Found 21 talks width keyword dwarf galaxies

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Tuesday October 4, 2022
Krzysztof Lisiecki
National Centre for Nuclear Research, Warsaw, Poland

Abstract

Vimos Public Extragalactic Redshift Survey (VIPERS) is a spectroscopic survey designed to  investigate the spatial distribution of ~90k galaxies on redshift 0.4<z<1.2. The catalogue of spectroscopic observations, combined with auxiliary photometric data, is perfect for evolutionary studies of different types of galaxies. But also for tracing rare objects. One of them are the so-called “red nuggets”, progenitors of the most massive galaxies in the local Universe.  The discovery of red nuggets - highly massive, passive and extremely compact galaxies  -  at high redshift challenged the leading cosmological models, as they do not fit into the evolutionary paths of passive galaxies. Taking into account  that  the galaxies' mergers are stochastic events, it is possible that some red nuggets  remain relatively unaltered for billions of years. Those survivors constitute a group of unique galaxies in the local Universe,  commonly named “relics”. Despite numerous studies dedicated to red nuggets and relics, the link between the population of compact, massive, passive galaxies in the early Universe and their remnants in the local Universe, is still poorly understood.

In my talk I  will present the first spectroscopically selected catalogue of red nuggets at the intermediate redshift.  It is the most extensive catalogue of this kind of galaxies above redshift z > 0.5.  Selected under the most strict criteria, the group of 77 objects consists of a statistically important sample, which allows for analysis of physical properties of those rare passive giants. I will discuss the influence of compactness criteria on the sample size. Moreover I will present  VIPERS red nuggets number densities and discuss the environmental preferences of those exceptional galaxies.


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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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Tuesday March 6, 2018
Dr. Giuseppina Battaglia
IAC

Abstract

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. 


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Thursday May 21, 2015
Dr. Shoko Jin
Kapteyn Astronomical Institute, Groningen, NL

Abstract

The immediate surroundings of our Milky Way galaxy are home to a number of dwarf galaxies, whose variety in shape, size, spatial location and velocity tells us that these Galactic satellites all have different tales to tell. While some look round, pristine and undisturbed, others have disturbed morphologies or show gradients in their metallicity, while yet others have unusual kinematic features or clearly show their dissolution into a stellar stream. Very few of them contain significant levels of gas, also prompting the question of what mechanism is responsible for stripping out their gas content. This talk will explore the eclectic mix of Milky Way dwarf galaxies and what their properties can reveal to us about their different stories, and also what they can collectively tell us of our own Galaxy. I will also discuss how looking at the Galactic vicinity is aiding us, via this population of Galactic satellites, in the increasingly popular area of near-field cosmology.


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

Abstract

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.


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Thursday October 9, 2014
Dr. Eva Grebel
Director Astronomisches Rechen-Institut Zentrum für Astronomie der Universität Heidelberg

Abstract

Dwarf galaxies are the most common type of galaxy in the Universe andinclude the most dark-matter-dominated objects known. They offerintriguing insights into evolutionary processes at low halo masses and low metallicities. Moreover, as survivors of a once much more numerous population of building blocks of larger galaxies, they are key to understanding very early star formation processes. The Local Group and particularly the Milky Way's dwarf galaxy entourage offer us the unique possibility to compare in detail dwarf and Galactic populations. This is an important step towards quantifying the magnitude and time scales of dwarf contributions to the build-up of the Milky Way and allows us to test predictions of cosmological theories and hierarchical structure formation.


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Tuesday June 24, 2014
Dr. Ewa Lokas
Nicolaus Copernicus Astronomical Center, Warsaw

Abstract

I will present an evolutionary model for the origin of Andromeda II, a dSph satellite of M31, involving a merger between two disky dwarf galaxies than explains the origin of prolate rotation recently detected in the kinematic data for And II. The simulation traces the evolution of two dwarfs, whose structural parameters differ only in their disk scale lengths, placed on a radial orbit towards each other with their angular momenta inclined by 90 deg. After 5 Gyr the merger remnant forms a stable triaxial galaxy with rotation only around the longest axis. This prolate rotation is naturally explained as due to the symmetry of the initial configuration which leads to the conservation of angular momentum components along the direction of the merger. The stars originating from the two dwarfs show significantly different surface density profiles while having very similar kinematics in agreement with the properties of separate stellar populations in And II. I will also discuss an alternative scenario for the formation of And II, via tidal stirring of a disky dwarf galaxy. While intrinsic rotation occurs naturally in this model as a remnant of the initial rotation of the disk, it is mostly around the shortest axis of the stellar component. The rotation around the longest axis is induced only occasionally and remains much smaller that the system's velocity dispersion. I conclude that although tidal origin of the velocity distribution in And II cannot be excluded, it is much more naturally explained within the scenario involving a past merger event. Thus, in principle, the presence of prolate rotation in dSph galaxies of the Local Group and beyond may be used as an indicator of major mergers in their history or even as a way to distinguish between the two scenarios of their formation.


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Thursday April 10, 2014
Dr. Andreas Pawlik
MPA (Garching)

Abstract

The first galaxies are thought to have started the reionization of the Universe, that is the transformation of the cosmic hydrogen from its initial neutral to its present ionized state that occurred during the first few hundred million years after the Big Bang. I will review the key physics of reionization by the first galaxies and highlight the computational challenges of simulating the relevant processes, primarily the transport of ionizing photons. I will introduce the radiative transfer method TRAPHIC that we have developed to address these challenges. I will discuss the application of TRAPHIC in zoomed cosmological simulations of the first galaxies and evaluate the prospects for observing these galaxies with the upcoming James Webb Space Telescope. I will conclude by presenting first results from Aurora, a new suite of simulations to investigate reionization and galaxy formation across a large range of scales.


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Wednesday March 26, 2014
Dr. Thorsten Lisker
Astronomisches Rechen-Institut (ARI), Heidelberg

Abstract

Dwarf galaxies are a complex population. They comprise objects with young and old stellar populations, slow and fast rotation, as well as single- and multi-component structure. These characteristics show correlations with environmental density - we thus believe that dwarf galaxies hold a fossil record of how environment affected galaxy evolution. In this talk I will review and discuss recent progress on our understanding of dwarf galaxies in clusters, both from the observational and the modelling side. In particular, I will attempt to reconcile the proposed formation mechanisms of early-type dwarf galaxies - the most abundant population in clusters - with the continuous environmental influence predicted by cosmological simulations.


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Wednesday January 8, 2014
Dr. Ruben Sanchez-Janssen
NRC Herzberg Institute of Astrophysics

Abstract

Two competing effects appear to govern galaxy multiplicity (pairs orgroups) at low masses: while associations of low-mass haloes are naturally expected in a LCDM cosmology, galaxy formation within these haloes is thought to be rendered inefficient due to the action of several ionizing agents. Yet associations of dwarf galaxies are known to exist in the Local Volume, and their frequency appears to be unexpectedly high for LCDM expectations even in our own Local Group. Unfortunately, it is not yet well understood what role do interactions between low-mass galaxies play in determining their star formation histories, structural properties, and neutral gas content. Here I will present an investigation of the impact of dwarf-dwarf galaxy tidal interactions on their morphological and star formation properties. The UGC5205 close pair consists of two low-mass (M* ~ 5E7 Msun), late-type galaxies with a relative projected distance of only 10 kpc, and no nearby massive companions. I will show that these equal-mass interactions can be an important 'pre-processing' mechanism that acts before dwarfs are affected by a more massive central galaxy, profoundly impacting their star formation histories and morphologies.


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