Found 73 talks width keyword galaxy evolution
AbstractThe SAURON survey has revised our view of early type galaxies discovering that central disks and multiple kinematic components are common; 75% of the sample have extended ionized gas, often misaligned with the stars; half of S0s and 25% of Es have intermediate age populations. There is a tight relationship between the escape velocity and Mg line strength which holds both within and between galaxies raising uncomfortable questions for hierarchical assembly. Many of the properties of ETGs are related to a measure of their specific angular momentum : slow rotators are triaxial, close to spherical, isotropic and frequently exhibit decoupled central kinematics, whereas fast rotators are intrinsically flatter, oblate, have disk-like (anisotropic) kinematics and often have Mg enhanced disks. In general the slow rotators are more massive and have older populations Only half of the elliptical galaxies exhibit slow rotation, the remainder have stellar disks showing that the historic division by morphological class is physically misleading. We suggest that the contrasting physical properties of fast and slow rotators arise through distinct assembly histories with slow rotators forming in gas free, dry mergers and fast rotators retaining a disk component through a dissipative merger.
AbstractObservations have shown that massive galaxies at high redshift have much smaller sizes than galaxies of similar mass today. The mean stellar density of such objects was almost two orders of magnitude higher than the ones we measured in the most massive nearby galaxies, reaching, in some cases, densities similar to those observed in globular clusters. What is the nature of these objects? And, how these objects have been transformed into the present population of massive galaxies? We will summarize the recent findings our group has done on this topic. In particular, we will focus on our search for finding relics of these compact galaxies in the nearby universe, and the effort we have done for measuring the evolution of the velocity dispersion of these galaxies in the last 10 Gyr. The implications of this research within the galaxy formation scenario will be discussed.
In the next decade astronomers will attempt to constrain the nature of dark matter, dark energy and the (perhaps inflationary) processes which generated structure as well as understanding the astrophysics of galaxy evolution and the formation and evolution of our Milky Way and Local Group. Large-scale spectroscopic surveys on large telescopes will be critical to achieving reliable results in all these areas. The desideratum is a survey which obtains the spectra of a few times 105 galaxies from the visible into the near IR at each of a sufficient number of redshift slices that one can follow the evolution of all interesting populations. Large samples of different stellar populations in different Local Group environments will also be targeted. I will summarize the outline of a multi-object 0.4-1.7 μ spectrograph for GTC and discuss the status of miniSIDE. MiniSIDE has been conceived as a pathfinder for a large fiber-fed survey spectrograph but will be a scientific instrument on its own, capable of providing high quality science data and be competitive within the instrumentation suite of GTC. A Letter of Intent has been submitted recently to propose miniSIDE as a facility science instrument for GTC.
AbstractLarge-scale outflows from galaxies are a crucially important yet poorly understood aspect of galaxy evolution. They redistribute gas and metals into the IGM, regulate star formation, affect the galaxy luminosity function and mass-metallicity relation, etc. Unfortunately, their detailed context in galaxy evolution is difficult to understand: locally, they are identified and studied in heterogeneous manners, while we have only recently begun to study them on cosmological scales and then only in known bright, starbursting galaxies. I will discuss increasing evidence that the so-called ultra-strong MgII intervening quasar absorbers select galactic superwinds over a large range of redshift in a manner independent of luminosity. As superwinds cover a small fraction of the sky at any epoch, only with recent huge quasar absorption lines surveys has it been possible to identify significant numbers of outflows in this manner. I will present new results from several of our studies -- including the measurement of the average SFR of their hosts using [O II] emission from SDSS composite spectra, WIYN, Gemini and WHT imaging of the superwind environments, Gemini/GMOS spectroscopy of superwind host galaxies, and VLT/UVES echellegrams of the absorption lines -- with the aim of understanding the nature of the outflows, their host galaxies, environments, and their evolution over cosmic time.
AbstractThe COSMOS survey is the largest high redshift galaxy evolution survey ever done -- imaging 2 square degrees with all major space-based and ground based observatories. I will describe the key data in the survey and then present recent results on large-scale structures, the dark matter distributions and galaxy evolution.
AbstractThe Sloan Digital Sky Survey is currently the largest spectroscopic survey of extragalactic objects and one of the most ambitious observational programs ever undertaken in astronomy, measuring about 1 million redshifts and thus providing a three dimensional mapping of the local universe up to a depth of several hundreds of Mpc. The main characteristic of galaxy distribution in this survey, and in the Two degree Field Galaxy redshift Survey completed few years ago, is that large scale structures have been found to extend to scales of the order of hundreds of mega parsecs. However the standard determination of a characteristic length scale, statistically describing galaxy correlations, is of only few mega parsecs: the standard explanation of this apparent mismatch is that large scale structures have small amplitude relative to the average density. We show that, in the newest galaxy samples, large scale structures are quite typical and correspond to large fluctuation in the galaxy density field, making the standard interpretation untenable. We show that the standard statistical analysis is affected by systematics which are due to inconsistent assumptions. We point out that standard theoretical models of structure formation are unable to explain the existence of the large fluctuations in the galaxy density field detected in these samples. This conclusion is reached in two ways: by considering the scale, determined by a linear perturbation analysis of a self-gravitating fluid, below which large fluctuations are expected in standard models and through the determination of statistical properties of mock galaxy catalogs generated from cosmological N-body simulations. Finally we discuss the implications of this results in relation to recent attempts to describe inhomogeneous models in general relativity and to the recent discoveries of large scale coherent bulk flows.
AbstractFrom galaxy formation theory we expect galaxies to be embedded in massive dark matter haloes. For spiral and dwarf galaxies this has indeed been observationally confirmed, by modeling the kinematics from the large cold gas discs that often surround these galaxies. These gas discs are however rare in elliptical galaxies, so that we have to resort to other tracers when we want to probe their dark matter haloes, which are not always easily accessible. As a result, dark haloes for only a handful of early-type galaxies have been mapped. In this talk I will give an overview of the methods that can be used to find dark matter in early-type galaxies. I will then focus on two projects that I worked on with the integral-field spectrograph SAURON, using two different methods to constrain the dark halo. The first is based on the combination of two-dimensional ionised gas and cold gas kinematics. The second method uses SAURON as a 'photon collector', to obtain spectra at large radii in galaxies. From these spectra we can not only obtain the velocity profile and construct mass models to constrain the dark halo, but also infer the properties of the stellar halo population. I will show the results from these two projects and discuss some future prospects.
AbstractWe are going to present a new code to derive the SFH of a complex stellar population system, like a galaxy. This code has been used to obtain the SFH of six dwarf galaxies from the Local Constrains form Isolated Dwarf (LCID) project for which we are presenting the first results. The project has been designed to obtain the SFH of isolated dwarf galaxies free from strong interactions with massive host galaxies, like the MW or M31. The results obtained could help us to understand the spatial structure of dwarf galaxies and how galaxies form and evolve.
In the Λ-CDM galaxy formation paradigm, the star formation history of a galaxy is coupled to the total mass of its dark matter halo through processes like galaxy-galaxy merging, satellite accretion, and gas retention. Globular cluster formation is known to coincide with strong star formation events in the early Universe. To develop an accurate model of galaxy formation, the relationship between such systems and their hosting dark matter halos must be understood. Employing weak gravitational lensing galaxy mass analysis, we have discovered that the number of globular clusters in a given galaxy is directly proportional to its total dark matter halo mass. This result holds in both dwarf and giant ellipticals, spirals and in all types of galaxy environments. I will present these observations and initiate a discussion on the implications for scenarios of globular cluster system formation and evolution.
AbstractIn our now-standard picture for the growth of structure, dark matter halos are the basic unit of nonlinear structure in the present Universe. I will report results from simulations of galaxy-scale dark halos with more than an order of magnitude better mass resolution than any previously published work. Tests demonstrate detailed convergence for (sub)structures well below a millionth the mass of the final system. Even with such resolution the fraction of halo mass in bound subhalos does not rise above a few percent within the half-mass radius. I will also present a new simulation technique which allows structure in the dark matter distribution to be studied on very much smaller scales. This is required for accurate forecasts of the expected signal both in earth-bound experiments designed to detect dark matter directly, and in indirect detection experiments like GLAST which attempt to image dark matter annihilation radiation at gamma-ray wavelengths.
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- TBDDr. Nancy LevensonWednesday October 16, 2019 - 10:30 (Aula)