Found 21 talks width keyword galactic structure
Dark Matter in Galaxies is an important subject of current astrophysical research. I will concentrate on spiral galaxies, and first give an overview of the subject from the standpoint of a radioastronomer with a long involvement in the subject. This includes a historical introduction and a review of some of the present-day debates. The currently popular Lambda-CDM model has problems on the scale of galaxies. In a second part I will address more specifically the problem that we still do not know how much dark matter there is in spiral galaxies, and how it is distributed. This is due to the fact that the M/L of the visible matter is poorly constrained and that there is a 'conspiracy' between the dark and the baryonic material. I will present various dynamical methods that have been proposed to constrain the dark matter mass distribution and discuss their advantages and disadvantages.
AbstractEarly-type dwarfs (dEs) are by far the most abundant galaxy population in nearby clusters. Whether these objects are primordial, or recent end-products of the different physical mechanisms that can transform galaxies once they enter these high-density environments, is still a matter of debate. Here we present a novel approach to test the latter scenario by comparing the properties of the globular cluster systems of dEs and their potential progenitors with simple predictions from gravitational and hydrodynamical interactions. Current data in the literature do not favour violent mechanisms, but gentle processes with long timescales or that took place at the early stages of their formation.
AbstractMassive (≥ 1011 M⊙) galaxies at high redshift (z ≥ 1.5) remain mysterious objects. Their extremely small sizes (effective radii of 1-2 kpc) make them as dense as modern globular clusters. It is thought that a highly dissipational merger is needed to create such compact type of galaxies. We will discuss this issue, along with state-of-the-art morphological and kinematic observations of these objects. In the present day Universe massive galaxies show large sizes, and harbor old and metal-rich stellar populations. In order to explore their development, we present near-IR IFU observations with SINFONI@VLT for ten massive galaxies at z=1.4 solely selected by their high stellar mass which allow us to retrieve velocity dispersions, kinematic maps and dynamical masses. We joined this with data and works coming from the GOODS NICMOS Survey, the largest sample of massive galaxies (80 objects) with high-resolution imaging at high redshift (1.7 < z < 3) acquired to date. As a result, we show how their morphology changes possibly through elusive minor merging.
AbstractGalaxies are the basic building blocks of the Universe, and understanding their formation and evolution is crucial to many areas of current astrophysical research. Nearby galaxies, being the 'fossil record' of the evolution of galaxies, provide a wealth of detail to test extensively the current models of galaxy formation and evolution. A galaxy's structure is linked to both its mass and evolutionary history. Probing galactic structure requires understanding the distribution of stars among galaxies of all types and luminosities across the full range of environments. We are performing a complete volume-limited (d < 40 Mpc) survey of over 2200 nearby spiral, elliptical and dwarf galaxies at 3.6 and 4.5 μ in the Spitzer Warm Mission to address fundamental questions of galactic structure that are united by the common need for deep, uniform, unbiased maps of the stellar mass in galaxies. I will introduce the survey, give examples of images and of the science that can be done, and explain how other researchers at the IAC can become involved in analysing these exciting data.
AbstractΛCDM-based numerical simulations predict a scenario consistent with observational evidence in Milky Way-like halos. However, less clear is the role of low-mass galaxies in the big picture. The best way to answer this question is to study the nearest example of a dwarf spiral galaxy, M33. We will use star clusters to understand the structure, kinematics and stellar populations of this galaxy. We will present our current status and future plans of a comprehensive study of the star cluster system of M33. This study will provide key insights into the star formation history, composition and kinematics of low-mass galaxies as well as place M33 within the context of galaxy formation process.
AbstractThe colour distribution of globular cluster (GC) systems in the majority of galaxies is bi/multimodal in optical colours. It is widely accepted that multiple populations differing in metallicity exist implying different mechanisms/epochs of star formation, with small age differences still being allowed due to the large current uncertainties. Recently Yoon, Yi and Lee (2006) challenged this interpretation stating that the metallicity bimodality is an artifact of the horizontal branch (HB) morphologies that can transform a unimodal metallicity distribution in a bimodal (optical) colour distribution. The combination of optical and near-infrared (NIR) colours can in principal break the age/metallicity degeneracy inherent in optical colours alone, allowing age estimates for a large sample of GCs possible at the same time. It has been shown that the colours that best represent the true metallicity distributions are the combination of optical and NIR (eg. Puzia et al. 2002, Cantiello & Blakeslee 2007). Therefore studying GCs in the NIR is crucial to reveal their true metallicity distributions. We are currently building a homogeneous optical/NIR data set of GC systems in a large sample of elliptical and lenticular galaxies. I will present the sample, an attempt to estimate overall ages and metallicities for the GC systems and the optical/NIR colour distributions.
AbstractThe centers of massive galaxies are special in many ways, not least because all of them are believed to host supermassive black holes. Since the discovery of a number of relations linking the mass of this central black hole to the large scale properties of the dynamically hot component of its host galaxy (bulge) it has become clear that the growth of the central black hole is intimately connected to the evolution of its host galaxy. However, for bulge-less galaxies, the situation is much less clear. Interestingly, these galaxy often host star clusters in their nuclei, and unlike black holes, these nuclear star clusters provide a visible record of the accretion of stars and gas into the nucleus. I will present my ongoing projects on nuclear star clusters that aim to understand their formation process and might give a hint on how black holes get to the centers of galaxies.
I will review the status of our understanding of galaxy formation in the prevailing cold dark matter paradigm. After reviewing the successes and failures of the most natural predictions of this scenario I will focus on the consequences of two of its main predictions: the presence of large numbers of low-mass dark matter halos and the prevalence of accretion events during the formation of normal galaxies. In particular, I will discuss the interpretation of the recent discovery of a population of ultra-faint galaxies in the Local Group, and its relation to the profuse cold dark matter substructure expected in the Galactic halo. I will also discuss the importance that accretion events might have had in shaping not only the stellar halo but also the disk component(s) of the Milky Way.
AbstractWe examine the latest results concerning the evolution in the structures of galaxies from the local universe up to z ~ 6. We present results from the COSMOS, EGS and UDF surveys and characterise the structure of galaxies in terms of stellar masses. We find in general that galaxy structure becomes more asymmetric with time, and we use this information to determine the merger history of galaxies and the role of mergers in galaxy formation, placing the first firm constraints on the importance of this formation mode.
AbstractWarps of disk galaxies are ubiquitous. In almost every disk galaxy a bending of the disk occurs where the stars fade away and hence where the dark matter halo becomes dominant. A clear understanding of this phenomenon has not been reached yet. Analysing H I observations of a small sample of symmetric, warped disk galaxies we found that they exhibit a two-disk structure, the warp being the transition from the inner flat disk to an outer, inclined one. At the transition radius, the rotation curve changes. This points towards symmetric warps being a long-lived phenomenon reflecting an internal change in the structure of the Dark Matter halo.
While warps usually occur where the stellar disks fade, examples of extreme warps are known that commence already at the centre of galaxies. One is present in the neutral gas disk of the "Spindle Galaxy "NGC 2685, formerly thought of as being a two-ringed polar ring galaxy. Utilising deep HI observations, we found that the two-ringed appearance is due to projection effects and that it rather possesses one coherent,extremely warped HI disk. Our success in fitting a tilted-ring model to the HI component, and, with that, assuming circular orbits of the tracer material, and the shape of the fitted rotation curve hint towards a rather spherical shape of the overall potential.
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