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the relation between mass and concentration of galaxy clusters traces their formation and evolution. massive lensing clusters were observed to be overconcentrated and following a steep scaling in tension with predictions from the concordance λ cold dark matter (λcdm) paradigm. we critically revise the relation in the clash (cluster lensing and supernova survey with hubble), the sgas (sloan giant arcs survey), the locuss (local cluster substructure survey), and the high-redshift samples of weak lensing clusters. measurements of mass and concentration are anti-correlated, which can bias the observed relation towards steeper values. we corrected for this bias and compared the measured relation to theoretical predictions accounting for halo triaxiality, adiabatic contraction of the halo, presence of a dominant brightest cluster galaxy, and, mostly, selection effects in the observed sample. the normalization, the slope, and the scatter of the expected relation are strongly sample-dependent. for the considered samples, the predicted slope is much steeper than that of the underlying relation characterizing dark matter-only clusters. we found that the correction for statistical and selection biases in observed relations mostly solve the tension with the λcdm model. | the mass-concentration relation in lensing clusters: the role of statistical biases and selection effects |
we introduce a new parameter λds to quantify the dynamical state of galaxy clusters and test it using simulations from the three hundred cluster zoom suite. λds is a combination of three previously used dynamical state measures, namely virial ratio, centre of mass offset, and substructure mass fraction, crafted to assume a double-gaussian distribution, thereby yielding a natural division between relaxed and unrelaxed clusters where the gaussians cross. using dark matter-only simulations, we identify the optimal separator to be λds = 3.424. we test this same criterion on two sets of fully hydrodynamical the three hundred runs (gadget-x and gizmo-simba), and find only a weak dependence on the input baryonic physics. we correlate the evolution of λds with the mass accretion history and find that halo mass changes of $\frac{\delta m_{200}}{m_{200}} \lesssim 0.12$ do not typically alter the dynamical state. we examine the relaxation period, defined as the time taken to return to relaxation after becoming disturbed, and find a correlation between this relaxation period and the strength of halo mass change $\frac{\delta m_{200}}{m_{200}}$. by fitting this correlation, we show that the relaxation period can be estimated from $\frac{\delta m_{200}}{m_{200}}$ (even for multiple mass accretion events) with good accuracy. | the three hundred: cluster dynamical states and relaxation period |
one of the hottest questions in the cosmology of self-interacting dark matter (sidm) is whether scatterings can induce detectable core-collapse in halos by the present day. because gravitational tides can accelerate core-collapse, the most promising targets to observe core-collapse are satellite galaxies and subhalo systems. however, simulating small subhalos is computationally intensive, especially when subhalos start to core-collapse. in this work, we present a hierarchical framework for simulating a population of sidm subhalos, which reduces the computation time to linear order in the total number of subhalos. with this method, we simulate substructure lensing systems with multiple velocity-dependent sidm models, and show how subhalo evolution depends on the sidm model, subhalo mass and orbits. we find that an sidm cross section of $\gtrsim 200$ cm$^2$/g at velocity scales relevant for subhalos' internal heat transfer is needed for a significant fraction of subhalos to core-collapse in a typical lens system at redshift $z=0.5$, and that core-collapse has unique observable features in lensing. we show quantitatively that core-collapse in subhalos is typically accelerated compared to field halos, except when the sidm cross section is non-negligible ($\gtrsim \mathcal{o}(1)$ cm$^2$/g) at subhalos' orbital velocities, in which case evaporation by the host can delay core-collapse. this suggests that substructure lensing can be used to probe velocity-dependent sidm models, especially if line-of-sight structures (field halos) can be distinguished from lens-plane subhalos. intriguingly, we find that core-collapse in subhalos can explain the recently reported ultra-steep density profiles of substructures found by lensing with the \emph{hubble space telescope} | till the core collapses: the evolution and properties of self-interacting dark matter subhalos |
we compare subhalo mass and velocity functions obtained from different simulations with different subhalo finders among each other, and with predictions from the new semi-analytical model presented in paper i. we find that subhalo mass functions (shmfs) obtained using different subhalo finders agree with each other at the level of ∼20 per cent, but only at the low-mass end. at the massive end, subhalo finders that identify subhaloes based purely on density in configuration space dramatically underpredict the subhalo abundances by more than an order of magnitude. these problems are much less severe for subhalo velocity functions (shvfs), indicating that they arise from issues related to assigning masses to the subhaloes, rather than from detecting them. overall the predictions from the semi-analytical model are in excellent agreement with simulation results obtained using the more advanced subhalo finders that use information in six-dimensional phase-space. in particular, the model accurately reproduces the slope and host-mass-dependent normalization of both the subhalo mass and velocity functions. we find that the shmfs and shvfs have power-law slopes of 0.86 and 2.77, respectively, significantly shallower than what has been claimed in several studies in the literature. | statistics of dark matter substructure - ii. comparison of model with simulation results |
dark matter substructures are interesting since they can reveal the properties of dark matter. collisionless n-body simulations of cold dark matter show more substructures compared with the population of dwarf galaxy satellites observed in our local group. therefore, understanding the population and property of subhalos at cosmological scale would be an interesting test for cold dark matter. in recent years, it has become possible to detect individual dark matter subhalos near images of strongly lensed extended background galaxies. in this work, we discuss the possibility of using deep neural networks to detect dark matter subhalos, and showing some preliminary results with simulated data. we found that neural networks not only show promising results on detecting multiple dark matter subhalos, but also learn to reject the subhalos on the lensing arc of a smooth lens where there is no subhalo. | hunting for dark matter subhalos in strong gravitational lensing with neural networks |
substructures are known to be good tracers for the dynamical states and recent accretion histories of the most massive collapsed structures in the universe, galaxy clusters. observations find extremely massive substructures in some clusters, especially abell 2744 (a2744), which are potentially in tension with the λcdm paradigm because they are not found in simulations directly. however, the methods to measure substructure masses strongly differ between observations and simulations. using the fully hydrodynamical cosmological simulation suite magneticum pathfinder, we develop a method to measure substructure masses in projection from simulations, similarly to the observational approach. we identify a simulated a2744 counterpart that not only has eight substructures of similar mass fractions but also exhibits similar features in the hot gas component. this cluster formed only recently through a major merger together with at least six massive minor merger events since z = 1, where previously the most massive component had a mass of less than 1 × 1014 m ⊙. we show that the mass fraction of all substructures and of the eighth substructure separately are excellent tracers for the dynamical state and assembly history for all galaxy cluster mass ranges, with high fractions indicating merger events within the last 2 gyr. finally, we demonstrate that the differences between subhalo masses measured directly from simulations as bound and those measured in projection are due to methodology, with the latter generally 2-3 times larger than the former. we provide a predictor function to estimate projected substructure masses from subfind masses for future comparison studies between simulations and observations. | the hateful eight: connecting massive substructures in galaxy clusters like a2744 to their dynamical assembly state using the magneticum simulations |
we introduce phew ( parallel hi erarchical watershed), a new segmentation algorithm to detect structures in astrophysical fluid simulations, and its implementation into the adaptive mesh refinement (amr) code ramses. phew works on the density field defined on the adaptive mesh, and can thus be used on the gas density or the dark matter density after a projection of the particles onto the grid. the algorithm is based on a `watershed' segmentation of the computational volume into dense regions, followed by a merging of the segmented patches based on the saddle point topology of the density field. phew is capable of automatically detecting connected regions above the adopted density threshold, as well as the entire set of substructures within. our algorithm is fully parallel and uses the mpi library. we describe in great detail the parallel algorithm and perform a scaling experiment which proves the capability of phew to run efficiently on massively parallel systems. future work will add a particle unbinding procedure and the calculation of halo properties onto our segmentation algorithm, thus expanding the scope of phew to genuine halo finding. | phew: a parallel segmentation algorithm for three-dimensional amr datasets. application to structure detection in self-gravitating flows |
detecting substructure within strongly lensed images is a promising route to shed light on the nature of dark matter. however, it is a challenging task, which traditionally requires detailed lens modeling and source reconstruction, taking weeks to analyze each system. we use machine-learning to circumvent the need for lens and source modeling and develop a neural network to both locate subhalos in an image as well as determine their mass using the technique of image segmentation. the network is trained on images with a single subhalo located near the einstein ring across a wide range of apparent source magnitudes. the network is then able to resolve subhalos with masses $m\gtrsim 10^{8.5} m_{\odot}$. training in this way allows the network to learn the gravitational lensing of light, and remarkably, it is then able to detect entire populations of substructure, even for locations further away from the einstein ring than those used in training. over a wide range of the apparent source magnitude, the false-positive rate is around three false subhalos per 100 images, coming mostly from the lightest detectable subhalo for that signal-to-noise ratio. with good accuracy and a low false-positive rate, counting the number of pixels assigned to each subhalo class over multiple images allows for a measurement of the subhalo mass function (smf). when measured over three mass bins from $10^9m_{\odot}$--$10^{10} m_{\odot}$ the smf slope is recovered with an error of 36% for 50 images, and this improves to 10% for 1000 images with hubble space telescope-like noise. | extracting the subhalo mass function from strong lens images with image segmentation |
understanding the non-linear dynamics of satellite haloes (a.k.a. 'sub-haloes') is important for predicting the abundance and distribution of dark matter sub-structures and satellite galaxies, and for distinguishing among microphysical dark matter models using observations. typically, modelling these dynamics requires large n-body simulations with high resolution. semi-analytic models can provide a more efficient way to describe the key physical processes such as dynamical friction, tidal mass loss, and tidal heating, with only a few free parameters. in this work, we present a fast markov chain monte carlo fitting approach to explore the parameter space of such a sub-halo non-linear evolution model. we use the dynamical models described in an earlier work and calibrate the models to two sets of high-resolution cold dark matter n-body simulations, elvis and caterpillar. compared to previous calibrations that used manual parameter tuning, our approach provides a more robust way to determine the best-fitting parameters and their posterior probabilities. we find that jointly fitting for the sub-halo mass and maximum velocity functions can break the degeneracy between tidal stripping and tidal heating parameters, as well as providing better constraints on the strength of dynamical friction. we show that our semi-analytic simulation can accurately reproduce n-body simulations statistics, and that the calibration results for the two sets of n-body simulations agree at 95 per cent confidence level. dynamical models calibrated in this work will be important for future dark matter sub-structure studies. | a new calibration method of sub-halo orbital evolution for semi-analytic models |
a few dark matter substructures have recently been detected in strong gravitational lenses through their perturbations of highly magnified images. we derive a characteristic scale for lensing perturbations and show that they are significantly larger than the perturber’s einstein radius. we show that the perturber’s projected mass enclosed within this radius, scaled by the log-slope of the host galaxy’s density profile, can be robustly inferred even if the inferred density profile and tidal radius of the perturber are biased. we demonstrate the validity of our analytic derivation using several gravitational lens simulations where the tidal radii and the inner log-slopes of the density profile of the perturbing subhalo are allowed to vary. by modeling these simulated data, we find that our mass estimator, which we call the effective subhalo lensing mass, is accurate to within about 10% or smaller in each case, whereas the inferred total subhalo mass can potentially be biased by nearly an order of magnitude. we therefore recommend that the effective subhalo lensing mass be reported in future lensing reconstructions, as this will allow for a more accurate comparison with the results of dark matter simulations. | a robust mass estimator for dark matter subhalo perturbations in strong gravitational lenses |
we investigate the morphology of the stellar distribution (sd) in a sample of milky way-like galaxies in the tng50 simulation. using a local in shell iterative method as the main approach, we explicitly show evidence of twisting (in about 52% of halos) and stretching (in 48% of them) in real space. this is matched with the reorientation observed in the eigenvectors of the inertia tensor and gives us a clear picture of having a reoriented sd. we make a comparison between the shape profile of the dark matter (dm) halo and sd and quite remarkably see that their radial profiles are fairly close, especially at small galactocentric radii, where the stellar disk is located. this implies that the dm halo is somewhat aligned with stars in response to the baryonic potential. the level of alignment mostly decreases away from the center. we study the impact of substructures in the orbital circularity parameter. it is demonstrated that in some cases, faraway substructures are counterrotating compared with the central stars and may flip the sign of total angular momentum and thus the orbital circularity parameter. truncating them above 150 kpc, however, retains the disky structure of the galaxy as per initial selection. including the impact of substructures in the shape of stars, we explicitly show that their contribution is subdominant. overlaying our theoretical results on the observational constraints from previous literature, we establish fair agreement. | inferring the morphology of stellar distribution in tng50: twisted and twisted-stretched shapes |
we present a high-resolution dissection of the two-dimensional total mass distribution in the core of the hubble frontier fields galaxy cluster macs j0416.1-2403, at z = 0.396. we exploit hst/wfc3 near-ir (f160w) imaging, vlt/multi unit spectroscopic explorer spectroscopy, and chandra data to separate the stellar, hot gas, and dark-matter mass components in the inner 300 kpc of the cluster. we combine the recent results of our refined strong lensing analysis, which includes the contribution of the intracluster gas, with the modeling of the surface brightness and stellar mass distributions of 193 cluster members, of which 144 are spectroscopically confirmed. we find that, moving from 10 to 300 kpc from the cluster center, the stellar to total mass fraction decreases from 12% to 1% and the hot gas to total mass fraction increases from 3% to 9%, resulting in a baryon fraction of approximatively 10% at the outermost radius. we measure that the stellar component represents ∼30%, near the cluster center, and 15%, at larger clustercentric distances, of the total mass in the cluster substructures. we subtract the baryonic mass component from the total mass distribution and conclude that within 30 kpc (∼3 times the effective radius of the brightest cluster galaxy) from the cluster center the surface mass density profile of the total mass and global (cluster plus substructures) dark-matter are steeper and that of the diffuse (cluster) dark-matter is shallower than an nfw profile. our current analysis does not point to a significant offset between the cluster stellar and dark-matter components. this detailed and robust reconstruction of the inner dark-matter distribution in a larger sample of galaxy clusters will set a new benchmark for different structure formation scenarios. | mass profile decomposition of the frontier fields cluster macs j0416-2403: insights on the dark-matter inner profile |
cold dark matter scenarios of hierarchical large-scale structure formation predict the existence of abundant subhalos around large galaxies. however, the number of observed dwarf galaxies is far from this theoretical prediction, suggesting that most of the subhalos could be dark or quite faint. gravitational lensing is a powerful tool to probe the mass distribution directly irrespective of whether it is visible or dark. time delay anomalies in strongly lensed quasar systems are complementary to flux-ratio anomalies in probing dark matter substructure in galaxies. here we propose that lensed gravitational waves detected by the third-generation ground detectors with quite accurate time delay measurements could be a much better tool for this study than conventional techniques. combined with good quality images of lensed host galaxies identified by the electromagnetic counterpart measurements, lensed gravitational wave signals could make the systematic errors caused by dark matter substructures detectable at levels of several percent, depending on their mass functions, internal distribution of subhalos, and lensing system configuration. | anomalies in time delays of lensed gravitational waves and dark matter substructures |
we present a dynamical measurement of the tangential motion of the andromeda system, the ensemble consisting of the andromeda galaxy (m31) and its satellites. the system is modelled as a structure with cosmologically motivated velocity dispersion and density profiles, and we show that our method works well when tested using the most massive substructures in high-resolution λ cold dark matter (λcdm) simulations. applied to the sample of 40 currently known galaxies of this system, we find a value for the velocity along the east and north directions of veast = -111.5 ± 70.2 km s-1 and vnorth = 99.4 ± 60.0 km s-1, implying a transverse velocity significantly higher than previous estimates of the proper motion of m31 itself. this result has significant implications on estimates of the mass of the local group, as well as on its past and future history. | the transverse velocity of the andromeda system, derived from the m31 satellite population |
dark matter-only simulations are able to produce the cosmic structure of a lambda cold dark matter universe, at a much lower computational cost than more physically motivated hydrodynamical simulations. however, it is not clear how well smaller substructure is reproduced by dark matter-only simulations. to investigate this, we directly compare the substructure of galaxy clusters and of surrounding galaxy groups in hydrodynamical and dark matter-only simulations. we utilize thethreehundred project, a suite of 324 simulations of galaxy clusters that have been simulated with hydrodynamics, and in dark matter-only. we find that dark matter-only simulations underestimate the number density of galaxies in the centres of groups and clusters relative to hydrodynamical simulations, and that this effect is stronger in denser regions. we also look at the phase space of infalling galaxy groups, to show that dark matter-only simulations underpredict the number density of galaxies in the centres of these groups by about a factor of four. this implies that the structure and evolution of infalling groups may be different to that predicted by dark matter-only simulations. finally, we discuss potential causes for this underestimation, considering both physical effects, and numerical differences in the analysis. | the three hundred project: substructure in hydrodynamical and dark matter simulations of galaxy groups around clusters |
we present a morphological study of the 17 lensed lyα emitter (lae) galaxies of the baryon oscillation spectroscopic survey emission-line lens survey (bells) for the galaxy-lyα emitter systems (bells gallery) sample. this analysis combines the magnification effect of strong galaxy-galaxy lensing with the high resolution of the hubble space telescope to achieve a physical resolution of ∼80 pc for this 2 < z < 3 lae sample, allowing a detailed characterization of the lae rest-frame ultraviolet continuum surface brightness profiles and substructure. we use lens-model reconstructions of the laes to identify and model individual clumps, which we subsequently use to constrain the parameters of a generative statistical model of the lae population. since the bells gallery sample is selected primarily on the basis of lyα emission, the laes that we study here are likely to be directly comparable to those selected in wide-field, narrowband lae surveys, in contrast with the lensed laes identified in cluster-lensing fields. we find an lae clumpiness fraction of approximately 88%, which is significantly higher than that found in previous (non-lensing) studies. we find a well-resolved characteristic clump half-light radii of ∼350 pc, a scale comparable to the largest h ii regions seen in the local universe. this statistical characterization of lae surface-brightness profiles will be incorporated into future lensing analyses using the bells gallery sample to constrain the incidence of dark-matter substructure in the foreground lensing galaxies. | the boss emission-line lens survey. v. morphology and substructure of lensed lyα emitters at redshift z ≈ 2.5 in the bells gallery |
we study the mutual relationship between dark matter-electron scattering experiments and possible new dark matter substructure nearby hinted by the gaia data. we show how kinematic substructure could affect the average and modulation spectra of dark matter-electron scattering in semiconductors and the discovery reaches of future experiments with these targets. conversely, we demonstrate how future data could probe and constrain the fraction of dark matter in substructure, even when it constitutes a subdominant component of the local dark matter density. | dark matter substructure under the electron scattering lamppost |
we use a semi-analytical model for the substructure of dark matter haloes to assess the too big to fail (tbtf) problem. the model accurately reproduces the average subhalo mass and velocity functions, as well as their halo-to-halo variance, in n-body simulations. we construct thousands of realizations of milky way (mw)-size host haloes, allowing us to investigate the tbtf problem with unprecedented statistical power. we examine the dependence on host halo mass and cosmology, and explicitly demonstrate that a reliable assessment of tbtf requires large samples of hundreds of host haloes. we argue that previous statistics used to address tbtf suffer from the look-elsewhere effect and/or disregard certain aspects of the data on the mw satellite population. we devise a new statistic that is not hampered by these shortcomings, and, using only data on the nine known mw satellite galaxies with vmax > 15 km s-1, demonstrate that 1.4^{+3.3}_{-1.1} per cent of mw-size host haloes have a subhalo population in statistical agreement with that of the mw. however, when using data on the mw satellite galaxies down to vmax = 8 km s-1, this mw consistent fraction plummets to <5 × 10-4 (at 68 per cent confidence level). hence, if it turns out that the inventory of mw satellite galaxies is complete down to 8 km s-1, then the maximum circular velocities of mw satellites are utterly inconsistent with λ cold dark matter predictions, unless baryonic effects can drastically increase the spread in vmax values of satellite galaxies compared to that of their subhaloes. | comprehensive assessment of the too big to fail problem |
we investigate a recent claim that observed galaxy clusters produce an order of magnitude more galaxy-galaxy strong lensing (ggsl) than simulated clusters in a λ cold dark matter (cdm) cosmology. we take galaxy clusters from the c-eagle hydrodynamical simulations and calculate the expected amount of ggsl for sources placed behind the clusters at different redshifts. the probability of a source lensed by one of the most massive c-eagle clusters being multiply imaged by an individual cluster member is in good agreement with that inferred for observed clusters. we show that numerically converged results for the ggsl probability require higher resolution simulations than had been used previously. on top of this, different galaxy formation models predict cluster substructures with different central densities, such that the ggsl probabilities in λcdm cannot yet be robustly predicted. overall, we find that ggsl within clusters is not currently in tension with the λcdm cosmological model. | the galaxy-galaxy strong lensing cross-sections of simulated λcdm galaxy clusters |
in [1], kallosh and linde drew attention to a new family of superconformal inflationary potentials, subsequently called α-attractors [2]. the α-attractor family can interpolate between a large class of inflationary models. it also has an important theoretical underpinning within the framework of supergravity. we demonstrate that the α-attractors have an even wider appeal since they may describe dark matter and perhaps even dark energy. the dark matter associated with the α-attractors, which we call α-dark matter (αdm), shares many of the attractive features of fuzzy dark matter, with v(varphi) = ½m2varphi2, while having none of its drawbacks. like fuzzy dark matter, αdm can have a large jeans length which could resolve the cusp-core and substructure problems faced by standard cold dark matter. αdm also has an appealing tracker property which enables it to converge to the late-time dark matter asymptote, langlewrangle simeq 0, from a wide range of initial conditions. it thus avoids the enormous fine-tuning problems faced by the m2varphi2 potential in describing dark matter. | sourcing dark matter and dark energy from α-attractors |
macs j0717 is the most massive and extended of the hubble frontier field clusters. it is one of the more difficult clusters to model, and we argue that this is, in part, due to the line-of-sight structure (los) at redshifts beyond 2. we show that the grale mass reconstruction based on sources at 3 < zs < 4.1 has at least 1013 m⊙ more mass than that based on nearby sources, zs < 2.6, and attribute the excess mass to a putative los, which is at least 75 arcsec from the cluster centre. furthermore, the lens-model fitted zs's of the recent kawamata et al. reconstruction are biased systematically low compared to photometric zs's, and the bias is a function of images' distance from the cluster centre. we argue that these mimic the effect of los. we conclude that even in the presence of 100-200 images, lens-model adjusted source redshifts can conceal the presence of los, demonstrating the existence of degeneracies between zs and (sub)structure. also, a very good fit to image positions is not a sufficient condition for having a high-fidelity mass map: kawamata et al. obtain an rms of 0.52 arcsec for 173 images of 60 sources; our grale reconstruction of the exact same data yields a somewhat different map, but similarly low rms, 0.62 arcsec. in contrast, a grale model that uses reasonable, but fixed zs gives a worse rms of 1.28 arcsec for 44 sources with 126 images. unaccounted for los can bias the mass map, affecting the magnification and luminosity function estimates of high redshift sources. | evidence for the line-of-sight structure in the hubble frontier field cluster, macsj0717.5+3745 |
the massive substructures found in abell 2744 by jauzac et al. present a challenge to the cold dark matter paradigm due to their number and proximity to the cluster centre. we use one of the biggest n-body simulations, the millennium xxl, to investigate the substructure in a large sample of massive dark matter haloes. a range of effects that influence the comparison with the observations is considered, extending the preliminary evaluation carried out by jauzac et al. there are many tens of haloes in the simulation with a total mass comparable with or larger than that of abell 2744. however, we find no haloes with a number and distribution of massive substructures (>5 × 1013 m⊙) that is close to that inferred from the observations of abell 2744. the application of extreme value statistics suggests that we would need a simulation of at least 10 times the volume of the millennium xxl to find a single dark matter halo with a similar internal structure to abell 2744. explaining the distribution of massive substructures in clusters is a new hurdle for hierarchical models to negotiate, which is not weakened by appeals to baryonic physics or uncertainty over the nature of the dark matter particle. | abell 2744: too much substructure for λcdm? |
we report the serendipitous discovery of the first gravitationally lensed quasar candidate from pan-starrs. the grizy images reveal four point-like images with magnitudes between 14.9 and 18.1 mag. the colors of the point sources are similar, and they are more consistent with quasars than with stars or galaxies. the lensing galaxy is detected in the izy bands, with an inferred photometric redshift of ∼0.6, lower than that of the point sources. we successfully model the system with a singular isothermal ellipsoid with shear, using the relative positions of the five objects as constraints. while the brightness ranking of the point sources is consistent with that of the model, we find discrepancies between the model-predicted and observed fluxes, likely due to microlensing by stars and millilensing due to the dark matter substructure. in order to fully confirm the gravitational lens nature of this system and add it to the small but growing number of the powerful probes of cosmology and astrophysics represented by quadruply lensed quasars, we require further spectroscopy and high-resolution imaging. | discovery of the first quadruple gravitationally lensed quasar candidate with pan-starrs |
a promising route for revealing the existence of dark matter structures on mass scales smaller than the faintest galaxies is through their effect on strong gravitational lenses. we examine the role of local, lens-proximate clustering in boosting the lensing probability relative to contributions from substructure and unclustered line-of-sight (los) haloes. using two cosmological simulations that can resolve halo masses of mhalo ≃ 109 m⊙ (in a simulation box of length $l_{\rm box}{\sim }100\, {\rm mpc}$) and 107 m⊙ ($l_{\rm box}\sim 20\, {\rm mpc}$), we demonstrate that clustering in the vicinity of the lens host produces a clear enhancement relative to an assumption of unclustered haloes that persists to $\gt 20\, r_{\rm vir}$. this enhancement exceeds estimates that use a two-halo term to account for clustering, particularly within $2-5\, r_{\rm vir}$. we provide an analytic expression for this excess, clustered contribution. we find that local clustering boosts the expected count of 109 m⊙ perturbing haloes by $\sim \! 35{{\ \rm per\ cent}}$ compared to substructure alone, a result that will significantly enhance expected signals for low-redshift (zl ≃ 0.2) lenses, where substructure contributes substantially compared to los haloes. we also find that the orientation of the lens with respect to the line of sight (e.g. whether the line of sight passes through the major axis of the lens) can also have a significant effect on the lensing signal, boosting counts by an additional $\sim 50{{\ \rm per\ cent}}$ compared to a random orientations. this could be important if discovered lenses are biased to be oriented along their principal axis. | out of sight, out of mind? the impact of correlated clustering in substructure lensing |
galaxies and the dark matter haloes that host them are not spherically symmetric, yet spherical symmetry is a helpful simplifying approximation for idealized calculations and analysis of observational data. the assumption leads to an exact conservation of angular momentum for every particle, making the dynamics unrealistic. but how much does that inaccuracy matter in practice for analyses of stellar distribution functions, collisionless relaxation, or dark matter core-creation? we provide a general answer to this question for a wide class of aspherical systems; specifically, we consider distribution functions that are `maximally stable', i.e. that do not evolve at first order when external potentials (which arise from baryons, large-scale tidal fields or infalling substructure) are applied. we show that a spherically symmetric analysis of such systems gives rise to the false conclusion that the density of particles in phase space is ergodic (a function of energy alone). using this idea we are able to demonstrate that: (a) observational analyses that falsely assume spherical symmetry are made more accurate by imposing a strong prior preference for near-isotropic velocity dispersions in the centre of spheroids; (b) numerical simulations that use an idealized spherically symmetric setup can yield misleading results and should be avoided where possible; and (c) triaxial dark matter haloes (formed in collisionless cosmological simulations) nearly attain our maximally stable limit, but their evolution freezes out before reaching it. | milking the spherical cow - on aspherical dynamics in spherical coordinates |
we perform a set of cosmological simulations of structure formation in a mixed dark matter (mdm) model. our model is motivated by the recently identified 3.5 kev x-ray line, which can be explained by the decay of non-resonantly produced sterile neutrinos accounting for 20-60% of the dark matter in the universe. these non-resonantly produced sterile neutrinos have a sizable free-streaming length and hence behave effectively as warm dark matter (wdm). assuming the rest of dark matter is composed of some cold dark matter (cdm) particles, we follow the coevolution of a mixed wdm plus cdm cosmology. specifically, we consider the models with the warm component fraction of rwarm=0.25 and 0.50. our mdm models predict that the comoving jeans length at the matter-radiation equality is close to that of the thermally produced warm dark matter model with particle mass mwdm=2.4 kev, but the suppression in the fluctuation power spectrum is weaker. we perform large n-body simulations to study the structure of non-linear dark halos in the mdm models. the abundance of substructure is significantly reduced in the mdm models, and hence the so-called small-scale crisis is mitigated. the cumulative maximum circular velocity function (cvf) of at least one halo in the mdm models is in good agreement with the cvfs of the observed satellites in the milky way and the andromeda galaxy. we argue that the mdm models open an interesting possibility to reconcile the reported 3.5 kev line and the internal structure of galaxies. | structure formation in a mixed dark matter model with decaying sterile neutrino: the 3.5 kev x-ray line and the galactic substructure |
gravitational lensing is a powerful tool for constraining substructure in the mass distribution of galaxies, be it from the presence of dark matter sub-haloes or due to physical mechanisms affecting the baryons throughout galaxy evolution. such substructure is hard to model and is either ignored by traditional, smooth modelling, approaches, or treated as well-localized massive perturbers. in this work, we propose a deep learning approach to quantify the statistical properties of such perturbations directly from images, where only the extended lensed source features within a mask are considered, without the need of any lens modelling. our training data consist of mock lensed images assuming perturbing gaussian random fields permeating the smooth overall lens potential, and, for the first time, using images of real galaxies as the lensed source. we employ a novel deep neural network that can handle arbitrary uncertainty intervals associated with the training data set labels as input, provides probability distributions as output, and adopts a composite loss function. the method succeeds not only in accurately estimating the actual parameter values, but also reduces the predicted confidence intervals by 10 per cent in an unsupervised manner, i.e. without having access to the actual ground truth values. our results are invariant to the inherent degeneracy between mass perturbations in the lens and complex brightness profiles for the source. hence, we can quantitatively and robustly quantify the smoothness of the mass density of thousands of lenses, including confidence intervals, and provide a consistent ranking for follow-up science. | quantifying the structure of strong gravitational lens potentials with uncertainty-aware deep neural networks |
cluster mergers are an important laboratory for studying the behaviour of dark matter (dm) and intracluster gas. there are dissociative collisions that can separate the intracluster gas from the dm. abell 2034 presents clear dissociative features observed by x-rays and gravitational lensing. the cluster, at z = 0.114, consists of two substructures with mass ratio of about 1:2.2, separated by ∼720 kpc. the x-ray emission peak is offcentred from the south dm peak by ∼350 kpc. using n-body hydrodynamical simulations, we aim to reconstruct the dynamic history of the collision, reproducing the observed features, and also to explore the conditions that led to the dissociation. our best model assuming that the collision is close to the plane of the sky, with a small impact parameter, observed 0.26 gyr after central passage, reproduces the observed features of this cluster, such as the offset between x-ray and dm peaks, x-ray morphology, and temperatures. we explored several variations using different gas and dm concentrations for each cluster. the level of dissociation was quantified by the distances between x-ray and dm peaks, and also by the gas retention in the cluster cores. we found that the ratio of central gas densities is more important than the ratio of central dm densities in determining the level of dissociation. | simulations of the merging galaxy cluster abell 2034: what determines the level of separation between gas and dark matter |
we use cosmological n-body simulations from the aquarius project to study the tidal effects of a dark matter halo on the shape and orientation of its substructure. although tides are often assumed to enhance asphericity and to stretch subhaloes tangentially, these effects are short lived: as in earlier work, we find that subhaloes affected by tides become substantially more spherical and show a strong radial alignment towards the centre of the host halo. these results, combined with a semi-analytic model of galaxy formation, may be used to assess the effect of galactic tides on the observed population of dwarf spheroidal (dsph) satellites of the milky way and andromeda galaxies. if, as the model suggests, the relatively low dark matter content of luminous dsphs such as fornax and leo i is due to tidal stripping, then their gravitational potential must be substantially more spherical than that of more heavily dark matter-dominated systems such as draco or carina. the model also predicts a tidally-induced statistical excess of satellites whose major axis aligns with the direction to the central galaxy. we find tantalizing evidence of this in the m31 satellite population, which suggests that tides may have played an important role in its evolution. | galactic tides and the shape and orientation of dwarf galaxy satellites |
strongly lensed systems are powerful probes of the distribution of dark matter on small scales. in this paper, we show that line-of-sight haloes between the source and the observers give rise to a distinct anisotropic signature in the two-point function of the effective lensing deflection field. we show in particular that the non-linear coupling between line-of-sight haloes and the main lens plane imprints a characteristic quadrupole moment on this two-point function whose amplitude reflects the abundance of such haloes within the strongly lensed field. we discuss how, by taking ratios of different multipole moments, such observables could be made robust under the mass-sheet transform. we also demonstrate that future extremely large telescopes have the ability to detect the quadrupole moment due to this unique anisotropic signature under ideal conditions. our approach opens the door to statistically distinguish the effect of line-of-sight haloes from that of the main-lens substructure on lensed images, hence allowing one to probe dark matter physics in a new way. | interlopers speak out: studying the dark universe using small-scale lensing anisotropies |
the structural properties of individual dark matter haloes, including shape, spin, concentration, and substructure, are linked to the halo's growth history, but the exact connection between the two is unclear. one open question, in particular, is the effect of major mergers on halo structure. we have performed a large set of simulations of binary equal-mass mergers between isolated haloes with various density profiles, to map out the relationship between the initial conditions and merger parameters and the structure of the final remnant. in this paper we describe our initial set-up and analysis methods, and report on the results for the size, shape, and spin of the merger remnant. the outcomes of mergers are most easily understood in terms of a scaled dimensionless energy parameter κ and an angular momentum (or spin) parameter λ. we find that the axial ratio c/a scales roughly linearly with energy κ while the axial ratio c/b scales linearly with spin λ. qualitatively, mergers on radial orbits produce prolate remnants, while mergers on tangential orbits produce oblate remnants. the spin of the remnant can be predicted from angular momentum conservation, while the overall size changes as ∼κ-5, as expected from self-similar scaling at constant mean density. we discuss potential cosmological applications for these simple patterns. | major mergers between dark matter haloes - i. predictions for size, shape, and spin |
in this article we present the dark-photons&axion-like particles interferometer (dali), a novel experiment designed for the detection of photon-mixing cold dark matter in the microwave band between 6 and 60 ghz. dali is a haloscope for the simultaneous search for axions, axion-like particles and dark photons, with a number of novelties that make it unique. first, it is a dark matter telescope, with a capacity for pointing, tracking and rastering objects and areas in the sky. this potentially allows one to detect relativistic dark matter particles, substructures and flows, without compromising the simultaneous scanning for dark matter relic particles present in the laboratory. second, it has been designed using commercial technology. this will allow feasible manufacture at a reasonable cost, thereby mitigating the need for r&d and facilitating maintenance. finally, it benefits from a high sensitivity over a broad band of frequencies with only minimal reconfiguration. | a dark matter telescope probing the 6 to 60 ghz band |
the positions of multiple images in galaxy lenses are related to the galaxy mass distribution. smooth elliptical mass profiles were previously shown to be inadequate in reproducing the quad population. in this paper, we explore the deviations from such smooth elliptical mass distributions. unlike most other work, we use a model-free approach based on the relative polar image angles of quads, and their position in 3d space with respect to the fundamental surface of quads (fsq). the fsq is defined by quads produced by elliptical lenses. we have generated thousands of quads from synthetic populations of lenses with substructure consistent with lambda cold dark matter (λcdm) simulations, and found that such perturbations are not sufficient to match the observed distribution of quads relative to the fsq. the result is unchanged even when subhalo masses are increased by a factor of 10, and the most optimistic lensing selection bias is applied. we then produce quads from galaxies created using two components, representing baryons and dark matter. the transition from the mass being dominated by baryons in inner radii to being dominated by dark matter in outer radii can carry with it asymmetries, which would affect relative image angles. we run preliminary experiments using lenses with two elliptical mass components with non-identical axial ratios and position angles, perturbations from ellipticity in the form of non-zero fourier coefficients a4 and a6, and artificially offset ellipse centres as a proxy for asymmetry at image radii. we show that combination of these effects is a promising way of accounting for quad population properties. we conclude that the quad population provides a unique and sensitive tool for constraining detailed mass distribution in the centres of galaxies. | the impact of λcdm substructure and baryon-dark matter transition on the image positions of quad galaxy lenses |
dark matter (dm) direct detection experiments aim to place constraints on the dm-nucleon scattering cross-section and the dm particle mass. these constraints depend sensitively on the assumed local dm density and velocity distribution function. while astrophysical observations can inform the former (in a model-dependent way), the latter is not directly accessible with observations. here we use the high-resolution artemis cosmological hydrodynamical simulation suite of 42 milky way-mass halos to explore the spatial and kinematical distributions of the dm in the solar neighbourhood, and we examine how these quantities are influenced by substructures, baryons, the presence of dark discs, as well as general halo-to-halo scatter (cosmic variance). we also explore the accuracy of the standard maxwellian approach for modelling the velocity distribution function. we find significant halo-to-halo scatter in the density and velocity functions which, if propagated through the standard halo model for predicting the dm detection limits, implies a significant scatter about the typically quoted limit. we also show that, in general, the maxwellian approximation works relatively well for simulations that include the important gravitational effects of baryons, but is less accurate for collisionless (dm-only) simulations. given the significant halo-to-halo scatter in quantities relevant for dm direct detection, we advocate propagating this source of uncertainty through in order to derive conservative dm detection limits. | informing dark matter direct detection limits with the artemis simulations |
we show that the mass of a dark matter halo can be inferred from the dynamical status of its satellite galaxies. using nine dark matter simulations of halos like the milky way (mw), we find that the present-day substructures in each halo follow a characteristic distribution in the phase space of orbital binding energy and angular momentum, and that this distribution is similar from halo to halo, but has an intrinsic dependence on the halo formation history. we construct this distribution directly from the simulations for a specific halo and extend the result to halos of similar formation history but different masses by scaling. the mass of an observed halo can then be estimated by maximizing the likelihood in comparing the measured kinematic parameters of its satellite galaxies with these distributions. we test the validity and accuracy of this method with mock samples taken from the simulations. using the positions, radial velocities, and proper motions of nine tracers and assuming observational uncertainties comparable to those of mw satellite galaxies, we find that the halo mass can be recovered to within ∼ 40 % . the accuracy can be improved to within ∼25% if 30 tracers are used. however, the dependence of the phase-space distribution on the halo formation history sets a minimum uncertainty of ∼ 20 % that cannot be reduced by using more tracers. we believe that this minimum uncertainty also applies to any mass determination for a halo when the phase-space information of other kinematic tracers is used. | determination of dark matter halo mass from dynamics of satellite galaxies |
we simulate tidal streams in the presence and absence of substructures inside the zero-redshift snapshot of the via lactea ii (vl-2) simulation. a halo finder is used to remove and isolate the subhalos found inside the high-resolution dark matter halo of vl-2, and the potentials for both the main halo and all the subhalos are constructed individually using the self-consistent field method. this allows us to make direct comparison of tidal streams between a smooth halo and a lumpy halo without assuming idealized profiles or triaxial fits. we simulate the kinematics of a star cluster starting with the same orbital position but two different velocities. although these two orbits are only moderately eccentric and have similar apo- and pericentric distances, we find that the two streams have very different morphologies. we conclude that our model of the potential of vl-2 can provide insights about tidal streams that have not been explored by previous studies using idealized or axisymmetric models. | simulating tidal streams in a high-resolution dark matter halo |
in this second paper, we present the first n-body cosmological simulations of strongly coupled dark energy (scdew) models, a class of models that alleviates theoretical issues related to the nature of dark energy (de). scdew models assume a strong coupling between de and an ancillary cold dark matter (cdm) component together with the presence of an uncoupled warm dark matter (wdm) component. the strong coupling between cdm and de allows us to preserve small-scale fluctuations even if the warm particle is quite light (≈100 ev). our large-scale simulations show that, for 1011 < m/m⊙ < 1014, scdew haloes exhibit a number density and distribution similar to a standard lambda cold dark matter (λcdm) model, even though they have lower concentration parameters. high-resolution simulation of a galactic halo (m ∼ 1012 m⊙) shows ∼60 per cent less substructures than its λcdm counterpart, but the same cuspy density profile. on the scale of galactic satellites (m ∼ 109 m⊙), scdew haloes dramatically differ from λcdm. due to the high thermal velocities of the wdm component they are almost devoid of any substructures and present strongly cored dark matter density profiles. these density cores extend for several hundreds of parsecs, in very good agreement with milky way satellites observations. strongly coupled models, thanks to their ability to match observations on both large and small scales, might represent a valid alternative to a simple λcdm model. | strongly coupled dark energy cosmologies: preserving λcdm success and easing low-scale problems - ii. cosmological simulations |
a large population of extended substructures generates a stochastic gravitational field that is fully specified by the function p(f), which defines the probability that a tracer particle experiences a force f within the interval f, f+d{f}. this paper presents a statistical technique for deriving the spectrum of random fluctuations directly from the number density of substructures with known mass and size functions. application to the subhalo population found in cold dark matter simulations of milky way sized haloes shows that, while the combined force distribution is governed by the most massive satellites, the fluctuations of the tidal field are completely dominated by the smallest and most abundant subhaloes. in light of this result, we discuss observational experiments that may be sufficiently sensitive to galactic tidal fluctuations to probe the `dark' low end of the subhalo mass function and constrain the particle mass of warm and ultralight axion dark matter models. | fluctuations of the gravitational field generated by a random population of extended substructures |
we present an analysis of archival observations with the atacama large (sub-)millimetre array (alma) of the gravitationally lensed quasar mg j0414+0534, which show four compact images of the quasar and an einstein ring from the dust associated with the quasar host galaxy. we confirm that the flux-ratio anomalies observed in the mid-infrared and radio persist into the sub-mm for the continuum images of the quasar. we report the detection of co (11-10) spectral line emission, which traces a region of compact gas around the quasar nucleus. this line emission also shows evidence of a flux-ratio anomaly between the merging lensed images that is consistent with those observed at other wavelengths, suggesting high-excitation co can also provide a useful probe of substructures that is unaffected by microlensing or dust extinction. however, we do not detect the candidate dusty dwarf galaxy that was previously reported with this data set, which we conclude is due to a noise artefact. thus, the cause of the flux-ratio anomaly between the merging lensed images is still unknown. the composite compact and diffuse emission in this system suggest lensed quasar starbursts will make excellent targets for detecting dark sub-haloes and testing models for dark matter. | a flux-ratio anomaly in the co spectral line emission from gravitationally lensed quasar mg j0414+0534 |
paleodetectors are a proposed experimental technique to search for dark matter by reading out the damage tracks caused by nuclear recoils in small samples of natural minerals. unlike a conventional real-time direct detection experiment, paleodetectors have been accumulating these tracks for up to a billion years. these long integration times offer a unique possibility: by reading out paleodetectors of different ages, one can explore the time-variation of signals on megayear to gigayear timescales. we investigate two examples of dark matter substructure that could give rise to such time-varying signals. first, a dark disk through which the earth would pass every ∼45 myr , and second, a dark matter subhalo that the earth encountered during the past gigayear. we demonstrate that paleodetectors are sensitive to these examples under a wide variety of experimental scenarios, even in the presence of substantial background uncertainties. this paper shows that paleodetectors may hold the key to unraveling our galactic history. | galactic geology: probing time-varying dark matter signals with paleodetectors |
to provide a quantitative cosmological context to ongoing observational work on the formation histories and location of compact massive galaxies, we locate and study a sample of exceptionally compact systems in the bolshoi simulation, using the dark matter structural parameters from a real, compact massive galaxy (ngc 1277) as a basis for our working criteria. we find that over 80 per cent of objects in this nominal compact category are substructures of more massive groups or clusters, and that the probability of a given massive substructure being this compact increases significantly with the mass of the host structure; rising to ∼30 per cent for the most massive clusters in the simulation. tracking the main progenitors of this subsample back to z = 2, we find them all to be distinct structures with scale radii and densities representative of the population as a whole at this epoch. what does characterize their histories, in addition to mostly becoming substructures, is that they have almost all experienced below-average mass accretion since z = 2; a third of them barely retaining, or even losing mass during the intervening 10 gyr. | a cosmological context for compact massive galaxies |
we study the evolution of the dark matter (dm) halo profiles of dwarf galaxies driven by the accretion of dm substructures through controlled n-body experiments. our initial conditions assume that early supernova feedback erases the primordial dm cusps of haloes with z = 0 masses of 109 - 1010 m⊙. the orbits and masses of the infalling substructures are borrowed from the aquarius cosmological simulations. our experiments show that a fraction of haloes that undergo 1:3 down to 1:30 mergers are susceptible to reform a dm cusp by z ≈ 0. cusp regrowth is driven by the accretion of dm substructures that are dense enough to reach the central regions of the main halo before being tidally disrupted. the infall of substructures on the mean of the reported mass-concentration relation and a mass ratio above 1:6 systematically leads to cusp regrowth. substructures with 1:6-1:8, and 1:8-1:30 only reform dm cusps if their densities are 1σ and 2σ above the mean, respectively. the merging time-scales of these dense, low-mass substructures is relatively long (5 - 11 gyr), which may pose a time-scale problem for the longevity of dm cores in dwarfs galaxies and possibly explain the existence of dense dwarfs-like draco. these results suggest that within cold dark matter a non-negligible level of scatter in the mass profiles of galactic haloes acted on by feedback is to be expected given the stochastic mass accretion histories of low-mass haloes and the diverse star formation histories observed in the local group dwarfs. | under the sword of damocles: plausible regeneration of dark matter cusps at the smallest galactic scales. |
we present the first strong-gravitational-lensing analysis of the galaxy cluster rx j0437.1+0043 (rxj0437; z = 0.285). newly obtained, deep muse observations, keck/mosfire near-infrared spectroscopy, and hubble space telescope snapshot imaging reveal 13 multiply imaged background galaxies, three of them (at z = 1.98, 2.97, and 6.02, respectively) in hyperbolic umbilic (h-u) lensing configurations. the h-u images are located only 20-50 kpc from the cluster centre, i.e. at distances well inside the einstein radius where images from other lens configurations are demagnified and often unobservable. extremely rare (only one h-u lens was known previously) these systems are able to constrain the inner slope of the mass distribution - and unlike radial arcs, the presence of h-u configurations is not biased towards shallow cores. the galaxies lensed by rxj0437 are magnified by factors ranging from 30 to 300 and (in the case of h-u systems) stretched nearly isotropically. taking advantage of this extreme magnification, we demonstrate how the source galaxies in h-u systems can be used to probe for small-scale (~109 m⊙) substructures, providing additional insight into the nature of dark matter. | rxj0437+00: constraining dark matter with exotic gravitational lenses |
strong gravitationally lensed arcs produced by galaxy clusters have been observationally detected for several decades now. these strong lensing constraints provided high-fidelity mass models for cluster lenses that include substructure down to $10^{9{-}10}\, \mathrm{m}_\odot$. optimizing lens models, where the cluster mass distribution is modelled by a smooth component and subhaloes associated with the locations of individual cluster galaxies, has enabled deriving the subhalo mass function, providing important constraints on the nature and granularity of dark matter. in this work, we explore and present a novel method to detect and measure individual perturbers (subhaloes, line-of-sight haloes, and wandering supermassive black holes) by exploiting their proximity to highly distorted lensed arcs in galaxy clusters, and by modelling the local lensing distortions with curved arc bases. this method offers the possibility of detecting individual low-mass perturber subhaloes in clusters and haloes along the line of sight down to a mass resolution of $10^8\, \mathrm{m}_\odot$. we quantify our sensitivity to low-mass perturbers ($m\sim 10^{7{-}9}\, \mathrm{m}_\odot$) in clusters (m ~ 1014-15 m⊙), by creating realistic mock data. using three lensed images of a background galaxy in the cluster smacs j0723, taken by jwst, we study the retrieval of the properties of potential perturbers with masses $m=10^{7{-}9}\, \mathrm{m}_\odot$. from the derived posterior probability distributions for the perturber, we constrain its concentration, redshift, and ellipticity. by allowing us to probe lower mass substructures, the use of curved arc bases can lead to powerful constraints on the nature of dark matter as discrimination between dark matter models appears on smaller scales. | detecting low-mass perturbers in cluster lenses using curved arc bases |
the observational features of the massive galaxy cluster “el gordo” (act-cl j0102-4915), such as the x-ray emission, the sunyaev-zel’dovich (sz) effect, and the surface mass density distribution, indicate that they are caused by an exceptional ongoing high-speed collision of two galaxy clusters, similar to the well-known bullet cluster. we perform a series of hydrodynamical simulations to investigate the merging scenario and identify the initial conditions for the collision in act-cl j0102-4915. by surveying the parameter space of the various physical quantities that describe the two colliding clusters, including their total mass (m), mass ratio (ξ), gas fractions ({f}{{b}}), initial relative velocity (v), and impact parameter (p), we find an off-axis merger with p∼ 800 {h}70-1 {kpc}, v∼ 2500 {km} {{{s}}}-1, m∼ 3× {10}15 {m}⊙ , and ξ =3.6 that can lead to most of the main observational features of act-cl j0102-4915. those features include the morphology of the x-ray emission with a remarkable wake-like substructure trailing after the secondary cluster, the x-ray luminosity and the temperature distributions, and also the sz temperature decrement. the initial relative velocity required for the merger is extremely high and rare compared to that inferred from currently available λ cold dark matter (λcdm) cosmological simulations, which raises a potential challenge to the λcdm model, in addition to the case of the bullet cluster. | simulating the galaxy cluster “el gordo” and identifying the merger configuration |
a fundamental prediction of the cold dark matter cosmology is the existence of a large number of dark subhalos around galaxies, most of which should be entirely devoid of stars. confirming the existence of dark substructures stands among the most important empirical challenges in modern cosmology: if they are found and quantified with the mass spectrum expected, then this would close the door on a vast array of competing theories. but in order for observational programs of this kind to reach fruition, we need robust predictions. here we explore substructure predictions for lensing using galaxy lens-like hosts at z = 0.2 from the illustris simulations both in full hydrodynamics and dark matter only. we quantify substructures more massive than ∼109 m⊙, comparable to current lensing detections derived from hst, keck, and alma. the addition of full hydrodynamics reduces the overall subhalo mass function by about a factor of two. even for the dark matter only runs, most ({∼ } 85{{ per cent}}) projections through the halo of size close to an einstein radius contain no substructures larger than 109 m⊙. the fraction of empty projections through the halo rises to {∼ } 95{{ per cent}} in full physics simulations. this suggests we will likely need hundreds of strong lensing systems suitable for substructure studies, as well as predictions that include the effects of baryon physics on substructure, to properly constrain cosmological models. fortunately, the field is poised to fulfill these requirements. | through a smoother lens: an expected absence of lcdm substructure detections from hydrodynamic and dark matter only simulations |
this article reports on a search for dark matter pair production in association with a higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb-1 of p p collisions at a center-of-mass energy of 8 tev collected by the atlas detector at the lhc. the decay of the higgs boson is reconstructed as a high-momentum b b ¯ system with either a pair of small-radius jets, or a single large-radius jet with substructure. the observed data are found to be consistent with the expected standard model backgrounds. model-independent upper limits are placed on the visible cross sections for events with a higgs boson decaying into b b ¯ and large missing transverse momentum with thresholds ranging from 150 to 400 gev. results are interpreted using a simplified model with a z' gauge boson decaying into different higgs bosons predicted in a two-higgs-doublet model, of which the heavy pseudoscalar higgs decays into a pair of dark matter particles. exclusion limits are also presented for the mass scales of various effective field theory operators that describe the interaction between dark matter particles and the higgs boson. | search for dark matter produced in association with a higgs boson decaying to two bottom quarks in p p collisions at √{s }=8 tev with the atlas detector |
a clean measurement of the evolution of the galaxy cluster mass function can significantly improve our understanding of cosmology from the rapid growth of cluster masses below z < 0.5. here, we examine the consistency of cluster catalogues selected from the sloan digital sky survey by applying two independent gravity-based methods using all available spectroscopic redshifts from the dr10 release. first, we detect a gravitational redshift related signal for 20,119 and 13,128 clusters with spectroscopic redshifts contained in the gaussian mixture brightest cluster galaxy (gmbcg) and red-sequence matched-filter probabilistic percolation (redmapper) catalogues, respectively, at a level of ∼-10 km s-1. this we show is consistent with the magnitude expected using the richness-mass relations provided by the literature and after applying recently clarified relativistic and flux bias corrections. this signal is also consistent with the richest clusters in the larger catalogue of wen et al., corresponding to m200m ≳ 2 × 1014 m⊙ h-1; however, we find no significant detection of a gravitational redshift signal for lower richness clusters, which may be related to bulk motions from substructure and spurious cluster detections. secondly, we find all three catalogues generate mass-dependent levels of lensing magnification bias, which enhances the mean redshift of flux-selected background galaxies from the baryon oscillation spectroscopic survey survey. the magnitude of this lensing effect is generally consistent with the corresponding richness-mass relations advocated for the surveys. we conclude that all catalogues comprise a high proportion of reliable clusters, and that the gmbcg and redmapper cluster finder algorithms favour more relaxed clusters with a meaningful gravitational redshift signal, as anticipated by the red-sequence colour selection of the gmbcg and redmapper samples. | comparing gravitational redshifts of sdss galaxy clusters with the magnified redshift enhancement of background boss galaxies |
we introduce a method for producing a galaxy sample unbiased by surface brightness and stellar mass, by selecting star-forming galaxies via the positions of core-collapse supernovae (ccsne). whilst matching ∼2400 supernovae from the sdss-ii supernova survey to their host galaxies using iac stripe 82 legacy coadded imaging, we find ∼150 previously unidentified low surface brightness galaxies (lsbgs). using a sub-sample of ∼900 ccsne, we infer ccsn-rate and star formation rate densities as a function of galaxy stellar mass, and the star-forming galaxy stellar mass function. resultant star-forming galaxy number densities are found to increase following a power law down to our low-mass limit of ∼106.4 m⊙ by a single schechter function with a faint-end slope of α = -1.41. number densities are consistent with those found by the eagle simulations invoking a λ cold dark matter cosmology. overcoming surface brightness and stellar mass biases is important for assessment of the sub-structure problem. in order to estimate galaxy stellar masses, a new code for the calculation of galaxy photometric redshifts, zmedic, is also presented, and shown to be particularly useful for small samples of galaxies. | the galaxy stellar mass function and low surface brightness galaxies from core-collapse supernovae |
we study structure formation in a set of cosmological simulations to uncover the scales in the initial density field that gave rise to the formation of present-day structures. our simulations share a common primordial power spectrum (here λ cold dark matter, λcdm), but the introduction of hierarchical variations of the phase information allows us to systematically study the scales that determine the formation of structure at later times. we consider the variance in z = 0 statistics such as the matter power spectrum and halo mass function. we also define a criterion for the existence of individual haloes across simulations, and determine what scales in the initial density field contain sufficient information for the non-linear formation of unique haloes. we study how the characteristics of individual haloes such as the mass and concentration, as well as the position and velocity, are affected by variations on different scales, and give scaling relations for haloes of different mass. finally, we use the example of a cluster-mass halo to show how our hierarchical parametrization of the initial density field can be used to create variants of particular objects. with properties such as mass, concentration, kinematics, and substructure of haloes set on distinct and well-determined scales, and its unique ability to introduce variations localized in real space, our method is a powerful tool to study structure formation in cosmological simulations. | setting the stage: structures from gaussian random fields |
the galaxy distribution in dark matter-dominated halos is expected to approximately trace the details of the underlying dark matter substructure. in this paper we introduce halo `core-tracking' as a way to efficiently follow the small-scale substructure in cosmological simulations and apply the technique to model the galaxy distribution in observed clusters. the method relies on explicitly tracking the set of particles identified as belonging to a halo's central density core, once a halo has attained a certain threshold mass. the halo cores are then followed throughout the entire evolution of the simulation. the aim of core-tracking is to simplify substructure analysis tasks by avoiding the use of subhalos and, at the same time, to more easily account for the so-called ``orphan'' galaxies, which have lost substantial dark mass due to tidal stripping. we show that simple models based on halo cores can reproduce the number and spatial distribution of galaxies found in optically-selected clusters in the sloan digital sky survey. we also discuss future applications of the core-tracking methodology in studying the galaxy-halo connection. | modeling the galaxy distribution in clusters using halo cores |
in this paper, the recently proposed mass dimension one fermionic field is supposed to be responsible for the dark matter (dm) halo around galactic nuclei, through the quantum degeneracy pressure effect of the field. it will be shown that the mass-ratio relation for dwarf galaxies can be well explained for a particle dm mass of about 100-200ev. for a large galaxy, as milky way, the observational data for rotation curve can be well reproduced for a particle mass of about 23ev, with the addition of other substructures. | degeneracy pressure of mass dimension one fermionic fields and the dark matter halo of galaxies |
we constrain the mass of the milky way´s dark matter halo, based on the kinematics of 9627 k giants at galactocentric distances ranging over 5 kpc < r< 120 {kpc} drawn from lamost dr5. the substructure in this sample has been identified and removed carefully to enable construction of the underlying line-of-sight velocity dispersion at different radii from the galactic center. we interpret the radial profile of the line-of-sight velocity dispersion using a spherical jeans equation under the assumptions of anisotropy/isotropy and that radial velocity dispersion is approximately equal to line-of-sight velocity dispersion {σ }r(r)≈ {σ }los}(r). if we assume that the dark matter halo follows an nfw profile and the stellar halo is isotropic (β = 0), then {σ }los}(r) can be directly used to estimate the virial mass of the galactic dark matter halo, {m}vir}={1.08}-0.14+0.17× {10}12 {m}⊙ , and concentration parameter c={18.5}-2.9+3.6. in case that the stellar halo is anisotropic, we cannot avoid differentiation of sparse velocity dispersions according to the jeans equation, which may cause overestimation of the mass. we use an isotropic case to test and find that d{ln}({σ }los}2(r))/d{ln}r overestimates the virial mass by 15% but within 1-σ error. we use d{ln}({σ }los}2(r))/d{ln}r to fit the nfw profile and get {m}vir}={1.11}-0.20+0.24× {10}12 {m}⊙and c={13.8}-2.2+3.0 in case of β = 0.3. | the mass of the galactic dark matter halo from ∼9000 lamost dr5 k giants |
we recommend a deeper extension to the high-latitute wide area survey planned to be conducted by the nancy grace roman space telescope (\emph{roman}). while this deeper-tier survey extension can support a range of astrophysical investigations, it is particularly well suited to characterize the dark matter substructure in galactic halos and reveal the microphysics of dark matter through gravitational lensing. we quantify the expected yield of \emph{roman} for finding galaxy-galaxy-type gravitational lenses and motivate observational choices to optimize the \emph{roman} core community surveys for studying dark matter substructure. in the proposed survey, we expect to find, on average, one strong lens with a characterizable substructure per \emph{roman} tile (0.28 squared degrees), yielding approximately 500 such high-quality lenses. with such a deeper legacy survey, \emph{roman} will outperform any current and planned telescope within the next decade in its potential to characterize the concentration and abundance of dark matter subhalos in the mass range 10$^7$-10$^{11}$\,m$_{\odot}$. | searching for dark matter substructure: a deeper wide-area community survey for roman |
galaxy-scale strongly lensed systems have been shown to provide a unique technique for exploring the underlying physics of dark matter at sub-galactic scales. in the past, much attention was given to detecting and studying individual haloes in a strong lens system. in addition to the subhaloes, line-of-sight haloes contribute significantly to the small perturbations in lensed images. in prior work, we demonstrated that these line-of-sight haloes imprint a distinctive anisotropic signature and hence give rise to a detectable non-zero parity-even quadrupole moment in the effective convergence field's two-point correlation function. in this study, we show that these line-of-sight haloes also produce a non-zero curl component of the effective deflection field with a parity-odd quadrupole moment of the two-point function. these multipole moments have the ability to statistically separate line-of-sight haloes from dark matter substructure. in this paper, we examine how these multipole moments evolve in the presence of warm dark matter and self-interacting dark matter in terms of central density evolution and dark matter halo abundance. importantly, we show that these different multipole moments display exquisite sensitivity to both the amplitude and the velocity dependence of the dark matter self-interaction cross-section. our approach opens the door for strong lensing observations to probe dark matter self-interaction over a broad range of relative velocities. | anisotropic strong lensing as a probe of dark matter self-interactions |
we present the results of a multiwavelength investigation of the very x-ray luminous galaxy cluster macsj0553.4-3342 (z = 0.4270; hereafter macsj0553). combining high-resolution data obtained with the hubble space telescope and the chandra x-ray observatory with ground-based galaxy spectroscopy, our analysis establishes the system unambiguously as a binary, post-collision merger of massive clusters. key characteristics include perfect alignment of luminous and dark matter for one component, a separation of almost 650 kpc (in projection) between the dark-matter peak of the other subcluster and the second x-ray peak, extremely hot gas (kt > 15 kev) at either end of the merger axis, a potential cold front in the east, an unusually low gas mass fraction of approximately 0.075 for the western component, a velocity dispersion of 1490_{-130}^{+104} km s-1, and no indication of significant substructure along the line of sight. we propose that the macsj0553 merger proceeds not in the plane of the sky, but at a large inclination angle, is observed very close to turnaround, and that the eastern x-ray peak is the cool core of the slightly less massive western component that was fully stripped and captured by the eastern subcluster during the collision. if correct, this hypothesis would make macsj0553 a superb target for a competitive study of ram-pressure stripping and the collisional behaviour of luminous and dark matter during cluster formation. | fully stripped? the dynamics of dark and luminous matter in the massive cluster collision macsj0553.4-3342 |
hierarchical models of structure formation predict that dark matter halo assembly histories are characterized by episodic mergers and interactions with other haloes. an accurate description of this process will provide insights into the dynamical evolution of haloes and the galaxies that reside in them. using large cosmological n-body simulations, we characterize halo orbits to study the interactions between substructure haloes and their hosts, and how different evolutionary histories map to different classes of orbits. we use two new software tools - wherewolf, which uses halo group catalogues and merger trees to ensure that haloes are tracked accurately in dense environments, and orbweaver, which quantifies each halo's orbital parameters. we demonstrate how wherewolf improves the accuracy of halo merger trees, and we use orbweaver to quantify orbits of haloes. we assess how well analytical prescriptions for the merger time-scale from the literature compare to measured merger time-scales from our simulations and find that existing prescriptions perform well, provided the ratio of substructure-to-host mass is not too small. in the limit of small substructure-to-host mass ratio, we find that the prescriptions can overestimate the merger time-scales substantially, such that haloes are predicted to survive well beyond the end of the simulation. this work highlights the need for a revised analytical prescription for the merger time-scale that more accurately accounts for processes such as catastrophic tidal disruption. | extracting galaxy merger time-scales - i. tracking haloes with wherewolf and spinning orbits with orbweaver |
the information about the mass density of galaxy clusters provided by the gravitational lens effect has inspired many inversion techniques. in this article, updates to the previously introduced method in grale are described, and explored in a number of examples. the first looks into a different way of incorporating time delay information, not requiring the unknown source position. it is found that this avoids a possible bias that leads to 'overfocusing' the images, i.e. providing source position estimates that lie in a considerably smaller region than the true positions. the second is inspired by previous reconstructions of the cluster of galaxies macs j1149.6+2223, where a multiply imaged background galaxy contained a supernova, sn refsdal, of which four additional images were produced by the presence of a smaller cluster galaxy. the inversion for the cluster as a whole was not able to recover sufficient detail interior to this quad. we show how constraints on such different scales, from the entire cluster to a single member galaxy, can now be used, allowing such small-scale substructures to be resolved. finally, the addition of weak lensing information to this method is investigated. while this clearly helps recover the environment around the strong lensing region, the mass sheet degeneracy may make a full strong and weak inversion difficult, depending on the quality of the ellipticity information at hand. we encounter ring-like structure at the boundary of the two regimes, argued to be the result of combining strong and weak lensing constraints, possibly affected by degeneracies. | extended lens reconstructions with grale: exploiting time-domain, substructural, and weak lensing information |
forthcoming large-scale spectroscopic surveys will soon provide data on thousands of galaxy clusters. it is important that the systematics of the various mass estimation techniques is well understood and calibrated. we compare three different dynamical mass estimators using the c-eagle galaxy clusters, a set of high-resolution simulations with resolved galaxies a median total mass, m_{200c} = 10^{14.7} m_\odot. we quantify the bias and scatter of the jeans, virial, and caustic mass estimators using all galaxies with a stellar mass m_*> 10^9 m_\odot, both in the ideal 3d case and in the more realistic projected case. on average we find our mass estimates are unbiased, though relative to the true mass within r200c the scatter is large with a range of 0.09-0.15 dex. we see a slight increase in the scatter when projecting the clusters. selecting galaxies using the same criteria, we find no significant difference in the mass bias or scatter when comparing results from hydrodynamical and dark matter only simulations. however, selecting galaxies by stellar mass reduces the bias compared to selecting by total mass. comparing x-ray derived hydrostatic and dynamical masses, the former are ∼30 per cent lower. we find a slight dependence between substructure, measured using two different metrics, and mass bias. in conclusion, we find that dynamical mass estimators, when averaged together, are unbiased with a scatter of 0.11 ± 0.02 dex when including interloper galaxies and with no prior knowledge of r200c. | the cluster-eagle project: a comparison of dynamical mass estimators using simulated clusters |
lcdm is remarkably successful in predicting the cosmic microwave background and large-scale structure, and lcdm parameters have been determined with only mild tensions between different types of observations. hydrodynamical simulations starting from cosmological initial conditions are increasingly able to capture the complex interactions between dark matter and baryonic matter in galaxy formation. simulations with relatively low resolution now succeed in describing the overall galaxy population. for example, the eagle simulation in volumes up to 100 cubic mpc reproduces the observed local galaxy mass function nearly as well as semi-analytic models. it once seemed that galaxies are pretty smooth, that they generally grow in size as they evolve, and that they are a combination of disks and spheroids. but recent hst observations combined with high-resolution hydrodynamic simulations are showing that most star-forming galaxies are very clumpy; that galaxies often undergo compaction which reduces their radius and increases their central density; and that most lower-mass star-forming galaxies are not spheroids or disks but are instead elongated when their centers are dominated by dark matter. we also review lcdm challenges on smaller scales: cusp-core, "too big to fail," and substructure issues. although starbursts can rapidly drive gas out of galaxy centers and thereby reduce the dark matter density, it remains to be seen whether this or other baryonic physics can explain the observed rotation curves of the entire population of dwarf and low surface brightness galaxies. if not, perhaps more complicated physics such as self-interacting dark matter may be needed. but standard lcdm appears to be successful in predicting the dark matter halo substructure that is now observed via gravitational lensing and breaks in cold stellar streams, and any alternative theory must do at least as well. | cosmological structure formation |
recent studies found the densities of dark matter (dm) subhaloes which surround nearby dwarf spheroidal galaxies (dsphs) to be significantly lower than those of the most massive subhaloes expected around milky way-sized galaxies in cosmological simulations, the so-called too-big-to-fail (tbtf) problem. a caveat of previous work has been that dark substructures were assumed to contain steep density cusps in the centre of dm haloes even though the central density structure of dm haloes is still under debate. in this study, we re-examine the tbtf problem for models of dm density structure with cores or shallowed cusps. our analysis demonstrates that the tbtf problem is alleviated as the logarithmic slope of the central cusp becomes shallower. we find that the tbtf problem is avoided if the central cusps of dm haloes surrounding dsphs are shallower than r-0.6. | re-examining the too-big-to-fail problem for dark matter haloes with central density cores |
galaxy clusters constitute powerful cosmological probes thanks to comparisons between observed and simulated clusters. as such virgo constitutes a formidable source for detailed observations facilitated by its proximity. however, the diversity of clusters complicates the comparisons on a one-to-one basis. simulated clusters must be carefully selected, a daunting task since most properties are unknown. alternatively, lookalikes produced in the proper large-scale environment can be used. additionally, their statistical study give access to the mean properties of the observed cluster including its most probable history as well as its deviation from an average cluster. this paper presents such a statistical study with 200 virgo-like and 400+ cluster-size random dark matter haloes. only 18 per cent (0.5 per cent) of these random haloes comply within 3(2)σ with the mean values (radius, velocity dispersion, number of substructures, spin, velocity, concentration, centre of mass offset with respect to the spherical centre) of virgo haloes at z = 0 and abide by a similar merging history up to redshift 4. none are within 1σ because of environmentally induced properties (number of substructures and velocity). for further comparisons, random haloes are selected to reproduce the mass distribution of the lookalikes to cancel mass bias effects. redshift 1 appears then as a turning point: random to virgo-like property ratios are alternatively smaller/larger than 1. this highlights the importance of studying clusters within their proper large-scale environment: simulated galaxy population, grandly affected by the cluster history, can then be compared with the observed one in details. direct lookalikes simplify grandly the challenge. | virgo: an unlikely cluster of galaxies because of its environment |
understanding local stellar kinematic substructures in the solar neighbourhood helps build a complete picture of the formation of the milky way, as well as an empirical phase space distribution of dark matter that would inform detection experiments. we apply the clustering algorithm hdbscan on the gaia early third data release to identify a list of stable clusters in velocity space and action-angle space by taking into account the measurement uncertainties and studying the stability of the clustering results. we find 1405 (497) stars in 23 (6) robust clusters in velocity space (action-angle space) that are consistently not associated with noise. we discuss the kinematic properties of these structures and study whether many of the small clusters belong to a similar larger cluster based on their chemical abundances. they are attributed to the known structures: the gaia sausage-enceladus, the helmi stream, and globular cluster ngc 3201 are found in both spaces, while ngc 104 and the thick disc (sequoia) are identified in velocity space (action-angle space). although we do not identify any new structures, we find that the hdbscan member selection of already known structures is unstable to input kinematics of the stars when resampled within their uncertainties. we therefore present the stable subset of local kinematic structures, which are consistently identified by the clustering algorithm, and emphasize the need to take into account error propagation during both the manual and automated identification of stellar structures, both for existing ones as well as future discoveries. | robust clustering of the local milky way stellar kinematic substructures with gaia edr3 |
using realistic cosmological simulations of milky way sized haloes, we study their dynamical state and the accuracy of inferring their mass profiles with steady-state models of dynamical tracers. we use a new method that describes the phase-space distribution of a steady-state tracer population in a spherical potential without any assumption regarding the distribution of their orbits. applying the method to five haloes from the aquarius λ cold dark matter (λcdm) n-body simulation, we find that dark matter particles are an accurate tracer that enables the halo mass and concentration parameters to be recovered with an accuracy of 5 per cent. assuming a potential profile of the navarro, frenk & white (nfw) form does not significantly affect the fits in most cases, except for halo a whose density profile differs significantly from the nfw form, leading to a 30 per cent bias in the dynamically fitted parameters. the existence of substructures in the dark matter tracers only affects the fits by ∼1 per cent. applying the method to mock stellar haloes generated by a particle-tagging technique, we find the stars are farther from equilibrium than dark matter particles, yielding a systematic bias of ∼20 per cent in the inferred mass and concentration parameter. the level of systematic biases obtained from a conventional distribution function fit to stars is comparable to ours, while similar fits to dark matter tracers are significantly biased in contrast to our fits. in line with previous studies, the mass bias is much reduced near the tracer half-mass radius. | the orbital pdf: the dynamical state of milky way sized haloes and the intrinsic uncertainty in the determination of their masses |
we present a detailed high-resolution weak-lensing study of spt-cl j2106-5844 at z = 1.132, claimed to be the most massive system discovered at z > 1 in the south pole telescope sunyaev-zel’dovich survey. based on the deep imaging data from the advanced camera for surveys and wide field camera 3 on board the hubble space telescope, we find that the cluster mass distribution is asymmetric, composed of a main clump and a subclump ∼640 kpc west thereof. the central clump is further resolved into two smaller northwestern and southeastern substructures separated by ∼150 kpc. we show that this rather complex mass distribution is more consistent with the cluster galaxy distribution than a unimodal distribution as previously presented. the northwestern substructure coincides with the brightest cluster galaxy and the x-ray peak while the southeastern one agrees with the location of the peak in number density. these morphological features and the comparison with the x-ray emission suggest that the cluster might be a merging system. we estimate the virial mass of the cluster to be {m}200c=({10.4}-3.0+3.3+/- 1.0)× {10}14 {m}⊙ , where the second error bar is the systematic uncertainty. our result confirms that the cluster spt-cl j2106-5844 is indeed the most massive cluster at z > 1 known to date. we demonstrate the robustness of this mass estimate by performing a number of tests with different assumptions on the centroids, mass-concentration relations, and sample variance. | precise mass determination of spt-cl j2106-5844, the most massive cluster at z > 1 |
dark matter substructure can contribute significantly to local dark matter searches and may provide a large uncertainty in the interpretation of those experiments. for direct detection experiments, sub-halos give rise to an additional dark matter component on top of the smooth dark matter distribution of the host halo. in the case of dark matter capture in the sun, sub-halo encounters temporarily increase the number of captured particles. even if the encounter happened in the past, the number of dark matter particles captured by the sun can still be enhanced today compared to expectations from the host halo as those enhancements decay over time. using results from an analytical model of the sub-halo population of a milky way-like galaxy, valid for sub-halo masses between 10-5 msolar and 1011 msolar, we assess the impact of sub-halos on direct dark matter searches in a probabilistic way. we find that the impact on direct detection can be sizable, with a probability of ~ 10-3 to find an script o(1) enhancement of the recoil rate. in the case of the capture rate in the sun, we find that script o(1) enhancements are very unlikely, with probability lesssim 10-5, and are even impossible for some dark matter masses. | impact of substructure on local dark matter searches |
we establish a controlled comparison between the properties of galactic stellar haloes obtained with hydrodynamical simulations and with 'particle tagging'. tagging is a fast way to obtain stellar population dynamics: instead of tracking gas and star formation, it 'paints' stars directly on to a suitably defined subset of dark matter particles in a collisionless, dark-matter-only simulation. our study shows that 'live' particle tagging schemes, where stellar masses are painted on to the dark matter particles dynamically throughout the simulation, can generate good fits to the hydrodynamical stellar density profiles of a central milky way-like galaxy and its most prominent substructure. energy diffusion processes are crucial to reshaping the distribution of stars in infalling spheroidal systems and hence the final stellar halo. we conclude that the success of any particular tagging scheme hinges on this diffusion being taken into account, and discuss the role of different subgrid feedback prescriptions in driving this diffusion. | particle tagging and its implications for stellar population dynamics |
modelling self-gravity of collisionless fluids (e.g. ensembles of dark matter, stars, black holes, dust, and planetary bodies) in simulations is challenging and requires some force softening. it is often desirable to allow softenings to evolve adaptively, in any high-dynamic range simulation, but this poses unique challenges of consistency, conservation, and accuracy, especially in multiphysics simulations where species with different 'softening laws' may interact. we therefore derive a generalized form of the energy-and-momentum conserving gravitational equations of motion, applicable to arbitrary rules used to determine the force softening, together with consistent associated time-step criteria, interaction terms between species with different softening laws, and arbitrary maximum/minimum softenings. we also derive new methods to maintain better accuracy and conservation when symmetrizing forces between particles. we review and extend previously discussed adaptive softening schemes based on the local neighbour particle density, and present several new schemes for scaling the softening with properties of the gravitational field, i.e. the potential or acceleration or tidal tensor. we show that the 'tidal softening' scheme not only represents a physically motivated, translation and galilean invariant and equivalence-principle respecting (and therefore conservative) method but also imposes negligible time-step or other computational penalties, ensuring that pairwise two-body scattering is small compared to smooth background forces and can resolve outstanding challenges in properly capturing tidal disruption of substructures (minimizing artificial destruction) while also avoiding excessive n-body heating. we make all of this public in the gizmo code. | novel conservative methods for adaptive force softening in collisionless and multispecies n-body simulations |
the identity of dark matter has remained surprisingly elusive. while terrestrial experiments may be able to nail down a model, an alternative method is to identify dark matter based on astrophysical or cosmological signatures. a particularly sensitive approach is based on the unique signature of dark matter substructure in galaxy-galaxy strong lensing images. machine-learning applications have been explored for extracting this signal. because of the limited availability of high-quality strong lensing images, these approaches have exclusively relied on simulations. due to the differences with the real instrumental data, machine-learning models trained on simulations are expected to lose accuracy when applied to real data. here domain adaptation can serve as a crucial bridge between simulations and real data applications. in this work, we demonstrate the power of domain adaptation techniques applied to strong gravitational lensing data with dark matter substructure. we show with simulated data sets representative of euclid and hubble space telescope observations that domain adaptation can significantly mitigate the losses in the model performance when applied to new domains. lastly, we find similar results utilizing domain adaptation for the problem of lens finding by adapting models trained on a simulated data set to one composed of real lensed and unlensed galaxies from the hyper suprime-cam. this technique can help domain experts build and apply better machine-learning models for extracting useful information from the strong gravitational lensing data expected from the upcoming surveys. | domain adaptation for simulation-based dark matter searches with strong gravitational lensing |
we introduce the galaxy replacement technique (grt) that allows us to model tidal stripping of galaxies with very high mass (m star = 5.4 × 104 m ⊙ h -1) and high spatial resolution (10 pc h -1), in a fully cosmological context, using an efficient and fast technique. the technique works by replacing multiple low-resolution dark-matter (dm) halos in the base cosmological simulation with high-resolution models, including a dm halo and stellar disk. we apply the method to follow the hierarchical buildup of a cluster since redshift ~8 to now, through the hierarchical accretion of galaxies, individually or in substructures such as galaxy groups. we find we can successfully reproduce the observed total stellar masses of observed clusters since redshift ~1. the high resolution allows us to accurately resolve the tidal stripping process and well describe the formation of ultralow surface brightness features in the cluster (μv< 32 mag arcsec-2) such as the intracluster light (icl), shells, and tidal streams. we measure the evolution of the fraction of light in the icl and brightest cluster galaxy using several different methods. while their broad response to the cluster-mass growth history is similar, the methods show systematic differences, meaning we must be careful when comparing studies that use distinct methods. the grt represents a powerful new tool for studying tidal effects on galaxies and exploring the formation channels of the icl in a fully cosmological context and with large samples of simulated groups and clusters. | the galaxy replacement technique (grt): a new approach to study tidal stripping and formation of intracluster light in a cosmological context |
multicomponent dark matter with self-interactions, which allows for interconversions of species, is a promising paradigm that is known to successfully and simultaneously resolve major problems of the conventional lambda cold dark matter (λcdm) cosmology at galactic and subgalactic scales. in this paper, we present n-body simulations of the simplest two-component (2cdm) model aimed at studying the distribution of dark matter haloes with masses m≲ 10^{12} m_⊙. in particular, we investigate how the maximum circular velocity function of the haloes is affected by the velocity dependence of the self-interaction cross-sections, σ(v) ∝ va, and compare it with available observational data. the results demonstrate that the 2cdm paradigm with the range of self-interaction cross-section per particle mass (evaluated at v = 100 km s-1) of 0.01 ≲ σ0/m ≲ 1 cm2 g-1 and the mass degeneracy δm/m ∼ 10-7-10-8 robustly resolves the substructure and too-big-to-fail problems by suppressing the substructure having small maximum circular velocities, vmax ≲ 100 km s-1. we also discuss the disagreement between the radial distribution of dwarfs in a host halo observed in the local group and simulated with cdm. this can be considered as one more small-scale problem of cdm. we demonstrate that such a disagreement is alleviated in 2cdm. finally, the computed matter power spectra of the 2cdm structure indicate the model's consistency with the existing ly α forest constraints. | dark matter haloes in the multicomponent model - i. substructure |
aims: the hierarchical model of structure formation is a key prediction of the λ cold dark matter model, which can be tested by studying the large-scale environment and the substructure content of massive galaxy clusters. we present here a detailed analysis of the clusters rxc j0225.9-4154, rxc j0528.9-3927, and rxc j2308.3-0211, as part of a sample of massive x-ray luminous clusters located at intermediate redshifts.methods: we used a multiwavelength analysis, combining wfi photometric observations, vimos spectroscopy, and the x-ray surface brightness maps. we investigated the optical morphology of the clusters, we looked for significant counterparts in the residual x-ray emission, and we ran several statistical tests to assess their dynamical state. we correlated the results to define various substructure features, to study their properties, and to quantify their influence on simple dynamical mass estimators.results: rxc j0225.9-4154 has a bi-modal core, and two massive galaxy groups are located in its immediate surroundings; they are aligned in an elongated structure that is also detected in x-rays at the 1σ level. rxc j0528.9-3927 is located in a poor environment; an x-ray centroid shift and the presence of two central bcgs provide mild evidence for a recent and active dynamical history. rxc j2308.3-0211 has complex central dynamics, and it is found at the core of a superstes-cluster.conclusions: the complexity of the cluster's central dynamics reflects the richness of its large-scale environment: rxc j0225 and rxc j2308 present a mass fraction in substructures larger than the typical 5-15%, whereas the isolated cluster rxc j0528 does not have any major substructures within its virial radius. the largest substructures are found in the cluster outskirts. the optical morphology of the clusters correlates with the orientation of their bcg, and with the position of the main axes of accretion. based on observations from the very large telescope at paranal, chile.full table a.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/601/a145 | from the core to the outskirts: structure analysis of three massive galaxy clusters |
we present the first numerical simulations in coupled dark energy cosmologies with high enough resolution to investigate the effects of the coupling on galactic and subgalactic scales. we choose two constant couplings and a time-varying coupling function and we run simulations of three milky way-sized haloes (∼1012 m⊙), a lower mass halo (6 × 1011 m⊙) and a dwarf galaxy halo (5 × 109 m⊙). we resolve each halo with several million dark matter particles. on all scales, the coupling causes lower halo concentrations and a reduced number of substructures with respect to λ cold dark matter (λcdm). we show that the reduced concentrations are not due to different formation times. we ascribe them to the extra terms that appear in the equations describing the gravitational dynamics. on the scale of the milky way satellites, we show that the lower concentrations can help in reconciling observed and simulated rotation curves, but the coupling values necessary to have a significant difference from λcdm are outside the current observational constraints. on the other hand, if other modifications to the standard model allowing a higher coupling (e.g. massive neutrinos) are considered, coupled dark energy can become an interesting scenario to alleviate the small-scale issues of the λcdm model. | effects of coupled dark energy on the milky way and its satellites |
we present direct n-body simulations of tidally filling 30 000 m⊙ star clusters orbiting between 10 and 100 kpc in galaxies with a range of dark matter substructure properties. the time-dependent tidal force is determined based on the combined tidal tensor of the galaxy's smooth and clumpy dark matter components, the latter of which causes fluctuations in the tidal field that can heat clusters. the strength and duration of these fluctuations are sensitive to the local dark matter density, substructure fraction, sub-halo mass function, and the sub-halo mass-size relation. based on the cold dark matter framework, we initially assume sub-haloes are hernquist spheres following a power-law mass function between 105 and 1011 m⊙ and find that tidal fluctuations are too weak and too short to affect star cluster evolution. treating sub-haloes as point masses, to explore how denser sub-haloes affect clusters, we find that only sub-haloes with masses greater than 106 m⊙ will cause cluster dissolution times to decrease. these interactions can also decrease the size of a cluster while increasing the velocity dispersion and tangential anisotropy in the outer regions via tidal heating. hence increased fluctuations in the tidal tensor, especially fluctuations that are due to low-mass haloes, do not necessarily translate into mass-loss. we further conclude that the tidal approximation can be used to model cluster evolution in the tidal fields of cosmological simulations with a minimum cold dark matter sub-halo mass of 106 m⊙, as the effect of lower mass sub-haloes on star clusters is negligible. | modelling the effects of dark matter substructure on globular cluster evolution with the tidal approximation |
we study evolution of single subhaloes with their masses of ~109 m⊙ in a milky way-sized host halo for self-interacting dark matter (sidm) models. we perform dark-matter-only n-body simulations of dynamical evolution of individual subhaloes orbiting its host by varying self-scattering cross-sections (including a velocity-dependent scenario), subhalo orbits, and internal properties of the subhalo. we calibrate a gravothermal fluid model to predict time evolution in spherical mass density profiles of isolated sidm haloes with the simulations. we find that tidal effects of sidm subhaloes can be described with a framework developed for the case of collision-less cold dark matter (cdm), but a shorter typical time-scale for the mass loss due to tidal stripping is required to explain our sidm simulation results. as long as the cross-section is less than $\sim \! 10\, \mathrm{cm}^2\,\mathrm{g}^{ -1}$ and initial states of subhaloes are set within a 2σ-level scatter at redshifts of ~2 predicted by the standard λcdm cosmology, our simulations do not exhibit a prominent feature of gravothermal collapse in the subhalo central density for 10 gyr. we develop a semi-analytic model of sidm subhaloes in a time-evolving density core of the host with tidal stripping and self-scattering ram pressure effects. our semi-analytic approach provides a simple, efficient, and physically intuitive prediction of sidm subhaloes, but further improvements are needed to account for baryonic effects in the host and the gravothermal instability accelerated by tidal stripping effects. | modelling self-interacting dark matter substructures - i. calibration with n-body simulations of a milky-way-sized halo and its satellite |
this is the first of a series of three papers devoted to the study of halo substructure in hierarchical cosmologies by means of the cusp formalism. in the present paper, we derive the properties of subhaloes and diffuse dark matter (ddm) accreted on to haloes and their progenitors. specifically, we relate the ddm present at any time in the inter-halo medium of the real universe or a cosmological simulation with the corresponding free-streaming mass or the halo resolution mass, respectively, and establish the link between subhaloes and their seeds in the initial density field. by monitoring the collapse and virialization of haloes, we derive from first principles and with no single free parameter the abundance and radial distribution of ddm and subhaloes accreted on to them. our predictions are in excellent agreement with the results of simulations, but for the predicted fraction of accreted ddm, which is larger than reported in previous works as they only count the ddm accreted on to the final halo, not on to its progenitors. the derivation pursued here clarifies the origin of some key features of substructure. overall, our results demonstrate that cusp is a powerful tool for understanding halo substructure and extending the results of simulations to haloes with arbitrary masses, redshifts, and formation times in any hierarchical cosmology endowed with random gaussian density perturbations. | an accurate comprehensive approach to substructure - i. accreted subhaloes |
compact groups (cgs) of galaxies appear to be the densest galaxy systems containing a few luminous galaxies in close proximity to each other, which have a typical size of a few tens of kiloparsec in observation. on the other hand, in the modern hierarchical structure formation paradigm, galaxies are assembled and grouped in dark matter halos, which have a typical size of a few hundreds of kiloparsec. few studies have explored the physical connection between the observation-based cgs and halo model-based galaxy groups to date. in this study, by matching the largest local cg catalog of zheng & shen to the halo-based group catalog of yang et al., we find that cgs are physically heterogeneous systems and can be mainly separated into two categories, the isolated systems and those embedded in rich groups or clusters. by examining the dynamical features of cgs, we find that isolated cgs have systematically lower dynamical masses than noncompact ones at the same group luminosity, indicating a more evolved stage of isolated cgs. on the other hand, the embedded cgs are mixtures of chance alignments in poor clusters and recent infalling groups (substructures) of rich clusters. | compact groups of galaxies in sloan digital sky survey and lamost spectral survey. ii. dynamical properties of isolated and embedded groups |
the hubble space telescope frontier fields cluster macs j1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. we present results from deep (365 ks) chandra observations of the cluster, which reveal the most distant cold front (z = 0.544) discovered to date. in the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. the substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. the inclination of the mergers with respect to the plane of the sky poses significant observational challenges at x-ray wavelengths. macs j1149.6+2223 possibly hosts a steep-spectrum radio halo. if the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular icm morphology, could indicate that macs j1149.6+2223 is an old merging cluster. | frontier fields clusters: deep chandra observations of the complex merger macs~j1149.6+2223 |
wrapping around the milky way, the sagittarius stream is the dominant substructure in the halo. our statistical selection method has allowed us to identify 106 highly likely members of the sagittarius stream. spectroscopic analysis of metallicity and kinematics of all members provides us with a new mapping of the sagittarius stream. we find correspondence between the velocity distribution of stream stars and those computed for a triaxial model of the milky way dark matter halo. the sagittarius trailing arm exhibits a metallicity gradient, ranging from -0.59 to -0.97 dex over 142°. this is consistent with the scenario of tidal disruption from a progenitor dwarf galaxy that possessed an internal metallicity gradient. we note high metallicity dispersion in the leading arm, causing a lack of detectable gradient and possibly indicating orbital phase mixing. we additionally report on a potential detection of the sextans dwarf spheroidal in our data. | selecting sagittarius: identification and chemical characterization of the sagittarius stream |
the physics beyond the standard model with parameters of the compressed spectrum is well motivated both in the theory side and with phenomenological reasons, especially related to dark matter phenomenology. in this letter, we propose a method to tag soft final state particles from a decaying process of a new particle in this parameter space. by taking a supersymmetric gluino search as an example, we demonstrate how the large hadron collider experimental collaborations can improve sensitivity in these nontrivial search regions. | revealing the jet substructure in a compressed spectrum of new physics |
strong gravitational lensing is a unique observational tool for studying the dark and luminous mass distribution both within and between galaxies. given the presence of substructures, current strong lensing observations demand more complex mass models than smooth analytical profiles, such as power-law ellipsoids. in this work, we introduce a continuous neural field to predict the lensing potential at any position throughout the image plane, allowing for a nearly model-independent description of the lensing mass. we applied our method to simulated hubble space telescope imaging data containing different types of perturbations to a smooth mass distribution: a localized dark subhalo, a population of subhalos, and an external shear perturbation. assuming knowledge of the source surface brightness, we used the continuous neural field to model either the perturbations alone or the full lensing potential. in both cases, the resulting model was able to fit the imaging data, and we were able to accurately recover the properties of both the smooth potential and the perturbations. unlike many other deep-learning methods, ours explicitly retains lensing physics (i.e., the lens equation) and introduces high flexibility in the model only where required, namely, in the lens potential. moreover, the neural network does not require pretraining on large sets of labeled data and predicts the potential from the single observed lensing image. our model is implemented in the fully differentiable lens modeling code herculens. | modeling lens potentials with continuous neural fields in galaxy-scale strong lenses |
accurate estimation of the merger timescales of galaxy clusters is important for understanding the cluster merger process and further understanding the formation and evolution of the large-scale structure of the universe. in this paper, we explore a baryonic effect on the merger timescale of galaxy clusters by using hydrodynamical simulations. we find that the baryons play an important role in accelerating the merger process. the merger timescale decreases upon increasing the gas fraction of galaxy clusters. for example, the merger timescale is shortened by a factor of up to 3 for merging clusters with gas fractions of 0.15, compared with the timescale obtained with 0 gas fractions. the baryonic effect is significant for a wide range of merger parameters and is particularly more significant for nearly head-on mergers and high merging velocities. the baryonic effect on the merger timescale of galaxy clusters is expected to have an impact on the structure formation in the universe, such as the cluster mass function and massive substructures in galaxy clusters, and a bias of “no-gas” may exist in the results obtained from the dark matter-only cosmological simulations. | a baryonic effect on the merger timescale of galaxy clusters |
we present an extensive spectroscopic follow-up campaign of 29 strong lensing (sl) selected galaxy clusters discovered primarily in the second red-sequence cluster survey (rcs-2). our spectroscopic analysis yields redshifts for 52 gravitational arcs present in the core of our galaxy clusters, which correspond to 35 distinct background sources that are clearly distorted by the gravitational potential of these clusters. these lensed galaxies span a wide redshift range of 0.8 ≤ z ≤ 2.9, with a median redshift of zs = 1.8 ± 0.1. we also measure reliable redshifts for 1004 cluster members, allowing us to obtain robust velocity dispersion measurements for 23 of these clusters, which we then use to determine their dynamical masses by using a simulation-based σdm - m200 scaling relation. the redshift and mass ranges covered by our sl sample are 0.22 ≤ z ≤ 1.01 and 5× {10}13≤slant {m}200/{h}70-1 {m}⊙ ≤slant 1.9× {10}15, respectively. we analyze and quantify some possible effects that might bias our mass estimates, such as the presence of substructure, the region where cluster members are selected for spectroscopic follow-up, the final number of confirmed members, and line-of-sight effects. we find that 10 clusters of our sample with nmem ≳ 20 show signs of dynamical substructure. however, the velocity data of only one system is inconsistent with a uni-modal distribution. we therefore assume that the substructures are only marginal and not of comparable size to the clusters themselves. consequently, our velocity dispersion and mass estimates can be used as priors for sl mass reconstruction studies and also represent an important step toward a better understanding of the properties of the sl galaxy cluster population. | vlt/magellan spectroscopy of 29 strong lensing selected galaxy clusters |
we use a catalogue of stellar binaries with wide separations (up to 1 pc) identified by the gaia satellite to constrain the presence of extended substructure within the milky way galaxy. heating of the binaries through repeated encounters with substructure results in a characteristic distribution of binary separations, allowing constraints to be placed independent of the formation mechanism of wide binaries. across a wide range of subhalo density profiles, we show that subhaloes with masses $\gtrsim 65\, \mathrm{ m}_\odot$ and characteristic length scales similar to the separation of these wide binaries cannot make up 100 per cent of the galaxy's dark matter. constraints weaken for subhaloes with larger length scales and are dependent on their density profiles. for such large subhaloes, higher central densities lead to stronger constraints. subhaloes with density profiles similar to those expected from cold dark matter must be at least ~5000 times denser than predicted by simulation to be constrained by the wide binary catalogue. | constraining dark matter substructure with gaia wide binaries |
the hubble frontier fields (hffs) are six clusters of galaxies, all showing indications of recent mergers, which have recently been observed for lensed images. as such they are the natural laboratories to study the merging history of galaxy clusters. in this work, we explore the 2d power spectrum of the mass distribution pm(k) as a measure of substructure. we compare pm(k) of these clusters (obtained using strong gravitational lensing) to that of λ cold dark matter simulated clusters of similar mass. to compute lensing pm(k), we produced free-form lensing mass reconstructions of hff clusters, without any light traces mass (ltm) assumption. the inferred power at small scales tends to be larger if (i) the cluster is at lower redshift, and/or (ii) there are deeper observations and hence more lensed images. in contrast, lens reconstructions assuming ltm show higher power at small scales even with fewer lensed images; it appears the small-scale power in the ltm reconstructions is dominated by light information, rather than the lensing data. the average lensing derived pm(k) shows lower power at small scales as compared to that of simulated clusters at redshift zero, both dark matter only and hydrodynamical. the possible reasons are (i) the available strong lensing data are limited in their effective spatial resolution on the mass distribution; (ii) hff clusters have yet to build the small-scale power they would have at z ∼ 0 or (iii) simulations are somehow overestimating the small-scale power. | quantifying substructures in hubble frontier field clusters: comparison with λcdm simulations |
to investigate the spatial distribution of the intracluster medium temperature in galaxy clusters in a quantitative way and probe the physics behind it, we analyze the x-ray spectra from a sample of 50 clusters that were observed with the chandra acis instrument over the past 15 years and measure the radial temperature profiles out to 0.45r500. we construct a physical model that takes into consideration the effects of gravitational heating, thermal history (such as radiative cooling, active galactic nucleus feedback, and thermal conduction), and work done via gas compression, and use it to fit the observed temperature profiles by running bayesian regressions. the results show that in all cases our model provides an acceptable fit at the 68% confidence level. for further validation, we select nine clusters that have been observed with both chandra (out to ≳0.3r500) and suzaku (out to ≳1.5r500) and fit their chandra spectra with our model. we then compare the extrapolation of the best fits with the suzaku measurements and find that the model profiles agree with the suzaku results very well in seven clusters. in the remaining two clusters the difference between the model and the observation is possibly caused by local thermal substructures. our study also implies that for most of the clusters the assumption of hydrostatic equilibrium is safe out to at least 0.5r500 and the non-gravitational interactions between dark matter and its luminous counterparts is consistent with zero. | a chandra study of temperature distributions of the intracluster medium in 50 galaxy clusters |
flux ratio anomalies in strong gravitationally lensed quasars constitute a unique way to probe the abundance of non-luminous dark matter haloes, and hence the nature of dark matter. in this paper, we identify double-imaged quasars as a statistically efficient probe of dark matter, since they are 20 times more abundant than quadruply imaged quasars. using n-body simulations that include realistic baryonic feedback, we measure the full distribution of flux ratios in doubly imaged quasars for cold (cdm) and warm dark matter (wdm) cosmologies. through this method, we fold in two key systematics - quasar variability and line-of-sight structures. we find that wdm cosmologies predict a ∼6 per cent difference in the cumulative distribution functions of flux ratios relative to cdm, with cdm predicting many more small ratios. finally, we estimate that ∼600 doubly imaged quasars will need to be observed in order to be able to unambiguously discern between cdm and the two wdm models studied here. such sample sizes will be easily within reach of future large-scale surveys such as euclid. in preparation for this survey data, we require discerning the scale of the uncertainties in modelling lens galaxies and their substructure in simulations, plus a strong understanding of the selection function of observed lensed quasars. | exploiting flux ratio anomalies to probe warm dark matter in future large-scale surveys |
if the dark matter haloes of galaxies contain large numbers of subhaloes as predicted by the λ cold dark matter model, these subhaloes are expected to appear in strong galaxy-galaxy lens systems as small-scale perturbations in individual images. we simulate observations of multiply lensed sub-mm galaxies at z ∼ 2 as a probe of the dark matter halo of a lens galaxy at z ∼ 0.5. we present detection limits for dark substructures based on a visibility plane analysis of simulated atacama large millimeter/submillimeter array (alma) data in bands 7, 8 and 9. we explore two effects: local surface brightness anomalies on angular scales similar to the einstein radius and the astrometric shift of macroimages. this improves the sensitivity of our lens modelling to the mass of the lens perturber. we investigate the sensitivity of the detection of low-mass subhaloes to the projected position of the subhalo on the image plane as well as the source structure and inner density profile of the lens. we demonstrate that, using the most extended alma configuration, pseudo-jaffe subhaloes can be detected with 99 per cent confidence down to m = 107 m⊙. we show how the detection threshold for the three alma bands depends on the projected position of the subhalo with respect to the lensed images and conclude that, despite the highest nominal angular resolution, band 9 provides the poorest sensitivity due to observational noise. all simulations use the alma full ops most extended alma configuration setup in casa. | probing cold dark matter subhaloes with simulated alma observations of macrolensed sub-mm galaxies |
it was proposed that the two phenomena, wmap-planck haze and fermi bubbles, may have a common origin. in the present paper we analyze the spatial structure of the haze using the planck 2018 data release. it is found that the spatial dimensions and locations of wmap-planck haze and fermi bubbles are compatible within the experimental uncertainties. no substructures similar to the fermi bubbles cocoon are identified in the planck data. comparison with the spatial extent of possible synchrotron emission caused by the electron-positron pair emitted by the galactic center pulsar population and by the decay of dark matter particles in the galactic center region are performed. both galactic pulsars and dark matter decay remain viable explanations of the wmap-planck haze. | spatial structure of the wmap-planck haze |
the cold dark matter picture predicts an abundance of substructure within the galactic halo. however, most substructures host no stars and can only be detected indirectly. stellar streams present a promising probe of this dark substructure. these streams arise from tidally stripped star clusters or dwarf galaxies, and their low dynamical temperature and negligible self-gravity give them a sharp memory of gravitational perturbations caused by passing dark substructures. for this reason, perturbed stellar streams have been the subject of substantial study. while previous studies have been largely numerical, we show here that in the diffusion regime - where stream stars are subjected to many small velocity kicks - stream perturbations can be understood on a fully analytic level. in particular, we derive how the (three-dimensional) power spectrum of the substructure density field determines the power spectrum of the (one-dimensional) density of a stellar stream. our analytic description supplies a clear picture of the behaviour of stream perturbations in response to a perturbing environment, which may include contributions from both dark and luminous substructure. in particular, stream perturbations grow in amplitude initially, settle into a steady state, and ultimately decay. by directly relating stellar stream perturbations to the surrounding matter distribution, this analytic framework represents a versatile new tool for probing the nature of dark matter through astrophysical observations. | stellar streams and dark substructure: the diffusion regime |
in salvador-solé, manrique & botella (paper i), we used the confluent system of peak trajectories (cusp) formalism to derive from first principles and no single free parameter the accurate abundance and radial distribution of both diffuse dark matter (ddm) and subhaloes accreted on to haloes and their progenitors at all previous times. here we use those results as initial conditions for the monitoring of the evolution of subhaloes and ddm within the host haloes. specifically, neglecting dynamical friction, we accurately calculate the effects of repetitive tidal stripping and heating on subhaloes as they orbit inside the host halo and infer the amount of ddm and subsubhaloes they release into the intrahalo medium. we then calculate the expected abundance and radial distribution of stripped subhaloes and ddm. this derivation clarifies the role of halo concentration in substructure and unravels the origin of some key features found in simulations including the dependence of substructure on halo mass. in addition, it unveils the specific effects of dynamical friction on substructure. the results derived here are for purely accreting haloes. in salvador-solé et al. (paper iii), we complete the study by addressing the case of low-mass subhaloes, unaffected by dynamical friction, in ordinary haloes having suffered major mergers. | an accurate comprehensive approach to substructure - ii. stripped subhaloes |
a recent comparison of the massive galaxy cluster abell 2744 with the millennium xxl (mxxl) n-body simulation has hinted at a tension between the observed substructure distribution and the predictions of λ cold dark matter (λcdm). follow-up investigations indicated that this could be due to the contribution from the host halo and the subhalo finding algorithm used. to be independent of any subhalo finding algorithm, we therefore investigate the particle data of the mxxl simulation directly. we propose a wavelet-based method to detect substructures in 2d mass maps, which treats the simulation and observations equally. using the same criteria to define a subhalo in observations and simulated data, we find three abell 2744 analogues in the mxxl simulation. thus, the observations in abell 2744 are in agreement with the predictions of λcdm. we investigate the reasons for the discrepancy between the results obtained from the subfind and full particle data analyses. we find that this is due to incompatible substructure definitions in observations and subfind. | uncovering substructure with wavelets: proof of concept using abell 2744 |
a change in the mass of the galaxy with time will leave its imprint on the motions of the stars, with stars having radially outward (mass-loss) or inward (mass accretion) bulk motions. here, we test the feasibility of using the mean radial motion of stars in the stellar halo to constrain the rate of change of mass in the galaxy, e.g. due to decay of dark matter. in the lambda cold dark matter (λcdm) paradigm, the stellar halo is formed by accretion of satellites on to the host galaxy and its mean radial motion ⟨vr⟩ is eventually expected to be close to zero. but due to incomplete mixing most haloes have substructures and this can lead to non-zero ⟨vr⟩ in them. using simulations, we measure the mean radial motion of stars in 13 λcdm stellar haloes lying in a spherical shell of radius 30 kpc. for most haloes, the shell motion is quite small, with 75 per cent of haloes having $\langle v_\text{r}\rangle \lesssim 1.2 \:{\rm km}\, {\rm s}^{-1}$. when substructures are removed by using a clustering algorithm, ⟨vr⟩ is reduced even further, with 75 per cent of haloes having $\langle v_\text{r}\rangle \lesssim 0.6 \:{\rm km}\, {\rm s}^{-1}$. a value of $\langle v_\text{r}\rangle \approx 0.6 \:{\rm km}\, {\rm s}^{-1}$ can be attained corresponding to a galactic mass-loss rate of 2 per cent per gyr. we show that this can place constraints on dark matter decay parameters such as the decay lifetime and the kick velocity that is imparted to the daughter particle. the advent of all-sky stellar surveys involving millions to billions of stars is encouraging for detecting signatures of dark matter decay. | can radial motions in the stellar halo constrain the rate of change of mass in the galaxy? |
deap-3600 is the largest running dark matter detector filled with liquid argon, set at snolab, in sudbury, canada, 2 km underground. the experiment holds the most stringent exclusion limit in argon for wimps above 20 gev/c2. in the most recent published analysis, the background events due to α-induced scintillation in the neck of the detector limited the sensitivity. the sensitivity of the detector in the next wimp search will be improved thanks to the decrease in backgrounds achieved by hardware upgrades and applying multivariate analyses. moreover, the wimp analysis has been revisited in terms of a non-relativistic effective field theory framework, and the impact of possible substructures in the galactic dark matter halo was explored. this analysis was motivated by the latest results from gaia and the sloan sky digital survey. here deap-3600 set the world's best exclusion limit for xenon-phobic dark matter scenarios. finally, a custom-developed analysis has recently pointed out the extraordinary sensitivity to ultra-heavy, multi-scattering dark matter candidates, resulting in world-leading exclusion limits on two composite dark matter candidates up to planck scale masses. these proceedings, after a quick overview of the dark matter detection in deap-3600, outline the detector upgrades and the dark matter search results from the collaboration of the last three years. | recent results from deap-3600 |
we use high-resolution, hydrodynamic, galaxy simulations from the latte suite of fire-2 simulations to investigate the inherent variation of dark matter in sub-sampled regions around the solar circle of a milky way-type analogue galaxy and its impact on direct dark matter detection. these simulations show that the baryonic back reaction, as well as the assembly history of substructures, has lasting impacts on the dark matter's spatial and velocity distributions. these are experienced as 'gusts' of dark matter wind around the solar circle, potentially complicating interpretations of direct detection experiments on earth. we find that the velocity distribution function in the galactocentric frame shows strong deviations from the maxwell boltzmann form typically assumed in the fiducial standard halo model, indicating the presence of high-velocity substructures. by introducing a new numerical integration technique that removes any dependencies on the standard halo model, we generate event-rate predictions for both single-element germanium and compound sodium iodide detectors, and explore how the variability of dark matter around the solar circle influences annual modulation signal predictions. we find that these velocity substructures contribute additional astrophysical uncertainty to the interpretation of event rates, although their impact on summary statistics, such as the peak day of annual modulation, is generally low. | gusts in the headwind: uncertainties in direct dark matter detection |
schwinn et al. have recently compared the abundance and distribution of massive substructures identified in a gravitational lensing analysis of abell 2744 by jauzac et al. and n-body simulation, and found no cluster in lambda cold dark matter (λcdm) simulation that is similar to abell 2744. schwinn et al. identified the measured projected aperture masses with the actual masses associated with subhaloes in the millenium xxl n-body simulation. we have used the high-resolution phoenix cluster simulations to show that such an identification is incorrect: the aperture mass is dominated by mass in the body of the cluster that happens to be projected along the line of sight to the subhalo. this enhancement varies from factors of a few to factors of more than 100, particularly for subhaloes projected near the centre of the cluster. we calculate aperture masses for subhaloes in our simulation and compare them to the measurements for abell 2744. we find that the data for abell 2744 are in excellent agreement with the matched predictions from λcdm. we provide further predictions for aperture mass functions of subhaloes in idealized surveys with varying mass detection thresholds. | resolution of the apparent discrepancy between the number of massive subhaloes in abell 2744 and λcdm |
merging galaxy clusters may provide a unique window into the behavior of dark matter and the evolution of member galaxies. to interpret these natural collider experiments, we must account for how much time has passed since pericenter passage (tsp), the maximum relative speed of the merging subclusters, merger phase (outbound after first pericenter or returning for second pericenter), and other dynamical parameters that are not directly observable. these quantities are often inferred from staged simulations or analytical timing arguments that include neither substructure, nor large-scale structure, nor a cosmologically motivated range of impact parameters. we include all these effects by extracting dynamical parameters from analog systems in a cosmological n-body simulation, and we present constraints for 11 observed systems. the tsp and viewing angles we derive are consistent with those of staged hydrodynamical simulations, but we find lower maximum speeds. compared to the analytical mcmac method, we find lower tsp and viewing angles that put the separation vector closer to the plane of the sky; we attribute this to the mcmac assumption of zero pericenter distance. we discuss potential extensions to the basic analog method, as well as complementarities between methods. | dynamical properties of merging galaxy clusters from simulated analogs |
the galactic scale challenges of dark matter such as 'missing satellite' problem and 'too big to fail' problem are the main caveats of standard model of cosmology. these challenges could be solved either by implementing the complicated baryonic physics or it could be considered as an indication to a new physics beyond the standard model of cosmology. the modification of collisionless dark matter models or the standard initial conditions are two promising venues for study. in this work, we investigate the effects of the deviations from scale invariant initial curvature power spectrum on number density of dark matter haloes. we develop the non-markov extension of the excursion set theory to calculate the number density of dark matter substructures and dark matter halo progenitor mass distribution. we show that the plausible solution to 'too big to fail' problem could be obtained by a gaussian excess in initial power in the scales of k* ∼ 3 h mpc-1 that is related to the mass scale of m* ∼ 1011 m⊙. we show that this deviation leads to the decrement of dark matter subhaloes in galactic scale, which is consistent with the current status of the non-linear power spectrum. our proposal also has a prediction that the number density of milky way-type galaxies must be higher than the standard case. | modified initial power spectrum and too big to fail problem |
simulations of tidal streams show that close encounters with dark matter subhaloes induce density gaps and distortions in on-sky path along the streams. accordingly, observing disrupted streams in the galactic halo would substantiate the hypothesis that dark matter substructure exists there, while in contrast, observing collimated streams with smoothly varying density profiles would place strong upper limits on the number density and mass spectrum of subhaloes. here, we examine several measures of stellar stream 'disruption' and their power to distinguish between halo potentials with and without substructure and with different global shapes. we create and evolve a population of 1280 streams on a range of orbits in the via lactea ii simulation of a milky way-like halo, replete with a full mass range of λcold dark matter subhaloes, and compare it to two control stream populations evolved in smooth spherical and smooth triaxial potentials, respectively. we find that the number of gaps observed in a stellar stream is a poor indicator of the halo potential, but that (i) the thinness of the stream on-sky, (ii) the symmetry of the leading and trailing tails and (iii) the deviation of the tails from a low-order polynomial path on-sky ('path regularity') distinguish between the three potentials more effectively. we furthermore find that globular cluster streams on low-eccentricity orbits far from the galactic centre (apocentric radius ∼30-80 kpc) are most powerful in distinguishing between the three potentials. if they exist, such streams will shortly be discoverable and mapped in high dimensions with near-future photometric and spectroscopic surveys. | quantifying tidal stream disruption in a simulated milky way |
we study the outer regions of the milky way globular cluster ngc 7089 based on new dark energy camera observations. the resulting background-cleaned stellar density profile reveals the existence of an extended envelope. we confirm previous results that cluster stars are found out up to ~1° from the cluster's centre, which is nearly three times the value of the most robust tidal radii estimations. we also used results from direct n-body simulations in order to compare with the observations. we found a fairly good agreement between the observed and numerically generated stellar density profiles. because of the existence of gaps and substructures along globular cluster tidal tails, we closely examined the structure of the outer cluster region beyond the jacobi radius. we extended the analysis to a sample of 35 globular clusters, 20 of them with observed tidal tails. we found that if the stellar density profile follows a power law ∝ r-α, the α slope correlates with the globular cluster present mass, in the sense that, the more massive the globular cluster, the smaller the α value. this trend is not found in globular clusters without observed tidal tails. the origin of such a phenomenon could be related, among other reasons, to the proposed so-called potential escapers or to the formation of globular clusters within dark matter minihaloes. | on the physical size of the milky way globular cluster ngc 7089 (m2) |
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