arXiv subjects
Publications and source records attributed to Mark Vogelsberger.
We summarize progress made in theoretical astrophysics and cosmology over the past decade and areas of interest for the coming decade. This Report is prepared as the TF09 "Astrophysics and Cosmology" topical group summary for the Theory Frontier as part of the Snowmass 2021 process.
We study the effect of self-interacting dark matter (SIDM) and baryons on the shape of early-type galaxies (ETGs) and their dark matter haloes, comparing them to the predictions of the cold dark matter (CDM) scenario. We use five hydrodynamical zoom-in simulations of haloes hosting ETGs ($M_{\rm vir}\sim 10^{13}M_{\odot}$ and $M_{*}\sim10^{11}M_{\odot}$), simulated in CDM and a SIDM model with constant cross-section of $σ_T/m_χ= 1\ \mathrm{cm}^2 \mathrm{g}^{-1}$. We measure the three-dimensional and projected shapes of the dark matter haloes and their baryonic content using the inertia tensor and compare our measurements to the results of three $HST$ samples of gravitational lenses and $Chandra$ and $XMM-Newton$ X-ray observations. We find that the inclusion of baryons greatly reduces the differences between CDM and a SIDM, together with the ability to draw constraints based on shapes. Lensing measurements reject the predictions of CDM dark-matter-only simulations and prefer one of the hydro scenarios. When we consider the total sample of lenses, observational data prefer the CDM hydro scenario. The shapes of the X-ray emitting gas are compatible with observational results in both hydro runs, with CDM predicting higher elongations only in the very centre. Contrary to previous claims at the scale of elliptical galaxies, we conclude that both CDM and our SIDM model can still explain observed shapes once we include baryons in the simulations. Our results demonstrate that this is essential to derive realistic constraints and that new simulations are needed to confirm and extend our findings.
How the cosmic web feeds halos, and fuels galaxy formation is an open question with wide implications. This study explores the mass assembly in the Local Group within the context of the local cosmography by employing simulations whose initial conditions have been constrained to reproduce the local environment. The goal of this study is to inspect whether the direction of accretion of satellites on to the Milky Way and Andromeda galaxies, is related to the cosmic web. The analysis considers the three high-resolution simulations available in the HESTIA simulation suite, as well as the derived velocity shear and tidal tensors. We notice two eras in the Local Group accretion history, delimited by an epoch around $z \approx 0.7$. We also find that satellites can travel up to $\sim 4$ Mpc, relative to their parent halo before crossing its viral radius $R_{200}$. Finally, we observe a strong alignment of the infall direction with the axis of slowest collapse $\vec{e_3}$ of both tidal and shear tensors, implying satellites of the Local Group originated from one particular region of the cosmic web and were channeled towards us via the process of accretion.This alignment is dominated by the satellites that enter during the early infall era, i.e $z>0.7$.
Self-interacting dark matter (SIDM) cosmologies admit an enormous diversity of dark matter (DM) halo density profiles, from low-density cores to high-density core-collapsed cusps. The possibility of the growth of high central density in low-mass halos, accelerated if halos are subhalos of larger systems, has intriguing consequences for small-halo searches with substructure lensing. However, following the evolution of $\lesssim 10^8 M_\odot$ subhalos in lens-mass systems ($\sim 10^{13}M_\odot$) is computationally expensive with traditional N-body simulations. In this work, we develop a new hybrid semi-analytical + N-body method to study the evolution of SIDM subhalos with high fidelity, from core formation to core-collapse, in staged simulations. Our method works best for small subhalos ($\lesssim 1/1000$ host mass), for which the error caused by dynamical friction is minimal. We are able to capture the evaporation of subhalo particles by interactions with host halo particles, an effect that has not yet been fully explored in the context of subhalo core-collapse. We find three main processes drive subhalo evolution: subhalo internal heat outflow, host-subhalo evaporation, and tidal effects. The subhalo central density grows only when the heat outflow outweighs the energy gain from evaporation and tidal heating. Thus, evaporation delays or even disrupts subhalo core-collapse. We map out the parameter space for subhalos to core-collapse, finding that it is nearly impossible to drive core-collapse in subhalos in SIDM models with constant cross sections. Any discovery of ultra-compact dark substructures with future substructure lensing observations favors additional degrees of freedom, such as velocity-dependence, in the cross section.
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.
We analyze the velocity anisotropy of stars in real and energy space for a sample of Milky Way-like galaxies in the TNG50 simulation. We employ different selection criteria, including spatial, kinematic and metallicity cuts, and make three halo classes ($\mathcal{A}$-$\mathcal{C}$) which show mild-to-strong sensitivity to different selections. The above classes cover 48%, 16% and 36% of halos, respectively. We analyze the $β$ radial profiles and divide them into either monotonically increasing radial profiles or ones with peaks and troughs. We demonstrate that halos with monotonically increasing $β$ profiles are mostly from class $\mathcal{A}$, whilst those with peaks/troughs are part of classes $\mathcal{B}$-$\mathcal{C}$. This means that care must be taken as the observationally reported peaks/troughs might be a consequence of different selection criteria. We infer the anisotropy parameter $β$ energy space and compare that against the $β$ radial profile. It is seen that 65% of halos with very mild sensitivity to different selections in real space, are those for which the $β$ radial and energy profiles are closely related. Consequently, we propose that comparing the $β$ radial and energy profiles might be a novel way to examine the sensitivity to different selection criteria and thus examining the robustness of the anisotropy parameter in tracing stellar kinematics. We compare simulated $β$ radial profiles against various observations and demonstrate that, in most cases, the model diversity is comparable with the error bars from different observations, meaning that the TNG50 models are in good overall agreement with observations.
Observations of the high redshift universe provide a promising avenue for constraining the nature of the dark matter (DM). This will be even more true with the advent of the James Webb Space Telescope (JWST). We run cosmological simulations of galaxy formation as part of the Effective Theory of Structure Formation (ETHOS) project to compare high redshift galaxies in Cold (CDM) and alternative DM models which have varying relativistic coupling and self-interaction strengths. The interacting DM scenarios produce a cutoff in the linear power spectrum on small-scales, followed by a series of "dark acoustic oscillations". We find that DM interactions suppress the abundance of galaxies below $M_\star \sim 10^8\,M_\odot$ for the models considered. The cutoff in the power spectrum delays structure formation relative to CDM. Objects in ETHOS that end up at the same final masses as their CDM counterparts are characterised by a more vigorous phase of early star formation. While galaxies with $M_\star \lesssim 10^6\,M_\odot$ make up more than 60 per cent of star formation in CDM at $z\approx 10$, they contribute only about half the star formation density in ETHOS. These differences diminish with decreasing redshift. We find that the effects of DM self-interactions are negligible compared to effects of relativistic coupling (i.e. the effective initial conditions for galaxy formation) in all properties of the galaxy population we examine. Finally, we show that the clustering strength of galaxies at high redshifts depends sensitively on DM physics, although these differences are manifest on scales that may be too small to be measurable by JWST.
The Local Group is a unique environment in which to study the astrophysics of galaxy formation. The proximity of the Milky Way and M31 enhances the frequency of interactions of the low-mass halo population with more massive dark matter haloes, which increases their concentrations and strips them of gas and other material. Some low-mass haloes pass through the haloes of the Milky Way or M31 and are either ejected into the field or exchanged between the two primary hosts. We use high resolution gas-dynamical simulations to describe a new class of field haloes that passed through the haloes of both the Milky Way and M31 at early times and are almost twice as concentrated as field haloes that do not interact with the primary pair. These 'Hermeian' haloes are distributed anisotropically at larger distances from the Local Group barycentre than the primary haloes and appear to cluster along the line connecting the Milky Way and M31. Hermeian haloes facilitate the exchange of dark matter, gas, and stars between the Milky Way and M31 and can enhance the star formation rate of the gas in the primary haloes during their interactions with them. We also show that some Hermeian haloes can host galaxies that, because they are embedded in haloes that are more concentrated than regular field haloes, are promising targets for indirect dark matter searches beyond the Milky Way virial radius and can produce signals that are competitive with those of some dwarf galaxies. Hermeian galaxies in the Local Group should be detectable by forthcoming wide-field imaging surveys.
We present a new set of cosmological zoom-in simulations of a MW-like galaxy which for the first time include elastic velocity-dependent self interacting dark matter (SIDM) and IllustrisTNG physics. With these simulations we investigate the interaction between SIDM and baryons and its effects on the galaxy evolution process. We also introduce a novel set of modified DMO simulations which can reasonably replicate the effects of fully realized hydrodynamics on the DM halo while simplifying the analysis and lowering the computational cost. We find that baryons change the thermal structure of the central region of the halo to a greater extent than the SIDM scatterings for MW-like galaxies. Additionally, we find that the new thermal structure of the MW-like halo causes SIDM to create cuspier central densities rather than cores because the SIDM scatterings remove the thermal support by transferring heat away from the center of the galaxy. We find that this effect, caused by baryon contraction, begins to affect galaxies with a stellar mass of $10^8$ M$_\odot$ and increases in strength to the MW-mass scale. This implies that any simulations used to constrain the SIDM cross sections for galaxies with stellar masses between $10^8$ and at least $10^{11}$ M$_\odot$ will require baryons to make accurate predictions.
The presence of gaseous X-ray halos around massive galaxies is a basic prediction of all past and modern structure formation simulations. The importance of these X-ray halos is further emphasized by the fact that they retain signatures of the physical processes that shape the evolution of galaxies from the highest redshift to the present day. In this review, we overview our current observational and theoretical understanding of hot gaseous X-ray halos around nearby massive galaxies and we also describe the prospects of observing X-ray halos with future instruments.
Line intensity mapping (LIM) is rapidly emerging as a powerful technique to study galaxy formation and cosmology in the high-redshift Universe. We present LIM estimates of select spectral lines originating from the interstellar medium (ISM) of galaxies and 21 cm emission from neutral hydrogen gas in the Universe using the large volume, high resolution THESAN reionization simulations. A combination of sub-resolution photo-ionization modelling for HII regions and Monte Carlo radiative transfer calculations is employed to estimate the dust-attenuated spectral energy distributions (SEDs) of high-redshift galaxies ($z\gtrsim5.5$). We show that the derived photometric properties such as the ultraviolet (UV) luminosity function and the UV continuum slopes match observationally inferred values, demonstrating the accuracy of the SED modelling. We provide fits to the luminosity--star formation rate relation (L-SFR) for the brightest emission lines and find that important differences exist between the derived scaling relations and the widely used low-$z$ ones because the interstellar medium of reionization era galaxies is generally less metal-enriched than in their low redshift counterparts. We use these relations to construct line intensity maps of nebular emission lines and cross correlate with the 21 cm emission. Interestingly, the wavenumber at which the correlation switches sign ($k_\mathrm{transition}$) depends heavily on the reionization model and to a lesser extent on the targeted emission line, which is consistent with the picture that $k_\mathrm{transition}$ probes the typical sizes of ionized regions. The derived scaling relations and intensity maps represent a timely state-of-the-art framework for forecasting and interpreting results from current and upcoming LIM experiments.
We explore the nature of low surface brightness galaxies (LSBGs) in the hydrodynamic cosmological simulation TNG100 of the IllustrisTNG project, selecting a sample of LSBGs ($r$-band effective surface brightness $μ_r > 22.0$ mag arcsec$^{-2}$) at $z=0$ over a wide range of stellar masses ($M_{\ast} = 10^{9}$-$10^{12}$ M$_\odot$). We find LSBGs of all stellar masses, although they are particularly prevalent at $M_{\ast} < 10^{10}$ M$_\odot$. We show that the specific star formation rates of LSBGs are not significantly different from those of high surface brightness galaxies (HSBGs) but, as a population, LSBGs are systematically less massive and more extended than HSBGs, and tend to display late-type morphologies according to a kinematic criterion. At fixed stellar mass, we find that haloes hosting LSBGs are systematically more massive and have a higher baryonic fraction than those hosting HSBGs. We find that LSBGs have higher stellar specific angular momentum and halo spin parameter values compared to HSBGs, as suggested by previous works. We track the evolution of these quantities back in time, finding that the spin parameters of the haloes hosting LSBGs and HSBGs exhibit a clear bifurcation at $z \sim 2$, which causes a similar separation in the evolutionary tracks of other properties such as galactic angular momentum and effective radius, ultimately resulting in the values observed at $z =$ 0. The higher values of specific stellar angular momentum and halo spin in LSBGs seem to be responsible for their extended nature, preventing material from collapsing into the central regions of the galaxies, also causing LSBGs to host less massive black holes at their centres.
Early-type galaxies (ETGs) possess total density profiles close to isothermal, which can lead to non-Gaussian line-of-sight velocity dispersion (LOSVD) under anisotropic stellar orbits. However, recent observations of local ETGs in the MASSIVE Survey reveal outer kinematic structures at $1.5 R_{\mathrm{eff}}$ (effective radius) that are inconsistent with fixed isothermal density profiles; the authors proposed varying density profiles as an explanation. We aim to verify this conjecture and understand the influence of stellar assembly on these kinematic features through mock ETGs in IllustrisTNG. We create mock Integral-Field-Unit observations to extract projected stellar kinematic features for 207 ETGs with stellar mass $M_{\ast}\geqslant 10^{11} \mathrm{M_{\odot}}$ in TNG100-1. The mock observations reproduce the key outer ($1.5R_{\mathrm{eff}}$) kinematic structures in the MASSIVE ETGs, including the puzzling positive correlation between velocity dispersion profile outer slope $γ_{\mathrm{outer}}$ and the kurtosis $h_{4}$'s gradient. We find that $h_{4}$ is uncorrelated with stellar orbital anisotropy beyond $R_{\mathrm{eff}}$; instead we find that the variations in $γ_{\mathrm{outer}}$ and outer $h_{4}$ (a good proxy for $h_{4}$ gradient) are both driven by variations of the density profile at the outskirts across different ETGs. These findings corroborate the proposed conjecture and rule out velocity anisotropy as the origin of non-Gaussian outer kinematic structure in ETGs. We also find that the outer kurtosis and anisotropy correlate with different stellar assembly components, with the former related to minor mergers or flyby interactions while the latter is mainly driven by major mergers, suggesting distinct stellar assembly origins that decorrelates the two quantities.
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.
One of the main limitations in precision cluster cosmology arises from systematic errors and uncertainties in estimating cluster masses. Using the Mock-X pipeline, we produce synthetic X-ray images and derive cluster and galaxy group X-ray properties for a sample of over 30,000 simulated galaxy groups and clusters with $M_{\rm 500crit}$ between $10^{12}$ and $2\times 10^{15}$ M$_{\odot}$ in IllustrisTNG. We explore the similarities and differences between IllustrisTNG predictions of the Sunyaev-Zel'dovich and X-ray scaling relations with mass. We find a median hydrostatic mass bias $b = 0.125 \pm 0.003$ for $M_{\rm 500crit}$ $>10^{13}$ M$_{\odot}$. The bias increases to $b = 0.17 \pm 0.004$ when masses are derived from synthetic X-ray observations. We model how different underlying assumptions about the dependence of $Y_{\rm X}$ on halo mass can generate biases in the observed $Y_{\rm SZ} - M_{Y_{\rm X}}$ scaling relation. In particular, the simplifying assumption that $Y_{\rm X} - M_{\rm tot}$ is self-similar at all mass scales largely hides the break in $Y_{\rm SZ} - M_{\rm tot}$ and overestimates $Y_{\rm SZ}$ at galaxy and groups scales. We show that calibrating the $Y_{\rm X}-$mass proxy using a new model for a smoothly broken power law reproduces the true underlying $Y_{\rm SZ} - M_{\rm tot}$ scaling relation with high accuracy. Moreover, $M_{Y_{\rm X}}$ estimates calibrated with this method lead to $Y_{\rm SZ} - M_{Y_{\rm X}}$ predictions that are not biased by the presence of lower mass clusters or galaxy groups in the sample. Finally, we show that our smoothly broken power law model provides a robust way to derive the $Y_{\rm X}-$mass proxy, significantly reducing the level of mass bias for clusters, groups, and galaxies.
We use the IllustrisTNG simulations to explore the dynamic scaling relation between massive clusters and their central galaxies (BCGs). The Illustris TNG300-1 simulation we use includes 280 massive clusters with $M_{200} > 10^{14}$ M$_{\odot}$ enabling a robust statistical analysis. We derive the line-of-sight velocity dispersion of the stellar particles of the BCGs ($σ_{*, BCG}$), analogous to the observed BCG stellar velocity dispersion. We also compute the subhalo velocity dispersion to measure the cluster velocity dispersion ($σ_{cl}$). Both $σ_{*, BCG}$ and $σ_{cl}$ are proportional to the cluster halo mass, but the slopes differ slightly. Thus like the observed relation, $σ_{*, BCG} / σ_{cl}$ declines as a function of $σ_{cl}$, but the scatter is large. We explore the redshift evolution of $σ_{*, BCG} - σ_{cl}$ scaling relation for $z \lesssim 1$ in a way that can be compared directly with observations. The scaling relation has a similar slope at high redshift, but the scatter increases because of the large scatter in $σ_{*, BCG}$. The simulations imply that high redshift BCGs are dynamically more complex than their low redshift counterparts.
Galaxy mergers are known to host abundant young massive cluster (YMC) populations, whose formation mechanism is still not well-understood. Here, we present a high-resolution galaxy merger simulation with explicit star formation and stellar feedback prescriptions to investigate how mergers affect the properties of the interstellar medium and YMCs. Compared with a controlled simulation of an isolated galaxy, the mass fraction of dense and high-pressure gas is much higher in mergers. Consequently, the mass function of both molecular clouds and YMCs becomes shallower and extends to higher masses. Moreover, cluster formation efficiency is significantly enhanced and correlates positively with the star formation rate surface density and gas pressure. We track the orbits of YMCs and investigate the time evolution of tidal fields during the course of the merger. At an early stage of the merger, the tidal field strength correlates positively with YMC mass, $λ_{\rm tid}\propto M^{0.71}$, which systematically affects the shape of the mass function and age distribution of the YMCs. At later times, most YMCs closely follow the orbits of their host galaxies, gradually sinking into the center of the merger remnant due to dynamical friction, and are quickly dissolved via efficient tidal disruption. Interestingly, YMCs formed during the first passage, mostly in tidal tails and bridges, are distributed over a wide range of galactocentric radii, greatly increasing their survivability because of the much weaker tidal field in the outskirts of the merger system. These YMCs are promising candidates for globular clusters that survive to the present day.
We explore implications of a range of black hole (BH) seeding prescriptions on the formation of the brightest $z\gtrsim6$ quasars in cosmological hydrodynamic simulations. The underlying galaxy formation model is the same as in IllustrisTNG. Using constrained initial conditions, we study the growth of BHs in rare overdense regions (forming $\gtrsim10^{12}M_{\odot}/h$ halos by $z=7$) using a $(9~\mathrm{Mpc}/h)^3$ simulated volume. BH growth is maximal within halos that are compact and have a low tidal field. For these halos, we consider an array of gas-based seeding prescriptions wherein $M_{\mathrm{seed}}=10^4-10^6~M_{\odot}/h$ seeds are inserted in halos above critical thresholds for halo mass and dense, metal-poor gas mass (defined as $\tilde{M}_{\mathrm{h}}$ and $\tilde{M}_{\mathrm{sf,mp}}$, respectively, in units of $M_{\mathrm{seed}}$). We find that a seed model with $\tilde{M}_{\mathrm{sf,mp}}=5$ and $\tilde{M}_{\mathrm{h}}=3000$ successfully produces a $z\sim6$ quasar with $\sim10^9~M_{\odot}$ mass and $\sim10^{47}~\mathrm{ergs~s^ {-1}}$ luminosity. BH mergers play a crucial role at $z\gtrsim9$, causing an early boost in BH mass at a time when accretion-driven BH growth is negligible. When more stringent seeding conditions are applied (for e.g., $\tilde{M}_{\mathrm{sf,mp}}=1000$), the relative paucity of BH seeds results in a much lower merger rate. In this case, $z\gtrsim6$ quasars can only be formed if we enhance the maximum allowed BH accretion rates (by factors $\gtrsim10$) compared to the accretion model used in IllustrisTNG. This can be achieved either by allowing for super-Eddington accretion, or by reducing the radiative efficiency. Our results show that progenitors of $z\sim6$ quasars have distinct BH merger histories for different seeding models, which will be distinguishable with LISA observations.