Recent spectroscopic and high-resolution Hubble Space Telescope (HST) imaging observations have revealed significant numbers of '' passive '' spiral galaxies in distant clusters, with all the morphological hallmarks of a spiral galaxy (in particular, spiral arm structure), but with weak or absent star formation. Exactly how such spiral galaxies formed and whether they are the progenitors of present-day S0 galaxies is unclear. Based on analytic arguments and numerical simulations of the hydrodynamical evolution of a spiral galaxy's halo gas (which is a likely candidate for the source of gas replenishment for star formation in spirals), we show that the origin of passive spirals may well be associated with halo gas stripping. Such stripping results mainly from the hydrodynamical interaction between the halo gas and the hot intracluster gas. Our numerical simulations demonstrate that even if a spiral orbits a cluster with a pericenter distance $3 times larger than the cluster core radius, $80% of the halo gas is stripped within a few Gyr and, accordingly, cannot be accreted by the spiral. Furthermore, our study demonstrates that this dramatic decline in the gaseous infall rate leads to a steady increase in the Q parameter for the disk, with the spiral arm structure, although persisting, becoming less pronounced as the star formation rate gradually decreases. These results suggest that passive spirals formed in this way gradually evolve into red cluster S0s.

We first present a self‐consistent dynamical model in which ω Cen is formed from an ancient nucleated dwarf galaxy merging with the first generation of the Galactic thin disc in a retrograde manner with respect to the Galactic rotation. Our numerical simulations demonstrate that during merging between the Galaxy and the ω Cen host dwarf with MB≃−14 mag and its nucleus mass of 107 M⊙, the outer stellar envelope of the dwarf is nearly completely stripped, whereas the central nucleus can survive from the tidal stripping because of its compactness. The developed naked nucleus has a very bound retrograde orbit around the young Galactic disc, as observed for ω Cen, with apocentre and pericentre distances of ∼8 and ∼1 kpc, respectively. The Galactic tidal force can induce radial inflow of gas to the centre of the dwarf and consequently triggers moderately strong nuclear starbursts in a repetitive manner. This result implies that efficient nuclear chemical enrichment resulting from the later starbursts can be closely associated with the origin of the observed relatively young and metal‐rich stars in ω Cen. Dynamical heating by the ω Cen host can transform the young thin disc into the thick disc during merging.

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We present an N-body model that reproduces the morphology and kinematics of the Magellanic Stream (MS), a vast neutral hydrogen (HI) structure that trails behind the Large and Small Magellanic Clouds (LMC and SMC, respectively) in their orbit about the Milky Way. After investigating 8 × 10 6 possible orbits consistent with the latest proper motions, we adopt an orbital history in which the LMC and SMC have only recently become a strongly interacting binary pair. We find that their first close encounter ∼2 Gyr ago provides the necessary tidal forces to disrupt the disk of the SMC and thereby create the MS. The model also reproduces the on-sky bifurcation of the two filaments of the MS, and we suggest that a bound association with the Milky Way is required to reproduce the bifurcation. Additional HI structures are created during the tidal evolution of the SMC disk, including the Magellanic Bridge, the "Counter-Bridge," and two branches of leading material. Insights into the chemical evolution of the LMC are also provided, as a substantial fraction of the material stripped away from the SMC is engulfed by the LMC. Lastly we compare three different N-body realizations of the stellar component of the SMC, which we model as a pressure-supported spheroid motivated by recent kinematical observations. We find that an extended spheroid is better able to explain the stellar periphery of the SMC, and the tidal evolution of the spheroid may imply the existence of a stellar stream akin to the gaseous MS.

Context. The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations. Over its first five years it will be collecting data for six public surveys, one of which is the near-infrared Y JK s VISTA survey of the Magellanic Clouds system (VMC). This survey comprises the Large Magellanic Cloud (LMC), the Small Magellanic Cloud, the Magellanic Bridge connecting the two galaxies and two fields in the Magellanic Stream. Aims. This paper provides an overview of the VMC survey strategy and presents first science results. The main goals of the VMC survey are the determination of the spatially-resolved star-formation history and the three-dimensional structure of the Magellanic system. The VMC survey is therefore designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variables such as RR Lyrae stars and Cepheids. This paper focuses on observations of VMC fields in the LMC obtained between November 2009 and March 2010. These observations correspond to a completeness of 7% of the planned LMC fields. Methods. The VMC data are comprised of multi-epoch observations which are executed following specific time constraints. The data were reduced using the VISTA Data Flow System pipeline with source catalogues, including astrometric and photometric corrections, produced and made available via the VISTA Science Archive. The VMC data will be released to the astronomical community following the European Southern Observatory's Public Survey policy. The analysis of the data shows that the sensitivity in each wave band agrees with expectations. Uncertainties and completeness of the data are also derived. Results. The first science results, aimed at assessing the scientific quality of the VMC data, include an overview of the distribution of stars in colour-magnitude and colour-colour diagrams, the detection of planetary nebulae and stellar clusters, and the K s band light-curves of variable stars. Conclusions. The VMC survey represents a tremendous improvement, in spatial resolution and sensitivity, on previous panoramic observations of the Magellanic system in the near-infrared, providing a powerful complement to deep observations at other wavelengths.

A recent all‐object spectroscopic survey centred on the Fornax cluster of galaxies has discovered a population of subluminous and extremely compact members, called ‘ultra‐compact dwarf’ (UCD) galaxies. In order to clarify the origin of these objects, we have used self‐consistent numerical simulations to study the dynamical evolution a nucleated dwarf galaxy would undergo if orbiting the centre of the Fornax cluster and suffering from its strong tidal gravitational field. We find that the outer stellar components of a nucleated dwarf are removed by the strong tidal field of the cluster, whereas the nucleus manages to survive as a result of its initially compact nature. The developed naked nucleus is found to have physical properties (e.g. size and mass) similar to those observed for UCDs. We also find that although this formation process does not have a strong dependence on the initial total luminosity of the nucleated dwarf, it does depend on the radial density profile of the dark halo in the sense that UCDs are less likely to be formed from dwarfs embedded in dark matter haloes with central ‘cuspy’ density profiles. Our simulations also suggest that very massive and compact stellar systems can be rapidly and efficiently formed in the central regions of dwarfs through the merging of smaller star clusters. We provide some theoretical predictions on the total number and radial number density profile of UCDs in a cluster and their dependencies on cluster masses.

We derive the star formation history (SFH) for several regions of the Large Magellanic Cloud (LMC), using deep near-infrared data from the VISTA near-infrared Y JK s survey of the Magellanic system (VMC). The regions include three almost-complete 1.4 deg 2 tiles located ∼3.5• away from the LMC centre in distinct directions. They are split into 21.0 × 21.5 (0.12 deg 2 ) subregions, and each of these is analysed independently. To this dataset, we add two 11.3 × 11.3 (0.036 deg 2 ) subregions selected based on their small and uniform extinction inside the 30 Doradus tile. The SFH is derived from the simultaneous reconstruction of two different colour-magnitude diagrams (CMDs), using the minimization code StarFISH together with a database of "partial models" representing the CMDs of LMC populations of various ages and metallicities, plus a partial model for the CMD of the Milky Way foreground. The distance modulus (m− M) 0 and extinction A V is varied within intervals ∼0.2 and ∼0.5 mag wide, respectively, within which we identify the best-fitting star formation rate SFR(t) as a function of lookback time t, age-metallicity relation (AMR), (m− M) 0 and A V . Our results demonstrate that VMC data, due to the combination of depth and little sensitivity to differential reddening, allow the derivation of the space-resolved SFH of the LMC with unprecedented quality compared to previous wide-area surveys. In particular, the data clearly reveal the presence of peaks in the SFR(t) at ages log(t/yr) 9.3 and 9.7, which appear in most of the subregions. The most recent SFR(t) is found to vary greatly from subregion to subregion, with the general trend of being more intense in the innermost LMC, except for the tile next to the N11 complex. In the bar region, the SFR(t) seems remarkably constant over the time interval from log(t/yr) 8.4 to 9.7. The AMRs, instead, turn out to be remarkably similar across the LMC. Thanks to the accuracy in determining the distance modulus for every subregion -with typical errors of just ∼0.03 mag -we make a first attempt to derive a spatial model of the LMC disk. The fields studied so far are fit extremely well by a single disk of inclination i = 26.2 ± 2.0• , position angle of the line of nodes θ 0 = 129.1 ± 13.0• , and distance modulus of (m− M) 0 = 18.470 ± 0.006 mag (random errors only) up to the LMC centre. We show that once the (m− M) 0 values or each subregion are assumed to be identical to those derived from this best-fitting plane, systematic errors in the SFR(t) and AMR are reduced by a factor of about two.

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 disc components as well as the populations of the field stars and star clusters. The main results of the present simulations are as follows. Tidal interaction between the Clouds and the Galaxy during the last 9 Gyr has transformed the initially thin, non‐barred LMC disc into three different components: central bar, thick disc and kinematically hot stellar halo. The central bar is composed of both old field stars and newly formed ones, with the two fractions being equal in its innermost part. The final thick disc has central velocity dispersion of ∼30 km s−1 and shows rotationally supported kinematics with Vm/σ0∼ 2.3. The stellar halo is formed during the interaction, and consists mainly of old stars originating from the outer part of the initially thin LMC disc. The outer halo shows velocity dispersion of ∼40 km s−1 at a distance of 7.5 kpc from the LMC centre and has a somewhat inhomogeneous distribution of stars. The stellar halo contains relatively young, metal‐rich stars with a mass fraction of 2 per cent. Repetitive interaction between the Clouds and the Galaxy has moderately enhanced the star formation rate to ∼0.4 M⊙ yr−1 in the LMC disc. Most of the new stars (∼90 per cent) are formed within the central 3 kpc of the disc, in particular, within the central bar for the last 9 Gyr. Consequently, the half‐mass radius is different by a factor of 2.3 between old field stars and newly formed ones. Efficient globular cluster formation does not occur until the LMC starts interacting violently and closely with the SMC (∼3 Gyr ago). The newly formed globular cluster system has a disc‐like distribution with rotational kinematics, and its mean metallicity is ∼1.2 higher than that of new field stars because of pre‐enrichment by the formation of field stars prior to cluster formation. The LMC evolution depends on its initial mass and orbit with respect to the Galaxy and the SMC. In particular, the epoch of the bar and thick disc formation and the mass fraction of the stellar halo depend on the initial mass of the LMC. Based on these results, we discuss the entire formation history of the LMC, the possible fossil records of past interaction between the Clouds and the Galaxy, and the star formation history of the SMC for the past several Gyr.