We use $Λ$CDM cosmological hydrodynamical simulations to explore the kinematics of gaseous discs in late-type dwarf galaxies. We create high-resolution 21-cm 'observations' of simulated dwarfs produced in two variations of the EAGLE galaxy formation model: one where supernova-driven gas flows redistribute dark matter and form constant-density central 'cores', and another where the central 'cusps' survive intact. We 'observe' each galaxy along multiple sight lines and derive a rotation curve for each observation using a conventional tilted-ring approach to model the gas kinematics. We find that the modelling process introduces systematic discrepancies between the recovered rotation curve and the actual circular velocity curve driven primarily by (i) non-circular gas orbits within the discs; (ii) the finite thickness of gaseous discs, which leads to overlap of different radii in projection; and (iii) departures from dynamical equilibrium. Dwarfs with dark matter cusps often appear to have a core, whilst the inverse error is less common. These effects naturally reproduce an observed trend which other models struggle to explain: late-type dwarfs with more steeply-rising rotation curves appear to be dark matter-dominated in the inner regions, whereas the opposite seems to hold in galaxies with core-like rotation curves. We conclude that if similar effects affect the rotation curves of observed dwarfs, a late-type dwarf population in which all galaxies have sizeable dark matter cores is most likely incompatible with current measurements.
Cosmological simulations of the same spiral galaxy: satellite properties, the role of baryonic physics and star formation history in shaping dark matter cores/cusps
We use a compilation of disc galaxy rotation curves to assess the role of the luminous component ("baryons") in the rotation curve diversity problem. As in earlier work, we find that rotation curve shape correlates with baryonic surface density: high surface density galaxies have rapidly-rising rotation curves consistent with cuspy cold dark matter halos; slowly-rising rotation curves (characteristic of galaxies with inner mass deficits or "cores") occur only in low surface density galaxies. The correlation, however, seems too weak to be the main driver of the diversity. In addition, dwarf gal…
Cusp-to-Core Transition of Dark Matter Halos across Galaxy Mass Scales
National Institute of Technology, Sendai College（仙台高等专门学校）；Astronomical Institute, Tohoku University（东北大学天文研究所）；ICRR, The University of Tokyo（东京大学宇宙线研究所）；Graduate School of Science and Technology, University of Tsukuba（筑波大学理工学研究科）；Center for Computational Sciences , University of Tsukuba（筑波大学计算科学中心）
The existence of two kinematically and chemically distinct stellar subpopulations in the Sculptor and Fornax dwarf galaxies offers the opportunity to constrain the density profile of their matter haloes by measuring the mass contained within the well-separated half-light radii of the two metallicity subpopulations. Walker and Penarrubia have used this approach to argue that data for these galaxies are consistent with constant-density `cores' in their inner regions and rule out `cuspy' Navarro-Frenk-White (NFW) profiles with high statistical significance, particularly in the case of Sculptor. W…
An extensive catalog of spatially-resolved galaxy rotation curves and multi-band optical light profiles for 1752 observed spiral galaxies is assembled to explore the drivers of diversity in galaxy structural parameters, rotation curve shapes, and stellar mass profiles. Similar data were extracted from the NIHAO galaxy simulations to identify any differences between observations and simulations. Several parameters, including the inner slope "S" of a rotation curve (RC), were tested for diversity. Two distinct populations are found in observed and simulated galaxies; (i) blue, low mass spirals w…
The core-cusp problem is one of the controversial issues in the standard paradigm of $Λ$ cold dark matter ($Λ$CDM) 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 the centers. In this work, we revisit this problem using non-spherical 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 t…
We compare proposed solutions to the core vs cusp issue of spiral galaxies, which has also been framed as a diversity problem, and demonstrate that the cuspiness of dark matter halos is correlated with the stellar surface brightness. We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM). The SIDM model predicts a strong correlation between the core size and the stellar surface density, and it provides th…
Bursty star formation in dwarf galaxies can slowly transform a steep dark matter cusp into a constant density core. We explore the possibility that globular clusters (GCs) retain a dynamical memory of this transformation. To test this, we use the nbody6df code to simulate the dynamical evolution of GCs, including stellar evolution, orbiting in static and time-varying potentials for a Hubble time. We find that GCs orbiting within a cored dark matter halo, or within a halo that has undergone a cusp-core transformation, grow to a size that is substantially larger ($R_{\rm eff} > 10$ pc) than thos…
The Characteristic Mass and Energy Conversion Efficiency in the Cusp-Core Transition of Dark Matter Haloes: Implications for Scaling Relations and Supernova feedbacks
University of Tsukuba（筑波大学）；National Institute of Technology, Sendai College（国立仙台高等专门学校）；Tohoku University（东北大学）；The University of Tokyo（东京大学）
We characterize the photometric and kinematic properties of simulated early-type galaxy (ETG) stellar halos, and compare them to observations. We select a sample of ~1200 ETGs in the TNG100 and TNG50 simulations, spanning a stellar mass range of $10^{10.3}-10^{12}M_{\odot}$ and within the range of (g-r) colour and lambda-ellipticity diagram populated by observed ETGs. We determine photometric parameters, intrinsic shapes, and kinematic observables in their extended stellar halos. We study the variation in kinematics from center to halo and connect it to a change in the intrinsic shape of the g…
We test a non-parametric higher-order Jeans analysis method, GravSphere, on 32 simulated dwarf galaxies comparable to classical Local Group dwarfs like Fornax. The galaxies are selected from the APOSTLE suite of cosmological hydrodynamics simulations with Cold Dark Matter (CDM) and Self-Interacting Dark Matter (SIDM) models, allowing us to investigate cusps and cores in density distributions. We find that, for CDM dwarfs, the recovered enclosed mass profiles have a bias of no more than 10 per cent, with a 50 per cent scatter in the inner regions and a 20 per cent scatter near the half-light ra…
We present a suite of 16 high-resolution hydrodynamic simulations of an isolated dwarf galaxy (gaseous and stellar disk plus a stellar bulge) within an initially cuspy dark matter (DM) halo, including self-interactions between the DM particles (SIDM); as well as stochastic star formation and subsequent supernova feedback (SNF), implemented using the stellar feedback model SMUGGLE. The simulations start from identical initial conditions and we regulate the strength of SIDM and SNF by systematically varying the SIDM momentum transfer cross section and the gas density threshold for star formation…
In the standard Lambda cold dark matter paradigm, pure dark matter simulations predict dwarf galaxies should inhabit dark matter haloes with a centrally diverging density `cusp'. This is in conflict with observations that typically favour a constant density `core'. We investigate this `cusp-core problem' in `ultra-faint' dwarf galaxies simulated as part of the `Engineering Dwarfs at Galaxy formation's Edge' (EDGE) project. We find, similarly to previous work, that gravitational potential fluctuations within the central region of the simulated dwarfs kinematically heat the dark matter particles…
Dark matter haloes from dwarf to massive galaxies: no systematic inner-density tension with ΛCDM hydrodynamical simulations
Leiden University（莱顿大学）；University of Surrey（萨里大学）；Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Universidad de La Laguna（拉帕鲁纳大学）；Stockholm University（斯德哥尔摩大学）
Numerical simulations within a cold dark matter (DM) cosmology form halos whose density profiles have a steep inner slope (`cusp'), yet observations of galaxies often point towards a flat central `core'. We develop a convolutional mixture density neural network model to derive a probability density function (PDF) of the inner density slopes of DM halos. We train the network on simulated dwarf galaxies from the NIHAO and AURIGA projects, which include both DM cusps and cores: line-of-sight velocities and 2D spatial distributions of their stars are used as inputs to obtain a PDF representing the…
We examine the origin of scatter in the relationship between the gas fraction and mass of dark matter haloes hosting present-day $\sim L^\star$ central galaxies in the EAGLE simulations. The scatter is uncorrelated with the accretion rate of the central galaxy's black hole (BH), but correlates strongly and negatively with the BH's mass, implicating differences in the expulsion of gas by active galactic nucleus feedback, throughout the assembly of the halo, as the main cause of scatter. Haloes whose central galaxies host undermassive BHs also tend to retain a higher gas fraction, and exhibit el…
Cosmological simulations of structure formation are invaluable to study the evolution of the Universe and the development of galaxies in it successfully reproducing many observations in the context of the cosmological paradigm $Λ$CDM. However, there are remarkable discrepancies with observations that are a matter of debate. One of the most recently reported is the diversity of shapes in the rotation curves of dwarf galaxies in the local Universe which is in contrast to the apparent homogeneity of rotation curves in cosmological hydrodynamic simulations. Previous studies on similar problems hav…
Dark matter-baryon scaling relations in galaxies are important in order to constrain galaxy formation models. Here, we provide a modern quantitative assessment of those relations, by modelling the rotation curves of galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database with the Einasto dark halo model. We focus in particular on the comparison between the original SPARC parameters, with constant mass-to-light ratios for bulges and disks, and the parameters for which galaxies follow the tightest radial acceleration relation. We show that fits are improved in the seco…
Milky Way (MW) satellites reside within dark matter (DM) subhalos with a broad distribution of circular velocity profiles. This diversity is enhanced with the inclusion of ultra-faint satellites, which seemingly have very high DM densities, albeit with large systematic uncertainties. We argue that if confirmed, this large diversity in the MW satellite population poses a serious test for the structure formation theory with possible implications for the DM nature. For the Cold Dark Matter model, the diversity might be a signature of the combined effects of subhalo tidal disruption by the MW disk…
The Atlas3D project - XXVI. HI discs in real and simulated fast and slow rotators
室女座外四分之一的早期型星系（ETG）拥有HI盘/环，大小从几到几十kpc，质量高达~ 1 e +9太阳质量。在这里，我们调查是否这个HI是相关的主机内的恒星盘的存在下，利用ETG的分类在快速和慢速旋转（FR/SR）。我们发现一个大的多样性HI群众和形态在这两个家庭。令人惊讶的是，SR经常被检测到，宿主与FR一样多的HI，并且具有与FR相似的HI盘/环比率。因此，HI的吸积并不总是与内部恒星盘的生长有关。HI和恒星盘之间的弱关系证实了他们频繁的运动学失调的FR，包括极性和反向旋转气体的情况下。在SR中，HI通常是极性的。这幅复杂的图片突出了ETG形成历史的多样性，这些历史可能会在其内部结构的相对简单性中丢失，并在研究其外部区域时出现。我们发现，LCDM流体动力学模拟再现ETGs的HI属性有困难。在模拟中形成的气体盘要么太大，要么太小，这取决于恒星形成反馈的实现。运动学上的不对准只在定性上与观测结果相匹配。冲突的主要点是，几乎所有的模拟FR和所有的模拟SR主机共转HI的大部分。这确立了ETG的HI特性作为对模拟的新挑战。
SIRIUS: The relation between the diversity of dwarf galaxies and their formation histories
The University of Tokyo（东京大学）；Kobe University（神户大学）；Center for Planetary Science (CPS), Graduate School of Science, Kobe University（神户大学行星科学中心）；Tohoku University of Community Service and Science（东北社区服务科学大学）
The low dark matter density in the Fornax dwarf galaxy is often interpreted as being due to the presence of a constant density `core', but it could also be explained by the effects of Galactic tides. The latter interpretation has been disfavoured because it is apparently inconsistent with the orbital parameters and star formation history of Fornax. We revisit these arguments with the help of the APOSTLE cosmological hydrodynamics simulations. We show that simulated dwarfs with similar properties to Fornax are able to form stars after infall, so that star formation is not necessarily a good tra…
Apparent deviations between properties of dwarf galaxies from observations and simulations are known to exist, such as the "Missing Dwarfs" problem, the too-big-to-fail problem, and the cusp-core problem, to name a few. Recent studies have shown that these issues can at least be partially resolved by taking into account the systematic differences between simulations and observations. This work aims to investigate and address any systematic differences affecting the comparison of simulations with observations. To this aim, we analyzed a set of 24 realistically simulated MoRIA (Models of Realist…
