Found 181 talks archived in Galaxies

Thursday February 26, 2015
Dr. Julie Wardlow
Dark Cosmology Centre (Copenhagen)



Over the past ~20 years the high-redshift Universe has been increasingly opened to scrutiny at far-infrared wavelengths, where cool dust emission from star-formation dominates. The dusty star-forming galaxies (DSFGs) and submillimeter galaxies (SMGs), selected at these wavelengths likely represent an important, but short-lived phase in the growth of massive galaxies. These DSFGs often have star-formation rates in excess of ~1000 solar masses per year and are confirmed out to at least z~6, although their redshifts and high dust contents make them faint and difficult to study at other wavelengths. Now, using data from the Herschel Space Observatory we have identified a population of DSFGs that are strongly gravitationally lensed and therefore magnified and available for unprecedented multi-wavelength scrutiny. I will describe how this important gravitationally lensed population is identified, and present and interpret the data from our extensive multi-wavelength, multi-facility follow-up studies. I will also present follow-up observations of an intriguing sample of the highest redshift DSFGs (z>4) that are also selected via Herschel data, and that are proving troublesome to explain in galaxy formation simulations.


Tuesday January 27, 2015
Mr. Ben Hendricks
Univ of Heidelberg


Dwarf spheroidal (dSph) galaxies are the smallest, closest and most abundant galaxies in the Universe and therefore excellent laboratories to study star formation (SF) history and chemical evolution on the smallest
scales. However, the complexity within---and variations between---these objects are poorly understood, not least because the vast majority of present-day data is restricted to the most central regions of these systems.
Thus, the scope of this talk is to present the results from our chemodynamical analysis (i.e., combining chemical abundances, stellar
ages, and precise dynamical measurements from high-resolution spectra) of the outer regions of Fornax and to put them in a general context of the chemical evolution in dSphs and their key-regulating factors. On this basis, possible (and impossible) evolutionary scenarios for Fornax are discussed and compared with model predictions.  Furthermore, Fornax is one amongst very few dSphs with an own globular cluster population. In the last part of my talk I use the results from our analysis and discuss
ongoing projects designed to address the impact of globular clusters on the evolution of this galaxy, and vice versa.

Thursday January 15, 2015
Dr. Rosa Calvi


One of the important questions in extragalactic astronomy concerns the debate between nature and nurture scenarios. Are the observed galaxy local properties the end product of the different conditions at birth or the product of the interactions, or other local processes, since a galaxy is not an isolated object? In this talk I will present the results of the analysis of some galaxy properties, morphologies and mass functions, obtained comparing, for the first time in a consistent manner, galaxies in the widest range of environments at low redshift (groups, clusters, binary systems, isolated galaxies). The aim was to understand the most important factors that drive galaxy evolution, trying to disentangle the importance of galaxy mass and global environment.

In addition I will present the first results concerning the two projects in which I am involved at IAC: the ALBA project, aimed to explore the signs of a proto-cluster at z~6.5, and the analysis of dust emission of a sample of local tadpole galaxies. 

Thursday December 18, 2014
Dr. Gustavo Bruzual
Universidad Nacional Autónoma de México (UNAM)


Stellar population synthesis has reached a high degree of sophistication that has been exploited to understand to a certain extent the mechanisms of formation, assembling, and evolution of galaxies in our universe. Progress is based on solid results in the field of stellar evolution and spectrophotometric observations of large numbers of stars and galaxies. However, there are certain phases of stellar evolution, like the thermally pulsing asymptotic giant branch (TP-AGB) phase, the Wolf-Rayet stage, and the presence of interacting binaries, whose treatment is either ignored or extremely simplified in galaxy evolution models due to the uncertainties in their description. In this talk I will present results from models that add the state of the art in the treatment of these evolutionary phases to traditional population synthesis models. 

Tuesday December 9, 2014
Dr. Rodriguez Ardila
Laboratorio Nacional de Astrofísica (Itajubá, Brasil)


FeII comprises up to one third of the line emission in AGNs. For that reason it is an important coolant that needs to be taken into accountto fully understand the energetics of the broad line region (BLR). In thistalk I will discuss new approaches to study the excitation mechanisms ofthe FeII based on a semi-empirical template we derived in thenear-infrared region (NIR). We correlate the strength of the NIR andoptical iron lines to assess the relative contribution of the differentmechanisms that produces that emission. We found that in all casesLy_alpha fluorescence plays an important role, being a process that needsto be considered in any approach aimed at understanding this complexemission. We also compare the width of the individual FeII lines with thatof other lines emitted in BLR. Our results confirm previous assumptionsand results from variabilty studies that the gas responsible for the FeIIemission is the outer portion of the BLR.

Wednesday December 3, 2014
Dr. Tobias Goerdt
Wien Univ.


Cold gas streaming along the dark-matter filaments of the cosmic web is predicted to be the major provider of resources for disc buildup and star formation in massive galaxies in the early universe. We use hydrodynamical simulations to study to what extent these cold streams are traceable in the extended circum-galactic environment of galaxies via Ly alpha emission, Ly alpha absorption and selected low ionisation metal absorption lines. We predict the strength of the absorption signal produced by the streams and find that it is consistent with observations in high redshift galaxies. The characteristics of the Ly alpha emission of our simulated galaxies are similar in luminosity, morphology and extent to the observed Ly alpha blobs, with distinct kinematic features. We analyse the characteristics of the cold streams in simulations and present scaling relations for the amount of infall, its velocity, distribution and its clumpiness and compare our findings with observations.

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.

Wednesday November 5, 2014
Prof. Debra Meloy Elmegreen
Vassar College, Poughkeepsie, NY


Galaxies at redshifts z~2-5 are dominated by clumpy morphologies instead of the more familiar elliptical and spiral types seen in the local Universe. The clumpy galaxies are gas-rich and highly turbulent, with star-forming regions 100 times more massive than in today’s galaxies. Clumpy galaxies should evolve into spirals and barred spirals when the disks become less turbulent. We find transitional types midway between clumpy and spiral, primarily around z~1-2. We observed local analogs of these transitional spirals in the Kiso Survey of Ultraviolet Galaxies, whose clumps are comparable in mass and surface density to the clumps at high redshift. We also find local analogs of high redshift tadpole galaxies, whose measured low metallicities in star-forming regions suggest ongoing external gas accretion.

Friday October 31, 2014
Dr. Fabiola Hernández-Pérez
Centro de Investigaciones de Astronomía (CIDA), Venezuela


Many stars are observed to belong to multiple systems. Interactions between binary stars may change the evolutionary track of a star, creating atypical stars like Blue Stragglers and explaining the existence of extreme horizontal branch (EHB) stars. Using evolutionary population synthesis models including binary star evolutionary tracks from Hurley et al. and including the two He white dwarfs merger channel, suggested by Han et al., for the formation of EHB stars we compute a series of isochrones which include these atypical stars. We derive the integrated spectral energy distributions and the colors corresponding to these populations. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary stars or their products, e.g., EHB stars in the ultraviolet (UV) of early-type galaxies (ETGs) (Hernández-Pérez and Bruzual 2013). Using this binary population synthesis model we reproduce successfully the observed colour-colour diagram of a sample of 3417 ETGs observed both in the optical (SDSS -DR8) and the UV (GALEX-GR6) (Hernández-Pérez and Bruzual 2014). I will show how important is to consider binary interactions in evolutionary synthesis models.

Thursday October 30, 2014
Prof. Eline Tolstoy
Kaptein Astronomical Intistute


I will talk about how resolved stellar populations in the nearby Local Group dwarf galaxies have been used to study the detailed chemical, kinematic and star formation history of these systems and the link to the properties of the Milky Way. I will mainly discuss the results from the DART spectroscopic surveys of nearby dwarf spheroidal galaxies, determining detailed abundances, looking for CEMP stars and also combining spectroscopy with colour-magnitude diagram analysis to measure the time scale for star formation and chemical evolution.


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