Halo Region Research Articles

Stellar stripping efficiencies of satellites in numerical simulations: the effect of resolution, satellite properties and numerical disruption

Abstract The stellar stripping of satellites in cluster haloes is understood to play an important role in the production of intracluster light. Increasingly, cosmological simulations have been utilised to investigate its origin and assembly. However, such simulations typically model individual galaxies at relatively coarse resolutions, raising concerns about their accuracy. Although there is a growing literature on the importance of numerical resolution for the accurate recovery of the mass loss rates of dark matter (DM) haloes, there has been no comparable investigation into the numerical resolution required to accurately recover stellar mass loss rates in galaxy clusters. Using N-body simulations of satellite galaxies orbiting in a cluster halo represented by a static external potential, we conduct a set of convergence tests in order to explore the role of numerical resolution and force softening length on stellar stripping efficiency. We consider a number of orbital configurations, satellite masses and satellite morphologies. We find that stellar mass resolution is of minor importance relative to DM resolution. Resolving the central regions of satellite DM halos is critical to accurately recover stellar mass loss rates. Poorly resolved DM haloes develop cored inner profiles and, if this core is of comparable size to the stellar component of the satellite galaxy, this leads to significant over-stripping. To prevent this, relatively high DM mass resolutions of around MDM ∼ 106 M⊙, better than those achieved by many contemporary cosmological simulations, are necessary.

Gravitational lensing around dark matter in galactic halo region

The presence of dark matter in the galactic region has decisively confirmed by astronomical observations , however, the characteristics of dark matter yet to be recognized correctly. Utilizing the Einstein’s general theory of relativity and the observed rotational curve profile as input, we point out some features of galactic dark matter. Usually, dark matter is not directly visible but affects the lensing. In this paper, the deflection of a massive particle by galactic dark matter is studied using the Jacobi metric approach. We also provide a brief analysis of the image features of the deflection angle.

Exploring faint white dwarfs and the luminosity function with Subaru HSC and SDSS in Stripe 82

Abstract We present 5,080 white dwarf (WD) candidates selected from stars matching between the multi-band imaging datasets of the Subaru Hyper Suprime-Cam (HSC) Survey and the Sloan Digital Sky Survey (SDSS) in the Stripe82 region covering about 165 deg2. We select WD candidates from the “reduced proper motion” diagram by combining the apparent magnitude in the range i = 19 – 24 and the proper motion measured from the datasets among a baseline of ∼ 14 years. We refine the WD candidates by fitting blackbody and template WD atmosphere models to HSC photometries for each candidate, enabling the estimation of distance and tangential velocity (vt). The deep HSC data allow us to identify low-temperature (<4000 K) and faint WD candidates down to absolute magnitude, Mbol ≃ 17. We evaluate the selection function of our WD candidates using a mock catalogue of spatial and kinematic distributions of WDs in the (thin and thick) disc and halo regions based on a Galactic model. We construct samples of disc and halo WD candidates by selecting WDs with tangential velocity, 40 < vt/[km s−1] < 80 and 200 < vt/[km s−1] < 500, respectively. The total number densities of the disc and halo WDs are (9.33 ± 0.89) × 10−3 pc−3 and (6.34 ± 2.90) × 10−4 pc−3. Our luminosity functions (LF) extend down to fainter absolute magnitudes compared with previous work. The faint WDs could represent the oldest generation of building blocks over the past ∼10 billion years of the assembly history of our Milky Way.

Galactic-Seismology Substructures and Streams Hunter with LAMOST and Gaia. I. Methodology and Local Halo Results

We present a novel, deep-learning-based method—dubbed Galactic-Seismology Substructures and Streams Hunter, or GS3 Hunter for short—to search for substructures and streams in stellar kinematics data. GS3 Hunter relies on a combined application of Siamese neural networks to transform the phase space information and the K-means algorithm for the clustering. As a validation test, we apply GS3 Hunter to a subset of the Feedback in Realistic Environments (FIRE) cosmological simulations. The stellar streams and substructures thus identified are in good agreement with corresponding results reported earlier by the FIRE team. In the same vein, we apply our method to a subset of local halo stars from the Gaia Early Data Release 3 and GALAH DR3 data sets and recover several previously known dynamical groups, such as Thamnos 1+2, the hot thick disk, ED-1, L-RL3, Helmi 1+2, Gaia-Sausage-Enceladus, Sequoia, Virgo Radial Merger, Cronus, and Nereus. Finally, we apply our method without fine-tuning to a subset of K giant stars located in the inner halo region, obtained from the LAMOST Data Release 5 data set. We recover three previously known structures (Sagittarius, Hercules-Aquila Cloud, and the Virgo Overdensity), but we also discover a number of new substructures. We anticipate that GS3 Hunter will become a useful tool for the community dedicated to the search for stellar streams and structures in the Milky Way (MW) and the Local Group, thus helping advance our understanding of the stellar inner and outer halos and the assembly and tidal stripping history in and around the MW.

Galaxy shapes in Magneticum

Context. Despite being one of the most fundamental properties of galaxies that dictate the form of the potential, the 3D shapes are intrinsically difficult to determine from observations. The improving quality of triaxial modeling methods in recent years has made it possible to measure these shapes more accurately. Aims. This study provides a comprehensive understanding of the stellar and dark matter (DM) shapes of galaxies and the connection between them. As these shapes are the result of the formation history of a galaxy, we investigate which galaxy properties they are correlated with, which will be especially useful for interpreting the results from dynamical modeling. Methods. Using the hydrodynamical cosmological simulation Magneticum Pathfinder Box4 (uhr), we computed the stellar and DM intrinsic shapes of 690 simulated galaxies with stellar masses above 2 × 1010 M⊙ at three different radii with an iterative unweighted method. We also determined their morphologies, their projected morphological and kinematic parameters, and their fractions of in situ formed stars. Results. The DM follows the stellar component in shape and orientation at three half-mass radii, indicating that DM is heavily influenced by the baryonic potential in the inner parts of the halo. The outer DM halo is independent of the inner properties such as the DM shape or galaxy morphology, however, and is more closely related to the large-scale anisotropy of the gas inflow. Overall, DM halo shapes are prolate, consistent with previous literature. The stellar shapes of galaxies are correlated with their morphology, with early-type galaxies featuring more spherical and prolate shapes than late-type galaxies out to 3 R1/2. Galaxies with more rotational support are flatter, and the stellar shapes are connected to the mass distribution, though not to the mass itself. In particular, more extended early-type galaxies have larger triaxialities at a given mass. Finally, the shapes can be used to better constrain the in situ fraction of stars when combined with the stellar mass. Conclusions. The relations between shape, mass distribution, and in situ formed star fraction of galaxies show that the shapes depend on the details of the accretion history through which the galaxies are formed. The similarities between DM and stellar shapes in the inner regions of galaxy halos signal the importance of baryonic matter for the behavior of DM in galaxies and will be of use for improving the underlying assumptions of dynamical models for galaxies in the future. However, at large radii the shapes of the DM are completely decoupled from the central galaxy, and their shapes and spin are coupled more to the large scale inflow than to the galaxy in the center.

Anisotropic model for dark matter halo with Hernquist density profile

Using the observed flat galactic rotation curve feature and taking into account the presence of anisotropic dark matter with a Hernquist density profile, the space-time geometry of the halo region in galaxies is derived. The gravitational field inside the halo is attractive in nature, and the resultant space-time is flat. We find that our solution affirms the existence of stable circular orbits in the dark halo region. The expression for the equation of state parameter indicates that the matter within the dark halo is non-exotic in nature. An analysis is also conducted on several other aspects of the solution.

The exosphere of Mars can be tracked by a high-spectral resolution telescope, such as the Line Emission Mapper

Abstract Mars provides our local analogue for unmagnetized terrestrial planets and is thus key to understanding the habitability of exoplanets. The lack of a global magnetic field means that the atmosphere interacts directly with the solar wind, causing significant loss of the atmosphere. While in situ measurements provide a wealth of detailed local information, they are limited in deriving the global picture. In contrast, remote X-ray observations can provide important global instantaneous coverage over multiple seasons and sampling different solar wind. Previous XMM-Newton observations have detected significant flux via the solar wind charge exchange emission (SWCX) mechanism from an extended planetary halo, and from atmospheric fluorescence. In contrast, Chandra observations only detected a low-luminosity disk and a faint halo. It is postulated that these observational differences are due to transient solar wind with increased heavy ion fractions. Here, we present simulated spectra for the proposed NASA mission Line Emission Mapper, of both halo and disk regions, under quiet and transient solar wind. We show that even under moderate solar wind conditions, both SWCX and fluorescence emission lines are readily detected above the background, providing new insights into the loss of planetary atmospheres and the molecular composition of less well-characterised atmospheric abundances.

Wormholes in dwarf and spiral galactic halo regions

In this article, we study solutions which describe wormholes in the halos of dwarf and massive spiral galaxies with different morphologies, masses, sizes and gas fractions by taking observed flat rotation curves as input. We assume Singular Isothermal Sphere (SIS) dark matter density profile. This result confirms the possible existence of wormholes in both dwarf and massive spiral galaxies.

Properties of Central Regions of the Dark Matter Halos in the Model with a Bump in the Power Spectrum of Density Perturbations

A surprisingly large number of galaxies with masses of ~109–1010\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{M}_{ \\odot }}$$\\end{document} at redshifts of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z \\geqslant 9$$\\end{document} are discovered with the James Webb Space Telescope. A possible explanation for the increase in the mass function can be the presence of a local maximum (bump) in the power spectrum of density perturbations on the corresponding scale. In this paper, it is shown that simultaneously with the growth of the mass function, galaxies from the bump region must have a higher density (compactness) compared to cosmological models without a bump. These more compact galaxies have been partially included in larger galaxies and have been subjected to tidal gravitational disruption. They have been less destructed than “ordinary” galaxies of the same mass, and some of them could survive to z = 0 and persist on the periphery of some galaxies. The formation and evolution of compact halos in a cube with a volume of (47 Mpc)3 with (1024)3 dark matter particles in the redshift range from 120 to 0 have been numerically simulated and observational implications of the presence of such galaxies in the current Universe have been discussed.

MHD Simulation in Galactic Center Region with Radiative Cooling and Heating

We investigate the role of magnetic field on the gas dynamics in a galactic bulge region by three-dimensional simulations with radiative cooling and heating. While a high-temperature corona with T > 106 K is formed in the halo regions, the temperature near the midplane is ≲104 K following the thermal equilibrium curve determined by the radiative cooling and heating. Although the thermal energy of the interstellar gas is lost by radiative cooling, the saturation level of the magnetic field strength does not significantly depend on the radiative cooling and heating. The magnetic field strength is amplified to 10 μG on average and reaches several hundred microgauss locally. We find the formation of magnetically dominated regions at midlatitudes in the case with the radiative cooling and heating, which is not seen in the case without radiative effect. The vertical thickness of the midlatitude regions is 50–150 pc at the radial location of 0.4–0.8 kpc from the Galactic center, which is comparable to the observed vertical distribution of neutral atomic gas. When we take the average of different components of energy density integrated over the galactic bulge region, the magnetic energy is comparable to the thermal energy. We conclude that the magnetic field plays a substantial role in controlling the dynamical and thermal properties of the galactic bulge region.

Characterizing structure formation through instance segmentation

Dark matter haloes form from small perturbations to the almost homogeneous density field of the early universe. Although it is known how large these initial perturbations must be to form haloes, it is rather poorly understood how to predict which particles will end up belonging to which halo. However, it is this process that determines the Lagrangian shape of proto-haloes and it is therefore essential to understand their mass, spin, and formation history. We present a machine learning framework to learn how the proto-halo regions of different haloes emerge from the initial density field. We developed one neural network to distinguish semantically which particles become part of any halo and a second neural network that groups these particles by halo membership into different instances. This instance segmentation is done through the Weinberger method, in which the network maps particles into a pseudo-space representation where different instances can easily be distinguished through a simple clustering algorithm. Our model reliably predicts the masses and Lagrangian shapes of haloes object by object, as well as other properties such as the halo-mass function. We find that our model extracts information close to optimally by comparing it to the degree of agreement between two N-body simulations with slight differences in their initial conditions. We publish our model open source and suggest that it can be used to inform analytical methods of structure formation by studying the effect of systematic manipulations of the initial conditions.

Discovery of Optically Emitting Circumgalactic Nebulae around the Majority of UV-luminous Quasars at Intermediate Redshift

We report the discovery of large, ionized, [O ii]-emitting circumgalactic nebulae around the majority of 30 UV-luminous quasars at z = 0.4–1.4 observed with deep, wide-field integral field spectroscopy with the Multi-Unit Spectroscopy Explorer (MUSE) by the Cosmic Ultraviolet Baryon Survey and MUSE Quasar Blind Emitters Survey. Among the 30 quasars, seven (23%) exhibit [O ii]-emitting nebulae with major axis sizes greater than 100 kpc, 20 greater than 50 kpc (67%), and 27 (90%) greater than 20 kpc. Such large, optically emitting nebulae indicate that cool, dense, and metal-enriched circumgalactic gas is common in the halos of luminous quasars at intermediate redshift. Several of the largest nebulae exhibit morphologies that suggest interaction-related origins. We detect no correlation between the sizes and cosmological-dimming-corrected surface brightnesses of the nebulae and quasar redshift, luminosity, black hole mass, or radio-loudness, but find a tentative correlation between the nebulae and rest-frame [O ii] equivalent width in the quasar spectra. This potential trend suggests a relationship between interstellar medium content and gas reservoirs on CGM scales. The [O ii]-emitting nebulae around the z ≈ 1 quasars are smaller and less common than Lyα nebulae around z ≈ 3 quasars. These smaller sizes can be explained if the outer regions of the Lyα halos arise from scattering in more neutral gas, by evolution in the cool circumgalactic medium content of quasar-host halos, by lower-than-expected metallicities on ≳50 kpc scales around z ≈ 1 quasars, or by changes in quasar episodic lifetimes between z = 3 and 1.

Unraveling the kinematics of IZw18: A detailed study of ionized gas with MEGARA/GTC

This study offers an in-depth analysis of the kinematic behavior of ionized gas in IZw18, a galaxy notable for its extremely low metallicity and close proximity, utilizing data from MEGARA/GTC. We explored the structure and dynamics of the galaxy through Halpha line profiles, applying single and double Gaussian component fittings to create detailed maps of the luminosity, velocity, and velocity dispersion in the main body (MB) and halo regions. Additionally, we retrieved integrated spectra from various galactic regions to achieve a higher signal-to-noise ratio. In the MB, a rotational pattern is evident, yet a secondary, more complex kinematic pattern emerges from the double-component fitting, which is further enriched by the identification of a very broad component. Distinguished by a full width at half maximum of nearly 2000 km/s and a wide spatial extension, this component suggests a high-energy outflow and points toward large-scale, nonlocalized sources of high kinetic energy. Additionally, the observed significant velocity differences between the narrow and very broad components imply that these gases may occupy distinct spatial regions. This is potentially explained by high-density gas near the origin of the kinematic input, acting as a "wall" that reflects back the momentum of the gas. Regarding the halos, while the NE halo exhibits a tranquil state with low velocity dispersions, the SW halo presents higher velocities and more complex kinematics, indicative of diverse dynamic interactions. The identification of the very broad component across the MB and the high kinematic complexity in all regions of the galaxy points toward a scenario of widespread and subtle turbulent motion. This nuanced understanding of the kinematic behavior in IZw18, including the interplay of different gas components and the influence of internal structures, enhances our comprehension of the dynamics in blue compact dwarf galaxies. It may provide critical insights into early galaxy formation and the intricate kinematics characteristic of such environments.

Wormhole solutions under the effect of dark matter in f(R, L m ) gravity

In the background of f(R, L m ) gravity, this work investigates three distinct dark matter halo profiles to test the possibility of generalised wormhole geometry within the galactic halo regions. The current study aims to accomplish these goals by examining various dark matter profiles including universal rotation curves (URC), Navarro–Frenk–White (NFW) model-I, and NFW model-II inside two distinct f(R, L m ) gravity models. According to the f(R,Lm)=R2+Lmα model, the dark matter (DM) halo density profiles produce suitable shape functions that meet all the necessary requirements for exhibiting the wormhole geometries with appropriate choice of free parameters. In addition, to examine DM profiles under the f(R,Lm)=R2+(1+λR)Lm model, we consider a specific shape function. Further, we observed that the derived solution from both two models violates the null energy constraints, confirming that the DM supports wormholes to maintain in the galactic halo.

Exploring NGC 2345: A Comprehensive Study of a Young Open Cluster through Photometric and Kinematic Analysis

We conducted a photometric and kinematic analysis of the young open cluster NGC 2345 using CCD UBV data from 2 m Himalayan Chandra Telescope, Gaia Data Release 3, Two Micron All-Sky Survey, and the Photometric All-Sky Survey data sets. We found 1732 most probable cluster members with membership probability higher than 70%. The fundamental and structural parameters of the cluster are determined based on the cluster members. The mean proper motion of the cluster is estimated to be μαcosδ = −1.34 ± 0.20 and μ δ = 1.35 ± 0.21 mas yr−1. Based on the radial density profile, the estimated radius is ∼12.′8 (10.37 pc). Using color–color and color–magnitude diagrams, we estimate the reddening, age, and distance to be 0.63 ± 0.04 mag, 63 ± 8 Myr, and 2.78 ± 0.78 kpc, respectively. The mass function slope for main-sequence stars is determined as 1.2 ± 0.1. The mass function slope in the core, halo, and overall region indicates a possible hint of mass segregation. The cluster’s dynamical relaxation time is 177.6 Myr, meaning ongoing mass segregation, with complete equilibrium expected in 100–110 Myr. Apex coordinates are determined as −40.°89 ± 0.12, − 44.°99 ± 0.15. The cluster’s orbit in the Galaxy suggests early dissociation into field stars due to its close proximity to the Galactic disk.

Numerical analyses of M31 dark matter profiles

In this paper, we reproduce the rotation curve of the Andromeda galaxy (M31) by taking into account its bulge, disk and halo components, considering the last one to contain the major part of dark matter mass. Hence, our prescription is to split the galactic bulge into two components, namely, the inner and main bulges, respectively. Both bulges are thus modeled by exponential density profiles since we underline that the widely accepted de Vaucouleurs law fails to reproduce the whole galactic bulge rotation curve. In addition, we adopt various well-known phenomenological dark matter profiles to estimate the dark matter mass in the halo region. Moreover, we apply the least-squares fitting method to determine from the rotation curve the model free parameters, namely, the characteristic (central) density, scale radius and consequently the total mass. To do so, we perform Markov chain Monte Carlo statistical analyses based on the Metropolis algorithm, maximizing our likelihoods adopting velocity and radii data points of the rotation curves. We do not fit separately the components for bulges, disk and halo, but we perform an overall fit including all the components and employing all the data points. Thus, we critically analyze our corresponding findings and, in particular, we employ the Bayesian information criterion to assess the most accredited model to describe M31 dark matter dynamics.

The moist halo region around shallow cumulus clouds in large eddy simulations

AbstractIn this study, the moist buffering halo region of shallow maritime cumulus clouds is systematically investigated using large eddy simulations with various grid resolutions and numerical choices. Autocorrelation analyses of cloud liquid water and relative humidity suggest a converged size of 200–300 m for moist patches outside clouds when the model resolution is below 50 m, but may overestimate this size due to noncloudy moist regions. Based on a composite analysis, the structure of the moist halo immediately outside individual clouds is examined. It is found that, regardless of model resolution, the distribution of relative humidity in the halo region does not depend on cloud size, but on the real distance away from the cloud boundary, indicating some size‐independent length scales are responsible for the halo formation. The relative humidity decays with distance more quickly with finer horizontal resolution, which is possibly related to the model resolution dependence of the cloud spectrum. The halo size near the cloud base is larger than that within the cloud layer and this feature is robust across all simulations. Further analyses of backward and forward Lagrangian trajectories originating from the moist halo region reveal the possible role for subcloud coherent structures in cloud‐base halo formation. Possible mechanisms explaining cloud halo sizes and associated length scales are discussed.

Generalized wormhole models within galactic halo region in torsion and matter coupling gravity formalism

In the current analysis, we investigate the possible existence of generalized Wormhole models within the galactic halo region by analyzing specific dark matter models. The observational data is checked in the framework of torsion within minimal matter coupling gravity. By using the variational approach modified versions of the field equations under the anisotropic source of matter are calculated. To discuss the specific necessary characteristics of the embedded wormhole geometry, we have analyzed the energy conditions under the effect of dark matter halos. We consider two embedded wormhole-specific shape functions in terms of the tortoise coordinate for the current study. Further, we compare different wormhole solutions for the different regional ranges depending on the involved parametric values. To check the effect of the dark matter halos, we use the observational data within the signature of the M87 galaxy and the Milky Way galaxy.

Dark matter supporting traversable wormholes in the Galactic halo

We study the Morris-Thorne traversable asymptotically flat and non-flat wormholes in the galactic halo of the Milky Way Galaxy(MWG) based on the Einasto dark matter(DM) density profile. Our reported shape function is positive and increasing in nature, moreover, satisfies all the essential wormhole representing conditions i.e. the reported shape function forms wormhole like structures in the galactic halo region of the MWG. Furthermore, the wormhole containing the DM candidate of the halo shelters wormholes by violating the null energy condition(NEC) with respect to three different redshift functions. The wormholes, namely, WH1 and WH2 corresponding to the first two choices of redshift functions are asymptotically flat while the WH3 corresponding to the third choice of redshift function is asymptotically non-flat. We, here, also analyze the ANEC violating matter content, embedding surface, and proper radial distance for our solutions.

PG 1004+130: Hybrid Morphology Source or a Restarted FRII? A uGMRT Polarimetric Investigation

We present the polarization image of the hybrid morphology and broad absorption line quasar PG 1004+130 at 694 MHz obtained with the upgraded Giant Metrewave Radio Telescope. We detect linear polarization in this source’s core, jets, and lobes. The visible discontinuity in total intensity between the inner jets and the kiloparsec-scale lobes suggests that the source is restarted. The inferred poloidal magnetic (B-) field structure in the inner jet is consistent with that observed in Fanaroff–Riley (FR) type II sources, as are the B-fields aligned with the lobe edges. Moreover, archival Chandra and XMM-Newton data indicate that PG 1004+130 displays several FRII-jetlike properties in X-rays. We conclude that PG 1004+130 is a restarted quasar, with both episodes of activity being FRII type. The spectral index images show the presence of an inverted spectrum core (α = +0.30 ± 0.01) and a steep spectrum inner jet (α = −0.62 ± 0.06) surrounded by much steeper lobe emission (α ≈ −1.2 ± 0.1), consistent with the suggestion that the lobes are from a previous activity episode. The spectral age difference between the two activity episodes is likely to be small (<1.2 × 107 yr), in comparison to the lobe ages (∼3.3 × 107 yr). The inferred B-fields in the lobes are suggestive of turbulence and the mixing of plasma. This may account for the absence of X-ray cavities around this source, similar to what is observed in M87's radio halo region. The depolarization models reveal that thermal gas of mass ∼(2.4 ± 0.9) × 109 M ⊙ is mixed with the nonthermal plasma in the lobes of PG 1004+130.