Evolution of supermassive black holes : the role of galaxy mergers

In this thesis the connections between galaxy mergers and the growth of supermassive black holes (SMBHs) are investigated. In chapter 2 we investigate the links between galaxy mergers and active galactic nuclei (AGN) as a function of luminosity, using visual classification of galaxy images and a new measure of morphological disturbance to identify mergers, testing the hypothesis that cataclysmic events such as mergers are required to drive the most rapid periods of accretion. We find no correlation between merger fraction and AGN luminosity, nor any difference in the total merger fractions of AGN and matched control galaxies. We also explore the possibility that the role of galaxy mergers evolves through cosmic time over the redshift range 0.5-2.2, finding a modest evolution, with higher redshift AGN more likely to be found in mergers than controls with 99% confidence. In chapter 3 we compare samples of simulated (Illustris) galaxies to real observations, exploring the efficacy of different techniques of merger-identification as a function of merger parameters (mass ratio, time elapsed since the merger, stellar mass, star formation rate etc.). Detailed analysis of the ability of structural parameters and visual classification to identify mergers allows for reinterpretation of observational studies in which AGN merger fractions are measured. We find the intrinsic merger fractions in relevant studies are likely several times higher than reported, with 50 20% of AGN in the local Universe triggered by galaxy mergers. In chapter 4 AGN are selected in the optical, infrared and radio to investigate the role of mergers in triggering AGN in different physical environments. We use structural parameters to estimate merger fractions. It is found that infrared-selected AGN are more likely to be associated with mergers than their controls, optically selected AGN are equivalent to controls and radio-selected AGN show fewer signs of interactions than their controls. Collectively, this is interpreted as evidence that a substantial fraction of SMBH growth is driven by galaxy mergers, but care needs to be taken to control for various observational biases, which can hide or dilute real underlying causal relations

The redshift evolution of major merger triggering of luminous AGN:a slight enhancement at z∼2

TH was supported by STFC grant ST/M503812/1 during the course of this work. VW, JM-A, MP and KR acknowledge support from the European Research Council Starting Grant SEDmorph (P.I. V. Wild).Active galactic nuclei (AGN), particularly the most luminous AGN, are commonly assumed to be triggered through major mergers, however observational evidence for this scenario is mixed. To investigate any influence of galaxy mergers on AGN triggering and luminosities through cosmic time, we present a sample of 106 luminous X-ray selected type 1 AGN from the COSMOS survey. These AGN occupy a large redshift range (0.5 < z < 2.2) and two orders of magnitude in X-ray luminosity (∼1043 - 1045 erg s-1). AGN hosts are carefully mass and redshift matched to 486 control galaxies. A novel technique for identifying and quantifying merger features in galaxies is developed, subtracting galfit galaxy models and quantifying the residuals. Comparison to visual classification confirms this measure reliably picks out disturbance features in galaxies. No enhancement of merger features with increasing AGN luminosity is found with this metric, or by visual inspection. We analyse the redshift evolution of AGN associated with galaxy mergers and find no merger enhancement in lower redshift bins. Contrarily, in the highest redshift bin (z∼2) AGN are ∼4 times more likely to be in galaxies exhibiting evidence of morphological disturbance compared to control galaxies, at 99% confidence level (∼2.4σ) from visual inspection. Since only ∼15% of these AGN are found to be in morphologically disturbed galaxies, it is implied that major mergers at high redshift make a noticeable but subdominant contribution to AGN fuelling. At low redshifts other processes dominate and mergers become a less significant triggering mechanism.PostprintPeer reviewe

Evidence-based clinical practice guideline for the use of pit-and-fissure sealants

AbstractBackgroundThis article presents evidence-based clinical recommendations for the use of pit-and-fissure sealants on the occlusal surfaces of primary and permanent molars in children and adolescents. A guideline panel convened by the American Dental Association (ADA) Council on Scientific Affairs and the American Academy of Pediatric Dentistry conducted a systematic review and formulated recommendations to address clinical questions in relation to the efficacy, retention, and potential side effects of sealants to prevent dental caries; their efficacy compared with fluoride varnishes; and a head-to-head comparison of the different types of sealant material used to prevent caries on pits and fissures of occlusal surfaces.Types of Studies ReviewedThis is an update of the ADA 2008 recommendations on the use of pit-and-fissure sealants on the occlusal surfaces of primary and permanent molars. The authors conducted a systematic search in MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and other sources to identify randomized controlled trials reporting on the effect of sealants (available on the US market) when applied to the occlusal surfaces of primary and permanent molars. The authors used the Grading of Recommendations Assessment, Development, and Evaluation approach to assess the quality of the evidence and to move from the evidence to the decisions.ResultsThe guideline panel formulated 3 main recommendations. They concluded that sealants are effective in preventing and arresting pit-and-fissure occlusal carious lesions of primary and permanent molars in children and adolescents compared with the nonuse of sealants or use of fluoride varnishes. They also concluded that sealants could minimize the progression of noncavitated occlusal carious lesions (also referred to as initial lesions) that receive a sealant. Finally, based on the available limited evidence, the panel was unable to provide specific recommendations on the relative merits of 1 type of sealant material over the others.Conclusions and Practical ImplicationsThese recommendations are designed to inform practitioners during the clinical decision-making process in relation to the prevention of occlusal carious lesions in children and adolescents. Clinicians are encouraged to discuss the information in this guideline with patients or the parents of patients. The authors recommend that clinicians reorient their efforts toward increasing the use of sealants on the occlusal surfaces of primary and permanent molars in children and adolescents

Sealants for preventing and arresting pit-and-fissure occlusal caries in primary and permanent molars

AbstractBackgroundNational Health and Nutrition Examination Survey 2011-2012 data indicated that, in the United States, nearly one-fourth of children and over one-half of adolescents experienced dental caries in their permanent teeth. The purpose of this review was to summarize the available clinical evidence regarding the effect of dental sealants for the prevention and management of pit-and-fissure occlusal carious lesions in primary and permanent molars, compared with a control without sealants, with fluoride varnishes, or with other head-to head comparisons.Type of Studies ReviewedThe authors included parallel and split-mouth randomized controlled trials that included at least 2 years of follow-up, which they identified using MEDLINE (via PubMed), Embase, LILACS, the Cochrane Central Register of Controlled Trials, and registers of ongoing trials. Pairs of reviewers independently conducted the selection of studies, data extraction, risk of bias assessments, and quality of the evidence assessments by using the Grading of Recommendations Assessment, Development and Evaluation approach.ResultsOf 2,869 records screened, the authors determined that 24 articles (representing 23 studies) proved eligible. Moderate-quality evidence suggested that participants who received sealants had a reduced risk of developing carious lesions in occlusal surfaces of permanent molars compared with those who did not receive sealants (odds ratio [OR], 0.15; 95% confidence interval [CI], 0.08-0.27) after 7 or more years of follow-up. When the authors compared studies whose investigators had compared sealants with fluoride varnishes, they found that sealants reduced the incidence of carious lesions after 7 or more years of follow-up (OR, 0.19; 95% CI, 0.07-0.51); however, this finding was supported by low-quality evidence. On the basis of the evidence, the authors could not provide a hierarchy of effectiveness among the studies whose investigators had conducted head-to-head comparisons. The investigators of 2 trials provided information about adverse events, but they did not report any adverse events.Conclusions and Practical ImplicationsAvailable evidence suggests that sealants are effective and safe to prevent or arrest the progression of noncavitated carious lesions compared with a control without sealants or fluoride varnishes. Further research is needed to provide information about the relative merits of the different types of sealant materials

Newborn screening for primary congenital hypothyroidism: estimating test performance at different TSH thresholds

Public Health Englan

Cultural landscape changes in the built environment at World Heritage Sites: Lessons from Bukovina, Romania

World Heritage Sites (WHSs) are among the most visited destinations due to their unique cultural and natural features. Their recognition by UNESCO as having ‘outstanding universal value’, while meant to help preserve their characteristics, also leads to increased visitation that may put them at risk. This study focuses on the changes in the cultural landscape as a result of tourism development at WHSs in the region of Bukovina, Romania. The paper offers a comprehensive picture by employing a mixed-method approach and analysing a wealth of data collected from key stakeholders involved in tourism development. The findings show that there is agreement among stakeholders with regard to the importance of preserving the cultural landscape of heritage destinations, with most believing that stricter measures should be put in place. However, the lack of cooperation between the key stakeholders in policy formulation and implementation could pose a threat for the sustainable development of tourism in the region. The study contributes to expanding our knowledge and understanding of the challenges faced by heritage destinations in developing countries in Eastern Europe, in particular their struggle to keep up with the modern life style while preserving their cultural features and thus the authenticity of the area

New filovirus disease classification and nomenclature.

The recent large outbreak of Ebola virus disease (EVD) in Western Africa resulted in greatly increased accumulation of human genotypic, phenotypic and clinical data, and improved our understanding of the spectrum of clinical manifestations. As a result, the WHO disease classification of EVD underwent major revision

Determining crystal structures through crowdsourcing and coursework

We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit players achieved the most accurate structure. Analysing the target protein of the competition, YPL067C, uncovered a new family of histidine triad proteins apparently involved in the prevention of amyloid toxicity. From this study, we conclude that crystallographers can utilize crowdsourcing to interpret electron density information and to produce structure solutions of the highest quality