Found 196 talks archived in Galaxies

Thursday May 27, 2021
Dr. Manuela Bischetti


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


Tuesday April 27, 2021
Dr. Lorenzo Posti
Observatorie Astronomique de Strasbourg



It is widely understood that galaxies use, throughout the Hubble time, only a small fraction of the baryons associated to their dark matter halos to form stars. Such low baryon-to-stars conversion efficiencies are expected in galaxy formation scenarios where stellar & AGN feedback play a key role in regulating star formation in galaxies, respectively at the low- and high-mass end.
In this talk I will show how we can constrain this scenario using galaxy dynamics. Both robust determinations of disc dynamical scaling relations (e.g. Tully-Fisher, mass-size) and accurate measurements of dark matter halo masses from HI rotation curves of spirals and from the kinematics of globular clusters around ellipticals, provide compelling evidence that the population of massive spirals has systematically larger baryon-to-stars conversion efficiencies than ellipticals. In fact, we see that the baryon-to-stars conversion efficiency monotonically increases with mass for late-type galaxies, while it shows a clear turn over at about L* only for early-type galaxies. Thus, while massive early types are compatible with standard stellar-to-halo mass relations based on abundance matching, massive late types are systematically discrepant from it.
I will discuss the possible repercussions that these results have, highlighting in particular what they imply in terms of AGN feedback and merging in galaxies of different types. Finally I will show that current state-of-the-art cosmological hydrodynamical simulations (EAGLE, TNG) still struggle to reproduce what we observe for the most massive discs.

Tuesday April 20, 2021
Dr. Sebastian Trujillo Gomez
Heidelberg University


In this talk I will discuss how the stellar, globular cluster (GC), and gas components of galaxies allow us to trace the assembly of galaxies and their dark matter (DM) haloes, and how they constrain the complex physics of galaxy formation. I will use examples from three studies: in the first one, I will describe how the study of the phase-space distribution of the MW GC system using Gaia in the context of the E-MOSAICS simulations provides a detailed quantitative picture of the formation of the Galaxy. In the second example, I will show how the unusual GC populations in galaxies like the infamous NGC1052-DF2 and DF4 can be used to rewind the clock and obtain a snapshot of their galactic progenitors at cosmic noon. A simple model of star cluster formation points to an extremely dense birth environment and strong structural evolution, providing clues of the effect of clustered star formation on galaxy evolution. In the last part I will describe a follow-up study of the impact of clustered star formation on galaxy structure that provides clues on the origin of ultra-diffuse galaxies (UDGs), which are difficult to explain in the current paradigm of galaxy formation. I will show how anchoring an analytical model on galaxy scaling relations and numerical simulations predicts the emergence of UDGs that lack DM driven by clustered feedback from young GCs.

Thursday November 12, 2020
Dr. Gianluca Castignani


Galaxy clusters are the most massive gravitationally bound structures in the Universe. They are the sites where exceptional morphological transformations of galaxies occur, driven by their interactions within the complex cosmic web. Clusters are thus excellent laboratories to study galaxy evolution in extreme regimes. I will present the results of a large campaign based on IRAM facilities (30m and NOEMA) and targeting in mm different samples of galaxies in and around clusters. The final goal of the project is to evaluate the role of dense mega-parsec scale environments in processing cold gas of galaxies. The following samples of galaxies will be discussed. i) The largest sample of distant ~30 brightest cluster galaxies observed in CO, over a broad range of redshift (z~0.2-2.6). They are drawn from CLASH, COSMOS, SpARCS, and DES deep fields. ii) The largest sample of distant, intermediate redshift z~0.2-0.5, cluster LIRGs (luminous infrared galaxies), which have been observed in CO with the NOEMA interferometer and are drawn from the Herschel Lensing Survey (HLS) and the Local Cluster Substructure Survey (LoCuSS).  iii) I will also present ongoing results of a large campaign with the aim to evaluate the pre-processing of atomic (HI) and molecular (CO) gas of galaxies before they fall into the cluster core. The sample comprises 245 galaxies in cosmological filaments, up to 7 virial radii around Virgo, the benchmark cluster in the local Universe. The outlined studies reveal a complex scenario, where large-scale structures have a different impact in regulating the star formation fueling and mass assembly of the considered galaxies, depending on their morphological type, location with respect to the cluster core, and redshift.


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:

Tuesday June 9, 2020
Prof. Mariangela Bernardi
University of Pennsylvania


Stellar populations vary across the galaxy population. However, even within a single galaxy, there are stellar population gradients which spatially resolved spectroscopic studies are beginning to reveal. The MaNGA survey permits a study of gradients in a sample of early-type galaxies which is nearly two orders of magnitude larger than previous work. This allows us to quantify the effects of gradients on estimates of the stellar and dynamical masses of these galaxies, and to study how age and abundance gradients, and thus star formation and assembly histories, vary across the population. In this talk I will present results from our recent analysis.


zoom link:

Thursday May 28, 2020
Prof. Avishai Dekel
Hebrew University of Jerusalem


This talk will address the preferred mass and time for galaxy formation, in dark-matter haloes similar to that of the Milky way but when the Universe was a few Gigayears old. It is proposed that this is due to the interplay between two mechanisms, first *supernova* feedback that removes gas from the galaxy, and second *hot gas* in the deep potential well of massive haloes that suppresses cold gas supply to the galaxy, the two being effective in galaxies of lower and higher masses respectively. Cosmological simulations reveal that the same mechanisms are responsible for a robust sequence of events were galaxies undergo a dramatic gaseous *compaction*, sometimes caused by mergers, into a compact star-forming “blue nugget”. This triggers inside-out *quenching* of star formation, which is maintained by a hot massive halo aided by black-hole feedback, leading to todays passive elliptical galaxies. The blue-nugget phase is responsible for drastic transitions in the main galaxy structural, kinematic and compositional properties. In particular, the growth of the *black hole* in the galaxy center, first suppressed by supernova feedback when below the critical mass, is boosted by the compaction event and keeps growing once the halo is massive enough to lock the supernova ejecta by its deep potential well and the hot halo. The compaction events also trigger the formation of extended rings in high-z massive galaxies. These events all occur near the same characteristic halo mass, giving rise to the highest efficiency of galaxy formation and black-hole growth at this magic mass and time.


Zoom link:

Thursday May 7, 2020
Dr. Alexandre Vazdekis


Using deep photometry SBFs have been traditionally used to determine galaxy distances. We have recentlycomputed SBF spectra of stellar populations at moderately high resolution,which are fully based on empirical stellar spectral libraries. We show that the SBF spectraprovide new means to perform the stellar population studies, which, so far, have been tackled on the basis of the mean properties. We find that theSBFs are able to unveil very metal-poor components at the one percent level, which are not possible to disentangle with the standard analysis. In massive Early-Type Galaxies suchmetal-poor components correspond to the first stages in their chemicalenrichment and, therefore, the SBFs provide stringent constrains on their formation.

Thursday December 5, 2019
Prof. Raffaella Morganti
ASTRON, Netherlands


Our view of the gas and its physical conditions in the central region of AGN has been enriched by the discover of fast and massive outflows of HI and molecular gas. These outflows can be driven by radiation/winds but also by the interaction of the radio plasma with the ISM. Understanding the origin and quantifying their impact requires to trace their location and derive their physical conditions (density of the gas, mass, mass outflow rate and kinetic energy of the outflow etc.). Particularly interesting has been the finding that in the first phase of their life, jet in radio galaxies can be particularly effective in driving such outflows. This crucial phase is at the heart of the idea of feedback, therefore particularly relevant for studying feedback in action.


In this talk, I will present some of the results we have obtained to trace jet-driven HI and molecular gas outflows down to scales ranging from hundred to tens of pc. The impact of low-power radio jets will be discussed and the comparison with the predictions from numerical simulations will also be presented.

Outflows of up to few hundred Msun/yr have been found in molecular gas using ALMA while the HI observed with VLBI is showing that the outflowing gas is clumpy as also predicted from numerical simulations. I will describe the kinematics of the gas and its conditions and the relevance they may have for feedback.    

Thursday June 13, 2019
Dr. Jorge Sanchez Almeida


Although the name 'fundamental metallicity relation' (FMR) may sound a bit bombastic, it really represents a fundamental relation in the sense of revealing a fundamental process in galaxy formation. Numerical simulations predict that accretion of cosmic web gas feeds star formation in star-forming galaxies. However, this solid theoretical prediction has been extremely elusive to confirm. The FMR, i.e., the fact that galaxies of the same stellar mass but larger star formation rate (SFR) tend to have smaller gas-phase metallicity (Zg), is one of the best observational supports available yet. The talk will introduce the FMR and then present recent results of our group showing how the FMR emerges from a local anti-correlation between SFR and Zg existing in the disks of galaxies. Thus, understanding the FMR is equivalent to understanding why active star-forming regions tend to have low relative metallicity. The existence of the local anti-correlation SFR-vs-Zg is found by Sanchez-Menguiano+19 ApJ  and Sanchez Almeida+18 MNRAS, whereas the equivalence between local and global laws is in Sanchez Almeida & Sanchez-Menguiano 19 ApJL.

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