We formulate a new, revised and coherent understanding of the structure and dynamics of the Large Magellanic Cloud (LMC), and its orbit around and interaction with the Milky Way. Much of our understanding of these issues hinges on studies of the LMC line-of-sight kinematics. The observed velocity field includes contributions from the LMC rotation curve V (R ′ ), the LMC transverse velocity vector v t , and the rate of inclination change di/dt. All previous studies have assumed di/dt = 0. We show that this is incorrect, and that combined with uncertainties in v t this has led to incorrect estimates of many important structural parameters of the LMC. We derive general expressions for the velocity field which we fit to kinematical data for 1041 carbon stars. We calculate v t by compiling and improving LMC proper motion measurements from the literature, and we show that for known v t all other model parameters are uniquely determined by the data. The position angle of the line of nodes is Θ = 129.9 • ± 6.0 • , consistent with the value determined geometrically by van der Marel & Cioni (2001). The rate of inclination change is di/dt = −0.37 ± 0.22 mas yr −1 = −103 ± 61 degrees/Gyr. This is similar in magnitude to predictions from N -body simulations by Weinberg (2000), which predict LMC disk precession and nutation due to Milky Way tidal torques. The LMC rotation curve V (R ′ ) has amplitude 49.8 ± 15.9 km s −1 . This is 40% lower than what has previously (and incorrectly) been inferred from studies of HI, carbon stars, and other tracers. The line-of-sight velocity dispersion has an average value σ = 20.2 ± 0.5 km s −1 , with little variation as function of radius. The dynamical center of the carbon stars is consistent with the center of the bar and the center of the outer isophotes, but it is offset by 1.2 • ± 0.6 • from the kinematical center of the HI. The enclosed mass inside the last data point is M LMC (8.9 kpc) = (8.7 ± 4.3) × 10 9 M ⊙ , more than half of which is due to a dark halo. The LMC has a considerable vertical thickness; its V /σ = 2.9 ± 0.9 is less than the value for the Milky Way's thick disk (V /σ ≈ 3.9). Simple arguments for models stratified on spheroids indicate that the (out-of-plane) axial ratio could be ∼ 0.3 or larger. Isothermal disk models for the observed velocity dispersion profile confirm the finding of Alves & Nelson (2000) that the scale height must increase with radius. A substantial thickness for the LMC disk is consistent with the simulations of Weinberg, which predict LMC disk thickening due to Milky Way tidal forces. These affect LMC structure even inside the LMC tidal radius, which we calculate to be r t = 15.0 ± 4.5 kpc (i.e., 17.1 • ± 5.1 • ). The new insights into LMC structure need not significantly alter existing predictions for the LMC self-lensing optical depth, which to lowest order depends only on σ. The compiled proper motion data imply an LMC transverse velocity v t = 406 km s −1 in the direction of position angle 78.7 • (with errors of ∼ 40 km s −1 in each coordinate)...

The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims to map $7000 deg 2 of the high Galactic latitude sky visible from Arecibo, providing a H i line spectral database covering the redshift range between À1600 and 18,000 km s À1 with $5 km s À1 resolution. Exploiting Arecibo's large collecting area and small beam size, ALFALFA is specifically designed to probe the faint end of the H i mass function in the local universe and will provide a census of H i in the surveyed sky area to faint flux limits, making it especially useful in synergy with wide-area surveys conducted at other wavelengths. ALFALFA will also provide the basis for studies of the dynamics of galaxies within the Local Supercluster and nearby superclusters, allow measurement of the H i diameter function, and enable a first wide-area blind search for local H i tidal features, H i absorbers at z < 0:06, and OH megamasers in the redshift range 0:16 < z < 0:25. Although completion of the survey will require some 5 years, public access to the ALFALFA data and data products will be provided in a timely manner, thus allowing its application for studies beyond those targeted by the ALFALFA collaboration. ALFALFA adopts a two-pass, minimum intrusion, drift scan observing technique that samples the same region of sky at two separate epochs to aid in the discrimination of cosmic signals from noise and terrestrial interference. Survey simulations, which take into account large-scale structure in the mass distribution and incorporate experience with the ALFA system gained from tests conducted during its commissioning phase, suggest that ALFALFA will detect on the order of 20,000 extragalactic H i line sources out to z $ 0:06, including several hundred with H i masses M H i < 10 7:5 M .

Near infrared spectra were obtained for 117 red giants in the Fornax dwarf spheroidal galaxy with the FORS1 spectrograph on the VLT, in order to study the metallicity distribution of the stars and to lift the age-metallicity degeneracy of the red giant branch (RGB) in the color-magnitude diagram (CMD). Metallicities are derived from the equivalent widths of the infrared Calcium triplet lines at 8498, 8542, and 8662Å, calibrated with data from globular clusters, the open cluster M67 and the LMC. For a substantial portion of the sample, the strength of the Calcium triplet is unexpect-paring the metallicities of the stars with their positions in the CMD, we have derived the complex age-metallicity relation of Fornax. In the first few Gyr, the metal abundance rose to [Fe/H]∼ −1.0 dex. The enrichment accelerated in the past ∼ 1-4 Gyr to reach [Fe/H]∼ −0.4 dex. More than half the sample is constituted of star younger than ∼ 4 Gyr, thus indicating sustained recent star formation in Fornax. These results are briefly compared to the theoretical predictions on the evolution of dwarf galaxies. They indicate that the capacity of dwarf spheroidal galaxies to retain the heavy elements that they produce is larger than expected.

Ca II triplet spectroscopy has been used to derive stellar metallicities for individual stars in four LMC fields situated at galactocentric distances of 3 • , 5 • , 6 • -2and 8 • to the north of the Bar. Observed metallicity distributions show a well defined peak, with a tail toward low metallicities. The mean metallicity remains constant until 6 • ([Fe/H]∼-0.5 dex), while for the outermost field, at 8 • , the mean metallicity is substantially lower than in the rest of the disk ([Fe/H]∼-0.8 dex). The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age-metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age-metallicity relationships for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk age-metallicity relationship is similar to that for clusters. However, the lack of objects with ages between 3 and 10 Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the age-metallicity relationship of the bar. Simple chemical evolution models have been used to reproduce the observed age-metallicity relationships with the purpose of investigating which mechanism has participated in the evolution of the disk and bar. We find that while the disk age-metallicity relationship is well reproduced by close-box models or models with a small degree of outflow, that of the bar is only reproduced by models with combination of infall and outflow.