We present a new, open source, free, semi-analytic model (SAM) of galaxy formation, SHARK, designed to be highly flexible and modular, allowing easy exploration of different physical processes and ...ways of modelling them. We introduce the philosophy behind SHARK and provide an overview of the physical processes included in the model. SHARK is written in C++11 and has been parallelized with OpenMP. In the released version (V1.1), we implement several different models for gas cooling, active galactic nuclei, stellar and photo-ionization feedback, and star formation (SF). We demonstrate the basic performance of SHARK using the Planck Collaboration et al. (2016) cosmology SURFS simulations, by comparing against a large set of observations, including: the stellar mass function (SMF) and stellar-halo mass relation at z = 0-4; the cosmic evolution of the star formation rate density (SFRD), stellar mass, atomic and molecular hydrogen; local gas scaling relations; and structural galaxy properties, finding excellent agreement. Significant improvements over previous SAMs are seen in the mass-size relation for discs/bulges, the gas-stellar mass and stellar mass-metallicity relations. To illustrate the power of SHARK in exploring the systematic effects of the galaxy formation modelling, we quantify how the scatter of the SF main sequence and the gas scaling relations changes with the adopted SF law, and the effect of the starbursts H2 depletion time-scale on the SFRD and Ω _H_2. We compare SHARK with other SAMs and the hydrodynamical simulation EAGLE, and find that SAMs have a much higher halo baryon fractions due to large amounts of intra-halo gas, which in the case of EAGLE is in the intergalactic medium.
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.
Abstract
We use TheThreeHundred project, a suite of 324 resimulated massive galaxy clusters embedded in a broad range of environments, to investigate (i) how the gas content of the surrounding haloes ...correlates with the phase-space position at $z$ = 0 and (ii) the role that ram pressure plays in this correlation. By stacking all 324 normalized phase-space planes containing 169 287 haloes and subhaloes, we show that the halo gas content is tightly correlated with the phase-space position. At ${\sim }1.5\hbox{--}2\, {R}_{\text{200}}$ of the cluster dark matter halo, we find an extremely steep decline in the halo gas content of infalling haloes and subhaloes irrespective of cluster mass, possibly indicating the presence of an accretion shock. We also find that subhaloes are particularly gas-poor, even in the cluster outskirts, which could indicate active regions of ongoing pre-processing. By modelling the instantaneous ram pressure experienced by each halo and subhalo at $z$ = 0, we show that the ram pressure intensity is also well correlated with the phase-space position, which is again irrespective of cluster mass. In fact, we show that regions in the phase-space plane with high differential velocity between a halo or subhalo and its local gas environment are almost mutually exclusive with high halo gas content regions. This suggests a causal link between the gas content of objects and the instantaneous ram pressure they experience, where the dominant factor is the differential velocity.
ABSTRACT We present astrolink, an efficient and versatile clustering algorithm designed to hierarchically classify astrophysically relevant structures from both synthetic and observational data sets. ...We build upon clustar-nd, a hierarchical galaxy/(sub)halo finder, so that astrolink now generates a 2D representation of the implicit clustering structure as well as ensuring that clusters are statistically distinct from the noisy density fluctuations implicit within the n-dimensional input data. This redesign replaces the three cluster extraction parameters from clustar-nd with a single parameter, S – the lower statistical significance threshold of clusters, which can be automatically and reliably estimated via a dynamical model-fitting process. We demonstrate the robustness of this approach compared to astrolink’s predecessors by applying each algorithm to a suite of simulated galaxies defined over various feature spaces. We find that astrolink delivers a more powerful clustering performance while being $\sim 27~{{\ \rm per \, cent}}$ faster and using less memory than clustar-nd. With these improvements, astrolink is ideally suited to extracting a meaningful set of hierarchical and arbitrarily shaped astrophysical clusters from both synthetic and observational data sets – lending itself as a great tool for morphological decomposition within the context of hierarchical structure formation.
Abstract
We present the Synthetic UniveRses For Surveys (surfs) simulations, a set of N-body/Hydro simulations of the concordance Λ Cold Dark Matter (ΛCDM) cosmology. These simulations use Planck ...cosmology, contain up to 10 billion particles, and sample scales and halo masses down to 1 kpc and 108 M⊙. We identify and track haloes from z = 24 to today using a state-of-the-art 6D halo finder and merger tree builder. We demonstrate that certain properties of haloes merger trees are numerically converged for haloes composed of ≳100 particles. Haloes smoothly grow in mass, Vmax, with the mass history characterized by log M(a) ∝ exp −(a/β)α, where a is the scale factor, α(M) ≈ 0.8 & β(M) ≈ 0.024, with these parameters decreasing with decreasing halo mass. Subhaloes follow power-law cumulative mass and velocity functions, i.e. n( > f) ∝ f−α with αM = 0.83 ± 0.01 and $\alpha _{V_{\rm max}}=2.13\pm 0.03$ for mass and velocity, respectively, independent of redshift, as seen in previous studies. The halo-to-halo scatter in amplitude is 0.9 dex. The number of subhaloes in a halo weakly correlates with a halo's concentration c and spin λ:haloes of high c and low λ have 60 per cent more subhaloes than similar mass haloes of low c and high λ. High cadence tracking shows subhaloes are dynamic residents, with 25 per cent leaving their host halo momentarily, becoming a backsplash subhalo, and another 20 per cent changing hosts entirely, in agreement with previous studies. In general, subhaloes have elliptical orbits, e ≈ 0.6, with periods of $2.3^{+2.1}_{-1.7}$ Gyrs. Subhaloes lose most of their mass at pericentric passage with mass loss rates of ∼ 40 per cent Gyr−1. These catalogues will be made publicly available.
We describe a new algorithm for finding substructures within dark matter haloes from N-body simulations. The algorithm relies upon the fact that dynamically distinct substructures in a halo will have ...a local velocity distribution that differs significantly from the mean, i.e. smooth background halo. We characterize the large-scale mean field using a coarsely grained cell-based approach, while a kernel-smoothing process is used to determined the local velocity distribution. Comparing the ratio of these two estimates allows us to identify particles that are strongly clustered in velocity space relative to the background and thus resident in a substructure. From this population of outliers, groups are identified using a Friends-of-Friends-like approach. False positives are rejected using Poisson noise arguments. This approach does not require a search of the full phase-space structure of a halo, a non-trivial task, and is thus computationally advantageous. We apply our algorithm to several test cases and show that it identifies not only subhaloes, bound overdensities in phase space, but can recover tidal streams with a high purity. Our method can even find streams which do not appear significantly overdense either physically or in phase space.
Upcoming measurements of the highly redshifted 21 cm line with next-generation radio telescopes such as the Hydrogen Epoch of Reionization Array (HERA) and Square Kilometer Array will provide the ...intriguing opportunity to probe dark matter (DM) physics during the Epoch of Reionization, Cosmic Dawn, and the Dark Ages. With HERA already under construction, there is a pressing need to thoroughly understand the impact of DM physics on the intergalactic medium (IGM) during these epochs. We present first results of a hydrodynamic simulation suite with 2 × 5123 particles in a (100 h−1 Mpc)3 box with DM annihilation and baryonic cooling physics. We focus on redshift z ∼ 11, just before reionization starts in our simulations, and discuss the imprint of DM annihilation on the IGM and on structure formation. We find that whereas structure formation is not affected by thermal weakly interacting massive particles heavier than mχ 100 MeV, heating from (GeV) DM particles may leave a significant imprint on the IGM that alters the 21 cm signal. Cold gas in low-density regions is particularly susceptible to the effects of DM heating. We note, however, that delayed energy deposition is not currently accounted for in our simulations.
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 sample of simulated galaxy clusters to confirm.
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