We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star forming, dwarf galaxies in the Local Group, taken as part of the {\it Solo} survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613 and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2 and Phoenix) are close enough that their proper motions have already been derived using red giant branch stars. Systematic errors in Gaia DR2 are significant for NGC 6822, IC 1613 and WLM. We explore the orbits for these galaxies, and conclude that Phoenix, Leo A and WLM are unlikely to have interacted with the Milky Way or M31, unless these large galaxies are very massive ($\gtrsim 1.6 \times 10^{12}\,M_\odot$). We rule out a past interaction of NGC 6822 with M31 at $\sim 99.99\%$ confidence, and find there is a $<10$\% chance that NGC 6822 has had an interaction with the Milky Way. We examine the likely origins of NGC 6822 in the periphery of the young Local Group, and note that a future interaction of NGC 6822 with the Milky Way or M31 in the next 4\,Gyrs is essentially ruled out. Our measurements indicate that future Gaia data releases will provide good constraints on the interaction history for the majority of these galaxies.
The Solo (Solitary Local) Dwarf Galaxy survey is a volume limited, wide-field g- and i- band survey of all known nearby (<3 Mpc) and isolated (>300 kpc from the Milky Way or M31) dwarf galaxies. This set of 44 dwarfs are homogeneously analysed for quantitative comparisons to the satellite dwarf populations of the Milky Way and M31. In this paper, an analysis of the 12 closest Solo dwarf galaxies accessible from the northern hemisphere is presented, including derivation of their distances, spatial distributions, morphology, and extended structures, including their inner integrated light propert…
We compare and contrast the stellar structures of isolated Local Group dwarf galaxies, as traced by their oldest stellar populations, with the satellite dwarf galaxies of the Milky Way and M31. All Local Group dwarfs with Mv < -6 and surface brightness < 26.5 mags. per square arcsec. are considered, taking advantage of measurements from surveys that use similar observations and analysis techniques. For the isolated dwarfs, we use the results from Solitary Local (Solo) Dwarf Galaxy Survey. We begin by confirming that the structural and dynamical properties of the two satellite populations are n…
We introduce the Solitary Local Dwarfs Survey (Solo), a wide field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multi-band imaging from CFHT/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than Mv = -18 situated beyond the nominal virial radius of the Milky Way and M31 (>300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius Dwarf Irregular Galaxy (Sag DIG), one of t…
We compare the distribution in position and velocity of nearby stars from the Gaia DR2 radial velocity sample with predictions of current theories for spirals in disc galaxies. Although the rich substructure in velocity space contains the same information, we find it more revealing to reproject the data into action-angle variables, and we describe why resonant scattering would be more readily identifiable in these variables. We compute the predicted changes to the phase space density, in multiple different projections, that would be caused by a simplified isolated spiral pattern, finding widel…
CONTEXT. This is the second paper of a series on Galactic OB groups that uses astrometric and photometric data from Gaia and spectral classifications from GOSSS and LiLiMaRlin. The previous paper was based on Gaia DR2, this is based on Gaia EDR3. AIMS. The two aims of this paper are to revise the results for the sample from paper I using Gaia EDR3 data and to expand the sample of analyzed stellar groups to 26, from Villafranca O-001 to Villafranca O-026. METHODS. We use GOSSS to select Galactic stellar groups with O stars and an updated version of the method in paper 0 of this series, combinin…
Gaia DR2 has revealed new small-scale and large-scale patterns in the phase-space distribution of stars in the Milky Way. In cylindrical Galactic coordinates $(R,ϕ,z)$, ridge-like structures can be seen in the \vphiR{} plane and asymmetric arch-like structures in the \vphivR{} plane. We show that the ridges are also clearly present when the third dimension of the \vphiR{} plane is represented by $\langle z \rangle$, $\langle V_z \rangle$, $\langle V_R \rangle$, $\langle$[Fe/H]$\rangle$ and $\langle[α/{\rm Fe}]\rangle$. The maps suggest that stars along the ridges lie preferentially close to th…
$N$-body modelling of the ED-2 stream progenitor shows Gaia BH3's formation involved dynamical interactions
Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik（海德堡大学天体物理中心理论天体物理研究所）；Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB)（巴塞罗那宇宙科学研究所）；Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB)（巴塞罗那大学量子物理与天体物理系）；ICREA（加泰罗尼亚高级研究学院）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究院）
Search for Quasar Pairs with ${\it Gaia}$ Astrometric Data. I. Method and Candidates
Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；College of Intelligent Systems Science and Engineering, Hubei Minzu University（湖北民族大学智能系统科学与工程学院）；Department of Physics, Nanchang University（南昌大学物理系）；Center for Relativistic Astrophysics and High Energy Physics, Nanchang University（南昌大学相对论天体物理与高能物理中心）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）
We study the spontaneous generation and evolution of bending waves in $N$-body simulations of two isolated Milky Way-like galaxy models. The models differ by their disc-to-halo mass ratios, and hence by their susceptibility to the formation of a bar and spiral structure. Seeded from shot noise in the particle distribution, bending waves rapidly form in both models and persist for many billions of years. Waves at intermediate radii manifest as corrugated structures in vertical position and velocity that are tightly wound, morphologically leading, and dominated by the $m=1$ azimuthal Fourier com…
High-Mass X-ray Binaries (HMXBs) are produced after the first supernova event in a massive binary. These objects are intrinsically young, and can suffer from a significant natal kick. As such, the progenitors of HMXBs are likely to have formed away from the current location of the X-ray emitting systems. We aim to find the birthplace of the known HMXBs of our Milky Way. Specifically, we want to answer the question whether the formation of HMXBs can be associated to open stellar clusters and/or Galactic spiral structures, and infer from that the time elapsed since the first supernova event. We …
Gravitational microlensing may detect dark stellar remnants - black holes or neutron stars - even if they are isolated. However, it is challenging to estimate masses of isolated dark stellar remnants using solely photometric data for microlensing events. A recent analysis of OGLE-III long-timescale microlensing events exhibiting the annual parallax effects claimed that a number of bright events were due to "mass-gap" objects (with masses intermediate between those of neutron stars and black holes). Here, we present a detailed description of the updated and corrected method that can be used to …
The role of accretion efficiency, natal kicks, and angular momentum transport in the formation of the Gaia black holes
Universität Heidelberg（海德堡大学）；University of Padova（帕多瓦大学）；INAF - Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Universitat de Barcelona（巴塞罗那大学）
We apply Noether's theorem to observations of main-sequence stars from the Gaia Data Release 2 archive to probe the matter distribution function of the Galaxy. That is, we examine the axial symmetry of stars at vertical heights $z$, $0.2 \le |z| \le 3$ kpc, to probe the quality of the angular momentum $L_z$ as an integral of motion. The failure of this symmetry test would speak to a Milky Way, in both its visible and dark matter, that is not isolated and/or not in steady state. The left-right symmetry-breaking pattern we have observed, north and south, reveals both effects, with a measured dev…
We search for runaway stars in the Large Magellanic Cloud (LMC) by computing the space velocities of the visually brightest stars in the LMC that are included in the Gaia TGAS proper motion catalog. We compare with predictions from stellar dynamical models to obtain (peculiar) velocities relative to their local stellar environment. Two of the 31 stars have unusually high proper motions. Of the remaining 29 stars we find that most objects in this sample have velocities in very good agreement with model predictions of a circularly rotating disk model. Indeed the excellent fit to the model implie…
The Contribution of Disrupted Dense Star Clusters to Gaia's Compact Object Binaries
University of Toronto（多伦多大学）；Canadian Institute for Theoretical Astrophysics, University of Toronto（加拿大理论天体物理研究所，多伦多大学）；McMaster University（麦克马斯特大学）；Instituto Galego de Física de Altas Enerxías, Universidade de Santiago de Compostela（加利西亚高能物理研究所，圣地亚哥-德孔波斯特拉大学）；California Institute of Technology（加州理工学院）
We aim to observationally and statistically constrain the influence of flybys in the formation and evolution of debris disks. We compiled a sample of 254 debris disks with ages between 2 Myr and 8 Gyr that are either part of an association or isolated, drawing the binary and planetary companions of the systems mainly from the literature. Using the Gaia eDR3 astrometric data and radial velocities of our sample, as well as all the sources in a specific region of the sky, we reconstructed the relative linear motions in the last 5 Myr and made predictions for the next 2 Myr. Relating the Hill radi…
The Milky Way's progenitor experienced several merger events which left their imprints on the stellar halo, including the Gaia-Sausage/Enceladus. Recently, it has been proposed that this event perturbed the proto-disk and gave rise to a metal rich ([Fe/H] $>-1$) low angular momentum ($v_ϕ < 100$ km/s) stellar population. These stars have dynamical and chemical properties different from the accreted stellar halo, but are continuous with the canonical thick disk. In this letter, we use a hydrodynamical simulation of an isolated galaxy which develops clumps that produce a bimodal thin$+$thick dis…
Context. Hypervelocity stars move fast enough to leave the gravitational field of their home galaxies and venture into intergalactic space. The most extreme examples known have estimated speeds in excess of 1000 km/s. These can be easily induced at the centres of galaxies via close encounters between binary stars and supermassive black holes; however, a number of other mechanisms operating elsewhere can produce them as well. Aims. Recent studies suggest that hypervelocity stars are ubiquitous in the local Universe. In the Milky Way, the known hypervelocity stars are anisotropically distributed…
Within $Λ$CDM, dwarf galaxies like the Large Magellanic Cloud (LMC) are expected to host numerous dark matter subhalos, several of which should host faint dwarf companions. Recent Gaia proper motions confirm new members of the LMC-system in addition to the previously known SMC, including two classical dwarf galaxies ($M_\ast$ > $10^5$ M$_{\odot}$; Carina and Fornax) as well as several ultra-faint dwarfs (Car2, Car3, Hor1, and Hyd1). We use the Feedback In Realistic Environments (FIRE) simulations to study the dark and luminous (down to ultrafaint masses, $M_\ast$ ~ $6\times10^3$ M$_{\odot}$) s…
Based on observations from the \emph{FourStar} near-infrared camera on the 6.5m Baade-Magellan telescope at Las Campanas, Chile, we present calibrations of the $JHK$ luminosities of stars defining the tip of the red giant branch (TRGB) in the halo of the Local Group dwarf galaxy IC 1613. We employ metallicity-independent (rectified) T-band magnitudes---constructed using $J,H$ and $K$-band magnitudes and both $(J-H)~ \& ~(J-K)$ colors in order to flatten the upward-sloping red giant branch tips as otherwise seen in their apparent color-magnitude diagrams. We describe and quantify the advantages…
Stars slingshotted by the supermassive black hole at the Galactic centre will escape the Milky Way so quickly that their trajectories will be almost straight lines. Previous works have shown how these `hypervelocity stars' are subsequently deflected by the gravitational field of the Milky Way and the Large Magellanic Cloud (LMC), but have neglected to account for the reflex motion of the Milky Way in response to the fly by of the LMC. A consequence of this motion is that the hypervelocity stars we see on the outskirts of the Milky Way today were ejected from where the Milky Way centre was hund…
The direction of the spin vectors of disk galaxies change over time. We present the tilting rate of a sample of galaxies in the NIHAO suite of cosmological hydrodynamical simulations. Galaxies in our sample have been selected to be isolated and to have well determined spins. We compare the tilting rates to the predicted observing limit of Gaia, finding that our entire sample lies above the limit, in agreement with previous work. To test the role of dark matter and of gas we compare the weighted Pearson's correlation coefficients between the tilting rates and various properties. We find no corr…
We study the vertical perturbations in the galactic disc of the Milky Way-size high-resolution hydrodynamical cosmological simulation named GARROTXA. We detect phase spirals in the vertical projection $Z- V_{Z}$ of disc's stellar particles for the first time in this type of simulations. Qualitatively similar structures were detected in the recent Gaia data, and their origin is still under study. In our model the spiral-like structures in the phase space are present in a wide range of times and locations across the disc. By accounting for an evolving mix of stellar populations, we observe that,…
We present a panoramic survey of the isolated Local Group dwarf irregular galaxy NGC 6822. Our photometry reaches $\sim2-3$ magnitudes deeper than most previous studies and spans the widest area around the dwarf compared to any prior work. We observe no stellar over-densities in the outskirts of NGC 6822 to $V\sim 30$ mag$\,$arcsec$^{-2}$ and a projected radius of $16.5$ kpc. This indicates that NGC 6822 has not experienced any recent interaction with a companion galaxy, despite previous suggestions to the contrary. Similarly, we find no evidence for any dwarf satellites of NGC 6822 to a limit…
The Milky Way's stellar disk can tilt in response to torques that result from infalling satellite galaxies and their associated tidal debris. In this work, we explore the dynamics of disk tilting by running N-body simulations of mergers in an isolated, isotropic Milky Way-like host galaxy, varying over satellite virial mass, initial position, and orbit. We develop and validate a first-principles understanding of the dynamics that govern how the host galaxy's stellar disk responds to the satellite's dark matter debris. We find that the degree of disk tilting can be large for cosmologically-moti…
Charting the Galactic Underworld I: Comprehensive simulations of the kinematics, rates, and demographics of Milky Way black holes
Center for Computational Astrophysics, Flatiron Institute（计算天体物理学中心，平顿研究所）；McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University（麦威廉斯宇宙学与天体物理学中心，卡内基梅隆大学物理系）；University of Arizona, Department of Astronomy & Steward Observatory（亚利桑那大学，天文系与斯图尔德天文台）；Department of Astronomy, University of Washington（华盛顿大学天文系）
