Found 55 talks width keyword galactic formation

Thursday June 15, 2023


Using CGMS deep integral field data we have discovered that the massive galaxy NGC 1277 has no dark matter. This is the first time that a galaxy as massive as the Milky Way or more is found to be dark matter deficient. This result is unexpected within the Lambda-CDM cosmological paradigm. We propose several alternatives to explain this intriguing observation but none is completely satisfactory, so the mystery about how to generate a galaxy without dark matter remains.


ID: 818 9512 1297

Passcode: 460746


Friday May 26, 2023
Universidad Nacional Autonoma de Mexico


We present the extended data release of the Calar Alto Legacy Integral Field Area (CALIFA) survey (eDR). It comprises science-grade quality data for 895 galaxies obtained with the PMAS/PPak instrument at the 3.5 m telescope at the Calar Alto Observatory along the last 12 years, using the V500 setup (3700-7500Å, 6Å/FWHM) and the CALIFA observing strategy. It includes galaxies of any morphological type, star-formation stage, a wide range of stellar masses ( ∼10^7-10^12 Msun), at an average redshift of  ∼0.015 (90\% within 0.005 < z <0.05). Primarily selected based on the projected size and apparent magnitude, we demonstrate that it can be volume corrected resulting in a statistically limited but representative sample of the population of galaxies in the nearby Universe. All the data were homogeneously re-reduced, introducing a set of modifications to the previous reduction. The most relevant is the development and implementation of a new cube-reconstruction algorithm that provides an (almost) seeing-limited spatial resolution (FWHM PSF  ∼1.0").  Furthermore we present the analysis performed using the pyPipe3D pipeline for these dataset. We include a description of (i) the analysis performed by the pipeline, (ii) the adopted datamodel for the derived spatially resolved properties and (iii) the catalog of integrated, characteristics and slope of the radial gradients for a set of observational and physical parameters derived for each galaxy. All these data has been distributed through the following webpage:

Thursday March 2, 2023



Early-type galaxies: instructions to build them through mergers
Massive early-type galaxies (ETGs) are "red and dead" systems mainly composed of old and metal-rich stellar populations. In a cosmological context, present-day ETGs are believed to be the remnants of a complex stellar mass assembly history marked by several mergers, which are the consequence of the underlying hierarchical assembly of their host dark matter halos. In this talk, I will deal mainly with the merger-driven evolution of ETGs. Firstly, I will illustrate a comparison between observed ETGs from the MaNGA survey and simulated galaxies from the IllustrisTNG cosmological simulation suite. The aim of this study is to provide an interpretative scenario of the stellar mass assembly history of observed present-day ETGs, comparing the radial distributions of their stellar properties with those of simulated galaxies, in which it is possible to disentangle the contribution of stars formed in situ (i.e. within the main progenitor galaxy) and stars formed ex situ (i.e. in other galaxies) and then accreted through mergers. Then, I will describe how the scaling relation between the stellar mass and stellar velocity dispersion in ETGs evolves across cosmic time. Specifically, by extending the results of Cannnarozzo, Sonnenfeld & Nipoti (2020), I model the aforementioned relation through a Bayesian hierarchical approach, considering ETGs with log(M∗/M⊙) > 9 over the redshift range 0 ≲ z ≲ 4. Together with a new characterisation of the relation, I reconstruct the back-in-time evolutionary pathways of individual ETGs on the stellar mass-velocity dispersion plane to answer the question “how did high-redshift ETGs assemble through cosmic time to reach the functional form of the relation in the present-day Universe?“.
After the main topic, if time permits, I would like to spend a few minutes presenting another extra content (below you can find the title and a brief abstract of this further content). Feel free to include it or not in the announcement mail.
EXTRA - Inferring the Dark Matter halo mass in galaxies from other observables with Machine Learning
In the context of the galaxy-halo connection, it is widely known that the Dark Matter (DM) halos show correlations with some physical properties of the hosted galaxy: the most well-known relation is the so-called Stellar-to-Halo-Mass Relation. However, we know that there are several other empirical relations among galaxy properties, involving, for example, the stellar mass, the gas and stellar metallicities, the black hole mass, etc. Given the complexity of the problem and the high number of galaxy properties that might be related to DM halos, the study of the galaxy-halo connection can be approached by relying on machine learning techniques to shed light on this intricate network of relations. With the aim of inferring the DM halo mass and then finding a unique functional form able to link the halo mass to other observables in real galaxies, I rely on the state-of-the-art Explainable Boosting Machine, a novel implementation of generalised additive models with pairwise interactions, training a model on the IllustrisTNG simulation suite at different redshift.





Thursday January 26, 2023


Within the hierarchical framework for galaxy formation, merging and
tidal interactions are expected to shape large galaxies up to the
present day. While major mergers are quite rare at present, minor
mergers and satellite disruptions - that result in stellar streams -
should be common, and are indeed seen in the stellar halos of the Milky
Way and the Andromeda galaxy. In the last years, the Stellar Stream
Legacy Survey (PI. Martinez-Delgado) has exploited available deep
imaging of some nearby spiral galaxies with the ultimate aim of
estimating the frequency, morphology and stellar luminosity/mass
distribution of these structures in the local Universe. In this talk, I
will present the first results of our systematic survey of stellar
streams together with some recent follow-up observations (e.g. Megara,
Subaru) and N-body modelling of the most striking streams. Finally,
I will discuss what we can learn about galaxy formation from the results
of this survey, including the comparison with the available L-CDM
cosmological simulations, and our plans to extend this stream survey
at lower surface brightness regime with the recently approved ARRAKHIS,
the first ESA fast-mission lead by Spain.

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


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.

Thursday September 29, 2022
Max Planck Institute for Astrophysics


The formation of the first galaxies in the Universe is the new frontier of both galaxy formation and reionization studies. In fact, we will soon directly observe primeval galaxies thanks to the James Webb Space Telescope, and witness the reionization process through 21cm intensity mapping experiments. This unique moment in human history creates a fierce new challenge, i.e. to simultaneously understand in a unique and coherent picture the processes of galaxy formation and reionization, and – crucially – their connection. The latter, in particular, has escaped past numerical efforts. In this talk I will present the first results on this front from an years-long effort geared toward achieving such comprehensive picture, culminated in the Thesan suite of cosmological radiation-magneto-hydrodynamical simulations. I will briefly introduce the features of Thesan, highlighting the successes and failures of its physical model. Thesan produces realistic galaxy populations thanks to state-of-the-art physics, including self-consistent dust production+destruction and radiation transport. I will then show how Thesan can, for the first time, reproduce the connection between IGM and galaxies, as measured from the modulation of the Lyman-alpha flux around galaxies. Finally, I will chart the way forward towards and even deeper understanding of the emergence of the first structures in the Universe.

Thursday April 21, 2022


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. 

Thursday March 17, 2022
ICC Durham



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.





Thursday December 2, 2021
Kavli Cambridge


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.

Thursday May 13, 2021
Imperial College


Bosonic ultra-light dark matter (ULDM) in the mass range m ~ $10^{-22} - 10^{-21} \rm eV$ has been invoked as a motivated candidate with new input for the small-scale `puzzles' of cold dark matter. Numerical simulations show that these models form cored density distributions at the center of galaxies ('solitons'). These works also found an empirical scaling relation between the mass of the large-scale host halo and the mass of the central soliton. We show that this relation predicts that the peak circular velocity of the outskirts of the galaxy should approximately repeat itself in the central region. Contrasting this prediction to the measured rotation curves of well-resolved near-by galaxies, we show that ULDM in the mass range m ~ $10^{-22} - 10^{-21} \rm eV$ is in tension with the data.

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