Relevant bibliographies by topics / Quasars : absorption

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Academic literature on the topic 'Quasars : absorption'

Author: Grafiati
Published: 30 November 2024

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Journal articles on the topic "Quasars : absorption"

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Mishra, Sapna, M. Vivek, Hum Chand, and Ravi Joshi. "Appearance versus disappearance of broad absorption line troughs in quasars." Monthly Notices of the Royal Astronomical Society 504, no. 3 (April 1, 2021): 3187–202. http://dx.doi.org/10.1093/mnras/stab782.

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ABSTRACT We present a new set of 84 broad absorption line (BAL) quasars (1.7 < zem < 4.4) exhibiting an appearance of C iv BAL troughs over 0.3–4.8 rest-frame years by comparing the Sloan Digital Sky Survey Data Release (SDSSDR)-7, SDSSDR-12, and SDSSDR-14 quasar catalogues. We contrast the nature of BAL variability in this appearing BAL quasar sample with a disappearing BAL quasar sample studied in the literature by comparing the quasar’s intrinsic, BAL trough, and continuum parameters between the two samples. We find that appearing BAL quasars have relatively higher redshift and smaller probed time-scales as compared to the disappearing BAL quasars. To mitigate the effect of any redshift bias, we created control samples of appearing and disappearing BAL quasars that have similar redshift distribution. We find that the appearing BAL quasars are relatively brighter and have shallower and wider BAL troughs compared to the disappearing BAL sample. The distribution of quasar continuum variability parameters between the two samples is clearly separated, with the appearance of the BAL troughs being accompanied by the dimming of the continuum and vice versa. Spectral index variations in the two samples also point to the anticorrelation between the BAL trough and continuum variations consistent with the ‘bluer when brighter’ trend in quasars. We show that the intrinsic dust model is less likely to be a favourable scenario in explaining BAL appearance/disappearance. Our analysis suggests that the extreme variations of BAL troughs like BAL appearance/disappearance are mainly driven by changes in the ionization conditions of the absorbing gas.
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Chen, Zhi-Fu, Huan-Chang Qin, Jin-Ting Cai, Yu-Tao Zhou, Zhe-Geng Chen, Ting-Ting Pang, Zhi-Wen Wang, and Kang-Fa Cheng. "The Study of the Circumgalactic Medium with Quasar Pairs." Astrophysical Journal Supplement Series 265, no. 2 (March 29, 2023): 46. http://dx.doi.org/10.3847/1538-4365/acbe01.

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Abstract We have collected 10,025 foreground–background quasar pairs with projected distances d p < 500 kpc from the large quasar catalog of the Sloan Digital Sky Survey DR16Q. We investigate the properties of the Mg ii absorption lines with W r > 0.15 Å around foreground quasars, including both the line of sight (LOS; of foreground quasars) and transverse (TRA; perpendicular to the LOS) absorptions. Both the equivalent width (the correlation coefficient ρ = −0.915 and the probability P < 10−4 of no correlation) and incident rate (ρ = −0.964 and P < 10−6) of TRA Mg ii absorption lines are obviously anticorrelated with projected distance. The incident rate of TRA Mg ii absorption lines is obviously (>4σ) greater than that of LOS Mg ii absorption lines at projected distances d p < 200 kpc, while the TRA and LOS Mg ii both have similar (<3σ) incident rates at scales d p > 200 kpc. The anisotropic radiation from quasars would be the most possible interpretation for the anisotropic absorption around quasars. This could also indicate that the quasar radiation is not obviously impacting the gas halos of quasars at scales d p > 200 kpc.
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Harutyunian, Haik A. "Are There Quasars at Non-Cosmological Distances?" Symposium - International Astronomical Union 194 (1999): 428–31. http://dx.doi.org/10.1017/s0074180900162485.

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In Dravskikh & Dravskikh (1996) the results of a statistical analysis of quasar luminosity as a function of redshift, if it is assumed to be cosmological, are given (see Fig.1). Three quasar samples were analyzed separately: •quasars with absorption lines;•quasars associated with galaxies or association-quasars not having absorption lines (from Burbidge et al. 1996);•other quasars not included in the first two groups.
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Wang, Xilin. "Direct observation evidence for the origin of broad emission lines in quasars: Understanding emission via absorption." Theoretical and Natural Science 26, no. 1 (December 20, 2023): 261–72. http://dx.doi.org/10.54254/2753-8818/26/20241105.

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This year marks the 60^th anniversary of quasar discovery in 1963. The kinematics of gaseous clouds in quasars have been the subject of decades-long debate, focusing on two modelsrotation and blowing-wind. The rotation model, wherein gaseous clouds orbit black holes, is widely accepted by astronomers and frequently used to measure supermassive black hole (SMBH) masses in quasars. Another model is blowing-wind model, in which the gaseous clouds are outflows and in linear motion toward all directions. Our study creatively employs the quasar absorption line technique, utilizing atomic hydrogen Balmer absorption lines for identification, especially during eclipses of inner emitting clouds. The ambiguous presence of hydrogen Balmer absorption lines hints at massive eclipse clouds near central black holes, but detection is hindered by obscuration from dusty tori outside the broad emission line-producing region. We conduct an intensive survey among million quasars in Sloan Digital Sky Survey (SDSS) and acquire a small sample of quasars with hydrogen Balmer absorptions on their spectra. Three quasars exhibit significant variabilities over a decade, contradicting the blowing-wind model, which predicts constant motion along the line of sight with no absorption variabilities. The discovery servers as the direct observation evidence for the rotation model of broad emission lines in quasars. Rotation velocities of eclipse clouds, consistent with expected velocities of emission line clouds, confirm homology between absorption and emission clouds.
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Peng, Xing-Long, Zhi-Fu Chen, Zhi-Cheng He, Ting-Ting Pang, and Zhi-Wen Wang. "Comprehensive Connection among the Quasars with Different Types of Outflow Absorption Lines." Astrophysical Journal 963, no. 1 (February 21, 2024): 3. http://dx.doi.org/10.3847/1538-4357/ad1e5e.

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Abstract It is commonly accepted that outflows from the central regions of quasars play a substantial role in regulating the global properties of the host galaxy. These outflows are typically detected through blueshifted absorption lines. However, the question remains whether outflows observed with different absorption line types indeed reflect the same environmental or evolutionary stage of the host galaxy. In this study, we use the Sloan Digital Sky Survey quasar catalog and employ the flux ratio of [O II] and [Ne V] emission lines as indicators to compare star formation rates (SFRs) within host galaxies of quasars exhibiting various outflow absorption line types: low-ionization broad absorption line (LoBAL), low-ionization Mini-BAL (LoMini-BAL), low-ionization narrow absorption line (LoNAL), high-ionization broad absorption line (HiBAL), high-ionization Mini-BAL (HiMini-BAL), and high-ionization narrow absorption line (HiNAL). Our findings indicate that the SFR of LoMini-BAL quasars is comparable to that of LoNAL quasars, somewhat less than that of LoBAL quasars, but markedly greater than that of HiBAL quasars. Furthermore, the SFR of HiMini-BAL quasars mirrors that of HiNAL or Non-abs (no associated absorption lines) quasars, but is significantly higher than that of HiBAL quasars. If we consider that differing absorption line types are indicative of the quasar evolution stage, our results propose an inclusive evolution sequence: LoBALs evolve into LoMini-BALs/LoNALs, then progress to HiBALs, and ultimately morph into HiMini-BALs/HiNALs/Non-abs. Concomitantly, the SFR within the host galaxies of quasars appears to decline noticeably nearing the LoNAL phase’s end and rejuvenates before the HiMini-BAL phase.
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Misawa, Toru, Rikako Ishimoto, Satoshi Kobu, Nobunari Kashikawa, Katsuya Okoshi, Akatoki Noboriguchi, Malte Schramm, and Qiang Liu. "Exploratory Study of the Transverse Proximity Effect around BAL Quasars." Astrophysical Journal 933, no. 2 (July 1, 2022): 239. http://dx.doi.org/10.3847/1538-4357/ac7715.

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Abstract We aim to determine why there exists anisotropic H i absorption around quasars; i.e., the environments around quasars are highly biased toward producing strong H i absorption in the transverse direction while there exists a significant deficit of H i absorption within a few megaparsecs of quasars along the line of sight. The most plausible explanation for this opposite trend is that the transverse direction is shielded from quasar UV radiation by dust torus. However, a critical weakness of this explanation is that we do not have any information on the inclination angle of our sightline relative to the torus. In this study, we examine environments of quasars with broad-absorption troughs in their spectra (i.e., BAL quasars) because it is widely believed that BAL troughs are observed if the central continuum is viewed from the side through their powerful outflows near the dust torus. With closely separated 12 projected quasar pairs at different redshifts with a separation angle of θ < 120″, we examine H i absorption at foreground BAL quasars in the spectra of background quasars. We confirm that there exists optically thick gas around two of 12 BAL quasars, and that the mean H i absorption strength is EWrest ∼ 1 Å. This is consistent with past results of studies of non-BAL quasars, although not statistically significant. The origins of optically thick H i absorbers around BAL and non-BAL quasars could be different since their column densities are different by ∼3 orders of magnitude. A larger sample is required to narrow down possible scenarios explaining the anisotropic H i absorption around quasars.
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Hennawi, Joe. "The Circumgalactic Medium of Quasars." Proceedings of the International Astronomical Union 9, S304 (October 2013): 355. http://dx.doi.org/10.1017/s174392131400430x.

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AbstractI will argue that observations of the diffuse gas in the outskirts of quasar host galaxies, or the so called circumgalactic medium, are essential for understanding how luminous quasars evolve in a cosmological context. Such observations also provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than the complicated processes which trigger quasar activity. A novel technique will be introduced, whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30 kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around quasars. Hydrodynamical simulations of the massive dark matter halos which host luminous quasars under predict the amount of cool gas observed in quasar environs by a large factor, challenging our understanding of how massive galaxies form. I will also discuss a very sensitive search for Ly-alpha emission from the same gas which we study in absorption.
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Aldcroft, T., J. Bechtold, P. Smith, C. Foltz, and G. Schmidt. "Optical Polarization and Line Variability in Quasars with Associated Absorption." International Astronomical Union Colloquium 163 (1997): 681–82. http://dx.doi.org/10.1017/s0252921100043396.

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AbstractThe physical origin of associated absorption lines (zabs ≈ zqso) which are observed in radio-loud quasar is generally not well understood. Two observable properties, line variability and quasar optical polarization, can serve to constrain the possibilities. To this end, we have obtained high-resolution spectra (1 Å) and broad-band optical polarizations for over 30 radio-loud quasars with known CIV associated absorption. The quasars are at redshifts between about 1 and 2, and were previously observed spectroscopically at similar resolution between 1985 – 1986 by Foltz et al (1987). The associated CIV absorption systems include a variety of velocity profiles from weak single lines to very complex multi-component systems to the BAL-like profile of PHL 1157+0128. In this poster we show the first strong evidence for line variability in z > 1 radio-loud quasars. We find that in general the variability is less than ~ 30%. The optical polarization of CIV absorbed quasars is consistent with all radio-loud quasars.
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Ennesser, Lauren, Paul Martini, Andreu Font-Ribera, and Ignasi Pérez-Ràfols. "The impact and mitigation of broad-absorption-line quasars in Lyman α forest correlations." Monthly Notices of the Royal Astronomical Society 511, no. 3 (February 3, 2022): 3514–23. http://dx.doi.org/10.1093/mnras/stac301.

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ABSTRACT Correlations in and with the flux transmission of the Lyman α (Ly α) forest in the spectra of high-redshift quasars are powerful cosmological tools, yet these measurements can be compromised if the intrinsic quasar continuum is significantly uncertain. One particularly problematic case is broad-absorption-line (BAL) quasars, which exhibit blueshifted absorption associated with many spectral features that are consistent with outflows of up to ∼0.1c. As these absorption features can both fall in the forest region and be difficult to distinguish from Ly α absorption, cosmological analyses eliminate the ∼12–16 per cent of quasars that exhibit BALs. In this paper, we explore an alternate approach that includes BALs in the Ly α autocorrelation function, with the exception of the expected locations of the BAL absorption troughs. This procedure returns over 95 per cent of the path-length that is lost by the exclusion of BALs, as well as increasing the density of sightlines. We show that including BAL quasars reduces the fractional uncertainty in the covariance matrix and correlation function by 12 per cent and does not significantly change the shape of the correlation function relative to analyses that exclude BAL quasars. We also evaluate different definitions of BALs, masking strategies, and potential differences in the quasar continuum in the forest region for BALs with different amounts of absorption.
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Miller, Timothy R., Nahum Arav, Xinfeng Xu, and Gerard A. Kriss. "The contribution of quasar absorption outflows to AGN feedback." Monthly Notices of the Royal Astronomical Society 499, no. 1 (September 28, 2020): 1522–29. http://dx.doi.org/10.1093/mnras/staa2981.

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ABSTRACT Determining the distance of quasar absorption outflows from the central source (R) and their kinetic luminosity ($\dot{E}_\mathrm{\scriptstyle k}$) is crucial for understanding their contribution to active galactic nucleus (AGN) feedback. Here, we summarize the results for a sample of nine luminous quasars that were observed with the Hubble Space Telescope. We find that the outflows in more than half of the objects are powerful enough to be the main agents for AGN feedback, and that most outflows are found at R &gt; 100 pc. The sample is representative of the quasar absorption outflow population as a whole and is unbiased towards specific ranges of R and $\dot{E}_\mathrm{\scriptstyle k}$. Therefore, the analysis results can be extended to the majority of such objects, including broad absorption line quasars. We find that these results are consistent with those of another sample (seven quasars) that is also unbiased towards specific ranges of R and $\dot{E}_\mathrm{\scriptstyle k}$. Assuming that all quasars have absorption outflows, we conclude that most luminous quasars produce outflows that can contribute significantly to AGN feedback. We also discuss the criterion for whether an outflow is energetic enough to cause AGN feedback effects.
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Dissertations / Theses on the topic "Quasars : absorption"

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Storrie-Lombardi, Lisa Jo. "Absorption in the highest redshift quasars." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339500.

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Krogager, J. K., J. P. U. Fynbo, K. E. Heintz, S. Geier, C. Ledoux, P. Møller, P. Noterdaeme, B. P. Venemans, and M. Vestergaard. "THE EXTENDED HIGH A(V) QUASAR SURVEY: SEARCHING FOR DUSTY ABSORBERS TOWARD MID-INFRARED-SELECTED QUASARS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/624064.

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We present the results of a new spectroscopic survey for dusty intervening absorption systems, particularly damped Ly alpha absorbers (DLAs), toward reddened quasars. The candidate quasars are selected from mid-infrared photometry from the Wide-field Infrared Survey Explorer combined with optical and near-infrared photometry. Out of 1073 candidates, we secure low-resolution spectra for 108 using the Nordic Optical Telescope on La Palma, Spain. Based on the spectra, we are able to classify 100 of the 108 targets as quasars. A large fraction (50%) is observed to have broad absorption lines (BALs). Moreover, we find six quasars with strange breaks in their spectra, which are not consistent with regular dust reddening. Using template fitting, we infer the amount of reddening along each line of sight ranging from A(V). approximate to. 0.1 to 1.2 mag (assuming a Small Magellanic Cloud extinction curve). In four cases, the reddening is consistent with dust exhibiting the 2175 angstrom feature caused by an intervening absorber, and for two of these, an Mg II absorption system is observed at the best-fit absorption redshift. In the rest of the cases, the reddening is most likely intrinsic to the quasar. We observe no evidence for dusty DLAs in this survey. However, the large fraction of BAL quasars hampers the detection of absorption systems. Out of the 50 non-BAL quasars, only 28 have sufficiently high redshift to detect Ly alpha in absorption.
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Xu, Xinfeng. "How Do Quasars Impact Their Host Galaxies? From the Studies of Quasar Outflows in Absorption and Emission." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/98572.

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``Quasar-mode feedback'' occurs when momentum and energy from the environment of accreting supermassive black hole couple to the host galaxy. One mechanism for such a coupling is by high-velocity (up to $sim$ 0.2c) quasar-driven ionized outflows, appearing as blue-shifted absorption and emission lines in quasar spectra. Given enough energy and momentum, these outflows are capable of affecting the evolution of their host galaxies. This dissertation presents the studies of emission and absorption quasar outflows from different perspectives. (1). By conducting large broad absorption line (BAL) quasar surveys in both Sloan Digital Sky Survey and Very Large Telescopes (VLT), we determined various physics properties of quasar absorption outflows, e.g., the electron number density (ne), the distance of outflows to the central quasar ($R$), and the kinetic energy carried by the outflow ($dot{E}_{k}$). We demonstrated that half of the typical BAL outflows are situated at $R$ $>$ 100 pc, i.e., having the potential to affect the host galaxies. (2). Our group carried out a Hubble Space Telescope program (PI: Arav) for studying the outflows in the Extreme-UV, collaborating with Dr. Gerard Kriss from Space Telescope Science Institute (STScI). We developed a novel method to fit the multitude of quasar absorption troughs efficiently and accurately. We have identified the most energetic quasar-driven outflows on record and discovered the largest acceleration and velocity-shift for a quasar absorption outflow. (3). By using the VLT data, Xu led the project to study the relationships between BAL outflows and emission line outflows. We found possible connections between these two types of quasar outflows, e.g., the luminosity of the [oiii] ly 5007 emission profile decreases with increasing ne derived from the BAL outflow in the same quasar. These findings are consistent with BAL and emission outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution.
Doctor of Philosophy
Super massive black holes (SMBHs) are believed to exist in the center of almost all massive galaxies, where the brightest accreting ones are named ``quasars''. ``Quasar-mode feedback'' occurs when momentum and energy from the environment of accreting SMBHs couple to the host galaxy. One mechanism for such a coupling is by high-velocity (up to $sim$ 0.2c) quasar-driven ionized outflows, appearing as blue-shifted absorption and emission lines in quasar spectra. Given enough energy and momentum, these outflows are capable of affecting the evolution of their host galaxies. Such quasar outflows are invoked to explain a variety of observations, e.g., the chemical enrichment of the intergalactic medium (IGM), the shape of the observed quasar luminosity function, and the self-regulation of the growth of the SMBHs. In this dissertation, I focus on studying the emission and absorption outflows observed in quasars spectra, collected with the largest telescopes and most powerful instruments in the world. (1). By conducting large broad absorption line (BAL) quasar surveys in both Sloan Digital Sky Survey and Very Large Telescopes (VLT), we determined various physics properties of quasar absorption outflows, e.g., the electron number density (ne), the distance of outflows to the central quasar ($R$), and the kinetic energy carried by the outflow ($dot{E}_{k}$). We demonstrated that half of the typical BAL outflows are situated at $R$ $>$ 100 pc, i.e., having the potential to affect the host galaxies. (2). Our group carried out a Hubble Space Telescope program (PI: Arav) for studying the outflows in the Extreme-UV, collaborating with Dr. Gerard Kriss from Space Telescope Science Institute (STScI). We developed a novel method to fit the multitude of quasar absorption troughs efficiently and accurately. We have identified the most energetic quasar-driven outflows on record and discovered the largest acceleration and velocity-shift for a quasar absorption outflow. (3). By using the VLT data, Xu led the project to study the relationships between BAL outflows and emission line outflows. We found possible connections between these two types of quasar outflows, e.g., the luminosity of the [oiii] ly 5007 emission profile decreases with increasing ne derived from the BAL outflow in the same quasar. These findings are consistent with BAL and emission outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution.
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Morrison, Sean Stephen. "Using quasar absorption to study inhomogeneities in the UV background." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0501.

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L'étude du fond UV (UVB) est importante pour comprendre l'évolution de l'Univers. Le UVB évolue et est inhomogène. Cette thèse se concentre sur l'étude des inhomogénéités à grande échelle dans le UVB extragalactique, et les modifications des métaux du fait de proximité des quasars. Nous commençons par explorer les échelles dominante de ces inhomogénéités dans le UVB en combinant l'absorption intergalactique par l'hydrogène, l'hélium (HeII) et l'oxygène dans les lignes de visée du 2 quasars. Elle a révélé des inhomogénéités sur des échelles de ~10cMpc et \gtrsim 200cMpc à \bar{z}\approx 2.6. Cette analyse a également été appliquée au «HeII Gunn-Peterson trough» et n'a montré aucun signe de réionisation de HeII par rapport aux données de la «forêt» de HeII. Nous poursuivons par l'exploration de la relation directe entre les quasars et l'ionisation des métaux, en regroupant les absorbeurs de l'IGM par proximité aux quasars les plus proches dans SDSS eBOSS. Bien qu’une tendance à une absorption plus faible par des espèces caracterisées par l’ionisation élevée et par une plus grande séparation soit observée, les échantillons actuels des quasars sont incomplets, limitent donc l'interprétation détaillée de ces resultats. Cependant, nous démontrons que la contribution des quasars à le UVB peut être explorée à l'aide des métaux IGM. Finalement, nous discutons ma contribution pour atteindre échantillon complet de quasar, à l'effort de validation des outils de réduction WEAVE, ainsi qu'à la compréhension de la population des quasars et de la qualité spectrale attendues pour cet sondage. Nous terminons par un évaluation de l'impact potentiel de cet échantillon sur notre analyse
The study of the background radiation in the UV band is important for understanding the evolution of the Universe. The UV background (UVB) evolves and is inhomogeneous. It arises by virtue of quasars and star-forming galaxies, modifies the matter of the Universe by ionizing and heating gas. The focus of this thesis is the study of large-scale inhomogeneities in the extragalactic UVB and the modifications of metals by quasar proximity. We begin with the exploration of the dominant scales of inhomogeneities in the UVB by combining intergalactic absorption by hydrogen, helium (HeII), and oxygen in 2 quasar lines-of-sight. This combination was studied on various filtering scales and by comparing the lines-of-sight. It revealed inhomogeneities on scales of ~10cMpc and \gtrsim 200cMpc at \bar{z}\approx 2.6. This analysis was also applied to the HeII Gunn-Peterson trough, which showed no evidence of HeII reionization when compared to HeII forest data. We continue with an exploration of the direct relationship of quasars and metal ionization, by grouping intergalactic medium (IGM) absorbers by their proximity to their closest quasars in SDSS-IV/eBOSS. While this shows sensitivity to large-scale 3D quasar proximity, the current incomplete quasar samples limit detailed interpretation. It does demonstrate that the quasar contribution to the UVB can be explored by examining the metal absorption in the IGM. Finally, we discuss my contributions towards a complete quasar sample through validating the WEAVE reduction pipeline, as well assessing the expected quasar population and spectral quality. We close by discussing the potential impact of this sample on our analysis
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Maureira, Pinochet María José. "The structure of MgII absorption systems from spectra of gravitationally lensed quasars." Tesis, Universidad de Chile, 2012. http://www.repositorio.uchile.cl/handle/2250/111198.

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Magíster en Ciencias, Mención Astronomía
In this thesis I present a search for MgII absorption systems in the resolved spectra of 10 high redshifts gravitationally lensed quasars. The goal of the thesis is to study the spatial structure of MgII systems. The quasars were observed at resolutions $R\sim4\,500$ and $R\sim40\,000$. The search yielded a sample of 31 MgII absorption systems at $0.4
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Brienza, Marisa. "Multy-frequency continuum radio observations of broad absorption line quasars." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5672/.

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Bruni, Gabriele <1981&gt. "Origin and Nature of Radio-Loud Broad Absorption Line Quasars." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4402/1/bruni_gabriele_tesi.pdf.

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The origin of Broad Absorption Line Quasars (BAL QSOs) is still an open issue. Accounting for ~20% of the QSO population, these objects present broad absorption lines in their optical spectra generated from outflows with velocities up to 0.2 c. Nowadays, the hypotheses about their nature are principally related to orientation or evolutionary scenarios. In the first one, absorption lines are produced by outflows originated by the accretion disk, basically present in all QSOs, but seen only when they intercept the line of sight. In the second hypothesis, BAL QSOs would be young or recently re-fueled QSOs, still ejecting their dust cocoon. In this case orientation would not play a role, since the absorption features would be produced by spherically ejected matter. In this work we present the results of a multi-frequency study of a Radio-Loud BAL QSO sample, and a comparison sample of Radio-Loud non-BAL QSOs. We performed observations from radio to Near-Infrared, aiming at collecting useful informations about the orientation, the age, and the morphologies of these objects. Various techniques have been applied, including local and continental radio interferometry, single dish observations and spectroscopy. The comparison with the non-BAL QSO sample allows us to conclude that no particular orientation is present in BAL QSOs. Moreover, various morphologies and ages can be found, analogously to "normal" QSOs. Thus, the solution to this astrophysical problem seems not to reside in a peculiarity of the BAL QSO subclass with respect to non-BAL QSOs, since both the studied models do not completely explain the observed characteristics. Further experiments with future instrumentation will allow us to underline useful differences and test the physical conditions in BAL QSOs.
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Bruni, Gabriele <1981&gt. "Origin and Nature of Radio-Loud Broad Absorption Line Quasars." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4402/.

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The origin of Broad Absorption Line Quasars (BAL QSOs) is still an open issue. Accounting for ~20% of the QSO population, these objects present broad absorption lines in their optical spectra generated from outflows with velocities up to 0.2 c. Nowadays, the hypotheses about their nature are principally related to orientation or evolutionary scenarios. In the first one, absorption lines are produced by outflows originated by the accretion disk, basically present in all QSOs, but seen only when they intercept the line of sight. In the second hypothesis, BAL QSOs would be young or recently re-fueled QSOs, still ejecting their dust cocoon. In this case orientation would not play a role, since the absorption features would be produced by spherically ejected matter. In this work we present the results of a multi-frequency study of a Radio-Loud BAL QSO sample, and a comparison sample of Radio-Loud non-BAL QSOs. We performed observations from radio to Near-Infrared, aiming at collecting useful informations about the orientation, the age, and the morphologies of these objects. Various techniques have been applied, including local and continental radio interferometry, single dish observations and spectroscopy. The comparison with the non-BAL QSO sample allows us to conclude that no particular orientation is present in BAL QSOs. Moreover, various morphologies and ages can be found, analogously to "normal" QSOs. Thus, the solution to this astrophysical problem seems not to reside in a peculiarity of the BAL QSO subclass with respect to non-BAL QSOs, since both the studied models do not completely explain the observed characteristics. Further experiments with future instrumentation will allow us to underline useful differences and test the physical conditions in BAL QSOs.
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BECHTOLD, JILL ELEANOR. "HIGH RESOLUTION SPECTROSCOPY OF QUASAR ABSORPTION LINES (INTERGALACTIC MEDIUM, EXTRAGALACTIC, GALAXIES)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188085.

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This dissertation investigates the properties of the metal-containing absorption lines seen in quasar spectra which have Z(abs) < < Z(em). These systems, which probably originate in the halos of galaxies at high redshift, are then compared to observations of the halo and interstellar medium of the Milky Way. We obtained echelle spectra at the Multiple Mirror Telescope (MMT) of the Z = 1.79 absorption system of the quasar B2 1225+317. The velocity profiles showed complex structure which varied from ion to ion, with ionization and column densities varying from component to component. The relative colums were consistent with the expectations for approximately interstellar abundance, low density material, in equilibrium with the ultraviolet radiation field of a spiral galaxy for λ > 912 A, and the integrated light from QSOs at Z = 1.79 for λ < 912 A. The aggregate C IV profile has a width of about 450 km/sec, larger than that expected for a single galaxy halo, however. With the MMT spectrograph and echellette grating, and MMT echelle, we studied the properties of three other redshift systems of B2 1225+317, which are optically thin at the Lyman limit, but have saturated Lyman alpha, and unlike material in the Milky Way, have strong C IV and no detectable C II. In some cases Si III and Si IV are weakly detected. Constructing photoionization models, we derive low total densities, cloud diameters on the order of a few kiloparsecs, and abundances which are consistent with the interstellar values. We calculated the contribution of quasars to the UV radiation field as a function of redshift. The calculated field depends on a number of uncertain assumptions, which were varied in order to estimate their effect on the result. Finally, we discuss an important input into these calculations, the continuum spectral energy distribution for quasars, with particular attention to the extreme ultraviolet.
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Murphy, Michael T. Physics Faculty of Science UNSW. "Probing variations in the fundamental constants with quasar absorption lines." Awarded by:University of New South Wales. School of Physics, 2002. http://handle.unsw.edu.au/1959.4/19062.

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Precision cosmology challenges many aspects of fundamental physics. In particular, quasar absorption lines test the assumed constancy of fundamental constants over cosmological time-scales and distances. Until recently, the most reliable technique was the alkali doublet (AD) method where the measured doublet separation probes variations in the fine-structure constant, ???? e2/??c. However, the recently introduced many-multiplet (MM) method provides several advantages, including a demonstrated ???10-fold precision gain. This thesis presents detailed MM analyses of 3 independent Keck/HIRES samples containing 128 absorption systems with 0.2 > zabs > 3.7. We find 5.6 ?? statistical evidence for a smaller ?? in the absorption clouds: ????/?? = (-0.574 ?? 0.102) x 10-5. All three samples separately yield consistent, significant ????/??. The data marginally prefer constant d??/dt rather than constant ????/??. The two-point correlation function for ?? and the angular distribution of ????/?? give no evidence for spatial variations. We also analyse 21 Keck/HIRES Si iv doublets, obtaining a 3-fold relative precision gain over previous AD studies: ????/?? = (-0.5 ?? 1.3) x 10-5 for 2.0 > zabs > 3.1. Our statistical evidence for varying ?? requires careful consideration of systematic errors. Modelling demonstrates that atmospheric dispersion is potentially important. However, the quasar spectra suggest a negligible effect on ????/??. Cosmological variation in Mg isotopic abundances may affect ????/?? at zabs > 1.8. Galactic observations and theory suggest diminished 25;26Mg abundances in the low metallicity quasar absorbers. Removing 25;26Mg isotopes yields more negative ????/?? values. Overall, known systematic errors can not explain our results. We also constrain variations in y ?? ?? 2gp, comparing H i 21-cm and millimetrewave molecular absorption in 2 systems. Fitting both the H i and molecular lines yields the tightest, most reliable current constraints: ??y/y = (-0.20??0.44)x10-5 and (-0.16??0.54)x10-5 at zabs = 0.2467 and 0.6847 respectively. Possible line-ofsight velocity differences between the H i and molecular absorbing regions dominate these 1 ?? errors. A larger sample of mm/H i comparisons is required to reliably quantify this uncertainty and provide a potentially crucial check on the MM result.
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Books on the topic "Quasars : absorption"

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United States. National Aeronautics and Space Administration., ed. High-resolution spectroscopy of quasars and quasar absorption-line systems. [Washington, DC: National Aeronautics and Space Administration, 1995.

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United States. National Aeronautics and Space Administration., ed. High-resolution spectroscopy of quasars and quasar absorption-line systems. [Washington, DC: National Aeronautics and Space Administration, 1995.

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Lin, Zuo, and United States. National Aeronautics and Space Administration., eds. The dust-to-gas ratio in the damped LyÜ clouds toward the gravitationally lensed QSO 0957+561. [Washington, D.C: National Aeronautics and Space Administration, 1997.

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Lin, Zuo, and United States. National Aeronautics and Space Administration., eds. The dust-to-gas ratio in the damped LyÜ clouds toward the gravitationally lensed QSO 0957+561. [Washington, D.C: National Aeronautics and Space Administration, 1997.

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Columbia Astrophysics Laboratory (Columbia University) and United States. National Aeronautics and Space Administration., eds. Strong associated C IV absorption in low redshift quasars. [Washington, D.C.?]: National Aeronautics and Space Administration, Astrophysics Data Program, 1989.

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Ćirković, Milan M. QSO absorption spectroscopy and baryonic dark matter. Belgrad: Astronomical Observatory, 2005.

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M, Viegas Sueli, Gruenwald Ruth, and Carvalho Reinaldo R. de, eds. Young galaxies and QSO absorption-line systems: Proceedings of a workshop held in Santos, Brazil, 8-12 April 1996. San Francisco, Calif: Astronomical Society of the Pacific, 1997.

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Colloquium, International Astronomical Union. Probing galaxies through quasar absorption lines: Proceedings of the 199th colloquium of the International Astronomical Union held in Shanghai, People's Republic of China, March 14-18, 2005. Cambridge: Cambridge University Press, 2005.

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G, Meylan, and European Southern Observatory, eds. QSO absorption lines: Proceedings of the ESO workshop held at Garching, Germany, 21-24 November 1994. Berlin: Springer, 1995.

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C, Begelman Mitchell, and United States. National Aeronautics and Space Administration., eds. Radiation pressure-driven magnetic disk winds in broad absorption line quasi-stellar objects. [Washington, DC: National Aeronautics and Space Administration, 1995.

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Book chapters on the topic "Quasars : absorption"

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Turnshek, David A. "Broad Absorption Line QSOs." In Quasars, 317–30. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4716-0_76.

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Swarup, G., D. J. Saikia, M. Beltrametti, R. P. Sinha, and C. J. Salter. "Absorption Lines and the Radio Structure of Quasars." In Quasars, 195–96. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4716-0_51.

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Peterson, Bruce A. "QSO Absorption Lines: Heavy Elements and Lyman-α Clouds." In Quasars, 555–62. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4716-0_130.

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Hunstead, R. W., H. S. Murdoch, J. C. Blades, and M. Pettini. "Absorption spectrum of the z=3.78 QSO 2000-330 at High Resolution." In Quasars, 569–70. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4716-0_132.

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Blades, J. Chris, Richard W. Hunstead, Hugh S. Murdoch, and Max Pettini. "High Resolution Spectroscopy of Absorption Lines in the Z = 1.7 BL LAC Object 0215+015." In Quasars, 571–72. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4716-0_133.

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Weymann, Ray. "Broad Absorption Line Quasars: An Overview." In QSO Absorption Lines, 213–22. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-540-49458-4_45.

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Friaca, Amancio C. S., and Sueli M. Viegas. "Hot Galactic Halos and Lyman Limit Systems of Quasars." In QSO Absorption Lines, 439–40. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-540-49458-4_94.

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Combes, Françoise, Patrick Boissé, Alain Mazure, and Alain Blanchard. "The Absorption-Line Systems of Quasars." In Galaxies and Cosmology, 269–91. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-662-03190-2_11.

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Elvis, Martin, and Fabrizio Fiore. "Associated X-Ray Absorption in High Redshift Quasars." In Cold Gas at High Redshift, 239–44. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1726-2_25.

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Fried, Josef W. "Galaxies Close to the Line of Sight to two z=1 Quasars — Implications for Galactic Halos and Gravitational Lensing." In QSO Absorption Lines, 287–88. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-540-49458-4_57.

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Conference papers on the topic "Quasars : absorption"

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Ceglowski, M., Magdalena Kunert-Bajraszewska, B. Pazderska, and Marcin Gawronski. "30 GHz monitoring of broad absorption line (BAL) quasars." In 11th European VLBI Network Symposium & Users Meeting. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.178.0080.

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Danezis, E., L. Č Popović, E. Lyratzi, and M. S. Dimitrijević. "The Peculiar Absorption And Emission Phenomena From Stars To Quasars." In THE PHYSICS OF IONIZED GASES: 23rd Summer School and International Symposium on the Physics of Ionized Gases; Invited Lectures, Topical Invited Lectures and Progress Reports. AIP, 2006. http://dx.doi.org/10.1063/1.2406047.

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RISALITI, G., M. ELVIS, and E. MEMOLA. "X-RAY WEAK QUASARS: ABSORPTION OR AN INTRINSICALLY DIFFERENT SED?" In Proceedings of the Guillermo Haro Conference 2003. WORLD SCIENTIFIC, 2004. http://dx.doi.org/10.1142/9789812702432_0066.

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Bruni, Gabriele. "Morphology and orientation of radio-loud Broad Absorption Line quasars." In 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radio arrays. Trieste, Italy: Sissa Medialab, 2011. http://dx.doi.org/10.22323/1.125.0036.

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Gawronski, Marcin. "High resolution studies of Broad Absorption Lines radio-loud quasars." In 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radio arrays. Trieste, Italy: Sissa Medialab, 2011. http://dx.doi.org/10.22323/1.125.0037.

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Kunert-Bajraszewska, Magdalena. "Broad absorption line (BAL) quasars as a class of low luminosity AGNs." In 12th European VLBI Network Symposium and Users Meeting. Trieste, Italy: Sissa Medialab, 2015. http://dx.doi.org/10.22323/1.230.0008.

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Danezis, E., E. Lyratzi, L. Č Popović, M. S. Dimitrijević, A. Antoniou, Marco Antonio Gigosos, and Manuel Ángel González. "Similarity Between DACs∕SACs Phenomena in Hot Emission Stars and Quasars Absorption Lines." In SPECTRAL LINE SHAPES: Volume 15–19th International Conference on Spectral Line Shapes. AIP, 2008. http://dx.doi.org/10.1063/1.3026466.

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Reimer, A. "GeV photon absorption in cosmologically evolving quasar environments." In THE FIRST GLAST SYMPOSIUM. AIP, 2007. http://dx.doi.org/10.1063/1.2757350.

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Chartas, George, Luka Č Popović, and Milan S. Dimitrijević. "X-ray Absorption Line Diagnostics of Quasar Outflows." In SPECTRAL LINE SHAPES IN ASTROPHYSICS: VI Serbi an Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA). AIP, 2007. http://dx.doi.org/10.1063/1.2800150.

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Scaringi, Simone, Christopher E. Cottis, Christian Knigge, Michael R. Goad, and Coryn A. L. Bailer-Jones. "Broad Absorption Line Quasar catalogues with Supervised Neural Networks." In CLASSIFICATION AND DISCOVERY IN LARGE ASTRONOMICAL SURVEYS: Proceedings of the International Conference: “Classification and Discovery in Large Astronomical Surveys”. AIP, 2008. http://dx.doi.org/10.1063/1.3059042.

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Reports on the topic "Quasars : absorption"

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Miniutti, Giovanni, D. R. Ballantyne, S. W. Allen, A. C. Fabian, and R. R. Ross. Fe Emission And Ionized Excess Absorption in the Luminous Quasar 3C109 With XMM-Newton. Office of Scientific and Technical Information (OSTI), June 2006. http://dx.doi.org/10.2172/883240.

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