1,721,063 research outputs found
A Multi-band view of high-redshift QSOs and future outlook for LSST
No full textActive Galactic Nuclei (AGN) are highly luminous sources (L ∼ 1042 − 1048 erg/s), powered by accretion onto supermassive black holes (SMBHs) with masses ranging from MBH ∼ 106 − 109M⊙, located at the centers of galaxies. The observed tight correlations between SMBH properties and those of their host galaxies has led to the understanding that they co-evolve, influencing one another. Over the past few years, AGN research has increasingly focused on their role in galaxy evolution, although the physical processes underlying this interaction remain still unclear. Growing evidence indicates that AGN-driven outflows can deposit energy and momentum into the interstellar medium of their host galaxies, influencing star formation activity. This suggests these outflows as a potential feedback mechanism in regulating galaxy evolution. This feedback effect is expected to be particularly strong during the Cosmic Noon, at z = 2 − 3, when both AGN accretion and star formation activity are at their peak. As the efficiency in generating powerful outflows appears to scale with AGN luminosity, understanding the coupling between nuclear energy output and the host galaxy is an open issue particularly relevant for the most luminous AGN, known as quasars (hereafter QSOs). Another thriving field of study focuses on understanding the formation of these supermassive black holes. Indeed, due to their extreme luminosities, QSOs can be observed at very early cosmic epochs, reaching back to z = 6 − 7.5, when the Universe was less than 1 Gyr old. These extremely distant QSOs reveal the existence of fully formed SMBHs already in the early Universe, posing a significant challenge to our current models, which struggle to explain how such massive objects could form in such a short span of time. A direct approach to understanding the physical processes within AGN is through their spectral energy distri- bution (SED), which represents their emission across the electromagnetic spectrum. The AGN SED extends from the hard X-ray to the radio bands and is due to the sum of several contributions, arising from distinct regions and from different physical mechanisms. Specifically, gas inflow toward the SMBH via an accretion disk converts gravitational energy into thermal energy through viscous torques, producing the distinctive blue bump in UV and optical emission. This primary radiation is Compton up-scattered to X-ray energies in a region of hot electron gas called the corona. Additionally, a surrounding dusty torus absorbs photons emitted by the corona and the accretion disk, re-emitting them in the near and mid-IR. Dust at lower temperatures (T ≈ 20 − 100 K), located much farther from the nucleus and heated by both hot stars and partially by the AGN itself, generates far-IR emission. Finally, in approximately 10% of AGN, the presence of a relativistic jet accounts for their radio emission. This thesis focuses on high-redshift AGN, specifically on their SED. Initially, we concentrated on the WISSH sample, comprising 85 hyperluminous QSOs at redshifts 2–4. These QSOs, which can drive some of the fastest and most powerful outflows, are ideal targets for exploring the AGN-host galaxy connection. Then, we moved to even higher redshifts, studying the X-ray-to-NIR broadband emission of the HYPERION and E-XQR samples at z = 5.5 − 7.5. These quasars host the most massive SMBHs observed in this redshift range, challenging our current models of SMBH formation. Finally, we address preparatory work for the upcoming Vera Rubin Legacy Survey of Space and Time (LSST), which, with its wide and deep coverage of the southern sky, is expected to discover many new high-z QSOs, increasing the known population by at least an order of magnitude. This thesis is organized as follows: - Chapter 1 provides a brief introduction to AGN, covering their powering mechanism, structure and resulting spectral energy distribution. Sec. 1.5 highlights the particular interest in studying luminous QSOs within the broader AGN population. - Chapter 2 presents the derivation of a X-ray to FIR mean SED for the WISSH sample, which consists of 85 hyperluminous QSOs at Cosmic Noon, and its comparison with other averaged AGN SEDs from the literature. - Chapter 3 is dedicated to investigating the broadband emission of 54 QSOs at the Epoch of Reionization, drawn from the HYPERION and E-XQR-30 samples. 1 - Chapter 4 describes the AGILE pipeline, developed to produce a realistic photometric catalog that closely mirrors the data expected from LSST observations. This chapter particularly focuses on the modeling and assignment of multiwavelength SEDs for AGN in the catalog. - Chapter 5 presents the results of applying machine learning tools on datasets with LSST-like features to efficiently identify luminous, high-redshift QSOs within the vast amount of data that LSST will deliver, and, more generally, to distinguish AGN from inactive galaxies and stars. - Chapter 6 provides a brief summary of the results of the work and outlines future perspectives for continuing the analysis of high-z QSOs
How complex is the obscuration in active galactic nuclei? new cluesfrom the suzaku monitoring of the x-ray absorbers in ngc 7582
No full textWe present the results of a Suzaku monitoring campaign of the Seyfert 2galaxy, NGC 7582. The source is characterized by very rapid (ontimescales even lower than a day) changes of the column density of aninner absorber, together with the presence of constant componentsarising as reprocessing from a Compton-thick material. The best-fittingscenario implies important modifications to the zeroth-order view ofUnified Models. While the existence of a pc-scale torus is needed inorder to produce a constant Compton reflection component and an ironKa-emission line, in this Seyfert 2 galaxy this is not viewed along theline of sight. On the other hand, the absorption of the primarycontinuum is due to another material, much closer to the black hole,roughly at the distance of the broad-line region, which can produce theobserved rapid spectral variability. On top of that, the constantpresence of a 10(22) cm(-2) column density can be ascribed to thepresence of a dust lane, extended on a galactic scale, as previouslyconfirmed by Chandra. There is now mounting evidence that complexity inthe obscuration of active galactic nuclei (AGNs) may be the rule ratherthan the exception. We therefore propose to modify the UnificationModel, adding to the torus the presence of two furtherabsorbers/emitters. Their combination along the line of sight canreproduce all the observed phenomenology
Investigating the Complex X-Ray Spectrum of a Broad-Line 2MASS Red Quasar: XMM-Newton Observation of FTM 0830+3759
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The NGC 3341 minor merger: a panchromatic view of the active galactic nucleus in a dwarf companion
No full text"We present X-ray (Chandra), radio (Expanded Very Large Array and European VLBI Network) and archival optical data of the triple-merging system in NGC 3341. Our panchromatic analysis confirms the presence of a Seyfert 2 active galactic nucleus (AGN) in NGC 3341B, one of the secondary dwarf companions. On the other hand, the nucleus of the primary galaxy, consistent with a star-forming region of a few solar masses per year, and NGC 3341C are very unlikely to host an AGN. We therefore suggest that NGC 3341 is an exceptional example of an AGN triggered in the satellite galaxy of a minor-merging system. The existence of such a system can have important implications in the models of hierarchical growth of structures. Further observational and theoretical efforts on NGC 3341 and potentially similar sources are needed in order to understand the role of minor mergers on the onset of AGN activity, and in the evolution of massive galaxies.
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A study of X-ray emission of galaxies hosting molecular outflows (MOX Sample)
No full textWe have carried out an extensive X-ray spectral analysis of a sample of galaxies exhibiting molecular outflows (MOX sample) to characterize the X-ray properties and investigate the effect of active galactic nuclei (AGNs) on the dynamical properties of the molecular outflows (MOs). We find that the X-ray bolometric correction (L 2-10 keV/L AGN) of these sources ranges from ∼10-4.5 to 10-0.5, with ∼70% of the sources below 10-2, implying a weak X-ray emission relative to the AGN bolometric luminosity (L AGN). However, the upper limit on the 2-10 keV luminosity () obtained from 12 μm flux, following the correlation derived by Asmus et al., is ∼0.5-3 orders of magnitude larger than the L 2-10 keV values estimated using X-ray spectroscopy, implying a possibility that the MOX sources host normal AGNs (not X-ray weak), and their X-ray spectra are extremely obscured. We find that both L 2-10 keV and L AGN correlate strongly with the MO velocity and the mass outflow rates (), implying that the central AGN plays an important role in driving these massive outflows. However, we also find statistically significant positive correlations between the starburst emission and MO mass outflow rate, versus , and L 0.6-2keV versus , which implies that starbursts can generate and drive the MOs. The correlations of MO velocity and with AGN luminosities are found to be stronger compared to those with the starburst luminosities. We conclude that both starbursts and AGNs play a crucial role in driving the large-scale MO.</p
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