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context. new-generation cosmological simulations are providing huge amounts of data, whose analysis becomes itself a pressing computational problem. in particular, the identification of gravitationally bound structures, known as halo finding, is one of the main analyses. several codes that were developed for this task have been presented during the past years.aims: we present a deep revision of the code asohf. the algorithm was thoroughly redesigned in order to improve its capabilities of finding bound structures and substructures using both dark matter particles and stars, its parallel performance, and its abilities of handling simulation outputs with vast amounts of particles. this upgraded version of asohf is conceived to be a publicly available tool.methods: a battery of idealised and realistic tests are presented in order to assess the performance of the new version of the halo finder.results: in the idealised tests, asohf produces excellent results. it is able to find virtually all the structures and substructures that we placed within the computational domain. when the code is applied to realistic data from simulations, the performance of our finder is fully consistent with the results from other commonly used halo finders. the performance in substructure detection is remarkable. in addition, asohf is extremely efficient in terms of computational cost.conclusions: we present a publicly available deeply revised version of the asohf halo finder. the new version of the code produces remarkable results in terms of halo and subhalo finding capabilities, parallel performance, and low computational cost. | the halo-finding problem revisited: a deep revision of the asohf code |
motivated by the idea that a subset of high-velocity clouds (hvcs) trace dark matter substructure in the local group, we search for signs of star formation in the smith cloud, a nearby ∼2 × 106 m⊙ hvc currently falling into the milky way. using galex nuv and wise/2mass nir photometry, we apply a series of colour and apparent magnitude cuts to isolate candidate o and b stars that are plausibly associated with the smith cloud. we find an excess of stars along the line of sight to the cloud, but not at a statistically significant level relative to a control region. the number of stars found in projection on the cloud after removing an estimate of the contamination by the milky way implies an average star formation rate surface density of 10-4.8±0.3 m⊙ yr-1 kpc-2, assuming the cloud has been forming stars at a constant rate since its first passage through the milky way ∼70 myr ago. this value is consistent with the star formation rate expected based on the average gas density of the cloud. we also discuss how the newly discovered star-forming galaxy leo p has very similar properties to the smith cloud, but its young stellar population would not have been detected at a statistically significant level using our method. thus, we cannot yet rule out the idea that the smith cloud is really a dwarf galaxy. | a search for star formation in the smith cloud |
context. local group (lg) analogs (lgas) are galaxy associations dominated by a few bright spirals reminiscent of the lg. the ngc 3447/ngc 3447a system is a member of the lgg 225 group, a nearby lga. this system is considered a physical pair composed of an intermediate-luminosity late-type spiral, ngc 3447 itself, and an irregular companion, ngc 3447a, linked by a faint, short filament of matter. a ring-like structure in the ngc 3447 outskirts has been emphasised by galaxy evolution explorer (galex) observations.aims: this work aims to contribute to the study of galaxy evolution in low-density environments, a favourable habitat to highly effective encounters, shedding light on the evolution of the ngc 3447/ngc 3447a system.methods: we performed a multi-λ analysis of the surface photometry of this system to derive its spectral energy distribution and structural properties using ultraviolet (uv), swift uvot, and optical sloan digital sky survey (sdss) images complemented with available far-ir observations. we also characterised the velocity field of the pair using two-dimensional hα kinematical observations of the system obtained with puma fabry-perot interferometer at the 2.1 m telescope of san pedro mártir (mexico). all these data are used to constrain smooth particle hydrodynamic simulations with chemo-photometric implementation to shed light on the evolution of this system.results: the luminosity profiles, from uv to optical wavelengths, are all consistent with the presence of a disc extending and including ngc 3447a. the overall velocity field does not emphasise any significant rotation pattern, rather a small velocity gradient between ngc 3447 and ngc 3447a. our simulation, detached from a large grid explored to best-fit the global properties of the system, suggests that this arises from an encounter between two halos of equal mass.conclusions: ngc 3447 and ngc 3447a belong to the same halo, ngc 3447a being a substructure of the same disk including ngc 3447. the halo gravitational instability, enhanced by the encounter, fuels a long-lived instability in this dark-matter-dominated disk, driving the observed morphology. the ngc 3447/ngc 3447a system may warn of a new class of "false pairs" and the potential danger of a misunderstanding of such objects in pair surveys that could produce a severe underestimate of the total mass of a system. the reduced images and datacubes are 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/610/a8 | galaxy evolution in groups. ngc 3447/ngc 3447a: the odd couple in lgg 225 |
the first paper in this series showed that quantum chromodynamic axion dark matter, as a highly correlated bose fluid, contains extra-classical physics on cosmological scales. the source of the derived extra-classical physics is exchange-correlation interactions induced by the constraints of symmetric particle exchange and interaxion correlations from self-gravitation. the paper also showed that the impact of extra-classical physics on early structure formation is marginal, as the exchange-correlation interaction is inherently non-linear. this paper continues the study of axion structure formation into the non-linear regime, considering the case of full collapse and virialization. the n-body method is chosen to study the collapse, and its algorithms are derived for a condensed bose fluid. simulations of isolated gravitational collapse are performed for both bose and cold dark matter fluids using a prototype n-body code. unique bose structures are found to survive even the most violent collapses. bose post-collapse features include dynamical changes to global structures, creation of new broad sub-structures, violations of classical binding energy conditions, and new fine structures. effective models of the novel structures are constructed and possibilities for their observation are discussed. | axion structure formation - ii. the wrath of collapse |
cosmological n-body simulations represent an excellent tool to study the formation and evolution of dark matter (dm) haloes and the mechanisms that have originated the universal profile at the largest mass scales in the universe. in particular, the combination of the velocity dispersion σv with the density ρ can be used to define the pseudo-entropy $s(r)=\sigma _\mathrm{v}^2/\rho ^{\, 2/3}$ , whose profile is well described by a simple power law $s\propto \, r^{\, \alpha }$ . we analyse a set of cosmological hydrodynamical re-simulations of massive galaxy clusters and study the pseudo-entropy profiles as traced by different collisionless components in simulated galaxy clusters: dm, stars, and substructures. we analyse four sets of simulations, exploring different resolution and physics (n-body and full hydrodynamical simulations) to investigate convergence and the impact of baryons. we find that baryons significantly affect the inner region of pseudo-entropy profiles as traced by substructures, while dm particles profiles are characterized by an almost universal behaviour, thus suggesting that the level of pseudo-entropy could represent a potential low-scatter mass-proxy. we compare observed and simulated pseudo-entropy profiles and find good agreement in both normalization and slope. we demonstrate, however, that the method used to derive observed pseudo-entropy profiles could introduce biases and underestimate the impact of mergers. finally, we investigate the pseudo-entropy traced by the stars focusing our interest in the dynamical distinction between intracluster light and the stars bound to the brightest cluster galaxy: the combination of these two pseudo-entropy profiles is well described by a single power law out to almost the entire cluster virial radius. | on the phase-space structure of galaxy clusters from cosmological simulations |
aims: we investigate the core-cusp problem of the λ cold dark matter (λcdm) scenario in the context of the modified newtonian dynamics (mond) paradigm while exploiting the concept of an equivalent newtonian system (ens).methods: by means of particle-mesh n-body simulations in mond, we explored the processes of galaxy formation via cold dissipationless collapse and the merging of smaller substructures. from the end states of our simulations, we recovered the associated ens and studied the properties of their dark matter halos. we compared the simulation results with simple analytical estimates with a family of γ-models.results: we find that the dark matter density of enss of most spherical cold collapses have a markedly cored structure, particularly for the lowest values of the initial virial ratios. end states of some simulations with initially clumpy conditions have more complex profiles, and some of their enss exhibit a moderate cusp, with the logarithmic density slope always shallower than one.conclusions: in contrast to what one would expect from theoretical and numerical arguments in λcdm, these results seem to point towards the fact that the absence of a central dm cusp in most observed galaxies would be totally consistent in a mondian description. | structure of the equivalent newtonian systems in mond n-body simulations. density profiles and the core-cusp problem |
the star formation history and the internal dynamics of milky way satellite galaxies are often complicated. in the last years, a substantial fraction of the known faint dwarf satellites have been studied. some of them show embedded stellar substructures, such as star clusters and even globular star clusters. in this work, we study eridanus ii, a dwarf spheroidal satellite that hosts a star cluster, using published and archival data from the hubble space telescope advanced camera for surveys. we employ a bayesian hierarchical method to infer the star formation history of eridanus ii. we find that the bulk of the stars in eridanus ii are very old ($13.5_{-1}^{+0.5}$ gyr) and quite metal-poor (z = 0.000 01). we do not find any evidence of the presence of an intermediate age or young population in eri ii. we cannot date the embedded star cluster as a separate entity, but we find it likely that the cluster has a similar age and metallicity as the bulk of the stars in eri ii. the existence of an old star cluster in a dark matter dominated old metal-poor dwarf galaxy is of major importance to cast light on the dark matter distribution within dwarf galaxies. the existence of intermediate age stars is required by the recent detection of carbon stars in eri ii. since no recent star formation is detected, blue-straggler fusions of lower mass stars are the most likely origin of the carbon star progenitors. | star cluster survival in dark matter haloes: an old cluster in eridanus ii? |
with this paper, we complete a comprehensive study of substructure in dark matter haloes. in paper i, we derived the radial distribution and mass function (mf) of accreted subhaloes (scaled to the radius and mass of the host halo) and showed that they are essentially universal. this is not the case, however, for those of stripped subhaloes, which depend on halo mass and assembly history. in paper ii, we derived these latter properties in the simplest case of purely accreting haloes. here, we extend the study to ordinary haloes having suffered major mergers. after showing that all the properties of substructure are encoded in the mean truncated-to-original subhalo mass ratio profile, we demonstrate that the dependence of the subhalo mf on halo mass arises from their mass-dependent concentration, while the shape of the subhalo radial distribution depends on the time of the last major merger of the host halo. in this sense, the latter property is a better probe of halo formation time than the former. unfortunately, this is not the case for the radial distribution of satellites as this profile is essentially disconnected from subhalo stripping and the properties of accreted subhaloes are independent of the halo formation time. | an accurate comprehensive approach to substructure: iii. masses and formation times of the host haloes |
we study how gravitational focusing (gf) of dark matter by the sun affects the annual and biannual modulation of the expected signal in non-directional direct dark matter searches, in the presence of dark matter substructure in the local dark halo. we consider the sagittarius stream and a possible dark disk, and show that gf suppresses some, but not all, of the distinguishing features that would characterize substructure of the dark halo were gf neglected. | gravitational focusing and substructure effects on the rate modulation in direct dark matter searches |
we study the monojet and dijet channels at the lhc as a tool for searching for squarks and gluinos. we consider two separate r-parity conserving supersymmetric scenarios. in the first scenario we postulate a large mass hierarchy between squarks (q ~) and winos (w ~), and wino-like neutralino is assumed to be the lightest supersymmetric particle (lsp). the associated squark-wino production, pp →q ~w ~, then leads to a monojet-like signature, where the high pt jet is originated from the squark decay, q ~→ q + w ~. we demonstrate that this associated production, as well as the pp →w ~w ~ + jets production, have a significant impact on the exclusion limit in the squark-neutralino mass plane. the second scenario postulates that the lighter of the squark and gluino is only a few gev heavier than the lsp neutralino. the associated squark-gluino production, pp →q ~g ~, then leads to a distinctive monojet signature, where the high pt jet is produced from the decay of the heavier coloured particle into the lighter one (q ~→ q+g ~ for mq ~>mg ~ and g ~→ q+q ~ for mg ~>mq ~). the lighter coloured particle is effectively regarded as an invisible particle since the decay products are soft due to the approximate mass degeneracy. we recast existing monojet and dijet analyses and find a non-trivial exclusion limit in the squark-gluino mass plane in this scenario. | monojet signatures from gluino and squark decays |
we show that the $zww$ production process may give complementary informations about scale dependent heavy particle masses and possible final state interactions as compared to previously studied top quark production processes. we illustrate the $p_z$ distribution of the rate of longitudinal $z_l$ component showing its sensitivity to these effects which may arise from heavy particle substructure or a dark matter (dm) environment. | z polarization in $e^+e^-\\to zww $ for testing special interactions of massive particles |
non-resonant production of higgs-pair via heavy intermediate states may be a distinctive signature for extended discrete symmetries when accompaied by large missing transvers energy. we discuss $t$-parity as an example of such symmetry within the littlest higgs model, where a new heavy gauge boson $z'$, the $t$-odd partner of sm $z$-boson, predominately decays into to a higgs boson and a dark matter candidate $\chi$. in essence, $t$-parity stablises simultaneously both the higgs mass and the dark matter. production via $pp\rightarrow z' z'\rightarrow 2h 2\chi$ may therefore yield important clues about symmetries connecting the higgs and dark sectors. this paper makes a case for the search for this channel at the lhc by studying its discovery potential. it is demonstrated that in situations where a large $z'-\chi$ mass gap results in a boosted topology, the jet-substructure technique can be leveraged to reach the required significance for discovery in the $2h\rightarrow 2\gamma2b$ decay mode. | boosted higgs-pair production associated with large $e_t^{miss}$: a signal of $z^\\prime$ |
the multicomponent dark matter model with self-scattering and inter-conversions of species into one another is an alternative dark matter paradigm that is capable of resolving the long-standing problems of lambda cold dark matter (λcdm) cosmology at small scales. in this paper, we have studied in detail the properties of dark matter haloes with m ∼ 4-5 × 10^{11} m_{⊙} obtained in n-body cosmological simulations with the simplest two-component (2cdm) model. a large set of velocity-dependent cross-section prescriptions for elastic scattering and mass conversions, σ _s(v)∝ v^{a_s} and σ _c(v)∝ v^{a_c}, has been explored and the results were compared with observational data. the results demonstrate that self-interactions with the cross-section per particle mass evaluated at v = 100 km s-1 being in the range of 0.01 ≲ σ0/m ≲ 1 cm2 g-1 robustly suppress central cusps, thus resolving the core-cusp problem. the core radii are controlled by the values of σ0/m and the dm cross-section's velocity-dependent power-law indices (as, ac), but are largely insensitive to the species' mass degeneracy. these values are in full agreement with those resolving the substructure and too-big-to-fail problems. we have also studied the evolution of haloes in the 2cdm model with cosmic time. | dark matter haloes in the multicomponent model - ii. density profiles of galactic haloes |
we use a geometric method to derive (two-dimensional) separation functions among pairs of objects within populations of specified position function ${dn}/d{\boldsymbol{r}}$ . we present analytic solutions for separation functions corresponding to a uniform surface density within a circular field, a plummer sphere (viewed in projection), and the mixture thereof-including contributions from binary objects within both subpopulations. these results enable inferences about binary object populations via direct modeling of object position and pair separation data, without resorting to standard estimators of the two-point correlation function. analyzing mock data sets designed to mimic known dwarf spheroidal galaxies, we demonstrate the ability to recover input properties including the number of wide binary star systems and, in cases where the number of resolved binary pairs is assumed to be ≳a few hundred, characteristic features (e.g., steepening and/or truncation) of their separation function. combined with forthcoming observational capabilities, this methodology opens a window onto the formation and/or survival of wide binary populations in dwarf galaxies, and offers a novel probe of inferred dark matter substructure on the smallest galactic scales. | two-point separation functions for modeling wide binary systems in nearby dwarf galaxies |
accurately predicting the abundance and structural evolution of dark matter subhaloes is crucial for understanding galaxy formation, large-scale structure, and constraining the nature of dark matter. due to the nonlinear nature of subhalo evolution, cosmological n-body simulations remain its primary method of investigation. subhaloes in such simulations have recently been shown to still be heavily impacted by artificial disruption, diminishing the information content (at small scales) of the simulations and all derivative semi-analytical models calibrated against them.a model of the evolved subhalo density structure: our recent release of the dash library of high-resolution, idealized n-body simulations of the tidal evolution of subhaloes (unhindered by numerical over-merging due to discreteness noise or force softening) enables a more accurate calibration of semi-analytical treatments of dark matter substructure evolution. we use dash to calibrate a highly accurate, simply parametrized empirical model of the evolved subhalo density profile (eshdp), which captures the impact of tidal heating and stripping. by testing previous findings that the structural evolution of a tidally truncated subhalo depends solely on the fraction of mass stripped, independent of the details of the stripping, we identify an additional dependence on the initial subhalo concentration. we provide significantly improved fitting functions for the subhalo density profiles and structural parameters (v_{max} and r_{max}) that are unimpeded by numerical systematics and applicable to a wide range of parameter space. a model of the build-up and evolution of dark matter substructure: by combining our eshdp model with a physically motivated prescription for the subhalo mass stripping rate, we introduce a state-of-the-art model of the mass evolution of individual subhaloes. this model has been calibrated to reproduce the mass trajectories of subhaloes in the dash simulations. we incorporate this treatment of the subhalo internal structure and mass evolution into the recently released satgen semi-analytical model. satgen combines (i) analytical halo merger trees, (ii) a recipe for initial subhalo orbits at infall, (iii) an orbit integrator (which captures dynamical friction), and (iv) our dash-calibrated tidal evolution model in order to ultimately capture the build-up and evolution of populations of dark matter substructure. we also develop a model of artificial disruption that reproduces the statistical properties of disruption in the bolshoi simulation. using the dash-calibrated satgen framework, we generate independent predictions for key quantities in small-scale cosmology, including the evolved subhalo mass function, subhalo radial abundance, and the substructure mass fraction and study how these quantities are impacted by artificial disruption and mass resolution limits. we find that artificial disruption affects these quantities at the 10--20% level, ameliorating previous concerns that it may suppress the shmf by as much as a factor of two. we demonstrate that semi-analytical substructure modeling must include orbit integration in order to properly account for splashback haloes, which make up roughly half of the subhalo population. we show that the resolution limit of n-body simulations, rather than artificial disruption, is the primary cause of the radial bias in subhalo number density found in dark matter-only simulations. hence, we conclude that the mass resolution remains the primary limitation of using such simulations to study subhaloes.the impact of a galactic disc on the subhalo population: numerical simulations have shown that the formation of a central disc can drastically reduce the abundance of substructure compared to a dark matter-only simulation, which has been attributed to enhanced destruction of substructure due to disc shocking. we examine the impact of discs on substructure using satgen. using a sample of 10,000 merger trees of milky-way like haloes, we study the demographics of subhaloes that are evolved under a range of composite halo--disc potentials with unprecedented statistical power. we find that the overall subhalo abundance is relatively insensitive to properties of the disc aside from its total mass. for a disc that contains 5% of m_{vir}, the mean subhalo abundance within r_{vir} is suppressed by roughly less than 10% relative to the no-disc case, a difference that is dwarfed by halo-to-halo variance. for the same disc mass, the abundance of subhaloes within 50 kpc is reduced by ~30%. we argue that the disc mainly drives excess mass loss for subhaloes with small pericentric radii and that the impact of disc shocking is negligible.the three subhalo-focused studies described above constitute the primary thrust of this dissertation. however, the analytical monte carlo merger tree method, which is a key component of satgen, has additional utility beyond the realm of subhalo studies. indeed, an overarching theme of this program is that variation in assembly histories propagates to substantial halo-to-halo variance in many quantities of astrophysical and cosmological interest. we expand on this motif in the following two studies.the impact of assembly history variance on cluster scaling relations: x-ray and microwave cluster scaling relations are immensely valuable for cosmological analysis. however, their power is limited by astrophysical systematics that bias mass estimates and introduce additional scatter. turbulence injected into the intracluster medium via mass assembly contributes substantially to cluster non-thermal pressure support, a significant source of such uncertainties. we use an analytical model to compute the assembly-driven non-thermal pressure profiles of haloes based on monte carlo-generated accretion histories (leveraging the same method that is used to generate merger trees in satgen). we introduce a fitting function for the average non-thermal pressure fraction profile, which exhibits minimal dependence on redshift at fixed peak height. using the model, we predict deviations from self-similarity and the intrinsic scatter in the sunyaev--zel'dovich effect observable-mass scaling relation (y_{sz}-m) due solely to inter-cluster variation in mass accretion histories. we study the dependence of y_{sz}-m on aperture radius, cosmology, redshift, and mass limit. the model predicts 5--9% scatter in y_{sz}-m at z=0, increasing as the aperture used to compute y_{sz} increases from r_{500c} to 5r_{500c}. the predicted scatter lies slightly below that of studies based on non-radiative hydro-simulations, illustrating that assembly history variance is likely responsible for a substantial fraction of scatter in y_{sz}-m. this should be regarded as a lower bound, which will likely increase with the use of an updated gas density model that incorporates a more realistic response to halo assembly. as redshift increases, y_{sz}-m deviates more from self-similarity and scatter increases. we show that the y_{sz}-m residuals correlate strongly with the recent halo mass accretion rate, potentially providing an opportunity to infer the latter.estimating cluster masses via machine learning: we present a machine-learning approach for estimating galaxy cluster masses, trained using both chandra and erosita mock x-ray observations of 2041 clusters from the magneticum simulations. we train a random forest (rf) regressor, an ensemble learning method based on decision tree regression, to predict cluster masses using an input feature set. the feature set uses core-excised x-ray luminosity and a variety of morphological parameters, including surface brightness concentration, smoothness, asymmetry, power ratios, and ellipticity. the regressor is cross-validated and calibrated on a training sample of 1615 clusters (80% of sample), and then results are reported as applied to a test sample of 426 clusters (20% of sample). this procedure is performed for two different mock observation series in an effort to bracket the potential enhancement in mass predictions that can be made possible by including dynamical state information. the first series is computed from idealized chandra-like mock cluster observations, with high spatial resolution, long exposure time (1 ms), and the absence of background. the second series is computed from realistic-condition erosita mocks with lower spatial resolution, short exposures (2 ks), instrument effects, and background photons modeled. we report a 20% reduction in the mass estimation scatter when either series is used in our rf model compared to a standard regression model that only employs core-excised luminosity. the morphological parameters that hold the highest feature importance are smoothness, asymmetry, and surface brightness concentration. hence these parameters, which encode the dynamical state of the cluster, can be used to make more accurate predictions of cluster masses in upcoming surveys, offering a crucial step forward for cosmological analyses. | three-wave mixing in superconducting circuits: stabilizing cats with snails |
we present a comprehensive study on how perturbations due to a distribution of lambda cold dark matter (λcdm) dark matter subhalos can lead to star clusters deviating from their orbits. through a large suite of massless test particle simulations, we find that (i) subhalos with masses less than 108 m⊙ negligibly affect test particle orbits, (ii) perturbations lead to orbital deviations only in environments with substructure fractions $f_{\mathrm{ sub}} \ge 1{{\ \rm per\ cent}}$ , (iii) perturbations from denser subhalos produce larger orbital deviations, and (iv) subhalo perturbations that are strong relative to the background tidal field lead to larger orbital deviations. to predict how the variation in test particle orbital energy σe(t) increases with time, we test the applicability of theory derived from single-mass subhalo populations to populations where subhalos have a mass spectrum. we find σe(t) can be predicted for test particle evolution within a mass spectrum of subhalos by assuming subhalos all have masses equal to the mean subhalo mass and by using the local mean subhalo separation to estimate the change in test particle velocities due to subhalo interactions. furthermore, the orbital distance variation at an orbital distance r can be calculated via $\sigma _r=2.98 \times 10^{-5} \pm 8 \times 10^{-8} (\rm kpc^{-1} km^{-2} s^{2}) \times r \times \sigma _e$ with a dispersion about the line of best-fitting equalling 0.08 kpc. finally, we conclude that clusters that orbit within 100 kpc of milky way-like galaxies experience a change no greater than $2{{\ \rm per\ cent}}$ in their dissolution times. | the effects of λcdm dark matter substructure on the orbital evolution of star clusters |
the positions of images produced by the gravitational lensing of background sources provide unique insight into galaxy-lens mass distribution. however, even quad images of extended sources are not able to fully characterize the central regions of the host galaxy. most previous work has focused either on the radial density profile of the lenses or localized substructure clumps. here, we concentrate on the azimuthal mass asymmetries near the image circle. the motivation for considering such mass inhomogeneities is that the transition between the central stellar- and the outer dark matter-dominated regions, though well represented by a power-law density profile, is unlikely to be featureless, and encodes information about the dynamical state and assembly history of galaxies. it also happens to roughly coincide with the einstein radius. we ask if galaxies that have mass asymmetries beyond ellipticity can be modelled with simpler lenses, i.e. can complex mass distributions masquerade as simple elliptical+shear lenses? our preliminary study indicates that for galaxies with elliptical stellar and dark matter distributions, but with no mass asymmetry, and an extended source filling the diamond caustic, an elliptical+shear lens model can reproduce the images well, thereby hiding the potential complexity of the actual mass distribution. for galaxies with non-zero mass asymmetry, the answer depends on the size and brightness distribution of the source, and its location within the diamond caustic. in roughly half of the cases, we considered the mass asymmetries can easily evade detection. | testing the uniqueness of gravitational lens mass models |
as no evidence for classic wimp-based signatures of dark matter have been found at the lhc, several phenomenological studies have raised the possibility of accessing a strongly-interacting dark sector through new collider-event topologies. if dark mesons exist, their evolution and hadronization procedure are currently little constrained. they could decay promptly and result in qcd-like jet structures, even though the original decaying particles are dark sector ones; they could behave as semi-visible jets; or they could behave as completely detector-stable hadrons, in which case the final state is just the missing transverse momentum. in this contribution we will introduce a study performed to explore use of jet substructure methods to distinguish dark-sector from qcd jets in the first two scenarios, using observables in a irc-safe linear basis, and discuss ways forward for this approach to dark-matter at the lhc. | towards better discrimination and improved modelling of dark-sector showers |
we report near simultaneous imaging using lmircam on the lbti of the quadruply imaged lensed quasar hs 0810+2554 at wavelengths of 2.16, 3.7, and 4.78 μm with a full width at half maximum spatial resolution of 0.″13, 0.″12, and 0.″15 respectively, comparable to hubble space telescope optical imaging. in the z = 1.5 rest frame of the quasar, the observed wavelengths correspond to 0.86, 1.48, and 1.91 μm respectively. the two brightest images in the quad, a and b, are clearly resolved from each other with a separation of 0.″187. the flux ratio of these two images (a/b) trends from 1.79 to 1.23 at wavelengths from 2.16 to 4.78 μm. the trend in flux ratio is consistent with the 2.16 μm flux originating from a small sized accretion disk in the quasar that experiences only microlensing. the excess flux above the contribution from the accretion disk at the two longer wavelengths originates from a larger sized region that experiences no microlensing. a simple model employing multiplicative factors for image b due to stellar microlensing (m) and substructure millilensing (m) is presented. the result is tightly constrained to the product m × m = 1.79. given the observational errors, the 60% probability contour for this product stretches from m = 2.6, m = 0.69 to m = 1.79, m = 1.0, where the later is consistent with microlensing only. | image flux ratios of gravitationally lensed hs 0810+2554 with high-resolution infrared imaging |
in this paper, we investigate the strong lensing statistics in galaxyclusters. we extract dark matter haloes from the millennium-xxl simulation, compute their einstein radius distribution, and find a very good agreement with monte carlo predictions produced with the moka code. the distribution of the einstein radii is well described by a lognormal distribution, with a considerable fraction of the largest systems boosted by different projection effects. we discuss the importance of substructures and triaxiality in shaping the size of the critical lines for cluster size haloes. we then model and interpret the different deviations, accounting for the presence of a brightest central galaxy (bcg) and two different stellar mass density profiles. we present scaling relations between weak lensing quantities and the size of the einstein radii. finally, we discuss how sensible is the distribution of the einstein radii on the cosmological parameters ωm - σ8 finding that cosmologies with higher ωm and σ8 possess a large sample of strong lensing clusters. the einstein radius distribution may help distinguish planck13 and wmap7 cosmology at 3σ. | characterizing strong lensing galaxy clusters using the millennium-xxl and moka simulations |
the formation of galaxies can be understood in terms of the assembly patterns of each type of galactic component. to perform this kind of analysis, it is necessary to define some criteria to separate those components. decomposition methods based on dynamical properties are more physically motivated than photometry-based ones. we use the unsupervised gaussian mixture model of galactic structure finder to extract the components of a sub-sample of galaxies with milky way-like masses from the eagle simulations. a clustering in the space of first- and second-order dynamical moments of all identified substructures reveals five types of galaxy components: thin and thick discs, stellar haloes, bulges and spheroids. we analyse the dynamical, morphological and stellar population (sp) properties of these five component types, exploring to what extent these properties correlate with each other, and how much they depend on the total galaxy stellar and dark matter halo masses. all galaxies contain a bulge, a stellar halo and a disc. in total, 60 per cent of objects host two discs (thin and thick), and 68 per cent host also a spheroid. the dynamical disc-to-total ratio does not depend on stellar mass, but the median rotational velocities of the two discs do. thin discs are well separated in stellar ages, [fe/h] and α-enhancement from the three dispersion-dominated components, while thick discs are in between. except for thin discs, all components show correlations among their sp properties: older ages mean lower metallicities and larger α-enhancement. finally, we quantify the weak dependence of sp properties on each component's dynamics. | milky way-like galaxies: stellar population properties of dynamically defined discs, bulges and stellar haloes |
we investigate scalar-tensor theories where matter couples to the scalar field via a kinetically dependent conformal coupling. these models can be seen as the low-energy description of invariant field theories under a global abelian symmetry. the scalar field is then identified with the goldstone mode of the broken symmetry. it turns out that the properties of these models are very similar to the ones of ultralocal theories where the scalar-field value is directly determined by the local matter density. this leads to a complete screening of the fifth force in the solar system and between compact objects, through the ultralocal screening mechanism. on the other hand, the fifth force can have large effects in extended structures with large-scale density gradients, such as galactic halos. interestingly, it can either amplify or damp newtonian gravity, depending on the model parameters. we also study the background cosmology and the linear cosmological perturbations. the background cosmology is hardly different from its λ -cdm counterpart while cosmological perturbations crucially depend on whether the coupling function is convex or concave. for concave functions, growth is hindered by the repulsiveness of the fifth force while it is enhanced in the convex case. in both cases, the departures from the λ -cdm cosmology increase on smaller scales and peak for galactic structures. for concave functions, the formation of structure is largely altered below some characteristic mass, as smaller structures are delayed and would form later through fragmentation, as in some warm dark matter scenarios. for convex models, small structures form more easily than in the λ -cdm scenario. this could lead to an over-abundance of small clumps. we use a thermodynamic analysis and show that although convex models have a phase transition between homogeneous and inhomogeneous phases, on cosmological scales the system does not enter the inhomogeneous phase. on the other hand, for galactic halos, the coexistence of small and large substructures in their outer regions could lead to observational signatures of these models. | goldstone models of modified gravity |
multiple image gravitational lens systems, and especially quads, are invaluable in determining the amount and distribution of mass in galaxies. this is usually done by mass modelling using parametric or free-form methods. an alternative way of extracting information about lens mass distribution is to use lensing degeneracies and invariants. where applicable, they allow one to make conclusions about whole classes of lenses without model fitting. here, we use approximate, but observationally useful invariants formed by the three relative polar angles of quad images around the lens centre to show that many smooth elliptical+shear lenses can reproduce the same set of quad image angles within observational error. this result allows us to show in a model-free way what the general class of smooth elliptical+shear lenses looks like in the three-dimensional (3d) space of image relative angles, and that this distribution does not match that of the observed quads. we conclude that, even though smooth elliptical+shear lenses can reproduce individual quads, they cannot reproduce the quad population. what is likely needed is substructure, with clump masses larger than those responsible for flux ratio anomalies in quads, or luminous or dark nearby perturber galaxies. | model-free analysis of quadruply imaged gravitationally lensed systems and substructured galaxies |
we test the darkexp model for relaxed, self-gravitating, collisionless systems against equilibrium dark matter halos from the millennium-ii simulation. while limited tests of darkexp against simulations and observations have been carried out elsewhere, this is the first time the testing is done with a large sample of simulated halos spanning a factor of ~ 50 in mass, and using independent fits to density and energy distributions. we show that darkexp, a one shape parameter family, provides very good fits to the shapes of density profiles, ρ(r), and differential energy distributions, n(e), of individual simulated halos. the best fit shape parameter phi0 obtained from the two types of fits are correlated, though with scatter. our most important conclusions come from ρ(r) and n(e) that have been averaged over many halos. these show that the bulk of the deviations between darkexp and individual millennium-ii halos come from halo-to-halo fluctuations, likely driven by substructure, and other density perturbations. the average ρ(r) and n(e) are quite smooth and follow darkexp very closely. the only deviation that remains after averaging is small, and located at most bound energies for n(e) and smallest radii for ρ(r). since the deviation is confined to 3-4 smoothing lengths, and is larger for low mass halos, it is likely due to numerical resolution effects. | testing darkexp against energy and density distributions of millennium-ii halos |
we present a novel method for determining the total matter surface density of the galactic disc by analysing the kinematics of a dynamically cold stellar stream that passes through or close to the galactic plane. the method relies on the fact that the vertical component of energy for such stream stars is approximately constant, such that their vertical positions and vertical velocities are interrelated via the matter density of the galactic disc. by testing our method on mock data stellar streams, with realistic phase-space dispersions and gaia uncertainties, we demonstrate that it is applicable to small streams out to a distance of a few kilo-parsec, and that the surface density of the disc can be determined to a precision of $6{{\ \rm per\ cent}}$ . this method is complementary to other mass measurements. in particular, it does not rely on any equilibrium assumption for stars in the galactic disc, and also makes it possible to measure the surface density to good precision at large distances from the sun. such measurements would inform us of the matter composition of the galactic disc and its spatial variation, place stronger constraints on dark disc substructure, and even diagnose possible non-equilibrium effects that bias other types of dynamical mass measurements. | measuring the matter density of the galactic disc using stellar streams |
dwarf spheroidal galaxies (dsph) orbiting the milky way are complex objects often with complicated star formation histories and internal dynamics. in this work, we search for stellar substructures in four of the classical dsph satellites of the milky way: sextans, carina, leo i, and leo ii. we apply two methods to search for stellar substructure: the minimum spanning tree method, which helps us find and quantify spatially connected structures, and the “brute-force” method, which is able to find elongated stellar substructures. we detected the previously known substructure in sextans and also found a new stellar substructure within sextans. furthermore, we identified a new stellar substructure close to the core radius of the carina dwarf galaxy. we report a detection of one substructure in leo i and two in leo ii, but we note that we are dealing with a low number of stars in the samples used. such old stellar substructures in dsphs could help us shed light on the nature of the dark matter halos, within which such structures form, evolve, and survive. | cold, old, and metal-poor: new stellar substructures in the milky way’s dwarf spheroidals |
the dynamical and virial mass of the milky way galaxy is estimated using latest high precision stellar halo and dwarf galaxy satellite kinematics. the new data suggest the galaxy is a highly compact, classically thermalized object. kinematics exhibit significant velocity-spatial substructure, distinctive dynamic partitions, and strong keplerian signatures that run counter to popular notions of featureless and massively extended dark matter halos. the effective local escape velocity profile of the galaxy is quantified in terms of distribution and kinematics to reveal the physics responsible for the mass discrepancy-acceleration (mdar) and radial acceleration (rar) relations. | a physical interpretation of milky way galaxy dynamics from precision astrometrics |
substructures of dark matter halo, called subhaloes, provide important clues to understand the nature of dark matter. we construct a useful model to describe the properties of subhalo mass functions based on the well-known analytical prescriptions, the extended press-schechter theory. the unevolved subhalo mass functions at arbitrary mass scales become describable without introducing free parameters. the different host halo evolution histories are directly recast to their subhalo mass functions. as applications, we quantify the effects from (i) the poisson fluctuation, (ii) the host-mass scatter, and the (iii) different tidal evolution models on observables in the current universe with this scheme. the poisson fluctuation dominates in the number count of the mass ratio to the host of $\sim {\cal o}(10^{-2})$, where the intrinsic scatter is smaller by a factor of a few. the host-mass scatter around its mean does not affect the subhalo mass function. different models of the tidal evolution predict a factor of ~2 difference in numbers of subhaloes with $\lesssim {\cal o}(10^{-5})$, while the dependence of the poisson fluctuation on the tidal evolution models is subtle. the scheme provides a new tool for investigating the smallest scale structures of our universe which are to be observed in near future experiments. | semi-analytical frameworks for subhaloes from the smallest to the largest scale |
tidal debris streams from galaxy satellites can provide insight into the dark matter distribution in halos. this is because we have more information about stars in a debris structure than about a purely random population of stars: we know that in the past they were all bound to the same dwarf galaxy; and we know that they form a dynamically cold population moving on similar orbits. they also probe a different region of the matter distribution in a galaxy than many other methods of mass determination, as their orbits take them far beyond the typical extent of those for the bulk of stars. although conclusive results from this information have yet to be obtained, significant progress has been made in developing the methodologies for determining both the global mass distribution of the milky way's dark matter halo and the amount of dark matter substructure within it. methods for measuring the halo shape are divided into "predictive methods," which predict the tidal debris properties from the progenitor satellite's mass and orbit, given an assumed parent galaxy mass distribution; and "fundamental methods," which exploit properties fundamental to the nature of tidal debris as global potential constraints. methods for quantifying the prevalence of dark matter subhalos within halos through the analysis of the gaps left in tidal streams after these substructures pass through them are reviewed. | tidal debris as a dark matter probe |
we present reconstructions of galaxy-cluster-scale mass distributions from simulated gravitational lensing data sets including strong lensing, weak lensing shear, and measurements of quadratic image distortions - flexion. the lensing data is constructed to make a direct comparison between mass reconstructions with and without flexion. we show that in the absence of flexion measurements, significant galaxy-group scale substructure can remain undetected in the reconstructed mass profiles, and that the resulting profiles underestimate the aperture mass in the substructure regions by ∼25-40 per cent. when flexion is included, subhaloes down to a mass of ∼3 × 1012 m⊙ can be detected at an angular resolution smaller than 10 arcsec. aperture masses from profiles reconstructed with flexion match the input distribution values to within an error of ∼13 per cent, including both statistical error and scatter. this demonstrates the important constraint that flexion measurements place on substructure in galaxy clusters and its utility for producing high-fidelity mass reconstructions. | reconstruction of small-scale galaxy cluster substructure with lensing flexion |
it has recently been proposed that if the galactic dark matter halo were triaxial it would induce lumpiness in the velocity distribution of halo stars in the solar neighbourhood through orbital resonances. these substructures could therefore provide a way of measuring its shape. we explore the robustness of this proposal by integrating numerically orbits starting from a realistic set of initial conditions in dark halo potentials of different shape. we have analysed the resulting velocity distributions in solar neighbourhood-like volumes, and have performed statistical tests for the presence of kinematic substructures. furthermore, we have characterized the particles' orbits using a fourier analysis. the local velocity distributions obtained are relatively smooth, statistically consistent with being devoid of substructures even for a dark halo potential with significant but plausible triaxiality. although resonances are indeed present and associated with specific regions of velocity space, the fraction of stars associated to these is relatively minor. the most significant imprint of the triaxiality of the dark halo is in fact, a variation in the shape of the velocity ellipsoid with spatial location. | on the feasibility of constraining the triaxiality of the galactic dark halo with orbital resonances using nearby stars |
the dynamics of binary stars provides a unique avenue to gather insight into the study of the structure and dynamics of star clusters and galaxies. in this paper, we present the results of a set of n-body simulations aimed at exploring the evolution of binary stars during the early evolutionary phases of ultra-faint dwarf galaxies (ufd). in our simulations, we assume that the stellar component of the ufd is initially dynamically cold and evolves towards its final equilibrium after undergoing the violent relaxation phase. we show that the early evolutionary phases of the ufd significantly enhance the disruption of wide binaries and leave their dynamical fingerprints on the semimajor axis distribution of the surviving binaries as compared to models initially in equilibrium. an initially thermal eccentricity distribution is preserved except for the widest binaries for which it evolves towards a superthermal distribution; for a binary population with an initially uniform eccentricity distribution, memory of this initial distribution is rapidly lost for most binaries as wider binaries evolve to approach a thermal/superthermal distribution. the evolution of binaries is driven both by tidal effects due to the potential of the ufd dark matter halo and collisional effects associated to binary-binary/single star encounters. collisional effects are particularly important within the clumpy substructure characterizing the system during its early evolution; in addition to enhancing binary ionization and evolution of the binary orbital parameters, encounters may lead to exchanges of either of the primordial binary components with one of the interacting stars. | evolution of binary stars in the early evolutionary phases of ultra-faint dwarf galaxies |
in the context of the beyond ultradeep frontier fields and legacy observations (buffalo) survey, we present a new analysis of the merging galaxy cluster macs j0416.1-2403 (z = 0.397) and its parallel field using hubble frontier fields (hff) data. we measure the surface mass density from a weak-lensing analysis and characterize the overall matter distribution in both the cluster and parallel fields. the surface mass distribution derived for the parallel field shows clumpy overdensities connected by filament-like structures elongated in the direction of the cluster core. we also characterize the x-ray emission in the parallel field and compare it with the lensing mass distribution. we identify five mass peaks at the >5σ level over the two fields, four of them being in the cluster one. three of them are located close to galaxy overdensities and one is also close to an excess in the x-ray emission. nevertheless, two of them have neither optical nor x-ray counterpart and are located close to the edges of the field of view, thus further studies are needed to confirm them as substructures. finally, we compare our results with the predicted subhalo distribution of one of the hydrangea/c-eagle simulated cluster. significant differences are obtained suggesting the simulated cluster is at a more advanced evolutionary stage than macs j0416.1-2403. our results anticipate the upcoming buffalo observations that will link the two hff fields, extending further the hst coverage. | setting the scene for buffalo: a study of the matter distribution in the hff galaxy cluster macs j0416.1-2403 and its parallel field |
we propose and test a method for applying statistical photometric parallax to main-sequence turnoff stars in the sloan digital sky survey (sdss). using simulated data, we show that if our density model is similar to the actual density distribution of our data, we can reliably determine the density model parameters of three major substructures in the milky way halo using the computational resources available on milkyway@home (a 20-parameter fit). we fit the stellar density in sdss stripe 19 with a smooth stellar spheroid component and three major streams. one of these streams is consistent with the sagittarius tidal stream at 21.1 kpc away, one is consistent with the trailing tail of the sagittarius tidal stream in the north galactic cap at 48 kpc away, and one is possibly part of the virgo overdensity at 6 kpc away. we find the 1σ widths of these three streams to be 1.0 kpc, 17.6 kpc, and 6.1 kpc, respectively. the width of the trailing tail is extremely wide (41 kpc full width at half maximum). this large width could have implications for the shape of the milky way dark matter halo. the width of the virgo overdensity-like structure is consistent with what we might expect for a “cloudlike” structure; analysis of additional stripes of data are needed to outline the full extent of this structure and confirm its association with the virgo overdensity. | fitting the density substructure of the stellar halo with milkyway@home |
associations of dwarf galaxies are loose systems composed exclusively of dwarf galaxies. these systems were identified in the local volume for the first time more than 30 yr ago. we study these systems in the cosmological framework of the λ cold dark matter (λcdm) model. we consider the small multidark planck simulation and populate its dark matter haloes by applying the semi-analytic model of galaxy formation sag. we identify galaxy systems using a friends-of-friends algorithm with a linking length equal to $b=0.4 \, {\rm mpc}\, h^{-1}$ to reproduce the size of dwarf galaxy associations detected in the local volume. our samples of dwarf systems are built up removing those systems that have one or more galaxies with stellar mass larger than a maximum threshold mmax. we analyse three different samples defined by ${\rm log}_{10}(m_{\rm max}[{\rm m}_{\odot }\, h^{-1}]) = 8.5, 9.0$ , and 9.5. on average, our systems have typical sizes of $\sim 0.2\, {\rm mpc}\, h^{-1}$ , velocity dispersion of $\sim 30 {\rm km\, s^{-1}}$ , and estimated total mass of $\sim 10^{11} {\rm m}_{\odot }\, h^{-1}$ . such large typical sizes suggest that individual members of a given dwarf association reside in different dark matter haloes and are generally not substructures of any other halo. indeed, in more than 90 per cent of our dwarf systems their individual members inhabit different dark matter haloes, while only in the remaining 10 per cent members do reside in the same halo. our results indicate that the λcdm model can naturally reproduce the existence and properties of dwarf galaxies' associations without much difficulty. | associations of dwarf galaxies in a λcdm universe |
the lambda cold dark matter (lcdm) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. these predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. a number of potential challenges to lcdm have been identified when confronting the expected properties of dwarfs with observation. i review our understanding of a few of these issues, including the ``missing satellites'' and the ``too-big-to-fail'' problems, and argue that neither poses an insurmountable challenge to lcdm. solving these problems requires that most dwarf galaxies inhabit halos of similar mass, and that there is a relatively sharp minimum halo mass threshold to form luminous galaxies. these predictions are eminently falsifiable. in particular, lcdm predicts a large number of ``dark'' low-mass halos, some of which should have retained enough primordial gas to be detectable in deep 21 cm or hα surveys. detecting this predicted population of ``mini-halos'' would be a major discovery and a resounding success for lcdm on small scales. | dwarf galaxies as cosmological probes |
the milky way's (mw) satellite population is a powerful probe of warm dark matter (wdm) models as the abundance of small substructures is very sensitive to the properties of the wdm particle. however, only a partial census of the mw's complement of satellite galaxies exists because surveys of the mw's close environs are incomplete both in depth and in sky coverage. we present a new bayesian analysis that combines the sample of satellites recently discovered by the dark energy survey (des) with those found in the sloan digital sky survey (sdss) to estimate the total satellite galaxy luminosity function down to mv = 0. we find that there should be at least 124 - 27 + 40 (68% cl, statistical error) satellites as bright or brighter than mv = 0 within 300 kpc of the sun, with only a weak dependence on mw halo mass. when it comes online the large synoptic survey telescope should detect approximately half of this population. we also show that wdm models infer the same number of satellites as in λcdm, which will allow us to rule out those models that produce insufficient substructure to be viable. | the milky way's total satellite population and constraining the mass of the warm dark matter particle |
we present a new strong-lensing (sl) mass reconstruction of the six hubble frontier fields (hff) clusters with the maximum-entropy reconstruction (mars) algorithm. mars is a new free-form inversion method, which suppresses spurious small-scale fluctuations while achieving excellent convergence in positions of multiple images. for each hff cluster, we obtain a model-independent mass distribution from the compilation of the self-consistent sl data in the literature. with 100-200 multiple images per cluster, we reconstruct solutions with small scatters of multiple images in both source (~0.″02) and image planes (0.″05-0.″1), which are lower than the previous results by a factor of 5-10. an outstanding case is the macs j0416.1-2403 mass reconstruction, which is based on the largest high-quality sl data set where all 236 multiple images/knots have spectroscopic redshifts. although our solution is smooth on a large scale, it reveals group/galaxy-scale peaks where the substructures are required by the data. we find that in general, these mass peaks are in excellent spatial agreement with the member galaxies, although mars never uses the galaxy distributions as priors. our study corroborates the flexibility and accuracy of the mars algorithm and demonstrates that mars is a powerful tool in the jwst era, when a 2-3 times larger number of multiple image candidates become available for sl mass reconstruction, and self-consistency within the data set becomes a critical issue. | model-independent mass reconstruction of the hubble frontier field clusters with mars based on self-consistent strong-lensing data |
we use mid-infrared 3.6 and 4.5 μm imaging of ngc 3906 from the spitzer survey of stellar structure in galaxies (s4g) to understand the nature of an unusual offset between its stellar bar and the photometric center of an otherwise regular, circular outer stellar disk. we measure an offset of ∼910 pc between the center of the stellar bar and photometric center of the stellar disk; the bar center coincides with the kinematic center of the disk determined from previous hi observations. although the undisturbed shape of the disk suggests that ngc 3906 has not undergone a significant merger event in its recent history, the most plausible explanation for the observed offset is an interaction. given the relatively isolated nature of ngc 3906 this interaction could be with dark matter substructure in the galaxy's halo or from a recent interaction with a fast moving neighbor that remains to be identified. simulations aimed at reproducing the observed offset between the stellar bar/kinematic center of the system and the photometric center of the disk are necessary to confirm this hypothesis and constrain the interaction history of the galaxy. | the odd offset between the galactic disk and its bar in ngc~3906 |
the abundance of galaxy clusters in the low-redshift universe provides an important cosmological test, constraining a product of the initial amplitude of fluctuations and the amount by which they have grown since early times. the degeneracy of the test with respect to these two factors remains a limitation of abundance studies. clusters will have different mean assembly times, however, depending on the relative importance of initial fluctuation amplitude and subsequent growth. thus, structural probes of cluster age such as concentration, shape, or substructure may provide a new cosmological test that breaks the main degeneracy in number counts. we review analytical predictions for how mean assembly time should depend on cosmological parameters, and test these predictions using cosmological simulations. given the overall sensitivity expected, we estimate the cosmological parameter constraints that could be derived from the cluster catalogues of forthcoming surveys such as euclid, the nancy grace roman space telescope, erosita, or cmb-s4. we show that by considering the structural properties of their cluster samples, such surveys could easily achieve errors of δσ8 = 0.01 or better. | cluster assembly times as a cosmological test |
context. the study of cluster substructures is important for the determination of the cluster dynamical status, assembly history, and the evolution of cluster galaxies, and it allows us to set constraints on the nature of dark matter and cosmological parameters.aims: we present and test ds+, a new method for the identification and characterization of group-sized substructures in clusters.methods: our new method is based on the projected positions and line-of-sight (l.o.s. hereafter) velocities of cluster galaxies, and it is an improvement and extension of the traditional method of dressler & shectman (1988, aj, 95, 985). we tested it on cluster-size cosmological halos extracted from the illustristng simulations, with virial masses 14 ≲ log(m200/m⊙) ≲ 14.6 that contain ~190 galaxies on average. we also present an application of our method on a real data set, the bullet cluster.results: ds+ is able to identify ~80% of real group galaxies as members of substructures, and at least 60% of the galaxies assigned to substructures belong to real groups. the physical properties of the real groups are significantly correlated with those of the corresponding detected substructures, but with significant scatter, and they are overestimated on average. application of the ds+ method to the bullet cluster confirms the presence and main properties of the high-speed collision and identifies other substructures along the main cluster axis.conclusions: ds+ proves to be a reliable method for the identification of substructures in clusters. the method is made freely available to the community as a python code. | ds+: a method for the identification of cluster substructures |
recent observations have revealed a trove of unexpected morphological features in many of the milky way's stellar streams. explanations for such features include time-dependent deformations of the galactic gravitational potential, local disruptions induced by dark matter substructure, and special configurations of the streams' progenitors. in this paper, we study how these morphologies can also arise in certain static, nonspherical gravitational potentials that host a subset of resonantly trapped orbit families. the transitions, or separatrices, between these orbit families mark abrupt discontinuities in the orbital structure of the potential. we develop a novel numerical approach for measuring the libration frequencies of resonant and near-resonant orbits and apply it to study the evolution of stellar streams on these orbits. we reveal two distinct morphological features that arise in streams on near-resonant orbits: fans, which come about due to a large spread in the libration frequencies near a separatrix, and bifurcations, which arise when a separatrix splits the orbital distribution of the stellar stream between two (or more) distinct orbit families. we demonstrate that these effects can arise in some milky way streams for certain choices of the dark matter halo potential and discuss how this might be used to probe and constrain the global shape of the milky way's gravitational potential. | stream fanning and bifurcations: observable signatures of resonances in stellar stream morphology |
we present new mid-ir observations of the quadruply lensed quasar q2237+0305 taken with canaricam on the gran telescopio canarias. mid-ir emission by hot dust, unlike the optical and near-ir emission from the accretion disk, is unaffected by the interstellar medium (extinction/scattering) or stellar microlensing. we compare these “true” ratios to the (stellar) microlensed flux ratios observed in the optical/near-ir to constrain the structure of the quasar accretion disk. we find a half-light radius of {r}1/2={3.4}-2.1+5.3\sqrt{< m> /0.3{m}⊙ } lt-day at {λ }{rest}=1736 \mathringa and an exponent for the temperature profile r\propto {λ }p of p=0.79+/- 0.55, where p=4/3 for a standard thin-disk model. if we assume that the differences in the mid-ir flux ratios measured over the years are due to microlensing variability, we find a lower limit for the size of the mid-ir-emitting region of {r}1/2≳ 200 \sqrt{< m> /0.3{m}⊙ } lt-day. we also test for the presence of substructure/satellites by comparing the observed mid-ir flux ratios with those predicted from smooth lens models. we can explain the differences if the surface density fraction in satellites near the lensed images is α ={0.033}-0.019+0.046 for a singular isothermal ellipsoid plus external shear mass model or α ={0.013}-0.008+0.019 for a mass model combining ellipsoidal nfw and de vaucouleurs profiles in an external shear. | observations of the lensed quasar q2237+0305 with canaricam at gtc |
we propose a novel method to select satellite galaxies in outer regions of galaxy groups or clusters using weak gravitational lensing. the method is based on the theoretical expectation that the tangential shear pattern around satellite galaxies would appear with negative values at an offset distance from the center of the main halo. we can thus locate the satellite galaxies statistically with an offset distance of several lensing smoothing scales by using the standard reconstruction of surface mass density maps from weak lensing observation. we test the idea using high-resolution cosmological simulations. we show that subhalos separated from the center of the host halo are successfully located even without assuming the position of the center. for a number of such subhalos, the characteristic mass and offset length can be also estimated on a statistical basis. we perform a fisher analysis to show how well upcoming weak lensing surveys can constrain the mass density profile of satellite galaxies. in the case of the large synoptic survey telescope with a sky coverage of 20,000 deg2, the mass of the member galaxies in the outer region of galaxy clusters can be constrained with an accuracy of ~0.1 dex for galaxy clusters with mass 1014 h -1 m ⊙ at z = 0.15. finally we explore the detectability of tidal stripping features for subhalos having a wide range of masses of 1011-1013 h -1 m ⊙. | weak gravitational lensing as a probe of physical properties of substructures in dark matter halos |
in this work, we explore the idea that substructures like stellar clusters could be formed from the tidal stream produced in galactic minor mergers. we use n-body and sph simulations of satellite galaxies interacting with a larger galaxy. we study the distribution of mass in streams to identify overdensity regions in which a substructure could be formed. we find that without gas, no substructure forms as none of the overdensities shows a definite morphology nor dynamical stability. including gas we find that several clumps appear and prove to be real long standing physical structures (t≥1 gyr). we analyze the orbits, ages and masses of these structures, finding their correspondence with the halo subsystems. we conclude that it is possible to form cluster-like structures from the material in tidal streams and find evidence in favour of the presence of dark matter in these systems. | substructure formation in tidal streams of galactic minor mergers |
we report the 4σ detection of a faint object with a flux of ∼ 0.3 {mjy}, in the vicinity of the quadruply lensed qso mg 0414+0534 using the atacama large millimeter/submillimeter array (alma) band 7. the object is most probably a dusty dark dwarf galaxy, which has not been detected in either the optical, near-infrared, or radio (centimeter) bands. an anomaly in the flux ratio of the lensed images observed in band 7 and the mid-infrared band and the reddening of the qso light color can be simultaneously explained if we consider the object as a lensing substructure with an ellipticity of ∼0.7 at a redshift of 0.5≲ z≲ 1. using the best-fit lens models with three lenses, we find that the dark matter plus baryon mass associated with the object is ∼ {10}9 {m}⊙ , the dust mass is ∼ {10}7 {m}⊙ , and the linear size is ≳ 5 kpc. thus, our findings suggest that the object is a dusty dark dwarf galaxy. a substantial portion of faint submillimeter galaxies (smgs) in the universe may be attributed to such dark objects. | evidence for a dusty dark dwarf galaxy in the quadruple lens mg 0414+0534 |
nyx is a nearby, prograde, and high-eccentricity stellar stream physically contained in the thick disk, but its origin is unknown. nyx could be the remnant of a disrupted dwarf galaxy, in which case the associated dark matter substructure could affect terrestrial dark matter direct-detection experiments. alternatively, nyx could be a signature of the milky way's disk formation and evolution. to determine the origin of nyx, we obtained high-resolution spectroscopy of 34 nyx stars using keck/hires and magellan/mike. a differential chemical abundance analysis shows that most nyx stars reside in a metal-rich ([fe/h] > -1) high-α component that is chemically indistinguishable from the thick disk. this rules out the originally suggested scenario that nyx is the remnant of a single massive dwarf galaxy merger. however, we also identify 5 substantially more metal-poor stars ([fe/h] ~ -2.0) whose chemical abundances are similar to those of the metal-weak thick disk. it remains unclear how stars that are chemically identical to the thick disk can be on such prograde, high-eccentricity orbits. we suggest two most likely scenarios: that nyx is the result of an early minor dwarf galaxy merger, or that it is a record of the early spin-up of the milky way disk-although neither perfectly reproduces the chemodynamic observations. the most likely formation scenarios suggest that future spectroscopic surveys should find nyx-like structures outside of the solar neighborhood. | high-resolution chemical abundances of the nyx stream |
observations of diffuse starlight in the outskirts of galaxies provide fundamental constraints on the cosmological context of galaxy assembly in the lambda cold dark matter model, which predicts that galaxies grow through a combination of in-situ star formation and accretion of stars from other galaxies. accreted stars are expected to dominate in the outer parts of galaxies. since dynamical timescales are longer in these regions, substructures related to accretion, such as streams and shells, can persist over many gyr. in this work we use extremely deep g- and i-band images of six massive early- type galaxies (etgs) from the vegas survey to constrain the properties of their accreted stellar components. the wide field of view of omegacam on the vlt survey telescope (vst) also allows us to investigate the properties of small stellar systems (such as globular clusters, ultra-compact dwarfs and satellite galaxies) in the halos of our galaxies. by fitting light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in-situ and accreted stars. | unveiling the nature of giant ellipticals and their stellar halos with the vst |
we study the impact of thermal inflation on the formation of cosmological structures and present astrophysical observables which can be used to constrain and possibly probe the thermal inflation scenario. these are dark matter halo abundance at high redshifts, satellite galaxy abundance in the milky way, and fluctuation in the 21-cm radiation background before the epoch of reionization. the thermal inflation scenario leaves a characteristic signature on the matter power spectrum by boosting the amplitude at a specific wave number determined by the number of e-foldings during thermal inflation (n_{bc}), and strongly suppressing the amplitude for modes at smaller scales. for a reasonable range of parameter space, one of the consequences is the suppression of minihalo formation at high redshifts and that of satellite galaxies in the milky way. while this effect is substantial, it is degenerate with other cosmological or astrophysical effects. the power spectrum of the 21-cm background probes this impact more directly, and its observation may be the best way to constrain the thermal inflation scenario due to the characteristic signature in the power spectrum. the square kilometre array (ska) in phase 1 (ska1) has sensitivity large enough to achieve this goal for models with n_{bc} ≳ 26 if a 10000-hr observation is performed. the final phase ska, with anticipated sensitivity about an order of magnitude higher, seems more promising and will cover a wider parameter space. | small-scale effects of thermal inflation on halo abundance at high-z, galaxy substructure abundance, and 21-cm power spectrum |
we present the results of study the 2d distribution of galaxies in 254 rich open galaxy clusters. the clusters have no concentration to the center, so all kinds of substructures are clearly seen. regular linear substructures in galaxy clusters were described in rood & sastry scheme of morphological types according to positions of 10 brightest galaxies. another types of regular substructures were missed. our study fills the lacuna. we have found about 25% of clusters in our data set having four kinds of regular substructures, beyond founded before linear ones. new kinds of regular substructures are: crossing and divaricating filaments or x and y-type peculiarities, as well as curved strips and short dense chains. we suppose the distribution of dark matter in founded galaxy clusters with substructures have corresponded regular peculiarities. hot gas distribution in these clusters must be observed distorted x-ray halo. we suppose also the clusters will evolve in the different ways. | regular substructures in the rich open galaxy clusters |
we present and test tessellation-based recovery of amorphous halo concentrations (tesseract), a non-parametric technique for recovering the concentration of simulated dark matter halos using voronoi tessellation. tesseract is tested on idealized n-body halos that are axisymmetric, triaxial, or contain substructure and is compared to traditional least-squares fitting as well as to two non-parametric techniques that assume spherical symmetry. tesseract recovers halo concentrations within 3% of the true value regardless of whether the halo is spherical, axisymmetric, or triaxial. traditional fitting and non-parametric techniques that assume spherical symmetry can return concentrations for non-spherical halos that are systematically off by as much as 10% from the true value. tesseract also performs significantly better when there is substructure present outside 0.5 r200. given that cosmological halos are rarely spherical and often contain substructure, we discuss implications for studies of halo concentration in cosmological n-body simulations including how choice of technique for measuring concentration might bias scaling relations. | voronoi tessellation and non-parametric halo concentration |
gravitational lensing is a powerful tool for quantifying the mass content and distribution in distant galaxies. by using milliarcsecond angular resolution observations of radio-loud gravitationally lensed sources it is also possible to detect and quantify small deviations from a smooth mass density distribution, which can be due to low mass substructures in the lensing galaxy. we present high-resolution global vlbi observations of the gravitationally lensed radio source mg j0751+2716 (at z = 3.2), that shows evidence of both compact and extended structure (core-jet morphology) across several gravitational arcs. these data provide a wealth of observational constraints that are used to determine the inner (baryonic and dark matter) mass profile of a group of galaxies and also investigate the smoothness of the dark matter distribution on mas-scales, which is sensitive to possible structures of $10^{6-7}$ m$_{\odot}$ within the lensing halo or along the line-of-sight. our lens modelling finds evidence for astrometric anomalies in this system, which suggest presence of extra mass structure in the lens model. to date this kind of detailed studies of gravitational lensing systems like mg j0751+2716 has been limited by the currently small sample of radio-loud gravitational lenses. in this context, we also present a new pilot gravitational lens search in the vlbi survey mjive-20, in perspective of future surveys with the next generation of radio interferometers. | gravitational lensing at milliarcsecond angular resolution with vlbi observations |
as established in previous papers of this series, observables in highly distorted and magnified multiple images caused by the strong gravitational lensing effect can be used to constrain the distorting properties of the gravitational lens at the image positions. if the background source is extended and contains substructure, like star forming regions, which is resolved in multiple images, all substructure that can be matched across a minimum of three multiple images can be used to infer the local distorting properties of the lens. in this work, we replace the manual feature selection by an automated feature extraction based on sextractor for python and show its superior performance. despite its aimed development to improve our lens reconstruction, it can be employed in any other approach, as well. valuable insights on the definition of an 'image position' in the presence of noise are gained from our calibration tests. applying it to observations of a five-image configuration in galaxy cluster cl0024 and the triple-image configuration containing hamilton's object, we determine local lens properties for multiple wavebands separately. within current confidence bounds, all of them are consistent with each other, corroborating the wavelength-independence of strong lensing and offering a tool to detect deviations caused by micro-lensing and dust in further examples. | generalized model-independent characterization of strong gravitational lenses viii. automated multiband feature detection to constrain local lens properties |
we present the first flexion-focused gravitational lensing analysis of the hubble frontier field observations of abell 2744 (z = 0.308). we apply a modified analytic image model technique to measure source galaxy flexion and shear values at a final number density of 82 arcmin-2. by using flexion data alone, we are able to identify the primary mass structure aligned along the heart of the cluster in addition to two major substructure peaks, including an ne component that corresponds to previous lensing work and a new peak detection offset 1.43 arcmin from the cluster core towards the east. we generate two types of non-parametric reconstructions: flexion aperture mass maps, which identify central core, e, and ne substructure peaks with mass signal-to-noise contours peaking at 3.5σ, 2.7σ, and 2.3σ, respectively; and convergence maps derived directly from the smoothed flexion field. for the primary peak, we find a mass of (1.62 ± 0.12) × 1014 h-1 m⊙ within a 33 arcsec (105 h-1 kpc) aperture, a mass of (2.92 ± 0.26) × 1013 h-1 m⊙ within a 16 arcsec (50 h-1 kpc) aperture for the north-eastern substructure, and (8.81 ± 0.52) × 1013 h-1 m⊙ within a 25 arcsec (80 h-1 kpc) aperture for the novel eastern substructure. | flexion in abell 2744 |
the outer milky way stellar structure known as "the monoceros ring" was discovered in imaging data in 2002. since then, numerous photometric and spectroscopic explorations of this structure, some 18 kpc from the galactic center and at low galactic latitudes, have led to a rich discussion in the field on its composition, possible origins, and relevance for theories of galaxy formation and studies of dark matter. this substructure was initially thought to be either a tidal stream from a disrupted dwarf galaxy or the result of a warping and flaring of the milky way disk. a newer conjecture is that the structure is due to disk oscillations, possibly caused by a massive milky way satellite passing through the disk. | the monoceros ring, and other substructure near the galactic plane |
experimental results on no2 are explained based on the add-model of large extra compactified dimensions of space. we assume that gravity is sufficiently strong in a compactification space of the size of the molecule to affect the vibrational motion of the nuclei by causing an asymmetric perturbation in the symmetric stretch vibrational motion of the optically excited state. at the same excitation energy, there are also other electronic states of different symmetry (conical intersection of potential energy surfaces), which may couple with the optically excited state. due to the gravitational perturbation the nuclei being in the symmetric stretch vibration mode of the optically excited electronic state pass over into the asymmetric stretch vibration mode of an isoenergetic electronic state. this parity conserving change of the vibronic wave function enhances a small gravitational perturbation to an optically detectable signal. the perturbation is associated with a time constant of about 3 μs, which we attribute to fluctuations of the shape of the compactification space induced by a background cosmic field. | do extra compactified dimensions of space cause a substructure underlying the expected eigenstates of a molecule? |
we introduce a new halo/subhalo finder, hiker (a halo finder based on kernel-shift algorithm), which takes advantage of a machine learning method - the mean-shift algorithm combined with the plummer kernel function, to effectively locate density peaks corresponding to halos/subhalos in density field. based on these density peaks, dark matter halos are identified as spherical overdensity structures, and subhalos are bound substructures with boundaries at their tidal radius. by testing hiker code with mock halos, we show that hiker performs excellently in recovering input halo properties. in particular, hiker has higher accuracy in locating halo/subhalo centres than most halo finders. with cosmological simulations, we further show that hiker reproduces the abundance of dark matter halos and subhalos quite accurately, and the hiker halo/subhalo mass functions and vmax functions are in good agreement with two widely used halo finders, subfind and ahf. | hiker: a halo-finding method based on kernel-shift algorithm |
the morphology of haloes inform about both cosmological and galaxy formation models. we use the minkowski functionals (mfs) to characterize the actual morphology of haloes, only partially captured by smooth density profile, going beyond the spherical or ellipsoidal symmetry. we employ semi-analytical haloes with nfw and αβγ-profile and spherical or ellipsoidal shape to obtain a clear interpretation of mfs as function of inner and outer slope, concentration and sphericity parameters. we use the same models to mimic the density profile of n-body haloes, showing that their mfs clearly differ as sensitive to internal substructures. this highlights the benefit of mfs at the halo scales as promising statistics to improve the spatial modelling of dark matter, crucial for future lensing, sunyaev-zel'dovich, and x-ray mass maps as well as dark matter detection based on high-accuracy data. | morphology of dark matter haloes beyond triaxiality |
the predicted size of dark matter substructures in kilo-parsec scales is model-dependent. therefore, if the correlations between dark matter mass densities as a function of the distances between them are measured via observations, we can scrutinize dark matter scenarios. in this paper, we present an assessment procedure of dark matter scenarios. first, we use gaia's data to infer the single-body phase-space density of the stars in the fornax dwarf spheroidal galaxy. the latter, together with the jeans equation, after eliminating the gravitational potential using the poisson equation, reveals the mass density of dark matter as a function of its position in the galaxy. we derive the correlations between dark matter mass densities as a function of distances between them. no statistically significant correlation is observed. second, for the sake of comparison with the standard cold dark matter, we also compute the correlations between dark matter mass densities in a small halo of the eagle hydrodynamics simulation. we show that the correlations from the simulation and from gaia are in agreement. third, we show that gaia observations can be used to limit the parameter space of the ginzburg–landau statistical field theory of dark matter mass densities and subsequently shrink the parameter space of any dark matter model. as two examples, we show how to leave limitations on (i) a classic gas dark matter and (ii) a superfluid dark matter. | assessment of dark matter models using dark matter correlations across dwarf spheroidal galaxies |
gadget-4 (galaxies with dark matter and gas interact) is a parallel cosmological n-body and sph code that simulates cosmic structure formation and calculations relevant for galaxy evolution and galactic dynamics. it is massively parallel and flexible, and can be applied to a variety of different types of simulations, offering a number of sophisticated simulation algorithms. gadget-4 supports collisionless simulations and smoothed particle hydrodynamics on massively parallel computers. the code can be used for plain newtonian dynamics, or for cosmological integrations in arbitrary cosmologies, both with or without periodic boundary conditions. stretched periodic boxes, and special cases such as simulations with two periodic dimensions and one non-periodic dimension are supported as well. the modeling of hydrodynamics is optional. the code is adaptive both in space and in time, and its lagrangian character makes it particularly suitable for simulations of cosmic structure formation. several post-processing options such as group- and substructure finding, or power spectrum estimation are built in and can be carried out on the fly or applied to existing snapshots. through a built-in cosmological initial conditions generator, it is also particularly easy to carry out cosmological simulations. in addition, merger trees can be determined directly by the code. | gadget-4: parallel cosmological n-body and sph code |
measurements of velocity and density perturbations along stellar streams in the milky way provide a time-integrated measure of dark matter substructure at larger galactic radius than the complementary instantaneous inner-halo strong lensing detection of dark matter sub-halos in distant galaxies. an interesting case to consider is the proposed phoenix-hermus star stream, which is long, thin, and on a nearly circular orbit, making it a particular good target to study for velocity variations along its length. in the presence of dark matter sub-halos, the stream velocities are significantly perturbed in a manner that is readily understood with the impulse approximation. a set of simulations shows that only sub-halos above a few 107 m ⊙ lead to reasonably long-lived observationally detectable velocity variations of amplitude of order 1 km s-1, with an average of about one visible hit per (two-armed) stream over a 3 gyr interval. an implication is that globular clusters themselves will not have a visible impact on the stream. radial velocities have the benefit of being completely insensitive to distance errors. distance errors scatter individual star velocities perpendicular and tangential to the mean orbit, but their mean values remain unbiased. calculations like these help build the quantitative case to acquire large, fairly deep, precision velocity samples of stream stars. | velocity variations in the phoenix-hermus star stream |
a very general cosmological consideration suggests that, along with galactic dark matter halos, much smaller dark matter structures may exist. these structures are usually called `clumps', and their mass extends to 10-6 m ⊙ or even lower. the clumps should give the main contribution into the signal of dark matter annihilation, provided that they have survived until the present time. recent observations favor a cored profile for low-mass astrophysical halos. we consider cored clumps and show that they are significantly less firm than the standard nfw ones. in contrast to the standard scenario, the cored clumps should have been completely destroyed inside ~ 20 kpc from the milky way center. the dwarf spheroidals should not contain any dark matter clumps. on the other hand, even under the most pessimistic assumption about the clump structure, the clumps should have survived in the milky way at a distance exceeding 50 kpc from the center, as well as in low-density cosmic structures. there they significantly boost the dark matter annihilation. we show that at least 70% of the clumps endured the primordial structure formation should still exist untouched in the present-day universe. | can the dark matter annihilation signal be significantly boosted by substructures? |
the hawc observatory is a ground-based observatory of tev gamma rays located on the sierra negra drop volcano in mexico. hawc is sensitive to emission from extended gamma-ray sources, so it is able to search for emission from annihilation and decay of tev dark matter (dm) particles in galaxies and galaxy clusters. we present the limits for the dark matter annihilation cross-section for the virgo cluster. we also present computations for possible increased dark matter annihilation flux due to different density profiles and substructure configurations of the virgo cluster. such fluxes would increase the dark matter detection capability of hawc in the virgo cluster significantly. | searching dark matter signatures from the virgo cluster with hawc |
warm dark matter (wdm) models offer an attractive alternative to the current cold dark matter (cdm) cosmological model. we present a novel method to differentiate between wdm and cdm cosmologies, namely, using weak lensing; this provides a unique probe as it is sensitive to all of the “matter in the beam,” not just dark matter haloes and the galaxies that reside in them, but also the diffuse material between haloes. we compare the weak lensing maps of cdm clusters to those in a wdm model corresponding to a thermally produced 0.5 kev dark matter particle. our analysis clearly shows that the weak lensing magnification, convergence, and shear distributions can be used to distinguish between cdm and wdm models. wdm models increase the probability of weak magnifications, with the differences being significant to ≳5σ, while leaving no significant imprint on the shear distribution. wdm clusters analyzed in this work are more homogeneous than cdm ones, and the fractional decrease in the amount of material in haloes is proportional to the average increase in the magnification. this difference arises from matter that would be bound in compact haloes in cdm being smoothly distributed over much larger volumes at lower densities in wdm. moreover, the signature does not solely lie in the probability distribution function but in the full spatial distribution of the convergence field. | matter in the beam: weak lensing, substructures, and the temperature of dark matter |
in recent years, bose-einstein-condensed dark matter (bec-dm) has become a popular alternative to standard, collisionless cold dark matter (cdm). this bec-dm -also called scalar field dark matter (sfdm)- can suppress structure formation and thereby resolve the small-scale crisis of cdm for a range of boson masses. however, these same boson masses also entail implications for bec-dm substructure within galaxies, especially within our own milky way. observational signature effects of bec-dm substructure depend upon its unique quantum-mechanical features and have the potential to reveal its presence. ongoing efforts to determine the dark matter substructure in our milky way will continue and expand considerably over the next years. in this contribution, we will discuss some of the existing constraints and potentially new ones with respect to the impact of bec-dm onto baryonic tracers. studying dark matter substructure in our milky way will soon resolve the question, whether dark matter behaves classical or quantum on scales of $\lesssim 1$ kpc. | to observe, or not to observe, quantum-coherent dark matter in the milky way, that is a question |
the implementation of acacia, a new algorithm to generate dark matter halo merger trees with the adaptive mesh refinement code ramses, is presented. the algorithm is fully parallel and based on the message passing interface. as opposed to most available merger tree tools, it works on the fly during the course of the n-body simulation. it can track dark matter substructures individually using the index of the most bound particle in the clump. once a halo (or a sub-halo) merges into another one, the algorithm still tracks it through the last identified most bound particle in the clump, allowing to check at later snapshots whether the merging event was definitive, or whether it was only temporary, with the clump only traversing another one. the same technique can be used to track orphan galaxies that are not assigned to a parent clump anymore because the clump dissolved due to numerical overmerging. we study in detail the impact of various parameters on the resulting halo catalogues and corresponding merger histories. we then compare the performance of our method using standard validation diagnostics, demonstrating that we reach a quality similar to the best available and commonly used merger tree tools. as a proof of concept, we use our merger tree algorithm together with a parametrized stellar-mass-to-halo-mass relation and generate a mock galaxy catalogue that shows good agreement with observational data. | acacia: a new method to produce on-the-fly merger trees in the ramses code |
in this work we are going to build the halo mass function for a scalar field dark matter model. this will be done with the aim of determine the minimum size of halos that our model predicts, in contrast with the lcdm model, which predicts an overabundance of substructures. we find that, for a scalar field mass m = 10-22ev and a sharp-k window function, is possible to reproduce the suppression in the halo formation at small scales. | towards a calculation of the halo mass function of a scalar field dark matter |
recently a theory about the formation of overdensities of stars along tidal tails of globular clusters has been presented. this theory predicts the position and the time of the formation of such overdensities and was successfully tested with n-body simulations of globular clusters in a point-mass galactic potential. in this work, we present a comparison between this theory and our simulations using a dwarf galaxy orbiting two differently shaped dark matter haloes to study the effects of a cored and a cuspy halo on the formation and the evolution of tidal tails. we find no difference using a cuspy or a cored halo, however, we find an intriguing asymmetry between the leading arm and the trailing arm of the tidal tails. the trailing arm grows faster than the leading arm. this asymmetry is seen in the distance to the first overdensity and its size as well. we establish a relation between the distance to the first overdensity and the size of this overdensity. | formation and evolution of substructures in tidal tails: spherical dark matter haloes |
the degree of dark matter clustering on small scales presents a strong constraint on its physical nature. one of the most promising avenues for determining the clustering of dark matter on the smallest scales employs narrow stellar streams in the halo of the milky way. in this contribution, i review recent progress in modeling the effect of dark matter substructure on the structure of stellar streams and recent constraints on the amount of small ( {≈ }10^7 m_\odot ) dark matter substructure in the inner milky way halo. the next few years will likely see a large amount of progress both in the modeling of stellar streams and in the quantity and quality of the available data and i discuss future challenges and opportunities in this area. | constraining the small-scale clustering of dark matter with stellar streams |
wfirst's combination of wide field and high resolution will revolutionize the study of nearby galaxies. we propose to produce and analyze simulated wfirst data of nearby galaxies and their halos to maximize the scientific yield in the limited observing time available, ensuring the legacy value of wfirst's eventual archive. we will model both halo structure and resolved stellar populations to optimize wfirst's constraints on both dark matter and galaxy formation models in the local universe. wfirst can map galaxy structure down to ~35 mag/square arcsecond using individual stars. the resulting maps of stellar halos and accreting dwarf companions will provide stringent tests of galaxy formation and dark matter models on galactic (and even sub-galactic) scales, which is where the most theoretical tension exists with the lambda-cdm model. with a careful, coordinated plan, wfirst can be expected to improve current sample sizes by 2 orders of magnitude, down to surface brightness limits comparable to those currently reached only in the local group, and that are >4 magnitudes fainter than achievable from the ground due to limitations in star-galaxy separation. wfirst's maps of galaxy halos will simultaneously produce photometry for billions of stars in the main bodies of galaxies within 10 mpc. these data will transform studies of star formation histories that track stellar mass growth as a function of time and position within a galaxy. they also will constrain critical stellar evolution models of the near-infrared bright, rapidly evolving stars that can contribute significantly to the integrated light of galaxies in the near-infrared. thus, with wfirst we can derive the detailed evolution of individual galaxies, reconstruct the complete history of star formation in the nearby universe, and put crucial constraints on the theoretical models used to interpret near-infrared extragalactic observations. we propose a three-component work plan that will ensure these gains by testing and optimizing wfirst observing strategies and providing science guidance to trade studies of observatory requirements such as field of view, pixel scale and filter selection. first, we will perform extensive simulations of galaxies' halo substructures and stellar populations that will be used as input for optimizing observing strategies and sample selection. second, we will develop a pipeline that optimizes stellar photometry, proper motion, and variability measurements with wfirst. this software will: maximize data quality & scientific yield; provide essential, independent calibrations to the larger wfirst efforts; and rapidly provide accurate photometry and astrometry to the community. third, we will derive quantitative performance metrics to fairly evaluate trade-offs between different survey strategies and wfirst performance capabilities. the end result of this effort will be: (1) an efficient survey strategy that maximizes the scientific yield of what would otherwise be a chaotic archive of observations from small, un-coordinated programs; (2) a suite of analysis tools and a state-of-the-art pipeline that can be deployed after launch to rapidly deliver stellar photometry to the public; (3) a platform to independently verify the calibration and point spread function modeling that are essential to the primary wfirst goals, but that are best tested from images of stellar populations. these activities will be carried out by a science investigation team that has decades of experience in using nearby galaxies to inform fundamental topics in astrophysics. this team is composed of researchers who have led the charge in observational and theoretical studies of resolved stellar populations and stellar halos. with our combined background, we are poised to take full advantage of the large field of view and high spatial resolution wfirst will offer. | wings: wfirst infrared nearby galaxy survey |
in order to constrain the limitations of association methods applied to galaxy surveys, we analysed the catalogue of haloes at z = 0 of a cosmological simulation, trying to reproduce the limitations dealt with by an observational survey. we focused on the percolation method, usually called the friends of friends method, commonly used in the literature. the analysis was carried out on the dark matter cosmological simulation mdpl2, from the multidark project. the results point to a large fraction of contaminants for massive haloes in high-density environments. thresholds in the association parameters and the subsequent analysis of observational properties can mitigate the occurrence of fake positives. the use of tests for substructures can also be efficient in particular cases. | siblings, friends and acquaintances: testing galaxy association methods |
stellar halos give insight into the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites via their different stellar populations. an algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. cosang (coupling semi-analytic/n-body galaxies) is a new computational method that we are developing which couples pure dark matter n-body simulations with a semi-analytic galaxy formation model. at each timestep, results from the n-body simulation feed into the semi-analytic code, whose results feed back into the n-body code making the evolution of the dark matter and baryonic matter dependent on one another. cosang will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection. in this dissertation, i will describe the new simulation code cosang. the results from the extensive testing phase on cosang will be presented which indicate cosang is properly simulating feedback from galaxies within a dark matter halo. i used this validated code to analyze a cosang zoom simulation of a 1012m solar masses dark matter halo. results showed a flatter inner halo near the disk and a more spherical outer halo which is expected when a galaxy exists at the center of a dark matter halo. a comparison is made with a simulation run with the same initial conditions, but with the baryonic component simulated using a hydrodynamic algorithm. the semi-analytic model predicted galaxy types better than the hydrodynamic simulation leading to the conclusion that the cosang halo is more accurate. i also present a dark matter direct detection analysis on the cosang zoom halo to measure the dark matter velocity distributions and modulation amplitudes. the cosang results show that the dark matter velocity distribution does not fit well to a maxwell boltzmann distribution and the modulation amplitudes derived indicate an anisotropic dark matter velocity distribution. future work will include tagging dark matter particles with stellar properties to build and evolve a stellar halo. | coupling semi-analytic models and n-body simulations: a new way of making galaxies and stellar halos |
lamost is a special reflecting schmidt telescope. lamost breaks through the bottleneck of the large scale spectroscopic survey observation with both large aperture (effective aperture of 3.6 - 4.9m) and wide field of view (5 degrees). it is an innovative active reflecting schmidt configuration achieved by changing mirror surface continuously to achieve a series different reflecting schmidt system in different moments. by using the parallel controllable fiber positioning technique, the focal surface of 1.75 meters in diameter accommodates 4000 optical fibers. also, lamost has 16 spectrographs with 32 ccd cameras. lamost is the telescope of the highest spectrum acquiring rate.in the spectroscopic survey of lamost from october 2011 to june 2014, lamost has obtained more than 4.13 million spectra of celestial objects. there are 3.27 million spectra of stars, in which the stellar parameters of 2.16 million stars were obtained.in the five-year regular survey upto 2017, lamost will obtaine 5 million stellar spectra, which would make substantial contribution to the study of the stellar astrophysics and the structure of the galaxy, such as the spheroid substructure of the galaxy, the galactic gravitational potential and the distribution of the dark matter in the galaxy, the extremely metal poor stars and hypervelocity stars, the 3d extinction in the galaxy, the structure of thin and thick disks of the galaxy, and so on. | spectroscopic survey of lamost |
the milkyway (mw) is surrounded by numerous satellite objects: dwarf galaxies, globular clusters and streams of disrupted systems. together, these form a vast polar structure (vpos), a thin plane spreading to galactocentric distances as large as 250 kpc. the orbital directions of satellite galaxies and the preferred alignment of streams with the vpos demonstrate that the objects orbit within the structure. this strong phase-space correlation is at odds with the expectations from simulations of structure formation based on the cold dark matter cosmology (λcdm). the accretion of sub-halos along filaments has been suggested as the origin of the anisotropic distribution. we have tested this scenario using the results of high-resolution cosmological simulations and found it unable to account for the large degree of correlation of the mw satellite orbits. it is therefore advisable to search for alternative explanations. the formation of tidal dwarf galaxies (tdgs) in the debris expelled from interacting galaxies is a very natural formation scenario of the vpos. if a number of mwsatellites truly are tdgs, mistakenly interpreting them to trace the dark-matter sub-structure of the mw halo would significantly enhance the `small-scale' problems which are already known to plague the λcdm model. | the vast polar structure of the milky way and filamentary accretion of sub-halos |
being able to accurately predict the abundance and demographics of dark matter substructure is of paramount importance for many fields of astrophysics: gravitational lensing, galaxy evolution, halo occupation modeling, and even constraining the nature of dark matter. dark matter substructure is typically modeled using n-body simulations. however, in a pilot study the pi finds that subhalos in state-of-the-art cosmological simulations undergo copious amounts of artificial disruption as a consequence of both inadequate force softening and a discreteness-driven run-away instability. overcoming this problem in cosmological or zoom-in simulations requires orders-of-magnitude increase in resolution, and a scale-dependent treatment of force softening, neither of which will be achievable in the foreseeable future. this is a serious road-block for all astrophysical applications requiring accurate characterization of halo substructure. this proposal aims to salvage the immense potential of this science by running idealized simulations of dark matter subhalos in a fixed, external potential (the host halo) at exquisite resolution. the pi will construct a data-base of simulations covering a vast parameter space of orbits and halo properties, and carefully check that each individual simulation is properly converged, which requires as many as 10^6 particles per simulation! the pi will also characterize under what conditions subhalos undergo artificial disruption in n-body simulations, and use the data-base to calibrate a new semianalytical model describing the build-up and evolution of dark matter substructure. in the coming decade a number of nasa missions (e.g., jwst, wfirst, euclid) and ground-based surveys (e.g., desi, lsst) will provide astronomers with an unprecedented wealth of data regarding galaxy evolution and cosmology. in order to optimize the scientific impact of these huge investments, it is prudent that galaxy clustering in these surveys be interpreted in an unbiased, maximally informative manner. a popular method to do so is to compare the observations to mock data, obtained by populating dark matter (sub)halos in numerical simulations with `mock' galaxies, using methods such as subhalo abundance matching. this entire program faces a severe challenge if those simulations underpredict the abundance of subhalos due to artificial disruption. although one may correct for this by including `orphan' galaxies (i.e., mock galaxies without an associated subhalo in the simulation), this seriously diminishes the information content of small-scale clustering, unless it is known how many orphans to add and where. dark matter substructure is also an important discriminator between different dark matter models (cold dark matter vs. warm dark matter vs. self-interacting dark matter), and is important for translating a potential, observed dark matter annihilation signal into a mass and cross section of the dark matter particle. unless we can make accurate, and above all reliable, predictions regarding the abundance and structure of dark matter subhalos, we will forfeit one of the main handles we have on learning about the nature of dark matter. the outcome of this work will be an improved understanding of tidal evolution of substructure, and a unique data-base of simulations that allows users to correct large cosmological simulations for artificial disruption. this enables subhalo abundance matching without uncertainties regarding the number of `orphans', thereby opening a treasure trove of astrophysical information to be extracted from small-scale clustering. in addition, the products of this work will be instrumental for interpreting a variety of studies that use substructure to constrain the nature of dark matter, and for interpreting the fossil record of the milky way; tidal streams and stellar halo, both produced by stripping of satellite galaxies. the latter is one of the main science goals of wfirst and lsst. | dark matter substructure: from numerical noise to cosmological treasure trove |
a clear excess in the fermi-lat data is present at energies around a few gev. the spectrum of this so-called 'gev excess' is remarkably similar to the expected annihilation signal of wimp dark matter. however, a large bulge population of millisecond pulsars living below the fermi-lat detection threshold could also explain the excess spectrum. in a recent work we optimized the search for sub-threshold sources, by applying a wavelet transform to the fermi-lat gamma-ray data. in the inner-galaxy the wavelet signal is significantly enhanced, providing supportive evidence for the point source interpretation of the excess. in these proceedings we will extent our previous work with a spectral analysis and elaborate on the potential contamination from substructures in the gas. | millisecond pulsars in the galactic bulge? an extended discussion on the wavelet analysis of the fermi-lat data |
the work i have done during my thesis has consisted of both observational and theoretical projects involving dwarf galaxies and cold dark matter (cdm) sub-structure both around the milky way and in redshift z∼0.1 galaxies. the dwarf galaxies around the milky way are distributed in a so-called vast polar structure (vpos) that may be in conflict with λcdm simulations. for this project, we seek to investigate two key questions to determine if the vpos poses a serious challenge to the λcdm paradigm on galactic scales. first, we ask which dwarf galaxy satellites drive the fit to the vpos and create planar structure. second, we ask if the vpos remains coherent as a function of time. using the measured hst proper motions and associated uncertainties, we integrate the orbits of the classical milky way satellites backwards in time and find that for the mean of the measured hst proper motions, the vpos deteriorates in less than a dynamical time and resembles an isotropic structure. we also explore the effect of the uncertainties on the hst proper motions on the coherence of the vpos as a function of time. we find that nine of the eleven classical dwarfs have reliable proper motions; for these nine, the vpos also deteriorates in less than a dynamical time, indicating that the vpos is not a dynamically stable structure. i will also briefly discuss the observational work that i have done during my thesis, including hi observations of lensed spiral galaxies to constrain cdm sub-structure. | galactic building blocks: dwarf galaxies near and far |
we model the tidal stream of the milky way globular cluster palomar 5 (pal 5), and show that the unique geometry of the problem yields powerful constraints on the model parameters characterizing the local standard of rest (lsr), the milky way and pal 5 itself. using only sdss data and a few radial velocities from the literature, we find that the distance of the sun from the galactic center is 8.30+/-0.25 kpc, and the lsr transverse velocity is 242+/-16 km/s. assuming that the dark halo of the galaxy follows a nfw density profile, we fit it with a virial mass of (1.6+/-0.4) 1012msun, a virial radius of 195+/-19 kpc, and hence a rather low concentration of 5+/-2. moreover, we find it with a flattening of qz = 0.95(+0.16)(-0.12) to be essentially spherical - at least within the inner 25 kpc, which are effectively probed by pal 5. we also determine pal 5's mass, distance and proper motions independently from other methods, which enables us to perform vital cross-checks for these methods. we conclude that finding more globular cluster streams is essential for mapping out the structure of the halo of our galaxy to high precision. finally, we point out that all our best-fit models yield similar substructure patterns as the ones observed in the pal 5 stream within about 5 kpc of the cluster. the origin of these substructures is epicylic motion of stars along the stream. such epicylic substructures have to be taken into account when searching tidal streams for signs of past encounters with dark-matter subhalos | globular cluster streams as galactic high-precision scales - the poster child palomar 5 |
over the past decades the connection between the angular momentum of dark matter halos and their galaxies' has been discussed in several studies. in a hierarchical λcdm universe, structures grow through accretion of smaller substructures, but at the very beginning the gas cools and collapses into the dark matter halos to form the stars and galaxies at their centers. in this process, both components, gas and dark matter, gain a similar amount of angular momentum through tidal torques, albeit the gas can transport the angular momentum to the center of the halo. we use galaxies selected from the magneticum pathfinder simulations to investigate the correlation of the specific angular momentum of the stars j_* and the stellar mass of both disk and spheroidal galaxies at different redshifts as well as the spin parameter of the dark component. we find that the disk and spheroidal galaxies populate different regions in the m_*-j_* plane, in agreement with observations. this split-up is already present at z=2, however, the specific angular momenta are generally smaller at higher redshifts. similarly, the bimodality between disks and spheroids can also be seen in the spin parameter distribution of the according dark matter halos. | dynamical properties of galaxies with different morphological types at z=0 and z=2 |
the high altitude water cherenkov (hawc) observatory is an extensive air shower array sensitive to gamma rays between 500 gev - 100 tev. tev photons provide unique tests of fundamental physics phenomena, such as dark matter annihilation and decay. hawc is capable of performing indirect dark matter searches in a mass range that is inaccessible to most other experiments. for such searches, one promising class of objects are dwarf spheroidal galaxies, which are expected to have few astrophysical gamma rays but large dark matter content. in addition, we consider the milky way halo, the m31 galaxy and the virgo cluster, because of the expected flux boost due to the substructure of the main dark matter halo. we present limits on the dark matter annihilation cross-section and decay lifetime from 15 dwarf spheroidal galaxies within the hawc field of view, the milky way halo, the m31 galaxy and the virgo cluster. | dark matter searches with hawc |
in recent decades photometric surveys have revealed a wealth of stellar substructure in the galactic halo, evidence of the ongoing process of galaxy assembly in the milky way. however spectroscopic data are essential for determining the kinematics and abundances of the stars in these structures. in the southern hemisphere alone, over a dozen new stellar streams have been discovered to date. to study these we have embarked on an ongoing spectroscopic program, the southern stellar stream spectroscopic survey (s5), to map them with 2df+aaomega on the aat. the radial velocities and stellar metallicities from s5 - together with proper motions from gaia dr2 - provide us with a unique dataset. these data shed new light on the stellar populations of the milky way's halo, the progenitors and formation processes of the streams, the mass and overall morphology of the milky way's gravitational potential, and potentially could yield clues to the nature of dark matter. thus far, the s5 program has obtained 6d+1 phase space information for 10 streams in the des footprint, all of which are the first such measurements for these southern streams, and we now are expanding our program beyond the des footprint. i will give an overview of the s5 survey, present early science results, and discuss the complementarity of this targeted program to existing and future spectroscopic surveys with broader coverage, such as gaia-eso, galah, weave and 4most. | spectroscopic surveys and stellar substructure in the galactic halo |
we propose wfc3 ir imaging of a sample of 112 new strong galaxy-galaxy lensing candidates discovered within the dark energy spectroscopic instrument (desi) legacy imaging surveys, data release 7, using a deep neural network. these candidates are highly likely strong lensing systems (with > 90% confidence). many of these systems have multiple lensed images. we further estimate that the lenses in a large number of them are elliptical galaxies at redshifts of z 0.8 or higher. if confirmed, this will likely significantly increase the number of high redshift galaxy lenses, with the implication that the number of multiply lensed sources (including supernovae) at higher redshifts will also increase. this set can be added to the known lens sample to tackle the cosmologically significant problems of studying substructures in dark matter and measuring the hubble constant, h0, through a targeted search for multiply lensed supernovae in the future. | confirming strong galaxy gravitational lenses in the desi legacy imaging surveys |
a dark substructure of mass ~3×109 msun has previously been detected in the gravitational lens galaxy sdssj0946+1006 through its perturbation of the lensed images. we demonstrate that this substructure is consistent with being a tidally truncated subhalo, rather than a line-of-sight structure, and requires a concentration much higher than predicted by the halo mass-concentration relation observed in cold dark matter simulations. we discuss the ramifications for both cold collisionless and self-interacting dark matter models. | can the extremely high-concentration subhalo perturbing gravitational lens sdssj0946+1006 be reconciled with cold dark matter? |
the small-scale distribution of dark matter is, at present, poorly understood. cosmological simulations predict a large number of low-mass subhalos within galaxies, but observations in our local group find a lower number of corresponding satellite galaxies. this tension may be addressed by quantifying low-mass subhalos at cosmological distances. one of the few methods capable of this measurement is galaxy-scale strong gravitational lensing. we identify a set of lensed lyman-α emitting galaxies (laes) whose compact angular scales allow us to achieve lower mass detection thresholds, down to ~107 solar masses. these galaxies are imaged at high-resolution with the hst wfc3 to allow precise measurement of surface brightness profile anomalies associated with mass substructure in the lensing galaxy. rather than directly detecting subhalos, we use the bayesian evidence to infer the probability of each galaxy hosting a subhalo. from this statistical framework, we constrain the mass fraction and slope of the subhalo mass function (shmf) in this sample. our procedure is sensitive to subhalos ranging from 107 - 109 solar masses. we find a substructure mass fraction f=0.0020 +0.0027 -0.0013 and a slope α = 0.968 +0.485 -0.524. this mass fraction is consistent with both observational results and theoretical predictions. the slope, however, is significantly lower than cosmological predictions. our results are qualitatively in agreement with the number of satellites found in the local group. we discuss the implications for warm dark matter (wdm), one possible modification to dark matter theory. we also explore sources of systematic error. | quantifying the dark matter subhalo mass function in z≈0.5 galaxies using lensed lyman-α emitter galaxies. |
stars escaping globular clusters form thin, long and kinematically-cold tidal streams. in pristine conditions, these streams have nearly uniform density, however, new gaia observations of one such structure in the milky way halo have revealed a likely site of perturbation. the on-sky morphology suggests a recent, close encounter with a massive and dense perturber. known baryonic objects are unlikely perturbers based on their orbital properties, but observations permit a low-mass dark-matter subhalo as a plausible candidate. this observation opens up the possibility that detailed observations of streams could measure the mass spectrum of dark-matter substructures and even identify individual substructures and their orbits in the milky way halo. | dynamical evidence for a dark substructure in the milky way halo |
the desi milky way survey (mws) will observe over 8 million stars between 16<r<19 mag during bright time, in addition to brighter stars (10<r<16 mag) in a backup program for poor observing conditions. in this talk we highlight early results from desi commissioning and survey validation programs that showcase the potential of mws. we have verified that stellar radial velocities can be measured by desi to an accuracy of 5km/s, and stellar parameters to 0.1 dex at r=19. this will allow mws to characterize diffuse substructure in the galactic thick disk and stellar halo, discover extremely metal-poor stars and other rare stellar types, and improve constraints on the galaxy's 3d dark matter distribution from halo star kinematics. mws will also enable a detailed characterization of the stellar populations within 100 pc of the sun. 80 white dwarfs have been discovered in our early data, one of which shows clear signatures of on-going accretion of a tidally disrupted planetesimal. in full operation, desi will observe roughly 100 white dwarfs per night, building a rich sample from which we will we can derive detailed exoplanet compositions. | the desi milky way survey (mws) |
a generic prediction of galaxy formation in the standard cosmological model with cold dark matter is the hierarchical assembly of structure on mass scales ranging from ultra-faint galaxies to galaxy clusters. in the local group, dozens of galaxies have been found orbiting the milky way and andromeda. the question of whether the largest milky way satellites, the large and small magellanic clouds, brought in their own entourage of satellites has been a long standing puzzle, and has garnered renewed interest following the recent discovery of more than a dozen ultra-faint galaxy candidates in the southern hemisphere. the on-going magellanic satellites survey (maglites) aims to complete an annulus of contiguous deep optical imaging with blanco/decam around the periphery of the magellanic clouds, enabling a systematic search for ultra-faint galaxies and other low-surface-brightness stellar substructures associated with the magellanic system. i will report on the progress of maglites and discuss science highlights from the first observing season, including a new ultra-faint galaxy candidate located ~11 kpc from the large magellanic cloud. | the magellanic satellites survey: searching for hierarchical structure formation within the local group |
ram-pressure stripped tails have been observed in a handful of individualinteracting galaxies. in an xmm mosaic program targeting the outskirts ofthe hydra a cluster, we discovered a spectacular infalling galaxy groupwith a very long tail (> 400 kpc long) of hot x-ray emitting gas. thissystem shows a striking similarity with simulated infalling galaxygroups. it provides a unique opportunity to test our understanding ofthe ram-pressure stripping process and study the virialization of theinfalling gas within the main dark-matter halo. we propose a new 130 ksobservation of this accreting substructure with xmm. | a textbook example of ram-pressure stripping in hydra a |
over five observing seasons, which started in august 2013, the dark energy survey (des) will carry out a wide field survey of 5000 square degrees of the southern galactic cap. as much of the wide-field area has not yet been systematically surveyed, we expect to discover many new strongly lensed galaxies and quasars.des has identified 24 strong lens candidate objects (galaxy- and galaxy clusters-scale) in data from the science verification season and has performed spectroscopic follow-up on a subset of these candidates as part of a gemini large and long program. we present the current state of progress on the photometric and spectroscopic analysis of the lens candidate systems.one of the main objectives of the strong lensing science program in des is to derive constraints on dark energy. the two major components of this part of the program will be exploiting (1) lenses with background sources at multiple redshifts and (2) lensed quasars. in addition to cosmology, we will use the cluster-scale lens sample to study dark matter mass profile, along with the large sample of sources at varying redshifts to study of galaxy evolution and substructure.to obtain precise lens and source positions and to verify the candidate system as a lensing system, we must obtain spectroscopic redshifts. in order to model the lens potential to the required level of precision, we also require high-resolution imaging, both available at the gemini south facility.to select lenses with arc-like features we use a combination of automated arc-finders, catalog searches and visual scans. we carry out these searches on the annual des data release. the first target list of 24 candidates comes from the science verification season, which was undertaken during the 2012/2013 observing season and is about 300 square degrees. using the upgraded gmos spectrographs at gemini south, we have begun spectroscopic observations through the gemini large and long program, awarded to pi liz buckley-geer to follow-up des strong lens candidate systems. | warped universe: analysis of strong lens candidates from early dark energy survey data |
we use xmm to map the cluster abell 2199 intermediate region (<3/4 virialradius) and search x-ray faint substructures in a wide spacial range froma galaxy to a cluster and larger sizes. we observed this area with suzakuand found a number of structures and a hint of asymmetric large scaleemission. these substructures along with unresolved background sourcesshould be resolved spatially and covered fully with xmm imaging. errorsof the epic background will be reduced by our suzaku deep spectra. thesex-ray maps will be compared with our wide area weak-lensing data observedwith subaru hyper suprime-cam. the xmm observations provide uniquely adirect comparison among structures of galaxies, icm, and dark matter. | x-ray large scale survey of the nearby galaxy cluster abell2199 |
theory suggests that galactic bars spin down throughout their evolution due to an angular momentum exchange with the inner parts of their dark matter halos. as opposed to a bar with a fixed pattern speed, chiba et al. (2019) proposed that 'resonance sweeping' due to a decelerating galactic bar can explain local kinematic substructure in the solar neighborhood, like the hercules stream. to date, resonance sweeping — a process of trapping and dragging the orbits of stars — has been explored both analytically and with test particle simulations that lack self-gravity. here, we take such analyses a step further and examine resonance sweeping with a high resolution (~109 particle) self-consistent n-body simulation. like chiba et al. (2019), the bar patten speed in our adopted simulated galaxy slowly decelerates over the course of the simulation, with ωbar decreasing from 49.88 to 28.84 km s-1 kpc-1 in 4 gyr (δωbar/δt = 5.25 km s-1 kpc-1 gyr-1). for our preliminary test, we calculated frequencies of the stars using agama. we identify stars in corotation resonance and outer lindblad resonance and find a significant number of stars remain in resonance later in time suggesting resonant sweeping of orbits due to the decelerating bar. this result in a more realistic, self-gravitating disk indicates that the method of resonance sweeping can indeed be applied to gaia data. | resonance sweeping in barred galaxy simulations |
the fundamental properties of dark matter, such as its mass, self-interaction, and coupling to other particles, can have a major impact on the evolution of cosmological density fluctuations on small length scales. strong gravitational lenses have long been recognized as powerful tools to study the dark matter distribution on these small subgalactic scales. in this talk, we discuss how gravitationally lensed quasars and extended lensed arcs could be used to probe non minimal dark matter models. we comment on the possibilities enabled by precise astrometry, deep imaging, and time delays to extract information about mass substructures inside lens galaxies. to this end, we introduce a new lensing statistics that allows for a robust diagnostic of the presence of perturbations caused by substructures. we determine which properties of mass substructures are most readily constrained by lensing data and forecast the constraining power of current and future observations. | small but mighty: dark matter substructures |
the milky way halo contains several thin, dynamically-cold stellar streams that likely formed from the tidal disruption of low-mass stellar systems like globular clusters. these streams are powerful tools for testing dark matter theories: streams will enable mapping the global structure of mass in the galaxy, and are extremely sensitive to gravitational perturbations such as interactions with dark substructure. recent data from the gaia mission (dr2) have enabled a high-contrast view of the longest milky way thin stream, the gd-1 stream, and have revealed a number of under-densities and a "spur" of stars associated with one such density gap in this stream. the observed morphology of gd-1 (the gap and spur) is naturally reproduced in models of the stream that include an encounter with a massive (~10^6-10^8), dense perturber, and is not expected in simple simulations of the stream formation. i will show models of the stream and discuss ways to test the substructure encounter scenario. if confirmed, the gd-1 stream would provide the first direct dynamical evidence of dark substructure in the milky way halo. | the gd-1 stellar stream suggests the existence of dark substructure in the milky way halo |
we have extended two recently developed theoretical methods, the quantum finite elements (qfe) and the euclidean-signature semi-classical method (esscm). the qfe is a technique for constructing lattice field theories (lfts) on curved riemannian manifolds. we extended the applicability of the qfe to formulating lfts on certain three and four dimensional riemannian manifolds such as $\\mathbb{s}. {3}$ and $\\mathbb{r} \\cross \\mathbb{s}. {3}$. this was done by first constructing a novel simplicial approximation to $\\mathbb{s}. {3}$. then, after correctly computing the weights of the links and vertices that make up this simplicial approximation, we defined a laplacian on it, whose low lying spectrum was observed to approach the known continuum limit as we further refined our simplicial complex. to facilitate a comparison between the qfe and the bootstrap, we calculated an estimate of the fourth-order binder cumulant using cft data extracted from the conformal bootstrap. the esscm is a methodology for facilitating the use of already known mathematical theorems/results to approach lorentzian signature problems in bosonic field theory and quantum gravity in terms of their euclidean-signature analogs. we further developed this method by applying it in a novel fashion to quantum cosmological models with matter sources. in particular, for the taub models, we proved for the first time the existence of a countably infinite number of well behaved 'excited' state solutions when $\\lambda$ is present. both methods are promising and have applications for field theory, beyond standard model physics, and quantum gravity. | the tidal evolution of dark matter substructure and the significance of halo-to-halo assembly history variance |
despite being ubiquitous throughout the universe, the fundamental properties of dark matter remain a mystery. while dark matter physics plays little role in the current evolution of large-scale cosmic structures, it does have a major impact on small causal length scales. studying the astrophysical structures that resulted from the gravitational collapse of fluctuations on these small scales can thus yield important clues about the physics of dark matter. today, most of these structures are locked in deep inside the potential wells of galaxies, making the study of their properties difficult. fortunately, due to fortuitous alignments between high-redshift bright sources and us, some of these galaxies act as spectacular strong gravitational lenses, allowing us to probe their inner structure. in this talk, we present a unified framework to extract information about the power spectrum of mass substructures inside lens galaxies. we determine which properties of mass substructures are most readily constrained by lensing data and forecast the constraining power of current and future observations. | unlocking dark matter physics out of galactic substructures |
pulsars are precise clocks that can serve as galactic accelerometers. traditionally, the accelerations of stars within the galaxy have been estimated using kinematic analyses that assume the galaxy is in equilibrium. we use pulsar timing measurements to directly measure the galactic acceleration. given the measured galactic acceleration, we derive the oort limit for the first time without making any assumptions about spherical symmetry or equilibrium, and the local dark matter density given an accounting of the baryon budget. our value for the local dark matter density is lower than typical jeans estimates, and has implications for direct detection experiments. these measurements can also provide constraints on exotic forms of dark matter, such as collisional disk dark matter models. finally, we obtain a constraint on the oblateness of the milky way potential, which implies that the pulsars trace the oblateness of the disk rather than the halo. larger samples of pulsars should give us a direct view of dark matter sub-structure in the milky way. extreme precision rv measurements towards pulsars may also constrain theories of gravity and post-newtonian parameters. | using galactic accelerometers to directly measure dark matter |
msl applies simulation-based inference techniques to the problem of substructure inference in galaxy-galaxy strong lenses. it leverages additional information extracted from the simulator, then trains neural networks to estimate likelihood ratios associated with population-level parameters characterizing dark matter substructure. the package including five high-level scripts which run the simulation and create samples, combing multiple simulation runs into a single file to use for training, then train the neural networks. after training, the estimated likelihood ratio is tested, and calibrated network predictions are made based on histograms of the network output. | msl: mining for substructure lenses |
the spherical jeans equation is widely used to estimate mass profiles of systems from star clusters to galactic stellar halos to clusters of galaxies. the cumulative mass profile, m(<r), is derived from kinematics of tracers of the potential under the assumptions of spherical symmetry and dynamical equilibrium. we consider the application of the jeans equation to mapping the outer reaches of the milky way, specifically to determine the dark matter distribution from field halo stars. we present a new non-parametric routine for solving the spherical jeans equation by fitting b-splines to the 3-dimensional velocity and density distributions of halo stars obtained by the gaia survey and spectroscopic surveys such as desi. while most implementations of the jeans method assume parametric forms for these profiles, b-splines provide non-parametric fitting curves and make no sacrifice in the convenience or accuracy of their derivatives. despite jeans modeling's prevalence, there is little work quantifying the errors introduced when breaking the assumptions of spherical symmetry and dynamical equilibrium. we validate our routine on several progressively more complex and realistic mock datasets that break these assumptions. we find that our spherical jeans routine recovers the mass profiles of even quite flattened halos and systems including a stellar disk and bulge very well (<5% error). however, our tests with a mock data set from the cosmological hydrodynamic auriga simulations (galaxy 6), yield significantly larger errors on the mass profile (~30%). this larger error suggests that the output of spherical jeans modeling is more sensitive to deviations from dynamical equilibrium and the presence of substructure in the halo than deviations from sphericity. this work is funded in part by nasa grants nnx15ak79g and 80nssc20k0509 and a micde catalyst grant. | non-parametric spherical jeans mass estimation with b-splines |
we present mid-ir observations taken with canaricam at gran telescopio canarias of the quadruply lensed quasar qso2237+0305. we have obtained flux ratios between the four images that, unlike optical, near-ir and, to a lesser extent, radio emission, are unaffected by the ism (extinction/scattering) or stellar microlensing. we are using these flux ratios to obtain a mass model for the lensing galaxy and test for the presence of cdm substructure. we also compare these ``true" ratios to the (stellar) microlensed flux ratios observed in the optical/near-ir to constrain the structure of the quasar accretion disk and the fraction of the lens mass in stars as compared to dark matter. | observations of the einstein cross with canaricam |
orbits of individual stars in the milky way trace the underlying gravitational potential, and as such, they provide a unique insight into the distribution of matter in our galaxy. large astronomical projects like gaia, sdss and desi are now measuring precise motions of stars deep into the dark matter-dominated outer regions of our galaxy. i will discuss how these measurements allow us to precisely reconstruct the 3d distribution of dark matter throughout the galaxy, and for the first time, open the possibility of identifying individual dark-matter substructures. | reconstruction of the dark matter distribution in the milky way |
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