arXiv subjects

Dylan Nelson

Publications and source records attributed to Dylan Nelson.

At least 91 records · Page 5Linked to original sources

arXiv2023

The Circumgalactic Medium of Milky Way-like Galaxies in the TNG50 Simulation -- II: Cold, Dense Gas Clouds and High-Velocity Cloud Analogs

We use the TNG50 simulation of the IllustrisTNG project to study cold, dense clouds of gas in the circumgalactic media (CGM) of Milky Way-like galaxies. We find that their CGM is typically filled with of order one hundred (thousand) reasonably (marginally) resolved clouds, possible analogs of high-velocity clouds (HVCs). There is a large variation in cloud abundance from galaxy to galaxy, and the physical properties of clouds that we explore -- mass, size, metallicity, pressure, and kinematics -- are also diverse. We quantify the distributions of cloud properties and cloud-background contrasts, providing cosmological inputs for idealized simulations. Clouds characteristically have sub-solar metallicities, diverse shapes, small overdensities ($χ= n_{\rm cold} / n_{\rm hot} \lesssim 10$), are mostly inflowing, and have sub-virial rotation. At TNG50 resolution, resolved clouds have median masses of $\sim 10^6\,\rm{M_\odot}$ and sizes of $\sim 10$ kpc. Larger clouds are well converged numerically, while the abundance of the smallest clouds increases with resolution, as expected. In TNG50 MW-like haloes, clouds are slightly (severely) under-pressurised relative to their surroundings with respect to total (thermal) pressure, implying that magnetic fields may be important. Clouds are not distributed uniformly throughout the CGM, but are clustered around other clouds, often near baryon-rich satellite galaxies. This suggests that at least some clouds originate from satellites, via direct ram-pressure stripping or otherwise. Finally, we compare with observations of intermediate and high velocity clouds from the real Milky Way halo. TNG50 shows a similar cloud velocity distribution as observations, and predicts a significant population of currently difficult-to-detect low velocity clouds.

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arXiv2023

The atomic-to-molecular hydrogen transition in the TNG50 simulation: Using realistic UV fields to create spatially resolved HI maps

Cold gas in galaxies provides a crucial test to evaluate the realism of cosmological hydrodynamical simulations. To extract the atomic and molecular hydrogen properties of the simulated galaxy population, postprocessing methods taking the local UV field into account are required. We improve upon previous studies by calculating realistic UV fields with the dust radiative transfer code SKIRT to model the atomic-to-molecular transition in TNG50, the highest-resolution run of the IllustrisTNG suite. Comparing integrated quantities such as the HI mass function, we study to what detail the UV field needs to be modelled in order to calculate realistic cold gas properties. We then evaluate new, spatially resolved comparisons for cold gas in galaxies by exploring synthetic maps of atomic hydrogen at redshift zero and compare them to 21-cm observations of local galaxies from the WHISP survey. In terms of non-parametric morphologies, we find that TNG50 HI maps are less concentrated than their WHISP counterparts (median $ΔC\approx0.3$), due in part to central HI deficits related to the ejective character of supermassive black hole feedback in TNG. In terms of the HI column density distribution function, we find discrepancies between WHISP and IllustrisTNG that depend on the total HI abundance in these datasets as well as the postprocessing method. To fully exploit the synergy between cosmological simulations and upcoming deep HI/H2 data, we advocate the use of accurate methods to estimate the UV radiation field and to generate mock maps.

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arXiv2023

Expectations of the size evolution of massive galaxies at $3 \leq z \leq 6$ from the TNG50 simulation: the CEERS/JWST view

We present a catalog of about 25,000 images of massive ($M_{\star} \ge 10^9 M_{\odot}$) galaxies at redshift $3 \leq z \leq 6$ from the TNG50 cosmological simulation, tailored for observations at multiple wavelengths carried out with JWST. The synthetic images were created with the SKIRT radiative transfer code, including the effects of dust attenuation and scattering. The noiseless images were processed with the mirage simulator to mimic the Near Infrared Camera (NIRCam) observational strategy (e.g., noise, dithering pattern, etc.) of the Cosmic Evolution Early Release Science (CEERS) survey. In this paper, we analyze the predictions of the TNG50 simulation for the size evolution of galaxies at $3 \leq z \leq 6$ and the expectations for CEERS to probe that evolution. In particular, we investigate how sizes depend on wavelength, redshift, mass, and angular resolution of the images. We find that the effective radius accurately describes the three-dimensional half-mass radius of TNG50 galaxies. Sizes observed at 2~$μ$m are consistent with those measured at 3.56~$μ$m at all redshifts and masses. At all masses, the population of higher-$z$ galaxies is more compact than their lower-$z$ counterparts. However, the intrinsic sizes are smaller than the mock observed sizes for the most massive galaxies, especially at $z \lesssim 4$. This discrepancy between the mass and light distribution may point to a transition in the galaxy morphology at $z$=4-5, where massive compact systems start to develop more extended stellar structures.

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arXiv2023

The Circumgalactic Medium of Milky Way-like Galaxies in the TNG50 Simulation -- I: Halo Gas Properties and the Role of SMBH Feedback

We analyze the physical properties of gas in the circumgalactic medium (CGM) of 132 Milky Way (MW)-like central galaxies at $z=0$ from the cosmological magneto-hydrodynamical simulation TNG50, part of the IllustrisTNG project. The properties and abundance of CGM gas across the sample are diverse, and the fractional budgets of different phases (cold, warm, and hot), as well as neutral HI mass and metal mass, vary considerably. Over our stellar mass range of $10^{10.5} < M_\star / \rm{M}_\odot < 10^{10.9}$, radial profiles of gas physical properties from $0.15 < R\rm{ / R_{\rm 200c}} < 1.0$ reveal great CGM structural complexity, with significant variations both at fixed distance around individual galaxies, and across different galaxies. CGM gas is multi-phase: the distributions of density, temperature and entropy are all multimodal, while metallicity and thermal pressure distributions are unimodal; all are broad. We present predictions for magnetic fields in MW-like halos: a median field strength of $|B|\sim\,1μ$G in the inner halo decreases rapidly at larger distance, while magnetic pressure dominates over thermal pressure only within $\sim0.2 \times \rm{R_{200c}}$. Virial temperature gas at $\sim 10^6\,$K coexists with a sub-dominant cool, $< 10^5\,$K component in approximate pressure equilibrium. Finally, the physical properties of the CGM are tightly connected to the galactic star formation rate, in turn dependent on feedback from supermassive black holes (SMBHs). In TNG50, we find that energy from SMBH-driven kinetic winds generates high-velocity outflows ($\gtrsim 500-2000$ km/s), heats gas to super-virial temperatures ($> 10^{6.5-7}$ K), and regulates the net balance of inflows versus outflows in otherwise quasi-static gaseous halos.

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arXiv2022

The cosmic web in Lyman-alpha emission

We develop a comprehensive theoretical model for Lyman-alpha emission, from the scale of individual Lyman-alpha emitters (LAEs) to Lyman-alpha halos (LAHs), Lyman-alpha blobs (LABs), and Lyman-alpha filaments (LAFs) of the diffuse cosmic web itself. To do so, we post-process the high-resolution TNG50 cosmological magnetohydrodynamical simulation with a Monte Carlo radiative transfer method to capture the resonant scattering process of Lyman-alpha photons. We build an emission model incorporating recombinations and collisions in diffuse gas, including radiative effects from nearby AGN, as well as emission sourced by stellar populations. Our treatment includes a physically motivated dust model, which we empirically calibrate to the observed LAE luminosity function. We then focus on the observability, and physical origin, of the $z=2$ Lyman-alpha cosmic web, studying the dominant emission mechanisms and spatial origins. We find that diffuse Lyman-alpha filaments are, in fact, illuminated by photons which originate, not from the intergalactic medium itself, but from within galaxies and their gaseous halos. In our model, this emission is primarily sourced by intermediate mass halos ($10^{10} - 10^{11}\,$M$_{\odot}$), principally due to collisional excitations in their circumgalactic media as well as central, young stellar populations. Observationally, we make predictions for the abundance, area, linear size, and embedded halo/emitter populations within filaments. Adopting an isophotal surface brightness threshold of $10^{-20}\,$erg$\,$s$^{-1}\,$cm$^{-2}\,$arcsec$^{-2}$, we predict a volume abundance of Lyman-alpha filaments of ${\sim}10^{-3}$ cMpc$^{-3}\,$ for lengths above $400\,$pkpc. Given sufficiently large survey footprints, detection of the Lyman-alpha cosmic web is within reach of modern integral field spectrographs, including MUSE, VIRUS, and KCWI.

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arXiv2022

Emission-line properties of IllustrisTNG galaxies: from local diagnostic diagrams to high-redshift predictions for JWST

We compute synthetic, rest-frame optical and ultraviolet (UV) emission-line properties of galaxy populations at redshifts from z$\approx$0 to z=8 in a full cosmological framework. We achieve this by coupling, in post-processing, the cosmological IllustrisTNG simulations with new-generation nebular-emission models, accounting for line emission from young stars, post-asymptotic-giant-branch (PAGB) stars, accreting black holes (BHs) and, for the first time, fast radiative shocks. The optical emission-line properties of simulated galaxies dominated by different ionizing sources are largely consistent with those expected from classical diagnostic diagrams and reflect the observed increase in [OIII]/H$β$ at fixed [NII]/H$α$ and the evolution of the H$α$, [OIII]$\lambda5007$ and [OII]$\lambda3727$ luminosity functions from z$\approx$0 to z$\sim$2. At higher redshift, we find that the emission-line galaxy population is dominated by star-forming and active galaxies, with negligible fractions of shock- and PAGB-dominated galaxies. We highlight 10 UV-diagnostic diagrams able to robustly identify the dominant ionizing sources in high-redshift galaxies. We also compute the evolution of several optical- and UV-line luminosity functions from z=4 to z=7, and the number of galaxies expected to be detectable per field of view in deep, medium-resolution spectroscopic observations with the NIRSpec instrument on board the James Webb Space Telescope. We find that 2-hour-long exposures are sufficient to achieve unbiased censuses of H$α$ and [OIII]$\lambda5007$ emitters, while at least 5 hours are required for H$β$, and even 10 hours will detect only progressively smaller fractions of [OII]$\lambda3727$, OIII]$\lambda1663$, CIII]$\lambda1908$, CIV$\lambda1550$, [NII]$\lambda6584$, SiIII]$\lambda1888$ and HeII$\lambda1640$ emitters, especially in the presence of dust.

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arXiv2022

MUSE-ALMA Haloes VIII: Statistical Study of Circumgalactic Medium Gas

The distribution of gas and metals in the circumgalactic medium (CGM) plays a critical role in how galaxies evolve. The MUSE-ALMA Halos survey combines MUSE, ALMA and HST observations to constrain the properties of the multi-phase gas in the CGM and the galaxies associated with the gas probed in absorption. In this paper, we analyse the properties of galaxies associated with 32 strong \ion{H}{i} Ly-$α$ absorbers at redshift $0.2 \lesssim z \lesssim 1.4$. We detect 79 galaxies within $\pm 500$ \kms \!of the absorbers in our 19 MUSE fields. These associated galaxies are found at physical distances from 5.7 kpc and reach star-formation rates as low as $0.1$ \Moyr. The significant number of associated galaxies allows us to map their physical distribution on the $Δv$ and $b$ plane. Building on previous studies, we examine the physical and nebular properties of these associated galaxies and find the following: i) 27/32 absorbers have galaxy counterparts and more than 50 per cent of the absorbers have two or more associated galaxies, ii) the \ion{H}{i} column density of absorbers is anti-correlated with the impact parameter (scaled by virial radius) of the nearest galaxy as expected from simulations, iii) the metallicity of associated galaxies is typically larger than the absorber metallicity which decreases at larger impact parameters. It becomes clear that while strong \ion{H}{i} absorbers are typically associated with more than a single galaxy, we can use them to statistically map the gas and metal distribution in the CGM.

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arXiv2022

MUSE-ALMA Haloes VII: Survey Science Goals & Design, Data Processing and Final Catalogues

The gas cycling in the circumgalactic regions of galaxies is known to be multi-phase. The MUSE-ALMA Haloes survey gathers a large multi-wavelength observational sample of absorption and emission data with the goal to significantly advance our understanding of the physical properties of such CGM gas. A key component of the MUSE-ALMA Haloes survey is the multi-facility observational campaign conducted with VLT/MUSE, ALMA and HST. MUSE-ALMA Haloes targets comprise 19 VLT/MUSE IFS quasar fields, including 32 $z_{\rm abs}<$0.85 strong absorbers with measured N$_{HI}$ $\geq 10^{18}$ cm$^{\rm -2}$ from UV-spectroscopy. We additionally use a new complementary HST medium program to characterise the stellar content of the galaxies through a 40-orbit three-band UVIS and IR WFC3 imaging. Beyond the absorber-selected targets, we detect 3658 sources all fields combined, including 703 objects with spectroscopic redshifts. This galaxy-selected sample constitutes the main focus of the current paper. We have secured millimeter ALMA observations of some of the fields to probe the molecular gas properties of these objects. Here, we present the overall survey science goals, target selection, observational strategy, data processing and source identification of the full sample. Furthermore, we provide catalogues of magnitude measurements for all objects detected in VLT/MUSE, ALMA and HST broad-band images and associated spectroscopic redshifts derived from VLT/MUSE observations. Together, this data set provides robust characterisation of the neutral atomic gas, molecular gas and stars in the same objects resulting in the baryon census of condensed matter in complex galaxy structures.

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arXiv2022

Calibrating cosmological simulations with implicit likelihood inference using galaxy growth observables

In a novel approach employing implicit likelihood inference (ILI), also known as likelihood-free inference, we calibrate the parameters of cosmological hydrodynamic simulations against observations, which has previously been unfeasible due to the high computational cost of these simulations. For computational efficiency, we train neural networks as emulators on ~1000 cosmological simulations from the CAMELS project to estimate simulated observables, taking as input the cosmological and astrophysical parameters, and use these emulators as surrogates to the cosmological simulations. Using the cosmic star formation rate density (SFRD) and, separately, stellar mass functions (SMFs) at different redshifts, we perform ILI on selected cosmological and astrophysical parameters (Omega_m, sigma_8, stellar wind feedback, and kinetic black hole feedback) and obtain full 6-dimensional posterior distributions. In the performance test, the ILI from the emulated SFRD (SMFs) can recover the target observables with a relative error of 0.17% (0.4%). We find that degeneracies exist between the parameters inferred from the emulated SFRD, confirmed with new full cosmological simulations. We also find that the SMFs can break the degeneracy in the SFRD, which indicates that the SMFs provide complementary constraints for the parameters. Further, we find that the parameter combination inferred from an observationally-inferred SFRD reproduces the target observed SFRD very well, whereas, in the case of the SMFs, the inferred and observed SMFs show significant discrepancies that indicate potential limitations of the current galaxy formation modeling and calibration framework, and/or systematic differences and inconsistencies between observations of the stellar mass function.

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arXiv2022

Feedback reshapes the baryon distribution within haloes, in halo outskirts, and beyond: the closure radius from dwarfs to massive clusters

We explore three sets of cosmological hydrodynamical simulations, IllustrisTNG, EAGLE, and SIMBA, to investigate the physical processes impacting the distribution of baryons in and around haloes across an unprecedented mass range of $10^8<M_{\rm 200c}/{\rm M_{\odot}}<10^{15}$, from the halo centre out to scales as large as $30\,R_{\rm 200c}$. We demonstrate that baryonic feedback mechanisms significantly redistribute gas, lowering the baryon fractions inside haloes while simultaneously accumulating this material outside the virial radius. To understand this large-scale baryonic redistribution and identify the dominant physical processes responsible, we examine several variants of TNG that selectively exclude stellar and AGN feedback, cooling, and radiation. We find that heating from the UV background in low-mass haloes, stellar feedback in intermediate-mass haloes, and AGN feedback in groups ($10^{12} \leq M_{\rm 200c}/{\rm M_{\odot}}<10^{14}$) are the dominant processes. Galaxy clusters are the least influenced by these processes on large scales. We introduce a new halo mass-dependent characteristic scale, the closure radius $R_{\rm c}$, within which all baryons associated with haloes are found. For groups and clusters, we introduce a universal relation between this scale and the halo baryon fraction: $R_{\rm c}/R_{\rm 200c,500c}-1=β(z)(1-f_{\rm b}(<R_{\rm 200c,500c})/f_{\rm b,cosmic})$, where $β(z)=α\,(1+z)^γ$, and $α$ and $γ$ are free parameters fit using the simulations. Accordingly, we predict that all baryons associated with observed X-ray haloes can be found within $R_{\rm c}\sim 1.5-2.5 R_{\rm 200c}$. Our results can be used to constrain theoretical models, particularly the physics of supernova and AGN feedback, as well as their interplay with environmental processes, through comparison with current and future X-ray and SZ observations.

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arXiv2022

High redshift JWST predictions from IllustrisTNG: III. Infrared luminosity functions, obscured star formation and dust temperature of high-redshift galaxies

We post-process galaxies in the IllustrisTNG simulations with SKIRT radiative transfer calculations to make predictions for the rest-frame near-infrared (NIR) and far-infrared (FIR) properties of galaxies at $z\geq 4$. The rest-frame $K$- and $z$-band galaxy luminosity functions from TNG are overall consistent with observations, despite a $\sim 0.5\,\mathrm{dex}$ underprediction at $z=4$ for $M_{\rm K}\lesssim -25$ and $M_{\rm z}\lesssim -24$. Predictions for the JWST MIRI observed galaxy luminosity functions and number counts are given. Based on theoretical estimations, we show that the next-generation survey conducted by JWST can detect 500 (30) galaxies in F1000W in a survey area of $500\,{\rm arcmin}^{2}$ at $z=6$ ($z=8$). As opposed to the consistency in the UV, optical and NIR, we find that TNG, combined with our dust modelling choices, significantly underpredicts the abundance of most dust-obscured and thus most luminous FIR galaxies. As a result, the obscured cosmic star formation rate density (SFRD) and the SFRD contributed by optical/NIR dark objects are underpredicted. The discrepancies discovered here could provide new constraints on the sub-grid feedback models, or the dust contents, of simulations. Meanwhile, although the TNG predicted dust temperature and its relations with IR luminosity and redshift are qualitatively consistent with observations, the peak dust temperature of $z\geq 6$ galaxies are overestimated by about $20\,{\rm K}$. This could be related to the limited mass resolution of our simulations to fully resolve the porosity of the interstellar medium (or specifically its dust content) at these redshifts.

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arXiv2022

The merger and assembly histories of Milky Way- and M31-like galaxies with TNG50: disk survival through mergers

We analyze the merger and assembly histories of Milky Way (MW) and Andromeda (M31)-like galaxies to quantify how, and how often, disk galaxies of this mass can survive recent major mergers (stellar mass ratio $\ge$ 1:4). For this, we use the cosmological magneto-hydrodynamical simulation TNG50 and identify 198 analog galaxies, selected based on their $z=0$ stellar mass ($10^{10.5-11.2} {\rm M_{\odot}}$), disky stellar morphology and local environment. Firstly, major mergers are common: 85 per cent (168) of MW/M31-like galaxies in TNG50 have undergone at least one major merger across their lifetime. In fact, 31 galaxies (16 per cent) have undergone a recent major merger, i.e. in the last 5 Gyr. The gas available during the merger suffices to either induce starbursts at pericentric passages or to sustain prolonged star formation after coalescence: in roughly half of the cases, the pre-existing stellar disk is destroyed because of the merger but reforms thanks to star formation. Moreover, higher merger mass ratios are more likely to destroy the stellar disks. In comparison to those with more ancient massive mergers, MW/M31-like galaxies with recent major mergers have, on average, somewhat thicker stellar disks, more massive and somewhat shallower stellar haloes, larger stellar ex-situ mass fractions, but similarly massive kinematically-defined bulges. All this is qualitatively consistent with the different observed properties of the Galaxy and Andromeda and with the constraints on their most recent major mergers, 8-11 and ~2 Gyr ago, respectively. According to contemporary cosmological simulations, a recent quiet merger history is not a pre-requisite for obtaining a relatively-thin stellar disk at $z=0$.

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arXiv2022

Modeling globular clusters in the TNG50 simulation: predictions from dwarfs to giants

We present a post-processing catalog of globular clusters (GCs) for the $39$ most massive groups and clusters in the TNG50 simulation of the IlllustrisTNG project (virial masses $M_{200} =[5\times 10^{12} \rm - 2 \times 10^{14}$] M$_{\odot}$). We tag GC particles to all galaxies with stellar mass $M_* \geq 5\times10^6$ M$_{\odot}$, and we calibrate their masses to reproduce the observed power-law relation between GC mass and halo mass for galaxies with $M_{200} \geq 10^{11}$ M$_{\odot}$ (corresponding to $M_* \sim 10^9$ $M_{\odot}$). Here we explore whether an extrapolation of this $M_{\rm GC}$-$M_{200}$ relation to lower-mass dwarfs is consistent with current observations. We find a good agreement between our predicted number and specific frequency of GCs in dwarfs with $\rm M_*=[5 \times 10^6 \rm - 10^9]$ M$_{\odot}$ and observations. Moreover, we predict a steep decline in the GC occupation fraction for dwarfs with $M_*<10^9$ M$_{\odot}$ which agrees well with current observational constraints. This declining occupation fraction is due to a combination of tidal stripping in all dwarfs plus a stochastic sampling of the GC mass function for dwarfs with $M_* < 10^{7.5}$ M$_{\odot}$. Our simulations also reproduce available constraints on the abundance of intra-cluster GCs in Virgo and Centaurus A. These successes provide support to the hypothesis that the $M_{\rm GC}$-$M_{200}$ relation holds, albeit with more scatter, all the way down to the regime of classical dwarf spheroidals in these environments. Our GC catalogs are publicly available as part of the IllustrisTNG data release.

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arXiv2022

UV to submillimetre luminosity functions of TNG50 galaxies

We apply the radiative transfer (RT) code SKIRT on a sample of ~14000 low-redshift (z<= 0.1) galaxies extracted from the TNG50 simulation to enable an apples-to-apples comparison with observations. The RT procedure is calibrated via comparison of a subsample of TNG50 galaxies with the DustPedia observational sample: we compare several luminosity and colour scaling relations and spectral energy distributions in different specific SFR bins. We consistently derive galaxy luminosity functions for the TNG50 simulation in 14 broadband filters from UV to submillimetre wavelengths and investigate the effects of the aperture, orientation, radiative transfer recipe, and numerical resolution. We find that, while our TNG50+RT fiducial model agrees well with the observed luminosity functions at the knee (+/- 0.04 dex typical agreement), the TNG50+RT luminosity functions evaluated within 5R_1/2 are generally higher than observed at both the faint and bright ends, by 0.004 (total IR)-0.27 (UKIDSS H) dex and 0.12 (SPIRE250)-0.8 (GALEX FUV) dex, respectively. A change in the aperture does affect the bright end of the luminosity function, easily by up to 1 dex depending on the choice. However, we also find that the galaxy luminosity functions of a worse-resolution run of TNG50 (TNG50-2, with 8 times worse mass resolution than TNG50, similar to TNG100) are in better quantitative agreement with observational constraints. Finally, we publicly release the photometry for the TNG50 sample in 53 broadbands from FUV to submillimetre, in three orientations and four apertures, as well as galaxy spectral energy distributions.

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arXiv2022

Ionizing photon production and escape fractions during cosmic reionization in the TNG50 simulation

In this work we investigate the dependence of the escape fraction of ionizing photons, $f_{\rm esc}$, on various galaxy and host halo properties during the epoch of reionization. We post-process the TNG50 magneto-hydrodynamical simulation from the IllustrisTNG project using the 3D multi-frequency radiative transfer code CRASH. Our work covers the stellar mass range $10^6 \lesssim M_\star/{\rm M_\odot} \lesssim 10^8$ at redshifts $6 < z < 10$. Adopting an unresolved, cloud-scale escape fraction parameter of unity, the halo escape fraction $f_{\rm esc}$ increases with mass from $\sim 0.3$ at $M_\star = 10^6$M$_\odot$ to $\sim 0.6$ at $M_\star = 10^{7.5}$M$_\odot$, after which we find hints of a turnover and decreasing escape fractions for even more massive galaxies. However, we demonstrate a strong and non-linear dependence of $f_{\rm esc}$ on the adopted sub-grid escape fraction. In addition, $f_{\rm esc}$ has significant scatter at fixed mass, driven by diversity in the ionizing photon rate together with a complex relationship between (stellar) source positions and the underling density distribution. The global emissivity is consistent with observations for reasonable cloud-scale absorption values, and halos with a stellar mass $\lesssim 10^{7.5}$M$_\odot$ contribute the majority of ionizing photons at all redshifts. Incorporating dust reduces $f_{\rm esc}$ by a few percent at $M_\star \lesssim 10^{6.5}$M$_\odot$, and up to 10\% for larger halos. Our multi-frequency approach shows that $f_{\rm esc}$ depends on photon energy, and is reduced substantially at $E>54.4$eV versus lower energies. This suggests that the impact of high energy photons from binary stars is reduced when accounting for an energy dependent escape fraction.

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arXiv2022

Morphological decomposition of TNG50 galaxies: methodology and catalogue

We present MORDOR (MORphological DecOmposeR, a new algorithm for structural decomposition of simulated galaxies based on stellar kinematics. The code measures the properties of up to five structural components (a thin/cold and a thick/warm disc, a classical and a secular bulge, and a spherical stellar halo), and determines the properties of a stellar bar (if present). A comparison with other algorithms presented in the literature yields overall good agreement, with MORDOR displaying a higher flexibility in correctly decomposing systems and identifying bars in crowded environments (e.g. with ongoing fly-bys, often observable in cosmological simulations). We use MORDOR to analyse galaxies in the TNG50 simulation and find the following: ($i$) the thick disc component undergoes the strongest evolution in the binding energy-circularity plane, as expected when disc galaxies decrease their turbulent-rotational support with cosmic time; ($ii$) smaller galaxies (with stellar mass, $10^{9} \lesssim M_{*} / {\rm M_{\odot}} \leq 5 \times 10^{9}$) undergo a major growth in their disc components after $z\sim 1$, whereas ($iii$) the most massive galaxies ($5 \times 10^{10} < M_{*} / {\rm M_{\odot}} \leq 5\times10^{11}$) evolve toward more spheroidal dominated objects down to $z=0$ due to frequent gravitational interactions with satellites; ($iv$) the fraction of barred galaxies grows rapidly at high redshift and stabilizes below $z\sim 2$, except for the most massive galaxies that show a decrease in the bar occupation fraction at low redshift; ($v$) galaxies with $M_{*} \sim 10^{11}~{\rm M_{\odot}}$ exhibit the highest relative occurrence of bars at $z=0$, in agreement with observational studies. We publicly release MORDOR and the morphological catalogue of TNG50 galaxies.

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arXiv2022

Exploring the effect of baryons on the radial distribution of satellite galaxies with GAMA and IllustrisTNG

We explore the radial distribution of satellite galaxies in groups in the Galaxy and Mass Assembly (GAMA) survey and the IllustrisTNG simulations. Considering groups with masses $12.0 \leq \log_{10} (\mathcal{M}_h / h^{-1} \mathrm{M}_{\odot}) < 14.8$ at $z<0.267$, we find a good agreement between GAMA and a sample of TNG300 groups and galaxies designed to match the GAMA selection. Both display a flat profile in the centre of groups, followed by a decline that becomes steeper towards the group edge, and normalised profiles show no dependence on group mass. Using matched satellites from TNG and dark matter-only TNG-Dark runs we investigate the effect of baryons on satellite radial location. At $z=0$, we find that the matched subhaloes from the TNG-Dark runs display a much flatter radial profile: namely, satellites selected above a minimum stellar mass exhibit both smaller halo-centric distances and longer survival times in the full-physics simulations compared to their dark-matter only analogues. We then divide the TNG satellites into those which possess TNG-Dark counterparts and those which do not, and develop models for the radial positions of each. We find the satellites with TNG-Dark counterparts are displaced towards the halo centre in the full-physics simulations, and this difference has a power-law behaviour with radius. For the `orphan' galaxies without TNG-Dark counterparts, we consider the shape of their radial distribution and provide a model for their motion over time, which can be used to improve the treatment of satellite galaxies in semi-analytic and semi-empirical models of galaxy formation.

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arXiv2022

Sunyaev-Zel'dovich effect and X-ray scaling relations of galaxies, groups and clusters in the IllustrisTNG simulations

Observable thermodynamical properties of the intracluster medium (ICM) reflect the complex interplay between AGN feedback and the gravitational collapse of haloes. Using the large volume TNG300 simulation of the IllustrisTNG project we provide predictions for X-ray and Sunyaev-Zel'dovich (SZ) scaling relations for a sample of over 30,000 haloes that cover a wide mass range from galaxies to massive galaxy clusters ($M_{\rm 500crit}$ $\in [10^{12}$ M$_{\odot} - 2\times 10^{15}$ M$_{\odot}$]). We produce mock X-ray observations of simulated haloes using methods that are consistent with observational techniques. Thus, we investigate the scaling relations between the soft-band X-ray luminosity, spectroscopic temperature, gas mass fraction, $Y_{\rm X}$ and $Y_{\rm SZ}$ as a function of halo mass, and we find broad agreement between IllustrisTNG and the observed relations. Our results highlight the scatter and bias introduced by estimated masses, and thus the importance of converting simulated ICM properties to the observable space when comparing simulations to current X-ray observations. The wide range of halo masses in our sample provides new insights into the shape of the X-ray and SZ scaling relations across three orders of magnitude in mass. Our findings show strong evidence for a break in $z=0$ scaling relations. We introduce a smoothly broken power law model which robustly captures the location of this break, the width of the transition region around the break, as well as the slope dependence on halo mass. Our results inform the next generation of subgrid black hole feedback models and provide predictions for ongoing and future observational surveys.

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