Found 24 talks width keyword accretion, accretion discs

Finally, I will summarise our ongoing JWST work within the GATOS (Galactic Activity, Torus and Outflow Survey) collaboration. In particular, I will focus on our recent study about the survival of PAH molecules in AGN-driven outflows.

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).

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.

The field of Galactic archaeology has been very active in recent years, with a major influx of data from the Gaia satellite and large spectroscopic surveys. The major science questions in the field include Galactic structure and dynamics, the accretion history of the Milky Way, chemical tagging, and age-abundance relations. I will give an overview of GALAH as a large spectroscopic survey, and describe how it is complementary to other ongoing and future survey projects. I will also discuss recent science highlights from the GALAH team and compelling questions for future work.

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.

This talk will be dedicated to luminous (LBol~1E47 erg/s),
high-redshift quasars, which are ideal targets to investigate (i) feedback
from SMBHs, and (ii) the early growth phases of giant galaxies. I will
present evidence of  SMBH-driven outflows  at all Cosmic epochs, back to
the early Universe. These outflows involve all gas phases (molecular,
neutral, ionised) and extend on nuclear to galactic and circum-galactic
scales. I will report on the first systematic study of the molecular gas
properties in the host-galaxies of the most luminous quasars, fundamental
to probe the impact of SMBH feedback on the host-galaxy evolution. I will
show that luminous quasars pinpoint high-density sites where giant galaxies
assemble, and I will discuss the major contribution of mergers to the final
galaxy mass. To this aim, I will present a wealth of multi-wavelength (UV
to sub-millimeter) observations from the WISE/SDSS hyper-luminous quasars
survey  at z~2-5 (WISSH), and recent results from the ESO large program
XQR-30, the Ultimate X-SHOOTER Legacy Survey of Quasars at the Reionization
epoch.

At present, our understanding of the formation history of the MW is limited due to the complexity of observing the imprints of accretion events and of reproducing them in numerical simulations. Moreover, though being the only galaxy, in which the Galactic potential can be probed in detail, the distribution of mass in the MW, and hence of the dark matter, is poorly constraint, especially at large distances. In addition, the MW is not isolated, and it has recently been suggested that the infall of the LMC can induce a perturbation in the stellar and dark matter distribution of the MW. As a consequence, the details of the formation history of our Galaxy are still unknown, such as the number of accretion events, the mass of the accreted galaxies, and the epoch of these events. Yet this information is crucial to understand our environment and to constrain the theoretical models and simulations that try to reproduce it.

One of the major challenges of the field is that a tremendous number of multi-aspect (astrometric, photometric and spectroscopic) observations at significant depth is required to study the morphology, the kinematics and the chemistry of the outskirts of our Galaxy, where are located the signatures of these events. Hopefully, the advent of recent and incoming complementary large surveys, such as the European Gaia mission, UNIONS (Ultraviolet Near Infrared Optical Northern Survey), Pristine, Pan-STARRS (PS), WEAVE or LSST (Legacy Survey of Space and Time), is offering a new global point of view on our Galaxy’s halo, allowing us to precisely probe the Galactic potential our the MW, and to retrace itsaccretion history.

In this talk I will present recent works that have been conducted to better catarerized our Galaxy and its history with some of the existing surveys mentioned above. In addition, I will present the major improvement that will bring this new generation of large, multi-aspect surveys, to study both our Galactic history, as well as the fundamental nature of the dark matter.

(This seminar is organized by the IAU G5 commission on stellar and planetary atmospheres) 

Task-based computing is a method where computational problems are split
   into a large number of semi-independent tasks (cf.
   2018MNRAS.477..624N). The method is a general one, with application not
   limited to traditional grid-based simulations; it can be applied with
   advantages also to particle-based and hybrid simulations, which involve
   both particles and fields. The main advantages emerge when doing
   simulations of very complex and / or multi-scale systems, where the
   cost of updating is very unevenly distributed in space, with perhaps
   large volumes with very low update cost and small but important regions
   with large update costs.

   Possible applications in the context of stellar atmospheres include
   modelling that covers large scales, such as whole active regions on the
   Sun or even the entire Sun, while at the same time allows resolving
   small-scale details in the photosphere, chromosphere, and corona. In
   the context of planetary atmospheres, models of pebble-accreting hot
   primordial atmospheres that cover all scales, from the surfaces of
   Mars- and Earth-size embryos to the scale heights of the surrounding
   protoplanetary disks, have already been computed (2018MNRAS.479.5136P,
   2019MNRAS.482L.107P), and one can envision a number of applications
   where the task-based computing advantage is leveraged, for example to
   selectively do the detailed chemistry necessary to treat atmospheres
   saturated with evaporated solids, or to do complex cloud chemistry
   combined with 3-D radiative transfer.

   In the talk I will give a quick overview of the principles behind
   task-based computing, and then use both already published and still
   on-going work to illustrate how this may be used in practice. I will
   finish by discussing how these methods could be applied with great
   advantage to problems such as non-equilibrium ionization, non-LTE
   radiative transfer, and partial redistribution diagnostics of spectral
   lines.

The improvement on the Imaging Air Cherenkov Technique led to the discovery of a new class of compact binaries: the gamma-ray binaries. This small class consist  of only five members, all of them composed by a massive star and a compact object. The nature of the compact object is unknown for all of them but PSR B1259-63, which contains a pulsar. It is crucial to study and monitor these systems not only to understand their behavior, the scenario accounting for the gamma-ray emission and their nature but also to comprehend why we have not detected more sources of this exclusive family. In this presentation, I will review the state-of-the-art of this field and I will present the observations performed with the MAGIC telescopes in order to unveil the nature of gamma-ray binaries.

MASTER-Kislovodsk auto-detection system discovered a faint transient in the Andromeda galaxy on January 13th 2015. It was originally identified as a classical nova and received designation M31N 2015-01a. Further observations showed discrepancies with the spectra and lightcurves typical for the classical novae. The transient was re-identified as a likely stellar merger (aka Luminous Red Nova (LRN)), similar to V838Mon. In this presentation I will deliver a short overview of our current understanding of this class of objects and a summary of the current state of the ongoing observing campaign of the M31 LRN. Recent results will be discussed with a particular emphasis on the contributions made possible by GTC and other observing facilities at Observatorio Roque de los Muchachos. At the final part of the presentation I will touch on follow up observations once M31 is available for observations again.