Growth of Nanosize and Colloid Particles by Controlled Addition of Singlets

We outline a theoretical framework for estimating the evolution of the particle size distribution in colloid and nanoparticle synthesis, when the primary growth mode is by externally controlled addition of singlet building blocks. The master equations, analyzed in the leading "non-diffusive" expansion approximation, are reduced to a set of easily numerically programmable relations that yield information on the time evolution of the particle size distribution.Comment: 9 pages in PD

The 2XMMi/SDSS Galaxy Cluster Survey. III. Clusters associated with spectroscopically targeted luminous red galaxies in SDSS-DR10

We present a sample of 383 X-ray selected galaxy groups and clusters with spectroscopic redshift measurements (up to z ~ 0.79) from the 2XMMi/SDSS Galaxy Cluster Survey. The X-ray cluster candidates were selected as serendipitously detected sources from the 2XMMi-DR3 catalogue that were located in the footprint of the Sloan Digital Sky Survey (SDSS-DR7). The cluster galaxies with available spectroscopic redshifts were selected from the SDSS-DR10. We developed an algorithm for identifying the cluster candidates that are associated with spectroscopically targeted luminous red galaxies and for constraining the cluster spectroscopic redshift. A cross-correlation of the constructed cluster sample with published optically selected cluster catalogues yielded 264 systems with available redshifts. The present redshift measurements are consistent with the published values. The current cluster sample extends the optically confirmed cluster sample from our cluster survey by 67 objects. Moreover, it provides spectroscopic confirmation for 78 clusters among our published cluster sample, which previously had only photometric redshifts. Of the new cluster sample that comprises 67 systems, 55 objects are newly X-ray discovered clusters and 52 systems are sources newly discovered as galaxy clusters in optical and X-ray wavelengths. Based on the measured redshifts and the fluxes given in the 2XMMi-DR3 catalogue, we estimated the X-ray luminosities and masses of the cluster sample.Comment: A&A in press, 12 pages, 15 figures, 1 table, http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361/20132297

The 2XMMi/SDSS Galaxy Cluster Survey. II. The optically confirmed cluster sample and the L_X-T relation

We compile a sample of X-ray-selected galaxy groups and clusters from the XMM-Newton serendipitous source catalogue (2XMMi-DR3) with optical confirmation and redshift measurement from the Sloan Digital Sky Survey (SDSS). The X-ray cluster candidates were selected from the 2XMMi-DR3 catalogue in the footprint of the SDSS-DR7. We developed a finding algorithm to search for overdensities of galaxies at the positions of the X-ray cluster candidates in the photometric redshift space and to measure the redshifts of the clusters from the SDSS data. The detection algorithm provides the photometric redshift of 530 galaxy clusters. Of these, 310 clusters have a spectroscopic redshift for at least one member galaxy. About 75 percent of the optically confirmed cluster sample are newly discovered X-ray clusters. Moreover, 301 systems are known as optically selected clusters in the literature while the remainder are new discoveries in X-ray and optical bands. The optically confirmed cluster sample spans a wide redshift range 0.03-0.70 (median z=0.32). In this paper, we present the catalogue of X-ray-selected galaxy groups and clusters from the 2XMMi/SDSS galaxy cluster survey. The catalogue has two subsamples: (i) a cluster sample comprising 345 objects with their X-ray spectroscopic temperature and flux from the spectral fitting, and (ii) a cluster sample consisting of 185 systems with their X-ray flux from the 2XMMi-DR3 catalogue, because their X-ray data are insufficient for spectral fitting. The updated L_X-T relation of the current sample with X-ray spectroscopic parameters is presented. We see no evidence for evolution in the slope and intrinsic scatter of the L_X-T relation with redshift when excluding the low-luminosity groups.Comment: A&A in press, 18 pages, 25 figures, 3 tables (revised version after language editing

Distant clusters of galaxies in the 2XMM/SDSS footprint: follow-up observations with the LBT

Context: Galaxy clusters at high redshift are important to test cosmological models and models for the growth of structure. They are difficult to find in wide-angle optical surveys, however, leaving dedicated follow-up of X-ray selected candidates as one promising identification route. Aims: We aim to increase the number of galaxy clusters beyond the SDSS-limit, z ~ 0.75. Methods: We compiled a list of extended X-ray sources from the 2XMMp catalogue within the footprint of the Sloan Digital Sky Survey. Fields without optical counterpart were selected for further investigation. Deep optical imaging and follow-up spectroscopy were obtained with the Large Binocular Telescope, Arizona (LBT), of those candidates not known to the literature. Results: From initially 19 candidates, selected by visually screening X-ray images of 478 XMM-Newton observations and the corresponding SDSS images, 6 clusters were found in the literature. Imaging data through r,z filters were obtained for the remaining candidates, and 7 were chosen for multi-object (MOS) spectroscopy. Spectroscopic redshifts, optical magnitudes, and X-ray parameters (flux, temperature, and luminosity) are presented for the clusters with spectroscopic redshifts. The distant clusters studied here constitute one additional redshift bin for studies of the L-T relation, which does not seem to evolve from high to low redshifts. ...Comment: This is a abridged version of the paper. The full version can be downloaded at the following URL: https://cloud.aip.de/index.php/s/2Btv7ST1KTLHfT

The unusual host galaxy of the BL Lac object PKS 1413+135

The BL Lacertae object PKS 1413+135 is associated with a disk dominated galaxy which heavily absorbs the BL Lac nucleus at optical and X-ray wavelengths. It has been argued whether this galaxy is actually the host galaxy of PKS 1413+135 or whether the BL Lac is a background QSO, gravitationally lensed by the apparent host galaxy. We have obtained deep high resolution H-band images of this unusual BL Lac object using the UKIRT IRCAM3. Our observations show that the BL Lac nucleus is centered within < 0.05 arcsec of the galaxy. Based on this result we assess the probability for the lensing scenario and come to the conclusion that the disk galaxy is indeed the host of PKS 1413+135. The galaxy shows peanut-shaped isophotes, suggesting the presence of a central bar which is a common feature of AGNComment: accepted for publication in MNRAS, 5 pages with 2 Postscript figure

Strange magnification pattern in the large separation lens SDSS J1004+4112 from optical to X-rays

We present simultaneous XMM-Newton UV and X-ray observations of the quadruply lensed quasar SDSS J1004+4112 (RBS 825). Simultaneously with the XMM-Newton observations we also performed integral field spectroscopy on the two closest lens images A and B using the Calar Alto PMAS spectrograph. In X-rays the widely spaced components C and D are clearly resolved, while the closer pair of images A and B is marginally resolved in the XMM-EPIC images. The integrated X-ray flux of the system has decreased by a factor of 6 since it was observed in the ROSAT All Sky Survey in 1990, while the X-ray spectrum became much harder with the power law index evolving from Gamma=-2.3 to -1.86. By deblending the X-ray images of the lensed QSO we find that the X-ray flux ratios between the lens images A and B are significantly different from the simultaneously obtained UV ratios and previously measured optical flux ratios. Our optical spectrum of lens image A shows an enhancement in the blue emission line wings, which has been observed in previous epochs as a transient feature. We propose a scenario where intrinsic UV and X-ray variability gives rise to line variations which are selectively magnified in image A by microlensing. The extended emission of the lensing cluster of galaxies is clearly detected in the EPIC images, we measure a 0.5-2.0 keV luminosity of 1.4 E44 erg/s. Based on the cluster X-ray properties, we estimate a mass of 2-6 E14 solar masses.Comment: 11 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

Neglecting the \u27Right on Which All Other Rights Depend\u27: Press Freedom in the International Human Rights Discourse

Historically and philosophically, press freedom has closely been linked to the fight against tyranny and the advancement of human rights. But coverage of press freedom as a distinct human right is surprisingly absent from scholarship and the human rights agenda. This dissertation fills this gap in the academic literature by examining why press freedom has not become part of the established international human rights debate, despite its centrality to democratic theory. It does so in three steps: First, it outlines the distinction between press freedom and other human rights to which it is usually subjugated, like free speech and freedom of information, thus highlighting the importance of press freedom as a distinct human right. Second, it examines in detail how press freedom is treated at the UN, and traces the historical path of the freedom of the press debate at the UN to determine how and why press freedom is neglected. Third, the dissertation examines the roles of transnational actors, the media and NGOs, in the context of the international promotion of press freedom. The dissertation finds that, despite the popularity of ideational explanations in the field of human rights studies, in the case of promoting press freedom, considerations of power and strategic interests rather than ideas dominate state behavior. No state, not even Western liberal ones, goes out of its way to promote press freedom, because it undermines state power. The dissertation further finds that there is no domestic constituency for press freedom and that human rights NGOs as well as the media themselves do surprisingly little to promote press freedom. These findings imply that the current place of press freedom in the human rights discourse needs to be rethought. The findings also have implications for the idea of democracy and human rights and for their future not only in developing countries, but in liberal democracies as well. If the goal is to implement these ideas, the `right on which all other rights depend\u27 should be at the center of human rights advocacy at home and abroad

2XMM J083026+524133: The most X-ray luminous cluster at redshift 1

In the distant universe X-ray luminous clusters of galaxies are rare objects. Large area surveys are therefore needed to probe the high luminosity end of the cluster population at redshifts z >= 1. We correlated extended X-ray sources from the second XMM-Newton source catalogue (2XMM) with the SDSS in order to identify new clusters of galaxies. Distant cluster candidates in empty SDSS fields were imaged in the R and z bands with the Large Binocular Telescope. We extracted the X-ray spectra of the cluster candidates and fitted thermal plasma models to the data. We determined the redshift 0.99 +-0.03 for 2XMM J083026+524133 from its X-ray spectrum. With a bolometric luminosity of 1.8 x 10^45 erg/sec this is the most X-ray luminous cluster at redshifts z >= 1. We measured a gas temperature of 8.2 +- 0.9 keV and and estimate a cluster mass M(500) = 5.6 x 10^14 M(solar). The optical imaging revealed a rich cluster of galaxies.Comment: New version, as accepted for publication in Astronomy & Astrophysic