Found 198 talks archived in Galaxies

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Tuesday September 7, 2021
Dr. Jesús Vega-Ferrero
IAC

Abstract

Galaxy morphologies are one of the key diagnostics of galaxy evolutionary tracks, but visual classifications are extremely time-consuming. The sheer size of Big Data surveys, containing millions of galaxies, make this approach completely impractical. Deep Learning (DL) algorithms, where no image pre-processing is required, have already come to the rescue for image analysis of large data surveys. In this seminar, I will present the largest multi-band catalog of automated galaxy morphologies to date containing morphological classifications of ∼27 million galaxies from the Dark Energy Survey. The classification separates: (a) early-type galaxies (ETGs) from late-types (LTGs); and (b) face-on galaxies from edge-on. These classifications have been obtained using a supervised DL algorithm. Our Convolutional Neural Networks (CNNs) are trained on a small subset of DES objects with previously known classifications, but hese typically have mr < 17.7 mag. We overcome the lack ofa training sample by modeling fainter objects up to mr < 21.5 mag, i.e., by simulating what thebrighter objects with well-determined classifications would look like if they were at higher redshifts.The CNNs reach a 97% accuracy to mr < 21.5 on their training sets, suggesting that they are ableto recover features more accurately than the human eye. We obtain secure classifications for 87%and 73% of the catalog for the ETG vs. LTG and edge-on vs. face-on models, respectively.

 


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Thursday July 8, 2021
Dr. Sebastián F. Sánchez
UNAM

Abstract

We summarize here some of the results reviewed recently by Sanchez (2020) and Sanchez  et al. (2021), comprising the advances in the comprehension of galaxies in the nearby universe based on integral field spectroscopic galaxy surveys. We review our current knowledge of the spatially resolved spectroscopic properties of low-redshift star-forming galaxies (and their retired counterparts) using results from the most recent optical integral field spectroscopy galaxy surveys. We briefly summarize the global spectroscopic properties of these galaxies, discussing the main ionization processes, and the global relations described by the star-formation rates, gas-phase oxygen abundances, and average properties of their stellar populations (age and metallicity) in comparison with the stellar mass. Then, we present the local distribution of the ionizing pro-cesses down to kiloparsec scales, and how the global scaling relations found using integrated parameters (like the star-formation main sequence, mass–metallicity relation, and Schmidt–Kennicutt law) have local/resolved counterparts, with the global ones being, for the most part, just integrated/average versions of the local ones.  The main conclusions of the most recent explorations are that the evolution of galaxies is mostly governed by local processes but clearly affected by global ones.


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Thursday May 27, 2021
Dr. Manuela Bischetti
INAF/Trieste

Abstract

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.

 


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

Abstract

 

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.

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

Abstract

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.


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Thursday November 12, 2020
Dr. Gianluca Castignani
EPFL

Abstract

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.

 

https://rediris.zoom.us/j/83038801735


 



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

Abstract

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:  https://rediris.zoom.us/j/97154760685


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

Abstract

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: https://rediris.zoom.us/j/97614680345


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

Abstract

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:  https://rediris.zoom.us/j/98813487304


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Thursday May 7, 2020
Dr. Alexandre Vazdekis
IAC

Abstract

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.

 

https://rediris.zoom.us/j/92233220080



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