Abstract
The core–cusp problem is one of the controversial issues in the standard paradigm of Λ cold dark matter (ΛCDM) theory. However, under the assumption of conventional spherical symmetry, the ...strong degeneracy among model parameters makes it unclear whether dwarf spheroidal (dSph) galaxies indeed have cored dark matter density profiles at their centers. In this work, we revisit this problem using nonspherical mass models, which have the advantage of being able to alleviate the degeneracy. Applying our mass models to the currently available kinematic data of the eight classical dSphs, we find that within finite uncertainties, most of these dSphs favor cusped central profiles rather than cored ones. In particular, Draco has a cusped dark matter halo with high probability even considering a prior bias. We also find the diversity of the inner slopes in their dark matter halos. To clarify the origin of this diversity, we investigate the relation between the inner dark matter density slope and stellar-to-halo mass ratio for the sample dSphs and find that this relation is generally in agreement with the predictions from recent ΛCDM and hydrodynamical simulations. We also find that the simulated subhalos have an anticorrelation between the dark matter density at 150 pc and pericenter distance, which is consistent with the observed one. We estimate their astrophysical factors for dark matter indirect searches and circular velocity profiles associated with huge uncertainties. To more precisely estimate their dark matter profiles, wide-field spectroscopic surveys for the dSphs are essential.
Abstract
Recent advances in photon detectors have provided exceptional sensitivities to dark matter with high angular resolution. Motivated by this, we present a detailed study of photon flux from ...dark matter decay in dwarf spheroidal galaxies (dSphs) by focusing on the detectors with arcsecond-level field of view and/or angular resolution. We propose to use differential
D
-factors since such detectors are sensitive to their dark matter distributions. We carefully estimate the differential
D
-factors of 35 dSphs. By using the differential
D
-factors, it turns out that the resulting signal flux can have a more than
O
(1–10) enhancement compared to conventional estimations. Based on this analysis, we find that the Infrared Camera and Spectrograph (IRCS) installed on the 8.2 m Subaru Telescope can be an excellent dark matter detector for the mass in the eV range, particularly axion-like particles (ALPs). Observing the Draco or Ursa Major II dSphs with the IRCS for
O
(
1
)
night will enable us to place the most stringent bound for the ALP dark matter in the mass range of 1 eV ≲
m
a
≲ 2 eV.
ABSTRACT NGC 1052-DF2 was recently discovered as the dark-matter-deficient galaxy claimed by van Dokkum et al. However, large uncertainties on its dynamical mass estimate have been pointed out, ...concerning the paucity of sample, statistical methods, and distance measurements. In this work, we discuss the effects of the difference in modelling of the tracer profile of this galaxy on the dynamical mass estimate. To do this, we assume that the tracer densities are modelled with power-law and Sérsic profiles, and then we solve the spherical Jeans equation to estimate the dynamical mass. Applying these models to kinematic data of globular clusters in NGC 1052-DF2, we compare 90 per cent upper limits of dynamical mass-to-light ratios estimated from this analysis and from van Dokkum et al. We find that the upper limit obtained by the power-law is virtually the same as the result from van Dokkum et al, whilst this limit estimated by the Sérsic is significantly greater than that from van Dokkum et al, thereby suggesting that NGC 1052-DF2 can still be a dark-matter-dominated system. Consequently, we propose that dynamical mass estimate of a galaxy is largely affected by not only the small kinematic sample but the choice of tracer distributions, and thus the estimated mass still remains quite uncertain.
A microscopic model of interacting oscillators, which admits two conserved quantities, volume, and energy, is investigated. We begin with a system driven by a general nonlinear potential under ...high-temperature regime by taking the inverse temperature of the system asymptotically small. As a consequence, one can extract a principal part (by a simple Taylor expansion argument), which is driven by the harmonic potential, and we show that previous results for the harmonic chain are covered with generality. We consider two fluctuation fields, which are defined as a linear combination of the fluctuation fields of the two conserved quantities, volume, and energy, and we show that the fluctuations of one field converge to a solution of an additive stochastic heat equation, which corresponds to the Ornstein–Uhlenbeck process, in a weak asymmetric regime, or to a solution of the stochastic Burgers equation, in a stronger asymmetric regime. On the other hand, the fluctuations of the other field cross from an additive stochastic heat equation to a fractional diffusion equation given by a skewed Lévy process.
Abstract
Elucidating dark matter density profiles in Galactic dwarf satellites is essential to understanding not only the quintessence of dark matter, but also the evolution of the satellites ...themselves. In this work, we present the current constraints on dark matter densities in Galactic ultrafaint dwarf (UFD) and diffuse galaxies. Applying our constructed nonspherical mass models to the currently available kinematic data of the 25 UFDs and two diffuse satellites, we find that whereas most of the galaxies have huge uncertainties on the inferred dark matter density profiles, Eridanus II, Segue I, and Willman 1 favor cuspy central profiles even when considering effects of a prior bias. We compare our results with the simulated subhalos on the plane between the dark matter density at 150 pc and the pericenter distance. We find that the most observed satellites and the simulated subhalos are similarly distributed on this plane, except for Antlia 2, Crater 2, and Tucana 3, which are less than one-tenth of the density. Despite considerable tidal effects, the subhalos detected by commonly used subhalo finders have difficulty explaining such a huge deviation. We also estimate the dynamical mass-to-light ratios of the satellites and confirm the ratio is linked to stellar mass and metallicity. Tucana 3 deviates largely from these relations, while it follows the mass–metallicity relation. This indicates that Tucana 3 has a cored dark matter halo, despite a significant uncertainty in its ratios.
ABSTRACT
In the fuzzy dark matter (FDM) model, gravitationally collapsed objects always consist of a solitonic core located within a virialized halo. Although various numerical simulations have ...confirmed that the collapsed structure can be described by a cored Navarro–Frenk–White-like density profile, there is still disagreement about the relation between the core mass and the halo mass. To fully understand this relation, we have assembled a large sample of cored haloes based on both idealized soliton mergers and cosmological simulations with various box sizes. We find that there exists a sizeable dispersion in the core–halo mass relation that increases with halo mass, indicating that the FDM model allows cores and haloes to coexist in diverse configurations. We provide a new empirical equation for a core–halo mass relation with uncertainties that can encompass all previously found relations in the dispersion, and emphasize that any observational constraints on the particle mass m using a tight one-to-one core–halo mass relation should suffer from an additional uncertainty of the order of 50 per cent for halo masses ${\gtrsim} 10^9 \, 8\times 10^{-23} \, \mathrm{eV}/(mc^2)^{3/2} \, \mathrm{M}_\odot$. We suggest that tidal stripping may be one of the effects contributing to the scatter in the relation.
The dwarf spheroidal galaxies (dSphs) in the Milky Way are the primary targets in the indirect searches for particle dark matter. To set robust constraints on candidate dark matter particles, ...understanding the dark halo structure of these systems is of substantial importance. In this paper, we first evaluate the astrophysical factors for dark matter annihilation and decay for 24 dSphs, taking into account a non-spherical dark halo, using generalized axisymmetric mass models based on axisymmetric Jeans equations. First, from a fitting analysis of the most recent kinematic data available, our axisymmetric mass models are a much better fit than previous spherical ones, thus, our work should be the most realistic and reliable estimator for astrophysical factors. Secondly, we find that among analysed dSphs, the ultra-faint dwarf galaxies Triangulum II and Ursa Major II are the most promising but large uncertain targets for dark matter annihilation while the classical dSph Draco is the most robust and detectable target for dark matter decay. It is also found that the non-sphericity of luminous and dark components influences the estimate of astrophysical factors, even though these factors largely depend on the sample size, the prior range of parameters and the spatial extent of the dark halo. Moreover, owing to these effects, the constraints on the dark matter annihilation cross-section are more conservative than those of previous spherical works. These results are important for optimizing and designing dark matter searches in current and future multi-messenger observations by space and ground-based telescopes.
Abstract
We present a new observation of satellite galaxies around seven Milky Way (MW)–like galaxies located outside of the Local Group (LG) using Subaru/Hyper Suprime-Cam imaging data to ...statistically address the missing satellite problem. We select satellite galaxy candidates using magnitude, surface brightness, Sérsic index, axial ratio, FWHM, and surface brightness fluctuation cuts, followed by visual screening of false positives such as optical ghosts of bright stars. We identify 51 secure dwarf satellite galaxies within the virial radius of nine host galaxies, two of which are drawn from the pilot observation presented in Paper I. We find that the average luminosity function of the satellite galaxies is consistent with that of the MW satellites, although the luminosity function of each host galaxy varies significantly. We observe an indication that more massive hosts tend to have a larger number of satellites. Physical properties of the satellites such as the size–luminosity relation are also consistent with the MW satellites. However, the spatial distribution is different; we find that the satellite galaxies outside of the LG show no sign of concentration or alignment, while that of the MW satellites is more concentrated around the host and exhibits a significant alignment. As we focus on relatively massive satellites with
M
V
< −10, we do not expect that the observational incompleteness can be responsible here. This trend might represent a peculiarity of the MW satellites, and further work is needed to understand its origin.
Most of the existing analysis methods for tensors (or multi-way arrays) only assume that tensors to be completed are of low rank. However, for example, when they are applied to tensor completion ...problems, their prediction accuracy tends to be significantly worse when only a limited number of entries are observed. In this paper, we propose to use relationships among data as auxiliary information in addition to the low-rank assumption to improve the quality of tensor decomposition. We introduce two regularization approaches using graph Laplacians induced from the relationships, one for moderately sparse cases and the other for extremely sparse cases. We also give present two kinds of iterative algorithms for approximate solutions: one based on an EM-like algorithms which is stable but not so scalable, and the other based on gradient-based optimization which is applicable to large scale datasets. Numerical experiments on tensor completion using synthetic and benchmark datasets show that the use of auxiliary information improves completion accuracy over the existing methods based only on the low-rank assumption, especially when observations are sparse.
Dwarf spheroidals are low-luminosity satellite galaxies of the Milky Way highly dominated by dark matter (DM). Therefore, they are prime targets to search for signals from dark matter annihilation ...using gamma-ray observations. While the typical assumption is that the dark matter density profile of these satellite galaxies can be described by a spherical symmetric Navarro-Frenk-White (NFW) profile, recent observational data of stellar kinematics suggest that the DM halos around these galaxies are better described by axisymmetric profiles. Motivated by such evidence, we analyze about seven years of pass8 Fermi data for seven classical dwarf galaxies, including Draco, adopting both the widely used NFW profile and observationally motivated axisymmetric density profiles. For four of the selected dwarfs (Sextans, Carina, Sculptor and Fornax), axisymmetric mass models suggest a cored density profile rather than the commonly adopted cusped profile. We found that upper limits on the annihilation cross section for some of these dwarfs are significantly higher than the ones achieved using an NFW profile. Therefore, upper limits in the literature obtained using spherical symmetric cusped profiles, such as the NFW, might be overestimated. Our results show that it is extremely important to use observationally motivated density profiles going beyond the usually adopted NFW in order to obtain accurate constraints on the dark matter annihilation cross section.
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