Found 32 talks width keyword active galaxies

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Tuesday April 18, 2023
University of Oxford

Abstract

 

Nowadays, it is widely accepted that most galaxies undergo an active phase in their evolution. The impact of the energy released by active galactic nuclei (AGN) in the interstellar medium (ISM) of the host galaxy has been proposed as a key mechanism responsible for regulating star formation (SF). The mid-infrared (IR) is the ideal spectral range to investigate the nuclear/circumnuclear regions of AGN since dust extinction is significantly lower compared to the visible range. Furthermore, it provides unique tracers to study the AGN-SF connection such as H2 rotational lines, fine structure lines and Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are also a powerful tool to characterize the ISM in different environments.

Recently, we presented new JWST/MIRI MRS spectroscopy of three Seyfert AGN in which we compare their nuclear PAH emission with that of star-forming regions. This study represents the first of its kind to use sub-arcsecond angular resolution data of local luminous Seyferts (Lbol > 10^44.5 erg/s) with a wide wavelength coverage (4.9-28.1 μm). Our results showed that a suite of PAH features is present in the innermost parts of these Seyfert galaxies. We found that the nuclear regions of AGN lie at different positions of the PAH diagnostic diagrams, whereas the SF regions are concentrated around the average values of SF galaxies. Furthermore, we find that the nuclear PAH emission mainly originates in neutral PAHs while, in contrast, PAH emission originating in the star forming regions favours small ionised PAH grains. Therefore, our results provide evidence that the AGN have a significant impact on the ionization state and size of the PAH grains on scales of ~142-245 pc. This is fundamental since PAH bands are routinely used to measure star-formation activity in near and far SF and active galaxies.

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.


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Thursday February 16, 2023
Astronomy Department of the Physics Institute of the Federal Universisty of Rio Grande do Sul (UFRGS)

Abstract

 

Since the pioneering studies linking the mass of supermassive black holes (SMBH) with the velocity dispersion of their host galaxies bulges it has become accepted that the products of active galactic nuclei (AGN) accretion and star-formation (SF) are somehow related. It is also accepted that nuclear SF and AGN can coexist in the inner region of galaxies, suggesting that the growth of SMBH (by gas accretion) and galaxies (by forming stars) are coupled.  In terms of galaxy evolution, it is established that AGN feedback plays a fundamental role by impacting SF (quenching, suppressing, or triggering). Cosmological simulations performed without the inclusion of feedback (SNR/AGN) effects are not able to reproduce the low and high luminosity ends of the galaxy luminosity function and underestimate the ages of the stars of the most massive galaxies when compared with observations.  While observations have shown that nuclear star formation is common in AGNs, properly measuring the stellar population properties in AGNs hosts is particularly difficult, since the active nucleus will dilute the absorption features and contribute to a large number of ionizing photons that will make it difficult to use emission line fluxes to infer the stellar properties.  In this seminar, I will discuss the results we have obtained in our group when mapping the stellar population in the inner region of active galaxies, with a special focus on the near-infrared spectral region, which allows for a better untangling of the AGN and stellar contributions for the spectral energy distribution of the galaxies. 
Zoom: https://rediris.zoom.us/j/81704623667?pwd=ejRHci8vTUR0QmZ5YkxrNTVoRU9mQT09

Meeting ID: 817 0462 3667
Passcode: 643393


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Thursday December 2, 2021
Kavli Cambridge

Abstract

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.


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Tuesday July 13, 2021
Max Planck Institut fuer Physik (Múnich)

Abstract

The MAGIC telescopes are a stereoscopic system
of two 17m mirror diameter Cherenkov telescopes for gamma-ray observations, in operation since many years on the island of
La Palma at the Observatorio del Roque de los Muchachos.
A new installation allows us to use those telescopes as optical
intensity interferometer which enables us to measure the size of bright
objects in the range of 0.6-1.5 milli-arcsec and other physical
parameters. In this presentation the setup is explained, our physics
targets, first results and also a future outlook of this project
with respect to the Cherenkov telescope array (CTA) currently
in construction.


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Thursday July 8, 2021
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
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 October 1, 2019
Instituto de Radioastronomía y Astrofísica, México

Abstract


The dust component of active galactic nuclei (AGN) produces a broad infrared spectral energy distribution (SED), whose power and shape depends on the fraction of the source absorbed, and the geometry of the absorber respectively. This emitting region is expected to be concentrated within the inner ∼5 pc of the AGN which makes almost impossible to image it with the current instruments. The study of the infrared SED by comparison between infrared AGN spectra and predicted models is one of the few ways to infer the properties of the AGN dust. We explore a set of six dusty models of AGN with available SEDs, namely Fritz et al. (2006), Nenkova et al. (2008B), Hoenig & Kishimoto (2010), Siebenmorgen et al. (2015), Stalevski et al. (2016), and Hoenig & Kishimoto (2017). They cover a wide range of morphologies, dust distributions, and compositions.

We explore the discrimination among models and parameter restriction using synthetic spectra (Gonzalez-Martin et al. 2019A), and perform spectral fitting of a sample of 110 AGN with Spitzer/IRS drawn from the Swift/BAT survey (Gonzalez-Martin et al. 2019B). Our conclusion is that most of these models can be discriminated using only mid-infrared spectroscopy as long as the host galaxy contribution is less than 50%. The best model describing the sample is the clumpy disk-wind model by Hoenig & Kishimoto (2017). However, large residuals are shown irrespective of the model used, indicating that AGN dust is more complex than models. We found that the parameter space covered by models is not completely adequate. This talk will give tips for observers and modelers to actually answer the question: how is the dust arrange in AGN? This question will be one of the main subjects of future research using JWST in the AGN field.


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Tuesday December 4, 2018
INAF Observatory of Trieste

Abstract

Why did galaxies stop forming stars? Why do black holes in galactic nuclei have masses proportional to bulge masses? What are the physical mechanisms leading the transition from gas-rich, star-forming galaxies, to red gas-deprived passive galaxies? Theoretical models predict that AGN should play a major role in this co-evolution, by driving super winds that are eventually able to remove gas from galaxies, thus quenching star-formation and preventing them from over growing.  
Today’s flagship Instruments - like ALMA and MUSE/VLT - allow to routinely detect AGN-driven massive winds, and to spatially resolve and measure their main parameters. AGN driven galactic winds seem a widespread feature in AGN host galaxies in the local universe, with mounting numbers also in the distant universe.  
But questions arise about their net impact on the surrounding ISM, on the relative importance of quenching versus stimulating star-formation, on the removal of the gas reservoirs from the disks of the host galaxies. 
Do we really understand the interplay of these AGN super-winds with the ISM of the host galaxy, and -perhaps more importantly- with the entire AGN/host galaxy/circum-galactic medium (CGM) ecosystem? I will discuss both observational and theoretical recent results on this topic - and highlight possible strategies to progress. 


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Thursday November 17, 2016
IAC

Abstract

The Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes reported the discovery of the most distant gamma-ray source ever observed at very high energies, thanks to the “replay” of an enormous flare by a galactic gravitational lens as foreseen by Einstein’s General Relativity. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components separated by a 10–12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma-ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1. MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light. Very high energy gamma-ray emission was detected from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.

Work published in A&A 595, A98 (2016) ( http://www.aanda.org/articles/aa/abs/2016/11/aa29461-16/aa29461-16.html)

https://magic.mpp.mpg.de/outsiders/results/magic-highlights-5/

http://www.iac.es/divulgacion.php?op1=16&id=1133


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Tuesday December 1, 2015
IAC

Abstract

The search for detection of gamma-rays in the very-high-energy range (VHE, >100GeV) from distant AGNs by Imaging Atmospheric Cherenkov Telescopes (IACTs) gets very complicated at high redshifts, not only because of the lower flux due to the distance of the source, but also due to the consequent absorption of gamma-rays by the extragalactic background light (EBL), affecting VHE sources at z~0.1 and beyond. The farthest source ever detected in the VHE domain was the blazar PKS1424+240, at redshift z>0.6. In the last months MAGIC, a system of two 17 m of diameter IACTs located in the Canary island of La Palma, has been able to go beyond that limit and to push the boundaries for VHE detection to redshifts z~1. The two sources detected and analyzed, blazar S30218+35 (Atel discovery #6349) and FSRQ PKS1441+25 (Atel discovery #7416) are located at redshift z=0.944 and z=0.939 respectively. S30218+35 is also the first gravitational lensed blazar ever detected in VHE. The multiwavelength dataset collected allowed us to test for the first time the present generation of EBL models at such distances. I will show results on MAGIC analysis on S30218+35 and PKS1441-25, including spectral energy distributions and EBL absorption studies, in a multi-wavelength context.


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