Found 11 talks width keyword galactic halos

Tuesday May 24, 2022
Prof. Kfir Blum
Weizmann Institute


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.

Thursday May 19, 2022
Dr. Ignacio Martin-Navarro


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.

Thursday April 21, 2022
Dr. Robert Grand


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
Dr. Alis Deason
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 May 13, 2021
Prof. Diego Blas
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.

Thursday June 25, 2020
Prof. Francesco Shankar
University of Southampton


It has been claimed for decades that almost all galaxies in the local Universe host at their centre a supermassive black hole (SMBH) the mass of which appears to be tightly correlated with the stellar mass and the random motion ("velocity dispersion", sigma) of the stars in the host galaxy. In this talk I will first review the state of the art in this field. I will then highlight that significant biases affect local black hole-galaxy correlations.  I will specifically show that the majority of quiescent early-type galaxies with central black hole dynamical mass estimates have significantly higher velocity dispersions than local typical galaxies of similar stellar mass. Through aimed Monte Carlo simulations, residual analysis, and the comparison with latest AGN clustering measurements, I will then illustrate that present data sets of active and quiescent galaxies strongly favour on average lower SMBH masses than previously thought, and point to velocity dispersion as more ``fundamental'' than galaxy stellar mass, galaxy size or Sérsic index. I will then move on discussing the main implications of these findings, in particular: 1) The implied black hole radiative efficiencies and obscured fractions; 2) the consequences on feedback from active black holes and SMBH binary gravitational waves; 3) the connection to cosmological models that rely on velocity dispersion, rather than stellar mass, as main driver of black hole growth.

Zoom link:

Monday June 29, 2015
Dr. Nathalie Ouellette
Queen's University


Major tests of cosmological and galaxy formation models can be constructed through dynamical and structural parameters of galaxies. Towards this end, we present the SHIVir (Spectroscopic and H-band Imaging of Virgo cluster galaxies) survey, which provides dynamical information and stellar population diagnostics for hundreds of galaxies. We construct scaling relations and dynamical profiles within the optical radius of most galaxies, paying close attention to the baryon-to-dark matter transition region and selected metrics which reduce scatter in fundamental scaling relations. Salient results include bimodal mass and surface brightness distributions for Virgo galaxies, a possible bifurcation in the stellar-to-halo mass relation for low-mass galaxies, and the need for deep velocity dispersions to extract meaningful science. Once complete, ours should be the most extensive mass catalogue ever assembled for a galaxy cluster.

Thursday October 10, 2013
Dr. Alberto Molino


The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical; Moles et al. 2008) survey has observed 8 different regions of the sky, including sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 contiguous, ~300A width, filters covering the optical range, plus deep JHKs imaging. The observations, carried out with the Calar Alto 3.5m telescope using the wide field (0.25 deg2 FOV) optical camera LAICA and the NIR instrument Omega-2000, correspond to ~700hrs of on-target science images. The photometric system was specifically designed to maximize the effective depth of the survey in terms of accurate spectral-type and photometric redshift estimation along with the capability of identification of relatively faint emission lines.

The ALHAMBRA Gold catalogue corresponds to a subsample of ~100k bright galaxies (+20.000 stars in the galactic halo and ~1000 AGN candidates), photometrically complete down to magnitude I=23AB, with very accurate and reliable photometric redshift estimations.

Considering that the Spanish community will have privileged access to the data until Nov15th 2013, this seminar is intended to be a brief introduction to the potential (doable) science with the ALHAMBRA-survey.

Thursday April 12, 2012
Dr. Lodovico Coccato


Stellar halos of galaxies offer an important laboratory to understand the galaxies’ formation process and evolution. In fact, the dynamic time scale in the halos are large, and the imprint of the formation mechanisms may still be preserved at large radii in the kinematics, in the orbital structure, in streams and substructures, or in the chemical composition and distribution of stars.

I will discuss i) the kinematic and dynamical properties of stellar halos in early type galaxies as derived from tracers like planetary nebulae and globular clusters; and ii) the stellar population properties as derived from deep long-slit spectra in a number of massive ellipticals. Results are then discussed in the framework of galaxy halo formation mechanisms.

Thursday November 13, 2008
Prof. Simon White
Max-Planck Institut für Astrophysik, Garching, Germany


In our now-standard picture for the growth of structure, dark matter halos are the basic unit of nonlinear structure in the present Universe. I will report results from simulations of galaxy-scale dark halos with more than an order of magnitude better mass resolution than any previously published work. Tests demonstrate detailed convergence for (sub)structures well below a millionth the mass of the final system. Even with such resolution the fraction of halo mass in bound subhalos does not rise above a few percent within the half-mass radius. I will also present a new simulation technique which allows structure in the dark matter distribution to be studied on very much smaller scales. This is required for accurate forecasts of the expected signal both in earth-bound experiments designed to detect dark matter directly, and in indirect detection experiments like GLAST which attempt to image dark matter annihilation radiation at gamma-ray wavelengths.

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