Found 70 talks width keyword galaxy evolution

Wednesday July 25, 2018
Dr. Sugata Kaviraj
University of Hertfordshire


A new era of observational surveys that are both deep and wide is poised to revolutionise our understanding of galaxy evolution, by enabling, for the first time, statistical studies of the low-surface-brightness (LSB) Universe. While largely inaccessible in past wide-area surveys like the SDSS (due to their lack of depth), the uncharted LSB regime holds the key to a complete understanding of galaxy evolution. While small, deep surveys and new instruments have long hinted at the existence of a rich population of LSB galaxies below the surface-brightness limits of surveys like the SDSS, the mechanisms that create these galaxies remain unexplored. We use, Horizon-AGN, a cosmological hydrodynamical simulation to study how and why low-surface-brightness galaxies (LSBGs;  mu > 23 mag arcsec^-2), and in particular, the recently studied population of ultra-diffuse galaxies, form and evolve over time. For stellar masses greater than 10^7  MSun, LSBGs contribute 85, 10 and 11 per cent of the local number, mass and luminosity densities respectively. When controlled for stellar mass, today's LSBGs have similar dark-matter fractions and angular momenta to their high-surface-brightness (HSB) counterparts but larger (x 2.5) effective radii and lower (< 5% vs 30%) star-forming gas fractions. Interestingly, LSBGs originate from the same progenitors as HSB systems at high redshift (z~3). However, LSBG progenitors form stars more rapidly at early epochs. The higher resultant supernova energy injection flattens their gas-density profiles which, in turn, creates shallow stellar profiles that are more susceptible to tidal processes. After z~1, harassment and tidal heating steadily expand LSBG stellar distributions and quench star formation by heating cold gas, creating the population of diffuse, gas-poor LSB systems seen today. In clusters, ram-pressure stripping provides an additional mechanism that assists in gas removal in LSBG progenitors. The study of LSBGs will be one of most exciting advances in galaxy evolution in the coming years. This study offers insights into the demographics and properties of a population of galaxies that will have a transformational impact on our understanding of galaxy evolution.

Thursday May 10, 2018
Dr. Iacopo Bartalucci
CEA, Université Paris-Saclay


We present a detailed study of the spatially resolved thermodynamic and hydrostatic mass profiles of the five most massive clusters detected at z~1 via the Sunyaev-Zel'dovich effect. These objects represent an ideal laboratory to test our models in a mass regime where structure formation is driven mainly by gravity. We present a method to study these objects that optimally exploits information from XMM-Newton and Chandra observations. The combination of Chandra’s excellent spatial resolution and XMM-Newton’s photon collecting power allows us to spatially resolve the profiles from the core to the outskirts, for the first time in such objects.  Evolution properties are investigated by comparison with the REXCESS  local galaxy cluster sample. Finally, we discuss the current limitations of this method in the context of  joint analysis of future Chandra and XMM large programs and, more generally, of  multi-wavelength efforts to study high redshift objects.

Tuesday March 6, 2018
Dr. Giuseppina Battaglia


In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this talk I will first give an overview of some of the main properties of the Milky Way stellar halo based on literature studies. I will then present results concerning the chemical properties of the outer regions of the Milky Way stellar halo, based on the elemental abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, -3.1 ≲ [Fe/H] ≲-0.6. We show that the ratio of α-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H] ≳-1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples. 

Thursday October 15, 2015
Dr. Jorge Sanchez Almeida


Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter haloes. Although these predictions are unambiguous, the observational support has been indirect so far. I will report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of localized starbursts associated with gas having low metallicity. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr),  the observed metallicity inhomogeneities are only possible if the metal-poor gas producing stars fell onto the disk recently. I will analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. In addition, I will show model galaxies in cosmological numerical simulations with starbursts of low metallicity like to the star-forming regions in XMPs.

Thursday October 8, 2015
Prof. Joop Schaye
Univ. of Leiden


The realism of hydrodynamical simulations of the formation and evolution of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success, focusing in particular on the importance of subgrid models and the associated limitations. I will also present recent results from the cosmological EAGLE simulations as well as from higher-resolution simulations of individual galaxies.

Thursday September 17, 2015
Dr. Dimitri Gadotti


In this talk I will present my view on what we know and what we don't know about the so-called secular evolution processes in galaxies. I will focus on the processes that lead to the building of main stellar components in the centre of disc galaxies, and explore how these processes fit in the current cosmological paradigm of galaxy formation and evolution. I will also make an attempt at clarifying misconceptions and discussing outstanding open questions.

Tuesday May 26, 2015
Dr. Alberto Domínguez
Clemnson University


The extragalactic background light (EBL) is the second most energetic diffuse background that fills our Universe. It is produced by star formation processes and supermassive black hole accretion over the history of the  Universe. Thus, it contains fundamental information about galaxy evolution and cosmology. Interestingly, it brings together classical astronomy and high energy astrophysics since gamma-rays from extragalactic sources such as blazars and gamma-ray bursts interact by pair-production with EBL photons. Therefore, it is also essential for extragalactic gamma-ray astronomy to understand precisely and accurately the EBL in order to interpret correctly high energy observations. In this talk, I will review the present EBL knowledge, and describe how we can extract information, such as the value of the expansion rate of the Universe, from the EBL. Finally, the latest all-sky Fermi-LAT catalog of hard sources (E>50 GeV), called 2FHL, and future directions of EBL research will also be discussed.

Thursday March 12, 2015
Prof. Annette Ferguson
Royal Astronomical Observatory of Edinburgh, UK


Evidence is mounting for the presence of complex low surface brightness structures in the outer regions of galaxies. While the most spectacular examples are provided by systems hosting coherent debris streams, the most common examples may be extremely diffuse stellar envelopes. Wide-field imagers on large telescopes are allowing us to quantitatively explore the resolved stellar populations in these components within and well beyond the Local Group. I will highlight some recent  results from our work and discuss the insight these outer structures provide on understanding massive  galaxy assembly.  I will also discuss how we are using deep HST studies of M31's outer regions to probe its evolutionary history in unprecedented detail.

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. 

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