The Quasar-frame Velocity Distribution of Narrow CIV Absorbers

We report on a survey for narrow (FWHM < 600 km/s) CIV absorption lines in a sample of bright quasars at redshifts $1.8 \le z < 2.25$ in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow CIV absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad MgII emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find a substantial number ($\ge 43\pm6$ per cent) of absorbers with REW $> 0.3$ \AA in the velocity range +750 km/s \la v \la +12000 km/s are intrinsic to the AGN outflow. This `outflow fraction' peaks near $v=+2000$ km/s with a value of $f_{outflow} \simeq 0.81 \pm 0.13$. At velocities below $v \approx +2000$ km/s the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disk. Furthermore, we find that outflow-absorbers are on average broader and stronger than cosmologically-intervening systems. Finally, we find that $\sim 14$ per cent of the quasars in our sample exhibit narrow, outflowing CIV absorption with REW $> 0.3$\AA, slightly larger than that for broad absorption line systems.Comment: 11 pages, 9 figures, accepted for publication in MNRA

Renormalized coordinate approach to the thermalization process

We consider a particle in the harmonic approximation coupled linearly to an environment. modeled by an infinite set of harmonic oscillators. The system (particle--environment) is considered in a cavity at thermal equilibrium. We employ the recently introduced notion of renormalized coordinates to investigate the time evolution of the particle occupation number. For comparison we first present this study in bare coordinates. For a long ellapsed time, in both approaches, the occupation number of the particle becomes independent of its initial value. The value of ocupation number of the particle is the physically expected one at the given temperature. So we have a Markovian process, describing the particle thermalization with the environment. With renormalized coordinates no renormalization procedure is required, leading directly to a finite result.Comment: 16 pages, LATEX, 2 figure

Landslide Risk: Economic Valuation in the North-Eastern Zone of Medellin City

Natural disasters of a geodynamic nature can cause enormous economic and human losses. The economic costs of a landslide disaster include relocation of communities and physical repair of urban infrastructure. However, when performing a quantitative risk analysis, generally, the indirect economic consequences of such an event are not taken into account. A probabilistic approach methodology that considers several scenarios of hazard and vulnerability to measure the magnitude of the landslide and to quantify the economic costs is proposed. With this approach, it is possible to carry out a quantitative evaluation of the risk by landslides, allowing the calculation of the economic losses before a potential disaster in an objective, standardized and reproducible way, taking into account the uncertainty of the building costs in the study zone. The possibility of comparing different scenarios facilitates the urban planning process, the optimization of interventions to reduce risk to acceptable levels and an assessment of economic losses according to the magnitude of the damage. For the development and explanation of the proposed methodology, a simple case study is presented, located in north-eastern zone of the city of Medellín. This area has particular geomorphological characteristics, and it is also characterized by the presence of several buildings in bad structural conditions. The proposed methodology permits to obtain an estimative of the probable economic losses by earthquake-induced landslides, taking into account the uncertainty of the building costs in the study zone. The obtained estimative shows that the structural intervention of the buildings produces a reduction the order of 21 % in the total landslide risk. © Published under licence by IOP Publishing Ltd

Diffuse Ionized Gas in the Dwarf Irregular Galaxy DDO 53

The spectral characteristics throughout the dwarf irregular galaxy DDO 53 are studied. The results are very similar to those for other irregular galaxies: high excitation and low values of the [SII]/Halpha ratio. The most likely ionization source is photon leakage from the classical HII regions, without any other source, although the interstellar medium of the galaxy is quite perturbed. Moreover, the physical conditions throughout the galaxy do not change very much because both the photon leakage percentage and the ionization temperature are very similar. In addition, the determined metal content for two HII regions indicates that DDO 53 is a low-metallicity galaxy.Comment: 32 pages, 9 figures, 7 tables. AJ, in pres

Spatially resolved LMC star formation history: I. Outside in evolution of the outer LMC disk

We study the evolution of three fields in the outer LMC disk Rgc=3.5-6.2 Kpc. Their star formation history indicates a stellar populations gradient such that younger stellar populations are more centrally concentrated. We identify two main star forming epochs, separated by a period of lower activity between ~7 and ~4 Gyr ago. Their relative importance varies from a similar amount of stars formed in the two epochs in the innermost field, to only 40% of the stars formed in the more recent epoch in the outermost field. The young star forming epoch continues to the present time in the innermost field, but lasted only till ~0.8 and 1.3 Gyr ago at Rgc=5.5 degrees and 7.1 degrees, respectively. This gradient is correlated with the measured HI column density and implies an outside-in quenching of the star formation, possibly related to a variation of the size of the HI disk. This could either result from gas depletion due to star formation or ram-pressure stripping, or from to the compression of the gas disk as ram-pressure from the Milky Way halo acted on the LMC interstellar medium. The latter two situations may have occurred when the LMC first approached the Milky Way.Comment: 15 pages, 13 figures, 4 tables. MNRAS, in pres

Discrete Fracture Model with Anisotropic Load Sharing

A two-dimensional fracture model where the interaction among elements is modeled by an anisotropic stress-transfer function is presented. The influence of anisotropy on the macroscopic properties of the samples is clarified, by interpolating between several limiting cases of load sharing. Furthermore, the critical stress and the distribution of failure avalanches are obtained numerically for different values of the anisotropy parameter $\alpha$ and as a function of the interaction exponent $\gamma$. From numerical results, one can certainly conclude that the anisotropy does not change the crossover point $\gamma_c=2$ in 2D. Hence, in the limit of infinite system size, the crossover value $\gamma_c=2$ between local and global load sharing is the same as the one obtained in the isotropic case. In the case of finite systems, however, for $\gamma\le2$, the global load sharing behavior is approached very slowly

Heavy boson production through the collision of an ultrahigh-energy neutrino on a target nucleon

We discuss W and Z production through the deep inelastic neutrino-nucleon scattering in the context of the standard model SU(3)x SU(2)x U(1) of the strong and electroweak interactions. We find the cross section rates for the process neutrino + nucleon --> lepton(-) + W(+) + X for the case of ultrahigh-energy neutrinos colliding on a target nucleon.Comment: 20 pages, 6 figure

Bounds on the mass and abundance of dark compact objects and black holes in dwarf spheroidal galaxy halos

We establish new dynamical constraints on the mass and abundance of compact objects in the halo of dwarf spheroidal galaxies. In order to preserve kinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMi dSph) against gravitational scattering, we place upper limits on the density of compact objects as a function of their assumed mass. The mass of the dark matter constituents cannot be larger than 1000 solar masses at a halo density in UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenario in which dark halo cores are formed by two-body relaxation processes. Our bounds on the fraction of dark matter in compact objects with masses >3000 solar masses improve those based on dynamical arguments in the Galactic halo. In particular, objects with masses $\sim 10^{5}$ solar masses can comprise no more than a halo mass fraction $\sim 0.01$. Better determinations of the velocity dispersion of old overdense regions in dSphs may result in more stringent constraints on the mass of halo objects. For illustration, if the preliminary value of 0.5 km/s for the secondary peak of UMi is confirmed, compact objects with masses above $\sim 100$ solar masses could be excluded from comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter