The Fermi Bubbles. II. The Potential Roles of Viscosity and Cosmic Ray Diffusion in Jet Models

The origin of the Fermi bubbles recently detected by the Fermi Gamma-ray Space Telescope in the inner Galaxy is mysterious. In the companion paper Guo & Mathews (Paper I), we use hydrodynamic simulations to show that they could be produced by a recent powerful AGN jet event. Here we further explore this scenario to study the potential roles of shear viscosity and cosmic ray (CR) diffusion on the morphology and CR distribution of the bubbles. We show that even a relatively low level of viscosity (\mu_{visc} >~ 3 g cm^{-1} s^{-1}, or ~0.1% - 1% of Braginskii viscosity in this context) could effectively suppress the development of Kelvin-Helmholtz instabilities at the bubble surface, resulting in smooth bubble edges as observed. Furthermore, viscosity reduces circulating motions within the bubbles, which would otherwise mix the CR-carrying jet backflow near bubble edges with the bubble interior. Thus viscosity naturally produces an edge-favored CR distribution, an important ingredient to produce the observed flat gamma-ray surface brightness distribution. Generically, such a CR distribution often produces a limb-brightened gamma-ray intensity distribution. However, we show that by incorporating CR diffusion which is strongly suppressed across the bubble surface (as inferred from sharp bubble edges) but is close to canonical values in the bubble interior, we obtain a reasonably flat gamma-ray intensity profile. The similarity of the resulting CR bubble with the observed Fermi bubbles strengthens our previous result in Paper I that the Fermi bubbles were produced by a recent AGN jet event. Studies of the nearby Fermi bubbles may provide a unique opportunity to study the potential roles of plasma viscosity and CR diffusion on the evolution of AGN jets and bubbles.Comment: Revised version, accepted for publication in ApJ. 14 pages, 9 figure

Is nonhelical hydromagnetic turbulence peaked at small scales?

Nonhelical hydromagnetic turbulence without an imposed magnetic field is considered in the case where the magnetic Prandtl number is unity. The magnetic field is entirely due to dynamo action. The magnetic energy spectrum peaks at a wavenumber of about 5 times the minimum wavenumber in the domain, and not at the resistive scale, as has previously been argued. Throughout the inertial range the spectral magnetic energy exceeds the kinetic energy by a factor of about 2.5, and both spectra are approximately parallel. At first glance, the total energy spectrum seems to be close to k^{-3/2}, but there is a strong bottleneck effect and it is suggested that the asymptotic spectrum is k^{-5/3}. This is supported by the value of the second order structure function exponent that is found to be \zeta_2=0.70, suggesting a k^{-1.70} spectrum.Comment: 6 pages, 6 figure

Lensing Probabilities for Spectroscopically Selected Galaxy-Galaxy Strong Lenses

Spectroscopic galaxy-galaxy lens searches are presently the most prolific method of identifying strong lens systems in large data sets. We study the probabilities associated with these lens searches, namely the probability of identifying a candidate with rogue [OII] emission lines in a galaxy's spectrum, and the probability that the candidate will show features of strong lensing in follow-up photometric observations. We include selection effects unique to spectroscopic data, and apply them to the Sloan Lens ACS (SLACS) survey (Bolton et al. 2006). The most significant selection effect is the finite size of the spectroscopic fiber which selects against large separation lenses and results in a non-monotonic dependence of the rogue line probability on velocity dispersion. For example, with the 3 arcsec diameter SDSS fiber and 2 arcsec FWHM seeing, we find that the probability that a given LRG has a rogue [OII] line in its spectrum decreases with velocity dispersion from 150 km/s to 300 km/s and then increases up to 400 km/s for a given source size. The total probability for observing a rogue line in a single survey spectrum is ~0.9-3.0%, and the total lensing rate is ~0.5-1.3%. The range is due to uncertainties in the physical size of [OII] emission regions, and in the evolution of the [OII] luminosity function. Our estimates are a factor of ~5 higher than the results of the SLACS survey, a discrepancy which we attribute to the SLACS requirement that multiple rogue lines be observed simultaneously.Comment: 13 pages, 11 figures; submitted to Ap

Hybrids and inbred lines of silkworm (Lepidoptera: Bombyx mori L.): preliminary productive results

TIn Argentina sericulture is a new activity and is carried out by small producers as a complementary activity. The use of hybrid vigor in the silk production is used in several developed countries and the productivity and the quality depend on the hybrid involved. The objective of this work is to evaluate, in a preliminary way, some productive features of hybrids derived from inbred lines from the Faculty of Agronomy of the University of Buenos Aires. Were used four inbred and six crosses between them were bred in controlled conditions of temperature and humidity. Were fed four times a day with fresh mulberry leaves. In a 20 individuals sample four quantitative variables were measured: larval weight in the 5th stage, whole cocoon weight, cocoon without pupa weight and cocoon length. Significant differences between the means of the 10 genotypes for all the variables analyzed were detected. The crosses have shown different results depending on the crossing and the studied character. The overall result is that the hybrids productivity in these preliminary trials shows the superiority of some crosses over others and over the inbred lines.Fil: Basso, C.P. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información. Cátedra de Producciones Animales Alternativas. Buenos Aires, ArgentinaFil: Dobler, S. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información. Cátedra de Producciones Animales Alternativas. Buenos Aires, ArgentinaFil: Lopez Zieher, X. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información. Cátedra de Producciones Animales Alternativas. Buenos Aires, ArgentinaFil: Bartoloni, N. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información. Cátedra de Producciones Animales Alternativas. Buenos Aires, ArgentinaEn Argentina la sericicultura es una actividad novedosa y es llevada a cabo por pequeños productores como actividad complementaria. La utilización del vigor híbrido en la producción de seda se emplea en la mayoría de los países desarrollados y la productividad y calidad dependen del híbrido involucrado. El objetivo del trabajo es evaluar, en forma preliminar, algunas características productivas de híbridos obtenidos a partir de líneas endocriadas en la Facultad de Agronomía de la Universidad de Buenos Aires. Se utilizaron 4 líneas endocriadas y 6 cruzamientos entre ellas, criadas en condiciones de temperatura y humedad controladas. La alimentación se realizó 4 veces al día con hojas frescas de moreras. En una muestra de 20 individuos, se midieron 4 variables cuantitativas: peso larval en el 5º estadio, peso del capullo entero, peso del capullo sin pupa y largo de capullos. Se detectaron diferencias significativas entre las medias de los 10 genotipos para todas las variables analizadas. Los cruzamientos realizados han exhibido diferentes resultados según el cruzamiento y el carácter estudiado. El resultado general es que la productividad de los híbridos en estas pruebas preliminares muestra la superioridad de determinados cruzamientos sobre otros y sobre las líneas endocriadas

Sommerfeld Enhancement of DM Annihilation: Resonance Structure, Freeze-Out and CMB Spectral Bound

In the last few years there has been some interest in WIMP Dark Matter models featuring a velocity dependent cross section through the Sommerfeld enhancement mechanism, which is a nonrelativistic effect due to massive bosons in the dark sector. In the first part of this article, we find analytic expressions for the boost factor for three different model potentials, the Coulomb potential, the spherical well and the spherical cone well and compare with the numerical solution of the Yukawa potential. We find that the resonance pattern of all the potentials can be cast into the same universal form. In the second part of the article we perform a detailed computation of the Dark Matter relic density for models having Sommerfeld enhancement by solving the Boltzmann equation numerically. We calculate the expected distortions of the CMB blackbody spectrum from WIMP annihilations and compare these to the bounds set by FIRAS. We conclude that only a small part of the parameter space can be ruled out by the FIRAS observations.Comment: 15 pages, 15 figures, version accepted by JCA

Systematic effects in the extraction of the 'WMAP haze'

The extraction of a 'haze' from the WMAP microwave skymaps is based on subtraction of known foregrounds, viz. free-free (bremsstrahlung), thermal dust and synchrotron, each traced by other skymaps. While the 408 MHz all-sky survey is used for the synchrotron template, the WMAP bands are at tens of GHz where the spatial distribution of the radiating cosmic ray electrons ought to be quite different because of the energy-dependence of their diffusion in the Galaxy. The systematic uncertainty this introduces in the residual skymap is comparable to the claimed haze and can, for certain source distributions, have a very similar spectrum and latitudinal profile and even a somewhat similar morphology. Hence caution must be exercised in interpreting the 'haze' as a physical signature of, e.g., dark matter annihilation in the Galactic centre.Comment: 17 pages, 12 figures; improved diffusion model; extended discussion of spectral index maps; clarifying comments, figures and references added; to appear in JCA

A Spectroscopic Study of the Environments of Gravitational Lens Galaxies

(Abridged) We present the first results from our spectroscopic survey of the environments of strong gravitational lenses. The lens galaxy belongs to a poor group of galaxies in six of the eight systems in our sample. We discover three new groups associated with the lens galaxies of BRI 0952-0115 (five members), MG 1654+1346 (seven members), and B2114+022 (five members). We more than double the number of members for another three previously known groups around the lenses MG 0751+2716 (13 total members), PG 1115+080 (13 total members), and B1422+231 (16 total members). We determine the kinematics of the six groups, including their mean velocities, velocity dispersions, and projected spatial centroids. The velocity dispersions of the groups range from 110 +170, -80 to 470 +100, -90 km/s. In at least three of the lenses -- MG0751, PG1115, and B1422 -- the group environment significantly affects the lens potential. These lenses happen to be the quadruply-imaged ones in our sample, which suggests a connection between image configuration and environment. The lens galaxy is the brightest member in fewer than half of the groups. Our survey also allows us to assess for the first time whether mass structures along the line of sight are important for lensing. We first show that, in principle, the lens potential may be affected by line-of-sight structures over a wide range of spatial and redshift offsets from the lens. We then quantify real line-of-sight effects using our survey and find that at least four of the eight lens fields have substantial interloping structures close in projection to the lens, and at least one of those structures (in the field of MG0751) significantly affects the lens potential.Comment: Accepted for publication in the Astrophysical Journal. Figure 6 posted as a JPEG image. Requires emulateapj.st

Biological Activity of Volatiles from Marine and Terrestrial Bacteria

The antiproliferative activity of 52 volatile compounds released from bacteria was investigated in agar diffusion assays against medically important microorganisms and mouse fibroblasts. Furthermore, the activity of these compounds to interfere with the quorum-sensing-systems was tested with two different reporter strains. While some of the compounds specific to certain bacteria showed some activity in the antiproliferative assay, the compounds common to many bacteria were mostly inactive. In contrast, some of these compounds were active in the quorum-sensing-tests. γ-Lactones showed a broad reactivity, while pyrazines seem to have only low intrinsic activity. A general discussion on the ecological importance of these findings is given