Structure of brightest cluster galaxies and intracluster light

The first part of this thesis presents the results of a photometric survey of Brightest Cluster Galaxies (BCGs), specifically targeting their low-surface-brightness Intracluster Light (ICL) outskirts. It is the deepest and largest sample of galaxy clusters to this date, consisting of 170 local (z<0.08) clusters in the northern hemisphere. The observations have been obtained with the Wendelstein Telescope Wide Field Imager (WWFI). Surface brightness (SB) profiles are measured down to ~2000 times fainter levels than the sky brightness in a dark, moonless night. Precise calibration is crucial here to exclude systematics. Background inhomogeneities induced by scattered light are reduced down to ∆SB > 31 g' mag arcsec^(-2) by large dithering and subtraction of night-sky flats. The extended wings of bright foreground stars are subtracted, relative bias offsets between the readout ports of the CCDs are corrected, and charge persistence is masked. For the first time, the broadening effect of the point-spread function is determined and corrected down to the faintest SBs. Residual background inhomogeneities brighter than SB_σ < 27.6 g' mag arcsec^(-2) caused by galactic cirrus are detected in front of 23% of the clusters. However, the large field of view allows discrimination between accretion signatures and galactic cirrus. I detect accretion signatures in form of tidal streams in 22%, shells in 9.4% and multiple nuclei in 47% of the brightest cluster galaxies (BCGs) and find two BCGs in 7% of the clusters. Semimajor-axis SB profiles of the BCGs and their surrounding ICL are measured down to a limiting SB of SB = 30 g' mag arcsec^(-2). The spatial resolution in the inner regions is increased by combining the WWFI light profiles with those that we measured from archival Hubble Space Telescope images or deconvolved WWFI images. I find that 71% of the BCG+ICL systems have SB profiles that are well described by a single Sérsic (SS) function, whereas 29% require a double Sérsic (DS) function to obtain a good fit. SS BCGs, having more symmetric isophotal shapes and fewer detected accretion signatures than DS BCGs, appear to have slightly more relaxed morphology than their DS counterparts. Members of the latter type encompass S2 = 52±21% of their total light in the outer Sérsic component. There is a wide scatter in transition radii r_× between the two Sérsic components and SB at the transition radii SB(r_×). The integrated brightnesses of the BCG+ICL systems correlate only weakly with S2, r_× and SB(r_×). That indicates that the outer Sérsic component is unlikely to trace the dynamically hot ICL since BCG+ICL systems grow at present epoch predominantly in their outskirts. I find that BCGs have scaling relations that differ markedly from those of normal ellipticals, likely due to their indistinguishable embedding in the ICL. The most extended BCG+ICL systems have luminosities and radii comparable to whole clusters. I use different plausible estimates for the ICL component (based on an integrated brightness threshold, SB thresholds and profile decompositions), and find that they do not affect the conclusions about the ICL properties. On average, the ICL seems to be better aligned than the BCG with the host cluster in terms of position angle and centering. That makes it a potential Dark Matter tracer. I find positive correlations between BCG+ICL brightness and cluster mass, cluster radius, cluster richness and integrated satellite brightness, confirming that BCG/ICL growth is indeed coupled with cluster growth. The second part of this thesis documents the WWFI data reduction pipeline, which I have developed during the course of this PhD thesis project and applied to process the raw observational data. It is optimized for low-SB photometry of extended objects. However, its utility is not limited to that specific science case. It can be used as a standard pipeline to reduce any WWFI images. This documentation provides detailed technical descriptions about all basic and advanced features. It is meant to serve as both a reference and a manual for the pipeline

Structure of brightest cluster galaxies and intracluster light

The first part of this thesis presents the results of a photometric survey of Brightest Cluster Galaxies (BCGs), specifically targeting their low-surface-brightness Intracluster Light (ICL) outskirts. It is the deepest and largest sample of galaxy clusters to this date, consisting of 170 local (z<0.08) clusters in the northern hemisphere. The observations have been obtained with the Wendelstein Telescope Wide Field Imager (WWFI). Surface brightness (SB) profiles are measured down to ~2000 times fainter levels than the sky brightness in a dark, moonless night. Precise calibration is crucial here to exclude systematics. Background inhomogeneities induced by scattered light are reduced down to ∆SB > 31 g' mag arcsec^(-2) by large dithering and subtraction of night-sky flats. The extended wings of bright foreground stars are subtracted, relative bias offsets between the readout ports of the CCDs are corrected, and charge persistence is masked. For the first time, the broadening effect of the point-spread function is determined and corrected down to the faintest SBs. Residual background inhomogeneities brighter than SB_σ < 27.6 g' mag arcsec^(-2) caused by galactic cirrus are detected in front of 23% of the clusters. However, the large field of view allows discrimination between accretion signatures and galactic cirrus. I detect accretion signatures in form of tidal streams in 22%, shells in 9.4% and multiple nuclei in 47% of the brightest cluster galaxies (BCGs) and find two BCGs in 7% of the clusters. Semimajor-axis SB profiles of the BCGs and their surrounding ICL are measured down to a limiting SB of SB = 30 g' mag arcsec^(-2). The spatial resolution in the inner regions is increased by combining the WWFI light profiles with those that we measured from archival Hubble Space Telescope images or deconvolved WWFI images. I find that 71% of the BCG+ICL systems have SB profiles that are well described by a single Sérsic (SS) function, whereas 29% require a double Sérsic (DS) function to obtain a good fit. SS BCGs, having more symmetric isophotal shapes and fewer detected accretion signatures than DS BCGs, appear to have slightly more relaxed morphology than their DS counterparts. Members of the latter type encompass S2 = 52±21% of their total light in the outer Sérsic component. There is a wide scatter in transition radii r_× between the two Sérsic components and SB at the transition radii SB(r_×). The integrated brightnesses of the BCG+ICL systems correlate only weakly with S2, r_× and SB(r_×). That indicates that the outer Sérsic component is unlikely to trace the dynamically hot ICL since BCG+ICL systems grow at present epoch predominantly in their outskirts. I find that BCGs have scaling relations that differ markedly from those of normal ellipticals, likely due to their indistinguishable embedding in the ICL. The most extended BCG+ICL systems have luminosities and radii comparable to whole clusters. I use different plausible estimates for the ICL component (based on an integrated brightness threshold, SB thresholds and profile decompositions), and find that they do not affect the conclusions about the ICL properties. On average, the ICL seems to be better aligned than the BCG with the host cluster in terms of position angle and centering. That makes it a potential Dark Matter tracer. I find positive correlations between BCG+ICL brightness and cluster mass, cluster radius, cluster richness and integrated satellite brightness, confirming that BCG/ICL growth is indeed coupled with cluster growth. The second part of this thesis documents the WWFI data reduction pipeline, which I have developed during the course of this PhD thesis project and applied to process the raw observational data. It is optimized for low-SB photometry of extended objects. However, its utility is not limited to that specific science case. It can be used as a standard pipeline to reduce any WWFI images. This documentation provides detailed technical descriptions about all basic and advanced features. It is meant to serve as both a reference and a manual for the pipeline

Minor Mergers are not enough: The importance of Major Mergers during Brightest Cluster Galaxy assembly

We investigate the roles of major and minor mergers during Brightest Cluster Galaxy (BCG) assembly using surface brightness profiles, line indices, and fundamental plane relations. Based on our own sample (Kluge et al.) and consistently reanalyzed SDSS data, we find that BCGs and luminous normal Ellipticals (LNEs) have similar central velocity dispersions, central absorption line strengths, and central surface brightnesses. However, BCGs are more luminous due to their much larger radial extent. These properties result in a flattening of the Faber-Jackson and Mg$_{\rm b}$-luminosity relations above 10$^{10.6}$ L$_{\odot,g'}$. We use this effect to estimate an amount of 60-80% of accreted and merged light in BCGs relative to LNEs, which agrees with results from cosmological simulations. We determine the contribution of this excess light (EL) at each radius from the difference between the surface flux profiles of BCGs and LNEs. It is small in the center but increases steeply to 50% at already $\sim$3 kpc radius. The shape of these profiles suggests that BCGs could be formed from LNEs in 3 major merger processes. This is also consistent with the mild increase of the S\'ersic indices from $n\approx4$ to $n\approx6$, as confirmed in merger simulations. We note that minor mergers cannot be the dominant origin of the BCG's EL because they deposit too few stars at intermediate radii $r\lesssim20$ kpc. The shape of the EL profile also explains a detected offset of 0.14 dex of the fundamental planes for BCGs and LNEs relative to each other.Comment: 40 pages, 20 figures, 10 tables. Submitted to ApJ

A Systematic Approach to Constructing Incremental Topology Control Algorithms Using Graph Transformation

Communication networks form the backbone of our society. Topology control algorithms optimize the topology of such communication networks. Due to the importance of communication networks, a topology control algorithm should guarantee certain required consistency properties (e.g., connectivity of the topology), while achieving desired optimization properties (e.g., a bounded number of neighbors). Real-world topologies are dynamic (e.g., because nodes join, leave, or move within the network), which requires topology control algorithms to operate in an incremental way, i.e., based on the recently introduced modifications of a topology. Visual programming and specification languages are a proven means for specifying the structure as well as consistency and optimization properties of topologies. In this paper, we present a novel methodology, based on a visual graph transformation and graph constraint language, for developing incremental topology control algorithms that are guaranteed to fulfill a set of specified consistency and optimization constraints. More specifically, we model the possible modifications of a topology control algorithm and the environment using graph transformation rules, and we describe consistency and optimization properties using graph constraints. On this basis, we apply and extend a well-known constructive approach to derive refined graph transformation rules that preserve these graph constraints. We apply our methodology to re-engineer an established topology control algorithm, kTC, and evaluate it in a network simulation study to show the practical applicability of our approachComment: This document corresponds to the accepted manuscript of the referenced journal articl

A Systematic Approach to Constructing Families of Incremental Topology Control Algorithms Using Graph Transformation

In the communication systems domain, constructing and maintaining network topologies via topology control (TC) algorithms is an important cross-cutting research area. Network topologies are usually modeled using attributed graphs whose nodes and edges represent the network nodes and their interconnecting links. A key requirement of TC algorithms is to fulfill certain consistency and optimization properties to ensure a high quality of service. Still, few attempts have been made to constructively integrate these properties into the development process of TC algorithms. Furthermore, even though many TC algorithms share substantial parts (such as structural patterns or tie-breaking strategies), few works constructively leverage these commonalities and differences of TC algorithms systematically. In previous work, we addressed the constructive integration of consistency properties into the development process. We outlined a constructive, model-driven methodology for designing individual TC algorithms. Valid and high-quality topologies are characterized using declarative graph constraints; TC algorithms are specified using programmed graph transformation. We applied a well-known static analysis technique to refine a given TC algorithm in a way that the resulting algorithm preserves the specified graph constraints. In this paper, we extend our constructive methodology by generalizing it to support the specification of families of TC algorithms. To show the feasibility of our approach, we reneging six existing TC algorithms and develop e-kTC, a novel energy-efficient variant of the TC algorithm kTC. Finally, we evaluate a subset of the specified TC algorithms using a new tool integration of the graph transformation tool eMoflon and the Simonstrator network simulation framework.Comment: Corresponds to the accepted manuscrip

Vorschläge zur Einrichtung der Publikumsbereiche für digitale Medien in der Stadtbücherei Coburg

Anlässlich der Einführung von Internet-Plätzen in der Stadtbibliothek Coburg entstand diese Diplomarbeit, die, ausgehend von einem beispielhaften Konzept, mehrere Raumprogramme und Einrichtungspläne für die elektronischen Medien entwickelt. Als Grundlage für die Einrichtung von Bildschirmplätzen werden bauliche Anforderungen zitiert und eine Typologie der verschiedenen Recherche- und Arbeitsplätze erstellt. Abschließend folgt eine Zusammenstellung wichtiger Bedingungen für Arbeitsplatzumgebungen nach der deutschen DIN-Norm. Typologien der Möblierung und der Medienarten zeigen an ausgewählten Modellen von Bibliothekseinrichtungsfirmen welche Möglichkeiten bei der Präsentation von digitalen Medien bestehen

A Trail of the Invisible: Blue Globular Clusters Trace the Radial Density Distribution of the Dark Matter -- Case Study of NGC 4278

We present new, deep optical observations of the early-type galaxy NGC 4278, which is located in a small loose group. We find that the galaxy lacks fine substructure, i.e., it appears relaxed, out to a radius of $\sim$70 kpc. Our $g$- and $i$-band surface brightness profiles are uniform down to our deepest levels of $\sim$28 mag arcsec$^{-2}$. This spans an extremely large radial range of more than 14 half-mass radii. Combined with archival globular cluster (GC) number density maps and a new analysis of the total mass distribution obtained from archival Chandra X-ray data, we find that the red GC subpopulation traces well the stellar mass density profile from 2.4 out to even 14 half-mass radii, while the blue GC subpopulation traces the total mass density profile of the galaxy over a large radial range. Our results reinforce the scenario that red GCs form mostly in-situ along with the stellar component of the galaxy, while the blue GCs are more closely aligned with the total mass distribution in the halo and were accreted along with halo matter. We conclude that for galaxies where the X-ray emission from the hot halo is too faint to be properly observable and as such is not available to measure the dark matter profile, the blue GC population can be used to trace this dark matter component out to large radii.Comment: 11 pages, 10 figures, 1 table. Accepted for publication in MNRA

The interplay of incentives and mode-choice design in self-administered mixed-mode surveys

Self-administered mixed-mode surveys are increasingly used as an alternative to face-to-face surveys for collecting data from the general population. However, little is known about how decisions regarding the incentive scheme and the mode-choice design jointly affect key outcomes such as response rates, net sample composition, and survey costs. To study this, we drew a probability sample of the residential population of the city of Mannheim, Germany (N = 2,980) and randomly assigned target persons to one of four incentive schemes (€0, €1, or €2 prepaid incentive on first contact, and €2 delayed prepaid incentive) and one of two mode-choice designs (concurrent or sequential [web-push]). Our results indicate that small prepaid monetary incentives work better in concurrent than in sequential designs. Moreover, a €2 prepaid incentive in a concurrent design proved particularly successful for older target persons, probably reinforcing their sense of trust and reciprocity, while also fitting better with their survey-mode preferences. Finally, a €2 delayed prepaid incentive in a sequential design primarily motivated target persons aged under 50 years. This combination of incentive scheme and mode-choice design also proved to be most cost-effective in that age group. Based on our results, we recommend using sampling frame information on age to address different age groups with different combinations of incentive scheme and mode-choice design. This may help to maximize response rates, achieve a balanced net sample composition, and minimize survey costs

New Function for an Old Enzyme: NEP Deficient Mice Develop Late-Onset Obesity

BACKGROUND: According to the World Health Organization (WHO) there is a pandemic of obesity with approximately 300 million people being obese. Typically, human obesity has a polygenetic causation. Neutral endopeptidase (NEP), also known as neprilysin, is considered to be one of the key enzymes in the metabolism of many active peptide hormones. METHODOLOGY/PRINCIPAL FINDINGS: An incidental observation in NEP-deficient mice was a late-onset excessive gain in body weight exclusively from a ubiquitous accumulation of fat tissue. In accord with polygenetic human obesity, mice were characterized by deregulation of lipid metabolism, higher blood glucose levels, with impaired glucose tolerance. The key role of NEP in determining body mass was confirmed by the use of the NEP inhibitor candoxatril in wild-type mice that increased body weight due to increased food intake. This is a peripheral and not a central NEP action on the switch for appetite control, since candoxatril cannot cross the blood-brain barrier. Furthermore, we demonstrated that inhibition of NEP in mice with cachexia delayed rapid body weight loss. Thus, lack in NEP activity, genetically or pharmacologically, leads to a gain in body fat. CONCLUSIONS/SIGNIFICANCE: In the present study, we have identified NEP to be a crucial player in the development of obesity. NEP-deficient mice start to become obese under a normocaloric diet in an age of 6-7 months and thus are an ideal model for the typical human late-onset obesity. Therefore, the described obesity model is an ideal tool for research on development, molecular mechanisms, diagnosis, and therapy of the pandemic obesity