In order to understand the interaction between dark matter and baryonic matter in the galaxy evolution history, it is fundamental to constrain dark matter (DM) distribution in galaxies. However, it is difficult to constrain DM profile in the central region of early type galaxy because of the lack of extended neutral hydrogen gas and the degeneracy between dynamical stellar M/L and DM profile. To resolve this difficulty, we conducted combined analysis of ALMA cold molecular gas kinematics and MUSE stellar kinematics of early type fast rotator galaxy NGC1380. In addition, we used HST image to trace the stellar luminosity distribution. With the help of high resolution of ALMA image and large field of view of MUSE, we derived the central BH mass, stellar bulge, disk and DM profile.

LAMOST has obtained a large number of spectra for K-giant stars whose metallicities are well measured and released in DR5. Combining with the distances, radial velocities and proper motions provided by Gaia DR2, the full position and velocity information has been obtained. Using the Bayesian method we have constrained the rotational velocity of the halo and thick disk components in the local volume within 4 kpc from the Sun. The values of the rotational velocity are and for the halo and disk respectively, with the velocity of LSR assumed to be 232 km s−1. The dispersions of the rotational velocity are and for the two components. What’s more, another hot retrogradely rotating component is discovered.

Orbital resonances in the Galactic halo have been studied using the Galactic mass model of Pichardo et al. (2003, 2004), including a Galactic bar. For the two moving groups of the Galactic halo, G18-39 and G21-22 (Silva et al. 2012), the majority of stars in both groups appear trapped in two resonances over the Galactic plane, generated by the bar. We have taken the rotation speed of the bar, Ωb, as 45-55 km s-1 kpc-1. So, these two moving groups are part of stellar supergroups which populate these two resonances. The position of these two groups in the Bottlinger diagram can be explained by the mean (U,V) field generated by these two resonances crossing the solar vicinity, in contrast with the alternate explanation of Silva et al. (2012), based on the simulations of Meza et al. (2005), that these two groups, seen as two peaks in the U Galactic velocity, have been created by the accretion of a dwarf galaxy by the Milky Way, such as that of Ω Centauri.

The AAOmega Evolution of Galactic Structure (AEGIS) survey (P.I. Keller) was a moderate scale (45 nights) spectroscopic survey carried out with the AAOmega multi-fiber spectrograph at the Anglo-Australian Telescope. The input catalogue for the spectroscopic observations was derived from photometry of approximately 200 two-degree diameter fields obtained during the commissioning of the SkyMapper survey. The data consists of medium-resolution (R ~ 2,000) spectroscopy for approximately 70,000 thick disk and halo stars spanning a survey footprint of 4,900 square degrees. We plan to use the AEGIS data to further characterize the properties of the disk and halo systems and better constrain the assembly history of the Galaxy based on the behavior of the CEMP-no and CEMP-s stars in the sample.

We describe the implementation and performance results of our massively parallel MPI†/OpenMP‡ hybrid TreePM code for large-scale cosmological N-body simulations. For domain decomposition, a recursive multi-section algorithm is used and the size of domains are automatically set so that the total calculation time is the same for all processes. We developed a highly-tuned gravity kernel for short-range forces, and a novel communication algorithm for long-range forces. For two trillion particles benchmark simulation, the average performance on the fullsystem of K computer (82,944 nodes, the total number of core is 663,552) is 5.8 Pflops, which corresponds to 55% of the peak speed.

The contribution of massive star clusters to their hosting halo dramatically depends on their formation mechanism and their early evolution. Massive globular clusters in the Milky Way (and in other galaxies) have been shown to display peculiar chemical patterns (light-elements correlations and anti-correlations) indicative of a complex star formation, confirmed by photometric evidence (spread or split sequences). I use these chemical signatures to try to understand what is the fraction of halo stars originally born in globular clusters.

The mass and cumulative mass profile of the Galaxy are its most fundamental properties. Estimating these properties, however, is not a trivial problem. We rely on the kinematic information from Galactic satellites such as globular clusters and dwarf galaxies, and this data is incomplete and subject to measurement uncertainty. In particular, the complete 3D velocity vectors of objects are sometimes unavailable, and there may be selection biases due to both the distribution of objects around the Galaxy and our measurement position. On the other hand, the uncertainties of these data are fairly well understood. Thus, we would like to incorporate these uncertainties and the incomplete data into our estimate of the Milky Way's mass. The Bayesian paradigm offers a way to deal with both the missing kinematic data and measurement errors using a hierarchical model. An application of this method to the Milky Way halo mass profile, using the kinematic data for globular clusters and dwarf satellites, is shown.

Kim 1 & 2 are two new star clusters discovered in the Stromlo Missing Satellite Survey. Kim 1, located at a heliocentric distance of 19.8 ± 0.9 kpc, features an extremely low total luminosity (MV = 0.3 ± 0.5 mag) and low star concentration. Together with the large ellipticity (ε = 0.42 ± 0.10) and irregular isophotes, these properties suggest that Kim 1 is an intermediate mass star cluster being stripped by the Galactic tidal field. Kim 2 is a rare ultra-faint outer halo globular cluster located at a heliocentric distance of 104.7 ± 4.1 kpc. The cluster exhibits evidence of significant mass loss such as extra-tidal stars and mass-segregation. Kim 2 is likely to follow an orbit confined to the peripheral region of the Galactic halo, and/or to have formed in a dwarf galaxy that was later accreted into the Galactic halo.

The smallest dark matter halos are formed first in the early universe. According to recent studies, the central density cusp is much steeper in these halos than in larger halos and scales as ρ ∝ r−(1.5−1.3). We present results of very large cosmological N-body simulations of the hierarchical formation and evolution of halos over a wide mass range, beginning from the formation of the smallest halos. We confirmed early studies that the inner density cusps are steeper in halos at the free streaming scale. The cusp slope gradually becomes shallower as the halo mass increases. The slope of halos 50 times more massive than the smallest halo is approximately -1.3. The concentration parameter is nearly independent of halo mass, and ruling out simple power law mass-concentration relations. The steeper inner cusps of halos near the free streaming scale enhance the annihilation luminosity of a Milky Way sized halo between 12 to 67%.

In general, a tidal stream is misaligned with the orbit of its progenitor. Here we present the formation of tidal streams in angle-action space to discuss the effect of this misalignment on orbit-fitting algorithms for constraining the Galactic potential. We close by presenting and testing an alternative algorithm which more fully accounts for the dynamics of streams by using the angle-action formalism.

Studies of stellar populations have been reinvigorated during the last decade by the advent of large-area sky surveys such as SDSS, 2MASS, RAVE, and others. These data, together with theoretical and modeling advances, are revolutionizing our understanding of the nature of the Milky Way, and galaxy formation and evolution in general. The abundance of substructure in the multi-dimensional space of various observables, such as position, kinematics, and metallicity, is by now proven beyond doubt, and demonstrates the importance of mergers in the growth of galaxies. Unlike smooth models that involve simple components, the new data reviewed here clearly exhibit many irregular structures, such as the Sagittarius dwarf tidal stream and the Virgo and Pisces overdensities in the halo, and the Monoceros stream closer to the Galactic plane. These recent developments have made it clear that the Milky Way is a complex and dynamic structure, one that is still being shaped by the merging of neighboring smaller galaxies. Here we summarize developments over the last decade in our mapping of the stellar content of the Milky Way, as well as recent attempts to map the dark matter halo by Loebman et al. (2012) and ISM dust distribution by Berry et al. (2012). We also briefly discuss the next generation of wide-field sky surveys, exemplified by Gaia and LSST, which will improve measurement precision manyfold, and comprise billions of individual stars.

We report on the discovery and characterization of a possibly new signature related to the formation of the Milky Way stellar local halo.

The theory of the Milky Way formation, in the framework of the ΛCDM model, predicts galactic stellar halos to be built from multiple accretion events starting from the first structure to collapse in the Universe.

Evidences in the past few decades have indicated that the Galactic halo consists of two overlapping structural components, an inner and an outer halo. We provide a set of numerical N-body simulations aimed to study the formation of the outer Milky Way (MW) stellar halo through accretion events between a (bulgeless) MW-like system and a satellite galaxy. After these minor mergers take place, in several orbital configurations, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions of the mergers where a signal of retrograde rotation in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the MW stellar halo.

Our results show that the dynamical friction has a fundamental role in assembling the final velocity distributions originated by different orbits and that retrograde satellites moving on low inclination orbits deposit more stars in the outer halo regions and therefore can produce the counter-rotating behavior observed in the outer MW halo.

In the framework of he ESO Large Program “First Stars”, high resolution (R=45000) high S/N ratio spectra have been obtained for a sample of Extremely Metal Poor Stars (EMP stars), 35 giants and 18 turnoff stars. Among them 37 have a very low metallicity: [Fe/H]< −2.9.

The Sloan Extension for Galactic Exploration and Understanding (SEGUE) has now been completed. This is one of three surveys that were executed as part of the first extension of the Sloan Digital Sky Survey (SDSS-II), which consist of LEGACY, SUPERNOVA SURVEY, and SEGUE. The SEGUE program has obtained over 3600 square degrees of ugriz imaging of the sky outside the original SDSS-I footprint. The regions of sky targeted for SEGUE imaging were primarily at lower Galactic latitudes (|b| < 35°), in order to better sample the disk/halo interface of the Milky Way. SEGUE also obtained medium-resolution (R = 2000) spectroscopy, over the wavelength range 3800-9200 Å, for over 200,000 stars in 200 selected areas over the sky available from Apache Point, New Mexico. We discuss the determination of stellar atmospheric parameters (Teff, log g, and [Fe/H]) for these stars, and highlight several of the scientific results obtained to date. The proposed second extension of SDSS, known as SDSS-III, will include SEGUE-2, a program to roughly double the numbers of stars with available spectroscopy, as well as APOGEE, a program to obtain high-resolution (R = 20000) near-IR spectroscopy for over 100,000 stars in the disk, bulge and halo populations of the Galaxy. Other massive spectroscopic surveys of interest to Galactic science are also briefly discussed.

To this contribution we present a brief review of our recent abundance surveys (Reddy et al. 2003; Reddy et al. 2006) of the Milky Way galaxy. Survey focussed on controlled samples of stars selected based on their kinematic properties to belong either thin disk, thick disk or halo components of the Galaxy. Abundance and kinematic results were obtained for about 400 F-, G- and K- dwarfs. Abundances for 22 elements representing different production mechanisms (α-process, p-capture, Fe-peak, s- and r-process) and sites (AGB, SNIa, SNII) were obtained using high quality and high resolution echelle spectra.

Results showed thin and thick disk components are distinct stellar populations with different chemical history. The ratios of α-elements and a few other elements (like Al, V, and Co) are clearly enhanced for stars in the thick disk compared to thin disk stars at given metallicity. Abundance ratios for halo and thick disk stars are very similar. Dispersion in [X/Fe] ratios at given metallicity is comparable to measurement errors inferring lack of cosmic' scatter. Thick disk stars are older (10-13 Gyrs) compared to their counter parts (1-10 Gyrs) in the thin disk. Abundance results for thin and thick disk stars favor the models of hierarchical formation of the galaxy.

Kinematics and abundances have been determined for a large sample of K giants in a field at ∼2 kpc from the center to study the relationship between the bulge and the halo. There are two different kinematic groups evident. The metal-poor stars have low rotation and high velocity dispersion, and so can be associated with the halo. The metal-richer stars have intermediate rotation. Our data suggest that the bulge and halo could be separate kinematical entities.

The Baade's Window bulge is a metal-rich, rotationally supported entity, whereas the solar neighbourhood halo is metal-poor and non-rotating; what is the connection between these two spheroid components?

We present results of a spectroscopic survey of 847 K-giants from 3 low absorption windows at (5,-12), (-5,-12) and (-25,-12). This is a seven times larger sample than has been previously studied in this region.