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تسجيل مستخدم جديدThe Proper Motion Field Along the Magellanic Bridge: a New Probe of the LMC-SMC Interaction
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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.
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The Magellanic Clouds are a nearby pair of interacting dwarf galaxies and satellites of the Milky Way. Studying their kinematic properties is essential to understanding their origin and dynamical evolution. They have prominent tidal features and the
kinematics of these features can give hints about the formation of tidal dwarfs, galaxy merging and the stripping of gas. In addition they are an example of dwarf galaxies that are in the process of merging with a massive galaxy. The goal of this study is to investigate the kinematics of the Magellanic Bridge, a tidal feature connecting the Magellanic Clouds, using stellar proper motions to understand their most recent interaction. We calculated proper motions based on multi-epoch $K_{s}$-band aperture photometry, which were obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA), spanning a time of 1-3 yr, and we compared them with $Gaia$ Data Release 2 (DR2) proper motions. We tested two methods for removing Milky Way foreground stars using $Gaia$~DR2 parallaxes in combination with VISTA photometry or using distances based on Bayesian inference. We obtained proper motions for a total of 576,411 unique sources over an area of $23$ deg$^{2}$ covering the Magellanic Bridge including mainly Milky Way foreground stars, background galaxies, and a small population of possible Magellanic Bridge stars ($<$15,000). The first proper motion measurement of the Magellanic Bridge centre is $1.80pm0.25$ mas yr$^{-1}$ in right ascension and $-0.72pm0.13$ mas yr$^{-1}$ in declination. The proper motion measurements confirm a flow motion from the Small to the Large Magellanic Cloud. This flow can now be measured all across the entire length of the Magellanic Bridge. Our measurements indicate that the Magellanic Bridge is stretching.
We present a measurement of the systemic proper motion of the Small Magellanic Cloud (SMC) made using the Advanced Camera for Surveys (ACS) on the textit{Hubble Space Telescope} (textit{HST}). We tracked the SMCs motion relative to 4 background QSOs
over a baseline of approximately 2 years. The measured proper motion is : $mu_W = -1.16 pm 0.18 masyr, mu_N = -1.17 pm 0.18 masyr$. This is the best measurement yet of the SMCs proper motion. We combine this new result with our prior estimate of the proper motion of the Large Magellanic Cloud (LMC) from the same observing program to investigate the orbital evolution of both Clouds over the past 9 Gyr. The current relative velocity between the Clouds is $105 pm 42 kms$. Our investigations of the past orbital motions of the Clouds in a simple model for the dark halo of the Milky Way imply that the Clouds could be unbound from each other. However, our data are also consistent with orbits in which the Clouds have been bound to each other for approximately a Hubble time. Smaller proper motion errors and better understanding of the LMC and SMC masses would be required to constrain their past orbital history and their bound vs. unbound nature unambiguously. The new proper motion measurements should be sufficient to allow the construction of improved models for the origin and properties of the Magellanic Stream. In turn, this will provide new constraints on the properties of the Milky Way dark halo.
We present $it{Hubble}$ $it{Space}$ $it{Telescope}$ proper motions in the direction of the star cluster NGC$,$419 in the Small Magellanic Cloud. Because of the high precision of our measurements, for the first time it is possible to resolve the compl
ex kinematics of the stellar populations located in the field, even along the tangential direction. In fact, the proper motions we measured allow us to separate cluster stars, which move on average with ($mu_{alpha}cosdelta^{rm NGC,419}, mu_{delta}^{rm NGC,419}$) = ($+0.878pm0.055$, $-1.246pm0.048$) mas yr$^{-1}$, from those of the Small Magellanic Cloud and those belonging to a third kinematic feature that we recognise as part of the Magellanic Bridge. Resolving such a kinematic complexity enables the construction of decontaminated colour-magnitude diagrams, as well as the measurement of the absolute proper motion of the three separate components. Our study therefore sets the first steps towards the possibility of dynamically investigating the Magellanic system by exploiting the resolved kinematics of its stellar clusters.
We present a new measurement of the systemic proper motion of the Small Magellanic Cloud (SMC), based on an expanded set of 30 fields containing background quasars and spanning a $sim$3 year baseline, using the textit{Hubble Space Telescope} (textit{
HST}) Wide Field Camera 3. Combining this data with our previous 5 textit{HST} fields, and an additional 8 measurements from the textit{Gaia}-Tycho Astrometric Solution Catalog, brings us to a total of 43 SMC fields. We measure a systemic motion of $mu_{W}$ = $-0.82$ $pm$ 0.02 (random) $pm$ 0.10 (systematic) mas yr$^{-1}$ and $mu_{N}$ = $-1.21$ $pm$ 0.01 (random) $pm$ 0.03 (systematic) mas yr$^{-1}$. After subtraction of the systemic motion, we find little evidence for rotation, but find an ordered mean motion radially away from the SMC in the outer regions of the galaxy, indicating that the SMC is in the process of tidal disruption. We model the past interactions of the Clouds with each other based on the measured present-day relative velocity between them of $103 pm 26$ km s$^{-1}$. We find that in 97% of our considered cases, the Clouds experienced a direct collision $147 pm 33$ Myr ago, with a mean impact parameter of $7.5 pm 2.5$ kpc.
In recent years, with new ground-based and HST measurements of proper motions of the Magellanic Clouds being published, a need of a reanalysis of possible orbital history has arisen. As complementary to other studies, we present a partial examination
of the parameter space -- aimed at exploring the uncertainties in the proper motions of both Clouds, taking into account the updated values of Galactic constants and Solar motion, which kinematically and dynamically influence the orbits of the satellites. In the chosen setup of the study, none of the binding scenarios of this pair could be neglected.
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