High-redshift microlensing and the spatial distribution of dark matter in the form of MACHOs

A substantial part of the dark matter of the Universe could be in the form of compact objects (MACHOs), detectable through gravitational microlensing effects as they pass through the line of sight to background light sources. So far, most attempts to model the effects of high-redshift microlensing by a cosmologically distributed population of MACHOs have assumed the compact objects to be randomly and uniformly distributed along the line of sight. Here, we present a more realistic model, in which the MACHOs are assumed to follow the spatial clustering of cold dark matter. Because of sightline-to-sightline variations in surface mass density, this scenario leads to substantial scatter in MACHO optical depths, which we quantify as a function of source redshift. We find that while optical depth estimates based on a uniform line-of-sight distribution are reasonable for the highest-redshift light sources, such estimates can be incorrect by a factor of ~2 for the nearby (z~0.25) Universe. Hence, attempts to derive the cosmological density of MACHOs from microlensing observations of only a few independent sightlines can be subject to substantial uncertainties. We also apply this model to the prediction of microlensing-induced variability in quasars not subject to macrolensing, and demonstrate that relaxing the assumption of randomly and uniformly distributed MACHOs only has a modest impact on the predicted light curve amplitudes. This implies that the previously reported problems with microlensing as the dominant mechanism for the observed long-term optical variability of quasars cannot be solved by taking the large-scale clustering of dark matter into account.Comment: 15 pages, 9 figures, accepted for publication in Astronomy & Astrophysic

Gravitational lensing as a probe of cold dark matter subhalos

In the cold dark matter scenario, dark matter halos are assembled hierarchically from smaller subunits. Some of these subunits are disrupted during the merging process, whereas others survive temporarily in the form of subhalos. A long-standing problem with this picture is that the number of subhalos predicted by simulations exceeds the number of luminous dwarf galaxies seen in the the vicinity of large galaxies like the Milky Way. Many of the subhalos must therefore have remained dark or very faint. If cold dark matter subhalos are as common as predicted, gravitational lensing may in principle offer a promising route to detection. In this review, we describe the many ways through which lensing by subhalos can manifest itself, and summarize the results from current efforts to constrain the properties of cold dark matter subhalos using such effects.Comment: 13 pages, 7 figures. Invited review/tutorial paper to appear in the Advances in Astronomy special edition "Dwarf-Galaxy Cosmology". v2: Accepted version. Minor changes only, mainly in the reference lis

What happens during a blackout: Consequences of a prolonged and wide-ranging power outage

Power outages in Europe and North America in recent years have given a lasting impression of the vulnerability of modern and high-tech societies. Although the power supply was interrupted for a week at most and only locally, massive functional and supply disruptions, threats to public order and damage amounting to billions of euros have already become apparent. This book shows what consequences a prolonged and widespread power blackout could have on society and its critical infrastructures and how Germany is prepared for such a large-scale disaster. By means of comprehensive consequence analyses, the authors drastically demonstrate that after only a few days, the supply of the population with (vital) goods and services can no longer be guaranteed in the affected area. It is also made clear that considerable efforts are required to increase the sustainability of critical infrastructures and to further optimise the capacities of the national disaster management system. The book is based on TAB Report Nr. 141 "Gefährdung und Verletzbarkeit moderner Gesellschaften - am Beispiel eines großräumigen und langandauernden Ausfalls der Stromversorgung"

Prospects for CDM sub-halo detection using high angular resolution observations

In the CDM scenario, dark matter halos are assembled hierarchically from smaller subunits. A long-standing problem with this picture is that the number of sub-halos predicted by CDM simulations is orders of magnitudes higher than the known number of satellite galaxies in the vicinity of the Milky Way. A plausible way out of this problem could be that the majority of these sub-halos somehow have so far evaded detection. If such "dark galaxies" do indeed exist, gravitational lensing may offer one of the most promising ways to detect them. Dark matter sub-halos in the 1e6 - 1e10 solar mass range should cause strong gravitational lensing on (sub)milliarcsecond scales. We study the feasibility of a strong lensing detection of dark sub-halos by deriving the image separations expected for density profiles favoured by recent simulations and comparing these to the angular resolution of both existing and upcoming observational facilities. We find that there is a reasonable probability to detect sub-halo lensing effects in high resolution observations at radio wavelengths, such as produced by the upcoming VSOP-2 satellite, and thereby test the existence of dark galaxies.Comment: 9 pages, 5 figures, Proceedings for "The Universe under the Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to be published in Journal of Physics: Conference Series by Institute of Physics Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.

Gefährdung und Verletzbarkeit moderner Gesellschaften - am Beispiel eines großräumigen und langandauernden Ausfalls der Stromversorgung. Endbericht zum TA-Projekt

In modernen, arbeitsteiligen und hochtechnisierten Gesellschaften erfolgt die Versorgung der Bevölkerung mit (lebens)notwendigen Gütern und Dienstleistungen durch ein hochentwickeltes, eng verflochtenes Netzwerk »Kritischer Infrastrukturen«. Dazu zählen u. a. Informationstechnik und Telekommunikation, Transport und Verkehr, Energieversorgung oder das Gesundheitswesen. Diese sind aufgrund ihrer internen Komplexität sowie der großen Abhängigkeit voneinander hochgradig verletzbar. Terroristische Anschläge, Naturkatastrophen oder besonders schwere Unglücksfälle haben nicht erst im zurückliegenden Jahrzehnt offenkundig gemacht, welche weitreichenden Folgen die Beeinträchtigung oder der Ausfall Kritischer Infrastrukturen für das gesellschaftliche System insgesamt haben können. Aufgrund der nahezu vollständigen Durchdringung der Lebens- und Arbeitswelt mit elektrisch betriebenen Geräten würden sich die Folgen eines langandauernden und großflächigen Stromausfalls zu einer Schadenslage von besonderer Qualität summieren. Betroffen wären alle Kritischen Infrastrukturen, und ein Kollaps der gesamten Gesellschaft wäre kaum zu verhindern. Trotz dieses Gefahren- und Katastrophenpotenzials ist ein diesbezügliches gesellschaftliches Risikobewusstsein nur in Ansätzen vorhanden. INHALT ZUSAMMENFASSUNG 3 I. EINLEITUNG 29 1. Verletzlichkeit moderner Gesellschaften 29 2. Stromausfall als Auslöser einer »nationalen Katastrophe« 31 3. Beauftragung, Vorgehen, Aufbau des Berichts 33 II. DAS SYSTEM DES KRISENMANAGEMENTS IN DEUTSCHLAND 39 1. Rechtsgrundlagen der Katastrophenbewältigung 41 2. Krisenmanagement in Deutschland: Akteure, Strukturen und Verfahren 46 III. FOLGEN EINES LANGANDAUERNDEN UND GROSSRÄUMIGEN STROMAUSFALLS 59 1. Einleitung 59 1.1 Anmerkungen zu den Ursachen eines langandauernden und großräumigen Stromausfalls 59 1.2 Kosten 61 2. Folgenanalysen ausgewählter Sektoren Kritischer Infrastrukturen 64 2.1 Informationstechnik und Telekommunikation 66 2.2 Transport und Verkehr 89 2.3 Wasserversorgung und Abwasserentsorgung 117 2.4 Lebensmittelversorgung 138 2.5 Das Gesundheitswesen 151 2.6 Finanzdienstleistungen 164 2.7 Öffentliche Einrichtungen – Fallbeispiel »Gefängnis« 184 3. Verhaltensbezogene Folgen eines Stromausfalls und ihre Bestimmungsfaktoren 192 3.1 Psychologische Bestimmungsfaktoren 193 3.2 Thesen zu den verhaltensbezogenen Folgen eines langandauernden Stromausfalls 197 3.3 Informations- und Forschungsbedarf 202 IV. VERLETZBARKEIT, BEWÄLTIGUNGSOPTIONEN UND HANDLUNGSBEDARF – SCHLUSSFOLGERUNGEN 205 1. Informationstechnik und Telekommunikation 205 2. Transport und Verkehr 207 3. Wasser und Abwasser 209 4. Versorgung mit Lebensmitteln 214 5. Gesundheitswesen 216 6. Finanzdienstleistungen 219 7. Fallbeispiel »Gefängnisse« 220 8. Bereichs- und organisationsübergreifendes Katastrophenmanagement 222 9. Vernetzte Katastrophenbewältigung –ohne Netz 225 10. Krisenkommunikation ohne Strom 230 11. Versorgung mit Treibstoff, Sicherstellung einer robusten Notstromversorgung 231 12. Inselnetze als Option zur Steigerung der Resilienz der Stromversorgung nach einem Stromausfall 233 13. Information und Sensibilisierung der Bevölkerung 235 14. Fazit 237 V. LITERATUR 239 1. In Auftrag gegebene Gutachten 239 2. Weitere Literatur 239 3. Internetadressen 252 VI. ANHANG 255 1. Tabellenverzeichnis 255 2. Abbildungsverzeichnis 255 3. Abkürzungsverzeichnis 25

Near-IR search for lensed supernovae behind galaxy clusters: III. Implications for cluster modeling and cosmology

Massive galaxy clusters at intermediate redshifts act as gravitational lenses that can magnify supernovae (SNe) occurring in background galaxies. We assess the possibility to use lensed SNe to put constraints on the mass models of galaxy clusters and the Hubble parameter at high redshift. Due to the standard candle nature of Type Ia supernovae (SNe Ia), observational information on the lensing magnification from an intervening galaxy cluster can be used to constrain the model for the cluster mass distribution. A statistical analysis using parametric cluster models was performed to investigate the possible improvements from lensed SNe Ia for the accurately modeled galaxy cluster A1689 and the less well constrained cluster A2204. Time delay measurements obtained from SNe lensed by accurately modeled galaxy clusters can be used to measure the Hubble parameter. For a survey of A1689 we estimate the expected rate of detectable SNe Ia and of multiply imaged SNe. The velocity dispersion and core radius of the main cluster potential show strong correlations with the predicted magnifications and can therefore be constrained by observations of SNe Ia in background galaxies. This technique proves especially powerful for galaxy clusters with only few known multiple image systems. The main uncertainty for measurements of the Hubble parameter from the time delay of strongly lensed SNe is due to cluster model uncertainties. For the extremely well modeled cluster A1689, a single time delay measurement could be used to determine the Hubble parameter with a precision of ~ 10%. We conclude that observations of SNe Ia behind galaxy clusters can be used to improve the mass modeling of the large scale component of galaxy clusters and thus the distribution of dark matter. Time delays from SNe strongly lensed by accurately modeled galaxy clusters can be used to measure the Hubble constant at high redshifts.Comment: 10 pages, 8 figures, 3 tables. Accepted for publication in A&

Strong lensing by subhalos in the dwarf-galaxy mass range I: Image separations

The cold dark matter scenario predicts that a large number of dark subhalos should be located within the halo of each Milky-way sized galaxy. One tell-tale signature of such dark subhalos could be additional milliarcsecond-scale image splitting of quasars previously known to be multiply-imaged on arcsecond scales. Here, we estimate the image separations for the subhalo density profiles favoured by recent N-body simulations, and compare these to the angular resolution of both existing and upcoming observational facilities. We find, that the image separations produced are very sensitive to the exact subhalo density profile assumed, but in all cases considerably smaller than previous estimates based on the premise that subhalos can be approximated by singular isothermal spheres. Only the most optimistic subhalo models produce image separations that would be detectable with current technology, and many models produce image separations that will remain unresolved with all telescopes expected to become available in the foreseeable future. Detections of dark subhalos through image-splitting effects will therefore be far more challenging than currently believed, albeit not necessarily impossible.Comment: 7 pages, 3 figures, accepted for publication in Ap

E-Commerce in Deutschland : Eine kritische Bestandsaufnahme zum elektronischen Handel

Kann das Thema E-Commerce nicht ad acta gelegt werden, nachdem der Hype um die New Economy abgeklungen ist? Dieser Band zeigt, daß E-Commerce nichts von seiner enormen Bedeutung für die Modernisierung von Wirtschaft und Gesellschaft verloren hat und nach wie vor eine wichtige Herausforderung auch für die Politik darstellt. In vielen Bereichen ist der elektronische Handel bereits fest etabliert, und die dadurch mittel- und längerfristig ausgelösten Strukturveränderungen müssen bewältigt werden. Aber die Bedingungen für den elektronischen Handel unterscheiden sich grundlegend je nach Branche, Gütern, Akteuren und den ökonomischen und politischen Rahmenbedingungen. Dieser Erkenntnis folgend wurden acht Wirtschaftsbereiche für eine nähere Analyse ausgewählt, nämlich der Handel mit Lebensmitteln, Automobilen, Arzneimitteln, Medienprodukten (Buch, Tonträger, Video), Strom, Wertpapieren und Dienstleistungen sowie die Beschaffungsprozesse im öffentlichen Bereich. Ergänzt werden diese Detailuntersuchungen um Abschätzungen zu den Folgen des E-Commerce (z.B. Arbeitsmarkteffekte, verkehrliche und ökologische Folgen). Außerdem werden Handlungsfelder für Forschung und Politik benannt, die sich insbesondere an den Auftraggeber dieser Studie, den Deutschen Bundestag, richten

Near-IR Search for Lensed Supernovae Behind Galaxy Clusters - II. First Detection and Future Prospects

Powerful gravitational telescopes in the form of massive galaxy clusters can be used to enhance the light collecting power over a limited field of view by about an order of magnitude in flux. This effect is exploited here to increase the depth of a survey for lensed supernovae at near-IR wavelengths. A pilot SN search program conducted with the ISAAC camera at VLT is presented. Lensed galaxies behind the massive clusters A1689, A1835 and AC114 were observed for a total of 20 hours split into 2, 3 and 4 epochs respectively, separated by approximately one month to a limiting magnitude J<24 (Vega). Image subtractions including another 20 hours worth of archival ISAAC/VLT data were used to search for transients with lightcurve properties consistent with redshifted supernovae, both in the new and reference data. The feasibility of finding lensed supernovae in our survey was investigated using synthetic lightcurves of supernovae and several models of the volumetric Type Ia and core-collapse supernova rates as a function of redshift. We also estimate the number of supernova discoveries expected from the inferred star formation rate in the observed galaxies. The methods consistently predict a Poisson mean value for the expected number of SNe in the survey between N_SN=0.8 and 1.6 for all supernova types, evenly distributed between core collapse and Type Ia SN. One transient object was found behind A1689, 0.5" from a galaxy with photometric redshift z_gal=0.6 +- 0.15. The lightcurve and colors of the transient are consistent with being a reddened Type IIP SN at z_SN=0.59. The lensing model predicts 1.4 magnitudes of magnification at the location of the transient, without which this object would not have been detected in the near-IR ground based search described in this paper (unlensed magnitude J~25). (abridged)Comment: Accepted by AA, matches journal versio