities are not accurate enough on small scales to reduce the error on theoretical predictions to the level required to match the precision expected for measurements from future surveys. Here, we improve the modelling of the pairwise velocity distribution by using the Skew-T PDF, which has non-zero skewness and kurtosis. Our model accurately reproduces the redshift space multipoles (monopole, quadrupole, and hexadecapole) predicted by N -body simulations, above scales of about |$10\, h^{-1}{\rm Mpc}$|⁠. We illustrate how a Taylor expansion of the streaming model can reveal the contributions of the different moments to the clustering multipoles, which are independent of the shape of the velocity PDF. The Taylor expansion explains why the Gaussian streaming model works well in predicting the first two redshift space multipoles, although the velocity PDF is non-Gaussian even on large scales. Indeed, any PDF with the correct first two moments would produce precise results for the monopole down to scales of about |$10\, h^{-1}{\rm Mpc}$|⁠ , and for the quadrupole down to about |$30\, h^{-1}{\rm Mpc}$|⁠. An accurate model for the hexadecapole needs to include higher order moments. [ABSTRACT FROM AUTHOR]

We investigate if, for a fixed number density of targets and redshift, there is an optimal way to select a galaxy sample in order to measure the baryon acoustic oscillation (BAO) scale, which is used as a standard ruler to constrain the cosmic expansion. Using the mock galaxy catalogue built by Smith et al. in the Millennium-XXL N-body simulation with a technique to assign galaxies to dark matter haloes based on halo occupation distribution modelling, we consider the clustering of galaxies selected by luminosity, colour and local density. We assess how well the BAO scale can be extracted by fitting a template to the power spectrum measured for each sample. We find that the BAO peak position is recovered equally well for samples defined by luminosity or colour, while there is a bias in the BAO scale recovered for samples defined by density. The BAO position is contracted to smaller scales for the densest galaxy quartile and expanded to large scales for the two least dense galaxy quartiles. For fixed galaxy number density, density-selected samples have higher uncertainties in the recovered BAO scale than luminosity- or colour-selected samples. [ABSTRACT FROM AUTHOR]

We present the first application of a variance-based sensitivity analysis (SA) to a model that aims to predict the evolution and properties of the whole galaxy population. SA is a well-established technique in other quantitative sciences, but is a relatively novel tool for the evaluation of astrophysical models. We perform a multiparameter exploration of the GALFORM semi-analytic galaxy formation model, to compute how sensitive the present-day K -band luminosity function is to varying different model parameters. The parameter space is scanned using a low-discrepancy sampling technique proposed by Saltelli. We first demonstrate the usefulness of the SA approach by varying just two model parameters, one that controls supernova feedback and the other the heating of gas by active galactic nucleus. The SA analysis matches our physical intuition regarding how these parameters affect the predictions for different parts of the galaxy luminosity function. We then use SA to compute Sobol' sensitivity indices varying seven model parameters, connecting the variance in the model output to the variance in the input parameters. The sensitivity is computed in luminosity bins, allowing us to probe the origin of the model predictions in detail. We discover that the SA correctly identifies the least important and most important parameters. Moreover, the SA also captures the combined responses of varying multiple parameters at the same time. Our study marks a much needed step away from the traditional 'one-at-a-time' parameter variation often used in this area and improves the transparency of multiparameter models of galaxy formation. [ABSTRACT FROM AUTHOR]

We model the large-scale linear galaxy bias b g(x , z) as a function of redshift z and observed absolute magnitude threshold x for broad-band continuum emission from the far-infrared to ultraviolet, as well as for prominent emission lines, such as the H α, H β, Ly a, and [O  ii ] lines. The modelling relies on the semi-analytic galaxy formation model galform , run on the state-of-the-art N -body simulation surfs with the Planck 2015 cosmology. We find that both the differential bias at observed absolute magnitude x and the cumulative bias for magnitudes brighter than x can be fitted with a five-parameter model: b g(x , z) = a + b (1 + z) e (1 + exp [(x − c) d ]). We also find that the bias for the continuum bands follows a very similar form regardless of wavelength due to the mixing of star-forming and quiescent galaxies in a magnitude-limited survey. Differences in bias only become apparent when an additional colour separation is included, which suggest extensions to this work could look at different colours at fixed magnitude limits. We test our fitting formula against observations, finding reasonable agreement with some measurements within 1σ statistical uncertainties, and highlighting areas of improvement. We provide the fitting parameters for various continuum bands, emission lines, and intrinsic galaxy properties, enabling a quick estimation of the linear bias in any typical survey of large-scale structure. [ABSTRACT FROM AUTHOR]

Telescopes to be launched over the next decade and a half, such as JWST , EUCLID , ATHENA , and Lynx , promise to revolutionize the study of the high-redshift Universe and greatly advance our understanding of the early stages of galaxy formation. We use a model that follows the evolution of the masses and spins of supermassive black holes (SMBHs) within a semi-analytic model of galaxy formation to make predictions for the active galactic nucleus luminosity function at |$z$| ≥ 7 in the broadband filters of JWST and EUCLID at near-infrared wavelengths, and ATHENA and Lynx at X-ray energies. The predictions of our model are relatively insensitive to the choice of seed black hole mass, except at the lowest luminosities (L bol < 1043 erg s−1) and the highest redshifts (⁠|$z$| > 10). We predict that surveys with these different telescopes will select somewhat different samples of SMBHs, with EUCLID unveiling the most massive, highest accretion rate SMBHs, Lynx the least massive, lowest accretion rate SMBHs, and JWST and ATHENA covering objects inbetween. At |$z$|  = 7, we predict that typical detectable SMBHs will have masses, M BH ∼ 105–8 M⊙, and Eddington normalized mass accretion rates, |$\dot{M}/\dot{M}_{\mathrm{Edd}}\sim 0.6{-}2$|⁠. The SMBHs will be hosted by galaxies of stellar mass M ⋆ ∼ 108–10 M⊙, and dark matter haloes of mass M halo ∼ 1011–12 M⊙. We predict that the detectable SMBHs at |$z$|  = 10 will have slightly smaller black holes, accreting at slightly higher Eddington normalized mass accretion rates, in slightly lower mass host galaxies compared to those at |$z$|  = 7, and reside in haloes of mass M halo ∼ 1010–11 M⊙. [ABSTRACT FROM AUTHOR]

In the near future galaxy surveys will target Lyman alpha emitting galaxies (LAEs) to unveil the nature of dark energy. It has been suggested that the observability of LAEs is coupled to the large-scale properties of the intergalactic medium. Such coupling could introduce distortions into the observed clustering of LAEs, adding a new potential difficulty to the interpretation of upcoming surveys. We present a model of LAEs that incorporates Ly α radiative transfer processes in the interstellar and intergalactic medium. The model is implemented in the GALFORM semi-analytic model of galaxy of formation and evolution. We find that the radiative transfer inside galaxies produces selection effects over galaxy properties. In particular, observed LAEs tend to have low metallicities and intermediate star formation rates. At low redshift we find no evidence of a correlation between the spatial distribution of LAEs and the intergalactic medium properties. However, at high redshift the LAEs are linked to the line of sight velocity and density gradient of the intergalactic medium. The strength of the coupling depends on the outflow properties of the galaxies and redshift. This effect modifies the clustering of LAEs on large scales, adding non-linear features. In particular, our model predicts modifications to the shape and position of the baryon acoustic oscillation peak. This work highlights the importance of including radiative transfer physics in the cosmological analysis of LAEs. [ABSTRACT FROM AUTHOR]

We test different implementations of the halo occupation distribution (HOD) model to reconstruct the spatial distribution of galaxies as predicted by a version of the L-GALAXIES semi-analytical model (SAM). We compare the measured two-point correlation functions of the HOD mock catalogues and the SAM samples to quantify the fidelity of the reconstruction. We use fixed number density galaxy samples selected according to stellar mass or star formation rate (SFR). We develop three different schemes to populate haloes with galaxies with increasing complexity, considering the scatter of the satellite HOD as an additional parameter in the modelling. We modify the SAM output, removing assembly bias and using a standard Navarro–Frenk–White density profile for the satellite galaxies as the target to reproduce with our HOD mocks. We find that all models give similar reproductions of the two-halo contribution to the clustering signal, but there are differences in the one-halo term. In particular, the HOD mock reproductions work equally well using either the HOD of central and satellites separately or using a model that also accounts for whether or not the haloes contain a central galaxy. We find that the HOD scatter does not have an important impact on the clustering predictions for stellar mass-selected samples. For SFR selections, we obtain the most accurate results assuming a negative binomial distribution for the number of satellites in a halo. The scatter in the satellites HOD is a key consideration for HOD mock catalogues that mimic ELG or SFR-selected samples in future galaxy surveys. [ABSTRACT FROM AUTHOR]

We present predictions for the UV-to-mm extragalactic background light (EBL) from a recent version of the galform semi-analytical model of galaxy formation which invokes a top-heavy stellar initial mass function (IMF) for galaxies undergoing dynamically triggered bursts of star formation. We combine galform with the grasil radiative transfer code for computing fully self-consistent UV-to-mm spectral energy distributions for each simulated galaxy, accounting for the absorption and re-emission of stellar radiation by interstellar dust. The predicted EBL is in near-perfect agreement with recent observations over the whole UV-to-mm spectrum, as is the evolution of the cosmic spectral energy distribution over the redshift range for which observations are available (⁠|$z$|  ≲ 1). We show that approximately 90 per cent of the EBL is produced at |$z$|  < 2 although this shifts to higher redshifts for sub-mm wavelengths. We assess whether the top-heavy IMF in starbursts is necessary in order to reproduce the EBL at the same time as other key observables, and find that variant models with a universal solar-neighbourhood IMF display poorer agreement with EBL observations over the whole UV-to-mm spectrum and fail to match the counts of galaxies in the sub-mm. [ABSTRACT FROM AUTHOR]

Lyman-α emitters (LAEs) are a promising target to probe the large-scale structure of the Universe at high redshifts, z  ≳ 2. However, their detection is sensitive to radiative transfer effects that depend on local astrophysical conditions. Thus, modeling the bulk properties of this galaxy population remains challenging for theoretical models. Here we develop a physically motivated scheme to predict LAEs in cosmological simulations. The escape of Lyα photons is computed using a Monte Carlo radiative transfer code that outputs a Lyα escape fraction. To speed up the process of assigning escape fractions to individual galaxies, we employ fitting formulae that approximate the full Monte Carlo results within an accuracy of 10 per cent for a broad range of column densities, gas metallicities, and gas bulk velocities. We apply our methodology to the semi-analytical model galform on a large N -body simulation. The Lyα photons escape through an outflowing neutral gas medium, implemented assuming different geometries. This results in different predictions for the typical column density and outflow velocities of the LAE population. To understand the impact of radiative transfer on our predictions, we contrast our models against a simple abundance matching assignment. Our full models populate LAEs in less massive haloes than what is obtained with abundance matching. Overall, radiative transfer effects result in better agreement when confronting the properties of LAEs against observational measurements. This suggests that incorporating the effects of Lyα radiative transfer in the analysis of this galaxy population, including their clustering, can be important for obtaining an unbiased interpretation of future data sets. [ABSTRACT FROM AUTHOR]

Measurements of redshift space distortions (RSD) provide a means to test models of gravity on large scales. We use mock galaxy catalogues constructed from large N -body simulations of standard and modified gravity models to measure galaxy clustering in redshift space. We focus our attention on two of the most representative and popular families of modified gravity models: the Hu & Sawicki f (R) gravity and the normal branch of the Dvali−Gabadadze−Porrati (DGP) model. The galaxy catalogues are built using a halo occupation distribution (HOD) prescription with the HOD parameters in the modified gravity models tuned to match with the number density and the real-space clustering of boss-cmass galaxies. We employ two approaches to model RSD: the first is based on linear perturbation theory and the second models non-linear effects on small scales by assuming standard gravity and including biasing and RSD effects. We measure the monopole to real-space correlation function ratio, the quadrupole to monopole ratio, clustering wedges, and multipoles of the correlation function and use these statistics to find the constraints on the distortion parameter, β. We find that the linear model fails to reproduce the N -body simulation results and the true value of β on scales |$s \lt 40\, h^{-1}\, {\rm Mpc}$|⁠, while the non-linear modelling of RSD recovers the value of β on the scales of interest for all models. RSD on large scales (⁠|$s\gtrsim 20\!-\!40\, h^{-1}\, {\rm Mpc}$|⁠) have been found to show significant deviations from the prediction of standard gravity in the DGP models. However, the potential to use RSD to constrain f (R) models is less promising, due to the different screening mechanism in this model. [ABSTRACT FROM AUTHOR]

The Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) will be a survey of bright, low-redshift galaxies, which is planned to cover an area of |${\sim } 14\, 000$| square degrees in three passes. Each pass will cover the survey area with ∼2000 pointings, each of area ∼8 square degrees. The BGS is currently proposed to consist of a bright high priority sample to an r -band magnitude limit r  ∼ 19.5, with a fainter low priority sample to r  ∼ 20. The geometry of the DESI fibre positioners in the focal plane of the telescope affects the completeness of the survey and has a non-trivial impact on clustering measurements. Using a BGS mock catalogue, we show that completeness due to fibre assignment primarily depends on the surface density of galaxies. Completeness is high (>95 per cent) in low-density regions, but very low (<10 per cent) in the centre of massive clusters. We apply the pair inverse probability (PIP) weighting correction to clustering measurements from a BGS mock which has been through the fibre assignment algorithm. This method is only unbiased if it is possible to observe every galaxy pair. To facilitate this, we randomly promote a small fraction of the fainter sample to be high priority, and dither the set of tile positions by a small angle. We show that inverse pair weighting combined with angular upweighting provides an unbiased correction to galaxy clustering measurements for the complete three pass survey, and also after one pass, which is highly incomplete. [ABSTRACT FROM AUTHOR]

We use the semi-analytical model of galaxy formation GALFORM to characterize an indirect signature of active galactic nucleus (AGN) feedback in the environment of radio galaxies at high redshifts. The predicted environment of radio galaxies is denser than that of radio-quiet galaxies with the same stellar mass. This is consistent with observational results from the CARLA survey. Our model shows that the differences in environment are due to radio galaxies being hosted by dark matter haloes that are ∼1.5 dex more massive than those hosting radio-quiet galaxies with the same stellar mass. By running a control simulation in which AGN feedback is switched off, we identify AGN feedback as the primary mechanism affecting the build up of the stellar component of radio galaxies, thus explaining the different environment in radio galaxies and their radio-quiet counterparts. The difference in host halo mass between radio-loud and radio-quiet galaxies translates into different galaxies populating each environment. We predict a higher fraction of passive galaxies around radio-loud galaxies compared to their radio-quiet counterparts. Furthermore, such a high fraction of passive galaxies shapes the predicted infrared luminosity function in the environment of radio galaxies in a way that is consistent with observational findings. Our results suggest that the impact of AGN feedback at high redshifts and environmental mechanisms affecting galaxies in high halo masses can be revealed by studying the environment of radio galaxies, thus providing new constraints on galaxy formation physics at high redshifts. [ABSTRACT FROM AUTHOR]

We analyse the two-point and marked correlation functions (mCFs) of haloes and galaxies in three variants of the chameleon f (R) gravity model using N -body simulations, and compare to a fiducial Λ cold dark matter model based on general relativity (GR). Using a halo occupation distribution (HOD) prescription, we populate dark matter haloes with galaxies, where the HOD parameters have been tuned such that the galaxy number densities and the real-space galaxy two-point correlation functions in the modified gravity models match those in GR to within 1–3 per cent. We test the idea that since the behaviour of gravity is dependent on environment, mCFs may display a measurable difference between the models. For this we test marks based on the density field and the Newtonian gravitational potential. We find that the galaxy mCF shows significant differences measured in different models on scales smaller than r ≲ 20  h −1 Mpc. Guided by simulations to identify a suitable mark, this approach could be used as a new probe of the accelerated expansion of the Universe. [ABSTRACT FROM AUTHOR]

We present predictions for the outcome of deep galaxy surveys with the James Webb Space Telescope (JWST) obtained from a physical model of galaxy formation in Λ cold dark matter. We use the latest version of the GALFORM model, embedded within a new(800 Mpc)³ darkmatter only simulation with a halo mass resolution of Mhalo > 2 x 109 h-1 M⨀. For computing full UV-to-mm galaxy spectral energy distributions, including the absorption and emission of radiation by dust, we use the spectrophotometric radiative transfer code GRASIL. The model is calibrated to reproduce a broad range of observational data at ɀ ≲ 6, and we show here that it can also predict evolution of the rest-frame far-UV luminosity function for 7 ≲ ɀ ≲ 10 which is in good agreement with observations. We make predictions for the evolution of the luminosity function from ɀ = 16 to ɀ = 0 in all broad-band filters on the Near InfraRed Camera (NIRCam) and Mid InfraRed Instrument (MIRI) on JWST and present the resulting galaxy number counts and redshift distributions. Our fiducial model predicts that ~1 galaxy per field of view will be observable at ɀ ~ 11 for a 104 s exposure with NIRCam. A variant model, which produces a higher redshift of reionization in better agreement with Planck data, predicts number densities of observable galaxies ~5 x greater at this redshift. Similar observations with MIRI are predicted not to detect any galaxies at ɀ ≳ 6. We also make predictions for the effect of different exposure times on the redshift distributions of galaxies observable with JWST, and for the angular sizes of galaxies in JWST bands. [ABSTRACT FROM AUTHOR]

Author(s): Carlton Baugh [1] The Road to Galaxy Formation by William C. Keel Springer: 2002. 230 pp. €99.95, $109, £60 Galaxies are the building blocks of the Universe. Understanding the [...]

Future galaxy surveys require realistic mock catalogues to understand and quantify systematics in order to make precise cosmological measurements. We present a halo lightcone catalogue and halo occupation distribution (HOD) galaxy catalogue built using the Millennium-XXL simulation. The halo catalogue covers the full sky, extending to z = 2.2 with a mass resolution of ~1011 h-1M☉. We use this to build a galaxy catalogue, which has an r-band magnitude limit of r < 20.0, with a median redshift of z ~ 0.2. A Monte Carlo HOD method is used to assign galaxies to the halo lightcone catalogue, and we evolve the HODs to reproduce a target luminosity function; by construction, the luminosity function of galaxies in the mock is in agreement with the Sloan Digital Sky Survey (SDSS) at low redshifts and the Galaxy and Mass Assembly (GAMA) survey at high redshifts. A Monte Carlo method is used to assign a 0.1(g - r) colour to each galaxy, and the colour distribution of galaxies at different redshifts agrees with measurements from GAMA. The clustering of galaxies in the mock for galaxies in different magnitude and redshift bins is in good agreement with measurements from SDSS and GAMA, and the colour-dependent clustering is in reasonable agreement. We show that the baryon acoustic oscillation can be measured in the mock catalogue, and the redshift-space distortions are in agreement with measurements from SDSS illustrating that this catalogue will be useful for upcoming surveys. [ABSTRACT FROM AUTHOR]