Mock Galaxy Catalogs Research Articles

Dark Energy Survey Year 3 results: galaxy sample for BAO measurement

ABSTRACT In this paper, we present and validate the galaxy sample used for the analysis of the baryon acoustic oscillation (BAO) signal in the Dark Energy Survey (DES) Y3 data. The definition is based on a colour and redshift-dependent magnitude cut optimized to select galaxies at redshifts higher than 0.5, while ensuring a high-quality determination. The sample covers ${\sim }\, 4100$ deg2to a depth of i = 22.3 (AB) at 10σ. It contains 7031 993 galaxies in the redshift range from $z$ = 0.6 to 1.1, with a mean effective redshift of 0.835. Redshifts are estimated with the machine learning algorithm dnf, and are validated using the VIPERS PDR2 sample. We find a mean redshift bias of $z_{\mathrm{bias}} {\sim }\, 0.01$ and a mean uncertainty, in units of 1 + $z$, of $\sigma _{68} {\sim }\, 0.03$. We evaluate the galaxy population of the sample, showing it is mostly built upon Elliptical to Sbc types. Furthermore, we find a low level of stellar contamination of $\lesssim 4{{\ \rm per\ cent}}$. We present the method used to mitigate the effect of spurious clustering coming from observing conditions and other large-scale systematics. We apply it to the BAO sample and calculate weights that are used to get a robust estimate of the galaxy clustering signal. This paper is one of a series dedicated to the analysis of the BAO signal in DES Y3. In the companion papers, we present the galaxy mock catalogues used to calibrate the analysis and the angular diameter distance constraints obtained through the fitting to the BAO scale.

The halo light-cone catalogues of AbacusSummit

ABSTRACT We describe a method for generating halo catalogues on the light-cone using the AbacusSummit suite of N-body simulations. The main application of these catalogues is the construction of realistic mock galaxy catalogues and weak lensing maps on the sky. Our algorithm associates the haloes from a set of coarsely spaced snapshots with their positions at the time of light-cone crossing by matching halo particles to on-the-fly light-cone particles. It then records the halo and particle information into an easily accessible product, which we call the AbacusSummit halo light-cone catalogues. Our recommended use of this product is in the halo mass regime of Mhalo > 2.1 × 1011 M⊙ h−1 for the base resolution simulations, i.e. haloes containing at least 100 particles, where the interpolated halo properties are most reliable. To test the validity of the obtained catalogues, we perform various visual inspections and consistency checks. In particular, we construct galaxy mock catalogues of emission-line galaxies (ELGs) at z ∼ 1 by adopting a modified version of the AbacusHOD script, which builds on the standard halo occupation distribution (HOD) method by including various extensions. We find that the multipoles of the autocorrelation function are consistent with the predictions from the full-box snapshot, implicitly validating our algorithm. In addition, we compute and output CMB convergence maps and find that the auto- and cross-power spectrum agrees with the theoretical prediction at the sub-per-cent level. Halo light-cone catalogues for 25 base and 2 huge simulations at the fiducial cosmology are available at DOI:10.13139/OLCF/1825069

Gravitational-wave cosmology with extreme mass-ratio inspirals

ABSTRACTThe Laser Interferometer Space Antenna (LISA) will open the mHz frequency window of the gravitational-wave (GW) landscape. Among all the new GW sources expected to emit in this frequency band, extreme mass-ratio inspirals (EMRIs) constitute a unique laboratory for astrophysics and fundamental physics. Here, we show that EMRIs can also be used to extract relevant cosmological information, complementary to both electromagnetic (EM) and other GW observations. By using the loudest EMRIs (S/N > 100) detected by LISA as dark standard sirens, statistically matching their sky localization region with mock galaxy catalogues, we find that constraints on H0 can reach ∼1.1 per cent (∼3.6 per cent) accuracy, at the 90 per cent credible level, in our best(worst)- case scenario. By considering a dynamical dark energy (DE) cosmological model, with ΛCDM parameters fixed by other observations, we further show that in our best(worst)- case scenario ∼5.9 per cent (∼12.3 per cent) relative uncertainties at the 90 per cent credible level can be obtained on w0, the DE equation of state parameter. Besides being relevant in their own right, EMRI measurements will be affected by different systematics compared to both EM and ground-based GW observations. Cross-validation with complementary cosmological measurements will therefore be of paramount importance, especially if convincing evidence of physics beyond ΛCDM emerges from future observations.

Predicting halo occupation and galaxy assembly bias with machine learning

Abstract Understanding the impact of halo properties beyond halo mass on the clustering of galaxies (namely galaxy assembly bias) remains a challenge for contemporary models of galaxy clustering. We explore the use of machine learning to predict the halo occupations and recover galaxy clustering and assembly bias in a semi-analytic galaxy formation model. For stellar mass selected samples, we train a random forest algorithm on the number of central and satellite galaxies in each dark matter halo. With the predicted occupations, we create mock galaxy catalogues and measure the clustering and assembly bias. Using a range of halo and environment properties, we find that the machine learning predictions of the occupancy variations with secondary properties, galaxy clustering, and assembly bias are all in excellent agreement with those of our target galaxy formation model. Internal halo properties are most important for the central galaxies prediction, while environment plays a critical role for the satellites. Our machine learning models are all provided in a usable format. We demonstrate that machine learning is a powerful tool for modelling the galaxy–halo connection, and can be used to create realistic mock galaxy catalogues which accurately recover the expected occupancy variations, galaxy clustering, and galaxy assembly bias, imperative for cosmological analyses of upcoming surveys.

Laguerre reconstruction of the BAO feature in halo-based mock galaxy catalogues

Fitting half-integer generalized Laguerre functions to the evolved, real-space dark matter and halo correlation functions provides a simple way to reconstruct their initial shapes. We show that this methodology also works well in a wide variety of realistic, assembly biased, velocity biased and redshift-space distorted mock galaxy catalogs. We use the linear point feature in the monopole of the redshift-space distorted correlation function to quantify the accuracy of our approach. We find that the linear point estimated from the mock galaxy catalogs is insensitive to the details of the biasing scheme at the subpercent level. However, the linear point scale in the nonlinear, biased, and redshift-space distorted field is systematically offset from its scale in the unbiased linear density fluctuation field by more than 1%. In the Laguerre reconstructed correlation function, this is reduced to sub-percent values, so it provides comparable accuracy and precision to methods that reconstruct the full density field before estimating the distance scale. The linear point in the reconstructed density fields provided by these other methods is likewise precise, accurate, and insensitive to galaxy bias. All reconstructions depend on some input parameters, and marginalizing over uncertainties in the input parameters required for reconstruction can degrade both accuracy and precision. The linear point simplifies the marginalization process, enabling more realistic estimates of the precision of the distance scale estimate for negligible additional computational cost. We show this explicitly for Laguerre reconstruction.

Fast generation of mock galaxy catalogues in modified gravity models with COLA

We investigate the viability of producing galaxy mock catalogues with COmoving Lagrangian Acceleration (COLA) simulations in Modified Gravity (MG) models employing the Halo Occupation Distribution (HOD) formalism. In this work, we focus on two theories of MG: f(R) gravity with the chameleon mechanism, and a braneworld model (nDGP) that incorporates the Vainshtein mechanism. We use a suite of full N-body simulations in MG as a benchmark to test the accuracy of COLA simulations. At the level of Dark Matter (DM), we show that COLA accurately reproduces the matter power spectrum up to k ∼ 1 h Mpc-1, while it is less accurate in reproducing the velocity field. To produce halo catalogues, we find that the rockstar halo-finder does not perform well with COLA simulations. On the other hand, using a simple Friends-of-Friends (FoF) finder and an empirical mass conversion from FoF to spherical over-density masses, we are able to produce halo catalogues in COLA that are in good agreement with those in N-body simulations. To consider the effects of the MG fifth force on the halo profile, we derive simple fitting formulae for the concentration-mass and the velocity dispersion-mass relations that we calibrate using rockstar halo catalogues in N-body simulations. We then use these results to extend the HOD formalism to modified gravity simulations in COLA. We use an HOD model with five parameters that we tune to obtain galaxy catalogues in redshift space. We find that despite the great freedom of the HOD model, MG leaves characteristic imprints in the redshift space power spectrum multipoles and these features are well captured by the COLA galaxy catalogues.

Angular clustering and host halo properties of [O ii] emitters atz> 1 in the Subaru HSC survey

AbstractWe study the angular correlation function of star-forming galaxies and properties of their host dark matter halos at z > 1 using the Hyper-Suprime Cam (HSC) Subaru Stragetic Program (SSP) survey. We use [O ii] emitters identified using two narrow-band (NB) filters, NB816 and NB921, in the Deep/UltraDeep layers, which respectively cover large angular areas of 16.3 deg2 and 16.9 deg2. Our sample contains 8302 and 9578 [O ii] emitters at z = 1.19 (NB816) and z = 1.47 (NB921), respectively. We detect a strong clustering signal over a wide angular range, $0{_{.}^{\circ}} 001$ < θ < 1 °, with bias $b=1.61^{+0.13}_{-0.11}$ (z = 1.19) and $b=2.09^{+0.17}_{-0.15}$ (z = 1.47). We also find a clear deviation of the correlation from a simple power-law form. To interpret the measured clustering signal, we adopt a halo occupation distribution (HOD) model that is constructed to explain the spatial distribution of galaxies selected by star formation rate. The observed correlation function and number density are simultaneously explained by the best-fitting HOD model. From the constrained HOD model, the average mass of halos hosting the [O ii] emitters is derived to be $\log {M_{\rm eff}/(h^{-1}\, {M}_{\odot })}=12.70^{+0.09}_{-0.07}$ and $12.61^{+0.09}_{-0.05}$ at z = 1.19 and 1.47, respectively, which will become halos with the present-day mass M ∼ 1.5 × 1013 h−1 M⊙. The satellite fraction of the [O ii] emitter sample is found to be fsat ∼ 0.15. All these values are consistent with previous studies of similar samples, but we obtain tighter constraints even in a larger parameter space due to the larger sample size from the HSC. The results obtained for host halos of [O ii] emitters in this paper enable the construction of mock galaxy catalogs and the systematic forecast study of cosmological constraints from upcoming emission line galaxy surveys such as the Subaru Prime Focus Spectrograph survey.

DETECTIFz galaxy groups in the REFINE survey – I. Group detection and quenched fraction evolution at z < 2.5

ABSTRACT We use a large K-selected sample of 299 961 galaxies from the REFINE survey, consisting of a combination of data from three of the deepest near-infrared surveys, UKIDSS UDS, COSMOS/UltraVISTA, and CFHTLS-D1/VIDEO, that were homogeneously reduced to obtain photometric redshifts and stellar masses. We detect 2588 candidate galaxy groups up to z = 3.15 at S/N > 1.5. We build a very pure ($\gt 90{{\rm \,per\ cent}}$) sample of 448 candidate groups up to z = 2.5 and study some of their properties. Cluster detection is done using the DElaunay TEssellation ClusTer IdentiFication with photo-z (detectifz) algorithm that we describe. This new group finder algorithm uses the joint probability distribution functions of redshift and stellar-mass of galaxies to detect groups as stellar-mass overdensities in overlapping redshift slices, where density is traced using Monte Carlo realization of the Delaunay Tessellation Field Estimator. We compute the algorithm selection function using mock galaxy catalogues taken from cosmological N-body simulation lightcones. Based on these simulations, we reach a completeness of $\sim \! 80{{\,\rm per\ cent}}$ for clusters (M200 > 1014M⊙) at a purity of $\sim \! 90{{\, \rm per\ cent}}$ at z < 2.5. Using our 403 most massive candidate groups, we constrain the redshift evolution of the group galaxy quenched fraction at 0.12 ≤ z < 2.32, for galaxies with 10.25 < log M⋆/M⊙ < 11 in 0.5 × R200. We find that the quenched fraction in group cores is higher than in the field in the full redshift range considered, the difference growing with decreasing redshift. This indicates either more efficient quenching mechanisms in group cores at lower redshift or pre-processing by cosmic filaments.

Testing one-loop galaxy bias: Joint analysis of power spectrum and bispectrum

We present a joint likelihood analysis of the real-space power spectrum and bispectrum measured from a variety of halo and galaxy mock catalogs. A novel aspect of this work is the inclusion of nonlinear triangle configurations for the bispectrum, made possible by a complete next-to-leading order ("one-loop") description of galaxy bias, as is already common practice for the power spectrum. Based on the goodness-of-fit and the unbiasedness of the parameter posteriors, we accomplish a stringent validation of this model compared to the leading order ("tree-level") bispectrum. Using measurement uncertainties that correspond to an effective survey volume of $6\,(\mathrm{Gpc}/h)^3$, we determine that the one-loop corrections roughly double the applicable range of scales, from $\sim 0.17\,h/\mathrm{Mpc}$ (tree-level) to $\sim 0.3\,h/\mathrm{Mpc}$. This converts into a $1.5 - 2$x improvement on constraints of the linear bias parameter at fixed cosmology, and a $1.5 - 2.4$x shrinkage of uncertainties on the amplitude of fluctuations $A_s$, which clearly demonstrates the benefit of extracting information from nonlinear scales despite having to marginalize over a larger number of bias parameters. Besides, our precise measurements of galaxy bias parameters up to fourth order allow for thorough comparisons to coevolution relations, showing excellent agreement for all contributions generated by the nonlocal action of gravity. Using these relations in the likelihood analysis does not compromise the model validity and is crucial for obtaining the quoted improvements on $A_s$. We also analyzed the impact of higher-derivative and scale-dependent stochastic terms, finding that for a subset of our tracers the former can boost the performance of the tree-level model with constraints on $A_s$ that are only slightly degraded compared to the one-loop model.

The galaxy H i–(sub)halo connection and the H i spatial clustering of local galaxies

ABSTRACT We extend the local stellar galaxy–(sub)halo connection to the atomic hydrogen (H i) component by seeding semi-empirically galaxies into a large N-body dark matter (DM) simulation. The main input to construct the mock galaxy catalogue are: our constrained stellar mass-to-(sub)halo circular velocity (M*–VDM) relation, assuming a scatter independent of any galaxy property, and the empirical $M_{\rm H\, \small {I}}$ conditional probability distributions given M* for central and satellite galaxies. We find that the $\langle \log \mbox{$M_{\rm H\, \small {I}}$}\rangle -\log \mbox{$M_{\rm DM}$}$ relation is not a monotonic increasing function. It increases with mass up to $\mbox{$M_{\rm DM}$}\sim 10^{12}$ M⊙, attaining a maximum of $\langle \log (\mbox{$M_{\rm H\, \small {I}}$}/\mbox{M$_{\odot }$})\rangle \sim 9.2$, and at higher (sub)halo masses, $\langle \log (\mbox{$M_{\rm H\, \small {I}}$})\rangle$ decreases slightly with MDM. The scatter around it is also large and mass dependent. The bivariate $M_{\rm H\, \small {I}}$ and MDM distribution is broad and bimodal, specially at $\mbox{$M_{\rm DM}$}\gtrsim 10^{12}$ M⊙, which is inherited from the input $M_{\rm H\, \small {I}}$ conditional distributions. We also report the total (central+satellites) H i gas mass within haloes, $M^{\rm tot}_{\rm H\, \small {I}}$, as a function of MDM. The mean $\mbox{$M^{\rm tot}_{\rm H\, \small {I}}$}$–$\mbox{$M_{\rm DM}$}$ relation is an increasing monotonic function. The galaxy spatial clustering increases weakly as the $M_{\rm H\, \small {I}}$ threshold increases. Our H i mock galaxies cluster more in comparison to the blind H i ALFALFA (Arecibo Fast Legacy ALFA) survey but we show that it is mainly due to the selection effects. We discuss the implications of our results in the light of predictions from semi-analytical models and hydrodynamics simulations of galaxy evolution.

The Uchuu simulations: Data Release 1 and dark matter halo concentrations

ABSTRACT We introduce the Uchuu suite of large high-resolution cosmological N-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion (12 8003) dark matter particles in a box of side-length 2.0 $\, h^{-1} \, \rm Gpc$, with particle mass of 3.27 × 108$\, h^{-1}\, \rm M_{\odot }$. The highest resolution simulation, Shin-Uchuu, consists of 262 billion (64003) particles in a box of side-length 140 $\, h^{-1} \, \rm Mpc$, with particle mass of 8.97 × 105$\, h^{-1}\, \rm M_{\odot }$. Combining these simulations, we can follow the evolution of dark matter haloes and subhaloes spanning those hosting dwarf galaxies to massive galaxy clusters across an unprecedented volume. In this first paper, we present basic statistics, dark matter power spectra, and the halo and subhalo mass functions, which demonstrate the wide dynamic range and superb statistics of the Uchuu suite. From an analysis of the evolution of the power spectra, we conclude that our simulations remain accurate from the baryon acoustic oscillation scale down to the very small. We also provide parameters of a mass–concentration model, which describes the evolution of halo concentration and reproduces our simulation data to within 5 per cent for haloes with masses spanning nearly eight orders of magnitude at redshift 0 ≤ z ≤ 14. There is an upturn in the mass–concentration relation for the population of all haloes and of relaxed haloes at z ≳ 0.5, whereas no upturn is detected at z < 0.5. We make publicly available various N-body products as part of Uchuu Data Release 1 on the Skies & Universes site.1 Future releases will include gravitational lensing maps and mock galaxy, X-ray cluster, and active galactic nucleus catalogues.

Does jackknife scale really matter for accurate large-scale structure covariances?

ABSTRACT The jackknife method gives an internal covariance estimate for large-scale structure surveys and allows model-independent errors on cosmological parameters. Using the SDSS-III BOSS CMASS sample, we study how the jackknife size and number of resamplings impact the precision of the covariance estimate on the correlation function multipoles and the error on the inferred baryon acoustic scale. We compare the measurement with the MultiDark Patchy mock galaxy catalogues, and we also validate it against a set of lognormal mocks with the same survey geometry. We build several jackknife configurations that vary in size and number of resamplings. We introduce the Hartlap factor in the covariance estimate that depends on the number of jackknife resamplings. We also find that it is useful to apply the tapering scheme to estimate the precision matrix from a limited number of resamplings. The results from CMASS and mock catalogues show that the error estimate of the baryon acoustic scale does not depend on the jackknife scale. For the shift parameter α, we find an average error of 1.6 per cent, 2.2 per cent and 1.2 per cent, respectively, from CMASS, Patchy, and lognormal jackknife covariances. Despite these uncertainties fluctuate significantly due to some structural limitations of the jackknife method, our α estimates are in reasonable agreement with published pre-reconstruction analyses. Jackknife methods will provide valuable and complementary covariance estimates for future large-scale structure surveys.

Beyond the Yamamoto approximation: Anisotropic power spectra and correlation functions with pairwise lines of sight

Conventional estimators of the anisotropic power spectrum and two-point correlation function (2PCF) adopt the `Yamamoto approximation', fixing the line-of-sight of a pair of galaxies to that of just one of its members. Whilst this is accurate only to first-order in the characteristic opening angle $\theta_\max$, it allows for efficient implementation via Fast Fourier Transforms (FFTs). This work presents practical algorithms for computing the power spectrum and 2PCF multipoles using pairwise lines-of-sight, adopting either the galaxy midpoint or angle bisector definitions. Using newly derived infinite series expansions for spherical harmonics and Legendre polynomials, we construct estimators accurate to arbitrary order in $\theta_\max$, though note that the midpoint and bisector formalisms themselves differ at fourth order. Each estimator can be straightforwardly implemented using FFTs, requiring only modest additional computational cost relative to the Yamamoto approximation. We demonstrate the algorithms by applying them to a set of realistic mock galaxy catalogs, and find both procedures produce comparable results for the 2PCF, with a slight preference for the bisector power spectrum algorithm, albeit at the cost of greater memory usage. Such estimators provide a useful method to reduce wide-angle systematics for future surveys.

The H i and stellar mass bivariate distribution of centrals and satellites for all, late-, and early-type local galaxies

ABSTRACT We characterize the conditional distributions of the H i gas-to-stellar mass ratio, $\mbox{$R_{\rm H\,\rm{i}}$}\equiv \mbox{$M_{\rm H\,\rm{i}}$}/\mbox{$M_{\ast }$}$, given the stellar mass, M*, of local galaxies from M* ∼ 107–1012 M⊙ separated into centrals and satellites as well as into late- and early-type galaxies (LTGs and ETGs, respectively). To do so, we use (1) the homogeneous ‘eXtended GALEX Arecibo SDSS Survey’, xGASS (Catinella et al. 2018), by re-estimating their upper limits and taking into account them in our statistical analysis; and (2) the results from a large compilation of H i data reported in Calette et al. (2018). We use the $R_{\rm H\,\rm{i}}$ conditional distributions combined with the Galaxy Stellar Mass Function to infer the bivariate $M_{\rm H\,\rm{i}}$ and M* distribution of all galaxies as well of the late/early-type and central/satellite subsamples and their combinations. Satellites are on average less H i gas-rich than centrals at low and intermediate masses, with differences being larger for ETGs than LTGs; at M* > 3−5 × 1010 M⊙ the differences are negligible. The differences in the H i gas content are much larger between LTGs and ETGs than between centrals and satellites. Our empirical H i Mass Function is strongly dominated by central galaxies at all masses. The empirically constrained bivariate $M_{\rm H\,\rm{i}}$ and M* distributions presented here can be used to compare and constrain theoretical predictions as well as to generate galaxy mock catalogues.

Rosella: a mock catalogue from the P-Millennium simulation

ABSTRACT The scientific exploitation of the Dark Energy Spectroscopic Instrument Bright Galaxy Survey (DESI BGS) data requires the construction of mocks with galaxy population properties closely mimicking those of the actual DESI BGS targets. We create a high-fidelity mock galaxy catalogue, including information about galaxies and their host dark matter subhaloes. The mock catalogue uses subhalo abundance matching with scatter to populate the P-Millennium N-body simulation with galaxies at the median BGS redshift of ∼0.2, using formation redshift information to assign 0.1(g − r) rest-frame colours. The mock provides information about r-band absolute magnitudes, 0.1(g − r) rest-frame colours, and 3D positions and velocities of a complete sample of DESI BGS galaxies in a volume of (542 Mpc h−1)3, as well as the masses of host dark matter haloes. This P-Millennium DESI BGS mock catalogue is ideally suited for the tuning of approximate mocks unable to resolve subhaloes that DESI BGS galaxies reside in, to test for systematics in analysis pipelines and to interpret (non-cosmological focused) DESI BGS analysis.

A flexible modelling of galaxy assembly bias

ABSTRACT We use the illustris TNG300 magneto-hydrodynamic simulation, the sage semi-analytical model, and the subhalo abundance matching technique (SHAM) to examine the diversity in predictions for galaxy assembly bias (i.e. the difference in the large-scale clustering of galaxies at a fixed halo mass due to correlations with the assembly history and other properties of host haloes). We consider samples of galaxies selected according to their stellar mass or star formation rate at various redshifts. We find that all models predict an assembly bias signal of different magnitude, redshift evolution, and dependence with selection criteria and number density. To model these non-trivial dependences, we propose an extension to the standard SHAM technique so it can include arbitrary amounts of assembly bias. We do this by preferentially selecting subhaloes with the same internal property but different individual large-scale bias. We find that with this model, we can successfully reproduce the galaxy assembly bias signal in either sage or the tng, for all redshifts and galaxy number densities. We anticipate that this model can be used to constrain the level of assembly bias in observations and aid in the creation of more realistic mock galaxy catalogues.

Protocluster detection in simulations of HSC–SSP and the 10-yr LSST forecast, using PCcones

ABSTRACT The progenitors of present-day galaxy clusters give important clues about the evolution of the large-scale structure, cosmic mass assembly, and galaxy evolution. Simulations are a major tool for these studies since they are used to interpret observations. In this work, we introduce a set of ‘protocluster-light-cones’, dubbed PCcones. They are mock galaxy catalogues generated from the Millennium Simulation with the L-GALAXIES semi-analytic model. These light-cones were constructed by placing a desired structure at the redshift of interest in the centre of the cone. This approach allows to adopt a set of observational constraints, such as magnitude limits and uncertainties in magnitudes and photometric redshifts (photo-zs) to produce realistic simulations of photometric surveys. We show that photo-zs obtained with PCcones are more accurate than those obtained directly with the Millennium Simulation, mostly due to the difference in how apparent magnitudes are computed. We apply PCcones in the determination of the expected accuracy of protocluster detection using photo-zs in the z = 1−3 range in the wide layer of HSC–SSP and the 10-yr LSST forecast. With our technique, we expect to recover only $\sim 38{{\ \rm per\ cent}}$ and $\sim 43{{\ \rm per\ cent}}$ of all massive galaxy cluster progenitors with more than 70 per cent of purity for HSC–SSP and LSST, respectively. Indeed, the combination of observational constraints and photo-z uncertainties affects the detection of structures critically for both emulations, indicating the need of spectroscopic redshifts to improve detection. We also compare our mocks of the Deep CFHTLS at z < 1.5 with observed cluster catalogues, as an extra validation of the light-cones and methods.

Constraining M ν with the bispectrum. Part II. The information content of the galaxy bispectrum monopole

Massive neutrinos suppress the growth of structure on small scales and leave an imprint on large-scale structure that can be measured to constrain their total mass, M ν. With standard analyses of two-point clustering statistics, M ν constraints are severely limited by parameter degeneracies. Ref. [1] demonstrated that the bispectrum, the next higher-order statistic, can break these degeneracies and dramatically improve constraints on M ν and other cosmological parameters. In this paper, we present the constraining power of the redshift-space galaxy bispectrum monopole, Bg 0. We construct the Molino suite of 75,000 mock galaxy catalogs from the Quijote N-body simulations using the halo occupation distribution (HOD) model, which provides a galaxy bias framework well-suited for simulation-based approaches. Using these mocks, we present Fisher matrix forecasts for {Ωm, Ωb, h, ns , σ8, M ν} and quantify, for the first time, the information content of the Bg 0 down to nonlinear scales. For k max = 0.5 h/Mpc, Bg 0 improves constraints on Ωm, Ωb, h, ns , σ8, and M ν by 2.8, 3.1, 3.8, 4.2, 4.2, and 4.6× over the power spectrum, after marginalizing over HOD parameters. Even with priors from Planck, Bg 0 improves all of the cosmological constraints by ≳ 2×. In fact, for Pg 0+Pg 2 and Bg 0 out to k max = 0.5 h/Mpc with Planck priors, we achieve a 1σ M ν constraint of 0.048 eV, which is tighter than the current best cosmological constraint. While effects such as survey geometry and assembly bias will have an impact, these constraints are derived for (1 h-1 Gpc)3, a substantially smaller volume than upcoming surveys. Therefore, we conclude that the galaxy bispectrum will significantly improve cosmological constraints for upcoming galaxy surveys — especially for M ν.

Emerge: constraining merging probabilities and time-scales of close galaxy pairs

ABSTRACT Theoretical models are vital for exploring the galaxy merger process, which plays a crucial role in the evolution of galaxies. Recent advances in modelling have placed tight constraints on the build-up of stellar material in galaxies across cosmic time. Despite these successes, extracting the merger rates from observable data remains a challenge. Differences in modelling techniques, combined with limited observational data, drive conflicting conclusions on the merging time-scales of close pairs. We employ an empirical model for galaxy formation that links galaxy properties to the growth of simulated dark matter haloes, along with mock light-cone galaxy catalogues, to probe the dependences of pair merging probabilities and merging time-scales. In this work, we demonstrate that the pair merging probabilities are best described by a logistic function and that mean merging time-scales can be well approximated by a linear relation in the projected separation and line of sight velocity difference in observed pairs. Together, our fitting formulas can accurately predict merger rates from galaxy pairs to at least z ∼ 4 under a wide variety of pair selection criteria. Additionally, we show that some commonly used pair selection criteria may not represent a suitable sample of galaxies to reproduce underlying merger rates. Finally, we conclude from our analysis that observation time-scales are primarily driven by dynamics and are not strongly impacted by the star formation properties of the component galaxies.

Multiwavelength mock galaxy catalogues of the low-redshift Universe

ABSTRACT We present a new suite of mock galaxy catalogues mimicking the low-redshift Universe, based on an updated halo occupation distribution (HOD) model and a scaling relation between optical properties and the neutral hydrogen (H i) content of galaxies. Our algorithm is constrained by observations of the luminosity function and luminosity- and colour-dependent clustering of Sloan Digital Sky Survey (SDSS) galaxies, as well as the H i mass function and H i-dependent clustering of massive H i-selected galaxies in the Arecibo Legacy Fast ALFA (ALFALFA) survey. Mock central and satellite galaxies with realistic values of r-band luminosity, g − r and u − r colour, stellar mass and H i mass are populated in an N-body simulation, inheriting a number of properties of the density and tidal environment of their host haloes. The host halo of each central galaxy is also ‘baryonified’ with realistic spatial distributions of stars as well as hot and cold gas, along with the corresponding rotation curve. Our default HOD assumes that galaxy properties are a function of group halo mass alone, and can optionally include effects such as galactic conformity and colour-dependent galaxy assembly bias. The mocks predict the relation between the stellar mass and H i mass of massive H i galaxies, as well as the 2-point cross-correlation function of spatially co-located optical and H i-selected samples. They enable novel null tests for galaxy assembly bias, provide predictions for the H i velocity width function, and clarify the origin and universality of the radial acceleration relation in the Lambda cold dark matter framework.