Transition (LINER/HII) nuclei as evolved Composite (Seyfert 2/Starburst) nuclei

We compare the circumnuclear stellar population and environmental properies of Seyfert and Composite (Seyfert + Starburst) nuclei with those of LINERs and LINER/HII transition galaxies (TOs), and discuss evidences for evolution from Seyfert/Composite to LINER/TO nuclei.Comment: 2 pages, 1 figure; to appear in the Proceedings of IAU Symp. No. 222: The Interplay among Black Holes, Stars and ISM in Galactic Nuclei, CUP, eds. T. Storchi-Bergmann, L. Ho and H. R. Schmit

Global persistence exponent of the double-exchange model

We obtained the global persistence exponent $\theta_g$ for a continuous spin model on the simple cubic lattice with double-exchange interaction by using two different methods. First, we estimated the exponent $\theta_g$ by following the time evolution of probability $P(t)$ that the order parameter of the model does not change its sign up to time $t$ $[P(t)\thicksim t^{-\theta_g}]$. Afterwards, that exponent was estimated through the scaling collapse of the universal function $L^{\theta_g z} P(t)$ for different lattice sizes. Our results for both approaches are in very good agreement each other.Comment: 4 pages, 3 figures, and 3 tables. To appear in Physical Review

Interplay between superconductivity and itinerant magnetism in underdoped Ba1−x_{1-x}Kx_xFe2_2As2_2 (x=x= 0.2) probed by the response to controlled point-like disorder

The response of superconductors to controlled introduction of point-like disorder is an important tool to probe their microscopic electronic collective behavior. In the case of iron-based superconductors (IBS), magnetic fluctuations presumably play an important role in inducing high temperature superconductivity. In some cases, these two seemingly incompatible orders coexist microscopically. Therefore, understanding how this unique coexistence state is affected by disorder can provide important information about the microscopic mechanisms involved. In one of the most studied pnictide family, hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (BaK122), this coexistence occurs over a wide range of doping levels, 0.16~$\lesssim x \lesssim$~0.25. We used relativistic 2.5 MeV electrons to induce vacancy-interstitial (Frenkel) pairs that act as efficient point-like scattering centers. Upon increasing dose of irradiation, the superconducting transition temperature $T_c$ decreases dramatically. In the absence of nodes in the order parameter this provides a strong support for a sign-changing $s_{\pm}$ pairing. Simultaneously, in the normal state, there is a strong violation of the Matthiessen's rule and a decrease (surprisingly, at the same rate as $T_c$) of the magnetic transition temperature $T_{sm}$, which indicates the itinerant nature of the long-range magnetic order. Comparison of the hole-doped BaK122 with electron-doped Ba(Fe$_x$Co$_{1-x}$)$_2$As$_2$ (FeCo122) with similar $T_{sm}\sim$110~K, $x=$0.02, reveals significant differences in the normal states, with no apparent Matthiessen's rule violation above $T_{sm}$ on the electron-doped side. We interpret these results in terms of the distinct impact of impurity scattering on the competing itinerant antiferromagnetic and $s_{\pm}$ superconducting orders

Spin-Driven Nematic Instability of the Multi-Orbital Hubbard Model: Application to Iron-Based Superconductors

Nematic order resulting from the partial melting of density-waves has been proposed as the mechanism to explain nematicity in iron-based superconductors. An outstanding question, however, is whether the microscopic electronic model for these systems -- the multi-orbital Hubbard model -- displays such an ordered state as its leading instability. In contrast to usual electronic instabilities, such as magnetic and charge order, this fluctuation-driven phenomenon cannot be captured by the standard RPA method. Here, by including fluctuations beyond RPA in the multi-orbital Hubbard model, we derive its nematic susceptibility and contrast it with its ferro-orbital order susceptibility, showing that its leading instability is the spin-driven nematic phase. Our results also demonstrate the primary role played by the $d_{xy}$ orbital in driving the nematic transition, and reveal that high-energy magnetic fluctuations are essential to stabilize nematic order in the absence of magnetic order.Comment: 8 pages, 6 figure

Divergent nematic susceptibility in an iron arsenide superconductor

Within the Landau paradigm of continuous phase transitions, ordered states of matter are characterized by a broken symmetry. Although the broken symmetry is usually evident, determining the driving force behind the phase transition is often a more subtle matter due to coupling between otherwise distinct order parameters. In this paper we show how measurement of the divergent nematic susceptibility of an iron pnictide superconductor unambiguously distinguishes an electronic nematic phase transition from a simple ferroelastic distortion. These measurements also reveal an electronic nematic quantum phase transition at the composition with optimal superconducting transition temperature.Comment: 8 pages, 8 figure

Long Term Variability of SDSS Quasars

We use a sample of 3791 quasars from the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR), and compare their photometry to historic plate material for the same set of quasars in order to study their variability properties. The time base-line we attain this way ranges from a few months to up to 50 years. In contrast to monitoring programs, where relatively few quasars are photometrically measured over shorter time periods, we utilize existing databases to extend this base-line as much as possible, at the cost of sampling per quasar. Our method, however, can easily be extended to much larger samples. We construct variability Structure Functions and compare these to the literature and model functions. From our modeling we conclude that 1) quasars are more variable toward shorter wavelengths, 2) their variability is consistent with an exponentially decaying light-curve with a typical time-scale of ~2 years, 3) these outbursts occur on typical time-scales of ~200 years. With the upcoming first data release of the SDSS, a much larger quasar sample can be used to put these conclusions on a more secure footing.Comment: 16 pages, accepted for publication in AJ, Sept issu

An atlas of Calcium triplet spectra of active galaxies

We present a spectroscopic atlas of active galactic nuclei covering the region around the 8498, 8542, 8662 Calcium triplet (CaT) lines. The sample comprises 78 objects, divided into 43 Seyfert 2s, 26 Seyfert 1s, 3 Starburst and 6 normal galaxies. The spectra pertain to the inner ~300 pc in radius, and thus sample the central kinematics and stellar populations of active galaxies. The data are used to measure stellar velocity dispersions (sigma_star) both with cross-correlation and direct fitting methods. These measurements are found to be in good agreement with each-other and with those in previous studies for objects in common. The CaT equivalent width is also measured. We find average values and sample dispersions of W_CaT of 4.6+/-2.0, 7.0 and 7.7+/-1.0 angstrons for Seyfert 1s, Seyfert 2s and normal galaxies, respectively. We further present an atlas of [SIII]\lambda 9069 emission line profiles for a subset of 40 galaxies. These data are analyzed in a companion paper which addresses the connection between stellar and Narrow Line Region kinematics, the behaviour of the CaT equivalent width as a function of sigma_star, activity type and stellar population properties.Comment: 18 pages, 10 figures, accepted for publication in MNRA

Tradisi Pasambahan pada Masyarakat Minangkabau (Studi Tentang Pelaksanaan Tradisi Pasambahan Manjapuik Marapulai di Dusun Tampuak Cubadak, Jorong Koto Gadang, Nagari Koto Tinggi, Kecamatan Baso, Kabupaten Agam, Sumatera Barat)

Tradition pasambahan manjapuik marapulai is one type of Minangkabau oral literature. This tradition is carried on in traditional Minangkabau wedding ceremony. Pasambahan happens in the show is a kind of manjapuik marapulai pasambahan reciprocated. The study took place in the Dusun Tampuak Cubadak, Jorong Koto Gadang, Nagari Koto Tinggi, Baso, Agam, West Sumatra. The purpose of this study is to investigate the implementation of manjapuik marapulai pasambahan tradition is normative and the process of inheritance traditions manjapuik pasambahan marapulai. The method used in this research is descriptive qualitative research methods. Descriptive qualitative research is research that aims to uncover the facts, circumstances, and the various phenomena that occur. Relation to the disclosure of this research is the implementation of a normative tradition and shift implementation at this time. Therefore, the author will develop concepts, collect data and facts that occurred in the study area. Data collection techniques used were in-depth interviews and observation. While descriptive qualitative data analysis techniques through data collection, data reduction, data presentation and conclusion along with suggestions. Based on the implementation of the results of research, implementation pasambahan tradition manjapuik marapulai has happened persegeran of normative rules such as roles, responsibilities, and procedures for implementation. In the process of inheritance is also influenced by the level of interest or motivation, facilities and infrastructures, media information and communication, environmental conditions of society, and the media that are used during the process of inheritance. In the tradition of pasambahan manjapuik marapulai contained values such as the value of humility, value manners, the value of deliberation, the value of accuracy, and the value of adherence to customary rules applicable