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 Hubble Space Telescope (HST). We tracked the SMC's motion relative to four background QSOs over a baseline of approximately 2 yr. The measured proper motion is μW = -1.16 ± 0.18 mas yr-1, μN = -1.17 ± 0.18 mas yr-1. This is the best measurement yet of the SMC's 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 ± 42 km s-1. 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 versus 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.

https://iopscience.iop.org/article/10.1086/508014/pdf

Is the SMC Bound to the LMC? The Hubble Space Telescope Proper Motion of the SMC

We have used the latest H I observations of the Small Magellanic Cloud (SMC), obtained with the Australia Telescope Compact Array and the Parkes telescope, to reexamine the kinematics of this dwarf irregular galaxy. A large velocity gradient is found in the H I velocity field, with a significant symmetry in isovelocity contours, suggestive of a differential rotation. A comparison of H I data with the predictions from tidal models for the SMC evolution suggests that the central region of the SMC corresponds to the central disklike or barlike component left from the rotationally supported SMC disk prior to its last two encounters with the Large Magellanic Cloud. In this scenario, the velocity gradient is expected as a leftover from the original, preencounter angular momentum. We have derived the H I rotation curve and the mass model for the SMC. This rotation curve rapidly rises to about 60 km s-1 up to the turnover radius of ~3 kpc. A stellar mass-to-light ratio of about unity is required to match the observed rotation curve, suggesting that a dark matter halo is not needed to explain the dynamics of the SMC. A set of derived kinematic parameters agrees well with the assumptions used in tidal theoretical models that led to a good reproduction of observational properties of the Magellanic System. The dynamical mass of the SMC, derived from the rotation curve, is 2.4 × 109 M☉.

https://iopscience.iop.org/article/10.1086/381869/pdf

A New Look at the Kinematics of Neutral Hydrogen in the Small Magellanic Cloud

We have obtained spectra at the Ca II triplet of individual red giants in seven Small Magellanic Cloud (SMC) star clusters whose ages range from ~4 to 12 Gyr. The spectra have been used to determine mean abundances for six of the star clusters to a typical precision of 0.12 dex. When combined with existing data for other objects, the resulting SMC age-metallicity relation is generally consistent with that for a simple model of chemical evolution, scaled to the present-day SMC mean abundance and gas mass fraction. Two of the clusters (Lindsay 113 and NGC 339), however, have abundances that are ~0.5 dex lower than that expected from the mean age-metallicity relation. It is suggested that the formation of these clusters, which have ages of ~5 Gyr, may have involved the infall of unenriched gas, perhaps from the Magellanic Stream. The spectra also yield radial velocities for the seven clusters. The resulting velocity dispersion is 16 ± 4 km s-1, consistent with those of the SMC planetary nebula and carbon star populations.

http://iopscience.iop.org/article/10.1086/300340/pdf

Ca II Triplet Spectroscopy of Giants in Small Magellanic Cloud Star Clusters: Abundances, Velocities, and the Age-Metallicity Relation

A suite of high-resolution N-body simulations of the Magellanic Clouds–Milky Way system are presented and compared directly with newly available data from the H i Parkes All-Sky Survey (HIPASS). We show that the interaction between Small Magellanic Clouds (SMC) and Large Magellanic Clouds results in both a spatial and kinematical bifurcation of both the stream and the leading arm. The spatial bifurcation of the stream is readily apparent in the HIPASS data, and the kinematical bifurcation is also tentatively identified. This bifurcation provides strong support for the tidal disruption origin for the Magellanic stream. A fiducial model for the Magellanic Clouds (MCs) is presented upon completion of an extensive parameter survey of the potential orbital configurations of the MCs and the viable initial boundary conditions for the disc of the SMC. The impact of the choice of these critical parameters upon the final configurations of the stream and leading arm is detailed.

/pdf/n-body-simulations-of-the-magellanic-stream-4bblihltdu.pdf

N-body simulations of the Magellanic stream

We have obtained spectra at the Ca II triplet of individual red giants in seven SMC star clusters whose ages range from ~4 to 12 Gyr. The spectra have been used to determine mean abundances for six of the star clusters to a typical precision of 0.12 dex. When combined with existing data for other objects, the resulting SMC age-metallicity relation is generally consistent with that for a simple model of chemical evolution, scaled to the present-day SMC mean abundance and gas mass fraction. Two of the clusters (Lindsay 113 and NGC 339), however, have abundances that ~0.5 dex lower than that expected from the mean age-metallicity relation. It is suggested that the formation of these clusters, which have ages of ~5 Gyr, may have involved the infall of uneriched gas, perhaps from the Magellanic Stream. The spectra also yield radial velocities for the seven clusters. The resulting velocity dispersion is 16 +/- 4 km/sec, consistent with those of the SMC planetary nebula and carbon star populations.

Ca II Triplet Spectroscopy of Giants in SMC Star Clusters: Abundances, Velocities and the Age-Metallicity Relation

Kinematical and dynamical data for 44 SMC planetary nebulae (PNs) are presented at a velocity resolution of 12 km/s.The PNs form an unstructured spheroidal population apparently associated with the Bar with centroid at alpha 00 h 49 m 39 s, delta -73 deg 30 min (1950) and with a mean radial velocity of -17 km/s.Their velocity dispersion implies a mass of 900 million solar masses within a radius of 3 kpc of the centroid.These PNs, which form a population of age greater than about 100 million years, appear to be loosely associated with the lower velocity component of the H I, suggesting that the high-velocity H I component is dynamically young.A remarkably good correlation between the expansion velocity and the excitation class is found, which may show that the mass of the white dwarf central star is the major variable influencing the expansion velocity of PNs. 39 references.

Dopita

Papers

Kinematics and internal dynamics of planetary nebulae in the small Magellanic Cloud