ORCID Profile
0000-0002-6154-7224
Current Organisations
ICRAR-UWA/ASTRO 3D
,
Pawsey Supercomputing Centre
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Publisher: American Astronomical Society
Date: 20-01-2017
Publisher: Oxford University Press (OUP)
Date: 18-12-2021
Abstract: We build upon Ordering Points To Identify the Clustering Structure (optics ), a hierarchical clustering algorithm well known to be a robust data miner, in order to produce halo-optics , an algorithm designed for the automatic detection and extraction of all meaningful clusters between any two arbitrary sizes. We then apply halo-optics to the 3D spatial positions of halo particles within four separate synthetic Milky Way-type galaxies, classifying the stellar and dark matter structural hierarchies. Through visualization of the halo-optics output, we compare its structure identification to the state-of-the-art galaxy/(sub)halo finder VELOCIraptor , finding excellent agreement even though halo-optics does not consider kinematic information in this current implementation. We conclude that halo-optics is a robust hierarchical halo finder, although its determination of lower spatial-density features such as the tails of streams could be improved with the inclusion of extra localized information such as particle kinematics and stellar metallicity into its distance metric.
Publisher: Oxford University Press (OUP)
Date: 09-01-2019
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 08-07-2021
Publisher: Oxford University Press (OUP)
Date: 02-09-2019
Abstract: We combine the shark semi-analytic model of galaxy formation with the prospect software tool for spectral energy distribution (SED) generation to study the multiwavelength emission of galaxies from the far-ultraviolet (FUV) to the far-infrared (FIR) at 0 ≤ z ≤ 10. We produce a physical model for the attenuation of galaxies across cosmic time by combining a local Universe empirical relation to compute the dust mass of galaxies from their gas metallicity and mass, attenuation curves derived from radiative transfer calculations of galaxies in the eagle hydrodynamic simulation suite, and the properties of shark galaxies. We are able to produce a wide range of galaxies, from the z = 8 star-forming galaxies with almost no extinction, z = 2 submillimetre galaxies, down to the normal star-forming and red-sequence galaxies at z = 0. Quantitatively, we find that shark reproduces the observed (i) z = 0 FUV-to-FIR, (ii) 0 ≤ z ≤ 3 rest-frame K-band, and (iii) 0 ≤ z ≤ 10 rest-frame FUV luminosity functions, (iv) z ≤ 8 UV slopes, (v) the FUV-to-FIR number counts (including the widely disputed 850 μm), (vi) redshift distribution of bright $850\\, \\mu$m galaxies, and (vii) the integrated cosmic SED from z = 0 to 1 to an unprecedented level. This is achieved without the need to invoke changes in the stellar initial mass function, dust-to-metal mass ratio, or metal enrichment time-scales. Our model predicts star formation in galaxy discs to dominate in the FUV-to-optical, while bulges dominate at the NIR at all redshifts. The FIR sees a strong evolution in which discs dominate at z ≤ 1 and starbursts (triggered by both galaxy mergers and disc instabilities, in an even mix) dominate at higher redshifts, even out to z = 10.
Publisher: American Physical Society (APS)
Date: 25-08-2008
Publisher: Oxford University Press (OUP)
Date: 20-06-2022
Abstract: We present C luSTAR-ND, a fast hierarchical galaxy/(sub)halo finder that produces Clustering Structure via Transformative Aggregation and Rejection in N-Dimensions. It is designed to improve upon H alo-OPTICS – an algorithm that automatically detects and extracts significant astrophysical clusters from the 3D spatial positions of simulation particles – by decreasing run-times, possessing the capability for metric adaptivity, and being readily applicable to data with any number of features. We directly compare these algorithms and find that not only does C luSTAR-ND produce a similarly robust clustering structure, it does so in a run-time that is at least 3 orders of magnitude faster. In optimizing C luSTAR-ND’s clustering performance, we have also carefully calibrated 4 of the 7 C luSTAR-ND parameters which – unless specified by the user – will be automatically and optimally chosen based on the input data. We conclude that C luSTAR-ND is a robust astrophysical clustering algorithm that can be leveraged to find stellar satellite groups on large synthetic or observational data sets.
Publisher: Oxford University Press (OUP)
Date: 21-06-2017
Publisher: Oxford University Press (OUP)
Date: 12-10-2020
Abstract: We present the first detection of mass-dependent galactic spin alignments with local cosmic filaments with & σ confidence using IFS kinematics. The 3D network of cosmic filaments is reconstructed on Mpc scales across GAlaxy and Mass Assembly fields using the cosmic web extractor DisPerSe. We assign field galaxies from the SAMI survey to their nearest filament segment in 3D and estimate the degree of alignment between SAMI galaxies’ kinematic spin axis and their nearest filament in projection. Low-mass galaxies align their spin with their nearest filament while higher mass counterparts are more likely to display an orthogonal orientation. The stellar transition mass from the first trend to the second is bracketed between $10^{10.4}$ and $10^{10.9}\\, \\mathrm{ M}_{\\odot }$, with hints of an increase with filament scale. Consistent signals are found in the Horizon-AGN cosmological hydrodynamic simulation. This supports a scenario of early angular momentum build-up in vorticity rich quadrants around filaments at low stellar mass followed by progressive flip of spins orthogonal to the cosmic filaments through mergers at high stellar mass. Conversely, we show that dark matter only simulations post-processed with a semi-analytical model treatment of galaxy formation struggles to reproduce this alignment signal. This suggests that gas physics is key in enhancing the galaxy-filament alignment.
Publisher: Oxford University Press (OUP)
Date: 05-08-2019
Abstract: Accurately predicting the shape of the H i velocity function (VF) of galaxies is regarded widely as a fundamental test of any viable dark matter model. Straightforward analyses of cosmological N-body simulations imply that the Λ cold dark matter (ΛCDM) model predicts an overabundance of low circular velocity galaxies when compared to observed H i VFs. More nuanced analyses that account for the relationship between galaxies and their host haloes suggest that how we model the influence of baryonic processes has a significant impact on H i VF predictions. We explore this in detail by modelling H i emission lines of galaxies in the shark semi-analytic galaxy formation model, built on the surfs suite of ΛCDM N-body simulations. We create a simulated ALFALFA survey, in which we apply the survey selection function and account for effects such as beam confusion, and compare simulated and observed H i velocity width distributions, finding differences of ≲ 50 per cent, orders of magnitude smaller than the discrepancies reported in the past. This is a direct consequence of our careful treatment of survey selection effects and, importantly, how we model the relationship between galaxy and halo circular velocity – the H i mass–maximum circular velocity relation of galaxies is characterized by a large scatter. These biases are complex enough that building a VF from the observed H i linewidths cannot be done reliably.
Publisher: American Physical Society (APS)
Date: 11-12-2009
Publisher: Oxford University Press (OUP)
Date: 09-03-2021
Abstract: Using high-resolution Hubble Space Telescope imaging data, we perform a visual morphological classification of ∼36 000 galaxies at z & 1 in the deep extragalactic visible legacy survey/cosmological evolution survey region. As the main goal of this study, we derive the stellar mass function (SMF) and stellar mass density (SMD) sub- ided by morphological types. We find that visual morphological classification using optical imaging is increasingly difficult at z & 1 as the fraction of irregular galaxies and merger systems (when observed at rest-frame UV/blue wavelengths) dramatically increases. We determine that roughly two-thirds of the total stellar mass of the Universe today was in place by z ∼ 1. Double-component galaxies dominate the SMD at all epochs and increase in their contribution to the stellar mass budget to the present day. Elliptical galaxies are the second most dominant morphological type and increase their SMD by ∼2.5 times, while by contrast, the pure-disc population significantly decreases by $\\sim 85{{\\ \\rm per\\ cent}}$. According to the evolution of both high- and low-mass ends of the SMF, we find that mergers and in situ evolution in discs are both present at z & 1, and conclude that double-component galaxies are predominantly being built by the in situ evolution in discs (apparent as the growth of the low-mass end with time), while mergers are likely responsible for the growth of ellipticals (apparent as the increase of intermediate/high-mass end).
Publisher: American Astronomical Society
Date: 30-11-2020
Publisher: Oxford University Press (OUP)
Date: 24-09-2014
Publisher: Oxford University Press (OUP)
Date: 07-03-2016
DOI: 10.1093/MNRAS/STW513
Publisher: Oxford University Press (OUP)
Date: 16-02-2017
DOI: 10.1093/MNRAS/STX375
Publisher: Oxford University Press (OUP)
Date: 21-04-2020
Abstract: We study the Intra-Halo Stellar Component (IHSC) of Milky Way-mass systems up to galaxy clusters in the Horizon-AGN cosmological hydrodynamical simulation. We identify the IHSC using an improved phase-space galaxy finder algorithm which provides an adaptive, physically motivated, and shape-independent definition of this stellar component, that can be applied to haloes of arbitrary masses. We explore the IHSC mass fraction – total halo’s stellar mass, $f_{M_{*,\\mathrm{IHSC}}} - M_{*}$, relation, and the physical drivers of its scatter. We find that on average, the $f_{M_{*,\\mathrm{IHSC}}}$ increases with total stellar mass, with the scatter decreasing strongly with mass from 2 dex at $M_{*,\\mathrm{tot}}\\simeq 10^{11}\\, \\mathrm{M}_\\odot$ to 0.3 dex at group masses. At high masses, $M_{*,\\mathrm{tot}}\\gt 10^{11.5}\\, \\mathrm{M}_\\odot$, $f_{M_{*,\\mathrm{IHSC}}}$ increases with the number of substructures, and with the mass ratio between the central galaxy and largest satellite, at fixed M*, tot. From mid-size groups and systems below $M_{*,\\mathrm{tot}}\\lt 10^{12}\\, \\mathrm{M}_\\odot$, we find that the central galaxy’s stellar rotation-to-dispersion velocity ratio, V/σ, displays the strongest (anti)-correlation with $f_{M_{*,\\mathrm{IHSC}}}$ at fixed M*, tot of all the galaxy and halo properties explored, transitioning from $f_{M_{*,\\mathrm{IHSC}}}\\lt 0.1$ per cent for high V/σ, to $f_{M_{*,\\mathrm{IHSC}}}\\approx 5$ per cent for low V/σ galaxies. By studying the $f_{M_{*,\\mathrm{IHSC}}}$ temporal evolution, we find that, in the former, mergers not always take place, but if they did, they happened early (z & 1), while the high $f_{M_{*,\\mathrm{IHSC}}}$ population displays a much more active merger history. In the case of massive groups and galaxy clusters, $M_{*,\\mathrm{tot}}\\gtrsim 10^{12}\\, \\mathrm{M}_\\odot$, a fraction $f_{M_{*,\\mathrm{IHSC}}}\\approx 10-20$ per cent is reached at z ≈ 1 and then they evolve across lines of constant $f_{M_{*,\\mathrm{IHSC}}}$ modulo some small perturbations. Because of the limited simulation’s volume, the latter is only tentative and requires a larger s le of simulated galaxy clusters to confirm.
Publisher: American Astronomical Society
Date: 08-2016
Publisher: Oxford University Press (OUP)
Date: 03-08-2017
Publisher: Informa UK Limited
Date: 30-08-2023
Publisher: Oxford University Press (OUP)
Date: 10-01-2018
DOI: 10.1093/MNRAS/STY061
Publisher: Oxford University Press (OUP)
Date: 23-10-2021
Abstract: Predicting the merger time-scale (τmerge) of merging dark matter haloes, based on their orbital parameters and the structural properties of their hosts, is a fundamental problem in gravitational dynamics that has important consequences for our understanding of cosmological structure formation and galaxy formation. Previous models predicting τmerge have shown varying degrees of success when compared to the results of cosmological N-body simulations. We build on this previous work and propose a new model for τmerge that draws on insights derived from these simulations. We find that published predictions can provide reasonable estimates for τmerge based on orbital properties at infall, but tend to underpredict τmerge inside the host virial radius (R200) because tidal stripping is neglected, and overpredict it outside R200 because the host mass is underestimated. Furthermore, we find that models that account for orbital angular momentum via the circular radius Rcirc underpredict (overpredict) τmerge for bound (unbound) systems. By fitting for the dependence of τmerge on various orbital and host halo properties, we derive an improved model for τmerge that can be applied to a merging halo at any point in its orbit. Finally, we discuss briefly the implications of our new model for τmerge for semi-analytical galaxy formation modelling.
Publisher: Elsevier BV
Date: 07-2009
Publisher: Oxford University Press (OUP)
Date: 20-12-2017
Publisher: Oxford University Press (OUP)
Date: 15-05-2014
DOI: 10.1093/MNRAS/STU705
Publisher: Oxford University Press (OUP)
Date: 14-02-2020
Abstract: Linking the properties of galaxies to the assembly history of their dark matter haloes is a central aim of galaxy evolution theory. This paper introduces a dimensionless parameter s ∈ [0, 1], the ‘tree entropy’, to parametrize the geometry of a halo’s entire mass assembly hierarchy, building on a generalization of Shannon’s information entropy. By construction, the minimum entropy (s = 0) corresponds to smoothly assembled haloes without any mergers. In contrast, the highest entropy (s = 1) represents haloes grown purely by equal-mass binary mergers. Using simulated merger trees extracted from the cosmological N-body simulation SURFS, we compute the natural distribution of s, a skewed bell curve peaking near s = 0.4. This distribution exhibits weak dependences on halo mass M and redshift z, which can be reduced to a single dependence on the relative peak height δc/σ(M, z) in the matter perturbation field. By exploring the correlations between s and global galaxy properties generated by the SHARK semi-analytic model, we find that s contains a significant amount of information on the morphology of galaxies – in fact more information than the spin, concentration, and assembly time of the halo. Therefore, the tree entropy provides an information-rich link between galaxies and their dark matter haloes.
Publisher: Oxford University Press (OUP)
Date: 11-08-2009
Publisher: Cambridge University Press (CUP)
Date: 21-11-2013
DOI: 10.1017/S0022377813000895
Abstract: Tokamak edge plasma was analyzed by applying the multifractal detrend fluctuation analysis (MF-DFA) technique. This method has found wide application in the analysis of correlations and characterization of scaling behavior of the time-series data in physiology, finance, and natural sciences. The time evolution of the ion saturation current ( I s ), the floating potential fluctuation ( V f ), the poloidal electric field ( E p ), and the radial particle flux (Γ r ) has been measured by using a set of Langmuir probes consisting of four tips on the probe head. The generalized Hurst exponents ( h(q) ), local fluctuation function ( F q (s) ), the Rényi exponents (τ( q )) as well as the multifractal spectrum f (α h ) have been calculated by applying the MF-DFA method to I s , V f , and the magnetohydrodynamic (MHD) fluctuation signal. Furthermore, we perform the shuffling and the phase randomization techniques to detect the sources of multifractality. The nonlinearity shape of τ( q ) reveals a multifractal behavior of the time-series data. The results show that in the presence of biasing, I s , V f , E p , and Γ r reduce about 25%, 90%, 70%, and 50%, respectively, compared with the situation with no biasing. Also, they reduce about 15%, 90%, 35%, and 25%, respectively, after resonant helical magnetic field (RHF) application. In the presence of biasing or RHF, the litude of the power spectrum of I s , V f , Γ r , and MHD activity reduce remarkably in all the ranges of frequency, while their h(q) increase. The values of h(q) have been restricted between 0.6 and 0.68. These results are evidence of the existence of long-range correlations in the plasma edge turbulence. They also show the self-similar nature of the plasma edge fluctuations. Biasing or RHF reduces the amount of F q (s) . The multifractal spectrum width of I s , V f , and MHD fluctuation litude reduce about 60%, 70%, and 42%, respectively, by applying biasing. In the presence of RHF, their width reduces about 60%, 85%, and 75%, respectively. It means that biasing and RHF reduce the degree of multifractality.
Publisher: Oxford University Press (OUP)
Date: 06-2009
Publisher: Oxford University Press (OUP)
Date: 22-03-2017
DOI: 10.1093/MNRAS/STX657
Publisher: Oxford University Press (OUP)
Date: 23-04-2012
Publisher: Oxford University Press (OUP)
Date: 14-02-2019
DOI: 10.1093/MNRAS/STZ435
Publisher: Astrophysics Source Code Library
Date: 2013
DOI: 10.20356/C4BC7R
Publisher: American Astronomical Society
Date: 05-03-2014
Publisher: Oxford University Press (OUP)
Date: 14-11-2019
Abstract: Galaxy cluster outskirts mark the transition region from the mildly non-linear cosmic web to the highly non-linear, virialised, cluster interior. It is in this transition region that the intra-cluster medium (ICM) begins to influence the properties of accreting galaxies and groups, as ram pressure impacts a galaxy’s cold gas content and subsequent star formation rate. Conversely, the thermodynamical properties of the ICM in this transition region should also feel the influence of accreting substructure (i.e. galaxies and groups), whose passage can drive shocks. In this paper, we use a suite of cosmological hydrodynamical zoom simulations of a single galaxy cluster, drawn from the nIFTy comparison project, to study how the dynamics of substructure accreted from the cosmic web influences the thermodynamical properties of the ICM in the cluster’s outskirts. We demonstrate how features evident in radial profiles of the ICM (e.g. gas density and temperature) can be linked to strong shocks, transient and short-lived in nature, driven by the passage of substructure. The range of astrophysical codes and galaxy formation models in our comparison are broadly consistent in their predictions (e.g. agreeing when and where shocks occur, but differing in how strong shocks will be) this is as we would expect of a process driven by large-scale gravitational dynamics and strong, inefficently radiating, shocks. This suggests that mapping such shock structures in the ICM in a cluster’s outskirts (via e.g. radio synchrotron emission) could provide a complementary measure of its recent merger and accretion history.
Publisher: Oxford University Press (OUP)
Date: 06-03-2018
DOI: 10.1093/MNRAS/STY590
Publisher: Oxford University Press (OUP)
Date: 10-09-2014
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.34
Abstract: Merger trees harvested from cosmological N -body simulations encode the assembly histories of dark matter halos over cosmic time and are a fundamental component of semi-analytical models of galaxy formation. The ability to compare the tools used to construct merger trees, namely halo finders and tree building algorithms, in an unbiased and systematic manner is critical to assess the quality of merger trees. In this paper, we present the dendrogram, a novel method to visualise merger trees, which provides a comprehensive characterisation of a halo’s assembly history—tracking subhalo orbits, halo merger events, and the general evolution of halo properties. We show the usefulness of the dendrogram as a diagnostic tool of merger trees by comparing halo assembly simulation analysed with three different halo finders—VELOCI raptor , AHF, and R ockstar —and their associated tree builders. Based on our analysis of the resulting dendrograms, we highlight how they have been used to motivate improvements to VELOCI raptor . The dendrogram software is publicly available online, at: hyspoulton/MergerTree-Dendrograms .
Publisher: Oxford University Press (OUP)
Date: 19-08-2019
Abstract: We present a new self-consistent method for incorporating Dark Matter Annihilation Feedback (DMAF) in cosmological N-body simulations. The power generated by DMAF is evaluated at each dark matter (DM) particle which allows for flexible energy injection into the surrounding gas based on the specific DM annihilation model under consideration. Adaptive, in idual time-steps for gas and DM particles are supported and a new time-step limiter, derived from the propagation of a Sedov–Taylor blast wave, is introduced. We compare this donor-based approach with a receiver-based approach used in recent studies and illustrate the differences by means of a toy ex le. Furthermore, we consider an isolated halo and a cosmological simulation and show that for these realistic cases, both methods agree well with each other. The extension of our implementation to scenarios such as non-local energy injection, velocity-dependent annihilation cross-sections, and DM decay is straightforward.
Publisher: Oxford University Press (OUP)
Date: 02-03-2012
Publisher: Oxford University Press (OUP)
Date: 25-01-2020
Abstract: We model the large-scale linear galaxy bias bg(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: bg(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.
Publisher: Oxford University Press (OUP)
Date: 10-07-2018
Publisher: American Astronomical Society
Date: 10-11-2021
Publisher: Oxford University Press (OUP)
Date: 10-04-2018
DOI: 10.1093/MNRAS/STY879
Publisher: Oxford University Press (OUP)
Date: 03-08-2018
Publisher: Oxford University Press (OUP)
Date: 15-01-2018
DOI: 10.1093/MNRAS/STY118
Publisher: IOP Publishing
Date: 25-05-2017
Publisher: Oxford University Press (OUP)
Date: 21-01-2019
DOI: 10.1093/MNRAS/STZ212
Publisher: Elsevier BV
Date: 09-2020
Publisher: Oxford University Press (OUP)
Date: 09-01-2020
Abstract: The standard cosmological paradigm currently lacks a detailed account of physics in the dark sector, the dark matter and energy that dominate cosmic evolution. In this paper, we consider the distinguishing factors between three alternative models – warm dark matter, quintessence, and coupled dark matter–energy – and lambda cold dark matter (ΛCDM) through numerical simulations of cosmological structure formation. Key halo statistics – halo spin/velocity alignment between large-scale structure and neighbouring haloes, halo formation time, and migration – were compared across cosmologies within the redshift range 0 ≤ z ≤ 2.98. We found the alignment of halo motion and spin to large-scale structures and neighbouring haloes to be similar in all cosmologies for a range of redshifts. The search was extended to low-density regions, avoiding non-linear disturbances of halo spins, yet very similar alignment trends were found between cosmologies, which are difficult to characterize and use as a probe of cosmology. We found that haloes in quintessence cosmologies form earlier than their ΛCDM counterparts. Relating this to the fact that such haloes originate in high-density regions, such findings could hold clues to distinguishing factors for the quintessence cosmology from the standard model. However, in general, halo statistics are not an accurate probe of the dark sector physics.
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.18
Abstract: We present T ree F rog , a massively parallel halo merger tree builder that is capable comparing different halo catalogues and producing halo merger trees. The code is written in c++11, use the MPI and OpenMP API’s for parallelisation, and includes python tools to read/manipulate the data products produced. The code correlates binding energy sorted particle ID lists between halo catalogues, determining optimal descendant rogenitor matches using multiple snapshots, a merit function that maximises the number of shared particles using pseudo-radial moments, and a scheme for correcting halo merger tree pathologies. Focusing on VELOCI raptor catalogues for this work, we demonstrate how searching multiple snapshots spanning a dynamical time significantly reduces the number of stranded halos, those lacking a descendant or a progenitor, critically correcting poorly resolved halos. We present a new merit function that improves the distinction between primary and secondary progenitors, reducing tree pathologies. We find FOF accretion rates and merger rates show similar mass ratio dependence. The model merger rates from Poole, et al. [2017, 472, 3659] agree with the measured net growth of halos through mergers.
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.12
Abstract: We present VELOCI raptor , a massively parallel galaxy/(sub)halo finder that is also capable of robustly identifying tidally disrupted objects and separate stellar halos from galaxies. The code is written in C++11, use the Message Passing Interface (MPI) and OpenMP Application Programming Interface (API) for parallelisation, and includes python tools to read/manipulate the data products produced. We demonstrate the power of the VELOCI raptor (sub)halo finder, showing how it can identify subhalos deep within the host that have negligible density contrasts to their parent halo. We find a subhalo mass-radial distance dependence: large subhalos with mass ratios of ≳10 −2 are more common in the central regions than smaller subhalos, a result of dynamical friction and low tidal mass loss rates. This dependence is completely absent in (sub)halo finders in common use, which generally search for substructure in configuration space, yet is present in codes that track particles belonging to halos as they fall into other halos, such as hbt +. VELOCI raptor largely reproduces the dependence seen without tracking, finding a similar radial dependence to hbt + in well-resolved halos from our limited resolution fiducial simulation.
Publisher: Oxford University Press (OUP)
Date: 18-11-2019
Abstract: Hierarchical models of structure formation predict that dark matter halo assembly histories are characterised by episodic mergers and interactions with other haloes. An accurate description of this process will provide insights into the dynamical evolution of haloes and the galaxies that reside in them. Using large cosmological N-body simulations, we characterise halo orbits to study the interactions between substructure haloes and their hosts, and how different evolutionary histories map to different classes of orbits. We use two new software tools - WhereWolf, which uses halo group catalogues and merger trees to ensure that haloes are tracked accurately in dense environments, and OrbWeaver, which quantifies each halo’s orbital parameters. We demonstrate how WhereWolf improves the accuracy of halo merger trees, and we use OrbWeaver to quantify orbits of haloes. We assess how well analytical prescriptions for the merger timescale from the literature compare to measured merger timescales from our simulations and find that existing prescriptions perform well, provided the ratio of substructure-to-host mass is not too small. In the limit of small substructure-to-host mass ratio, we find that the prescriptions can overestimate the merger timescales substantially, such that haloes are predicted to survive well beyond the end of the simulation. This work highlights the need for a revised analytical prescription for the merger timescale that more accurately accounts for processes such as catastrophic tidal disruption.
Publisher: Oxford University Press (OUP)
Date: 07-10-2014
Publisher: Oxford University Press (OUP)
Date: 14-09-2011
Publisher: Oxford University Press (OUP)
Date: 14-07-2015
Publisher: Oxford University Press (OUP)
Date: 08-10-2019
Publisher: Oxford University Press (OUP)
Date: 22-10-2020
Abstract: Resolving faint galaxies in large volumes is critical for accurate cosmic reionization simulations. While less demanding than hydrodynamical simulations, semi-analytic reionization models still require very large N-body simulations in order to resolve the atomic cooling limit across the whole reionization history within box sizes ${\\gtrsim}100 \\, h^{-1}\\, \\rm Mpc$. To facilitate this, we extend the mass resolution of N-body simulations using a Monte Carlo algorithm. We also propose a method to evolve positions of Monte Carlo haloes, which can be an input for semi-analytic reionization models. To illustrate, we present an extended halo catalogue that reaches a mass resolution of $M_\\text{halo} = 3.2 \\times 10^7 \\, h^{-1} \\, \\text{M}_\\odot$ in a $105 \\, h^{-1}\\, \\rm Mpc$ box, equivalent to an N-body simulation with ∼68003 particles. The resulting halo mass function agrees with smaller volume N-body simulations with higher resolution. Our results also produce consistent two-point correlation functions with analytic halo bias predictions. The extended halo catalogues are applied to the meraxes semi-analytic reionization model, which improves the predictions on stellar mass functions, star formation rate densities, and volume-weighted neutral fractions. Comparison of high-resolution large-volume simulations with both small-volume and low-resolution simulations confirms that both low-resolution and small-volume simulations lead to reionization ending too rapidly. Lingering discrepancies between the star formation rate functions predicted with and without our extensions can be traced to the uncertain contribution of satellite galaxies.
Publisher: Oxford University Press (OUP)
Date: 06-04-2018
DOI: 10.1093/MNRAS/STY846
Publisher: Oxford University Press (OUP)
Date: 06-09-2018
No related grants have been discovered for Pascal Elahi.