We applied GALFIT and STARLIGHT to the r-band images and spectra, respectively, of ~1,100 dwarf galaxies to analyze the structural properties and stellar populations. In most cases, single component with n = 1 ~ 1.5 well describes the luminosity distribution of dwarf galaxies. However, a large fraction of dS0, dEbc, and dEblue galaxies show sub-structures such as spiral arms and rings. There is a bimodal distributions of stellar ages in dS0 galaxies. But other sub-types of dwarf galaxies show a single peak in the stellar distributions.

We have observed on-going interacting galaxies (NGC4631 and NGC4656) using Subaru/Hyper Suprime-Cam and reduced the data using HSC pipeline and conducted photometry based on DAOphot. Then, we have detected 8 new dwarf galaxy candidates in the outer region of NGC4631 and confirmed the three candidates previously reported by Karachentsev et al. 2014. The 3 or 4 candidates detected in this study may be a star-forming dwarf irregular galaxy and the other 7 candidates may be an old dwarf spheroidal galaxy based on these stellar populations. It looks like that the effective radius - absolute magnitude relation of dwarf galaxies in NGC4631 group is similar to the relation of the Local Group and the other galaxy systems.

We provide CNO and Fe abundance investigations for a sample of up to 45 NGC 1851 giants. High-resolution spectra were obtained with the VLT UVES spectrograph in the framework of the Gaia-ESO Survey. The stars in our sample can be separated into two groups with a difference of 0.1 dex in the mean metallicity, 0.3 dex in the mean C/N, and no significant difference in the mean values of C+N+O.

With the velocity de-projection technique, we derived the averaged 3 dimensional local velocity distribution using only the line-of-sight velocity for the 200,000 FGK type main-sequence stars from the LAMOST DR1 data. Taking the effective temperature as a proxy for age, we investigate the variation of the velocity distribution as a function of Teff and disk height within 100 < |z| < 500 pc. Using the mean velocities of the cool stars, we derive the solar motion of (U⊙, V⊙, W⊙)=(9.58±2.39, 10.52±1.96, 7.01±1.67) kms−1 with respect to the local standard of rest (LSR). Moreover, we find that the stars with Teff > 6000 K show a net asymmetric motion of 〈U〉~2 kms−1 and 〈W〉~3 kms−1 compared to the stars with Teff < 6000 K. And their azimuthal velocity increases when |z| increases. The asymmetric motion in the warmer stars is likely because they are too young and not completely relaxed.

Gas inflow and outflow are the most important processes, which determine the structural and chemical evolution of a disk galaxy like the Milky Way. In order to get new insights into these baryonic processes in Milky Way like galaxies (MWLGs), we consider the data of distant star-forming galaxies and investigate the evolution of the radial density profile of their stellar components and the associated total amount of gaseous inflow and outflow. For this purpose, we analyze the redshift evolution of their stellar mass distribution, combined with the scaling relations between the mass of baryonic components, star formation rate and chemical abundance for both high- and low-z star-forming galaxies. As a result, we find the new relations between star formation rate and inflow/outflow rate as deduced from these distant galaxies, which will provide fundamental information for understanding the structural and chemical evolution of MWLGs.

We examine metallicities, ages and orbital properties of halo stars in a Milky-Way like disk galaxy formed in the cosmological hydrodynamical MaGICC simulations. Halo stars were either accreted from satellites or they formed in situ in the disk or bulge of the galaxy and were then kicked up into the halo (“in situ/kicked-up” stars). Regardless of where they formed both types show surprisingly similar orbital properties: the majority of both types are on short-axis tubes with the same sense of rotation as the disk – implying that a large fraction of satellites are accreted onto the halo with the same sense of angular momentum as the disk.

Cosmological simulations predict that dark matter halos with circular velocities lower than 30 km/s should have lost most of their neutral gas by heating of the ultra-violet background. This is in stark contrast with gas-rich galaxies such as e.g. Leo T, Leo P and Pisces A, which all have circular velocities of ~15 km/s (Ryan-Weber et al. 2008, Bernstein-Cooper et al. 2014, Tollerud et al. 2015). We show that when we include feedback from the first stars into our models, simulated dwarfs have very different properties at redshift 0 than when this form of feedback is not included. Including this Population-III feedback leads to galaxies that lie on the baryonic Tully-Fisher relation over the entire mass range of star forming dwarf galaxies, as well as reproducing a broad range of other observational properties.

Galaxies in group and cluster environments are subject to ram pressure stripping by the hot intracluster medium, resulting in gas loss and the eventual suppression of star formation. Recent Chandra observations of galaxies in group and cluster environments show that 60 - 80% of these galaxies have compact (1-4 kpc), hot (~ 1 keV) X-ray coronae centered on their cores. These coronae have survived stripping and evaporation in the cluster, and their long-term survival poses a test of our understanding of the physical processes in the ICM. In this poster, I summarize results from Vijayaraghavan & Ricker (2015), where we simulated the evolution of populations of galaxies and their hot coronal gas in group and cluster environments, and evaluated their detectability with existing and future X-ray catalogs.

We tested the spatial distribution of UCDs and GCs in the halo of NGC 1399 in the Fornax cluster. In particular we tried to find out if globular clusters are more abundant in the vicinity of UCDs than what is expected from their global distribution. A local overabundance of globular clusters was found around UCDs on a scale of 1 kpc compared to what is expected from the large scale distribution of globulars in the host galaxy. This effect is stronger for the metal-poor blue GCs and weaker for the red GCs. An explanation for these clustered globulars is either that they are the remains of a GC system of an ancestor dwarf galaxy before it was stripped to its nucleus, which appears as UCD today. Alternatively these clustered GCs could have been originally part of a super star cluster complex.

Throughout the past decade, significant advances have been made in the size and scope of large-scale spectroscopic surveys, allowing for the opportunity to study in-depth the formation history of the Milky Way. Using the fourth data release of the RAdial Velocity Experiment (RAVE), we study the age-metallicity-velocity space of ~ 100,000 FGK stars in the extended solar neighborhood in order to explore evolutionary processes. Combining these three parameters, we better constrain our understanding of these interconnected, fundamental processes.

The LAMOST Complete Spectroscopic Survey of Pointing Area (LCSSPA) at Southern Galactic Cap (SGC), is one of the LAMOST Key Project, designed to complete the spectroscopic observations of all Galactic and extra-galactic sources in two selected fields of 20 degrees2 at SGC, with the limiting magnitude of r = 18.1 mag. The main purposes of the project are focused on the completeness of the LAMOST ExtraGAlactic Surveys (LEGAS), testing the selection methods of galaxies and stars, and obtaining the basic performance parameters of the LAMOST telescope. Meanwhile the scientific studies include galaxies, clusters of galaxies, variable sources (quasars and variable stars), infrared excess stars and luminous infrared galaxies. The project has considerable scientific value since it is the most complete spectral data in LEGAS up to now. The project completed its observation in the early of 2014, and obtained at least 5000 spectra of galaxies and 25000 spectra of stars.

In this work, we present a set of M-type star candidates selected from the LAMOST DR1. A discrimination method with the spectral index diagram is used to separate M giants and M dwarfs. Then, we have successfully assembled a set of M giants templates from M0 to M6, using the spectra identified from the LAMOST spectral database. After combining the M dwarf templates in Zhong et al. (2015a) and the new created M giant templates, we use the M-type spectral library to perform the template-fit method to classify and identify M-type stars in the LAMOST DR1. A catalog of M-type star candidates including 8639 M giants and 101690 M dwarfs/subdwarfs is provided. As an additional results, we also present other fundamental parameters like proper motion, photometry, radial velocity and spectroscopic distance.

We study the assembly history of the stellar halo of Milky Way-like galaxies using the six high-resolution Aquarius dark matter simulations combined with the Munich-Groningen semi-analytic galaxy formation model. Our goal is to understand the stellar population contents of the building blocks of the Milky Way halo, including their star formation histories and chemical evolution, as well as their internal dynamical properties. We are also interested in how they relate or are different from the surviving satellite population. Finally, we will use our models to compare to observations of halo stars in an attempt to reconstruct the assembly history of the Milky Way's stellar halo itself.