High-resolution radio observations of Seyfert galaxies in the extended 12-micron sample - II. The properties of compact radio components

We discuss the properties of compact nuclear radio components in Seyfert galaxies from the extended 12-micron AGN sample of Rush et al.(1993). Our main results can be summarised as follows. Type 1 and type 2 Seyferts produce compact radio components which are indistinguishable in strength and aspect, indicating that their central engines are alike as proposed by the unification model. Infrared IRAS fluxes are more closely correlated with low-resolution radio fluxes than high-resolution radio fluxes, suggesting that they are dominated by kiloparsec-scale, extra-nuclear emission regions; extra-nuclear emission may be stronger in type 2 Seyferts. Early-type Seyfert galaxies tend to have stronger nuclear radio emission than late-type Seyfert galaxies. V-shaped extended emission-line regions, indicative of `ionisation cones', are usually found in sources with large, collimated radio outflows. Hidden broad lines are most likely to be found in sources with powerful nuclear radio sources. Type 1 and type 2 Seyferts selected by their IRAS 12-micron flux densities have well matched properties

Dynamical influence of vortex-antivortex pairs in magnetic vortex oscillators

We study the magnetization dynamics in a nanocontact magnetic vortex oscillators as function of temperature. Low temperature experiments reveal that the dynamics at low and high currents differ qualitatively. At low currents, we excite a temperature independent standard oscillation mode, consisting in the gyrotropic motion of a free layer vortex about the nanocontact. Above a critical current, a sudden jump of the frequency is observed, concomitant with a substantial increase of the frequency versus current slope factor. Using micromagnetic simulation and analytical modeling, we associate this new regime to the creation of a vortex-antivortex pair in the pinned layer of the spin valve. The vortex-antivortex distance depends on the Oersted field which favors a separation, and on the exchange bias field, which favors pair merging. The pair in the pinned layer provides an additional spin torque altering the dynamics of the free layer vortex, which can be quantitatively accounted for by an analytical model

EVN observations of low-luminosity flat-spectrum AGNs

We present and discuss the results of VLBI (EVN) observations of three low-luminosity (P(5 GHz)<10^25 W/Hz) Broad Emission Line AGNs carefully selected from a sample of flat spectrum radio sources (CLASS). Based on the total and the extended radio power at 5 GHz and at 1.4 GHz respectively, these objects should be technically classified as radio-quiet AGN and thus the origin of their radio emission is not clearly understood. The VLBI observations presented in this paper have revealed compact radio cores which imply a lower limit on the brightness temperature of about 3X10^8 K. This result rules out a thermal origin for the radio emission and strongly suggests an emission mechanism similar to that observed in more powerful radio-loud AGNs. Since, by definition, the three objects show a flat (or inverted) radio spectrum between 1.4 GHz and 8.4 GHz, the observed radio emission could be relativistically beamed. Multi-epoch VLBI observations can confirm this possibility in two years time.Comment: Accepted for publication in MNRA

Linear radio structures in selected Seyfert and LINER galaxies

High resolution MERLIN 5 GHz observations (0.04") of 7 Seyfert galaxies, selected as the ones previously showing evidence of collimated ejection, have been compared with high resolution archive HST data. The radio maps reveal rich structures in all the galaxies. NGC 2639 and TXFS 2226-184 have multiple knot parsec-scale extended structures, Mrk 1034, Mrk 1210, NGC 4922C and NGC 5506 reveal one-sided jets, while IC 1481 exhibits a jet-like extension. The close correlation between the radio-emitting relativistic plasma and the ionized gas in the inner regions of these galaxies allows us to study in detail the physics close to the center of low luminosity AGN.Comment: American Institute of Physics (AIP) Conference Series "Recent Advances in Astronomy and Astrophysics

Radio structures of the nuclei of nearby Seyfert galaxies and the nature of the missing diffuse emission

We present archival high spatial resolution VLA and VLBA data of the nuclei of seven of the nearest and brightest Seyfert galaxies in the Southern Hemisphere. At VLA resolution (~0.1 arcsec), the nucleus of the Seyfert galaxies is unresolved, with the exception of MCG-5-23-16 and NGC 7469 showing a core-jet structure. Three Seyfert nuclei are surrounded by diffuse radio emission related to star-forming regions. VLBA observations with parsec-scale resolution pointed out that in MRK 1239 the nucleus is clearly resolved into two components separated by ~30 pc, while the nucleus of NGC 3783 is unresolved. Further comparison between VLA and VLBA data of these two sources shows that the flux density at parsec scales is only 20% of that measured by the VLA. This suggests that the radio emission is not concentrated in a single central component, as in elliptical radio galaxies, and an additional low-surface brightness component must be present. A comparison of Seyfert nuclei with different radio spectra points out that the ``presence'' of undetected flux on milli-arcsecond scale is common in steep-spectrum objects, while in flat-spectrum objects essentially all the radio emission is recovered. In the steep-spectrum objects, the nature of this ``missing'' flux is likely due to non-thermal AGN-related radiation, perhaps from a jet that gets disrupted in Seyfert galaxies because of the denser environment of their spiral hosts.Comment: 13 pages, 9 figures; paper accepted for publication in MNRA

Engineering T1 lipase for degradation of poly-(R)-3-hydroxybutyrate

Enzymes with broad substrate specificities that can act on a wide range of substrates would be valuable for industrial applications. T1 lipase is known to have broad substrate specificity in its native form, with active site residues that are similar to polyhydroxylalkanoate (PHA) depolymerase (PhaZ). PhaZ6 from Pseudomonas lemoignei (PhaZ6Pl) is one of PhaZs that can degrade semicrystalline poly-(R)-3-hydroxybutyrate [P(3HB)]. The objective of this study is to enable T1 lipase to degrade semicrystalline P(3HB) similar to PhaZ6Pl while maintaining its native function. Structural analyses on PhaZ6Pl built structure revealed that it does not contain a lid, as opposed to T1 lipase. Therefore, T1 lipase were designed by removing its lid region. This was performed by using Bacillus subtilis lipase A (BSLA) as the reference for T1 lipase modification as the latter does not have a lid region and that its structure fits almost perfectly with T1 lipase based on their superimposed structures. A total of three variants of T1 lipase without lid were successfully designed, namely D1 (without α6–loop–α7), D2 (without α6) and D3 (α6 and loop) in the lid region. All the variants showed PHA depolymerase activity towards P(3HB), with D2 variant exhibiting the highest activity amongst other variants. Further analysis on D2 showed that it was able to maintain its native hydrolytic activity towards olive oil, albeit with decrement in its catalytic efficiency. Results obtained in this study highlighted the fact that native T1 lipase is a versatile hydrolase enzyme which does not only perform triglyceride degradation but also P(3HB) degradation by simply removing the helix 6 which was specifically proven to affect catalytic activity and substrate specificity of the enzyme

The Role of Pressure in GMC Formation II: The H_2 - Pressure Relation

We show that the ratio of molecular to atomic gas in galaxies is determined by hydrostatic pressure and that the relation between the two is nearly linear. The pressure relation is shown to be good over three orders of magnitude for 14 galaxies including dwarfs, HI-rich, and H_2-rich galaxies as well as the Milky Way. The sample spans a factor of five in mean metallicity. The rms scatter of individual points of the relation is only about a factor of two for all the galaxies, though some show much more scatter than others. Using these results, we propose a modified star formation prescription based on pressure determining the degree to which the ISM is molecular. The formulation is different in high and low pressure regimes defined by whether the gas is primarily atomic or primarily molecular. This formulation can be implemented in simulations and provides a more appropriate treatment of the outer regions of spiral galaxies and molecule-poor systems such as dwarf irregulars and damped Lyman-alpha systems.Comment: 14 pages, 7 figures, Accepted to the Astrophysical Journa