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We study the satellite plane problem of the Milky Way (MW) by using the recently published simulation data of TNG50-1. Here, we only consider the satellite plane consisting of the brightest 14 MW satellites (11 classical satellites plus Canes Venatici I, Crater II, and Antlia II). One halo (haloID = 395, at z = 0, hereafter halo395) of 231 MW-like candidates possesses a satellite plane as spatially thin and kinematically coherent as the observed one has been found. Halo395 resembles the MW in a number of intriguing ways: it hosts a spiral central galaxy, and its satellite plane is almost (∼87°) perpendicular to the central stellar disk. In addition, halo395 is embedded in a sheet plane, with a void on the top and bottom, similar to the local environment of MW. More interestingly, we found that 11 of the 14 of the satellites on the plane of halo395 arise precisely from the peculiar geometry of its large-scale environment (e.g., sheet and voids). The remaining three members appeared at the right place with the right velocity by chance at z = 0. Our results support previous studies wherein the satellite plane problem is not seen as a serious challenge to the ΛCDM model and its formation is ascribed to the peculiarities of our environment. [ABSTRACT FROM AUTHOR]

The Fourier transformation is an effective and efficient operation of Gaussianization at the one-point level. Using a set of N -body simulation data, we verified that the one-point distribution functions of the dark matter momentum divergence and density fields closely follow complex Gaussian distributions. The one-point distribution function of the quotient of two complex Gaussian variables is introduced and studied. Statistical theories are then applied to model one-point statistics about the growth of individual Fourier modes of the dark matter density field, which can be obtained by the ratio of two Fourier-transformed cosmic fields. Our simulation results proved that the models based on the Gaussian approximation are impressively accurate, and our analysis revealed many interesting aspects of the growth of dark matter’s density fluctuation in Fourier space. [ABSTRACT FROM AUTHOR]

We present starduster, a supervised deep-learning model that predicts the multiwavelength spectral energy distribution (SED) from galaxy geometry parameters and star formation history by emulating dust radiative transfer simulations. The model is composed of three specifically designed neural networks, which take into account the features of dust attenuation and emission. We utilize the skirt radiative transfer simulation to produce data for the training data of neural networks. Each neural network can be trained using ∼4000â€"5000 samples. Compared with the direct results of the skirt simulation, our deep-learning model produces ∼0.005 mag and ∼0.1â€"0.2 mag errors for dust attenuation and emission, respectively. As an application, we fit our model to the observed SEDs of IC 4225 and NGC 5166. Our model can reproduce the observations and provide reasonable measurements of the inclination angle and stellar mass. However, some predicted geometry parameters are different from an image-fitting study. Our analysis implies that including a constraint at (rest-frame) ∼40 ÎĽ m could alleviate the degeneracy in the parameter space for both IC 4225 and NGC 5166, leading to broadly consistent results with the image-fitting predictions. Our SED code is publicly available and can be applied to both SED fitting and SED modeling of galaxies from semianalytic models. [ABSTRACT FROM AUTHOR]

A rare population of massive disk galaxies have been found to invade the red sequence dominated by early-type galaxies. The formation and origins of these red/quenched massive disk galaxies have recently gained great interest. The quenching mechanisms that are usually proposed, such as bar quenching and environment quenching, do not seem to be suitable for those bulgeless quenched disks in a low-density environment. In this paper, we use the TNG300 simulation to investigate the formation of massive quenched central disk galaxies. It is found that these galaxies contain less gas than their star-forming counterparts and harbor giant super massive black holes (SMBHs; above 108 M ⊙). By tracing their formation history, we found that quenched disk galaxies formed early and preserved disk morphology for cosmological timescales. They have experienced less than one major merger on average, and mini-mergers (mass ratio <1/10) have mainly contributed to the growth of their SMBHs. In the IllustrisTNG simulation, the black hole feedback mode switches from thermal to kinetic feedback when the black hole mass is more massive than ∼108 M ⊙, which is more efficient to eject gas outside of the galaxy and to suppress further cooling of the hot gaseous halo. We conclude that the dominant quenching mechanism in massive red/quenched disk galaxies is kinetic active galactic nuclei feedback. [ABSTRACT FROM AUTHOR]

Satellites are not randomly distributed around their central galaxies but show polar and planar structures. In this paper, we investigate the axis asymmetry or lopsidedness of satellite galaxy distributions around isolated galaxies in a hydrodynamic cosmological simulation. We find a statistically significant lopsided signal by studying the angular distribution of the satellite galaxies' projected positions around isolated central galaxies in a two-dimensional plane. The signal is dependent on galaxy mass, color, and large-scale environment. Satellites that inhabit low-mass blue hosts, or located further from the hosts, show the most lopsided signal. Galaxy systems with massive neighbors exhibit stronger lopsidedness. This satellite axis-asymmetry signal also decreases as the universe evolves. Our findings are in agreement with recent observational results and they provide a useful perspective for studying galaxy evolution, especially on the satellite accretion, internal evolution, and interaction with the cosmic large-scale structure. [ABSTRACT FROM AUTHOR]

We present a new study of the merger dynamics of A1775 by analyzing the high-quality Chandra and XMM-Newton archival data. We confirm/identify an arc-shaped edge (i.e., the head) at ∼48 kpc west of the X-ray peak, a split cold gas tail that extends eastward to ∼163 kpc, and a plume of spiral-like X-ray excess (within about 81–324 kpc northeast of the cluster core) that connects to the end of the tail. The head, across which the projected gas temperature rises outward from to keV, is found to be a cold front with a Mach number of. Along the surfaces of the cold front and tail, typical Kelvin–Helmholtz instability features (noses and wings, etc.) are found and are used to constrain the upper limit of the magnetic field (∼11.2 μG) and the viscosity suppression factor (∼0.01). Combining optical and radio evidence, we propose a two-body merger (instead of systematic motion in a large-scale gas environment) scenario and have carried out idealized hydrodynamic simulations to verify it. We find that the observed X-ray emission and temperature distributions can be best reproduced with a merger mass ratio of 5 after the first pericentric passage. The NAT radio galaxy is thus more likely to be a single galaxy falling into the cluster center at a relative velocity of 2800 km s−1, a speed constrained by its radio morphology. The infalling subcluster is expected to have a relatively low gas content, because only a gas-poor subcluster can cause central-only disturbances as observed in such an off-axis merger. [ABSTRACT FROM AUTHOR]

The complicated story of the Cetus Stream (CS) is recently revealed by its newly discovered ∼150 members with 6D kinematics from the cross-matched catalog of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR5 K giants and Gaia DR2. It exhibits a very diffuse structure at heliocentric distances between 20 and 50 kpc, extending over at least 100°, and crossing the Galactic plane. Interestingly, The CS is dynamically linked to a massive globular cluster, NGC 5824. A suggestive scenario is that NGC 5824 was the nuclear star cluster of the dwarf progenitor of the CS. We explore this scenario by modeling the disruption process of a dwarf galaxy in the Milky Way potential, on the orbit of NGC 5824, using a suite of N-body simulations. Our results show that the simulated stream can marginally recover the main component of the CS, which is the densest part of the observed stream. Inspired by this mismatch, we use a dwarf progenitor following the representative orbit of the main component members, and find it can reproduce the general morphology of the CS. This gives us a more favorable scenario of the CS progenitor, in which NGC 5824 was not the core, but located off-center. Our fiducial model also predicts a vast extension of the CS in the South, surprisingly coincident with a newly discovered wide southern stream "Palca." Another more diffuse substructure, the Eridanus–Phoenix overdensity is also likely to be related to the CS progenitor. [ABSTRACT FROM AUTHOR]

Mass segregation, a tendency for more massive galaxies to be distributed closer to the cluster center, is naturally expected from dynamical friction, but its presence is still controversial. Using deep optical observations of 14 Abell clusters (KYDISC) and a set of hydrodynamic simulations (YZiCS), we find in some cases a hint of mass segregation inside the virial radius. Segregation is visible more clearly when the massive galaxy fraction is used instead of mean stellar mass. The trend is more significant in the simulations than in the observations. To find out the mechanisms affecting mass segregation, we look into the evolution of individual simulated clusters. We find that the degree of mass segregation is different for different clusters: the trend is visible only for low-mass clusters. We compare the masses of galaxies and their dark halos at the time of infall and at the present epoch to quantify the amount of tidal stripping. We then conclude that satellites that get accreted at earlier epochs, or galaxies in more massive clusters, go through more tidal stripping. These combined effects result in a correlation between the host halo mass and the degree of stellar mass segregation. [ABSTRACT FROM AUTHOR]

Galaxies, as well as their satellites, are known to form within the cosmic web, the large, multi-scale distribution of matter in the universe. It is known that the surrounding large-scale structure (LSS) can impact and influence the formation of galaxies, e.g., the spin and shape of halos or galaxies are correlated with the LSS and the correlation depends on halo mass or galaxy morphology. In this work, we use group and filament catalogs constructed from the SDSS DR12 to investigate the correlation between satellite systems and the large-scale filaments they are located in. We find that the distribution of satellites is significantly correlated with filaments, namely the major axis of the satellite systems are preferentially aligned with the spine of the closest filament. Stronger alignment signals are found for the cases where the system is far from the filament spine, while systems close to the filament spine show significantly weaker alignment. Our results suggest that satellites are accreted along filaments, which agrees with previous works. The case where the system is far from the filament spine may help us to understand how the filament forms as well as the peculiar satellite distribution in the local universe. [ABSTRACT FROM AUTHOR]

Analysis of the Pangu N-body simulation validates that the bulk flow of halos follows a Maxwellian distribution with variance that is consistent with the prediction of the linear theory of structure formation. We propose that the consistency between the observed bulk velocity and theories should be examined at the effective scale of the radius of a spherical top-hat window function yielding the same smoothed velocity variance in linear theory as the sample window function does. We compared some recently estimated bulk flows from observational samples with the prediction of the ΛCDM model we used; some results deviate from expectation at a level of ∼3σ, but the discrepancy is not as severe as previously claimed. We show that bulk flow is only weakly correlated with the dipole of the internal mass distribution, that the alignment angle between the mass dipole and the bulk flow has a broad distribution peaked at ∼30°-50°, and also that the bulk flow shows little dependence on the mass of the halos used in the estimation. In a simulation of box size 1 h–1 Gpc, for a cell of radius 100 h–1 Mpc the maximal bulk velocity is >500 km s–1; dipoles of the environmental mass outside the cell are not tightly aligned with the bulk flow, but are rather located randomly around it with separation angles ∼20°-40°. In the fastest cell there is a slightly smaller number of low-mass halos; however, halos inside are clustered more strongly at scales ≳ 20 h–1 Mpc, which might be a significant feature since the correlation between bulk flow and halo clustering actually increases in significance beyond such scales. [ABSTRACT FROM AUTHOR]