5,230 research outputs found
Resolved Spectroscopy of the Narrow-Line Region in NGC 1068: Kinematics of the Ionized Gas
We have determined the radial velocities of the [O III] emitting gas in the
inner narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068, along a slit
at position angle of 202 degrees, from STIS observations at a spatial
resolution of 0.1 arcsec and a spectral resolving power of approximately 1000.
We use these data to investigate the kinematics of the NLR within 6 arcsec (430
pc) of the nucleus. The emission-line knots show evidence for radial
acceleration, to a projected angular distance of 1.7 arcsec in most cases,
followed by deceleration that approaches the systemic velocity at a projected
distance of about 4 arcsec. We find that a simple kinematic model of biconical
radial outflow can match the general trend of observed radial velocities. In
this model, the emitting material is evacuated along the bicone axis, and the
axis is inclined 5 degrees out of the plane of the sky. The acceleration of the
emission-line clouds provides support for dynamical models that invoke
radiation and/or wind pressure. We suggest that the deceleration of the clouds
is due to their collision with a patchy and anistropically distributed ambient
medium.Comment: 18 pages, Latex, includes 3 figures in postscript, to appear in the
Astrophysical Journal Letter
Jet triggered Type Ia supernovae in radio-galaxies?
We report the serendipitous discovery of a supernova (SN) in the nearby
radio-galaxy 3C 78. Observations obtained with the STIS spectrograph on board
the Hubble Space Telescope show, at a distance of 0.54 arcsec (300 pc) from the
galaxy nucleus, a second bright source, not present in previous images. As this
source was fortuitously covered by the spectrograph slit its spectrum was
obtained and it is characteristic of a Type Ia SN. This SN is closely aligned
with the radio-jet of 3C 78. Analysis of historical records shows that such a
close association between jet and supernova occurred in 6 of the 14 reported
SNe in radio-galaxies. The probability that this results from a random
distribution of SN in the host galaxy is less than 0.05%. We then argue that
jets might trigger supernova explosions.Comment: 9 pages, 3 figures, 1 table, to appear in ApJL, 20 Jul 200
On the magnetic equation of state in (2+1)-flavor QCD
A first study of critical behavior in the vicinity of the chiral phase
transition of (2+1)-flavor QCD is presented. We analyze the quark mass and
volume dependence of the chiral condensate and chiral susceptibilities in QCD
with two degenerate light quark masses and a strange quark. The strange quark
mass (m_s) is chosen close to its physical value; the two degenerate light
quark masses (m_l) are varied in a wide range 1/80 \le m_l/m_s \le 2/5, where
the smallest light quark mass value corresponds to a pseudo-scalar Goldstone
mass of about 75 MeV. All calculations are performed with staggered fermions on
lattices with temporal extent Nt=4. We show that numerical results are
consistent with O(N) scaling in the chiral limit. We find that in the region of
physical light quark mass values, m_l/m_s \simeq 1/20, the temperature and
quark mass dependence of the chiral condensate is already dominated by
universal properties of QCD that are encoded in the scaling function for the
chiral order parameter, the magnetic equation of state. We also provide
evidence for the influence of thermal fluctuations of Goldstone modes on the
chiral condensate at finite temperature. At temperatures below, but close to
the chiral phase transition at vanishing quark mass, this leads to a
characteristic dependence of the light quark chiral condensate on the square
root of the light quark mass.Comment: 18 pages, 18 EPS-file
Models relating the radio emission and ionised gas in Seyfert nuclei
Possible models are discussed in which the radio emitting components in Seyfert II nuclei can compress and accelerate the ambient nuclear medium to produce the characteristics of the narrow line region. A first order model, which considers only the expansion of the radio components, is briefly described. However, in many Seyfert nuclei it appears that the linear motion of the radio components is also important. This can result in shock heating of the ambient medium, and if the cooling time is long enough, can lead to a displacement between the radio component and the associated emission lines. This effect may be present in NGC 1068 and NGC 5929 and by considering ram pressure balance and the cooling length it is possible to estimate lobe velocities and ambient densities
A Simplified Model to Predict Long-Term Ozone Concentrations in Europe
In the preparation process for the Second Sulphur Protocol of the Convention on Long-range Transboundary Air Pollution, integrated assessment models played an important role in identifying cost-effective strategies for reducing SO2 emissions in Europe. Applying this effect-based approach to other environmental problems (e.g., photo-oxidants) seems appealing. In view of the timetable adopted for the current preparation of an updated Protocol on emissions of nitrogen oxides, an integrated assessment tool for ozone is required in the very near future.
The paper presents an outline of an integrated assessment model for tropospheric ozone in Europe, with modules on emissions, emission control technologies and costs, ozone formation and environmental impacts. In its central part the paper focuses on the core element of such an approach, i.e., a concise description of the relationships between the precursor emissions (nitrogen oxides and volatile organic compounds) and regional ozone levels, which must be computationally efficient for use in an integrated assessment model.
Critical levels, i.e., threshold levels protecting vegetation from damage, have been recently established using long-term exposure measures. Consequently, to be suitable for integrated assessment models, source-receptor relationships should be able to describe the long-term changes of ozone, e.g., over a six-month period. Based on numerous scenario runs of the EMEP ozone model, polynomial source-receptor relationships have been statistically identified. Using national annual emissions of NO, and VOC, the model predicts regional responses of the six-month mean of early afternoon ozone concentrations. From this concentration measure, excess exposure as used in the definition of the critical levels can be derived. The paper introduces the methodology of the approach, evaluates the results and discusses areas of further work.
The suggested model formulation can be incorporated into the framework of an integrated assessment model, enabling (i) the assessment of costs and environmental benefits from alternative strategies to reduce precursor emissions and (ii) the identification of cost-optimized strategies to achieve environmental targets
The morphology of Sersic-Pastoriza galaxies
The authors present the preliminary results of their radio-continuum and neutral hydrogen observations of Sersic-Pastoriza (S-P) galaxies. They show that the central regions contain a population of compact features thought to be young supernova remnants (SNRs) and discuss the overall morphology of the nuclei
On the Nature of Intrinsic Absorption in Reddened Seyfert 1 Galaxies
We discuss the origin of the ``dusty lukewarm absorber'', which we previously
identified in the reddened Seyfert 1 galaxies NGC 3227 and Akn 564. This
absorber is characterized by saturated UV absorption lines (C IV, N V) near the
systemic velocity of the host galaxy, and is likely responsible for reddening
both the continuum and the emission lines (including those from the narrow-line
region) from these Seyferts. From a large sample of Seyfert 1 galaxies, we find
that continuum reddening (as measured by UV color) tends to increase with
inclination of the host galaxy. Furthermore, reddened, inclined Seyfert
galaxies observed at moderate to high spectral resolution all show evidence for
dusty lukewarm absorbers. We suggest that these absorbers lie in the plane of
the host galaxy at distances > 100 pc from the nucleus, and are physically
distinct from the majority of intrinsic absorbers that are outflowing from the
nucleus.Comment: 14 pages, including 2 figures, accepted for publication in the
Astrophysical Journal (Letters
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