Search

In the central region of the galaxy cluster, Abell 2199 (A 2199) resides the cD galaxy NGC 6166, which spatially coincides with the 3C 338 radio source. Lobes, jets, and a more detached southern structure (similar to a jet labelled as ridge) are seen at kiloparsec-scale images of 3C 338. This unusual radio morphology has led to the proposition of different hypotheses about its physical origin in the literature. In this work, we study the feasibility of a dynamical scenario where NGC 6166 moves around the X-ray inferred centre of A 2199 from the point of view of three-dimensional hydrodynamic simulations. The physical characteristics of the intracluster medium in which the jet propagates are constrained to those derived from X-ray observations in the vicinity of NGC 6166. Possible orbits for the jet inlet region are derived from the estimated radial velocity of NGC 6166, while the jet parameters are constrained by parsec-scale interferometric radio observations and the estimated jet power of 3C 338 obtained from radio and X-ray data. Our results show that the hypothesis of NGC 6166 has been moving around the centre of A 2199 during the last tens of million of years is compatible with the general radio morphology of 3C 338. Furthermore, the proposed dynamic scenario for the motion of NGC 6166 may be linked to gravitational perturbations induced by the passage of a sub-cluster of galaxies hundreds of millions of years ago. [ABSTRACT FROM AUTHOR]

We present the stellar value-added catalogue based on the Dark Energy Spectroscopic Instrument (DESI) Early Data Release. The catalogue contains radial velocity and stellar parameter measurements for |$\simeq$| 400 000 unique stars observed during commissioning and survey validation by DESI. These observations were made under conditions similar to the Milky Way Survey (MWS) currently carried out by DESI but also include multiple specially targeted fields, such as those containing well-studied dwarf galaxies and stellar streams. The majority of observed stars have |$16\lt r\lt 20$| with a median signal-to-noise ratio in the spectra of |$\sim$| 20. In the paper, we describe the structure of the catalogue, give an overview of different target classes observed, as well as provide recipes for selecting clean stellar samples. We validate the catalogue using external high-resolution measurements and show that radial velocities, surface gravities, and iron abundances determined by DESI are accurate to 1 km s−1, 0.3 dex, and |$\sim$| 0.15 dex respectively. We also demonstrate possible uses of the catalogue for chemo-dynamical studies of the Milky Way stellar halo and Draco dwarf spheroidal. The value-added catalogue described in this paper is the very first DESI MWS catalogue. The next DESI data release, expected in less than a year, will add the data from the first year of DESI survey operations and will contain approximately 4 million stars, along with significant processing improvements. [ABSTRACT FROM AUTHOR]

The presence of dark gaps, a preferential light deficit along the bar minor axis, is observationally well known. The properties of dark gaps are thought to be associated with the properties of bars, and their spatial locations are often associated with bar resonances. However, a systematic study, testing the robustness and universality of these assumptions, is still largely missing. Here, we investigate the formation and evolution of bar-induced dark gaps using a suite of N -body models of (kinematically cold) thin and (kinematically hot) thick discs with varying thick disc mass fractions and different thin-to-thick disc geometries. We find that dark gaps are a natural consequence of the trapping of disc stars by the bar. The properties of dark gaps (such as strength and extent) are well correlated with the properties of bars. For stronger dark gaps, the fractional mass-loss along the bar minor axis can reach up to |${\sim} 60\!-\!80$|  per cent of the initial mass contained, which is redistributed within the bar. These trends hold true irrespective of the mass fraction in the thick disc and the assumed disc geometry. In all our models harbouring slow bars, none of the resonances (corotation, inner Lindblad resonance, and 4:1 ultraharmonic resonance) associated with the bar correspond to the location of dark gaps, thereby suggesting that the location of dark gaps is not a universal proxy for these bar resonances, in contrast with earlier studies. [ABSTRACT FROM AUTHOR]

Overdensities in the radial phase space |$(r,v_{\rm r})$| of the Milky Way's halo have previously been associated with the phase-mixed debris of a highly radial merger event such as Gaia Sausage–Enceladus. We present and test an alternative theory in which the overdense 'chevrons' are instead composed of stars trapped in resonances with the Galactic bar. We develop an analytic model of resonant orbits in the isochrone potential, and complement this with a test particle simulation of a stellar halo in a realistic barred Milky Way potential. These models are used to predict the appearance of action space |$(J_\phi ,J_{\rm r})$| and radial phase space in the Solar neighbourhood. They are able to reproduce almost all salient features of the observed chevrons. In particular, both the analytic model and simulation predict that the chevrons are more prominent at |$v_{\rm r}\ \lt\ 0$| when viewed near the Sun, as is observed by Gaia. This is inconsistent with formation by an ancient merger event. We also associate individual chevrons with specific resonances. At a bar pattern speed of |$\Omega _\mathrm{b}=35$| km s |$^{-1}$|  kpc |$^{-1}$|⁠ , the two most prominent prograde chevrons align very closely with the corotation and outer Lindblad resonances. The former can be viewed as a highly eccentric extension of the Hercules stream. Finally, our model predicts that the |$v_{\rm r}$| asymmetry changes sign as a function of Galactic radius and azimuth, and we find evidence that this is indeed the case in the Milky Way. [ABSTRACT FROM AUTHOR]

Active star formation in dwarf galaxies shapes the morphology of the surrounding nebular environment and ensures the non-uniformity of the chemical elements spatial distribution in it due to the superwind region expansion. Ionizing radiation within the nebular gas produces observed emission lines used for modelling and diagnostics. We introduce a multicomponent photoionization modelling (MPhM) approach that incorporates detailed calculation of diffuse ionizing radiation (DCDIR) based on chemodynamical simulations (ChDSs). Our models aim to replicate crucial emission line intensity ratios within the observed range, employing a thin dense shell between the superwind region and the outer nebular environment to address ChDSs resolution limitations, which render them insensitive to the presence of a superwind shock. MPhM-generated emission line spectra within a small central synthetic aperture and a thin long-slit exhibit excellent agreement with observations, confirming the accuracy of the ionization structure of the nebular environment obtained using the MPhM + DCDIR approach. However, the outward-only approximation fails to reproduce the dwarf galaxies ionization structure. We determined the oxygen abundance using the |$T_e$| - and |$R_{23}$| -methods based on emission lines from MPhM + DCDIR. The resulting abundances align well with values obtained by averaging over the 'observed' volume within synthetic apertures, weighted by mass. The escape fraction of ionizing photons from the dwarf galaxy was found to be larger than that obtained using the outward-only approximation. Employing Kennicutt's calibration corrected for near-UV data, the star formation rate (SFR) was calculated using the |${\rm H}\,\alpha$| luminosity from MPhM + DCDIR. The resulting SFR value is nearly 33 per cent higher than the true one. [ABSTRACT FROM AUTHOR]

Aims. Based on the available observational data from the literature, we analysed the dynamics of the NGC 6240 galaxy central supermassive black hole (SMBH) system. Methods. For the dynamical modelling of this triple SBMH system, we used the massively parallel and GPU accelerated φ-GPU direct summation N-body code. Following a long-timescale modelling of the triple system, we carried out a very detailed time output analysis of the von Zeipel–Lidov–Kozai (ZLK) oscillations for the black holes. Results. According to our Newtonian simulation results, for all models and randomisations, the bound system from S1+S2 components formed at ≈3.6 Myr. The formation of the bound hierarchical triple system S+N occurred at ≈18 Myr. Over the course of these Newtonian simulations of the evolution of the triple SMBH system and the surrounding environment in NGC 6240, ZLK oscillations were detected (in most cases) for the binary components. The inclination angle between the orbital angular momentum of binary components aptly coincides with the theoretical calculations of the ZLK mechanism. Conclusions. In our set of randomised 15 Newtonian N-body dynamical galaxy models in 13 systems, we were able to detect a ZLK mechanism. In contrast, our extra few-body post-Newtonian runs (for one randomisation case) show it is only for the large inner binary initial eccentricity (in our case ≳0.9) that we are able to observe the possibility of the inner binary merging, due to the post-Newtonian energy radiation effects. For the lower eccentricity cases, the test runs show no sign of possible merging or any ZLK oscillations in the system. [ABSTRACT FROM AUTHOR]

The Sagittarius dwarf spheroidal (Sgr dSph) galaxy provides one of the most convincing examples of tidal interaction between satellite galaxies and the Milky Way (MW). The main body of the dwarf was recently demonstrated to have an elongated, prolate, bar-like shape and to possess some internal rotation. Whether these features are temporary results of the strong tidal interaction at the recent pericenter passage or are due to a disky progenitor is a matter of debate. I present an analog of Sgr selected among bar-like galaxies from the TNG50 simulation of the IllustrisTNG project. The simulated dwarf is initially a disky galaxy with mass exceeding 1011 M⊙ and evolves around a MW-like host on a tight orbit with seven pericenter passages and a period of about 1 Gyr. At the second pericenter passage, the disk transforms into a bar and the bar-like shape of the stellar component is preserved until the end of the evolution. The morphological transformation is accompanied by strong mass loss, leaving a dwarf with a final mass of below 109 M⊙. The gas is lost completely and the star formation ceases at the third pericenter passage. At the last pericenters, the dwarf possesses a bar-like shape, a little remnant rotation, and the metallicity gradient, which are consistent with observations. The more concentrated metal-rich stellar population rotates faster and has a lower velocity dispersion than the more extended metal-poor one. The metallicity distribution evolves so that the most metal-poor stars are stripped first, which explains the metallicity gradient detected in the Sgr stream. This study demonstrates that a dSph galaxy with properties akin to the Sgr dwarf can form from a disky progenitor with a mass of above 1011 M⊙ by tidal evolution around the MW in the cosmological context. [ABSTRACT FROM AUTHOR]

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 Hα 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−1 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. [ABSTRACT FROM AUTHOR]

Context. Using the Illustris-1 and IllustrisTNG-100 simulations, we investigate the properties of the Fundamental Plane (FP), which is the correlation between the effective radius Re, the effective surface intensity Ie, and the central stellar velocity dispersion σ of galaxies, at different cosmic epochs. Aims. Our aim is to study the properties of galaxies in the FP and its projections across time, adopting samples covering different intervals of mass. We would like to demonstrate that the position of a galaxy in the FP space strongly depends on its degree of evolution, which might be represented by the β and L 0 ′ $ L^\prime_0 $ parameters entering the L = L 0 ′ $ L^\prime_0 $ (t)σβ(t) law. Methods. Starting from the comparison of the basic relations among the structural parameters of artificial and real galaxies at low redshift, we obtain the fit of the FP and its coefficients at different cosmic epochs for samples of different mass limits. Then, we analyze the dependence of the galaxy position in the FP space as a function of the β parameter and the star formation rate (SFR). Results. We find that: (1) the coefficients of the FP change with the mass range of the galaxy sample; (2) the low luminous and less massive galaxies do not share the same FP of the bright massive galaxies; (3) the scatter around the fitted FP is quite small at any epoch and increases when the mass interval increases; (4) the distribution of galaxies in the FP space strongly depends on the β values (i.e., on the degree of virialization and the star formation rate). Conclusions. The FP is a complex surface that is well approximated by a plane only when galaxies share similar masses and condition of virialization. [ABSTRACT FROM AUTHOR]

Context. Evolutionary models suggest that the initial growth phases of active galactic nuclei (AGN) and their central supermassive black holes (SMBHs) are dust-enshrouded and characterised by jet or wind outflows that should gradually clear the interstellar medium (ISM) in the host by heating and/or expelling the surrounding gas. eFEDSJ091157.4+014327 (z ∼ 0.6) was selected from X-ray samples of eROSITA (extended ROentgen Survey with an Imaging Telescope Array) for its characteristics: red colours, X-ray obscuration (NH = 2.7 × 1022 cm−2) and luminous (LX = 6.5 × 1044 erg s−1), similar to those expected in quasars with outflows. It hosts an ionised outflow as revealed by a broad [O III]λ5007 Å emission line in the SDSS integrated spectrum. For a proper characterisation of the outflow properties and their effects, we need spatially resolved information. Aims. We aim to explore the environment around the red quasar, morphology of the [O III] gas and characterise the kinematics, mass outflow rates and energetics within the system. Methods. We used spatially resolved spectroscopic data from Multi Unit Spectroscopic Explorer (MUSE) with an average seeing of 0.6″ to construct flux, velocity and velocity dispersion maps. Thanks to the spatially resolved [O III]λ5007 Å emission detected, we provide insights into the morphology and kinematics of the ionised gas and better estimates of the outflow properties. Results. We find that the quasar is embedded in an interacting and merging system with three other galaxies ∼50 kpc from its nucleus. Spatially resolved kinematics reveal that the quasar has extended ionised outflows of up to 9.2−0.4+1.2 kpc with positive and negative velocities up to 1000 km s−1 and −1200 km s−1, respectively. The velocity dispersion (W80) ranges from 600–1800 km s−1. We associate the presence of high-velocity components with the outflow. The total mass outflow rate is estimated to be ∼10 M⊙ yr−1, a factor of ∼3–7 higher than the previous findings for the same target and kinetic power of 2 × 1042 erg s−1. Considering different AGN bolometric luminosities, the kinetic coupling efficiencies range from 0.01%–0.03% and the momentum boosts are ∼0.2. Conclusions. The kinetic coupling efficiency values are low, which indicates that the ionised outflow is not energetically relevant. These values don't align with the theoretical predictions of both radiation-pressure-driven outflows and energy-conserving mechanisms. However, note that our results are based only on the ionised phase while theoretical predictions are multi-phase. Moreover, the mass loading factor of ∼5 is an indication that these outflows are more likely AGN-driven than star formation-driven. [ABSTRACT FROM AUTHOR]

Context. Empirical constraints on the internal dynamics of open clusters are important for understanding their evolution and evaporation. High-precision astrometry from Gaia DR3 is thus useful to observe aspects of the cluster dynamics. Aims. This work aims to identify dynamically peculiar clusters such as spinning and expanding clusters. We also quantify the spin frequency and expansion rate and compare them with N-body models to identify the origins of the peculiarities. Methods. We used the latest Gaia DR3 and archival spectroscopic surveys to analyse the radial velocities and proper motions of the cluster members in 1379 open clusters. A systematic analysis of synthetic clusters was performed to demonstrate the observability of the cluster spin along with effects of observational uncertainties. N-body simulations were used to understand the evolution of cluster spin and expansion for initially non-rotating clusters. Results. We identified spin signatures in ten clusters (and 16 candidates). Additionally, we detected expansion in 18 clusters and contraction in three clusters. The expansion rate is compatible with previous theoretical estimates based on the expulsion of residual gas. The orientation of the spin axis is independent of the orbital angular momentum. Conclusions. The spin frequencies are much larger than what was expected from simulated, initially non-rotating clusters. This indicates that > 1% of the clusters are born rotating and/or they have undergone strong interactions. Higher precision observations are required to increase the sample of such dynamically peculiar clusters and to characterise them. [ABSTRACT FROM AUTHOR]

The Universe expansion rate is modulated around local inhomogeneities due to their gravitational potential. Velocity waves are then observed around galaxy clusters in the Hubble diagram. This paper studies them in a ∼738 Mpc-wide, 20483-particle cosmological simulation of our cosmic environment (a.k.a. CLONE: Constrained LOcal & Nesting Environment Simulation). For the first time, the simulation shows that velocity waves that arise in the lines of sight of the most massive dark matter halos agree with those observed in local galaxy velocity catalogs in the lines of sight of Coma and several other local (Abell) clusters. For the best-constrained clusters such as Virgo and Centaurus – that is, those closest to us – secondary waves caused by galaxy groups, further into the non-linear regime, also stand out. This match was not utterly expected given that before being evolved into a fully non-linear z = 0 state, assuming ΛCDM, CLONE initial conditions are constrained solely with linear theory, the power spectrum, and highly uncertain and sparse local peculiar velocities. Additionally, Gaussian fits to velocity wave envelopes show that wave properties are tightly tangled with cluster masses. This link is complex, though, and involves the environment and formation history of the clusters. A proposed metric, measuring the distance between the observed and several re-centred simulated lines of sight, waves included, is shown to be capable of providing a tight mass range estimate for massive local clusters. Using machine learning techniques to grasp more thoroughly the complex wave-mass relation, velocity waves could in the near future be used to provide additional and independent mass estimates from galaxy dynamics within large cluster radii. [ABSTRACT FROM AUTHOR]

Context. Within the Λ cold dark matter (ΛCDM) cosmology, dark matter haloes are expected to deviate from spherical symmetry. The particular shape of a galactic halo reflects the environment and mass assembly history of its host, as well as the nature of dark matter. Constraining halo shapes at large galactocentric distances is challenging because of the low density of luminous tracers. The well-studied massive early-type galaxy NGC 5128, also known as Centaurus A (Cen A), has a large number of radial velocity measurements for globular clusters (GCs) and planetary nebulae (PNe) extending over a vast area of its extended low-surface-brightness stellar halo. Aims. In this work, we aim to determine the deviation from spherical symmetry of the dark matter halo of Cen A at 5 Re using its GCs as kinematic tracers of the gravitational potential. Methods. We investigated the largest photometric catalogue of GC candidates in order to accurately characterise the spatial distribution of the relaxed population of GCs. To investigate the presence of non-relaxed structures in the kinematic catalogue of GCs, we used the relaxed point-symmetric velocity field as determined by the host's PNe population. We used anisotropic Jeans modelling under axisymmetric assumptions together with the Gaussian likelihood and GCs as discrete tracers. The gravitational potential is generated by flattened stellar and dark matter distributions. We leveraged the different orbital properties of the blue and red GCs – such as rotation and velocity anisotropy – to model both populations separately. By minimising χ2, we iteratively find the best-fit parameters. Results. We find that the discrete kinematics of the GCs are consistent with being drawn from an underlying relaxed velocity field determined from PNe. The best-fit parameters of the gravitational potential recovered from the blue and red GCs separately agree well and we use them to compute the final results: M200 = 1.86−0.691.61 × 1012 M⊙, M⋆/LB = 2.98−0.78+0.96, and the flattening qDM = 1.45−0.53+0.78. Both GC populations show mild rotation, with red having a slightly stronger rotational signature and radially biased orbits, and blue GCs preferring negative velocity anisotropy. Conclusions. An oblate or a spherical dark matter halo of NGC 5128 is strongly disfavoured by our modelling. [ABSTRACT FROM AUTHOR]

Aims. The physical properties of galactic molecular outflows are important as they could constrain outflow formation mechanisms. In this work, we study the properties of the southwest (SW) outflow streamer including gas kinematics, optical depth, dense gas fraction, and shock strength through molecular emission in the central molecular zone of the starburst galaxy NGC 253. Methods. We imaged the molecular emission in NGC 253 at a spatial resolution of 1.6″(∼27 pc at D ∼ 3.5 Mpc) based on data from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program. We traced the velocity and velocity dispersion of molecular gas with the CO(1–0) line and studied the molecular spectra in the region of the SW streamer, the brightest CO streamer in NGC 253. We constrained the optical depth of the CO emission with the CO/13CO(1–0) ratio, the dense gas fraction with the HCN/CO(1–0), H13CN/13CO(1–0) and N2H+/13CO(1–0) ratios, as well as the shock strength with the SiO(2–1)/13CO(1–0) and CH3OH(2k–1k)/13CO(1–0) ratios. Results. The CO/13CO(1–0) integrated intensity ratio is ∼21 in the SW streamer region, which approximates the C/13C isotopic abundance ratio. The higher integrated intensity ratio compared to the disk can be attributed to the optically thinner environment of CO(1–0) emission inside the SW streamer. The HCN/CO(1–0) and SiO(2–1)/13CO(1–0) integrated intensity ratios both approach ∼0.2 in three giant molecular clouds (GMCs) at the base of the outflow streamers, which implies a higher dense gas fraction and strength of fast shocks in those GMCs than in the disk, while the HCN/CO(1–0) integrated intensity ratio is moderate in the SW streamer region. The contours of those two integrated intensity ratios are extended in the directions of outflow streamers, which connect the enhanced dense gas fraction and shock strength with molecular outflow. Moreover, the molecular gas with an enhanced dense gas fraction and shock strength located at the base of the SW streamer shares the same velocity as the outflow. Conclusions. The enhanced dense gas fraction and shock strength at the base of the outflow streamers suggest that star formation inside the GMCs can trigger shocks and further drive the molecular outflow. The increased CO/13CO(1–0) integrated intensity ratio coupled with the moderate HCN/CO(1–0) integrated intensity ratio in the SW streamer region are consistent with the picture that the gas velocity gradient inside the streamer may decrease the optical depth of CO(1–0) emission, as well as the dense gas fraction in the extended streamer region. [ABSTRACT FROM AUTHOR]

Context. Recent measurements of gas velocity in the outer parts of high redshift galaxies suggest that steeply falling rotation curves may be common or even universal in these galaxies, in contrast to the near universal flat, non-declining rotation curves in nearby galaxies. Aims. The aim was to investigate the implications of these postulated steeply falling rotation curves for the role of dark matter in galaxy formation. Methods. Using an established computer code, the collapse of dark matter and baryonic matter together, starting with a variety of initial conditions, was simulated for comparison with the observed rotation curves. A simulation of collapsing baryonic matter on its own without dark matter was also carried out. The masses of the protogalaxies were chosen to produce a stellar disc in the same mass range as the observed galaxies at roughly the same redshift. Results. As soon as a smooth stellar disc was formed in the baryonic matter, with properties similar to the observed high redshift galaxies, the computed rotation curves were without exception relatively flat to large radius in the gas disc. Only a simulation without a dark matter halo was able to reproduce the observed rotation curves. Conclusions. This implies that if the high redshift steeply falling rotation curves turn out to be common, then the standard scenario of galaxy formation by baryonic matter falling into the potential well of a massive dark matter halo must be wrong, unless there is pressure support via velocity dispersion significantly higher than has so far been observed or resulted from our simulations. It would also imply that for these galaxies the flat rotation curves at low redshift must be due to dark matter which has subsequently fallen into the galactic potential well, or there must be some other explanation for their contemporary flat rotation curves other than dark matter. [ABSTRACT FROM AUTHOR]

It is well established that black holes reside in the central regions of virtually all types of known galaxies. Recent observational and numerical studies however challenge this picture, suggesting that intermediate-mass black holes in dwarf galaxies may be found on orbits far from the center. In particular, constant-density cores minimize orbital energy losses due to dynamical friction, and allow black holes to settle on stable off-center orbits. Using controlled simulations, we study the dynamics of off-center black holes in dwarf galaxies with such cores. We propose a new scenario to describe off-center mergers of massive black holes, starting with a Jacobi capture. We focus on initially circular and co-planar black hole orbits and explore a large parameter space of black hole masses and orbital parameters. We find that Jacobi captures are a complex and chaotic phenomenon that occurs in about 13% of cases in this simplified setup, and we quantify how the likelihood of capture depends on the simulation parameters. We note that this percentage is likely an upper limit of the general case. Nevertheless, we show that Jacobi captures in cored dwarf galaxies can facilitate the formation of off-center black hole binaries, and that this process is sufficiently common to have a substantial effect on black hole growth. While our setup only allows for temporary captures, we expect dissipative forces from baryons and post-Newtonian corrections to maintain the captures over time and to lead to the formation of stable binary systems. This motivates future studies of the effectiveness of such dissipative forces, within stripped nuclei or globular clusters, in forming stable bound systems. [ABSTRACT FROM AUTHOR]

Supermassive black hole binaries (SMBHBs) are binary systems formed by black holes with masses exceeding millions of solar masses, and are expected to form and evolve in the nuclei of galaxies. The extremely compact nature of these objects leads to the intense and efficient emission of gravitational waves (GWs), which can be detected by the Pulsar Timing Array (PTA) experiment in the form of a gravitational wave background (GWB); that is, a superposition of GW signals coming from different sources. The modelling of the GWB requires some assumptions as to the binary population, and exploration of the whole parameter space involved is hindered by the great computational cost involved. We trained two neural networks (NN) on a semi-analytical modelling of the GWB generated by an eccentric population of MBHBs that interact with the stellar environment. We then used the NN to predict the characteristics of the GW signal in regions of the parameter space that we did not sample analytically. The developed framework allows us to quickly predict the amplitude, shape, and variance of the GWB signals produced in different realisations of the universe. [ABSTRACT FROM AUTHOR]

Eclipsing binary systems are significant objects for astrophysics in that direct observations can determine the fundamental parameters of stars. In this study, we precisely determined the fundamental parameters of the binary component stars obtained by simultaneous analysis of radial velocities and the TESS light curve using the Wilson and Devinney code. Following the analysis, the masses and radii of the primary and secondary components were determined as M1=1.58±0.01M⊙$$ {M}_1=1.58\pm 0.01{M}_{\odot } $$, M2=0.48±0.02M⊙$$ {M}_2=0.48\pm 0.02{M}_{\odot } $$, and R1=1.93±0.01R⊙$$ {R}_1=1.93\pm 0.01{R}_{\odot } $$, R2=1.14±0.01R⊙$$ {R}_2=1.14\pm 0.01{R}_{\odot } $$, respectively. Furthermore, the distance of IS CMa is calculated as 92.7±6.5$$ 92.7\pm 6.5 $$ pc. On the basis of the analysis of the mid‐eclipse times, it was found that the variation in the orbital period is represented by an upward parabola. It has an increasing rate of dP/dt$$ dP/ dt $$ = 1.09 ×$$ \times $$ 10−7$$ {}^{-7} $$ day year−1$$ {}^{-1} $$. Using PARSEC stellar evolutionary tracks and isochrones with solar metallicity estimated the age of IS CMa as 1.3±0.1$$ 1.3\pm 0.1 $$ Gyr. Kinematic and Galactic orbital parameters of IS CMa were obtained from the astrometric and spectroscopic data of the system. The Galactic orbit analysis reveals that IS CMa formed inside the solar circle and it is a member of the young thin‐disc population. [ABSTRACT FROM AUTHOR]

Structures in the Universe, ranging from globular clusters to entire galaxies, are not described by standard statistical mechanics at equilibrium. Instead, they are formed through a process of a very different nature, called violent relaxation that is now known to be possible also in other systems that exhibit long-range interactions. This mechanism was proposed theoretically and modelled numerically, but never directly observed in any physical system. Here, we develop a table-top experiment allowing us to directly observe violent relaxation in an optical setting. The resulting optical dynamics can also be likened to the formation of an analogue 2D-galaxy through the analogy of the underlying equations, where we can control a range of parameters, including the nonlocal interacting potential, allowing us to emulate the physics of gravitational quantum and classical dark matter models. Large structure in the Universe, such as galaxies, are believed to form by a process called violent relaxation, which occurs over millions of years. The authors present a nonlinear optics experiment which shows direct observation of violent relaxation, whose evolution can be related to the equations governing galaxy formation. [ABSTRACT FROM AUTHOR]

There have been many efforts in the last three decades to embed the empirical Modified Newtonian Dynamics (MOND) programme into a robust theoretical framework. While many such theories can explain the profile of galactic rotation curves, they usually cannot explain the evolution of the primordial fluctuations and the formation of large-scale structures in the Universe. The Aether Scalar Tensor theory seems to have overcome this difficulty, thereby providing the first compelling example of an extension of general relativity able to successfully challenge the particle dark matter hypothesis. Here, we study the phenomenology of this theory in the quasistatic weak-field regime and specifically for the idealized case of spherical isolated sources. We find the existence of three distinct gravitational regimes, that is, Newtonian, MOND, and a third regime characterized by the presence of oscillations in the gravitational potential which do not exist in the traditional MOND paradigm. We identify the transition scales between these three regimes and discuss their dependence on the boundary conditions and other parameters in the theory. Aided by analytical and numerical solutions, we explore the dependence of these solutions on the theory parameters. Our results could help in searching for interesting observable phenomena at low redshift pertaining to galaxy dynamics as well as lensing observations, however, this may warrant proper N -body simulations that go beyond the idealized case of spherical isolated sources. [ABSTRACT FROM AUTHOR]

We present LinearResponse.jl , an efficient, versatile public library written in julia to compute the linear response of self-gravitating (three-dimensional spherically symmetric) stellar spheres and (two-dimensional axisymmetric razor-thin) discs. LinearResponse.jl can scan the whole complex frequency plane, probing unstable, neutral and (weakly) damped modes. Given a potential model and a distribution function, this numerical toolbox estimates the modal frequencies as well as the shapes of individual modes. The libraries are validated against a combination of previous results for the spherical isochrone model and Mestel discs, and new simulations for the spherical Plummer model. Beyond linear response theory, the realm of applications of LinearResponse.jl also extends to the kinetic theory of self-gravitating systems through a modular interface. [ABSTRACT FROM AUTHOR]

This is a summary of the main results within the Scale-Invariant Vacuum (SIV) paradigm based on Weyl integrable geometry. We also review the mathematical framework and utilize alternative derivations of the key equations based on the reparametrization invariance as well. The main results discussed are related to the early universe; that is, applications to inflation, Big Bang Nucleosynthesis, and the growth of the density fluctuations within the SIV. Some of the key SIV results for the early universe are a natural exit from inflation within the SIV in a later time t exit with value related to the parameters of the inflationary potential along with the possibility for the density fluctuations to grow sufficiently fast within the SIV without the need for dark matter to seed the growth of structure in the universe. In the late-time universe, the applications of the SIV paradigm are related to scale-invariant dynamics of galaxies, MOND, dark matter, and dwarf spheroidals, where one can find MOND to be a peculiar case of the SIV theory. Finally, within the recent time epoch, we highlight that some of the change in the length-of-the-day (LOD), about 0.92 cm/yr, can be accounted for by SIV effects in the Earth–Moon system. [ABSTRACT FROM AUTHOR]

We investigate a mechanism to form and keep a planar spatial distribution of satellite galaxies in the Milky Way (MW), which is called the satellite plane. It has been pointed out that the ΛCDM cosmological model hardly explains the existence of such a satellite plane, so it is regarded as one of the serious problems in the current cosmology. We here focus on a rotation of the gravitational potential of a host galaxy, i.e. a so-called figure rotation, following the previous suggestion that this effect can induce the tilt of a so-called tube orbit. Our calculation shows that a figure rotation of a triaxial potential forms a stable orbital plane perpendicular to the rotational axis of the potential. Thus, it is suggested that the MW's dark halo is rotating with its axis being around the normal line of the satellite plane. Additionally, we find that a small velocity dispersion of satellites is required to keep the flatness of the planar structure, namely the standard derivation of their velocities perpendicular to the satellite plane needs to be smaller than their mean rotational velocity on the plane. Although not all the MW's satellites satisfy this condition, a fraction of them, called member satellites, which are prominently on the plane, do satisfy it. We suggest that this picture explaining the observed satellite plane can be achieved by the filamentary accretion of dark matter associated with the formation of the MW and a group infall of member satellites along this cosmic filament. [ABSTRACT FROM AUTHOR]

Barred galaxies constitute about two-thirds of observed disc galaxies. Bars affect not only the mass distribution of gas and stars but also that of the dark matter. An elongation of the inner dark matter halo is known as the halo bar. We aim to characterize the structure of the halo bars, with the goal of correlating them with the properties of the stellar bars. We use a suite of simulated galaxies with various bar strengths, including gas and star formation. We quantify the strengths, shapes, and densities of these simulated stellar bars. We carry out numerical experiments with frozen and analytic potentials in order to understand the role played by a live responsive stellar bar. We find that the halo bar generally follows the trends of the disc bar. The strengths of the halo and stellar bars are tightly correlated. Stronger bars induce a slight increase in dark matter density within the inner halo. Numerical experiments show that a non-responsive frozen stellar bar would be capable of inducing a dark matter bar, but it would be weaker than the live case by a factor of roughly two. [ABSTRACT FROM AUTHOR]

We present the first detailed chemical-abundance analysis of stars from the dwarf-galaxy stellar stream Wukong/LMS-1 covering a wide metallicity range (⁠|$-3.5 \lt \rm [Fe/H] \lesssim -1.3$|⁠). We find abundance patterns that are effectively indistinguishable from the bulk of Indus and Jhelum, a pair of smaller stellar streams proposed to be dynamically associated with Wukong/LMS-1. We confirmed a carbon-enhanced metal-poor star (⁠|$\rm [C/Fe] \gt +0.7$| and |$\rm [Fe/H] \sim -2.9$|⁠) in Wukong/LMS-1 with strong enhancements in Sr, Y, and Zr, which is peculiar given its solar-level [Ba/Fe]. Wukong/LMS-1 stars have high abundances of α elements up to |$\rm [Fe/H] \gtrsim -2$|⁠ , which is expected for relatively massive dwarfs. Towards the high-metallicity end, Wukong/LMS-1 becomes α-poor, revealing that it probably experienced fairly standard chemical evolution. We identified a pair of N- and Na-rich stars in Wukong/LMS-1, reminiscent of multiple stellar populations in globular clusters. This indicates that this dwarf galaxy contained at least one globular cluster that was completely disrupted in addition to two intact ones previously known to be associated with Wukong/LMS-1, which is possibly connected to similar evidence found in Indus. From these ≥3 globular clusters, we estimate the total mass of Wukong/LMS-1 to be |${\approx }10^{10} \, \mathrm{M}_\odot$|⁠ , representing ∼1 per cent of the present-day Milky Way. Finally, the [Eu/Mg] ratio in Wukong/LMS-1 continuously increases with metallicity, making this the first example of a dwarf galaxy where the production of r -process elements is clearly dominated by delayed sources, presumably neutron-star mergers. [ABSTRACT FROM AUTHOR]

The Jeans equations do not form a closed system, and to solve them a parametrization relating the velocity moments is often adopted. For axisymmetric models, a phenomenological choice (the ' b -ansatz') is widely used for the relation between the vertical (⁠|$\sigma _z^2$|⁠) and radial (⁠|$\sigma _R^2$|⁠) components of the velocity dispersion tensor, thus breaking their identity present in two-integral systems. However, the way in which the ansatz affects the resulting kinematical fields can be quite complicated, so that the analysis of these fields is usually performed only after numerically computing them. We present here a general procedure to study the properties of the ansatz-dependent fields |$\overline{v_{\varphi }^2}$|⁠ , |$\Delta =\overline{v_{\varphi }^2}- \sigma _z^2$| and |$\Delta _R= \overline{v_{\varphi }^2}- \sigma _R^2$|⁠. Specifically, the effects of the b -ansatz can be determined before solving the Jeans equations once the behaviour over the (R, z)-plane of three easy-to-build ansatz-independent functions is known. The procedure also constrains the ansatz to exclude unphysical results (as a negative |$\overline{v_{\varphi }^2}$|⁠). The method is illustrated by discussing the cases of three well-known galaxy models: the Miyamoto & Nagai and Satoh discs, and the Binney logarithmic halo, for which the regions and the constraints on the ansatz values can be determined analytically; a two-component (Miyamoto & Nagai plus logarithmic halo) model is also discussed. [ABSTRACT FROM AUTHOR]

We investigate how the phase space structure of a Three-Dimensional (3D) autonomous Hamiltonian system evolves across a series of successive Two-Dimensional (2D) and 3D pitchfork and period-doubling bifurcations, as the transition of the parent families of Periodic Orbits (POs) from stability to simple instability leads to the creation of new stable POs. Our research illustrates the consecutive alterations in the phase space structure near POs as the stability of the main family of POs changes. This process gives rise to new families of POs within the system, either maintaining the same or exhibiting higher multiplicity compared to their parent families. Tracking such a phase space transformation is challenging in a 3D system. By utilizing the color and rotation technique to visualize the Four-Dimensional (4D) Poincaré surfaces of section of the system, i.e. projecting them onto a 3D subspace and employing color to represent the fourth dimension, we can identify distinct structural patterns. Perturbations of parent and bifurcating stable POs result in the creation of tori characterized by a smooth color variation on their surface. Furthermore, perturbations of simple unstable parent POs beyond the bifurcation point, which lead to the birth of new stable families of POs, result in the formation of figure-8 structures of smooth color variations. These figure-8 formations surround well-shaped tori around the bifurcated stable POs, losing their well-defined forms for energies further away from the bifurcation point. We also observe that even slight perturbations of highly unstable POs create a cloud of mixed color points, which rapidly move away from the location of the PO. Our study introduces, for the first time, a systematic visualization of 4D surfaces of section within the vicinity of higher multiplicity POs. It elucidates how, in these cases, the coexistence of regular and chaotic orbits contributes to shaping the phase space landscape. [ABSTRACT FROM AUTHOR]

Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We carried out a comprehensive set of hydrodynamical N-body simulations with different combinations of bulge masses and gas fractions. In these models, both massive bulges and high gas content tend to inhibit the formation of strong bars. For low-mass bulges, the resulting bar is stronger in cases of low gas content. In the stronger bar models, bulges acquire more angular momentum and thus display considerable rotational velocity. Such bulges also develop anisotropic velocity dispersions and become triaxial in shape. We found that the rotation of the bulge becomes less pronounced as the gas fraction is increased from 0 to 30%. These results indicate that the gas content has a significant effect on the dynamics of the classical bulge, because it influences bar strength. Particularly in the case of the low-mass bulges (10% bulge mass fraction), all of the measured rotational and structural properties of the classical bulge depend strongly and systematically on the gas content of the galaxy. [ABSTRACT FROM AUTHOR]

The estimation of galactic component masses can be carried out through various approaches that involve a host of assumptions about baryon dynamics or the dark matter model. In contrast, this work introduces an alternative method for predicting the masses of the disk, bulge, stellar, and total mass using the k-nearest neighbours, linear regression, random forest, and neural network (NN) algorithms, reducing the dependence on any particular hypothesis. The ugriz photometric system was selected as the set of input features, and the training was performed using spiral galaxies in Guo's mock catalogue from the Millennium simulation. In general, all of the algorithms provide good predictions for the galaxy's mass from 10 9   M ⊙ to 10 11   M ⊙ , corresponding to the central region of the training domain. The NN algorithm showed the best performance. To validate the algorithm, we used the SDSS survey and found that the predictions of disk-dominant galaxies' masses lie within a 99 % confidence level, while galaxies with larger bulges are predicted at a 95 % confidence level. The NN also reveals scaling relations between mass components and magnitudes. However, predictions for less luminous galaxies are biased due to observational limitations. Our study demonstrates the efficacy of these methods with the potential for further enhancement through the addition of observational data or galactic dynamics. [ABSTRACT FROM AUTHOR]

It is already known that a simple nonlocal de Sitter gravity model, which we denote as d S gravity, contains an exact vacuum cosmological solution that mimics dark energy and dark matter and is in very good agreement with the standard model of cosmology. This success of d S gravity motivated us to investigate how it works at a lower-than-cosmic scale—galactic and the solar system. This paper contains our investigation of the corresponding Schwarzschild–de Sitter metric of the d S gravity model. To obtain an exact solution, it is necessary to solve the corresponding nonlinear differential equation, which is a very complicated and difficult problem. What we obtained is a solution to a linearized equation, which is related to space metrics far from the massive body, where the gravitational field is weak. The obtained approximate solution is of particular interest for examining the possible role of nonlocal de Sitter gravity d S in describing the effects in galactic dynamics that are usually attributed to dark matter. This solution was tested on the Milky Way and the spiral galaxy M33 and is in good agreement with observational measurements. [ABSTRACT FROM AUTHOR]

We try to understand the trends in the mass density slopes as a function of galaxy properties. We use the results from the best Jeans Anisotropic Modelling (JAM) of the integral-field stellar kinematics for near 6000 galaxies from the MaNGA DynPop project, with stellar masses |$10^9\ {\rm {\rm M}_{\odot }}\lesssim M_*\lesssim 10^{12}\ {\rm {\rm M}_{\odot }}$|⁠ , including both early-type and late-type galaxies. We use the mass-weighted density slopes for the stellar |$\overline{\gamma }_*$|⁠ , dark |$\overline{\gamma }_{_{\rm DM}}$| and total |$\overline{\gamma }_{_{\rm T}}$| mass from the MaNGA DynPop project. As previously reported, |$\overline{\gamma }_{_{\rm T}}$| approaches a constant value of |$\overline{\gamma }_{_{\rm T}}\approx 2.2$| for high σe galaxies, and flattens for |$\lg (\sigma _{\rm e}/{\rm km\ s^{-1}})\lesssim 2.3$| galaxies, reaching |$\overline{\gamma }_{_{\rm T}}\approx 1.5$| for |$\lg (\sigma _{\rm e}/{\rm km\ s^{-1}})\approx 1.8$|⁠. We find that total and stellar slopes track each other tightly, with |$\overline{\gamma }_{_{\rm T}}\approx \overline{\gamma }_*-0.174$| over the full σe range. This confirms the dominance of stellar matter within R e. We also show that there is no perfect conspiracy between baryonic and dark matter, as |$\overline{\gamma }_*$| and |$\overline{\gamma }_{_{\rm DM}}$| do not vary inversely within the σe range. We find that the central galaxies from TNG50 and TNG100 simulations do not reproduce the observed galaxy mass distribution, which we attribute to the overestimated dark matter fraction, possibly due to a constant IMF and excessive adiabatic contraction effects in the simulations. Finally, we present the stacked dark matter density profiles and show that they are slightly steeper than the pure dark matter simulation prediction of |$\overline{\gamma }_{_{\rm DM}}\approx 1$|⁠ , suggesting moderate adiabatic contraction in the central region of galaxies. Our work demonstrates the power of stellar dynamics modelling for probing the interaction between stellar and dark matter and testing galaxy formation theories. [ABSTRACT FROM AUTHOR]

Extreme-mass-ratio inspirals (EMRIs) are significant observational targets for spaceborne gravitational wave detectors, namely, LISA, Taiji, and Tianqin, which involve the inspiral of stellar-mass compact objects into massive black holes (MBHs) with a mass range of approximately 10 4 ∼ 10 7 M ⊙ . EMRIs are estimated to produce long-lived gravitational wave signals with more than 10 5 cycles before plunge, making them an ideal laboratory for exploring the strong-gravity properties of the spacetimes around the MBHs, stellar dynamics in galactic nuclei, and properties of the MBHs itself. However, the complexity of the waveform model, which involves the superposition of multiple harmonics, as well as the high-dimensional and large-volume parameter space, make the fully coherent search challenging. In our previous work, we proposed a 10-dimensional search using Particle Swarm Optimization (PSO) with local maximization over the three initial angles. In this study, we extend the search to an 8-dimensional PSO with local maximization over both the three initial angles and the angles of spin direction of the MBH, where the latter contribute a time-independent amplitude to the waveforms. Additionally, we propose a 7-dimensional PSO search by using a fiducial value for the initial orbital frequency and shifting the corresponding 8-dimensional Time Delay Interferometry responses until a certain lag returns the corresponding 8-dimensional log-likelihood ratio's maximum. The reduced dimensionality likelihoods enable us to successfully search for EMRI signals with a duration of 0.5 years and signal-to-noise ratio of 50 within a wider search range than our previous study. However, the ranges used by both the LISA Data Challenge (LDC) and Mock LISA Data Challenge (MLDC) to generate their simulated signals are still wider than the those we currently employ in our direct searches. Consequently, we discuss further developments, such as using a hierarchical search to narrow down the search ranges of certain parameters and applying Graphics Processing Units to speed up the code. These advances aim to improve the efficiency, accuracy, and generality of the EMRI search algorithm. [ABSTRACT FROM AUTHOR]

Galactic rotation curve is a powerful indicator of the state of the gravitational field within a galaxy. The flatness of these curves indicates the presence of dark matter (DM) in galaxies and their clusters. In this paper, we focus on the possibility of explaining the rotation curves of spiral galaxies without postulating the existence of DM in the framework of f (ℛ , T) gravity, where the gravitational Lagrangian is written by an arbitrary function of ℛ , the Ricci scalar and of T , the trace of energy–momentum tensor T μ ν . We derive the gravitational field equations in this gravity theory for the static spherically symmetric spacetime and solve the equations for metric coefficients using a specific model that has minimal coupling between matter and geometry. The orbital motion of a massive test particle moving in a stable circular orbit is considered and the behavior of its tangential velocity with the help of the considered model is studied. We compare the theoretical result predicted by the model with observations of a sample of 19 galaxies by generating and fitting rotation curves for the test particle to check the viability of the model. It is observed that the model could almost successfully explain the galactic dynamics of these galaxies without the need of DM at large distances from the galactic center. [ABSTRACT FROM AUTHOR]

Gaseous nuclear rings are large-scale coherent structures commonly found at the centres of barred galaxies. We propose that they are an accumulation of gas at the inner edge of an extensive gap that forms around the Inner Lindblad Resonance (ILR). The gap initially opens because the bar potential excites strong trailing waves near the ILR, which remove angular momentum from the gas disc and transport the gas inwards. The gap then widens because the bar potential continuously excites trailing waves at the inner edge of the gap, which remove further angular momentum, moving the edge further inwards until it stops at a distance of several wavelengths from the ILR. The gas accumulating at the inner edge of the gap forms the nuclear ring. The speed at which the gap edge moves and its final distance from the ILR strongly depend on the sound speed, explaining the puzzling dependence of the nuclear ring radius on the sound speed in simulations. [ABSTRACT FROM AUTHOR]

We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and near-infrared proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which four are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity. [ABSTRACT FROM AUTHOR]

Compact massive relic galaxies are a class of galaxies that exhibit characteristics suggesting they have remained largely unchanged since their initial formation, making them 'relics' of the early Universe. These galaxies represent a distinct class characterized by strongly peaked high-velocity dispersion profiles with large rotational velocities. This study investigates the formation of such galaxies within the framework of Milgromian dynamics (MOND), offering a unique perspective on their origin without invoking the presence of cold or warm dark matter. Our analysis focuses on the collapse dynamics of isolated non-rotating post-big bang gas clouds, revealing kinematic and density profiles comparable to observed compact massive relic galaxies like NGC 1277, Mrk 1216, and PGC 032873. The findings underscore the natural emergence of compact massive relic galaxies within a MOND-based Universe, providing valuable insights into the interplay between gravitational dynamics and galaxy formation. [ABSTRACT FROM AUTHOR]

Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the κ -model. An additional connection, between the κ -model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted Gravity (RG), is likewise presented. All these models are built to overtake the DM paradigm, or at least to strongly reduce the dark matter content. Whereas they rely on different formalisms, however, all four seem to suggest that the universal parameter, a 0 , appearing in MOND theory could intrinsically be correlated to either the sole baryonic mean mass density (RG and κ -model) and/or to the dimension of the object under consideration (NFDG and κ -model). We then confer to parameter a 0 a more flexible status of multiscale parameter, as required to explain the dynamics together in galaxies and in galaxy clusters. Eventually, the conformal gravity theory (CFT) also seems to have some remote link with the κ -model, even though the first one is an extension of general relativity, and the second one is Newtonian in essence. The κ -model has been tested on a small sample of spiral galaxies and in galaxy clusters. Now, we test this model on a large sample of galaxies issued from the SPARC database. [ABSTRACT FROM AUTHOR]

Since the middle of the 20th century, an understanding of the diversity of the natural magnetohydrodynamic phenomena surrounding us has begun to emerge. Magnetohydrodynamic nature manifests itself in such seemingly heterogeneous processes as the flow of water in the world's oceans, the movements of Earth's liquid core, the dynamics of the solar magnetosphere and galactic electromagnetic fields. Their close relationship and multifaceted influence on human life are becoming more and more clearly revealed. The study of these phenomena requires the development of theory both fundamental and analytical, unifying a wide range of phenomena, and specialized areas that describe specific processes. The theory of translational fluid motion is well developed, but for most natural phenomena, this condition leads to a rather limited model. The fluid motion in the cavity of a rotating body such that the Coriolis forces are significant has been studied much less. A distinctive feature of the problems under consideration is their significant nonlinearity, (i.e., the absence of a linear approximation that allows one to obtain nontrivial useful results). From this point of view, the studies presented here were selected. This review presents studies on the movements of ideal and viscous fluids without taking into account electromagnetic phenomena (non-conducting, non-magnetic fluid) and while taking them into account (conducting fluid). Much attention is payed to the macroscopic movements of sea water (conducting liquid) located in Earth's magnetic field, which spawns electric currents and, as a result, an induced magnetic field. Exploring the processes of generating magnetic fields in the moving turbulent flows of conducting fluid in the frame of dynamic systems with distributed parameters allows better understanding of the origin of cosmic magnetic fields (those of planets, stars, and galaxies). Various approaches are presented for rotational and librational movements. In particular, an analytical solution of three-dimensional unsteady magnetohydrodynamic equations for problems in a plane-parallel configuration is presented. [ABSTRACT FROM AUTHOR]

We use numerical simulations to model Gaia  DR3 data with the aim of constraining the Milky Way (MW) bar and spiral structure parameters. We show that both the morphology and the velocity field in MW-like galactic disc models are strong functions of time, changing dramatically over a few tens of Myr. This suggests that by finding a good match to the observed radial velocity field, vR (x, y), we can constrain the bar-spiral orientation. Incorporating uncertainties into our models is necessary to match the data; most importantly, a heliocentric distance uncertainty above 10–15 per cent distorts the bar's shape and vR quadrupole pattern morphology, and decreases its apparent angle with respect to the Sun-Galactocentric line. An excellent match to the Gaia   DR3 vR (x, y) field is found for a simulation with a bar length Rb ≈ 3.6 kpc. We argue that the data are consistent with an MW bar as short as ∼3 kpc, for moderate strength inner disc spiral structure (A 2/ A 0 ≈ 0.25) or, alternatively, with a bar length up to ∼5.2 kpc, provided that spiral arms are quite weak (A 2/ A 0 ≈ 0.1), and is most likely in the process of disconnecting from a spiral arm. We demonstrate that the bar angle and distance uncertainty can similarly affect the match between our models and the data – a smaller bar angle (20° instead of 30°) requires smaller distance uncertainty (20 per cent instead of 30 per cent) to explain the observations. Fourier components of the face-on density distribution of our models suggest that the MW does not have strong m = 1 and/or m  = 3 spirals near the solar radius. [ABSTRACT FROM AUTHOR]

To gain a better understanding of the Andromeda galaxy M31 and its role in the Local Group, measuring its mass precisely is essential. In this work, we have constructed the rotation curve of M31 out to ∼125 kpc using 13 679 M31 objects obtained from various sources, including the LAMOST data release 9 (LAMOST DR9), the DESI survey, and relevant literature. We divide all objects in our sample into bulge, disc, and halo components. For the sources in the M31 disc, we have measured their circular velocities by a kinematic model with asymmetric drift corrections. For the bulge and halo objects, we calculate their velocity dispersions and use the spherical and projected Jeans equation to obtain the circular velocities. Our findings indicate a nearly isotropic nature for the M31 bulge, while the halo exhibits tangential anisotropy. The results show that the rotation curve remains constant at ∼220 km s−1 up to radius ∼25 kpc and gradually decreases to ∼170 km s−1 further out. Based on the newly determined rotation curve, we have constructed a mass distribution model for M31. Our measurement of the M31 virial mass is |$M_{\rm vir} = 1.14^{+0.51}_{-0.35} \times 10^{12} M_\odot$| within r vir = 220 ± 25 kpc. [ABSTRACT FROM AUTHOR]

Relic galaxies are massive, compact, and quiescent objects observed in the local Universe that have not experienced any significant interaction episodes or merger events since about z  = 2, remaining relatively unaltered since their formation. On the other hand, massive and compact early-type galaxies (cETGs) in the local Universe appear to show similar properties to Relic galaxies, despite having substantial accretion history. Relic galaxies, with frozen history, can provide important clues about the intrinsic processes related to the evolutionary pathways of ETGs and the role that mergers play in their evolution. Using the high-resolution cosmological simulation TNG50-1 from IllustrisTNG project, we investigate the assembly history of a sample of massive, compact, old, and quiescent subhaloes split by satellite accretion fraction. We compare the evolutionary pathways at three cosmic epochs: z  = 2, z  = 1.5, and z  = 0, using the orbital decomposition numerical method to investigate the stellar dynamics of each galactic kinematical component and their environmental correlations. Our results point to a steady pathway across time that is not strongly dependent on the mergers or the environment. Relics and cETGs do not show a clear preference for high- or low-density environments within the volume explored at z  = 0, as they are found in both scenarios. However, the progenitors of Relic galaxies have consistently resided in high-density environments since z  = 2, while cETGs were shifted to such environments at a later stage. The merger history can be recovered from the stellar kinematics imprints in the local Universe. Relics and cETGs show consistently dynamical similarities at z  = 2 and differences at z  = 0 to disc, bulge, and hot inner stellar halo. In the current scenario, the mergers that drive the growth of cETGs do not give rise to a new and distinct evolutionary pathway when compared to Relics. [ABSTRACT FROM AUTHOR]

Ring galaxies are rare in the Universe. A head-on or off-centre collision between an intruder galaxy and a disc galaxy leads to a collisional ring galaxy (CRG) when the intruder-to-target mass ratio (ITMR) is over 0.1 in Newtonian dynamics. Within the framework of Milgromian dynamics, the strong equivalence principle is violated due to the presence of an external field. When two galaxies collide towards each other, the dynamical mass of the phantom dark halo in a galaxy is suppressed by the external field induced by the other galaxy. As a consequence of such suppression, the gravitational perturbation for the target galaxy introduced by a collision is weakened. In this case, a minor collision may not be capable of generating a CRG. In this work, we address this issue and perform a series of numerical simulations of collisions by tuning the values of ITMR. We find that the critical ITMR is 0.5 in MOND, which is much larger than that in Newtonian dynamics. The observed massive ring galaxies, such as Arp 147, can be effectively interpreted by CRGs in Milgrom's Modified Newtonian Dynamics (MOND). This interpretation does not necessitate the presence of dark matter halos for either the target or intruder galaxies. Moreover, for a larger inclination angle or a larger impact parameter, the off-centred ring structure is fainter. The larger critical ITMR indicates that it is harder to form a CRG in MOND. To account for the observed ring structures of the NGC 922-like galaxies in MOND, it is necessary to invoke other scenarios than a dry minor collision. [ABSTRACT FROM AUTHOR]

Many models have been proposed to minimize the dark matter (DM) content in various astronomical objects at every scale in the Universe. The most widely known model is MOdified Newtonian dynamics (MOND). MOND was first published by Mordehai Milgrom in 1983. A second concurrent model is modified gravity, which is a covariant scalar–tensor–vector extension of general relativity. Other theories also exist but have not been broadly applied to a large list of astronomical objects. Eventually, we can also mention the Newtonian fractional-dimension gravity, a gravity theory based on spaces with fractional (i.e., non-integer) dimension. A new model, called κ-model, based on very elementary phenomenological considerations, has recently been proposed in the astrophysics field. This model shows that the presence of DM can be considerably minimized with regard to the dynamics of galaxies. The κ-model belongs to the general family of theories descended from MOND. Under this family of theories, there is no need to develop a highly uncertain DM sector of physics to explain the observations. [ABSTRACT FROM AUTHOR]

The second data release of ESA's Gaia mission revealed numerous signatures of disequilibrium in the Milky Way's disc. These signatures are seen in the planar kinematics of stars, which manifest as ridges and ripples in R – v ϕ, and in vertical kinematics, where a prominent spiral is seen in the z – vz phase space. In this work, we show an equivalent Δ R – v R phase spiral forms following a perturbation to the disc. We demonstrate the behaviour of the Δ R – v R phase spirals in both a toy model and a high-resolution N -body simulation of a satellite interaction. We then confront these models with the data, where we find partial Δ R–v R phase spirals in the Solar neighbourhood using the most recent data from Gaia DR3. This structure indicates ongoing radial phase mixing in the Galactic disc, suggesting a history of recent perturbations, either through internal or external (e.g. satellite) processes. Future work modelling the z – vz and Δ R–v R phase spirals in tandem may help break degeneracy's between possible origins of the perturbation. [ABSTRACT FROM AUTHOR]

We study the long-term evolution of the Milky Way (MW) over cosmic time by modeling the star formation, cosmic rays, metallicity, stellar dynamics, outflows, and inflows of the galactic system to obtain various insights into the galactic evolution. The mass accretion is modeled by the results of cosmological N -body simulations for the cold dark matter. We find that the star formation rate is about half the mass accretion rate of the disk, given the consistency between observed Galactic diffuse X-ray emissions (GDXEs) and possible conditions driving the Galactic wind.Our model simultaneously reproduces the quantities of star formation rate, cosmic rays, metals, and the rotation curve of the current MW. The most important predictions of the model are that there is an unidentified accretion flow with a possible number density of ∼10−2 cm−3 and that part of the GDXEs originates from a hot, diffuse plasma which is formed by consuming about |$10\%$| of supernova explosion energy. The latter is the science case for future X-ray missions: XRISM, Athena, and so on. We also discuss further implications of our results for the planet formation and observations of external galaxies in terms of multi-messenger astronomy. [ABSTRACT FROM AUTHOR]

Double bars make up a significant fraction of barred galaxies. We propose a new formation scenario for double bars that involves tidal interactions. We demonstrate the viability of this scenario using two examples of simulated galaxies from run TNG50-1 of the IllustrisTNG project. In the proposed scenario the inner bar forms first, either in isolation, via instabilities, or through previous tides. The outer bar forms later from the material that is tidally distorted by a strong interaction. The inner and outer bars formed this way rotate with different pattern speeds and can be mistaken for a single bar when their phases align. The double-barred structure is stable and can last for at least 3 Gyr. The inner bars of the tidally induced double bars can also have big sizes, which can possibly explain the origin of sizable inner bars recently found in some galaxies. [ABSTRACT FROM AUTHOR]

The precise ascertainment of stellar ages is pivotal for astrophysical research into stellar characteristics and galactic dynamics. To address the prevalent challenges of suboptimal accuracy in stellar age determination and limited proficiency in apprehending nonlinear dynamics, this study introduces an enhanced model for stellar age determination, amalgamating the Feedforward Neural Network (FFNN) with TabNet (termed FFNN–TabNet). The methodology commences with the acquisition of a stellar dataset via meticulous cross-matching. Subsequent advancements encompass refinements to the activation functions within TabNet, coupled with augmentations to the Attentive transformer module by incorporating an FFNN module. These enhancements substantially boost training efficiency and precision in age estimation while amplifying the model's capability to decode complex nonlinear interactions. Leveraging Bayesian Optimization Algorithm (BOA) for hyperparameter fine-tuning further elevates the model's efficiency. Comprehensive ablation and comparative analyses validate the model's superior performance in stellar age determination, demonstrating marked enhancements in accuracy. The experiment also demonstrates an enhanced ability of the model to capture nonlinear relationships between features. [ABSTRACT FROM AUTHOR]

We investigate the effects of halo kinematics on the dynamics of stellar discs by simulating the evolution of isolated disc–halo systems from equilibrium initial conditions. Our main results come from four simulations where the initial disc is identical and the halo is either treated as a rigid potential or is 'live' with isotropic orbits or orbits that preferentially rotate with or counter to the disc. We confirm previous results that bar formation is more vigorous in models with a live halo than a rigid one and is further enhanced when halo orbits preferentially rotate with the disc. We discuss two types of buckling events with different symmetries about the mid-plane, one that occurs just as the bar is forming and the other well after the bar has been established. We also show that warps are most easily excited and maintained when the halo is counter-rotating with the disc, in agreement with theoretical predictions. Our most novel result is the discovery of a rotating halo instability, which causes the disc and halo cusp to spiral outward from the centre-of-mass of the system whether the halo rotates with the disc or counter to it and also occurs in a disc–bulge–halo system that does not form a bar. We provide a heuristic linear model that captures the essential dynamics of the instability. [ABSTRACT FROM AUTHOR]

Dark matter may be composed of ultralight bosons whose de Broglie wavelength in galaxies is |$\lambda \sim 1\, {\rm kpc}$|⁠. The standard model for this fuzzy dark matter (FDM) is a complex scalar field that obeys the Schrödinger–Poisson equations. The wavelike nature of FDM leads to fluctuations in the gravitational field that can pump energy into the stellar components of a galaxy. Heuristic arguments and theoretical analyses suggest that these fluctuations can be modelled by replacing FDM with a system of quasi-particles (QPs). We test this hypothesis by comparing self-consistent simulations of a Schrödinger field with those using a system of QPs in one spatial dimension. Simulations of pure FDM systems allow us to derive a phenomenological relation between the number of QPs that is required to model FDM with a given de Broglie wavelength. We also simulate systems of FDM and stars and find that the FDM pumps energy into the stars whether it is described by QPs or a Schrödinger field with the FDM adiabatically contracting and the stellar system adiabatically expanding. However, we find that QPs overestimate dynamical heating. [ABSTRACT FROM AUTHOR]