Radiative non-isothermal Bondi accretion onto a massive black hole

In this paper, we present the classical Bondi accretion theory for the case of non-isothermal accretion processes onto a supermassive black hole (SMBH), including the effects of X-ray heating and the radiation force due to electron scattering and spectral lines. The radiation field is calculated by considering an optically thick, geometrically thin, standard accretion disk as the emitter of UV photons and a spherical central object as a source of X-ray emission. In the present analysis, the UV emission from the accretion disk is assumed to have an angular dependence, while the X-ray/central object radiation is assumed to be isotropic. This allows us to build streamlines in any angular direction we need to. The influence of both types of radiation is evaluated for different flux fractions of the X-ray and UV emissions with and without the effects of spectral line driving. We find that the radiation emitted near the SMBH interacts with the infalling matter and modifies the accretion dynamics. In the presence of line driving, a transition resembles from pure type 1 & 2 to type 5 solutions (see Fig2.1 of Frank etal. 2002), which takes place regardless of whether or not the UV emission dominates over the X-ray emission. We compute the radiative factors at which this transition occurs, and discard type 5 solution from all our models. Estimated values of the accretion radius and accretion rate in terms of the classical Bondi values are also given. The results are useful for the construction of proper initial conditions for time-dependent hydrodynamical simulations of accretion flows onto SMBH at the centre of galaxies.Comment: 10 pages, 10 figures, Accepted to be published in A&

2D kinematics of the edge-on spiral galaxy ESO 379-G006

We present a kinematical study of the nearly edge-on galaxy ESO 379-G006 that shows the existence of extraplanar ionized gas. With Fabry-Perot spectroscopy at H-alpha, we study the kinematics of ESO 379-G006 using velocity maps and position-velocity diagrams parallel to the major and to the minor axis of the galaxy. We build the rotation curve of the disk and discuss the role of projection effects due to the fact of viewing this galaxy nearly edge-on. The twisting of the isovelocities in the radial velocity field of the disk of ESO 379-G006 as well as the kinematic asymmetries found in some position-velocity diagrams parallel to the minor axis of the galaxy suggest the existence of deviations to circular motions in the disk that can be modeled and explained with the inclusion of a radial inflow probably generated by a bar or by spiral arms. We succeeded in detecting extraplanar Diffuse Ionized Gas in this galaxy. At the same time, from the analysis of position-velocity diagrams, we found some evidence that the extraplanar gas could lag in rotation velocity with respect to the midplane rotation.Comment: 61 pages, 15 figures. Accepted for publication in A

Galaxy evolution in nearby groups. II. Galaxy evolution in nearby loose groups. II. Photometric and kinematic characterization of USGC U268 and USGC U376 group members in the Leo cloud

We present the photometric and kinematic characterization of two groups, USGC U268 and USGC U376 located in different regions of the Leo cloud. U268, composed of 10 catalogued members and 11 new added members, has a small fraction (~24%) of early-type galaxies (ETGs). U376 has 16 plus 8 new added members, with ~38% of ETGs. We find the presence of significant substructures in both groups suggesting that they are likely accreting galaxies. U268 is located in a more loose environment than U376. For each member galaxy, broad band integrated and surface photometry have been obtained in far-UV and near-UV with GALEX, and in u,g, r, i, z (SDSS) bands. H_alpha imaging and 2D high resolution kinematical data have been obtained using PUMA Scanning Fabry-Perot interferometer at the 2.12 m telescope in San Pedro M\'artir, (Baja California, M\'exico). We improved the galaxy classification and we detected morphological and kinematical distortions that may be connected to either on-going and/or past interaction/accretion events or environmental induced secular evolution. U268 appears more active than U376, with a large fraction of galaxies showing interaction signatures (60% vs. 13%). The presence of bars among late-type galaxies is ~10% in U268 and ~$29% in U376. The cumulative distribution of (FUV - NUV) colours of galaxies in U268 is significantly different than that in U376 with galaxies in U268 bluer than those in U376. In the (FUV-r vs. M_r) and (NUV-r vs. M_r) planes no members of U268 are found in the `red sequence', even early-type galaxies lie in the `blue sequence' or in the `green valley'. Most (80%) of the early-type members in U376 inhabits the `red sequence, a large fraction of galaxies, of different morphological types, are located in the `green valley', while the `blue sequence' is under-populated with respect to U268.Comment: 27 pages, 11 figures, 8 tables, accepted for publication in MNRAS (abridged abstract

The influence of numerical parameters on tidally triggered bar formation

The joint influence of numerical parameters such as the number of particles N, the gravitational softening length $\epsilon$ and the time-step $\Delta t$ is investigated in the context of galaxy simulations. For isolated galaxy models we have performed a convergence study and estimated the numerical parameters ranges for which the relaxed models do not deviate significantly from its initial configuration. By fixing N, we calculate the range of the mean interparticle separation $\lambda(r)$ along the disc radius. We have found that in the simulations with N=1310720 particles $\lambda$ varies by a factor of 6, and the corresponding final Toomre's parameters Q change by only about 5 per cent. By decreasing N, the $\lambda$ and Q ranges broaden. Large $\epsilon$ and small N cause an earlier bar formation. For a given set of parameters the disc heating is smaller with the Plummer softening than with the spline softening. For galaxy collision models numerical simulations indicate that the properties of the formed bars strongly depend upon the selection of N and $\epsilon$. Large values of the gravitational softening parameter and a small number of particles results in the rapid formation of a well defined, slowly rotating bar. On the other hand, small values of $\epsilon$ produce a small, rapidly rotating disc with tightly wound spiral arms, and subsequently a weak bar emerges. We have found that by increasing N, the bar properties converge and the effect of the softening parameter diminishes. Finally, in some cases short spiral arms are observed at the ends of the bar that change periodically from trailing to leading and vice-versa - the wiggle.Comment: 17 pages, 13 figures, 3 tables. Accepted for publication in A&A. A high resolution version of the paper is found at http://www.astro.inin.mx/ruslan/tidal_bars/gabbasov.pd

On the bar pattern speed determination of NGC 3367

An important dynamic parameter of barred galaxies is the bar pattern speed. Among several methods that are used for the determination of the pattern speed the Tremaine-Weinberg method has the advantage of model independency and accuracy. In this work we apply the method to a simulated bar including gas dynamics and study the effect of 2D spectroscopy data quality on robustness of the method. We added a white noise and a Gaussian random field to the data and measured the corresponding errors in the pattern speed. We found that a signal to noise ratio in surface density ~5 introduces errors of ~20% for the Gaussian noise, while for the white noise the corresponding errors reach ~50%. At the same time the velocity field is less sensitive to contamination. On the basis of the performed study we applied the method to the NGC 3367 spiral galaxy using H{\alpha} Fabry-Perot interferometry data. We found for the pattern speed 43 \pm 6 km/s/kpc for this galaxy.Comment: Accepted for publication in ApJ. 16 pages, 16 figure

Magnetic and spectral properties of multi-sublattice oxides SrY2O4:Er3+ and SrEr2O4

SrEr2O4 is a geometrically frustrated magnet which demonstrates rather unusual properties at low temperatures including a coexistence of long- and short-range magnetic order, characterized by two different propagation vectors. In the present work, the effects of crystal fields (CF) in this compound containing four magnetically inequivalent erbium sublattices are investigated experimentally and theoretically. We combine the measurements of the CF levels of the Er3+ ions made on a powder sample of SrEr2O4 using neutron spectroscopy with site-selective optical and electron paramagnetic resonance measurements performed on single crystal samples of the lightly Er-doped nonmagnetic analogue, SrY2O4. Two sets of CF parameters corresponding to the Er3+ ions at the crystallographically inequivalent lattice sites are derived which fit all the available experimental data well, including the magnetization and dc susceptibility data for both lightly doped and concentrated samples.Comment: 14 pages, 9 figure

Cosmological simulations using a static scalar-tensor theory

We present $\Lambda$CDM $N$-body cosmological simulations in the framework of a static general scalar-tensor theory of gravity. Due to the influence of the non-minimally coupled scalar field, the gravitational potential is modified by a Yukawa type term, yielding a new structure formation dynamics. We present some preliminary results and, in particular, we compute the density and velocity profiles of the most massive group.Comment: 4 pages, 6 figures, to appear in Journal of Physics: Conference Series: VII Mexican School on Gravitation and Mathematical Physics. 26 November to 1 December 2006, Playa del Carmen, Quintana Roo, Mexic