Found 30 talks width keyword active galaxies
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.
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
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.
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
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.
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.
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)
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.
Recent works show that the restframe colours of X-ray selected AGN host galaxies at z~1 are no different from those of inactive galaxies once stellar mass selection effects are taken into account. However, there is a clear deficit of AGN among quiescent galaxies, and the average star formation rates of AGN hosts are comparable or higher than those of inactive star-forming galaxies. These apparently contradictory findings could be a consequence of higher extinction in star-forming AGN hosts compensating for their younger stellar populations in observed colours. In this talk I will present a new method of extinction correction that breaks the degeneracy with stellar age and metallicity by comparing the restframe U-V colour with measurements of the Dn(4000) index on intermediate band photospectra from SHARDS. I'll show that the distribution of extinction corrected U-V colours and Dn(4000) for AGN hosts at z<1 is significantly different from that of comparison samples of inactive galaxies, with a clear deficit of AGN in intrinsic red galaxies and a higher prevalence among those with intermediate age stellar populations.
FeII comprises up to one third of the line emission in AGNs. For that reason it is an important coolant that needs to be taken into accountto fully understand the energetics of the broad line region (BLR). In thistalk I will discuss new approaches to study the excitation mechanisms ofthe FeII based on a semi-empirical template we derived in thenear-infrared region (NIR). We correlate the strength of the NIR andoptical iron lines to assess the relative contribution of the differentmechanisms that produces that emission. We found that in all casesLy_alpha fluorescence plays an important role, being a process that needsto be considered in any approach aimed at understanding this complexemission. We also compare the width of the individual FeII lines with thatof other lines emitted in BLR. Our results confirm previous assumptionsand results from variabilty studies that the gas responsible for the FeIIemission is the outer portion of the BLR.
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