We investigate structural, kinematical, and chemical properties of stars and gas in the Small Magellanic Cloud (SMC) interacting with the Large Magellanic Cloud (LMC) and the Galaxy based on a series of self-consistent chemodynamical simulations. We adopt a new "dwarf spheroidal model" in which the SMC initially has both old stars with a spherical spatial distribution and an extended HI gas disk. We mainly investigate SMC's evolution for the last 3 Gyr within which the Magellanic stream (MS) and the Magellanic bridge (MB) can be formed as a result of the LMC-SMC-Galaxy interaction. Our principal results, which can be tested against observations, are as follows. The final spatial distribution of the old stars projected onto the sky is spherical even after the strong LMC-SMC-Galaxy interaction, whereas that of the new ones is significantly flattened and appears to form a bar structure. Old stars have the line-of-sight velocity dispersion (sigma) of ~ 30 km/s and slow rotation with the maximum rotational velocity (V) of less than slow rotation with the maximum rotational velocity (V) of less than 20 km/s and show asymmetry in the radial profiles. New stars have a smaller sigma than old ones and a significant amount of rotation (V/sigma >1). HI gas shows velocity dispersions of sigma = 10-40 km/s a high maximum rotational velocity (V ~ 50 km/s), and the spatial distribution similar to that of new stars. The new stars with ages younger than 3 Gyr show a negative metallicity gradient in the sense that more metal-rich stars are located in the inner regions of the SMC.
We investigate the dynamical and chemical evolution of the Large Magellanic Cloud (LMC) interacting with the Galaxy and the Small Magellanic Cloud (SMC) based on a series of self-consistent chemodynamical simulations. Our numerical models are aimed at explaining the entire properties of the LMC, i.e., the observed structure and kinematics of its stellar halo and disk components as well as the populations of the field stars and star clusters. The main results of the present simulations are summarized as follows. (1) Tidal interaction between the Clouds and the Galaxy during the last 9 Gyr trans…
Recent observations of the Small Magellanic Cloud (SMC) have revealed that the HI gas shows a significant amount of rotation (V_c 60 km/s), while no or little rotation is evident for the old stellar populations. We suggest that this unique kinematical difference between these components in the SMC can be caused by a major merger event which occurred in the early stage of the SMC formation. Our simulations show that dissipative dwarf-dwarf merging can transform two gas-rich dwarf irregulars into a new dwarf, which consists of a spheroidal stellar component and a rotating extended HI disk. The r…
The oldest and most metal-poor Milky Way stars form a kinematically hot halo, which motivates the two major formation scenarios for our galaxy: extended hierarchical accretion and rapid collapse. RR Lyrae stars are excellent tracers of old and metal-poor populations. We measure the kinematics of 43 RR Lyrae stars in the inner regions of the nearby Large Magellanic Cloud (LMC) galaxy. The velocity dispersion, σ_{true}=53\pm10 km/s, indicates that a kinematically hot metal-poor old halo also exists in the LMC. This suggests that our galaxy and smaller late-type galaxies like the LMC have similar…
We review our understanding of the kinematics of the LMC and the SMC, and their orbit around the Milky Way. The line-of-sight velocity fields of both the LMC and SMC have been mapped with high accuracy using thousands of discrete traces, as well as HI gas. The LMC is a rotating disk for which the viewing angles have been well-established using various methods. The disk is elliptical in its disk plane. The disk thickness varies depending on the tracer population, with V/sigma ranging from 2-10 from the oldest to the youngest population. For the SMC, the old stellar population resides in a spher…
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 HI Parkes All-Sky Survey (HIPASS). We show that the interaction between Small 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 Stre…
We discuss structural and kinematical properties of the stellar halo and the old globular cluster system (GCS) in the Large Magellanic Cloud (LMC) based on numerical simulations of the LMC formation. We particularly discuss the observed possible GCS's rotational kinematics (V/sigma > 2) that appears to be significantly different from the stellar halo's one with a large velocity dispersion (~50 km/s). We consider that both halo field stars and old GCs can originate from low-mass subhalos virialized at high redshifts (z >6). We investigate the final dynamical properties of the two old components…
We derive general expressions for the LMC velocity field which we fit to kinematical data for 1041 carbon stars. We demonstrate that all previous studies of LMC kinematics have made unnecessary over-simplifications that have led to incorrect estimates of important structural parameters. We compile and improve LMC proper motion estimates to support our analysis. We find that the kinematically determined position angle of the line of nodes is 129.9 +/- 6.0 deg. The LMC inclination changes at a rate di/dt = -103 +/- 61 deg/Gyr, a result of precession and nutation induced by Milky Way tidal torque…
Stellar radial velocity in the central region of the Large Magellanic Cloud (LMC) is used to estimate the radial velocity curve along various position angles (PA) including the line of nodes (LON). The central part of the radial velocity profile, along the LON, shows a V-shaped profile - a clear indication of counterrotation. The counterrotating region and the secondary bar have similar location and PA. The origin of the counter-rotating core could be internal(secondary bar) or external(accretion). To explain the observed velocity profile, we propose the existence of two disks in the inner LMC…
We are in a privileged location in the Universe which allows us to observe galactic interactions from close range -- the merger of our two nearest dwarf satellite galaxies, the LMC and SMC. It is important to understand the local merger process before we can have confidence in understanding mergers at high redshift. We present high resolution Nbody+SPH simulations of the disruption of the LMC and SMC and the formation of the Magellanic Stream, and discuss the implications for galaxy formation and evolution.
We explore the Magellanic Stream (MS) using a Gaussian decomposition of the HI velocity profiles in the Leiden-Argentine-Bonn (LAB) all-sky HI survey. This decomposition exposes the MS to be composed of two filaments distinct both spatially (as first pointed out by Putman et al.) and in velocity. Using the velocity coherence of the filaments, one can be traced back to its origin in what we identify as the SouthEast HI Overdensity (SEHO) of the Large Magellanic Cloud (LMC), which includes 30 Doradus. Parts of the Leading Arm (LA) can also be traced back to the SEHO in velocity and position. The…
We investigate the formation of a number of key large-scale HI features in the ISM of the Magellanic Bridge using dissipationless numerical simulation techniques. This study comprises the first direct comparison between detailed HI maps of the Bridge and numerical simulations. We confirm that the SMC forms two tidal filaments: a near arm, which forms the connection between the SMC and LMC, and a counterarm. We show that the HI of the most dense part of the Bridge can become arranged into a bimodal configuration, and that the formation of a "loop" of HI, located off the North-Eastern edge of th…
We show that a Magellanic Cloud origin for the warp of the Milky Way can explain most quantitative features of the outer HI layer recently identified by Levine, Blitz & Heiles (2005). We construct a model similar to that of Weinberg (1998) that produces distortions in the dark matter halo, and we calculate the combined effect of these dark-halo distortions and the direct tidal forcing by the Magellanic Clouds on the disk warp in the linear regime. The interaction of the dark matter halo with the disk and resonances between the orbit of the Clouds and the disk account for the large amplitudes o…
The origin of the arc-shaped stellar complexes in the LMC4 region is still unknown. These perfect arcs could not have been formed by O-stars and SNe in their centers; the strong arguments exist also against the possibility of their formation from infalling gas clouds. The origin from microquasars/GRB jets is not excluded, because there is the strong concentration of X-ray binaries in the same region and the massive old cluster NGC 1978, probable site of formation of binaries with compact components, is there also. The last possibility is that the source of energy for formation of the stellar a…
We analyze the velocity residuals of 551 carbon stars relative to a rotating-disk model of the inner $\sim 70 \rm deg^2$ of the Large Magellanic Cloud (LMC). We find that the great majority of the stars in this sample are best fit as being due to two different populations, a young disk population containing 20% of the stars with a velocity dispersion of $8 \kms$, and an old disk containing the remaining stars with a velocity dispersion of $22 \kms$. The young disk population has a metallicity $\sim 0.25$ dex higher than the old disk. With less certainty, the data also suggest at the $2σ$ level…
SHORTENED ABSTRACT: We present numerical investigations designed to critically test models of the origin of the Magellanic Stream. The most developed model is the tidal model which fails to reproduce several of its characteristic properties. We suggest an alternative model for the origin of the Stream which can explain all of its observed features and dynamics, as well as provide a strong constraint on the distribution of gas within the halo of the Milky Way. We propose that the Stream consists of material which was ram-pressure stripped from the Magellanic System during its last passage throu…
Recent observational studies of intermediate-age star clusters (SCs) in the Large Magellanic Cloud (LMC) have reported that a significant number of these objects show double main-sequence turn-offs (DMSTOs) in their color-magnitude diagrams (CMDs). One plausible explanation for the origin of these DMSTOs is that the SCs are composed of two different stellar populations with age differences of ~ 300 Myr. Based on analytical methods and numerical simulations, we explore a new scenario in which SCs interact and merge with star-forming giant molecular clouds (GMCs) to form new composite SCs with t…
We estimate the abundances of S and Fe in the high velocity cloud HVC 287.5+22.5+240, which has a velocity of +240 km/s with respect to the local standard of rest and is in the Galactic direction l~287, b~23. The measurements are based on UV absorption lines of these elements in the Hubble Space Telescope spectrum of NGC 3783, a background Seyfert galaxy, as well as new H I 21-cm interferometric data taken with the Australia Telescope. We find S/H=0.25+/-0.07 and Fe/H=0.033+/-0.006 solar, with S/Fe=7.6+/-2.2 times the solar ratio. The S/H value provides an accurate measure of the chemical enri…
This review contains: (1) the scientific motivations for studying Planetary Nebulae in the Magellanic Clouds; (2) a review of this field of study, from the origins to the most recent results, focusing on the papers that have been published since the last IAU Symposium on Planetary Nebulae; (3) a review of the Hubble contribution to the field, from the early results to our own Magellanic Cloud Planetary Nebula program.
The rotation of the disk of the Large Magellanic Cloud (LMC) is derived from the radial velocities of 422 carbon stars. New aspects of this analysis include the propagation of uncertainties in the LMC proper motion with a Monte Carlo, and a self-consistent modeling of the rotation curve and disk kinematics. The rotation curve is well fit by a truncated, finite-thickness exponential disk model with no dark halo. The velocity dispersion in radial bins decreases from 22 to 15 km/s, then increases to 20 km/s at larger radii. Constant-thickness models in virial equilibrium cannot be reconciled with…
Based on an analysis of the interstellar highly ionised species C IV, Si IV, N V, and O VI observed in the FUSE and HST/STIS E140M spectra of four hot stars in the Large Magellanic Cloud (LMC), we find evidence for a hot LMC halo fed by energetic outflows from the LMC disk and even possibly an LMC galactic wind. Signatures for such outflows are the intermediate and high-velocity components (v_LSR>100 km/s) relative to the LMC disk observed in the high- and low-ion absorption profiles. The stellar environments produce strong, narrow (T<20,000 K) components of C IV and Si IV associated with the …
The results of the interaction between the Milky Way and the Magellanic Clouds are revealed through several high velocity complexes which are connected to the Clouds. The exact mechanism of their formation is under some debate, but they remain the only group of high-velocity clouds (HVCs) for which we have an origin and roughly a distance. Given that, the Magellanic HVCs can be used as a calibrator for other HVCs, while also providing an opportunity to closely investigate the remnants of an interacting system. These HVCs may hold the key to the star formation history, kinematic structure, and …
We remeasure the ``light echo'' times to the near and far side of the ring around SN 1987A using the method of Gould (1995) and the new reductions of the original UV spectra by Sonneborn et al. (1996). Under the assumption that the ring is circular, we obtain an upper limit to the distance to the Large Magellanic Cloud μ_lmc < 18.37 +/- 0.04. This result is very close to Gould's original value, and contradicts claims that the new spectra measurements lead to a significant increase in the distance estimate and a substantial increase in the statistical errors. We present new evidence (partly pro…
The characteristics of the cluster systems of the Magellanic Clouds, as inferred from integrated properties, are compared with those from individual cluster studies and from the field population. The agreement is generally satisfactory though in the case of the LMC, the lack of clusters older than ~3 Gyr is not reflected in the field population. The possible origin(s) for this cluster ``age-gap'' are discussed. The SMC cluster age-metallicity relation is also presented and discussed.
From an analysis of the sky and velocity distributions of the high-velocity clouds (HVCs) we show that the majority of the HVCs has a common origin. We conclude that the HVCs surround the Galaxy, forming a metacloud of 300 kpc in size and with a mass of 3 10^9 M_sun, and that they are the product of a powerful ``superwind'' (about 10^58 ergs), which occurred in the Magellanic Clouds about 570 Myr ago as a consequence of the interaction of the Large and Small Magellanic Clouds. The HVCs might be magnetic bubbles of semi-ionized gas, blown from the Magellanic Clouds around 570 Myr ago, that circ…
The only microlensing events towards the Magellanic Clouds for which the location of the lens is strongly constrained are the two binary caustic crossing events. In at least one and possibly both cases, the lens lies at, or close to, the clouds themselves. On the face of it, this seems an improbable occurrence if the Galactic dark halo provides the bulk of the lensing population, as suggested by standard analyses of the MACHO dataset towards the Large Magellanic Cloud (LMC). We use a binomial statistic to assess the prior probability of observing $M$ non-halo binary caustic events given a tota…
Recently obtained kinematic data has shown that the Large Magellanic Cloud (LMC) possesses an old stellar halo. In order to further characterize the properties of this halo, parametric King models are fit to the surface density of RR Lyrae stars. Using data from both the MACHO and OGLE II microlensing surveys, the model fits yield the center of their distribution at RA = 05:21.1+-0.8, Dec = -69:45+-6 (J2000) and a core radius of 1.42+-0.12 kpc. As a check the halo model is compared with RR Lyrae star counts in fields near the LMC's periphery previously surveyed with photographic plates. These …
The 21cm line emission from a 7x6 degree region, east of and adjoining the Small Magellanic Cloud (SMC) has been observed with the Australia Telescope Compact Array and the Parkes telescopes. This region represents the westernmost part of the Magellanic Bridge, a gas-rich tail extending ~14 degrees to the Large Magellanic Cloud (LMC). A rich and complex neutral hydrogen (HI) structure containing shells, bubbles and filaments is revealed. On the larger scale, the HI of the Bridge is organised into two velocity components. This bimodality, which appears to originate in the SMC, converges to a si…
We present the list of potential multiple star clusters from the central part of the SMC. Presented systems were selected from the catalog of star clusters from the SMC. We find 23 suspected cluster pairs and 4 triple systems. The statistical analysis suggests that many of them may constitute physical systems. Size, equatorial coordinates and age of presented clusters are given. Age of clusters which form five pairs and one triple system is coeval suggesting common origin of these objects.
Three new X-ray pulsars have been detected in the Small Magellanic Cloud (SMC) and the positions of two others have been determined, with archive Chandra data. A series of five observations of the SMC took place between May and October 2002. Analysis of these data has revealed three previously unknown X-ray pulsars at pulse periods of 34, 503 and 138 seconds. The position of pulsar XTE J0052-725, which was originally detected by RXTE on June 19 2002, was also accurately determined and a previously detected 7.78s RXTE pulsar was identified as the source SMC X-3.
An extended HI cloud (VIRGOHI 21) with an HI mass of $\sim10^8$ M$_{\odot}$ and no apparent optical counterpart was recently discovered in the Virgo cluster. In order to understand the origin of physical properties of apparently isolated HI clouds like the VIRGOHI21, we numerically investigate physical properties of tidal HI debris that were formed by galaxy-galaxy interaction in clusters of galaxies. Our hydrodynamical simulations demonstrate that tidal debris with total HI masses of $10^8-10^9$ M$_{\odot}$ can have (1) wide HI velocity widths ($>200$ km s$^{-1}$), (2) a small mass fraction o…
We present a study of the old globular clusters (GC) using archival F606W and F814W HST/ACS images of 19 Magellanic-type dwarf Irregular (dIrr) galaxies found in nearby (2 - 8 Mpc) associations of only dwarf galaxies. All dIrrs have absolute magnitudes fainter than or equal to the SMC (Mv = -16.2 mag). We detect 50 GC candidates in 13 dIrrs, of which 37 have (V-I) colors consistent with "blue" (old, metal-poor) GCs (bGC). The luminosity function (LF) of the bGCs in our sample peaks at Mv = -7.41 +/- 0.22 mag, consistent with other galaxy types. The width of the LF is sigma = 1.79 +/- 0.31 whic…
We present 100 multiple cluster candidates selected from the OGLE catalog of star clusters in the Large Magellanic Cloud. Statistical analysis shows that the significant fraction of these objects may constitute physical systems. Coeval ages of 102 components of multiple objects suggest their common origin. 53 components have very different ages. The comparison of the population of multiple clusters candidates from the SMC and the LMC shows that: a) distributions of sizes and ages of multiple and single clusters from the Magellanic Clouds are very similar, b) the difference of sizes of componen…
Planetary nebulae (PNe) exist in a range of different morphologies, from very simple and symmetric round shells, to elliptical, bipolar, and even quadrupolar shapes. They present extremely complex ensembles of filaments, knots, ansae, and shell multiplicity. It is then overwhelmingly complicated to derive reasonable evolutionary paths to justify the observed shapes of PNe. The confrontation between the evolution of the shells and that of the central stars is needed to understand the origin of the morphological variety. We present some background and recent results on the correlations between P…
We present the radial velocities, metallicities and the K-band magnitudes of 74 RR Lyrae stars in the inner regions of the LMC. The intermediate resolution spectra and infrared images were obtained with FORS1 at the ESO VLT and with the SOFI infrared imager at the ESO NTT. The best 43 RR Lyrae with measured velocities yield an observed velocity dispersion of 61+-7 km/s. We obtain a true LMC RR Lyrae velocity dispersion of 53 km/s, which is higher than the velocity dispersion of any other LMC population previously measured. This is the first empirical evidence for a kinematically hot, metal-poo…
We describe ISO observations of the obscured Asymptotic Giant Branch (AGB) star IRAS04496-6958 in the Large Magellanic Cloud (LMC). This star has been classified as a carbon star. Our new ISOCAM CVF spectra show that it is the first carbon star with silicate dust known outside of the Milky Way. The existence of this object, and the fact that it is one of the highest luminosity AGB stars in the LMC, provide important information for theoretical models of AGB evolution and understanding the origin of silicate carbon stars.
We first show that a large amount of metal-poor gas is stripped from the Small Magellanic Cloud (SMC) and fallen into the Large Magellanic Cloud (LMC) during the tidal interaction between the SMC, the LMC, and the Galaxy over the last 2 Gyrs. We propose that this metal-poor gas can closely be associated with the origin of LMC's young and intermediate-age stars and star clusters with distinctively low-metallicities with [Fe/H] < -0.6. We numerically investigate whether gas initially in the outer part of the SMC's gas disk can be stripped during the LMC-SMC-Galaxy interaction and consequently ca…
We investigate the present distributions of gas and young stars in the Large and Small Magellanic Clouds (LMC and SMC) based on fully self-consistent numerical simulations of the Clouds for the last ~ 0.8 Gyr. Our principal results, which can be tested against observations, are as follows. The last dynamical and hydrodynamical interaction between the Clouds about ~ 0.2 Gyr ago can form the apparently off-center bar and peculiar HI spirals of the LMC. The present spatial distributions of young stars with ages less than 20 Myr in the LMC can be significantly asymmetric and clumpy owing to the in…
We present preliminary results from spectral observations of four candidate radio sources co-identified with known planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). These were made using the Radcliffe 1.9-meter telescope in Sutherland, South Africa. These radio PNe were originally found in Australia Telescope Compact Array (ATCA) surveys of the SMC at 1.42 and 2.37 GHz, and were further confirmed by new high resolution ATCA images at 6 and 3 cm (4"/2"). Optical PNe and radio candidates are within 2" and may represent a subpopulation of selected radio bright objects. Nebular ionized …
ROSAT observations of the Large Magellanic Cloud (LMC) have revealed a large diffuse X-ray arc around the point source RX J053335-6854.9. The relative locations of the diffuse and point sources suggest that they might originate from a common supernova explosion. We have analyzed the physical properties of the diffuse X-ray emission and determined that it is most likely a supernova remnant in a low-density medium in the LMC. We have also analyzed the X-ray and optical observations of RX J053335-6854.9 and concluded that it is a foreground dMe star in the solar neighborhood. Therefore, despite t…
Based on the results of N-body simulations on the last 2.5 Gyr evolution of the Large and Small Magellanic Clouds (LMC and SMC, respectively) interacting with the Galaxy, we firstly show when and where the leading arms (LAs) of the Magellanic stream (MS) can pass through the Galactic plane after the MS formation. We secondly show collisions between the outer Galactic HI disk and the LAs of the MS can create giant HI holes and chimney-like structures in the disk about 0.2 Gyr ago. We thirdly show that a large amount of metal-poor gas is stripped from the SMC and transfered to the LMC during the…
The HST proper motion (PM) measurements of the Clouds have severe implications for their interaction history with the Milky Way (MW) and with each other. The Clouds are likely on their first passage about the MW and the SMC's orbit about the LMC is better described as quasi-periodic rather than circular. Binary L/SMC orbits that satisfy observational constraints on their mutual interaction history (e.g. the formation of the Magellanic Bridge during a collision between the Clouds ~300 Myr ago) can be located within 1 sigma of the mean PMs. However, these binary orbits are not co-located with th…
Field Horizontal branch (HB) stars can be used as tracers for the study of early stages of the evolution of our galaxy. Since the age of individual HB stars is not known a priori, we have studied the kinematics of a sample of field HB stars measured with Hipparcos to look for signs of age and population nature. We found that the kinematics of the HBA stars is very different from that of the sdB/O stars. The HBAs have low, sometimes negative, orbital velocities and feature orbits with large eccentricities, often venturing far above the galactic plane. In contrast, the sdB/O stars show disk-like…
We report the first detection of [CI] (3P1-3P0) emission at 609 um in a region of the Small Magellanic Cloud (N27). Environments poor in heavy elements and dust such as the SMC are thought to be dominated by photodissociation regions. This is the lowest metallicity source where submillimeter neutral carbon emission has been detected. Studying the [CI]/CO intensity ratio in several sources spanning more than an order of magnitude in metallicity, Z, we find that the [CI]/CO ratio increases for decreasing Z. The existence of such a trend points to a photodissociation origin for most of neutral ca…
We investigate the structural, kinematical, and spectrophotometric properties of ``E+A'' galaxies -- those with strong Balmer absorption lines but no significant [OII] emission -- using numerical simulations combined with stellar population synthesis codes. We particularly focus on the two-dimensional (2D) distributions of line-of-sight velocity, velocity dispersion, colors, line index in E+A galaxies formed via the interaction and merging of two gas-rich spirals. Our numerical simulations demonstrate that E+A elliptical galaxies formed by major galaxy merging have positive radial color gradie…
We present period-luminosity relations for more than 3,200 red variable stars in the Small Magellanic Cloud observed in the second phase of the Optical Gravitational Lensing Experiment (OGLE-II). Periods of multiply-periodic light curve solutions combined with the single-epoch 2MASS JHK_S magnitudes, reveal very similar distributions to those for the Large Magellanic Cloud in Paper I. The main features include four pulsating Asymptotic Giant Branch (AGB) ridges, three distinct short-period sequences below the tip of the Red Giant Branch and two long-period sequences of ambiguous origin. We der…
We study the acceleration of the star HE0437-5439, to hypervelocity and discuss its possible origin in the Large Magellanic Cloud (LMC). The star has a radial velocity of 723 km/s and is located at a distance of 61 kpc from the Sun. With a mass of about 8 Msun, the travel time from the Galactic centre is of about 100 Myr, much longer than its main sequence lifetime. Given the relatively small distance to the LMC (18 kpc), we consider it likely that HE0437-5439 originated in the cloud rather than in the Galactic centre, like the other hypervelocity stars. The minimum ejection velocity required …
A Chandra observation has defined the extent of the SNR B 0454-692 in the LMC H II region N9. The remnant has dimension 2.3" x 3.6" and is elongated in the NS direction. The brightest emission comes from a NS central ridge which includes three bright patches. There is good agreement between X-ray and [O III] and [S II] morphology. The remnant is old enough so that optical data give more information about dynamics than do the X-ray data. The SN energy release was >= 4 x 10^50 ergs and the age is ~3 x 10^4 years. There are several unresolved sources nearby but none are clearly associated with th…
Significant numbers of high-velocity HI clouds (HVCs) have now been detected in H-alpha, with a subset seen in low ionization lines (e.g. [NII]). It was originally hoped that the observed H-alpha strength would provide a distance constraint to individual clouds. This idea requires that a useful fraction (f_esc > 1%) of ionizing photons escape the Galaxy, and that the halo ionizing field is relatively smooth, as we discuss. Most HVCs which are known to be close to the Sun are H-alpha; the brightest clouds also show enhanced [NII] emission, in contrast to the Magellanic Stream where the low ioni…
The Magellanic Stream is a 100°x 10°filament of gas which lies within the Galactic halo and contains ~ 2 x 10^8 \Msun of neutral hydrogen. We present data from the HI Parkes All Sky Survey (HIPASS) in the first complete survey of the entire Magellanic Stream and its surroundings. We also present a summary of the reprocessing techniques used to recover large-scale structure in the Stream. The Stream properties revealed include: bifurcation along the main Stream filament; dense, isolated clouds which follow the entire length of the Stream; head-tail structures; and a complex filamentary web at t…
Recent proper motion measurements of the Large and Small Magellanic Clouds (LMC and SMC, respectively) by Kallivayalil et al (2006a,b) suggest that the 3D velocities of the Clouds are substantially higher (~100 km/s) than previously estimated and now approach the escape velocity of the Milky Way (MW). Previous studies have also assumed that the Milky Way can be adequately modeled as an isothermal sphere to large distances. Here we re-examine the orbital history of the Clouds using the new velocities and a LCDM-motivated MW model with virial mass Mvir = 1e12 Msun (e.g. Klypin et al 2002). We co…
We present deep colour-magnitude diagrams for three rich intermediate-age star clusters in the Large Magellanic Cloud, constructed from archival ACS F435W and F814W imaging. All three clusters exhibit clear evidence for peculiar main-sequence turn-offs. NGC 1846 and 1806 each possess two distinct turn-off branches, while the turn-off for NGC 1783 shows a much larger spread in colour than can be explained by the photometric uncertainties. We demonstrate that although all three clusters contain significant populations of unresolved binary stars, these cannot be the underlying cause of the observ…
A recent data analysis of the far-infrared (FIR) map of the Galaxy and the Magellanic Clouds has shown that there is a tight correlation between two FIR colours: the 60 um-100 um and 100 um-140 um colours. This FIR colour relation called ``main correlation'' can be interpreted as indicative of a sequence of various interstellar radiation fields with a common FIR optical property of grains. In this paper, we constrain the FIR optical properties of grains by comparing the calculated FIR colours with the observational main correlation. We show that neither of the ``standard'' grain species (i.e. …
Recent observational and theoretical studies on the three-dimensional (3D) space motions of the Large and the Small Magellanic Clouds (LMC and SMC, respectively) have strongly suggested that the latest proper motion measurements of the Magellanic Clouds (MCs) are consistent with their orbital evolution models in which the MCs have arrived in the Galaxy quite recently for the first time. The suggested orbital models appear to be seriously inconsistent with the tidal interaction models in which the Magellanic Stream (MS) can be formed as a result of the mutual tidal interaction between the MCs a…
Pulsar surveys offer one of the few opportunities to monitor even a small fraction (~0.00001) of the radio sky for impulsive burst-like events with millisecond durations. In analysis of archival survey data, we have discovered a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the Universe imply a distance to the burst of <1 Gpc No further bursts are seen in 90-hr of additional observations, implyi…
The Large Magellanic Cloud (LMC) has a unique cluster formation history in that nearly all of its globular clusters were formed either $\sim$ 13 Gyr ago or less than $\sim$ 3 Gyr ago. It is not clear what physical mechanism is responsible for the most recent cluster formation episode and thus the mysterious age gap between the LMC clusters. We first present results of gas dynamical N-body simulations of the evolution of the LMC in the context of its Galactic orbit and interactions with the SMC, paying special attention to the effect of tidal forces. We find that the first close encounter betwe…
We have used the latest HI observations of the Small Magellanic Cloud (SMC), obtained with the Australia Telescope Compact Array and the Parkes telescope, to re-examine the kinematics of this dwarf, irregular galaxy. A large velocity gradient is found in the HI velocity field with a significant symmetry in iso-velocity contours, suggestive of a differential rotation. A comparison of HI data with the predictions from tidal models for the SMC evolution suggests that the central region of the SMC corresponds to the central, disk- or bar-like, component left from the rotationally supported SMC dis…
