The Chandra view of the 3C/FRI sample of low luminosity radio-galaxies

We present results from Chandra observations of the 3C/FRI sample of low luminosity radio-galaxies. We detected a power-law nuclear component in 12 objects out of the 18 with available data. In 4 galaxies we detected nuclear X-ray absorption at a level of about N_H= (0.2-6)e22 cm-2. X-ray absorbed sources are associated with the presence of highly inclined dusty disks (or dust filaments projected onto the nuclei) seen in the HST images. This suggests the existence of a flattened X-ray absorber, but of much lower optical depth than in classical obscuring tori. We thus have an un-obstructed view toward most FR~I nuclei while absorption plays only a marginal role in the remaining objects. Three pieces of evidence support an interpretation for a jet origin for the X-ray cores: i) the presence of strong correlations between the nuclear luminosities in the radio, optical and X-ray bands, extending over 4 orders of magnitude and with a much smaller dispersion (about 0.3 dex) when compared to similar trends found for other classes of AGNs, pointing to a common origin for the emission in the three bands; ii) the close similarity of the broad-band spectral indices with the sub-class of BL Lac objects sharing the same range of extended radio-luminosity, in accord with the FRI/BL Lacs unified model; iii) the presence of a common luminosity evolution of spectral indices in both FRI and BL Lacs. The low luminosities of the X-ray nuclei, regardless of their origin, strengthens the interpretation of low efficiency accretion in low luminosity radio-galaxies.Comment: Accepted in A&

Interacting nuclei in distant galaxies

The N-galaxy 3C 390.3 has been monitored spectroscopically since 1974 (Osterbrock, Koski and Phillips 1975; Oke 1988). From various archives and literature, it is found that the Balmer lines change their intensities and profiles in a dramatic manner. The H alpha profile is very broad and peculiar, and the relative intensities of its two humps changes consistently with time, possibly periodically. Before 1980, the blue hump was significantly stronger than the one in the red. From 1980 to 1983 the blue hump became stronger (see Oke 1988). After 1983 the H alpha profile has returned to its early shape and seems to have completed a full circle. Unlike the rapid (on the order of a month or even less) and aperiodic variation in the continuum and integrated line intensities, the change in broad profile seems slow and consistent. Taking the analogy of cataclysmic variables, the double-horn profiles have been observed in cases of interacting stars. For example, the emission lines, both in He II and hydrogen Balmer lines in GD 552 (Stover 1985) show double-horn profiles and periodical changes in their line profiles, including the change in ratios of two humps. It is understood that the D-wave components (Smak 1976) are the signature of an emitting disk and the S-wave component is from the emission at a hot spot which rotates and results in a moving component in the velocity space. The mass flow from the nearby interacting star provides the stream toward the core of a neutron star or white dwarf. Therefore, it is proposed that the variation of broad line profiles observed in 3C 390.3 may be the result of a pair of interacting massive cores. The rotational velocity dominates and produces a variable double-horn profile. However, the line widths observed in broad line radio galaxies are one order larger than that in interacting stars. The Balmer decrements imply a much smaller density (10(exp 10-12) cm(exp-3)) than that in the cataclysmic variables. The much larger velocity and much thinner density make it unlikely that the broad line emission is simply formed in an accretion disk. The authors postulate that a significant rotational motion is involved. If the observed squared profiles are indeed due to the rotational velocity field, one can naturally explain their rare occurrence

Phenomenological Renormalization Group Methods

Some renormalization group approaches have been proposed during the last few years which are close in spirit to the Nightingale phenomenological procedure. In essence, by exploiting the finite size scaling hypothesis, the approximate critical behavior of the model on infinite lattice is obtained through the exact computation of some thermal quantities of the model on finite clusters. In this work some of these methods are reviewed, namely the mean field renormalization group, the effective field renormalization group and the finite size scaling renormalization group procedures. Although special emphasis is given to the mean field renormalization group (since it has been, up to now, much more applied an extended to study a wide variety of different systems) a discussion of their potentialities and interrelations to other methods is also addressed.Comment: Review Articl

The luminosity function of cluster galaxies. II. Data reduction procedures applied to the cluster Abell 496

We initiated a large project aimed to estimate the Luminosity Function of galaxies in clusters and to evaluate its relation to cluster morphology. With this paper we deem necessary to outline the general procedures of the data reduction and details of the data analysis. The cluster sample includes the brightest southern ROSAT all-sky survey clusters with z < 0.1. These have been observed in three colours g, r, i, and mapped up to a few core radii using a mosaic of CCD frames. E/S0 galaxies in the cluster core are singled out both by morphology (for the brightest galaxies), and by colour. The details of the data reduction procedure are illustrated via the analysis of the cluster Abell 496, which has been used as a pilot cluster for the whole program. The related photometric catalogue consists of 2355 objects. The limiting magnitudes (the reference Surface Brightness is given in parenthesis) in the various colours are respectively g(25.5) = 24.14, r(25.5) = 24.46, i(25.0) = 23.75$. These correspond to the limiting absolute magnitudes -12.28, -11.96 and -12.67 (H_0=50 km/sec/Mpc).Comment: 17 pages, 19 ps figures, aa.cl

High-energy neutrinos from FR0 radio-galaxies?

The sources responsible for the emission of high-energy ($\gtrsim$ 100 TeV) neutrinos detected by IceCube are still unknown. Among the possible candidates, active galactic nuclei with relativistic jets are often examined, since the outflowing plasma seems to offer the ideal environment to accelerate the required parent high-energy cosmic rays. The non-detection of single point sources or -- almost equivalently -- the absence, in the IceCube events, of multiplets originating from the same sky position, constrains the cosmic density and the neutrino output of these sources, pointing to a numerous population of faint sources. Here we explore the possibility that FR0 radiogalaxies, the population of compact sources recently identified in large radio and optical surveys and representing the bulk of radio-loud AGN population, can represent suitable candidates for neutrino emission. Modeling the spectral energy distribution of a FR0 radiogalaxy recently associated to a $\gamma$-ray source detected by the Large Area Telescope onboard Fermi, we derive the physical parameters of its jet, in particular the power carried by it. We consider the possible mechanisms of neutrino production, concluding that $p\gamma$ reactions in the jet between protons and ambient radiation is too inefficient to sustain the required output. We propose an alternative scenario, in which protons, accelerated in the jet, escape from it and diffuse in the host galaxy, producing neutrinos as a result of $pp$ scattering with the interstellar gas, in strict analogy with the processes taking place in star-forming galaxies.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Vortex solutions of the Lifshitz-Chern-Simons theory

We study vortex-like solutions to the Lifshitz-Chern-Simons theory. We find that such solutions exists and have a logarithmically divergent energy, which suggests that a Kostelitz-Thouless transition may occur, in which voxtex-antivortex pairs are created above a critical temperature. Following a suggestion made by Callan and Wilzcek for the global U(1) scalar field model, we study vortex solutions of the Lifshitz-Chern-Simons model formulated on the hyperbolic plane, finding that, as expected, the resulting configurations have finite energy. For completeness, we also explore Lifshitz-Chern-Simons vortex solutions on the sphere.Comment: Published version, added appendix on electromagnetic duality in Lifshitz system

Generalized Pomeranchuk instabilities in graphene

We study the presence of Pomeranchuk instabilities induced by interactions on a Fermi liquid description of a graphene layer. Using a recently developed generalization of Pomeranchuk method we present a phase diagram in the space of fillings versus on-site and nearest neighbors interactions. Interestingly, we find that for both interactions being repulsive an instability region exists near the Van Hove filling, in agreement with earlier theoretical work. In contrast, near half filling, the Fermi liquid behavior appears to be stable, in agreement with theoretical results and experimental findings using ARPES. The method allows for a description of the complete phase diagram for arbitrary filling.Comment: 9 pages, 3 figure