Found 20 talks width keyword galactic structure

Wednesday November 12, 2014
Prof. Bruce G. Elmegreen
IBM Research Division


The exponential radial profiles of spiral galaxies have been observed for decades with various explanations offered, but none of these explanations hold up now that the profiles have been traced to 10 scale lengths in some cases. Profiles with breaks also have their outer parts remarkably close to exponential. This is true in both spirals and dwarfs, with a particular problem for non-barred dwarfs where there are no strong torques or shears in the stellar disks for radial scattering. We have shown that scattering from disk clumps can make exponentials, and indeed dwarfs have fairly massive clumps and irregularities in their HI distributions. Spiral waves also have clumps in the form of persistent wave enhancements at corotation and at points of wave interference. This talk reviews the observations of exponential profiles and profile breaks in spiral and dwarf galaxies, and considers various theories to explain them.

Tuesday April 22, 2014
Dr. Martin Stringer
Instituto de Astrofisica de Canarias


Any viable theory of the formation and evolution of galaxies should be able to broadly account for the emergent properties of the galaxy population, and their evolution with time, in terms of fundamental physical quantities. Yet, when citing the key processes we believe to be central to the story, we often find ourselves listing from a vast and confusing melee of modelling strategies & numerical simulations, rather than appealing to traditional analytic derivations where the connections to the underlying physics are more tangible. By re-examining both complex models and recent observational surveys in the spirit of the classic theories, we will investigate to what extent the trends in the galaxy population can still be seen as an elegant fingerprint of cosmology and fundamental physics.

Tuesday January 29, 2013
Dr. Jairo Méndez Abreu


The effects that environment produce on galaxy disks and how they modify the subsequent formation of bars need to be distinguished to fully understand the relationship between bars and environment. To shed light on this issue, we derive the bar fraction in three different environments ranging from the field to Virgo and Coma Clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Coma Cluster is statistically significant, with Virgo being an intermediate case. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies, the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges probed by the galaxy samples studied so far.

Thursday November 8, 2012
Prof. Piet van der Kruit
University Groningen


Disks in spiral galaxies consist of stars and gas. The stellar disks show radially an exponential surface brightness distribution (and vertically one resembling an isothermal sheet), with relatively sharp truncations at of order 4 scalelengths. These truncations are most easily seen in edge-on galaxies. The evidence for these truncations and their statistics will be reviewed. Truncations appear to be not only truncations in the distribution of stars, but also in the total density. The origin of these truncations seem related to the maximum specific angular momentum in the material that formed the disks. Disks are extremely flat. The HI-gas often extends beyond the eructations in the stellar disks, but when they do they also show a warp. Again edge-on galaxies show this mostly readily. Analysis shows that the warps start abruptly, just beyond the truncation radius and some other properties also show abrupt changes at the radius of the onset of the warp. This suggests that warps are the result of infall of gas at later times, when the formation of the stellar disks has been completed. The open issue is still that we have not conclusively shown that we can discover the face-on analogs of the truncations we see in edge-on disk. I will outline some recent research I have been involved in and some ideas for further work and collaborations.

Thursday July 12, 2012
Dr. Sébastien Comerón
Korea Astronomy and Space Science Institute


Thick discs are disc-like components with a scale height larger than that of the classical discs. They are  most easily detected in close to edge-on galaxies in which they appear as a roughly exponential excess of light which appears a few thin disc scale heights above the midplane. Their origin has been considered mysterious until recently and several formation theories have been proposed. Unveiling the origin of thick discs is important for understanding galaxy evolutionary processes.
I will review the results we obtained on thick discs using data from the S4G:
1) Thick discs are ubiquitous.
2) Thick discs are much more massive than previously thought. This advocates for an in situ origin of thick discs at high redshift and for them being a reservoir of missing baryons.
3) The superposition of thin and thick discs with different scale lengths is the reason of at least half of disc antitruncations.

Thursday April 19, 2012
Dr. Carlos González Fernández
Universidad de Alicante, Spain


Abstract: The study of the structure of our Galaxy, particularly its inner disc, has always been hindered by two factors: interstellar extinction dims even the brightest stars at optical wavelengths and the high source density prevents us, as the proverbial trees, to see the big galactic picture. 

With this talk we give a broad introduction of the historical efforts to alleviate these issues in the neverending quest to dig deeper into the Milky Way, followed by a overview of the first results obtained by the VVV-Vista survey, that maps the southern Galactic sky with unprecedent depth and resolution.

Tuesday September 27, 2011
Dr. Ignacio Trujillo
Instituto de Astrofísica de Canarias, Spain


In the last few years there has been cumulative evidence showing that massive galaxies have dramatically grown in size since z~3. This result has remained very controversial as it seems at odd with our previous knowledge based on the detailed analysis of the stellar populations of nearby massive spheroids which shows that their stars were form very early on and over a short time interval. In addition to this, there is growing observational support for a significant evolution of the morphologies of these galaxies with cosmic time. In this talk, I will summarize what we have learned since the discovery of the strong evolution of the morphological properties of the massive galaxies, the mechanisms proposed to explain their origin and size increase, and the pending questions still to solve.

Friday June 17, 2011
Dr. Mauro D'Onofrio
University of Padova, Italy


We present the K band FP of the ETGs members of the clusters observed by the WINGS survey. The data confirm a different tilt of the FP with respect to the V solution and the presence of a substantial tilt in the K band. This led us to further investigate the hypothesis that ETG non-homology greatly contribute to the tilt of the FP.

The WINGS data show that there are now several evidence of both structural and dynamical non-homology for the class of ETGs. Among these we will discuss in detail the tight relation between the mass of the ETGs, their stellar mass-to-light ratio M/L, and the Sersic index n describing the shape of their light profiles. We guess through a series of mock simulations that this relation acts as a fine-tuning that keeps small the scatter around the FP. We therefore conclude that ETG non-homology is closely connected either with the problem of the tilt and with the small scatter around the FP.

Tuesday June 7, 2011
Dr. Sharon Meidt
MPIA, Germany


With imaging at 3.6 and 4.5 microns where the light in nearby galaxies is dominated by old stars, the Spitzer Survey of Nearby Galaxies (S4G) stands poised for an optimal view of stellar mass and structure in the local Universe.  I will describe an effort to construct accurate 2D stellar mass maps from S4G images, starting with a correction for non-stellar (e.g. PAH and hot dust) contaminant emission using only the two S4G images as inputs; contaminant emission is isolated from the old stellar light using an Independent Component Analysis (ICA) technique designed to separate statistically independent source distributions.  An inventory of recovered contaminants is established via comparison to the non-stellar emission in archival 8 micron images.  Once these contaminants are removed, maps of the underlying distribution of old stars are revealed that retain a high degree of structural information and exhibit [3.6]-[4.5] colors consistent with those of K and M giants.  Contaminant-free S4G maps constructed with this approach should be ideally suited for tracing the stellar mass in galaxies spanning a range of morphological properties, dust contents and star formation histories.

Thursday March 17, 2011
Dr. Alber Bosma
Astronomy Observatory of Marseilles Provence, OAMP, France


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.

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