1,721,188 research outputs found
Correcting CIV-based virial black hole masses
No full textThe CIV broad emission line is visible in optical spectra to redshifts exceeding z~5. CIV has long been known to exhibit significant displacements to the blue and these `blueshifts' almost certainly signal the presence of strong outflows. As a consequence, single-epoch virial black hole (BH) mass estimates derived from CIV velocity-widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (log = 45.5-48 erg/s), redshift 1.55000 km/s. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H) we derive an empirical correction to all CIV BH-masses. The scatter between the corrected CIV masses and the Balmer masses is 0.24 dex at low CIV blueshifts (~0 km/s) and just 0.10 dex at high blueshifts (~3000 km/s), compared to 0.40 dex before the correction. The correction depends only on the CIV line properties - i.e. full-width at half maximum and blueshift - and can therefore be applied to all quasars where CIV emission line properties have been measured, enabling the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature
Kinematics of C iv and [O iii] emission in luminous high-redshift quasars
No full textWe characterize ionized gas outflows using a large sample of ≃330 high-luminosity [45.5 < log(Lbol/erg s−1) < 49.0], high-redshift (1.5 ≲ z ≲ 4.0) quasars via their [O III]λλ4960,5008 emission. The median velocity width of the [O III] emission line is 1540 kms−1, increasing with increasing quasar luminosity. Broad, blue-shifted wings are seen in the [O III] profiles of ≃42 per cent of the sample. Rest-frame ultraviolet spectra with well-characterized C IVλ1550 emission-line properties are available for more than 210 quasars, allowing an investigation of the relationship between the broad-line region (BLR) and narrow-line region (NLR) emission properties. The [O III] blueshift is correlated with C IV blueshift, even when the dependence of both quantities on quasar luminosity has been taken into account. A strong anticorrelation between the [O III] equivalent width (EW) and C IV blueshift also exists. Furthermore, [O III] is very weak, with EW < 1 Å in ≃10 per cent of the sample, a factor of 10 higher compared to quasars at lower luminosities and redshifts. If the [O III] emission originates in an extended NLR, the observations suggest that quasar-driven winds are capable of influencing the host-galaxy environment out to kilo-parsec scales. The mean kinetic power of the ionized gas outflows is then 1044.7 erg s−1, which is ≃0.15 per cent of the bolometric luminosity of the quasar. These outflow efficiencies are broadly consistent with those invoked in current active galactic nuclei feedback models
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Quasars Probing Quasars: The Circumgalactic Medium Surrounding z ~ 2 Quasars
Full text linkModels of galaxy formation make the most direct predictions on gas related processes. Specifically, a picture on how gas flows through dark matter halos and onto galaxies to fuel star formation. A major prediction is that massive halos, including those hosting the progenitors of massive elliptical galaxies, exhibit a higher fraction of hot gas with T ~ 10^7 K. Another prediction is that some mechanism must be invoked to quench the supply of cool gas in massive systems. Under the current galaxy formation paradigm, every massive galaxy has undergone a quasar phase, making high-redshift quasars the progenitors of inactive supermassive black holes found in the center of nearly all galaxies. Moreover, quasars clustering implies M_halo = 10^12.5 M_sun, making quasar-host galaxies the progenitors of present day, massive, red and dead galaxies.The Quasars Probing Quasars survey is well-suited to examine gas related processes in the context of massive galaxy formation, as well as quasar feedback. To date the survey has selected 700 closely projected quasar pairs. To study the circumgalactic medium, a sub-sample of pairs with projected separation within 300 kpc at the foreground quasar’s redshift are selected. From the first to seventh paper in the Quasars Probing Quasars series, the statistical results had been limited to covering fractions, equivalent widths, and without precise redshift measurements of the foreground quasars. Signatures of quasar feedback in the cool circumgalactic medium had not been identified. Hence, a sub-sample of 14 pairs with echellette spectra are selected for more detailed analysis. It is found that the low and high ions roughly trace each other in velocity structure. The HI and low ion surface densities decline with projected distance. HI absorption is strong even beyond the virial radius. Unresolved Ly-alpha emission in one case and NV detection in another case together imply that a fraction of transverse sightlines are illuminated. The ionization parameter U positively correlates with impact parameter, which implies the foreground quasar does not dominate the radiation field.The circumgalactic medium is significantly enriched even beyond the virial radius, and has median [M/H] = -0.6. O/Fe is supersolar. No evolution in the total H column is found up to projected distance of 200 kpc, within which the median N_H = 10^20.5 cm^-2. Within the virial radius, the mass of the cool CGM is estimated at M_CGM = 1.5*10^11 M_sun. In two cases, detection of CII* implies electron density n_e > 10 cm^-3. Motivated by the preliminary kinematic results from this high-resolution sample, kinematic analysis of 148 pairs with precise foreground quasar redshifts is performed. The background spectra of this sample are of low and high resolution. The mean absorptions in metals exhibit velocity widths sigma_v = 300 km s^-1 , however the large widths do not require outflows. The mean absorptions have centroids redshifted from the systemic redshift by +200 km s^-1. The asymmetry may be explained if the quasars are anisotropic or intermittent, and the gas is not flowing onto the galaxy. Finally, several observational and theoretical lines of future inquiry using multiwavelength data are presented
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Reconstructing Sea Surface Temperature Images: A Masked Autoencoder Approach for Cloud Masking and Reconstruction
Full text linkThis thesis presents a new algorithm to mitigate cloud masking in the analysis of sea surface temperature (SST) data generated by remote sensing technologies such as infrared sensor satellites like the Level-2 Visible-Infrared Imager-Radiometer Suite (VIIRS). Cloud coverage interferes with the analysis of all remote sensing data using wavelengths shorter than ≈ 2 microns, significantly limiting the quantity of usable data and creating a biased geographical distribution towards equatorial and coastal regions. Prior studies have led to use of in-painting algorithms like Navier-Stokes but was typically only used up to 5% masking and had limited success. To address this issue, we propose an unsupervised machine learning algorithm called ENKI which uses a Vision Transformer with Masked Autoencoding to reconstruct pixels that are masked out by clouds. We train four different models of ENKI with training mask ratios (referred to as t) set to 10%, 35%, 50%, and 75% on a generated Ocean General Circulation Model (OGCM) dataset known as LLC4320. To evaluate performance we reconstruct LLC 4320 SST images at a patch masking ratio of 10%, 20%, 30%, 40%, 50% (referred to as p) and examine reconstruction qualitatively and statistically by calculating the root means squared error (RMSE) of reconstructed patches. Through our analysis we discover that edge patches contain a higher error rate and that a bias appears in some models when reconstructing images at p masking ratios away from their training mask ratio t. But we consistently find that at all levels of p masking ratios there is one or multiple models that create reconstructions with a mean RMSE of less than ≈ 0.03K which is lower than the estimated sensor error of VIIRS data which is ≈ 0.078 K for daytime, along scan, and ≈ 0.05 K for nighttime, along-scan. We also conclude the complexity of dynamics within an image and the p masking ratio affect RMSE with higher complexity and p masking seeing higher RMSE values. Critically, we also discover at a patch level that despite RMSE having some correlation to complexity, they are not directly proportional, and RMSE increases at a slower rate as complexity within a patch increases. Our analysis concludes that ENKI shows great promise in surpassing in-painting as a means of reconstructing cloud masking, and future research seeks to analyze ENKI’s capabilities in reconstructing real world data
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The Baryonic Cycle
No full textA review on the cycle of baryons in and around galaxies with emphasis on observations of the low redshift universe
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