Found 217 talks archived in Galaxies

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Thursday September 15, 2022
Drs. Giuliana Fiorentino
Observatorio de Roma

Abstract

The first Gigayears of our Galactic halo can be probed by using ancient stellar populations as traced by RR Lyrae stars. Today, with the advancement in our knowledge of RR Lyrae properties belonging to the Halo and to Milky Way satellite systems (Globular clusters and dwarf galaxies) we are able
to provide solid constraints on the link between these stellar systems. Here, we present some recent results concerning the Halo formation by using a detailed evolutionary analysis of RR Lyrae stars for which chemical abundances are available.


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Thursday July 14, 2022
Dr. Jorge Sanchez-Almeida
IAC

Abstract

With the aim of detecting cosmological gas accretion onto galaxies of the local Universe, we examined the Ha emission in the halo of the 164 galaxies in the field of view of MUSE-Wide (Urrutia+19) with observable Ha (redshift < 0.42).  An exhaustive screening of the Ha images led us to select 118 reliable Ha emitting gas clouds. To our surprise, around 38 % of the time the Ha line profile shows a double peak centered at the rest-frame of the corresponding galaxy. We have explored several physical scenarios to explain this Ha emission, among which accretion disks around rogue  intermediate mass black holes (IMBHs) fit the observations best. I will describe the data analysis (to discard, e.g, instrumental artifacts and high redshift interlopers), the properties of the Ha emitting clumps (their fluxes, peak separation, and spatial distribution with respect to the central galaxy), and the arguments leading to the IMBH hypothesis rather than other alternatives (e.g., cosmological gas, expanding bubbles, or shocks in the circum galactic medium).


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Tuesday May 24, 2022
Prof. Kfir Blum
Weizmann Institute

Abstract

Gravitational dynamical friction affecting the orbits of globular clusters (GCs) was studied extensively as a possible formation mechanism for nuclear star clusters in galaxies. In well-known examples that showcase this phenomenon, like the Milky Way and M31 galaxies, the medium which affects the dynamical friction is dominated by bulge stars. In comparison, the case for dynamical friction in dark matter-dominated systems is much less clear. A puzzling example is the Fornax dwarf galaxy, where the observed positions of GCs have long been suspected to pose a challenge for dark matter, dynamical friction theory, or both. We search for additional systems that are dark matter-dominated and contain a rich population of GCs, offering a test of the mechanism. A possible example is the ultra diffuse galaxy NGC5846-UDG1: we show that GC photometry in this galaxy provide evidence for the imprint of dynamical friction, visible via mass segregation. If confirmed by future analyses of more GC-rich UDG systems, these observations could provide a novel perspective on the nature of dark matter.


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Thursday May 19, 2022
Dr. Ignacio Martin-Navarro
IAC

Abstract

Black hole feedback is central to our theoretical understanding of galaxies. The energy and momentum radiated by growing supermassive black holes is expected to regulate the baryonic cycle, in particular, within massive dark matter halos, modulating gas cooling and thus star formation. Observational evidence of the role of black hole feedback remains, however, scarce, casting serious doubt on our current galaxy formation modelling. In this talk I will summarize our recent efforts trying to empirically characterize the effect of black hole feedback on galactic scales. I will describe how the combination of detailed stellar population analysis and well-known scaling relations can be used to actually constrain the physical processes behind black hole feedback. Moreover, I will also present evidence of black hole feedback acting beyond the host galaxy, further supporting the importance of black hole feedback in regulating the evolution of galaxies.


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Tuesday May 17, 2022
Prof. Gastón Giribet
Universidad de Buenos Aires

Abstract

In this talk, I will review the recently discovered infinite-dimensional symmetries that emerge in the near horizon region of black hole horizons. I will explain how the conserved charges associated with those symmetries carry information of the black hole, and, in particular, about its thermodynamic properties. I will focus on the case of magnetized black holes; namely, black holes that are embedded in strong magnetic fields.




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Tuesday May 3, 2022
Dr. Mireia Montes
IAC

Abstract

 

There is a huge amount of astrophysical events that remain barely studied due to the lack of large, multiwavelength and deep optical surveys. This is the Universe at the lowest density of stars, largely unseen by past large field surveys like the Sloan Digital Sky Survey (SDSS).  For instance, only a handful of galaxy clusters have been observed with enough depth to witness the intracluster light (ICL), made up of stars that drift freely between galaxies in the cluster. Thought to form by the stripping of satellite galaxies as they fall into the cluster, characterising the ICL is key to understanding the assembly mechanisms occurring inside galaxy clusters. Despite its importance, little is known about this light as it is very difficult to observe due to its low surface brightness. 
The availability of deep surveys have expanded our knowledge of the properties, and therefore the origin, of the ICL. However, larger samples are needed to understand the evolution of this component with time and the efficiency of the different evolutionary processes inside galaxy clusters. 
In this talk, I will present the latest advances in our understanding of the ICL. I will also talk about how we can use this light to trace the dark matter in clusters of galaxies and recent results that show the potential of the intracluster light to study these massive structures. 

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Thursday April 21, 2022
Dr. Robert Grand
IAC

Abstract

Recent years have seen impressive development in cosmological simulations for spiral disc galaxies like the Milky Way. I present a suite of high-resolution magneto-hydrodynamic simulations that include many physical processes relevant for galaxy formation, including star formation, stellar evolution and feedback, active galactic nuclei and magnetic fields. I will discuss how these processes affect the formation of galactic discs, and what these simulations can tell us about the formation of the Milky Way, such as the properties of the Galaxy's putative last significant merger and its effect on the formation of the thick disc and stellar halo. 


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Thursday March 17, 2022
Dr. Alis Deason
ICC Durham

Abstract

 

The hierarchical nature of structure formation predicts that haloes grow by the aggregation of several lower-mass "clumps". A natural consequence of this process is the existence of an extended halo of stars surrounding galaxies, which is built up from the debris of destroyed lower mass objects. The nature of these haloes has been studied extensively from Milky Way to cluster-mass systems. However, the stellar haloes of dwarf galaxies have been given relatively little attention.  In this talk, I will discuss recent work using N-body cosmological simulations and empirical galaxy models to study the  build-up of stellar haloes surrounding dwarf galaxies. We find that the galaxy formation model parameters, namely the stellar mass-halo mass relation and the galaxy occupation fraction, strongly influence the stellar mass accreted onto dwarf galaxies. Moreover, the type of dark matter can also be important, as minor mergers are greatly suppressed in warm dark matter models. Finally, I will discuss the observational implications of these results, and the future prospects for constraining small-scale models with observational probes.

 

 

Youtube:

https://youtu.be/61vvPaHQft4

 


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Thursday December 2, 2021
Prof. Roberto Maiolino
Kavli Cambridge

Abstract

In the local universe most of the stellar mass is in passive galaxies, where star formation is
absent or at very low levels. Understanding what are the mechanisms that have been
responsible for quenching star formation in galaxies, and transforming them into passive,
quiescent systems, is one of the main observational and theoretical challenges of extragalactic
astrophysics. I will give a brief overview of the several possible quenching causes and physical
processes that have been proposed so far, ranging from feedback from black hole accretion and
starburst activity, to effects associated with the large scale environment in which galaxies live.
Although most of these mechanisms and causes play a role in different classes of galaxies and
at different epochs, multi-band observations are providing growing evidences that just a few of
them play the key, dominant role.
I will conclude by providing prospects for further investigating these aspects and tackling open
questions with the next generation of observing facilities.


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Tuesday September 7, 2021
Dr. Jesús Vega-Ferrero
IAC

Abstract

Galaxy morphologies are one of the key diagnostics of galaxy evolutionary tracks, but visual classifications are extremely time-consuming. The sheer size of Big Data surveys, containing millions of galaxies, make this approach completely impractical. Deep Learning (DL) algorithms, where no image pre-processing is required, have already come to the rescue for image analysis of large data surveys. In this seminar, I will present the largest multi-band catalog of automated galaxy morphologies to date containing morphological classifications of ∼27 million galaxies from the Dark Energy Survey. The classification separates: (a) early-type galaxies (ETGs) from late-types (LTGs); and (b) face-on galaxies from edge-on. These classifications have been obtained using a supervised DL algorithm. Our Convolutional Neural Networks (CNNs) are trained on a small subset of DES objects with previously known classifications, but hese typically have mr < 17.7 mag. We overcome the lack ofa training sample by modeling fainter objects up to mr < 21.5 mag, i.e., by simulating what thebrighter objects with well-determined classifications would look like if they were at higher redshifts.The CNNs reach a 97% accuracy to mr < 21.5 on their training sets, suggesting that they are ableto recover features more accurately than the human eye. We obtain secure classifications for 87%and 73% of the catalog for the ETG vs. LTG and edge-on vs. face-on models, respectively.