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We present the first emission spectrum of the hot Jupiter WASP-17 b using one eclipse observation from the JWST Near Infrared Imager and Slitless Spectrograph (NIRISS) Single Object Slitless Spectroscopy (SOSS) mode. Covering a wavelength range of 0.6 to 2.8 microns, our retrieval analysis reveals a strong detection of H2O in WASP-17b dayside atmosphere (6.4sigma). Our retrievals consistently favor a super-solar dayside H2O abundance and a non-inverted temperature-pressure profile over a large pressure range. Additionally, our examination of the brightness temperature reveals excess emission below 1 microns, suggesting the possibility of a high internal temperature (600 to 700 K) and/or contributions from reflected light. We highlight that JWST emission spectroscopy retrieval results can be sensitive to whether negative eclipse depths are allowed at optical wavelengths during light curve fitting. Our findings deepen our understanding of WASP-17b atmospheric composition while also highlighting the sensitivity of our results to pressure-temperature profile parameterizations. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS)., Comment: Accepted for Publication in the Astronomical Journal (AJ) October 4, 2024

We present the first spectroscopic characterisation of the dayside atmosphere of WASP-17b in the mid-infrared using a single JWST MIRI/LRS eclipse observation. From forward-model fits to the 5-12 $\mu$m emission spectrum, we tightly constrain the heat redistribution factor of WASP-17b to be 0.92$\pm$0.02 at the pressures probed by this data, indicative of inefficient global heat redistribution. We also marginally detect a supersolar abundance of water, consistent with previous findings for WASP-17b, but note our weak constraints on this parameter. These results reflect the thermodynamically rich but chemically poor information content of MIRI/LRS emission data for high-temperature hot Jupiters. Using the eclipse mapping method, which utilises the signals that the spatial emission profile of an exoplanet imprints on the eclipse light curve during ingress/egress due to its partial occultation by the host star, we also construct the first eclipse map of WASP-17b, allowing us to diagnose its multidimensional atmospheric dynamics for the first time. We find a day-night temperature contrast of order 1000 K at the pressures probed by this data, consistent with our derived heat redistribution factor, along with an eastward longitudinal hotspot offset of $18.7^{+11.1\deg}_{-3.8}$, indicative of the presence of an equatorial jet induced by day-night thermal forcing being the dominant redistributor of heat from the substellar point. These dynamics are consistent with general circulation model predictions for WASP-17b. This work is part of a series of studies by the JWST Telescope Scientist Team (JWST-TST), in which we use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS)., Comment: 28 pages, 8 figures. Published in The Astronomical Journal

We present the atmospheric characterization of the substellar companion HD 19467 B as part of the pioneering JWST GTO program to obtain moderate resolution spectra (R$\sim$2,700, 3-5$\mu$m) of a high-contrast companion with the NIRSpec IFU. HD 19467 B is an old, $\sim$9 Gyr, companion to a Solar-type star with multiple measured dynamical masses. The spectra show detections of CO, CO$_2$, CH$_4$, and H$_2$O. We forward model the spectra using Markov Chain Monte Carlo methods and atmospheric model grids to constrain the effective temperature and surface gravity. We then use NEWERA-PHOENIX grids to constrain non-equilibrium chemistry parameterized by $K_{zz}$ and explore molecular abundance ratios of the detected molecules. We find an effective temperature of 1103 K, with a probable range from 1000--1200 K, a surface gravity of 4.50 dex, with a range of 4.14--5.00, and deep vertical mixing, log$_{10}$($K_{zz}$), of 5.03, with a range of 5.00--5.44. All molecular mixing ratios are approximately Solar, leading to a C/O $\sim$0.55, which is expected from a T5.5 brown dwarf. Finally, we calculate an updated dynamical mass of HD 19467 B using newly derived NIRCam astrometry which we find to be $71.6^{+5.3}_{-4.6} M_{\rm{Jup}}$, in agreement with the mass range we derive from evolutionary models, which we find to be 63-75 $M_{\rm{Jup}}$.These observations demonstrate the excellent capabilities of the NIRSpec IFU to achieve detailed spectral characterization of substellar companions at high-contrast close to bright host stars, in this case at a separation of $\sim$1.6\arcsec with a contrast of 10$^{-4}$ in the 3-5 $\mu$m range., Comment: 35 pages, 20 figures

We analyze four epochs of HST imaging over 18 years for the Draco dwarf spheroidal galaxy. We measure precise proper motions (PMs) for hundreds of stars and combine these with existing line-of-sight (LOS) velocities. This provides the first radially-resolved 3D velocity dispersion profiles for any dwarf galaxy. These constrain the intrinsic velocity anisotropy and resolve the mass-anisotropy degeneracy. We solve the Jeans equations in oblate axisymmetric geometry to infer the mass profile. We find the velocity dispersion to be radially anisotropic along the symmetry axis and tangentially anisotropic in the equatorial plane, with a globally-averaged value $\overline{\beta_{\mathrm B}}=-0.20^{+ 0.28}_{- 0.53}$, (where $1 - \beta_{\mathrm B} \equiv \langle v_{\mathrm{ tan}}^2 \rangle / \langle v_{\mathrm{ rad}}^2 \rangle$ in 3D). The logarithmic dark matter (DM) density slope over the observed radial range, $\Gamma_{\mathrm{ dark}}$, is $-0.83^{+ 0.32}_{- 0.37}$, consistent with the inner cusp predicted in $\Lambda$CDM cosmology. As expected given Draco's low mass and ancient star formation history, it does not appear to have been dissolved by baryonic processes. We rule out cores larger than 487, 717, 942 pc at respective 1-, 2-, 3-$\sigma$ confidence, thus imposing important constraints on the self-interacting DM cross-section. Spherical models yield biased estimates for both the velocity anisotropy and the inferred slope. The circular velocity at our outermost data point (900 pc) is $24.19^{+ 6.31}_{- 2.97} \ \mathrm{km~s^{-1}}s$. We infer a dynamical distance of $75.37^{+ 4.73}_{- 4.00}$ kpc, and show that Draco has a modest LOS rotation, with $\left = 0.22 \pm 0.09$. Our results provide a new stringent test of the so-called `cusp-core' problem that can be readily extended to other dwarfs., Comment: 35 pages, 18 figures, 3 Tables. Accepted for publication in ApJ. Journal version has better readability. Data is available at Zenodo: https://zenodo.org/records/11111113

We present the first JWST/NIRCam observations of the directly-imaged gas giant exoplanet $\beta$ Pic b. Observations in six filters using NIRCam's round coronagraphic masks provide a high signal-to-noise detection of $\beta$ Pic b and the archetypal debris disk around $\beta$ Pic over a wavelength range of $\sim$1.7-5 $\mu$m. This paper focuses on the detection of $\beta$ Pic b and other potential point sources in the NIRCam data, following a paper by Rebollido et al. which presented the NIRCam and MIRI view of the debris disk around $\beta$ Pic. We develop and validate approaches for obtaining accurate photometry of planets in the presence of bright, complex circumstellar backgrounds. By simultaneously fitting the planet's PSF and a geometric model for the disk, we obtain planet photometry that is in good agreement with previous measurements from the ground. The NIRCam data supports the cloudy nature of $\beta$ Pic b's atmosphere and the discrepancy between its mass as inferred from evolutionary models and the dynamical mass reported in the literature. We further identify five additional localized sources in the data, but all of them are found to be background stars or galaxies based on their color or spatial extent. We can rule out additional planets in the disk midplane above 1 Jupiter mass outward of 2 arcsec ($\sim$40 au) and away from the disk midplane above 0.05 Jupiter masses outward of 4 arcsec ($\sim$80 au). The inner giant planet $\beta$ Pic c remains undetected behind the coronagraphic masks of NIRCam in our observations., Comment: 30 pages, 14 figures, published in AJ

Context. Within $\Lambda$ Cold Dark Matter ($\Lambda$CDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3-5 members rather than individually. It was also suggested that this might be the reason behind the origin of satellite planes. Objects accreted in groups are expected to share similar specific total energy and angular momentum, and also identical orbital planes and directions. Aims. Looking at observations of Milky Way satellites, the dwarf galaxies Leo II, IV, V, Crater II, and the star cluster Crater 1 were proposed to be a vestige of group infall. The suggested "Crater-Leo group" shows a coherent distance gradient and all these objects align along a great circle on the sky. We use proper motion data to investigate whether the phase-space distribution of the members of the proposed group are indeed consistent with group infall. Methods. To further investigate this possibility, we use Gaia Data Release 3 (DR3) and new Hubble Space Telescope (HST) proper motions, $(\mu_{\alpha*}, \mu_\delta) = (-0.1921 \pm 0.0514, -0.0686 \pm 0.0523)$ mas yr$^{-1}$ for Leo IV and $(\mu_{\alpha*}, \mu_\delta) = (0.1186 \pm 0.1943, -0.1183 \pm 0.1704)$ mas yr$^{-1}$ for Leo V, to derive accurate orbital properties for the proposed group objects. In addition, we explore other possible members of this putative association. Results. Leo II, Leo IV, and Crater 1 show orbital properties consistent with those we predict from assuming group infall. However, our results suggest that Crater II was not accreted with the rest of the objects. If confirmed with increasingly accurate proper motions in the future, the Crater-Leo objects appear to constitute the first identified case of a cosmologically expected, typical group infall event, as opposed to the highly hierarchical Magellanic Cloud system., Comment: Accepted for publication in A&A on 23-04-2024. 20 pages, 18 figures, 5 tables

The stellar initial mass function (IMF) describes the distribution of stellar masses that form in a given star formation event. The long main-sequence lifetimes of low-mass stars mean that the IMF in this regime (below $\sim 1 \rm{M}_\odot$) can be investigated through star counts. Ultrafaint dwarf galaxies are low-luminosity systems with ancient, metal-poor stellar populations. We investigate the low-mass IMF in four such systems (Reticulum II, Ursa Major II, Triangulum II, and Segue 1), using Hubble Space Telescope imaging data that reaches to $\lesssim 0.2 \rm{M}_\odot$ in each galaxy. The analysis techniques that we adopt depend on the number of low-mass stars in each sample. We use Kolmogorov-Smirnov tests for all four galaxies to determine whether their observed apparent magnitude distributions can reject a given combination of IMF parameters and binary fraction for the underlying population. We forward model 1000 synthetic populations for each combination of parameters, and reject those parameters only if each of the 1000 realizations reject the null hypothesis. We find that all four galaxies reject a variety of IMFs, and the IMFs that they cannot reject include those that are identical, or similar, to that of the stellar populations of the Milky Way. We determine the best-fit parameter values for the IMF in Reticulum II and Ursa Major II and find that the IMF in Reticulum II is generally consistent with that of the Milky Way, while the IMF in Ursa Major II is more bottom heavy. The interpretation of the results for Ursa Major II is complicated by possible contamination from two known background galaxy clusters., Comment: Replaced with the version of record, published by ApJ

We present deep Hubble Space Telescope (HST) photometry of ten targets from Treasury Program GO-14734, including six confirmed ultra-faint dwarf galaxies (UFDs), three UFD candidates, and one likely globular cluster. Six of these targets are satellites of, or have interacted with, the Large Magellanic Cloud (LMC). We determine their structural parameters using a maximum-likelihood technique. Using our newly derived half-light radius ($r_h$) and $V$-band magnitude ($M_V$) values in addition to literature values for other UFDs, we find that UFDs associated with the LMC do not show any systematic differences from Milky Way UFDs in the magnitude-size plane. Additionally, we convert simulated UFD properties from the literature into the $M_V-r_h$ observational space to examine the abilities of current dark matter (DM) and baryonic simulations to reproduce observed UFDs. Some of these simulations adopt alternative DM models, thus allowing us to also explore whether the $M_V-r_h$ plane could be used to constrain the nature of DM. We find no differences in the magnitude-size plane between UFDs simulated with cold, warm, and self-interacting dark matter, but note that the sample of UFDs simulated with alternative DM models is quite limited at present. As more deep, wide-field survey data become available, we will have further opportunities to discover and characterize these ultra-faint stellar systems and the greater low surface-brightness universe., Comment: 42 pages, 13 figures, 13 tables, 2 appendices; Submitted to AAS Journals

We estimate the mass of the Large Magellanic Cloud (LMC) using the kinematics of 30 LMC globular clusters (GCs). We combine proper motions (PMs) measured with HST, Gaia, or a combination of the two, from a recent study by Bennet et al. (2022) with literature line-of-sight velocities (LOSVs) to give 3 components of motion. With these, we derive a 3D velocity dispersion anisotropy $\beta = -0.72 ^{+0.62} _{-1.07}$, consistent with the GCs forming a flattened system with significant azimuthal motion. We then apply a tracer mass estimator and measure an enclosed mass $M (<13.2 \mathrm{kpc})= 2.66^{+0.42} _{-0.36} \times 10^{10} \mathrm{M}_\odot$. This is broadly consistent with results from previous studies of the LOSVs of GCs and other luminous tracers. Assuming a cosmologically-constrained NFW distribution for the dark matter, this implies a virial mass $M_\mathrm{virial} = 1.80^{+1.05} _{-0.54} \times 10^{11} \mathrm{M}_\odot$. Despite being an extrapolation by almost an order of magnitude in radius, this result is consistent with published estimates from other methods that are directly sensitive to the LMC's total mass. Our results support the conclusion that the LMC is approximately 17$^{+10}_{-6}$% of the Milky Way's mass, making it a significant contributor to the Local Group (LG) potential., Comment: 17 pages, 19 figures, 1 table, accepted for publication in ApJ

We present the first JWST MIRI and NIRCam observations of the prominent debris disk around Beta Pictoris. Coronagraphic observations in 8 filters spanning from 1.8 to 23~$\mu$m provide an unprecedentedly clear view of the disk at these wavelengths. The objectives of the observing program were to investigate the dust composition and distribution, and to investigate the presence of planets in the system. In this paper, we focus on the disk components, providing surface brightness measurements for all images and a detailed investigation of the asymmetries observed. A companion paper by Kammerer et al. will focus on the planets in this system using the same data. We report for the first time the presence of an extended secondary disk in thermal emission, with a curved extension bent away from the plane of the disk. This feature, which we refer to as the ``cat's tail", seems to be connected with the previously reported CO clump, mid-infrared asymmetry detected in the southwest side, and the warp observed in scattered light. We present a model of this secondary disk sporadically producing dust that broadly reproduces the morphology, flux, and color of the cat's tail, as well as other features observed in the disk, and suggests the secondary disk is composed largely of porous, organic refractory dust grains., Comment: Accepted to be published in AJ. 37 pages, 21 figures

We have determined the proper motions (PMs) of 12 dwarf galaxies in the Local Group (LG), ranging from the outer Milky Way (MW) halo to the edge of the LG. We used HST as the first and Gaia as the second epoch using the GaiaHub software. For Leo A and Sag DIG we also used multi-epoch HST measurements relative to background galaxies. Orbital histories derived using these PMs show that two-thirds of the galaxies in our sample are on first infall with $>$90\% certainty. The observed star formation histories (SFHs) of these first-infall dwarfs are generally consistent with infalling dwarfs in simulations. The remaining four galaxies have crossed the virial radius of either the MW or M31. When we compare their star formation (SF) and orbital histories we find tentative agreement between the inferred pattern of SF with the timing of dynamical events in the orbital histories. For Leo~I, SF activity rises as the dwarf crosses the MW's virial radius, culminating in a burst of SF shortly before pericenter ($\approx1.7$~Gyr ago). The SF then declines after pericenter, but with some smaller bursts before its recent quenching ($\approx0.3$~Gyr ago). This shows that even small dwarfs like Leo~I can hold on to gas reservoirs and avoid quenching for several Gyrs after falling into their host, which is longer than generally found in simulations. Leo~II, NGC~6822, and IC~10 are also qualitatively consistent with this SF pattern in relation to their orbit, but more tentatively due to larger uncertainties., Comment: 27 pages, 9 Figures, 8 Tables, Submitted to ApJ

We present a hierarchical Bayesian pipeline, BP3M, that measures positions, parallaxes, and proper motions (PMs) for cross-matched sources between Hubble~Space~Telescope (HST) images and Gaia -- even for sparse fields ($N_*<10$ per image) -- expanding from the recent GaiaHub tool. This technique uses Gaia-measured astrometry as priors to predict the locations of sources in HST images, and is therefore able to put the HST images onto a global reference frame without the use of background galaxies/QSOs. Testing our publicly-available code in the Fornax and Draco dSphs, we measure accurate PMs that are a median of 8-13 times more precise than Gaia DR3 alone for $20.5

The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of the most well-studied regions in astrophysics. Due to its proximity, we can study the center of our Galaxy on scales down to a few hundred AU, a hundred times better than in similar Local Group galaxies and thousands of times better than in the nearest active galaxies. The Galactic Center (GC) is therefore of outstanding astrophysical interest. However, in spite of intense observational work over the past decades, there are still fundamental things unknown about the GC. JWST has the unique capability to provide us with the necessary, game-changing data. In this White Paper, we advocate for a JWST NIRCam survey that aims at solving central questions, that we have identified as a community: i) the 3D structure and kinematics of gas and stars; ii) ancient star formation and its relation with the overall history of the Milky Way, as well as recent star formation and its implications for the overall energetics of our galaxy's nucleus; and iii) the (non-)universality of star formation and the stellar initial mass function. We advocate for a large-area, multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy in the form of a Treasury GO JWST Large Program that is open to the community. We describe how this survey will derive the physical and kinematic properties of ~10,000,000 stars, how this will solve the key unknowns and provide a valuable resource for the community with long-lasting legacy value., Comment: This White Paper will be updated when required (e.g. new authors joining, editing of content). Most recent update: 24 Oct 2023

The JWST NIRSpec integral field unit (IFU) presents a unique opportunity to observe directly imaged exoplanets from 3-5 um at moderate spectral resolution (R~2,700) and thereby better constrain the composition, disequilibrium chemistry, and cloud properties of their atmospheres. In this work, we present the first NIRSpec IFU high-contrast observations of a substellar companion that requires starlight suppression techniques. We develop specific data reduction strategies to study faint companions around bright stars, and assess the performance of NIRSpec at high contrast. First, we demonstrate an approach to forward model the companion signal and the starlight directly in the detector images, which mitigates the effects of NIRSpec's spatial undersampling. We demonstrate a sensitivity to planets that are 3e-6 fainter than their stars at 1'', or 3e-5 at 0.3''. Then, we implement a reference star point spread function (PSF) subtraction and a spectral extraction that does not require spatially and spectrally regularly sampled spectral cubes. This allows us to extract a moderate resolution (R~2,700) spectrum of the faint T-dwarf companion HD 19467 B from 2.9-5.2 um with signal-to-noise ratio (S/N)~10 per resolution element. Across this wavelength range, HD~19467~B has a flux ratio varying between 1e-5-1e-4 and a separation relative to its star of 1.6''. A companion paper by Hoch et al. more deeply analyzes the atmospheric properties of this companion based on the extracted spectrum. Using the methods developed here, NIRSpec's sensitivity may enable direct detection and spectral characterization of relatively old (~1 Gyr), cool (~250 K), and closely separated (~3-5 au) exoplanets that are less massive than Jupiter., Comment: Accepted to AJ. The data analysis scripts for this work are published https://github.com/jruffio/HD_19467_B (https://zenodo.org/doi/10.5281/zenodo.11391740). The main revisions of the manuscript are listed in the change history section of the readme

Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this work, we observe one transit of the hot Jupiter WASP-17b with JWST's MIRI LRS and generate a transmission spectrum from 5-12 $\rm{\mu}$m. These wavelengths allow us to probe absorption due to the vibrational modes of various predicted cloud species. Our transmission spectrum shows additional opacity centered at 8.6 $\rm{\mu}$m, and detailed atmospheric modeling and retrievals identify this feature as SiO$_2$(s) (quartz) clouds. The SiO$_2$(s) clouds model is preferred at 3.5-4.2$\sigma$ versus a cloud-free model and at 2.6$\sigma$ versus a generic aerosol prescription. We find the SiO$_2$(s) clouds are comprised of small ${\sim}0.01$ $\rm{\mu}$m particles, which extend to high altitudes in the atmosphere. The atmosphere also shows a depletion of H$_2$O, a finding consistent with the formation of high-temperature aerosols from oxygen-rich species. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS)., Comment: 19 pages, 7 figures, fixed typo in Equation 3

We present a kinematic study of a thousand of dwarf satellites of MW/M31-like hosts from the IllustrisTNG50 simulation. Internal kinematics were derived for all the snapshots to obtain a historical record of their rotation velocity in the plane of the sky ($|V_T|$) and the amplitude of their velocity gradients along the line of sight ($A_{\rm grad}^{v_z}$) measured from the host. For the majority of the satellites we initially detected rotation in the plane of the sky (65%) or velocity gradients (80%), and this was progressively reduced to 45% and 68% at $z = 0$ respectively. We find that the evolution of the rotation in the plane of the sky and the velocity gradients differs according to type of dwarfs, which could be explained in terms of their different masses and orbital histories. We observe that interaction with the host has an impact on the evolution of the internal kinematics of the satellites. The rotation signal of the satellites is progressively reduced during pericentric passages, the first pericentre being especially disruptive for the initial kinematics. We observe temporary increases in $A_{\rm grad}^{v_z}$ during pericentric passage caused by tidal interaction with the host, $A_{\rm grad}^{v_z}$ increasing as the satellites approach their pericentre and dropping as they move away. In summary, we conclude that the presence of detectable rotation in dwarf satellites is not uncommon, and that the evolution of their internal kinematics is clearly affected by their interaction with the host., Comment: 12 pages, 9 figures, 2 tables. Accepted for publication in MNRAS

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit., Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figures

We present the results of a spectroscopic survey of the outskirts of 4 globular clusters -- NGC 1261, NGC 4590, NGC 1904, and NGC 1851 -- covering targets within 1 degree from the cluster centres, with 2dF/AAOmega on the Anglo-Australian Telescope (AAT) and FLAMES on the Very Large Telescope (VLT). We extracted chemo-dynamical information for individual stars, from which we estimated the velocity dispersion profile and the rotation of each cluster. The observations are compared to direct $N$-body simulations and appropriate {\sc limepy}/{\sc spes} models for each cluster to interpret the results. In NGC 1851, the detected internal rotation agrees with existing literature, and NGC 1261 shows some rotation signal beyond the truncation radius, likely coming from the escaped stars. We find that the dispersion profiles for both the observations and the simulations for NGC 1261, NGC 1851, and NGC 1904 do not decrease as the {\sc limepy}/{\sc spes} models predict beyond the truncation radius, where the $N$-body simulations show that escaped stars dominate; the dispersion profile of NGC 4590 follows the predictions of the {\sc limepy}/{\sc spes} models, though the data do not effectively extend beyond the truncation radius. The increasing/flat dispersion profiles in the outskirts of NGC 1261, NGC 1851 and NGC 1904, are reproduced by the simulations. Hence, the increasing/flat dispersion profiles of the clusters in question can be explained by the tidal interaction with the Galaxy without introducing dark matter., Comment: 17 pages, 10 figures. Accepted by MNRAS. Comments are welcome

We have determined bulk proper motions (PMs) for 31 LMC GCs from Gaia eDR3 and Hubble Space Telescope data using multiple independent analysis techniques. Combined with literature values for distances, line-of-sight velocities and existing bulk PMs, we extract full 6D phase-space information for 32 clusters, allowing us to examine the kinematics of the LMC GC system in detail. Except for two GCs (NGC 2159 and NGC 2210) for which high velocities suggest they are not long-term members of the LMC system, the data are consistent with a flattened configuration that rotates like the stellar disk. The one-dimensional velocity dispersions are of order 30 km/s, similar to that of old stellar populations in the LMC disk. Similar to the case for Milky Way disk clusters, the velocity anisotropy is such that the dispersion is smallest in the azimuthal direction; however, alternative anisotropies cannot be ruled out due to distance uncertainties. The data are consistent with a single multi-dimensional Gaussian velocity distribution. Given the non-collisional nature of the LMC disk, this suggests that most, if not all, of the LMC GCs are formed by a single formation mechanism in the stellar disk, despite a significant spread in age and metallicity. Any accreted halo GC population is absent or far smaller in the LMC compared to the Milky Way., Comment: Accepted by ApJ, 19 pages, 5 figures, 4 tables

We examine the degree of energy equipartition in 9 Galactic globular clusters using proper motions measured with the Hubble Space Telescope. For most clusters in the sample, this is the first energy equipartition study ever performed. This study is also the largest of its kind, albeit with only 9 clusters. We begin by rigorously cleaning the catalogues to remove poor-quality measurements and to ensure high signal-to-noise for the study. Using the cleaned catalogues, we investigate how velocity dispersion $\sigma$ changes with stellar mass $m$. We fit two functional forms: the first, a classic power-law of the form $\sigma \propto m^{-\eta}$ where $\eta$ is the degree of energy equipartition, and the second from Bianchini et al. (2016) parameterised by an equipartition mass $m_{eq}$ where $\eta$ changes with stellar mass. We find that both functions fit well but cannot distinguish with statistical significance which function provides the best fit. All clusters exhibit varying degrees of partial equipartition; no cluster is at or near full equipartition. We search for correlations of $\eta$ and $m_{eq}$ with various cluster properties. The most significant correlation is observed with the number of core or median relaxation times ($N_{core}$ or $N_{half}$) the cluster has experienced. Finally, we determine the radial equipartition profile for each cluster, that is, how the degree of equipartition changes with projected distance from the cluster centre. We do not detect statistically significant trends in the degree of equipartition with radius. Overall, our observational findings are in broad agreement with theoretical predictions from N-body models published in recent years., Comment: 26 pages, 16 figures, 2 tables, accepted for publication in ApJ

We measure homogeneous distances to M31 and 38 associated stellar systems ($-$16.8$\le M_V \le$ $-$6.0), using time-series observations of RR Lyrae stars taken as part of the Hubble Space Telescope Treasury Survey of M31 Satellites. From $>700$ orbits of new/archival ACS imaging, we identify $>4700$ RR Lyrae stars and determine their periods and mean magnitudes to a typical precision of 0.01 days and 0.04 mag. Based on Period-Wesenheit-Metallicity relationships consistent with the Gaia eDR3 distance scale, we uniformly measure heliocentric and M31-centric distances to a typical precision of $\sim20$ kpc (3%) and $\sim10$ kpc (8%), respectively. We revise the 3D structure of the M31 galactic ecosystem and: (i) confirm a highly anisotropic spatial distribution such that $\sim80$% of M31's satellites reside on the near side of M31; this feature is not easily explained by observational effects; (ii) affirm the thin (rms $7-23$ kpc) planar "arc" of satellites that comprises roughly half (15) of the galaxies within 300 kpc from M31; (iii) reassess physical proximity of notable associations such as the NGC 147/185 pair and M33/AND XXII; and (iv) illustrate challenges in tip-of-the-red-giant branch distances for galaxies with $M_V > -9.5$, which can be biased by up to 35%. We emphasize the importance of RR Lyrae for accurate distances to faint galaxies that should be discovered by upcoming facilities (e.g., Rubin Observatory). We provide updated luminosities and sizes for our sample. Our distances will serve as the basis for future investigation of the star formation and orbital histories of the entire known M31 satellite system., Comment: 32 pages, 15 figures, accepted for publication on ApJ

We present GaiaHub, a publicly available tool that combines $Gaia$ measurements with $Hubble$ $Space$ $Telescope$ ($HST$) archival images to derive proper motions (PMs). It increases the scientific impact of both observatories beyond their individual capabilities. $Gaia$ provides PMs across the whole sky, but the limited mirror size and time baseline restrict the best PM performance to relatively bright stars. $HST$ can measure accurate PMs for much fainter stars over a small field, but this requires two epochs of observation which are not always available. GaiaHub yields considerably improved PM accuracy compared to $Gaia$-only measurements, especially for faint sources $(G \gtrsim 18)$, requiring only a single epoch of $HST$ data observed more than $\sim 7$ years ago (before 2012). This provides considerable scientific value especially for dynamical studies of stellar systems or structures in and beyond the Milky Way (MW) halo, for which the member stars are generally faint. To illustrate the capabilities and demonstrate the accuracy of GaiaHub, we apply it to samples of MW globular clusters (GCs) and classical dwarf spheroidal (dSph) satellite galaxies. This allows us, e.g., to measure the velocity dispersions in the plane of the sky for objects out to and beyond $\sim 100$ kpc. We find, on average, mild radial velocity anisotropy in GCs, consistent with existing results for more nearby samples. We observe a correlation between the internal kinematics of the clusters and their ellipticity, with more isotropic clusters being, on average, more round. Our results also support previous findings that Draco and Sculptor dSph galaxies appear to be radially anisotropic systems., Comment: 24 pages, 18 figures. Accepted for publication in ApJ

We present deep Hubble Space Telescope (HST) photometry of the ultra-faint dwarf (UFD) galaxies Pegasus III (Peg III) and Pisces II (Psc II), two of the most distant satellites in the halo of the Milky Way (MW). We measure the structure of both galaxies, derive mass-to-light ratios with newly determined absolute magnitudes, and compare our findings to expectations from UFD-mass simulations. For Peg III, we find an elliptical half-light radius of $a_h=1.88^{+0.42}_{-0.33}$ arcminutes ($118^{+31}_{-30}$ pc) and $M_V{=}{-4.17}^{+0.19}_{-0.22}$; for Psc II, we measure $a_h{=}1.31^{+0.10}_{-0.09}$ arcminutes ($69\pm8$ pc) and $M_V{=}{-4.28}^{+0.19}_{-0.16}$. We do not find any morphological features that indicate a significant interaction between the two has occurred, despite their close separation of only $\sim$40 kpc. Using proper motions (PMs) from Gaia early Data Release 3, we investigate the possibility of any past association by integrating orbits for the two UFDs in a MW-only and a combined MW and Large Magellanic Cloud (LMC) potential. We find that including the gravitational influence of the LMC is crucial, even for these outer-halo satellites, and that a possible orbital history exists where Peg III and Psc II experienced a close ($\sim$10-20 kpc) passage about each other just over $\sim$1 Gyr ago, followed by a collective passage around the LMC ($\sim$30-60 kpc) just under $\sim$1 Gyr ago. Considering the large uncertainties on the PMs and the restrictive priors imposed to derive them, improved PM measurements for Peg III and Psc II will be necessary to clarify their relationship. This would add to the rare findings of confirmed pairs of satellites within the Local Group., Comment: 24 pages, 13 figures; 1 appendix; published in ApJ

We present analysis of the proper-motion (PM) field of the red clump stars in the Large Magellanic Cloud (LMC) disk using the Gaia Early Data Release 3 catalog. Using a kinematic model based on old stars with 3D velocity measurements, we construct the residual PM field by subtracting the center-of-mass motion and internal rotation motion components. The residual PM field reveals asymmetric patterns, including larger residual PMs in the southern disk. Comparisons between the observed residual PM field with those of five numerical simulations of an LMC analog that is subject to the tidal fields of the Milky Way and the Small Magellanic Cloud (SMC) show that the present-day LMC is not in dynamical equilibrium. We find that both the observed level of disk heating (PM residual root-mean-square of 0.057$\pm$0.002 mas yr$^{-1}$) and kinematic asymmetry are not reproduced by Milky Way tides or if the SMC impact parameter is larger than the size of the LMC disk. This measured level of disk heating provides a novel and important method to validate numerical simulations of the LMC-SMC interaction history. Our results alone put constraints on an impact parameter $\lesssim$10 kpc and impact timing $<$250 Myr. When adopting the impact timing constraint of $\sim$140--160 Myr ago from previous studies, our results suggest that the most recent SMC encounter must have occurred with an impact parameter of $\sim$5 kpc. We also find consistent radial trends in the kinematically- and geometrically-derived disk inclination and line-of-node position angles, indicating a common origin., Comment: 17 pages, 10 figures, resubmitted to AAS Journal

We present the color-magnitude diagrams and star formation histories (SFHs) of seven ultra-faint dwarf galaxies: Horologium 1, Hydra 2, Phoenix 2, Reticulum 2, Sagittarius 2, Triangulum 2, and Tucana 2, derived from high-precision Hubble Space Telescope photometry. We find that the SFH of each galaxy is consistent with them having created at least 80% of the stellar mass by $z\sim6$. For all galaxies, we find quenching times older than 11.5 Gyr ago, compatible with the scenario in which reionization suppresses the star formation of small dark matter halos. However, our analysis also reveals some differences in the SFHs of candidate Magellanic Cloud satellites, i.e., galaxies that are likely satellites of the Large Magellanic Cloud and that entered the Milky Way potential only recently. Indeed, Magellanic satellites show quenching times about 600 Myr more recent with respect to those of other Milky Way satellites, on average, even though the respective timings are still compatible within the errors. This finding is consistent with theoretical models that suggest that satellites' SFHs may depend on their host environment at early times, although we caution that within the error bars all galaxies in our sample are consistent with being quenched at a single epoch., Comment: 7 pages, 3 figures, 2 tables. Accepted for publication in ApJL

We present an analysis of the kinematics of 14 satellites of the Milky Way (MW). We use proper motions (PMs) from the $Gaia$ Early Data Release 3 (EDR3) and line-of-sight velocities ($v_{\mathrm{los}}$) available in the literature to derive the systemic 3D motion of these systems. For six of them, namely the Carina, Draco, Fornax, Sculptor, Sextans, and Ursa Minor dwarf spheroidal galaxies (dSph), we study the internal kinematics projecting the stellar PMs into radial, $V_R$ (expansion/contraction), and tangential, $V_T$ (rotation), velocity components with respect to the centre of mass. We find significant rotation in the Carina ($|V_T| = 9.6 \pm 4.5 \ {\rm{km \ s^{-1}}}\>$), Fornax ($|V_T| = 2.8 \pm 1.3 \ {\rm{km \ s^{-1}}}\>$), and Sculptor ($|V_T| = 3.0 \pm 1.0 \ {\rm{km \ s^{-1}}}\>$) dSphs. Besides the Sagittarius dSph, these are the first measurements of internal rotation in the plane of the sky in the MW's classical dSphs. All galaxies except Carina show $|V_T| / \sigma_v < 1$. We find that slower rotators tend to show, on average, larger sky-projected ellipticity (as expected for a sample with random viewing angles) and are located at smaller Galactocentric distances (as expected for tidal stirring scenarios in which rotation is transformed into random motions as satellites sink into the parent halo). However, these trends are small and not statistically significant, indicating that rotation has not played a dominant role in shaping the 3D structure of these galaxies. Either tidal stirring had a weak impact on the evolution of these systems or it perturbed them with similar efficiency regardless of their current Galactocentric distance., Comment: 12 pages, 5 figures, 3 tables. Accepted for publication in MNRAS

We present new WFC3/UVIS observations of UGC 4483, the closest example of a metal-poor blue compact dwarf galaxy, with a metallicity of $Z \simeq 1/15\ Z_{\odot}$ and located at a distance of $D \simeq 3.4$ Mpc. The extremely high quality of our new data allows us to clearly resolve the multiple stellar evolutionary phases populating the color-magnitude diagram (CMD), to reach more than 4 mag deeper than the tip of the red giant branch, and to detect for the first time core He-burning stars with masses $\lesssim 2$ M$_{\odot}$, populating the red clump and possibly the horizontal branch (HB) of the galaxy. By applying the synthetic CMD method to our observations, we determine an average star formation rate over the whole Hubble time of at least $(7.01\pm0.44) \times 10^{-4}$ $\mathrm{M_{\odot}/yr}$, corresponding to a total astrated stellar mass of $(9.60\pm0.61)\times 10^6$ $\mathrm{M_{\odot}}$, 87% of which went into stars at epochs earlier than 1 Gyr ago. With our star formation history recovery method we find the best fit with a distance modulus of DM = $27.45\pm0.10$, slightly lower than previous estimates. Finally, we find strong evidence of an old ($\gtrsim 10$ Gyr) stellar population in UGC 4483 thanks to the detection of an HB phase and the identification of six candidate RR Lyrae variable stars., Comment: 14 pages, 12 figures, accepted for publication on ApJ

We present an astrometric study of the proper motions (PMs) in the core of the globular cluster NGC 6441. The core of this cluster has a high density and observations with current instrumentation are very challenging. We combine ground-based, high-angular-resolution NACO@VLT images with Hubble Space Telescope ACS/HRC data and measure PMs with a temporal baseline of 15 yr for about 1400 stars in the centermost 15 arcseconds of the cluster. We reach a PM precision of $\sim$30 $\mu$as yr$^{-1}$ for bright, well-measured stars. Our results for the velocity dispersion are in good agreement with other studies and extend already-existing analyses of the stellar kinematics of NGC 6441 to its centermost region never probed before. In the innermost arcsecond of the cluster, we measure a velocity dispersion of (19.1 $\pm$ 2.0) km s$^{-1}$ for evolved stars. Because of its high mass, NGC 6441 is a promising candidate for harbouring an intermediate-mass black hole (IMBH). We combine our measurements with additional data from the literature and compute dynamical models of the cluster. We find an upper limit of $M_{\rm IMBH} < 1.32 \times 10^4\,\textrm{M}_\odot$ but we can neither confirm nor rule out its presence. We also refine the dynamical distance of the cluster to $12.74^{+0.16}_{-0.15}$ kpc. Although the hunt for an IMBH in NGC 6441 is not yet concluded, our results show how future observations with extremely-large telescopes will benefit from the long temporal baseline offered by existing high-angular-resolution data., Comment: 16 pages, 12 figures, 2 tables. Accepted for publication in MNRAS

The Large and Small Magellanic Clouds (LMC and SMC) are the largest satellite galaxies of the Milky Way and close enough to allow for a detailed exploration of their structure and formation history. The Survey of the MAgellanic Stellar History (SMASH) is a community Dark Energy Camera (DECam) survey of the Magellanic Clouds using $\sim$50 nights to sample over $\sim$2400 deg$^2$ centered on the Clouds at $\sim$20% filling factor (but with contiguous coverage in the central regions) and to depths of $\sim$24th mag in $ugriz$. The primary goals of SMASH are to map out the extended stellar peripheries of the Clouds and uncover their complicated interaction and accretion history as well as to derive spatially-resolved star formation histories of the central regions and create a "movie" of their past star formation. Here we announce the second SMASH public data release (DR2), which contains all 197 fully-calibrated DECam fields including the main body fields in the central regions. The DR2 data are available through the Astro Data Lab hosted by the NSF's National Optical-Infrared Astronomy Research Laboratory. We highlight three science cases that make use of the SMASH DR2 data and will be published in the future: (1) preliminary star formation histories of the LMC; (2) the search for Magellanic star clusters using citizen scientists; and, (3) photometric metallicities of Magellanic Cloud stars using the DECam $u$-band., Comment: 18 pages, 9 figures. Accepted for publication in The Astronomical Journal

Parallaxes measured by the Gaia mission have huge significance for astronomy, but parallaxes in Gaia DR2 are known to have systematic errors that depend on the source position and other quantities. We use the abundant information in faint Milky Way stars, along with the GOG simulation of the Gaia catalog, to probe the spatial dependence of Gaia DR2 parallax systematic errors in an empirical way. The parallax signal, concentrated in thick disk turnoff stars with magnitude G ~ 17, is sufficient to construct maps of the parallax systematic error over the majority of the sky. These maps show a locally regular "waffle pattern" on ~1 degree scales following Gaia scan directions, stronger linear "scar" features, and coherent variations on larger scales. The parallax bias maps also retain traces of astrophysical effects such as dust clouds. The waffle pattern, known from earlier maps of the Magellanic Clouds, extends over the entire sky; its local rms amplitude averages 15 microarcsec and varies by about a factor of two. The strength of this pattern increases by a factor ~6 from magnitude G = 13 to G = 20. Correlations with parallaxes of quasars and of stars with independent distance estimates support our bias estimates. Using similar methods, we map systematic errors in the proper motion and examine the relationship with the parallax systematics. We provide a code package to access and query our bias maps. Similar tests on the general stellar population should be useful in quantifying systematic errors in future Gaia releases., Comment: Accepted in AJ. 17 pages, 11 figures. Higher resolution figures available in journal. Eagerly anticipating Gaia EDR3

We present a detailed study of the internal structure and kinematics of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). Using machine-learning techniques, we have combined the information provided by 3300 RR Lyrae stars, more than 2000 spectroscopically observed stars, and the Gaia second data release to derive the full phase space, i.e. 3D positions and kinematics, of more than $1.2\times10^5$ member stars in the core of the galaxy. Our results show that Sgr has a bar structure $\sim 2.5$ kpc long, and that tidal tails emerge from its tips to form what it is known as the Sgr stream. The main body of the galaxy, strongly sheared by tidal forces, is a triaxial (almost prolate) ellipsoid with its longest principal axis of inertia inclined $43^\circ\pm6^\circ$ with respect to the plane of the sky and axis ratios of 1:0.67:0.60. Its external regions are expanding mainly along its longest principal axis, yet the galaxy conserves an inner core of about $500\times330\times300$ pc that shows no net expansion and is rotating at $v_{\rm rot} = 4.13 \pm 0.16$ ${\rm{ km \ s^{-1}}}$. The internal angular momentum of Sgr forms an angle $\theta = 18^\circ\pm6^\circ$ with respect to its orbital angular momentum, meaning that the galaxy is in an inclined prograde orbit around the Milky Way. We compared our results with predictions from $N$-body models with spherical, pressure-supported progenitors and a model whose progenitor is a flattened rotating disk. Only the rotating model, based on preexisting simulations aimed at reproducing the line-of-sight velocity gradients observed in Sgr, was able to reproduce the observed properties in the core of the galaxy., Comment: 37 pages, 26 figures, 2 tables. Accepted for publication in the Astrophysical Journal

We present a new kinematic model for the Small Magellanic Cloud (SMC), using data from the \gaia\ Data Release 2 catalog. We identify a sample of astrometrically well-behaved red giant (RG) stars belonging to the SMC and cross-match with publicly available radial velocity (RV) catalogs. We create a 3D spatial model for the RGs, using RR Lyrae for distance distributions, and apply kinematic models with varying rotation properties and a novel tidal expansion prescription to generate mock proper motion (PM) catalogs. When we compare this series of mock catalogs to the observed RG data, we find a combination of moderate rotation (with a magnitude of $\sim10-20$ km s$^{-1}$ at 1 kpc from the SMC center, inclination between $\sim50-80$ degrees, and a predominantly north-to-south line of nodes position angle of $\sim180$ degrees) and tidal expansion (with a scaling of $\sim10$ km s$^{-1}$ kpc$^{-1}$) is required to explain the PM signatures. The exact best-fit parameters depend somewhat on whether we assess only the PMs or include the RVs as a qualitative check, leaving some small tension remaining between the PM and RV conclusions. In either case, the parameter space preferred by our model is different both from previously inferred rotational geometries, including from the SMC H{\small I} gas and from the RG RV-only analyses, and new SMC PM analyses which conclude that a rotation signature is not detectable. Taken together this underscores the need to treat the SMC as a series of different populations with distinct kinematics., Comment: 17 pages, 11 figures, 2 tables, submitted to ApJ

The presence of massive stars (MSs) in the region close to the Galactic Center (GC) poses several questions about their origin. The harsh environment of the GC favors specific formation scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogs have errors better than 0.5 mas yr$^{-1}$. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3-4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions suggesting they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogs publicly available., Comment: 28 pages, 33 figures, 9 tables. Accepted for publication in MNRAS. [v3: Fixed bibliography]

We present the first proper motion (PM) measurements for the dwarf elliptical galaxies NGC 147 and NGC 185, two satellite galaxies of M31, using multi-epoch HST imaging data with time baselines of $\sim 8$ years. For each galaxy, we take an error-weighted average of measurements from HST ACS/WFC and WFC3/UVIS to determine the PMs. Our final results for the PMs are $(\mu_\mathrm{W}, \mu_\mathrm{N})_\mathrm{N147} = (-0.0232, 0.0378) \pm (0.0143, 0.0146)\,\mathrm{mas}\,\mathrm{yr}^{-1}$ for NGC 147, and $(\mu_\mathrm{W}, \mu_\mathrm{N})_\mathrm{N185} = (-0.0242, 0.0058) \pm (0.0141, 0.0147)\,\mathrm{mas}\,\mathrm{yr}^{-1}$ for NGC 185. The 2-dimensional direction of motion for NGC 147 about M31 is found to be aligned with its tidal tails. The 3-d positions and velocities of both galaxies are transformed into a common M31-centric coordinate system to study the detailed orbital histories of the combined M31+NGC 147+NGC 185 system via numerical orbit integration. We find that NGC 147 (NGC 185) had its closest passage to M31 0.3-0.5~Gyr ($\gtrsim 1.6$~Gyr) within the past 6 Gyr at distances of $\sim 70$ kpc (70-260 kpc). The pericentric times of NGC 147/NGC 185 correlate qualitatively well with the presence/absence of tidal tails seen around the galaxies. Our PMs show that the orbital poles of NGC 147, and also NGC 185 albeit to a lesser degree, agree within the uncertainties with the normal of the Great Plane of Andromeda (GPoA). These are the first measurements of the 3-d angular momentum vector of any satellite identified as original GPoA members. Our results strengthen the hypothesis that the GPoA may be a dynamically coherent entity. We revisit previous claims that NGC 147 and NGC 185 are binary galaxies and conclude that it is very unlikely the two galaxies were ever gravitationally bound to each other., Comment: 20 pages, 9 figures, 4 tables, accepted for publication in ApJ

The periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the extended stellar structure of the SMC using deep colour-magnitude diagrams (CMDs), obtained as part of the Survey of the MAgellanic Stellar History (SMASH). Special care was taken in the decontamination of our data from MW foreground stars, including from foreground globular clusters NGC 362 and 47 Tuc. We derived the SMC surface brightness using a ``conservative'' approach from which we calculated the general parameters of the SMC, finding a staggered surface brightness profile. We also traced the fainter outskirts by constructing a stellar density profile. This approach, based on stellar counts of the oldest main sequence turn-off (MSTO) stars, uncovered a tidally disrupted stellar feature that reaches as far out as 12 degrees from the SMC centre. We also serendipitously found a faint feature of unknown origin located at $\sim 14$ degrees from the centre of the SMC and that we tentatively associated to a more distant structure. We compared our results to in-house simulations of a $1\times10^{9} M_\odot$ SMC, finding that its elliptical shape can be explained by its tidal disruption under the combined presence of the MW and the LMC. Finally, we found that the older stellar populations show a smooth profile while the younger component presents a jump in the density followed by a flat profile, confirming the heavily disturbed nature of the SMC., Comment: 18 pages, 15 figures, submitted to MNRAS

With the release of Gaia DR2, it is now possible to measure the proper motions (PMs) of the lowest mass, ultra-faint satellite galaxies in the Milky Way's (MW) halo for the first time. Many of these faint satellites are posited to have been accreted as satellites of the Magellanic Clouds (MCs). Using their 6-dimensional phase space information, we calculate the orbital histories of 13 ultra-faint satellites and five classical dwarf spheroidals in a combined MW+LMC+SMC potential to determine which galaxies are dynamically associated with the MCs. These 18 galaxies are separated into four classes: i.) long-term Magellanic satellites that have been bound to the MCs for at least the last two consecutive orbits around the MCs (Carina 2, Carina 3, Horologium 1, Hydrus 1); ii.) Magellanic satellites that were recently captured by the MCs $<$ 1 Gyr ago (Reticulum 2, Phoenix 2); iii.) MW satellites that have interacted with the MCs (Sculptor 1, Tucana 3, Segue 1); and iv.) MW satellites (Aquarius 2, Canes Venatici 2, Crater 2, Draco 1, Draco 2, Hydra 2, Carina, Fornax, Ursa Minor). Results are reported for a range of MW and LMC masses. Contrary to previous work, we find no dynamical association between Carina, Fornax, and the MCs. Finally, we determine that the addition of the SMC's gravitational potential affects the longevity of satellites as members of the Magellanic system (long-term versus recently captured), but it does not change the total number of Magellanic satellites., Comment: 32 pages, 11 figures. Accepted to ApJ

Globular clusters are collisional systems, meaning that the stars inside them interact on timescales much shorter than the age of the Universe. These frequent interactions transfer energy between stars and set up observable trends that tell the story of a cluster's evolution. This contribution focuses on what we can learn by studying velocity anisotropy and energy equipartition in globular clusters with Hubble Space Telescope proper motions., Comment: 4 pages, 3 figures. To appear in Proceedings IAU Symposium No. 351 "Star Clusters: From the Milky Way to the Early Universe", 2019

Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions. We present new deep images of a shell-like over-density of stars in the outskirts of the Small Magellanic Cloud (SMC). The shell, also detected in photographic plates dating back to the fifties, is located at ~1.9 degr from the center of the SMC in the north-east direction.The structure and stellar content of this feature were studied with multi-band, optical data from the Survey of the MAgellanic Stellar History (SMASH) carried out with the Dark Energy Camera on the Blanco Telescope at Cerro Tololo Inter-American Observatory. We also investigate the kinematic of the stars in the shell using the Gaia Data Release 2. The shell is composed of a young population with an age ~ 150 Myr, with no contribution from an old population. Thus, it is hard to explain its origin as the remnant of a tidally disrupted stellar system. The spatial distribution of the young main-sequence stars shows a rich sub-structure, with a spiral arm-like feature emanating from the main shell and a separated small arc of young stars close to the globular cluster NGC 362. We find that the absolute g-band magnitude of the shell is M_{g,shell} = -10.78+/- 0.02, with a surface brightness of mu_{g,shell} = 25.81+/- 0.01 mag/arcsec^{2}. We have not found any evidence that this feature is of tidal origin or a bright part of a spiral arm-like structure. Instead, we suggest that the shell formed in a recent star formation event, likely triggered by an interaction with the Large Magellanic Cloud and/or the Milky Way, ~150 Myr ago., Comment: 16 pages, 14 figures, submitted to Astronomy & Astrophysics

The Great Andromeda Galaxy (M31) is the nexus of the near-far galaxy evolution connection and a principal data point for near-field cosmology. Due to its proximity (780 kpc), M31 can be resolved into individual stars like the Milky Way (MW). Unlike the MW, we have the advantage of a global view of M31, enabling M31 to be observed with techniques that also apply to more distant galaxies. Moreover, recent evidence suggests that M31 may have survived a major merger within the last several Gyr, shaping the morphology of its stellar halo and triggering a starburst, while leaving the stellar disk largely intact. The MW and M31 thus provide complementary opportunities for in-depth studies of the disks, halos, and satellites of L* galaxies. Our understanding of the M31 system will be transformed in the 2020s if they include wide field facilities for both photometry (HST-like sensitivity and resolution) and spectroscopy (10-m class telescope, >1 sq. deg. field, highly multiplexed, R~ 3000 to 6000). We focus here on the power of these facilities to constrain the past, present, and future merger history of M31, via chemo-dynamical analyses and star formation histories of phase-mixed stars accreted at early times, as well as stars in surviving tidal debris features, M31's extended disk, and intact satellite galaxies that will eventually be tidally incorporated into the halo. This will yield an unprecedented view of the hierarchical formation of the M31 system and the subhalos that built it into the L* galaxy we observe today., Comment: Submitted as a science white paper to the Astro2020 Decadal Survey

The Wide Field Infrared Survey Telescope (WFIRST) is a 2.4m space telescope with a 0.281 deg^2 field of view for near-IR imaging and slitless spectroscopy and a coronagraph designed for > 10^8 starlight suppresion. As background information for Astro2020 white papers, this article summarizes the current design and anticipated performance of WFIRST. While WFIRST does not have the UV imaging/spectroscopic capabilities of the Hubble Space Telescope, for wide field near-IR surveys WFIRST is hundreds of times more efficient. Some of the most ambitious multi-cycle HST Treasury programs could be executed as routine General Observer (GO) programs on WFIRST. The large area and time-domain surveys planned for the cosmology and exoplanet microlensing programs will produce extraordinarily rich data sets that enable an enormous range of Archival Research (AR) investigations. Requirements for the coronagraph are defined based on its status as a technology demonstration, but its expected performance will enable unprecedented observations of nearby giant exoplanets and circumstellar disks. WFIRST is currently in the Preliminary Design and Technology Completion phase (Phase B), on schedule for launch in 2025, with several of its critical components already in production., Comment: 14 pages, 3 figures, 2 tables

The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) is a high-contrast imager and integral field spectrograph that will enable the study of exoplanets and circumstellar disks at visible wavelengths. Ground-based high-contrast instrumentation has fundamentally limited performance at small working angles, even under optimistic assumptions for 30m-class telescopes. There is a strong scientific driver for better performance, particularly at visible wavelengths. Future flagship mission concepts aim to image Earth analogues with visible light flux ratios of more than 10^10. CGI is a critical intermediate step toward that goal, with a predicted 10^8-9 flux ratio capability in the visible. CGI achieves this through improvements over current ground and space systems in several areas: (i) Hardware: space-qualified (TRL9) deformable mirrors, detectors, and coronagraphs, (ii) Algorithms: wavefront sensing and control; post-processing of integral field spectrograph, polarimetric, and extended object data, and (iii) Validation of telescope and instrument models at high accuracy and precision. This white paper, submitted to the 2018 NAS Exoplanet Science Strategy call, describes the status of key CGI technologies and presents ways in which performance is likely to evolve as the CGI design matures., Comment: Submitted in response to the 2018 NAS Exoplanet Science Strategy call. 5 pages, 2 figures

The Orphan Stream is one of the most prominent tidal streams in the Galactic halo. Using data on red giants, RR Lyrae, and horizontal branch stars from Gaia and other surveys, we determine the proper motion of the Orphan Stream over a path of more than 90 degrees on the sky. We also provide updated tracks for the sky position, distance, and radial velocity of the stream. Our tracks in these latter dimensions mostly agree with previous results. However, there are significant corrections to the earlier distance and latitude tracks as the stream approaches the Galactic disk. Stream stars selected with three-dimensional kinematics display a very tight red giant sequence. Concordantly, we find that applying a proper motion cut removes the most metal-rich stars from earlier spectroscopic samples of stream stars, though a significant dispersion remains indicating a dwarf galaxy origin. The deceleration of the stream towards its leading end suggests a circular velocity of ~200 km/s at a galactocentric radius ~30 kpc, consistent with other independent evidence. However, the track of the stream departs significantly from an orbit; the spatial track does not point along the same direction as the velocity vector, and it exhibits a lateral wiggle that is unlikely to match any reasonable orbit. The low metallicity and small dispersion of the stream in the various coordinates point to a progenitor with a relatively low dynamical mass ~$10^8$ Msun., Comment: 14 pages, 10 figures, 1 table; submitted to MNRAS

We present the first detailed kinematic analysis of the proper motions (PMs) of stars in the Magellanic Bridge, from both the \textit{Gaia} Data Release 2 catalog and from \textit{Hubble Space Telescope} Advanced Camera for Surveys data. For the \textit{Gaia} data, we identify and select two populations of stars in the Bridge region, young main sequence (MS) and red giant stars. The spatial locations of the stars are compared against the known H {\small I} gas structure, finding a correlation between the MS stars and the H {\small I} gas. In the \textit{Hubble Space Telescope} fields our signal comes mainly from an older MS and turn-off population, and the proper motion baselines range between $\sim 4$ and 13 years. The PMs of these different populations are found to be consistent with each other, as well as across the two telescopes. When the absolute motion of the Small Magellanic Cloud is subtracted out, the residual Bridge motions display a general pattern of pointing away from the Small Magellanic Cloud towards the Large Magellanic Cloud. We compare in detail the kinematics of the stellar samples against numerical simulations of the interactions between the Small and Large Magellanic Clouds, and find general agreement between the kinematics of the observed populations and a simulation in which the Clouds have undergone a recent direct collision., Comment: 13 pages, 10 figures, 2 tables, submitted to ApJ, accepted February 8th, 2019

The Halo Assembly in Lambda-CDM: Observations in 7 Dimensions (HALO7D) dataset consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope-measured proper motions of Milky Way (MW) halo main sequence turnoff stars in the CANDELS fields. In this paper, the second in the HALO7D series, we present the proper motions for the HALO7D sample. We discuss our measurement methodology, which makes use of a Bayesian mixture modeling approach for creating the stationary reference frame of distant galaxies. Using the 3D kinematic HALO7D sample, we estimate the parameters of the halo velocity ellipsoid, $\langle v_{\phi} \rangle, \sigma_r, \sigma_{\phi}, \sigma_{\theta}$, and the velocity anisotropy $\beta$. Using the full HALO7D sample, we find $\beta=0.63 \pm 0.05$ at $\langle r \rangle =24$ kpc. We also estimate the ellipsoid parameters for our sample split into three apparent magnitude bins; the posterior medians for these estimates of $\beta$, while consistent with one another, increase as a function of mean sample distance. Finally, we estimate $\beta$ in each of the individual HALO7D fields. We find that the velocity anisotropy $\beta$ can vary from field to field, which suggests that the halo is not phase mixed at $\langle r \rangle =24$ kpc. We explore the $\beta$ variation across the skies of two stellar halos from the \textit{Latte} suite of FIRE-2 simulations, finding that both simulated galaxies show $\beta$ variation over a similar range to the variation observed across the four HALO7D fields. The accretion histories of the two simulated galaxies result in different $\beta$ variation patterns; spatially mapping $\beta$ is thus a way forward in characterizing the accretion history of the Galaxy., Comment: 23 pages, 13 figures. Submitted to ApJ; comments welcome

We present a new distance estimation for the Milky Way dwarf spheroidal satellite Sculptor obtained from multi-epoch mid-infrared observations of RR Lyrae stars. The 3.6 {\mu}m observations have been acquired with the Infrared Array Camera on board the Spitzer Space Telescope as part of the SMHASH Program. Mid-infrared light curves for 42 RRL were obtained, from which we measured Sculptor's distance modulus to be {\mu} = 19.60 $\pm$ 0.02 (statistical) $\pm$ 0.04 (photometric) mag (with $\sigma_{sys}=$ = 0.09 mag), using the 3.6 {\mu}m empirical period-luminosity relations derived from the Galactic globular cluster M4, or {\mu} = 19.57 $\pm$ 0.02 (statistical) $\pm$ 0.04 (photometric) mag (with $\sigma_{sys}=$ = 0.11 mag) using empirical relations in the same passband recently derived from the Large Magellanic Cloud globular cluster Reticulum. Both these measurements are in good agreement with values presented in previous works with Sculptor RR Lyrae stars in optical bands, and are also consistent with recent near-infrared RR Lyrae results. Best agreement with the literature is found for the latter modulus which is equivalent to a distance of d = 82 $\pm$ 1 (statistical) $\pm$ 2 (photometric) kpc (with $\sigma_{sys}=$ = 4 kpc). Finally, using a subsample of RR Lyrae stars with spectroscopic metallicities, we demonstrate that these distance estimates are not affected by metallicity effects., Comment: 24 pages, 11 figures. Accepted for publication in MNRAS

The Hubble Tarantula Treasury Project (HTTP) has provided an unprecedented photometric coverage of the entire star-burst region of 30 Doradus down to the half Solar mass limit. We use the deep stellar catalogue of HTTP to identify all the pre--main-sequence (PMS) stars of the region, i.e., stars that have not started their lives on the main-sequence yet. The photometric distinction of these stars from the more evolved populations is not a trivial task due to several factors that alter their colour-magnitude diagram positions. The identification of PMS stars requires, thus, sophisticated statistical methods. We employ Machine Learning Classification techniques on the HTTP survey of more than 800,000 sources to identify the PMS stellar content of the observed field. Our methodology consists of 1) carefully selecting the most probable low-mass PMS stellar population of the star-forming cluster NGC 2070, 2) using this sample to train classification algorithms to build a predictive model for PMS stars, and 3) applying this model in order to identify the most probable PMS content across the entire Tarantula Nebula. We employ Decision Tree, Random Forest and Support Vector Machine classifiers to categorise the stars as PMS and Non-PMS. The Random Forest and Support Vector Machine provided the most accurate models, predicting about 20,000 sources with a candidateship probability higher than 50 percent, and almost 10,000 PMS candidates with a probability higher than 95 percent. This is the richest and most accurate photometric catalogue of extragalactic PMS candidates across the extent of a whole star-forming complex., Comment: 26 pages, 25 figures, Accepted for publication in MNRAS

The 3D velocities of M31 and M33 are important for understanding the evolution and cosmological context of the Local Group. Their most massive stars are detected by Gaia, and we use Data Release 2 (DR2) to determine the galaxy proper motions (PMs). We select galaxy members based on, e.g., parallax, PM, color-magnitude-diagram location, and local stellar density. The PM rotation of both galaxies is confidently detected, consistent with the known line-of-sight rotation curves: $V_{\rm rot} = -206\pm86$ km s$^{-1}$ (counter-clockwise) for M31, and $V_{\rm rot} = 80\pm52$ km s$^{-1}$ (clockwise) for M33. We measure the center-of-mass PM of each galaxy relative to surrounding background quasars in DR2. This yields that $({\mu}_{\alpha*},{\mu}_{\delta})$ equals $(65 \pm 18 , -57 \pm 15)$ $\mu$as yr$^{-1}$ for M31, and $(31 \pm 19 , -29 \pm 16)$ $\mu$as yr$^{-1}$ for M33. In addition to the listed random errors, each component has an additional residual systematic error of 16 $\mu$as yr$^{-1}$. These results are consistent at 0.8$\sigma$ and 1.0$\sigma$ with the (2 and 3 times higher-accuracy) measurements already available from Hubble Space Telescope (HST) optical imaging and VLBA water maser observations, respectively. This lends confidence that all these measurements are robust. The new results imply that the M31 orbit towards the Milky Way is somewhat less radial than previously inferred, $V_{\rm tan, DR2+HST} = 57^{+35}_{-31}$ km s$^{-1}$, and strengthen arguments that M33 may be on its first infall into M31. The results highlight the future potential of Gaia for PM studies beyond the Milky Way satellite system., Comment: 15 pages, 7 figures, ApJ, in press

We present the detection of very extended stellar populations around the Large Magellanic Cloud (LMC) out to R~21 degrees, or ~18.5 kpc at the LMC distance of 50 kpc, as detected in the Survey of the MAgellanic Stellar History (SMASH) performed with the Dark Energy Camera on the NOAO Blanco 4m Telescope. The deep (g~24) SMASH color magnitude diagrams (CMDs) clearly reveal old (~9 Gyr), metal-poor ([Fe/H]=-0.8 dex) main-sequence stars at a distance of 50 kpc. The surface brightness of these detections is extremely low with our most distant detection having 34 mag per arcsec squared in g-band. The SMASH radial density profile breaks from the inner LMC exponential decline at ~13-15 degrees and a second component at larger radii has a shallower slope with power-law index of -2.2 that contributes ~0.4% of the LMC's total stellar mass. In addition, the SMASH densities exhibit large scatter around our best-fit model of ~70% indicating that the envelope of stellar material in the LMC periphery is highly disturbed. We also use data from the NOAO Source catalog to map the LMC main-sequence populations at intermediate radii and detect a steep dropoff in density on the eastern side of the LMC (at R~8 deg) as well as an extended structure to the far northeast. These combined results confirm the existence of a very extended, low-density envelope of stellar material with disturbed shape around the LMC. The exact origin of this structure remains unclear but the leading options include a classical accreted halo or tidally stripped outer disk material., Comment: 9 pages, 5 figues, 1 table, submitted to ApJ