Halo Properties Research Articles

Barred Galaxies in the Illustris-1 and TNG100 Simulations: A Comparison Study

Abstract We carry out a comparison study on the bar structure in the Illustris-1 and TNG100 simulations. At z = 0, 8.9% of 1232 disk galaxies with stellar masses in Illustris-1 are barred, while the numbers are 55% of 1269 in TNG100. The bar fraction as a function of stellar mass in TNG100 agrees well with the survey . The median redshifts of bar formation are ∼0.4–0.5 and ∼0.25 in TNG100 and Illustris-1, respectively. Bar fraction generally increases with stellar mass and decreases with gas fraction in both simulations. For galaxies with bars at z = 0, their bar formation time is generally anti-correlated with their gas fraction at high redshift. When the bars were formed, the disk gas fractions were mostly lower than 0.4. The much higher bar fraction in TNG100 probably benefits from the much lower gas fractions in massive disk galaxies since z ∼ 3, which may result from the combination of more effective stellar and AGN feedback. The latter may be the primary factor at z < 2. Meanwhile, in both simulations, barred galaxies have higher star formation rates before bar formation and have stronger AGN feedback, at all times, than unbarred galaxies. The properties of dark matter halos hosting massive disk galaxies are similar between the two simulations and should have a minor effect on the frequencies of different bars. For individual galaxies under similar halo environments across the two simulations, different baryonic physics can lead to striking discrepancies in morphology. The morphologies of individual galaxies are subject to the combined effects of environment and internal baryonic physics and are often not predictable.

Tracing the anemic stellar halo of M 101

Models of galaxy formation in a cosmological context predict that massive disk galaxies should have structured extended stellar halos. Recent studies in integrated light, however, report that a few galaxies, including the nearby disk galaxy M 101, have no measurable stellar halos to the detection limit. We aim to quantify the stellar content and structure of M 101’s outskirts by resolving its stars. We present the photometry of its stars based on deepF606WandF814Wimages taken withHubbleSpace Telescope (HST) as part of the GHOSTS survey. The HST fields are placed along the east and west sides of M 101 out to galactocentric distance (R) of ∼70 kpc. The constructed color-magnitude diagrams of stars reach down to two magnitudes below the tip of the red giant branch. We derived radial number density profiles of the bright red giant branch (RGB) stars. The mean color of the RGB stars atR ∼ 40−60 kpc is similar to those of metal-poor globular clusters in the Milky Way. We also derived radial surface brightness profiles using the public image data provided by the Dragonfly team. Both the radial number density and surface brightness profiles were converted to radial mass density profiles and combined. We find that the mass density profiles show a weak upturn at the very outer region, where surface brightness is as faint asμg ≈ 33 mag arcsec−2. An exponential disk + power-law halo model on the mass density profiles finds the total stellar halo mass ofMhalo= 8.2−2.2+3.5× 107M⊙. The total stellar halo mass does not exceedMhalo = 3.2 × 108 M⊙when strongly truncated disk models are considered. In combining the halo mass with the total stellar mass of M 101, we obtain the stellar halo mass fraction ofMhalo/Mgal= 0.20−0.08+0.10% with an upper limit of 0.78%. We compare the halo properties of M 101 with those of six GHOSTS survey galaxies as well as the Milky Way and M 31 and find that M 101 has an anemic stellar halo similar to the Milky Way.

Constraining the Milky Way Mass Profile with Phase-space Distribution of Satellite Galaxies

Abstract We estimate the Milky Way (MW) halo properties using satellite kinematic data including the latest measurements from Gaia DR2. With a simulation-based 6D phase-space distribution function (DF) of satellite kinematics, we can infer halo properties efficiently and without bias, and handle the selection function and measurement errors rigorously in the Bayesian framework. Applying our DF from the EAGLE simulation to 28 satellites, we obtain an MW halo mass of and a concentration of with the prior based on the M–c relation. The inferred mass profile is consistent with previous measurements but with better precision and reliability due to the improved methodology and data. Potential improvement is illustrated by combining satellite data and stellar rotation curves. Using our EAGLE DF and best-fit MW potential, we provide much more precise estimates of the kinematics for those satellites with uncertain measurements. Compared to the EAGLE DF, which matches the observed satellite kinematics very well, the DF from the semi-analytical model based on the dark-matter-only simulation Millennium II (SAM-MII) over-represents satellites with small radii and velocities. We attribute this difference to less disruption of satellites with small pericenter distances in the SAM-MII simulation. By varying the disruption rate of such satellites in this simulation, we estimate a ∼5% scatter in the inferred MW halo mass among hydrodynamics-based simulations.

HIKER: a halo-finding method based on kernel-shift algorithm

We introduce a new halo/subhalo finder, HIKER (a Halo fInder based on KERnel-shift algorithm), which takes advantage of a machine learning method – the mean-shift algorithm combined with the Plummer kernel function, to effectively locate density peaks corresponding to halos/subhalos in density field. Based on these density peaks, dark matter halos are identified as spherical overdensity structures, and subhalos are bound substructures with boundaries at their tidal radius. By testing HIKER code with mock halos, we show that HIKER performs excellently in recovering input halo properties. In particular, HIKER has higher accuracy in locating halo/subhalo centres than most halo finders. With cosmological simulations, we further show that HIKER reproduces the abundance of dark matter halos and subhalos quite accurately, and the HIKER halo/subhalo mass functions and Vmax functions are in good agreement with two widely used halo finders, SUBFIND and AHF.

Mass-loss in tidally stripped systems: the energy-based truncation method

ABSTRACT The ability to accurately predict the evolution of tidally stripped haloes is important for understanding galaxy formation and testing the properties of dark matter. Most studies of substructure evolution make predictions based on empirical models of tidal mass-loss that are calibrated using numerical simulations. This approach can be accurate in the cases considered, but lacks generality and does not provide a physical understanding of the processes involved. Recently, we demonstrated that truncating NFW distribution functions sharply in energy results in density profiles that resemble those of tidally stripped systems, offering a path to constructing physically motivated models of tidal mass-loss. In this work, we review calculations of mass-loss based on energy truncation alone, and then consider what secondary effects may modulate mass-loss beyond this. We find that a combination of dependence on additional orbital parameters and variations in individual particle energies over an orbit results in a less abrupt truncation in energy space as a subhalo loses mass. Combining the energy truncation approach with a simple prediction for the mass-loss rate, we construct a full model of mass-loss that can accurately predict the evolution of a subhalo in terms of a single parameter ηeff. This parameter can be fully determined from the initial orbital and halo properties, and does not require calibration with numerical simulations.

Limitations to the ‘basic’ HOD model and beyond

ABSTRACT We use the IllustrisTNG cosmological, hydrodynamical simulations to test fundamental assumptions of the mass-based halo occupation distribution (HOD) approach to modelling the galaxy–halo connection. By comparing the clustering of galaxies measured in the 300 Mpc TNG box (TNG300) with that predicted by the standard (basic) HOD model, we find that, on average, the ‘basic’ HOD model underpredicts the real-space correlation function in the TNG300 box by ∼15 per cent on scales of $1 \,\,\lt\,\, r \,\,\lt\,\, 20 \ {\rm Mpc}\, h^{-1}$, which is well beyond the target precision demanded of next-generation galaxy redshift surveys. We perform several tests to establish the robustness of our findings to systematic effects, including the effect of finite box size and the choice of halo finder. In our exploration of ‘secondary’ parameters with which to augment the ‘basic’ HOD, we find that the local environment of the halo, the velocity dispersion anisotropy, β, and the product of the half-mass radius and the velocity dispersion, σ2Rhalfmass, are the three most effective measures of assembly bias that help reconcile the ‘basic’ HOD-predicted clustering with that in TNG300. In addition, we test other halo properties such as halo spin, formation epoch, and halo concentration. We also find that at fixed halo mass, galaxies in one type of environment cluster differently from galaxies in another. We demonstrate that a more complete model of the galaxy–halo connection can be constructed if we combine both mass and local environment information about the halo.

Modelling the tightest relation between galaxy properties and dark matter halo properties from hydrodynamical simulations of galaxy formation

ABSTRACT We investigate how a property of a galaxy correlates most tightly with a property of its host dark matter halo, using state-of-the-art hydrodynamical simulations of galaxy formation: EAGLE, Illustris, and IllustrisTNG. Unlike most of the previous work, our analyses focus on all types of galaxies, including both central and satellite galaxies. We find that the stellar mass of a galaxy at the epoch of the peak circular velocity with an evolution correction gives the tightest such correlation to the peak circular velocity Vpeak of the galaxy’s underling dark matter halo. The evolution of galaxy stellar mass reduces rather than increases scatter in such a relation. We also find that one major source of scatter comes from star stripping due to the strong interactions between galaxies. Even though, we show that the size of scatter predicted by hydrodynamical simulations has a negligible impact on the clustering of dense Vpeak-selected subhalo from simulations, which suggests that even the simplest subhalo abundance matching (SHAM), without scatter and any additional free parameter, can provide a robust prediction of galaxy clustering that can agree impressively well with the observations from the Sloan Digital Sky Survey (SDSS) main galaxy survey.

Nonlinear structure formation in Bound Dark Energy

We study nonlinear structure formation in the Bound Dark Energy model (BDE), where dark energy (DE) corresponds to a light scalar meson particle ϕ dynamically formed at a condensation energy scale Λc. The evolution of this dark-energy meson is determined by the potential V(ϕ)=Λc4+2/3ϕ−2/3, with a distinguishing phenomenology from other quintessence scenarios. Particularly, the expansion rate of the universe is affected not only at late times, but also when the condensation of ϕ occurs, which in linear theory leads to an enhancement (with respect to standard ΛCDM) of matter perturbations on small scales. We study how much of this signature is still present at late times as well as the properties of dark matter halos in the nonlinear regime through N-body simulations. Our results show that nonlinear corrections wash out this feature from the matter power spectrum even before DE becomes dominant. There is, however, a small but clear suppression of the BDE spectrum of 2% today on the largest scales due to the distinct late-time dynamics of DE. The differences on the clustering power between BDE and ΛCDM are reflected in the halo mass function, where small halos are more abundant in BDE as opposed to large heavy structures, whose formation is delayed because of the expansion history of the universe. This result is well captured by the semi-analytical Sheth-Tormen formula. However, despite these differences, the halo concentration parameter is essentially the same in both models, which suggest that clustering inside the halos decouple from the general expansion once the halos form.

A Comprehensive Catalog of Dark Matter Halo Models for SPARC Galaxies

Abstract We present rotation curve fits to 175 late-type galaxies from the Spitzer Photometry and Accurate Rotation Curves database using seven dark matter (DM) halo profiles: pseudo-isothermal, Burkert, Navarro–Frenk–White (NFW), Einasto, Di Cintio et al. (2014, hereafter DC14), cored-NFW, and a new semi-empirical profile named Lucky13. We marginalize over the stellar mass-to-light ratio, galaxy distance, disk inclination, halo concentration, and halo mass (and an additional shape parameter for Einasto) using a Markov Chain Monte Carlo method. We find that cored halo models, such as the DC14 and Burkert profiles, generally provide better fits to rotation curves than the cuspy NFW profile. The stellar mass-halo mass relation from abundance matching is recovered by all halo profiles once imposed as a Bayesian prior, whereas the halo mass–concentration relation is not reproduced in detail by any halo model. We provide an extensive set of figures as well as best-fit parameters in machine-readable tables to facilitate model comparison and the exploration of DM halo properties.

The Tessellation-Level-Tree: characterizing the nested hierarchy of density peaks and their spatial distribution in cosmological N-body simulations

ABSTRACT We use the Millennium and Millennium-II simulations to illustrate the Tessellation-Level-Tree (tlt), a hierarchical tree structure linking density peaks in a field constructed by voronoi tessellation of the particles in a cosmological N-body simulation. The tlt uniquely partitions the simulation particles into disjoint subsets, each associated with a local density peak. Each peak is a subpeak of a unique higher peak. The tlt can be persistence filtered to suppress peaks produced by discreteness noise. Thresholding a peak’s particle list at $\sim 80\left \langle \rho \right \rangle \,$ results in a structure similar to a standard friend-of-friends halo and its subhaloes. For thresholds below $\sim 7\left \langle \rho \right \rangle \,$, the largest structure percolates and is much more massive than other objects. It may be considered as defining the cosmic web. For a threshold of $5\left \langle \rho \right \rangle \,$, it contains about half of all cosmic mass and occupies $\sim 1{{\ \rm per\ cent}}$ of all cosmic volume; a typical external point is then ∼7h−1 Mpc from the web. We investigate the internal structure and clustering of tlt peaks. Defining the saddle point density ρlim as the density at which a peak joins its parent peak, we show the median value of ρlim for FoF-like peaks to be similar to the density threshold at percolation. Assembly bias as a function of ρlim is stronger than for any known internal halo property. For peaks of group mass and below, the lowest quintile in ρlim has b ≈ 0, and is thus uncorrelated with the mass distribution.

Constraining the properties of gaseous halos via cross-correlations of upcoming galaxy surveys and thermal Sunyaev-Zel’dovich maps

The thermal Sunyaev-Zel'dovich (tSZ) effect induces a Compton-$y$ distortion in cosmic microwave background (CMB) temperature maps that is sensitive to a line of sight integral of the ionized gas pressure. By correlating the positions of galaxies with maps of the Compton-$y$ distortion, one can probe baryonic feedback processes and study the thermodynamic properties of a significant fraction of the gas in the Universe. Using a model fitting approach, we forecast how well future galaxy and CMB surveys will be able to measure these correlations, and show that powerful constraints on halo pressure profiles can be obtained. Our forecasts are focused on correlations between galaxies and halos identified by the upcoming Dark Energy Spectroscopic Instrument survey and tSZ maps from the Simons Observatory and CMB-S4 experiments, but have general applicability to other surveys, such as the Large Synoptic Survey Telescope. We include prescriptions for observational systematics, such as halo miscentering and halo mass bias, demonstrating several important degeneracies with pressure profile parameters. Assuming modest priors on these systematics, we find that measurements of halo-$y$ and galaxy-$y$ correlations with future surveys will yield tight constraints on the pressure profiles of group-scale dark matter halos, and enable current feedback models to either be confirmed or ruled out.

Interpreting Observations of Absorption Lines in the Circumgalactic Medium with a Turbulent Medium

Abstract Single-phase photoionization equilibrium (PIE) models are often used to infer the underlying physical properties of galaxy halos probed in absorption with ions at different ionization potentials. To incorporate the effects of turbulence, we use the Models of Agitated and Illuminated Hindering and Emitting Media (MAIHEM) code to model an isotropic turbulent medium exposed to a redshift-zero metagalactic UV background, while tracking the ionizations, recombinations, and species-by-species radiative cooling for a wide range of ions. By comparing observations and simulations over a wide range of turbulent velocities, densities, and metallicity with a Markov chain Monte Carlo technique, we find that MAIHEM models provide an equally good fit to the observed low-ionization species compared to PIE models, while reproducing at the same time high-ionization species such as Si iv and O vi. By including multiple phases, MAIHEM models favor a higher metallicity (Z/Z ⊙ ≈ 40%) for the circumgalactic medium compared to PIE models. Furthermore, all of the solutions require some amount of turbulence (σ 3D 26 km s−1). Correlations between turbulence, metallicity, column density, and impact parameter are discussed alongside mechanisms that drive turbulence within the halo.

Aging haloes: implications of the magnitude gap on conditional statistics of stellar and gas properties of massive haloes

ABSTRACT Cold dark matter model predicts that the large-scale structure grows hierarchically. Small dark matter haloes form first. Then, they grow gradually via continuous merger and accretion. These haloes host the majority of baryonic matter in the Universe in the form of hot gas and cold stellar phase. Determining how baryons are partitioned into these phases requires detailed modelling of galaxy formation and their assembly history. It is speculated that formation time of the same mass haloes might be correlated with their baryonic content. To evaluate this hypothesis, we employ haloes of mass above $10^{14}\, \mathrm{M}_{\odot }$ realized by TNG300 solution of the IllustrisTNG project. Formation time is not directly observable. Hence, we rely on the magnitude gap between the brightest and the fourth brightest halo galaxy member, which is shown that traces formation time of the host halo. We compute the conditional statistics of the stellar and gas content of haloes conditioned on their total mass and magnitude gap. We find a strong correlation between magnitude gap and gas mass, BCG stellar mass, and satellite galaxies stellar mass, but not the total stellar mass of halo. Conditioning on the magnitude gap can reduce the scatter about halo property–halo mass relation and has a significant impact on the conditional covariance. Reduction in the scatter can be as significant as 30 per cent, which implies more accurate halo mass prediction. Incorporating the magnitude gap has a potential to improve cosmological constraints using halo abundance and allows us to gain insight into the baryon evolution within these systems.

On the absence of a universal surface density, and a maximum Newtonian acceleration in dark matter haloes: Consequences for MOND

Abstract We study the dark matter (DM) surface density using the SPARC sample and compare it to Donato et al. (2009) result. By means of MCMC method, we infer the best-fitting parameters for each galaxy. We reobtain the scaling relation between the surface density and luminosity, and several other scaling laws relating the dark matter halo properties to that of the galactic disc properties. We conclude, in contrast with Donato et al. (2009), that the dark matter surface density is not a universal (constant) quantity but correlates with the luminosity as well as with other galactic disc properties. A derived posterior probability distribution of ρ 0 r 0 shows that the null hypothesis of constancy is rejected at a very high confidence level. These results leave little room for the claimed universality of dark matter surface density. Since MOND has strong prediction on the surface density (Milgrom, 2009), we compared our result with those predictions, finding that MOND predictions are violated by data. To strengthen the previous result, we compared our results to another prediction of MOND (Milgrom and Sanders, 2005), the existence of a maximum Newtonian dark matter acceleration in the halo. Also in this case, MOND predictions are in contradiction with data. The dark matter Newtonian acceleration correlates with all the previously presented galactic disc properties, and data are distributed outside the bound predicted by Milgrom and Sanders (2005). We also find that the null hypothesis (constancy of DM Newtonian acceleration) is rejected at a very high confidence level.

Galaxy assembly bias of central galaxies in the Illustris simulation

ABSTRACT Galaxy assembly bias, the correlation between galaxy properties and halo properties at fixed halo mass, could be an important ingredient in halo-based modelling of galaxy clustering. We investigate the central galaxy assembly bias by studying the relation between various galaxy and halo properties in the Illustris hydrodynamic galaxy formation simulation. Galaxy stellar mass M* is found to have a tighter correlation with peak maximum halo circular velocity Vpeak than with halo mass Mh. Once the correlation with Vpeak is accounted for, M* has nearly no dependence on any other halo assembly variables. The correlations between galaxy properties related to star formation history and halo assembly properties also show a cleaner form as a function of Vpeak than as a function of Mh, with the main correlation being with halo formation time and to a less extent halo concentration. Based on the galaxy–halo relation, we present a simple model to relate the bias factors of a central galaxy sample and the corresponding halo sample, both selected based on assembly-related properties. It is found that they are connected by the correlation coefficient of the galaxy and halo properties used to define the two samples, which provides a reasonable description for the samples in the simulation and suggests a simple prescription to incorporate galaxy assembly bias into the halo model. By applying the model to the local galaxy clustering measurements in Lin et al., we infer that the correlation between star formation history or specific star formation rate and halo formation time is consistent with being weak.

Physical correlations of the scatter between galaxy mass, stellar content, and halo mass

ABSTRACT We use the UniverseMachine to analyse the source of scatter between the central galaxy mass, the total stellar mass in the halo, and the dark matter halo mass, for massive (Mvir > 1013 M⊙) haloes. We also propose a new halo mass estimator, the cen+N mass: the sum of the stellar mass of the central and the N most massive satellites. We show that, when real space positions are perfectly known, the cen+N mass has scatter competitive with that of richness-based estimators. However, in redshift space, using a simple cluster finder, the cen+N mass suffers less from projection effects in the UniverseMachine model. The cen+N mass is therefore a potential candidate to constrain cosmology with upcoming spectroscopic data from DESI. We analyse the scatter in stellar mass at fixed halo mass and show that the total stellar mass in a halo is uncorrelated with secondary halo properties, but that the central stellar mass is a function of both halo mass and halo age. This is because central galaxies in older haloes have had more time to grow via accretion. If the UniverseMachine model is correct, this implies that haloes selected using the centrals stellar mass will be biased old and that accurate galaxy-halo modelling of mass selected samples therefore needs to consider halo age in addition to mass.

On the Prospect of Using the Maximum Circular Velocity of Halos to Encapsulate Assembly Bias in the Galaxy–Halo Connection

Abstract We investigate a conceptual modification of the halo occupation distribution approach, using the halos’ present-day maximal circular velocity, V max, as an alternative to halo mass. In particular, using a semianalytic galaxy formation model applied to the Millennium WMAP7 simulation, we explore the extent that switching to V max as the primary halo property incorporates the effects of assembly bias into the formalism. We consider fixed number density galaxy samples ranked by stellar mass and examine the variations in the halo occupation functions with either halo concentration or formation time. We find that using V max results in a significant reduction in the occupancy variation of the central galaxies, particularly for concentration. The satellites’ occupancy variation on the other hand increases in all cases. We find effectively no change in the halo clustering dependence on concentration, for fixed bins of V max compared to fixed halo mass. Most crucially, we calculate the impact of assembly bias on galaxy clustering by comparing the amplitude of clustering to that of a shuffled galaxy sample, finding that the level of galaxy assembly bias remains largely unchanged. Our results suggest that while using V max as a proxy for halo mass diminishes some of the occupancy variations exhibited in the galaxy–halo relation, it is not able to encapsulate the effects of assembly bias potentially present in galaxy clustering. The use of other more complex halo properties, such as V peak, the peak value of V max over the assembly history, provides some improvement and warrants further investigation.

BE-HaPPY: bias emulator for halo power spectrum including massive neutrinos

We study the clustering properties of dark matter haloes in real- and redshift-space in cosmologies with massless and massive neutrinos through a large set of state-of-the-art N-body simulations. We provide quick and easy-to-use prescriptions for the halo bias on linear and mildly non-linear scales, both in real and redshift-space, which are valid also for massive neutrinos cosmologies. Finally we present a halo bias emulator, BE-HaPPY, calibrated on the N-body simulations, which is fast enough to be used in the standard Markov Chain Monte Carlo approach to cosmological inference. For a fiducial standard ΛCDM cosmology BE-HaPPY reproduces the simulation inputs with percent or sub-percent accuracy for the halo mass cuts it is calibrated on (M>{5×1011, 1012, 3× 1012, 1013} h-1 M⊙) on the scales of interest (linear and well into the mildly non-linear regime). The approach presented here represents a well defined route to meeting the halo-bias accuracy requirements for the analysis of next-generation large-scale structure surveys. The software BE-HaPPY can run both in emulator mode and in calibration mode, on user-supplied simulations outputs, and is made publicly available.

Mapping the dark matter halo of early-type galaxy NGC 2974 through orbit-based models with combined stellar and cold gas kinematics

ABSTRACT We present an orbit-based method of combining stellar and cold gas kinematics to constrain the dark matter profile of early-type galaxies. We apply this method to early-type galaxy NGC 2974, using Pan-STARRS imaging and SAURON stellar kinematics to model the stellar orbits, and introducing H i kinematics from VLA observation as a tracer of the gravitational potential. The introduction of the cold gas kinematics shows a significant effect on the confidence limits of especially the dark halo properties: we exclude more than $95{{\ \rm per\ cent}}$ of models within the 1σ confidence level of Schwarzschild modelling with only stellar kinematics, and reduce the relative uncertainty of the dark matter fraction significantly to $10{{\ \rm per\ cent}}$ within 5Re. Adopting a generalized Navarro–Frenk–White (NFW) dark matter profile, we measure a shallow cuspy inner slope of $0.6^{+0.2}_{-0.3}$ when including the cold gas kinematics in our model. We cannot constrain the inner slope with the stellar kinematics alone.

On the road to per cent accuracy – III. Non-linear reaction of the matter power spectrum to massive neutrinos

ABSTRACT We analytically model the non-linear effects induced by massive neutrinos on the total matter power spectrum using the halo model reaction framework of Cataneo et al. In this approach, the halo model is used to determine the relative change to the matter power spectrum caused by new physics beyond the concordance cosmology. Using standard fitting functions for the halo abundance and the halo mass–concentration relation, the total matter power spectrum in the presence of massive neutrinos is predicted to per cent-level accuracy, out to $k=10 \,{ h}\,{\rm Mpc}^{-1}$. We find that refining the prescriptions for the halo properties using N-body simulations improves the recovered accuracy to better than 1 per cent. This paper serves as another demonstration for how the halo model reaction framework, in combination with a single suite of standard Λ cold dark matter (ΛCDM) simulations, can recover per cent-level accurate predictions for beyond ΛCDM matter power spectra, well into the non-linear regime.