2,395 research outputs found
Electromagnetic Energy, Momentum, and Angular Momentum in an Inhomogeneous Linear Dielectric
In a previous work, Optics Communications 284 (2011) 2460--2465, we
considered a dielectric medium with an anti-reflection coating and a spatially
uniform index of refraction illuminated at normal incidence by a
quasimonochromatic field. Using the continuity equations for the
electromagnetic energy density and the Gordon momentum density, we constructed
a traceless, symmetric energy--momentum tensor for the closed system. In this
work, we relax the condition of a uniform index of refraction and consider a
dielectric medium with a spatially varying index of refraction that is
independent of time, which essentially represents a mechanically rigid
dielectric medium due to external constraints. Using continuity equations for
energy density and for Gordon momentum density, we construct a symmetric
energy--momentum matrix, whose four-divergence is equal to a generalized
Helmholtz force density four-vector. Assuming that the energy-momentum matrix
has tensor transformation properties under a symmetry group of space-time
coordinate transformations, we derive the global conservation laws for the
total energy, momentum, and angular momentum.Comment: added publication informatio
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
HST Observations of the Double-Peaked Emission Lines in the Seyfert Galaxy Markarian 78: Mass Outflows from a Single AGN
Previous ground based observations of the Seyfert 2 galaxy Mrk 78 revealed a
double set of emission lines, similar to those seen in several AGN from recent
surveys. Are the double lines due to two AGN with different radial velocities
in the same galaxy, or are they due to mass outflows from a single AGN?We
present a study of the outflowing ionized gas in the resolved narrow-line
region (NLR) of Mrk 78 using observations from Space Telescope Imaging
Spectrograph (STIS) and Faint Object Camera (FOC) aboard the Hubble Space
Telescope(HST) as part of an ongoing project to determine the kinematics and
geometries of active galactic nuclei (AGN) outflows. From the spectroscopic
information, we deter- mined the fundamental geometry of the outflow via our
kinematics modeling program by recreating radial velocities to fit those seen
in four different STIS slit positions. We determined that the double emission
lines seen in ground-based spectra are due to an asymmetric distribution of
outflowing gas in the NLR. By successfully fitting a model for a single AGN to
Mrk 78, we show that it is possible to explain double emission lines with
radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual
supermassive black holes.Comment: 22 pages, 7 figures (2 color), accepted for publication in The
Astrophysical Journa
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