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Showing 1 to 20 of 84 for “"Quasar"”.
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Monitoring Broad Absorption-Line Quasar Variability
… as broad absorption line (BAL) troughs in quasar spectra, and are measured at velocities as high as 60, 000 km s 1 at ultra-violet wavelengths. These BAL troughs have been observed to vary on both long (years) and short (weeks) rest-frame time-scales and can emerge in a quasar that had …
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Large Quasar Groups at Redshift ~ 2
… most important datasets for investigating Large Quasar Groups (LQGs) are the Sloan Digital Sky Survey (SDSS) and the 2dF Quasar Redshift Survey (2QZ). These have been used: to investigate stripe 82 of the SDSS; to discover large scale structures, specifically LQGs in the early universe; to …
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Characterising the Gravitationally Lensed Quasar Population
Understanding the co-evolution of quasars and their host galaxies remains one of astronomy's biggest questions. Observing the quasar and its host galaxy at low redshifts is relatively straightforward. However, this becomes more complex at higher redshifts. One method to study this co-evolution is …
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The transverse proximity effect in quasar spectra
… field generated by the overall population of quasars and galaxies. In the vicinity of sources of UV photons, such as luminous high-redshift quasars, the UV radiation field is enhanced due to the local source contribution. The higher degree of ionisation is visible as a reduced line density or …
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Probing quasar sight lines in three dimensions
… absorption (DLA) lines seen spectra of distant quasar are believed to arise when the sight line to the quasar goes trough the disc of a galaxy or a proto galaxy. Most of the neutral matter in the universe is contained in these clouds of neutral hydrogen that cause the absorption lines. Hence …
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Self-Similar Models of Quasar Outflow Shock Structures
… models of these structures in the context of quasar accretion disk winds; we then search for the bulk acceleration (positive or negative) of low-velocity Ca II in the quasar SDSS J030000.0+004828.0 (J0300) and compare our results to model predictions. We find a strong upper limit on the …
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Observational Studies of Rare Quasar Outflows: the FeLoBALs
The absorption spectra of quasar outflows are studied in order to determine their kinematic and energetic properties and how they affect their host galaxy and its surroundings. If an outflow is sufficiently powerful to have an effect, a process known as active galactic nucleus (AGN) feedback, it …
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Multifilter spectrophotometry of the environment of the quasar 3C281
… morphological types in a field centred on the quasar 3C281, with the intention of both testing the method and identifying members of the galaxy cluster surrounding the QSO. Photometry is performed on CCD images taken in twenty-four narrowband filters, and the resulting spectral energy …
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Quasar formation in the context of large scale structure
… results of an investigation of environments of quasars in the context of the large-scale structure in galaxy clusters. Our results are somewhat different from what was previously thought - a direct consequence of this new perspective and more powerful methods of analysis. In contrast with …
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Zooming in on quasar accretion disks using chromatic microlensing
… have prevented such a measurement for distant quasars. We present a new method for determining the size of quasar accretion disks at a range of wavelengths, thus constraining their temperature profiles. The technique uses single-epoch, multi-wavelength optical and nearinfrared imaging of …
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Parsec-scale polarization of the jet in quasar 4C 71.07
… appear to be well aligned with the jets in quasars on kiloparsec-scales, but on parsec-scales, the picture is less clear with apparently large misalignments between field and jet seen in a number of sources. This raises the question: are jet magnetic fields becoming aligned on parsec-scales? …
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A Study of Quasar Outflows: Physical Characteristics and Feedback Effects
Quasars can affect their surrounding environment through a process known as active galactic nucleus (AGN) feedback, through which the quasar can curtail the formation of stars, regulate the evolution of its host galaxy, and affect its surrounding environment in other ways. One possible mechanism …
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Size is everything : universal features of quasar microlensing with extended sources
We examine the effect that the shape of the source brightness profile has on the magnitude fluctuations of images in lens systems due to microlensing. We do this by convolving a variety of accretion disk models (including Gaussian disks, uniform disks, "cones," and a Shakura-Sunyaev thermal model) …
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Quasar Outflows: Their Scale, Behavior and Influence in the Host Galaxy
Quasar outflows are a major candidate for Active Galactic Nuclei (AGN) feedback, and their capacity to influence the evolution of their host galaxy depends on the mass-flow rate (M) and kinetic luminosity (E) of the outflowing material. Both quantities require measurement of the distance (R) to the …
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The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar Group
Quasars have been used as efficient probes of high-redshift galaxy clustering as they are known to favour overdense environments. Quasars may also trace the largescale structure of the early universe (0.4 1< z <1 2) in the form of Large Quasar Groups(LQGs), which have comparable sizes (r.J …
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Quasar continuum fitting and silicon absorption on the low redshift intergalactic medium
… We develop a new, reproducible method of quasar continuum fitting, designed to quickly identify absorption lines and measure the relative line strength (a proxy for equivalent width). Our method, which fails to identify the weakest lines, does manage to detect the strong features in a …
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The Origins and Environments of Quasar Absorption Lines in the Sloan Digital Sky Survey
… Digital Sky Survey (SDSS), tens of thousands of quasar absorption line (QAL) systems have been identified to date. QAL catalogs currently extend to z ∼ 4.6 and provide unique probes of the large scale structure of baryonic matter in the high-redshift universe; yet many critical questions …
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A synoptic survey of narrow quasar absorption lines from the Sloan Digital Sky Survey
… to study the properties of thousands of quasar absorption lines (QALs) in the time domain. Systems of QALs have proven to be one of the most sensitive and unbiased probes of baryonic matter in the high-redshift Universe. Short timescale absorption variability is one tool that has been …
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Quasar spectroscopy in UV and X-ray- probing the intergalactic medium using helium and oxygen
We employ ultraviolet (UV) and X-ray quasar spectroscopy to study the physical state of the Intergalactic Medium (IGM). First, we quantify the possibility of measuring the temperature of moderately over-dense regions of the IGM at high redshift (z [approx.] 2) using the strongest resonant …
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