Found 68 talks width keyword 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.
Abstract(1) We present SAURON integral-field stellar velocity and velocity dispersion maps for four double-barred early-type galaxies: NGC2859, NGC3941,NGC4725 and NGC5850. The presence of the nuclear bar is not evident from the radial velocity, but it appears to have an important effect in the stellar velocity dispersion maps: we find two sigma-hollows of amplitudes between 10 and 40 km/s at either sides of the center, at the ends of the nuclear bars. We have performed numerical simulations to explain these features. Ruling out other possibilities, we finally conclude that, although the sigma-hollows may be originated by a younger stellar population component with low velocity dispersion, more likely they are an effect of the contrast between two kinematically different components: the high velocity dispersion of the bulge and the ordered motion (low velocity dispersion) of the nuclear bar.
(2) We have explored radial color and stellar surface mass density profiles for a sample of 85 late-type galaxies with available deep (down to ~27.0 mag/arcsec2 SDSS g'- and r'-band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, exhibiting either truncations (Type II galaxies) or antitruncations (Type III galaxies). Their associated color profiles show significantly different behavior. For the truncated galaxies a radial inside-out bluing reaches a minimum of (g' - r') = 0.47 +/- 0.02 mag at the position of the break radius, this is followed by a reddening outwards. The anti-truncated galaxies reveal a more complex behavior: at the break position (calculated from the light profiles) the color profile reaches a plateau region - preceded with a reddening - with a mean color of about (g' - r') = 0.57 +/- 0.02 mag. Using the color to calculate the stellar surface mass density profiles reveals a surprising result. The breaks, well established in the light profiles of the Type II galaxies, are almost gone, and the mass profiles resemble now those of the pure exponential Type I galaxies. This result suggests that the origin of the break in Type II galaxies are most likely to be a radial change in stellar population, rather than being caused by an actual drop in the distribution of mass. The anti-truncated galaxies on the other hand preserve their shape to some extent in the stellar surface mass density profiles. We find that the stellar surface mass density at the break for truncated (Type II) galaxies is 13.6 +/- 1.6 Msun/pc2 and 9.9 +/- 1.3 Msun/pc2 for the anti-truncated (Type III) ones. We estimate that ~15% of the total stellar mass in case of Type II galaxies and ~9% in case of Type III galaxies are to be found beyond the measured break radii.
AbstractDwarf galaxies, being the most numerous and fragile galaxy population, provide unique clues on both the formation of baryonic systems and the role played by the environment in galaxy evolution. In this short talk, I will present the main observational properties of the dwarf galaxy population in a sample of 88 nearby (z < 0.1) galaxy clusters drawn from the SDSS-DR4. By comparing the different properties (spatial and velocity distribution, colour, etc.) of red and blue dwarfs we attempt to constrain the scenarios for the evolution of galaxies in high-density environments.
University of Sheffield, UK
1) In this brief seminar (<~25 minutes+questions) I will present recent results on the study of "deep", high resolution, surface brightness profiles of a sample of ~500 late-type galaxies in the redshift range 0.1—1.1, making use of publicly available HST/ACS imaging of the GOODS-South field. We have classified and parameterized, according to usual prescriptions in this kind of analysis, these profiles, with special emphasis put on the so called ``truncated'' disks. This is the case in which, beyond a certain radius, termed as ``Break Radius'', the exponentially decaying surface brightness profile along the stellar disk gives way to an even more abrupt exponential decay. This radius can be taken as an spatial "scale" for the disk, as observed in a given band (in our case, the rest-frame B-band). Comparing with analogous analysis for galaxies in the Local Universe, as we have done, it is possible to extract valuable information on the evolution of several photometric properties of the stellar disks of galaxies, related to the stellar populations distributions. I will also present results on the analysis of the color profiles of this sample of galaxies, which have yield an interesting result which is, perhaps, the main reason that justifies calling this talk a "breaking news" seminar, as I will show. Summarizing, an overview of the results we have obtained will be given, and our conclusions on them, explaining how they can be understood in the frame of Galaxy Evolution (2) Based on high quality near-infrared spectroscopy (obtained with WHT/LIRIS) we reveal that the nucleus of Mrk 573 is an obscured Narrow-Line Seyfert 1 and not an archetypal Seyfert 2 as it has been classified until now. Currently only four AGNs have been classified into this category. We have detected permitted OI and FeII transitions, which indicates the existence of a high density region similar to the BLRs detected in type 1 AGN.
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- Finding the double sunsets: close binary stars, large spectroscopic surveysDr. Carles BadenesThursday May 3, 2018 - 10:30
- XMM-Newton and Chandra combined analysis of the most massive galaxy clusters at z~1Iacopo BartalucciThursday May 10, 2018 - 10:30