114 research outputs found
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
A Search for Kinematic Evidence of Radial Gas Flows in Spiral Galaxies
CO and HI velocity fields of seven nearby spiral galaxies, derived from
radio-interferometric observations, are decomposed into Fourier components
whose radial variation is used to search for evidence of radial gas flows.
Additional information provided by optical or near-infrared isophotes is also
considered, including the relationship between the morphological and kinematic
position angles. To assist in interpreting the data, we present detailed
modeling that demonstrates the effects of bar streaming, inflow, and a warp on
the observed Fourier components. We find in all of the galaxies evidence for
either elliptical streaming or a warped disk over some range in radius, with
deviations from pure circular rotation at the level of ~20-60 km/s. Evidence
for kinematic warps is observed in several cases well inside R_{25}. No
unambiguous evidence for radial inflows is seen in any of the seven galaxies,
and we are able to place an upper limit of ~5-10 km/s (3-5% of the circular
speed) on the magnitude of any radial inflow in the inner regions of NGC 4414,
5033 and 5055. We conclude that the inherent non-axisymmetry of spiral galaxies
is the greatest limitation to the direct detection of radial inflows.Comment: 22 emulateapj pages with bitmapped colour figures, to appear in ApJ
(April 2004). For full resolution figures go to
http://www.atnf.csiro.au/people/twong/preprints
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
The effects of microgravity on thermostable T1 lipase protein crystal
The quest for the characterizations of intrinsically thermostable T1 lipase either physicochemically or structurally is a prominent task. T1 lipase can be effectively used as an additive in detergent formulations, and as a biocatalyst for natural oil-based pharmaceuticals, foods and fine chemicals. The thermoalkaliphilic T1 lipase gene of Geobacillus zalihae sp. nov. strain T1 T (Rahman et al., 2007) was overexpressed in the pGEX vector in E. coli (Loew et al., 2004). Expression of T1 lipase as a glutathione S-transferase (GST) fusion protein in prokaryotic systems was expected to allow rapid purification of recombinant T1 lipase through affinity chromatography. High-yield purification of T1 lipase was achieved through two-step affinity chromatography with a final specific activity and yield of 958.2 U/mg and 51.5%, respectively. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the purified T1 lipase appeared as 39 kDa after the removal of the 26 kDa GST tag from the digested fusion lipase. However, the native molecular weight of T1 lipase was determined to be approximately 43 kDa by gel filtration chromatography. The size was similar to its predicted molecular weight, but slightly bigger than its denatured form obtained through SDS-PAGE (Leow et al., 2007)
Evidence for an outflow from the Seyfert galaxy NGC 4051
New observations using narrow band imaging, long-slit spectroscopy and MERLIN
observations of the nuclear region of the Seyfert galaxy NGC~4051 have been
made. An edge brightened, triangular region of ionized gas extending 420 pc
from the centre of the galaxy has been detected. Long-slit spectra of this
ionised gas, taken at 1.5\arcsec\ from the core, show the \oiii\ emission line
to consist of two velocity components, both blue-shifted from the systemic
radial velocity, with velocity widths of 140\kms\ and separated by 120\kms.
This region is co-spatial with weak extended radio emission and is suggestive
of a centrally driven outflow. The \oiii\ line spectrum and image of this
region have been modelled as an outflowing conical structure at 50\degr\ to the
line of sight with a half opening angle of 23\degr .
In addition to the extended structure, high resolution MERLIN observations of
the 18-cm nuclear radio emission reveal a compact (1\arcsec) radio triple
source in PA 73. This source is coincident with the HST-imaged
emission line structure. These high resolution observations are consistent with
a more compact origin of activity (i.e. a Seyfert nucleus) than a starburst
region.Comment: latex, epsf.sty, 8 pages, 8 figures. Also available at
http://axp2.ast.man.ac.uk:8000/Preprints.htm
H-alpha Kinematics of the SINGS Nearby Galaxies Survey. II
This is the second part of an H-alpha kinematics follow-up survey of the
Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this program
is to shed new light on the role of baryons and their kinematics and on the
dark/luminous matter relation in the star forming regions of galaxies, in
relation with studies at other wavelengths. The data for 37 galaxies are
presented. The observations were made using Fabry-Perot interferometry with the
photon-counting camera FaNTOmM on 4 different telescopes, namely the
Canada-France-Hawaii 3.6m, the ESO La Silla 3.6m, the William Herschel 4.2m,
and the Observatoire du mont Megantic 1.6m telescopes. The velocity fields are
computed using custom IDL routines designed for an optimal use of the data. The
kinematical parameters and rotation curves are derived using the GIPSY
software. It is shown that non-circular motions associated with galactic bars
affect the kinematical parameters fitting and the velocity gradient of the
rotation curves. This leads to incorrect determinations of the baryonic and
dark matter distributions in the mass models derived from those rotation
curves.Comment: 18 pages, 5 figures, 4 tables. Accepted for publication in MNRAS. All
high-res. figures are available at
http://www.astro.umontreal.ca/fantomm/singsII
The orientation of the Seyfert nucleus in Markarian 348
Multi-frequency observations of Mrk 348 are presented consisting of 2 epochs
of MERLIN data at 5 GHz, ISOPHOT data at 170, 90, 60 and 25 micron, NOT images
at U, B, R and I bands and data at 1350 micron from the archive for SCUBA. The
new optical images reveal a disrupted arm that ends towards the eastern
companion of Mrk 348, consistent with the hypothesis that Mrk 348 and its
companion form an interacting system. 5 GHz MERLIN imaging shows that only one
of the radio components of Mrk 348 is polarized (%P=5). The broadband spectrum
of Mrk 348 is flat between the radio and millimetre bands, suggesting that
synchrotron emission extends to high frequencies. Mrk 348 has many of the
characteristics of a radio-loud object. We discuss the orientation of the radio
axis of Mrk 348 with respect to the line of sight. We conclude that the
evidence is conflicting, and the geometry in Mrk 348 is not well-described by a
simple edge-on or face-on model.Comment: Accepted for publication in MNRAS; higher resolution images at
http://www.oal.ul.pt/ftp-anon/Image
The Hamburg/SAO Survey for Emission--Line Galaxies. V. The Fifth List of 161 Galaxies
We present the fifth list with results of the Hamburg/SAO Survey for
Emission-Line Galaxies (HSS therein, SAO -- Special Astrophysical Observatory,
Russia). The list is a result of follow-up spectroscopy conducted with the 2.2m
CAHA and 4m Kitt Peak telescopes in 1999. The data of this snap-shot
spectroscopy survey confirmed 166 emission-line objects out of 209 observed
candidates and allowed their quantitative spectral classification and redshift
determination. We could classify 98 emission-line objects as BCG/HII galaxies
or probable BCGs, 5 -- as QSOs, 3 - as Seyfert galaxies, 2 - as
super-associations in subluminous spiral galaxies. 25 low-excitation objects
were classified as starburst nuclei (SBN), 24 as dwarf amorphous nuclei
starburst galaxies (DANS) and 3 as LINERs. Due to low signal-to-noise ratio we
could not classify 6 ELGs. Furthermore, for another 4 galaxies we did not
detect any significant emission lines. For 131 emission-line galaxies, the
redshifts and/or line intensities are determined for the first time. For the
remaining 30 previously known ELGs we give either improved data of the line
intensities or some independent measurements.Comment: 18 pages, A&A in press. Figures A1-A17 (spectra) available in
GIF-format. PS-file with Figures A1-A17 available via
http://precise.sao.ru/Laboratory/Publications/2001/HSSV_figs.ps.g
Main structural targets for engineering lipase substrate specificity
Microbial lipases represent one of the most important groups of biotechnological biocatalysts. However, the high-level production of lipases requires an understanding of the molecular mechanisms of gene expression, folding, and secretion processes. Stable, selective, and productive lipase is essential for modern chemical industries, as most lipases cannot work in different process conditions. However, the screening and isolation of a new lipase with desired and specific properties would be time consuming, and costly, so researchers typically modify an available lipase with a certain potential for minimizing cost. Improving enzyme properties is associated with altering the enzymatic structure by changing one or several amino acids in the protein sequence. This review detailed the main sources, classification, structural properties, and mutagenic approaches, such as rational design (site direct mutagenesis, iterative saturation mutagenesis) and direct evolution (error prone PCR, DNA shuffling), for achieving modification goals. Here, both techniques were reviewed, with different results for lipase engineering, with a particular focus on improving or changing lipase specificity. Changing the amino acid sequences of the binding pocket or lid region of the lipase led to remarkable enzyme substrate specificity and enantioselectivity improvement. Site-directed mutagenesis is one of the appropriate methods to alter the enzyme sequence, as compared to random mutagenesis, such as error-prone PCR. This contribution has summarized and evaluated several experimental studies on modifying the substrate specificity of lipase
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