203 research outputs found
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
- …