Stars born on near-circular orbits in spiral galaxies can subsequently migrate to different orbits due to interactions with non-axisymmetric disturbances within the disc such as bars or spiral arms. This paper extends the study of migration to examine the role of external influences using the example of the interaction of the Sagittarius dwarf galaxy (Sgr) with the Milky Way (MW). We first make impulse approximation estimates to characterize the influence of Sgr disc passages. The tidal forcing from Sgr can produce changes in both guiding radius ($ΔR_g$) and orbital eccentricity, as quantified by the maximum radial excursion, $ΔR_ {\rm max} $. These changes follow a quadrupole-like pattern across the face of the disc, with amplitude increasing with Galactocentric radius. We next examine a collisionless N-body simulation of a Sgr-like satellite interacting with a MW-like galaxy and find that Sgr's influence in the outer disc dominates over the secular evolution of orbits between disc passages. Finally, we use the same simulation to explore possible observable signatures of Sgr-induced migration by painting the simulation with different age stellar populations. We find that following Sgr disc passages, the migration it induces manifests within an annulus as an approximate quadrupole in azimuthal metallicity variations ($δ_ {\rm [Fe/H]} $), along with systematic variations in orbital eccentricity, $ΔR_ {\rm max} $. These systematic variations can persist for several rotational periods. We conclude that this combination of signatures may be used to distinguish between the different migration mechanisms shaping the chemical abundance patterns of the Milky Way's thin disc.
Stellar streams are a promising tool to study the Milky Way's dark matter subhalo population, as interactions with subhalos could produce substructure in streams. However, other possible causes for substructure first need to be well understood. Here we studied the kinematics and the unusual morphology of the stellar stream Jhelum. Using a combination of ground-based photometry and Gaia EDR3 astrometry, we characterized the morphology of Jhelum. We combined this new data with radial velocities from the literature to perform orbit integrations of the stream in static Galactic potentials. We also…
In this letter, we report the discovery of an intriguing HVS (J1443+1453) candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph). The star is an old and very metal-poor low-mass main-sequence turn-off star (age $\sim14.0$ Gyr and [Fe/H] $= -2.23$ dex) and has a total velocity of $559.01^{+135.07}_{-87.40}$ km s$^{-1}$ in the Galactic rest-frame and a heliocentric distance of $2.90^{+0.72}_{-0.48}$ kpc. The velocity of J1443+1453 is larger than the escape speed at its position, suggesting it a promising HVS candidate. By reconstructing its trajectory in the Galactic …
A compact gas cloud G2 is predicted to reach the pericenter of its orbit around the super massive black hole (SMBH) of our galaxy, Sagittarius A* (Sgr A*). This event will give us a rare opportunity to observe the interaction between SMBH and gas around it. We report the result of the fully three-dimensional simulation of the evolution of G2 during the first pericenter passage. The strong tidal force by the SMBH stretches the cloud along its orbit, and compresses it strongly in the vertical direction, resulting in the heating up and flaring up of the cloud. The bolometric luminosity will reach…
The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of SgrB2, we encounter the SgrB2(DS) region which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended HII region. We use the Very Large Array in its CnB and D configurations, and in the frequency bands C (4--8 GHz) and X (8--12 GHz) to observe the whole SgrB2 complex. Continuum and radio recombination line maps are obtained. We detect radio continuum emission in Sg…
The Monoceros ring is a collection of stars in nearly-circular orbits at roughly 18 kpc from the Galactic center. It may have originated (i) as the response of the disc to perturbations excited by satellite companions or (ii) from the tidal debris of a disrupted dwarf galaxy. The metallicity of Monoceros stars differs from that of disc stars at comparable Galactocentric distances, an observation that disfavours the first scenario. On the other hand, circular orbits are difficult to accommodate in the tidal-disruption scenario, since it requires a satellite which at the time of disruption was i…
We present a catalog of unbound stellar pairs, within 100 pc of the Sun, that are undergoing close, hyperbolic, encounters. The data are drawn from the GAIA EDR3 catalogue, and the limiting factors are errors in the radial distance and unknown velocities along the line of sight. Such stellar pairs have been suggested (Hansen & Zuckerman 2021) to be possible events associated with the migration of technological civilisations between stars. As such, this sample may represent a finite set of targets for a SETI search based on this hypothesis. Our catalog contains a total of 132 close passage even…
Recent knowledge of Galactic dynamics suggests that stars radially move on the disk when they encounter transient spiral arms that are naturally generated during the process of disk formation. We argue that a large movement of the solar system from the innermost disk over its lifetime is inferred from a comparison of the solar composition with those of solar twins within the Galactic chemical evolution framework. The implied metal-rich environment at the Sun's birthplace and formation time is supported by measured silicon isotopic ratios in presolar silicon carbide grains. We perform numerical…
Using the RAdial Velocity Experiment fourth data release (RAVE DR4), and a new metallicity calibration that will be also taken into account in the future RAVE DR5, we investigate the existence and the properties of super-solar metallicity stars ([M/H] > +0.1 dex) in the sample, and in particular in the Solar neighbourhood. We find that RAVE is rich in super-solar metallicity stars, and that the local metallicity distribution function declines remarkably slowly up to +0.4 dex. Our results show that the kinematics and height distributions of the super-solar metallicity stars are identical to tho…
We present the kinematics of Blue Straggler (BS) stars identified in the Canada-France-Imaging-Survey (CFIS), covering 4000 deg$^2$ on the sky in the $u$-band. The BS sample, characterised through CFIS and Pan-STARRS photometry, has been kinematically decomposed into putative halo and disc populations after cross-matching with Gaia astrometry and SDSS/SEGUE/LAMOST spectroscopy. This decomposition clearly reveals the strong flaring of the outer Milky Way disc. In particular, we show that we can detect this flaring up to a vertical height of $|Z| \simeq 8$ kpc at a Galactocentric distance of $R\…
We study the long-term evolution of two or more stellar black holes (BHs) on initially separated but unstable circular orbits around a supermassive BH (SMBH). Such a close-packed orbital configuration can naturally arise from BH migrations in the AGN disk. Dynamical instability of the orbits leads to recurring close encounters between two BHs, during which the BH separation $r_{\rm p}$ becomes less than the Hill radius $R_{\rm H}$. In the rare very close encounters (with $r_{\rm p}$ several orders of magnitude less than $R_{\rm H}$), a tight merging BH binary can form with the help of gravitat…
Galactic disks are highly responsive systems that often undergo external perturbations and subsequent collisionless equilibration, predominantly via phase-mixing. We use linear perturbation theory to study the response of infinite isothermal slab analogues of disks to perturbations with diverse spatio-temporal characteristics. Without self-gravity of the response, the dominant Fourier modes that get excited in a disk are the bending and breathing modes, which, due to vertical phase-mixing, trigger local phase-space spirals that are one- and two-armed, respectively. We demonstrate how the later…
The evolution of the Milky Way disk, which contains most of the stars in the Galaxy, is affected by several phenomena. For example, the bar and the spiral arms of the Milky Way induce radial migration of stars and can trap or scatter stars close to orbital resonances. External perturbations from satellite galaxies can also have a role, causing dynamical heating of the Galaxy, ring-like structures in the disk and correlations between different components of the stellar velocity. These perturbations can also cause 'phase wrapping' signatures in the disk, such as arched velocity structures in the…
We analyse the potential migration of massive planets forming far away from an inner planetary system. For this, we follow the dynamical evolution of the orbital elements of a massive planet undergoing a dissipative process with a gas disc centred around the central sun. We use a new method for post-Newtonian, high-precision integration of planetary systems containing a central sun by splitting the forces on a particle between a dominant central force and additional perturbations. In this treatment, which allows us to integrate with a very high-accuracy close encounters, all gravitational forc…
The main goal of Galactic Archaeology is understanding the formation and evolution of the basic Galactic components. This requires sophisticated chemo-dynamical modeling, where disc asymmetries (e.g., perturbations from the central bar, spirals arms, and infalling satellites) and non-equilibrium processes are taken into account self-consistently. Here we discuss the current status of Galactic chemo-dynamical modeling and focus on a recent hybrid technique, which helps circumvent traditional problems with chemical enrichment and star formation encountered in fully self-consistent cosmological s…
[Abridged] In this first paper of this series, we present a new approach for studying the chemo-dynamical evolution in disk galaxies, which consists of fusing disk chemical evolution models with compatible numerical simulations of galactic disks. This method avoids known star formation and chemical enrichment problems encountered in simulations. Here we focus on the Milky Way, by using a detailed thin-disk chemical evolution model and a simulation in the cosmological context, with dynamical properties close to those of our Galaxy. We show that, due to radial migration from mergers at high reds…
Observations by LIGO--Virgo of binary black hole mergers suggest a possible anti-correlation between black hole mass ratio ($q=m_{2}/m_{1}$) and the effective inspiral spin parameter $χ_{\rm eff}$, the mass-weighted spin projection onto the binary orbital angular momentum (Callister et al. 2021). We show that such an anti-correlation can naturally occur for binary black holes assembled in active galactic nuclei (AGN) due to spherical and planar symmetry-breaking effects. We describe a phenomenological model in which: 1) heavier black holes live in the AGN disk and tend to spin up into alignmen…
