637 research outputs found
Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks
We present new, high angular resolution (~0.22") MERLIN observations of
neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the
central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially
resolved HI absorption is detected against the morphologically complex and
extended 21-cm radio continuum emission, consistent with two counterrotating
disks of neutral hydrogen, with a small bridge of gas connecting the two.
We propose a merger model in which the two nuclei represent the galaxy cores
which have survived the initial encounter and are now in the final stages of
merging, similar to conclusions drawn from previous CO studies (Sakamoto,
Scoville & Yun 1999). However, we suggest that instead of being coplanar with
the main CO disk (in which the eastern nucleus is embedded), the western
nucleus lies above it and, as suggested by bridge of HI connecting the two
nuclei, will soon complete its final merger with the main disk. We suggest that
the collection of radio supernovae (RSN) detected in VLBA studies in the more
compact western nucleus represent the second burst of star formation associated
with this final merger stage and that free-free absorption due to ionised gas
in the bulge-like component can account for the observed RSN distribution.
(Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in
Ap
Dust emission from a parsec-scale structure in the Seyfert 1 nucleus of NGC 4151
We report mid-IR interferometric measurements with \sim 10 mas resolution,
which resolve the warm (T = 285 +25 / -50 K) thermal emission at the center of
NGC 4151. Using pairs of VLT 8.2 m telescopes with MIDI and by comparing the
data to a Gaussian model, we determined the diameter of the dust emission
region, albeit only along one position angle, to be 2.0 +/- 0.4 pc (FWHM). This
is the first size and temperature estimate for the nuclear warm dust
distribution in a Seyfert 1 galaxy. The parameters found are comparable to
those in Seyfert 2 galaxies, thus providing direct support for the unified
model. Using simple analytic temperature distributions, we find that the
mid-infrared emission is probably not the smooth continuation of the hot
nuclear source that is marginally resolved with K band interferometry. We also
detected weak excess emission around 10.5 micron in our shorter baseline
observation, possibly indicating that silicate emission is extended to the
parsec scale.Comment: 5 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
Atomic Hydrogen Properties of AGN Host Galaxies: HI in 16 NUclei of GAlaxies (NUGA) Sources
We present a comprehensive spectroscopic imaging survey of the distribution
and kinematics of atomic hydrogen (HI) in 16 nearby spiral galaxies hosting low
luminosity AGN, observed with high spectral and spatial resolution (resolution:
~20 arcsec, 5 km/s) using the NRAO Very Large Array (VLA). The sample contains
a range of nuclear types, ranging from Seyfert to star-forming nuclei and was
originally selected for the NUclei of GAlaxies project (NUGA) - a spectrally
and spatially resolved interferometric survey of gas dynamics in nearby
galaxies designed to identify the fueling mechanisms of AGN and the relation to
host galaxy evolution. Here we investigate the relationship between the HI
properties of these galaxies, their environment, their stellar distribution and
their AGN type. The large-scale HI morphology of each galaxy is classified as
ringed, spiral, or centrally concentrated; comparison of the resulting
morphological classification with AGN type reveals that ring structures are
significantly more common in LINER than in Seyfert host galaxies, suggesting a
time evolution of the AGN activity together with the redistribution of the
neutral gas. Dynamically disturbed HI disks are also more prevalent in LINER
host galaxies than in Seyfert host galaxies. While several galaxies are
surrounded by companions (some with associated HI emission), there is no
correlation between the presence of companions and the AGN type
(Seyfert/LINER).Comment: 54 pages, 7 figures, accepted for publication in AJ. The
full-resolution version is available at
http://www.mpia.de/homes/haan/research.htm
Assessing the bioconfinement potential of a Nicotiana hybrid platform for use in plant molecular farming applications
Background
The introduction of pharmaceutical traits in tobacco for commercial production could benefit from the utilization of a transgene bioconfinement system. It has been observed that interspecific F1Nicotiana hybrids (Nicotiana tabacum Ă— Nicotiana glauca) are sterile and thus proposed that hybrids could be suitable bioconfined hosts for biomanufacturing. We genetically tagged hybrids with green fluorescent protein (GFP), which was used as a visual marker to enable gene flow tracking and quantification for field and greenhouse studies. GFP was used as a useful proxy for pharmaceutical transgenes. Results
Analysis of DNA content revealed significant genomic downsizing of the hybrid relative to that of N. tabacum. Hybrid pollen was capable of germination in vitro, albeit with a very low frequency and with significant differences between plants. In two field experiments, one each in Tennessee and Kentucky, we detected outcrossing at only one location (Tennessee) at 1.4%. Additionally, from 50 hybrid plants at each field site, formation of 84 and 16 seed was observed, respectively. Similar conclusions about hybrid fertility were drawn from greenhouse crosses. In terms of above-ground biomass, the hybrid yield was not significantly different than that of N. tabacum in the field. Conclusion
N. tabacum Ă— N. glauca hybrids show potential to contribute to a bioconfinement- and biomanufacturing host system. Hybrids exhibit extremely low fertility with no difference of green biomass yields relative to N. tabacum. In addition, hybrids are morphologically distinguishable from tobacco allowing for identity preservation. This hybrid system for biomanufacturing would optimally be used where N. glauca is not present and in physical isolation of N. tabacum production to provide total bioconfinement
Direct measurement of the jet geometry in Seyfert galaxies
We demonstrate that, by combining optical, radio and X-ray observations of a
Seyfert, it is possible to provide a direct measurement of the angle
between the direction of the radio jet and the normal to the plane of the
spiral host galaxy. To do so, we make the assumptions that the inner radio jet
is perpendicular to the X-ray observed inner accretion disk, and that the
observed jet (or the stronger component, if the jet is two-sided) is physically
closer to Earth than the plane of the galaxy. We draw attention to the
possibility of measurement producing a result which is not self-consistent, in
which case for that galaxy, one of the assumptions must fail.Comment: 11 pages, 1 figure, accepted for publication in The Astrophysical
Journal Letter
Distribution and Kinematics of the Circum-nuclear Molecular Gas in the Seyfert 1 Galaxy NGC 3227
We present new interferometric observations of the 12CO(1-0), 12CO(2-1) and
HCN (1-0) molecular line emission in NGC 3227 obtained with the IRAM Plateau de
Bure interferometer (PdBI). We achieved an unprecedented angular resolution in
the 12CO(2-1) line of about 0.6'' corresponding to only about 80pc at a
distance of 17.3Mpc. The mapped 12CO emission is concentrated in the inner 8''
and accounts for 20% of the total 30m CO line flux. The 12CO emission is
resolved into an asymmetric nuclear ring with a diameter of about 3''. The HCN
line emission is mostly unresolved at our resolution of ~2.4'' and contains all
of the single dish flux. We have decomposed the observed molecular gas motions
into a circular and non-circular component revealing that about 80% of the gas
in the circum-nuclear region exhibits pure circular rotation. We find evidence
for bar streaming onto the nuclear ring and a redshifted emission knot on the
ring perimeter.
In the central arcsecond the gas shows apparent counter rotation. This
behavior can be best explained by a warping of the inner molecular gas disk
rather than gas motion in a nuclear bar potential. We detected molecular gas at
a distance from the nucleus of only ~13pc with a velocity of about 75 km/s with
respect to the systemic velocity and find that within the central arcsecond the
rotation curve is rising again. This is the first time that millimetric CO-line
emission has been detected interferometrically at such small distances to the
nucleus of a Seyfert galaxy. These measurements indicate a lower limit on the
enclosed mass of about 2x10^7 M_solar in the inner 15pc.Comment: accepted for Ap.J. April issue, 54 pages, 22 figure
The Resolved Narrow Line Region in NGC4151
We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from
the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the
kinematics and physical conditions of the emission line clouds in this region.
Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and
narrow band undispersed images, we have mapped the NLR velocity field from 1.2
kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud
distribution exhibits recessional velocities relative to the nucleus to the NE
and approaching velocities to the SW of the nucleus. We find evidence for at
least two kinematic components in the NLR. One kinematic component is
characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v|
< 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR
and their observed kinematics may be gravitationally associated with the host
galaxy. Another component is characterized by High Velocities and High Velocity
Dispersions (HVHVD clouds: 400 130 km/s). This
set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has
radial velocities which are too high to be gravitational in origin, but show no
strong correlation between velocity or velocity dispersion and the position of
the radio knots. Outflow scenarios will be discussed as the driving mechanism
for these HVHVD clouds.Comment: 38 pages, 14 figures, accepted by ApJ. For higher resolution images
see http://www.pha.jhu.edu/~kaiser
The Relative Orientation of Nuclear Accretion and Galaxy Stellar Disks in Seyfert Galaxies
We use the difference (delta) between the position angles of the nuclear
radio emission and the host galaxy major axis to investigate the distribution
of the angle (beta) between the axes of the nuclear accretion disk and the host
galaxy disk in Seyfert galaxies. We provide a critical appraisal of the quality
of all measurements, and find that the data are limited by observational
uncertainties and biases, such as the well known deficiency of Seyfert galaxies
of high inclination. There is weak evidence that the distribution of delta for
Seyfert 2 galaxies may be different (at the 90% confidence level) from a
uniform distribution, while the Seyfert 1 delta distribution is not
significantly different from a uniform distribution or from the Seyfert 2 delta
distribution. The cause of the possible non-uniformity in the distribution of
delta for Seyfert 2 galaxies is discussed. Seyfert nuclei in late-type spiral
galaxies may favor large values of delta (at the ~96% confidence level), while
those in early-type galaxies show a more or less random distribution of delta.
This may imply that the nuclear accretion disk in non-interacting late-type
spirals tends to align with the stellar disk, while that in early-type galaxies
is more randomly oriented, perhaps as a result of accretion following a galaxy
merger.
We point out that biases in the distribution of inclination translate to
biased estimates of beta in the context of the unified scheme. When this effect
is taken into account, the distributions of beta for all Seyferts together, and
of Seyfert 1's and 2's separately, agree with the hypothesis that the radio
jets are randomly oriented with respect to the galaxy disk. The data are
consistent with the expectations of the unified scheme, but do not demand it.Comment: To appear in the Astrophysical Journal, Vol 516 #1, May 1, 1999.
Corrected figure placement within pape
A Radio Study of the Seyfert Galaxy IC 5063: Evidence for Fast Gas Outflow
New radio continuum (8 GHz and 1.4 GHz) and HI 21 cm line observations of the
Seyfert 2 galaxy IC 5063 (PKS 2048-572) were obtained with the Australia
Telescope Compact Array (ATCA). The 8 GHz image reveals a linear triple
structure (~4'', 1.5 kpc) oriented perpendicular to the optical polarization
position angle. It is aligned with the inner dust lane and shows strong
morphological association with the narrow emission line region (NLR). At 21 cm,
very broad (~700 km/s) HI absorption is observed against the strong continuum
source. This absorption is almost entirely blueshifted, indicating a fast net
outflow, but a faint and narrow redshifted component is also present. In IC
5063 we see clear evidence for strong shocks resulting from the radio
plasma-ISM interaction in the central few kpc. However, the energy flux in the
radio plasma is an order of magnitude smaller than the energy emitted in
emission lines. Thus, shocks are unlikely to account solely for the global
ionization of the emission line region, particularly at large distances.
The HI emission outlines a warped disk associated with the system of dust
lanes some ~2' (~38 kpc) in radius. The lack of kinematically disturbed gas
outside the central few kpc, coupled with the disk warp and close morphological
connection of the inner dust lanes and the large-scale ionized gas, support the
idea that the gas at large radii is photoionized by the central region, while
shadowing effects are important in defining its X-shaped morphology. The
kinematics of the ionized and of the neutral gas suggests the existence of a
dark halo.Comment: 18 pages, 8 Postscript figures, 3 jpeg figures, Postscript preprint
is available from http://jhufos.pha.jhu.edu/~zlatan/papers.htm
An orange fluorescent protein tagging system for real-time pollen tracking
BACKGROUND: Monitoring gene flow could be important for future transgenic crops, such as those producing plant-made-pharmaceuticals (PMPs) in open field production. A Nicotiana hybrid (Nicotiana. tabacum x Nicotiana glauca) shows limited male fertility and could be used as a bioconfined PMP platform. Effective assessment of gene flow from these plants is augmented with methods that utilize fluorescent proteins for transgenic pollen identification.
RESULTS: We report the generation of a pollen tagging system utilizing an orange fluorescent protein to monitor pollen flow and as a visual assessment of transgene zygosity of the parent plant. This system was created to generate a tagged Nicotiana hybrid that could be used for the incidence of gene flow. Nicotiana tabacum \u27TN 90\u27 and Nicotiana glauca were successfully transformed via Agrobacterium tumefaciens to express the orange fluorescent protein gene, tdTomato-ER, in pollen and a green fluorescent protein gene, mgfp5-er, was expressed in vegetative structures of the plant. Hybrids were created that utilized the fluorescent proteins as a research tool for monitoring pollen movement and gene flow. Manual greenhouse crosses were used to assess hybrid sexual compatibility with N. tabacum, resulting in seed formation from hybrid pollination in 2% of crosses, which yielded non-viable seed. Pollen transfer to the hybrid formed seed in 19% of crosses and 10 out of 12 viable progeny showed GFP expression.
CONCLUSION: The orange fluorescent protein is visible when expressed in the pollen of N. glauca, N. tabacum, and the Nicotiana hybrid, although hybrid pollen did not appear as bright as the parent lines. The hybrid plants, which show limited ability to outcross, could provide bioconfinement with the benefit of detectable pollen using this system. Fluorescent protein-tagging could be a valuable tool for breeding and in vivo ecological monitoring
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