Found 188 talks archived in Galaxies

Thursday December 5, 2019
Prof. Raffaella Morganti
ASTRON, Netherlands


Our view of the gas and its physical conditions in the central region of AGN has been enriched by the discover of fast and massive outflows of HI and molecular gas. These outflows can be driven by radiation/winds but also by the interaction of the radio plasma with the ISM. Understanding the origin and quantifying their impact requires to trace their location and derive their physical conditions (density of the gas, mass, mass outflow rate and kinetic energy of the outflow etc.). Particularly interesting has been the finding that in the first phase of their life, jet in radio galaxies can be particularly effective in driving such outflows. This crucial phase is at the heart of the idea of feedback, therefore particularly relevant for studying feedback in action.


In this talk, I will present some of the results we have obtained to trace jet-driven HI and molecular gas outflows down to scales ranging from hundred to tens of pc. The impact of low-power radio jets will be discussed and the comparison with the predictions from numerical simulations will also be presented.

Outflows of up to few hundred Msun/yr have been found in molecular gas using ALMA while the HI observed with VLBI is showing that the outflowing gas is clumpy as also predicted from numerical simulations. I will describe the kinematics of the gas and its conditions and the relevance they may have for feedback.    

Thursday June 13, 2019
Dr. Jorge Sanchez Almeida


Although the name 'fundamental metallicity relation' (FMR) may sound a bit bombastic, it really represents a fundamental relation in the sense of revealing a fundamental process in galaxy formation. Numerical simulations predict that accretion of cosmic web gas feeds star formation in star-forming galaxies. However, this solid theoretical prediction has been extremely elusive to confirm. The FMR, i.e., the fact that galaxies of the same stellar mass but larger star formation rate (SFR) tend to have smaller gas-phase metallicity (Zg), is one of the best observational supports available yet. The talk will introduce the FMR and then present recent results of our group showing how the FMR emerges from a local anti-correlation between SFR and Zg existing in the disks of galaxies. Thus, understanding the FMR is equivalent to understanding why active star-forming regions tend to have low relative metallicity. The existence of the local anti-correlation SFR-vs-Zg is found by Sanchez-Menguiano+19 ApJ  and Sanchez Almeida+18 MNRAS, whereas the equivalence between local and global laws is in Sanchez Almeida & Sanchez-Menguiano 19 ApJL.

Thursday May 23, 2019
Patricia Sánchez Blázquez
Universidad Autónoma de Madrid


The Time Inference with MUSE in Extragalactic Rings, TIMER, is a project dedicated to study the central regions
of 24 nearby galaxies with the integral field spectrograph MUSE. The spatial resolution of this instruments
allows the detailed study of the different structural components in these galaxies and, therefore, disentangle
their star formation histories, kinematics and dynamics of both, the gaseous and the stellar constituents.
In this talk, I will give an overview of the project as well as some details on  how the  dataset can be used for a plethora of scientific applications, like
understanding the stellar and AGN feedback, the role of primary and secondary bars, the dynamics of nuclear
spiral arms, barlenses, box/peanuts and bulges.

Tuesday December 4, 2018
Dr. Chiara Feruglio
INAF Observatory of Trieste


Why did galaxies stop forming stars? Why do black holes in galactic nuclei have masses proportional to bulge masses? What are the physical mechanisms leading the transition from gas-rich, star-forming galaxies, to red gas-deprived passive galaxies? Theoretical models predict that AGN should play a major role in this co-evolution, by driving super winds that are eventually able to remove gas from galaxies, thus quenching star-formation and preventing them from over growing.  
Today’s flagship Instruments - like ALMA and MUSE/VLT - allow to routinely detect AGN-driven massive winds, and to spatially resolve and measure their main parameters. AGN driven galactic winds seem a widespread feature in AGN host galaxies in the local universe, with mounting numbers also in the distant universe.  
But questions arise about their net impact on the surrounding ISM, on the relative importance of quenching versus stimulating star-formation, on the removal of the gas reservoirs from the disks of the host galaxies. 
Do we really understand the interplay of these AGN super-winds with the ISM of the host galaxy, and -perhaps more importantly- with the entire AGN/host galaxy/circum-galactic medium (CGM) ecosystem? I will discuss both observational and theoretical recent results on this topic - and highlight possible strategies to progress. 

Wednesday November 28, 2018
Fernando Buitrago
Institute of Astrophysics and Space Sciences (IA)


There are galaxies that remain untouched since the ancient
Universe. These unique objects, the so-called relic galaxies, are several times
more massive than our Milky Way but with much smaller sizes, and
containing very old (>10 Gyr) stellar populations. For the very few of
them already found and analysed (most of them by our IAC colleagues),
they seem to host "too heavy" central
super massive black holes, also displaying an overabundance of low mass
versus high mass stars and retaining their primeval morphologies and
kinematics. How did they survive until the present day? Simulations
predict that they reside in galaxy overdensities whose large internal
random motions prevent galaxies from merging. However, we have not yet
determined observationally neither the environments these galaxies
inhabit nor how many there are (their number densities). We make use
of the GAMA survey, that allows us to conduct a complete
census of this elusive galaxy population, because of its large area and
spectroscopic completeness. After inspecting 180 square degrees of the sky
using the deepest photometric images available, we identified 29
massive ultracompact galaxies in the nearby Universe (0.02 < z < 0.3),
that are true windows to the ancient Universe. I will present the first paper
about this exceptional sample, describing their properties and
highlighting the fact that while some galaxies seem to be satellites
of bigger objects, others are not located in clusters, at odds with the
theoretical expectations.

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.

Tuesday July 17, 2018
Dr. Elena D'Onghia
Universidad Wisconsin-Madison


By providing information on distances and proper motions for one billion stars, the Gaia satellite allows us to investigate the major unsolved challenges in galaxy formation: the nature of dark matter, the origin of Galactic spiral activity and its relation to the bar, and more generally the history of the Milky Way. 
My research aims to develop a theoretical approach to modeling and exploiting the big data and address problems at the forefront of Galactic Dynamics at various scales. What is the origin of the spiral activity in the Milky Way? How are all of these perturbations to the structure of the Galaxy coupled to each other directly and through the dark-matter halo?  I will also present my ongoing work on statistical techniques of big-data analysis and advanced numerical simulations used to interpret the evolution of star clusters and discover streams in the stellar disk of the Milky Way.

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.

Thursday November 30, 2017
Dr. Francesco Sylos-Labini
Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Rome


We describe how a simple class of out of equilibrium, rotating and asymmetrical mass distributions evolve under their self-gravity to produce a quasi-planar spiral structure surrounding a virialized core, qualitatively resembling a spiral galaxy. The spiral structure is transient, but can survive tens of dynamical times, and further reproduces qualitatively noted features of spiral galaxies as the predominance of trailing two-armed spirals and large pitch angles. As our models are highly idealized, a detailed comparison with observations is not appropriate, but generic features of the velocity distributions can be identified to be potential observational signatures of such a mechanism. Indeed, the mechanism leads generically to a characteristic transition from predominantly rotational motion, in a region outside the core, to radial ballistic motion in the outermost parts. Such radial motions are excluded in our Galaxy up to 15 kpc, but could be detected at larger scales in the future by GAIA. We explore the apparent motions seen by external observers of the velocity distributions of our toy galaxies, and find that it is difficult to distinguish them from those of a rotating disc with sub-dominant radial motions at levels typically inferred from observations. These simple models illustrate the possibility that the observed apparent motions of spiral galaxies might be explained by non-trivial non-stationary mass and velocity distributions without invoking a dark matter halo or modification of Newtonian gravity. In this scenario the observed phenomenological relation between the centripetal and gravitational acceleration of the visible baryonic mass could have a simple explanation.

Thursday November 23, 2017
Prof. Sofia Feltzing
Lund University


Galactic Archeology is today a vibrant field of research. The adoption and launch of the Gaia astrometric satellite by ESA has resulted in many spectroscopic Galactic surveys that aim to complement the Gaia data with information (for the fainter Gaia stars) about stellar elemental abundances, radial velocities, and stellar parameters. This results in multi-dimensional data sets which will allow us to put the Milky Way stellar populations into a much broader galactic context, eg by comparing with models and galaxies at large look-back times. In this talk I will review a selection of recent exciting developments in Galactic Archeaology found via on-going surveys as well as look to the future and see what surveys like 4MOST and WEAVE will bring.  The proposed surveys will be put into a wider context of past, on-going and future spectroscopic surveys and how this can all be combined to understand the Milky Way as a galaxy.

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