6,032 research outputs found
Is the Broad-Line Region Clumped or Smooth? Constraints from the H alpha Profile in NGC 4395, the Least Luminous Seyfert 1 Galaxy
The origin and configuration of the gas which emits broad lines in Type I
active galactic nuclei is not established yet. The lack of small-scale
structure in the broad emission-line profiles is consistent with a smooth gas
flow, or a clumped flow with many small clouds. An attractive possibility for
the origin of many small clouds is the atmospheres of bloated stars, an origin
which also provides a natural mechanism for the cloud confinement. Earlier
studies of the broad-line profiles have already put strong lower limits on the
minimum number of such stars, but these limits are sensitive to the assumed
width of the lines produced by each cloud. Here we revisit this problem using
high-resolution Keck spectra of the H alpha line in NGC 4395, which has the
smallest known broad-line region (~10^14 cm). Only a handful of the required
bloated stars (each having r~10^14 cm) could fit into the broad-line region of
NGC 4395, yet the observed smoothness of the H alpha line implies a lower limit
of ~10^4-10^5 on the number of discrete clouds. This rules out conclusively the
bloated-stars scenario, regardless of any plausible line-broadening mechanisms.
The upper limit on the size of the clouds is ~10^12 cm, which is comparable to
the size implied by photoionization models. This strongly suggests that gas in
the broad-line region is structured as a smooth rather than a clumped flow,
most likely in a rotationally dominated thick disk-like configuration. However,
it remains to be clarified why such a smooth, gravity-dominated flow generates
double-peaked emission lines only in a small fraction of active galactic
nuclei.Comment: 12 pages, including 3 figures, accepted for publication in The
Astrophysical Journa
The End of the Lines for OX 169: No Binary Broad-Line Region
We show that unusual Balmer emission line profiles of the quasar OX 169,
frequently described as either self-absorbed or double peaked, are actually
neither. The effect is an illusion resulting from two coincidences. First, the
forbidden lines are quite strong and broad. Consequently, the [N II]6583 line
and the associated narrow-line component of H-alpha present the appearance of
twin H-alpha peaks. Second, the redshift of 0.2110 brings H-beta into
coincidence with Na I D at zero redshift, and ISM absorption in Na I D divides
the H-beta emission line. In spectra obtained over the past decade, we see no
substantial change in the character of the line profiles, and no indication of
intrinsic double-peaked structure. The H-gamma, Mg II, and Ly-alpha emission
lines are single peaked, and all of the emission-line redshifts are consistent
once they are correctly attributed to their permitted and forbidden-line
identifications. A systematic shift of up to 700 km/s between broad and narrow
lines is seen, but such differences are common, and could be due to
gravitational and transverse redshift in a low-inclination disk. Stockton &
Farnham (1991) had called attention to an apparent tidal tail in the host
galaxy of OX 169, and speculated that a recent merger had supplied the nucleus
with a coalescing pair of black holes which was now revealing its existence in
the form of two physically distinct broad-line regions. Although there is no
longer any evidence for two broad emission-line regions in OX 169, binary black
holes should form frequently in galaxy mergers, and it is still worthwhile to
monitor the radial velocities of emission lines which could supply evidence of
their existence in certain objects.Comment: 19 pages, 5 figures, accepted for publication in Ap.
Influence of s,p-d and s-p exchange couplings on exciton splitting in (Zn,Mn)O
This work presents results of near-band gap magnetooptical studies on
(Zn,Mn)O epitaxial layers. We observe excitonic transitions in reflectivity and
photoluminescence, that shift towards higher energies when the Mn concentration
increases and split nonlinearly under the magnetic field. Excitonic shifts are
determined by the s,p-d exchange coupling to magnetic ions, by the
electron-hole s-p exchange, and the spin-orbit interactions. A quantitative
description of the magnetoreflectivity findings indicates that the free
excitons A and B are associated with the Gamma_7 and Gamma_9 valence bands,
respectively, the order reversed as compared to wurtzite GaN. Furthermore, our
results show that the magnitude of the giant exciton splittings, specific to
dilute magnetic semiconductors, is unusual: the magnetoreflectivity data is
described by an effective exchange energy N_0(beta-alpha)=+0.2+/-0.1 eV, what
points to small and positive N_0 beta. It is shown that both the increase of
the gap with x and the small positive value of the exchange energy N_0 beta
corroborate recent theory describing the exchange splitting of the valence band
in a non-perturbative way, suitable for the case of a strong p-d hybridization.Comment: 8 pages, 8 figure
Correspondence in Quasiperiodic and Chaotic Maps: Quantization via the von Neumann Equation
A generalized approach to the quantization of a large class of maps on a
torus, i.e. quantization via the von Neumann Equation, is described and a
number of issues related to the quantization of model systems are discussed.
The approach yields well behaved mixed quantum states for tori for which the
corresponding Schrodinger equation has no solutions, as well as an extended
spectrum for tori where the Schrodinger equation can be solved.
Quantum-classical correspondence is demonstrated for the class of mappings
considered, with the Wigner-Weyl density going to the correct
classical limit. An application to the cat map yields, in a direct manner,
nonchaotic quantum dynamics, plus the exact chaotic classical propagator in the
correspondence limit.Comment: 36 pages, RevTex preprint forma
Nano silver and nano zinc-oxide in surface waters - exposure estimation for Europe at high spatial and temporal resolution
Nano silver and nano zinc-oxide monthly concentrations in surface waters across Europe were modeled at ~6 × 9 km spatial resolution. Nano-particle loadings from households to rivers were simulated considering household connectivity to sewerage, sewage treatment efficiency, the spatial distribution of sewage treatment plants, and their associated populations. These loadings were used to model temporally varying nano-particle concentrations in rivers, lakes and wetlands by considering dilution, downstream transport, water evaporation, water abstraction, and nano-particle sedimentation. Temporal variability in concentrations caused by weather variation was simulated using monthly weather data for a representative 31-year period. Modeled concentrations represent current levels of nano-particle production. Two scenarios were modeled. In the most likely scenario, half the river stretches had long-term average concentrations exceeding 0.002 ng/L nano silver and 1.5 ng/L nano zinc oxide. In 10% of the river stretches, these concentrations exceeded 0.18 ng/L and 150 ng/L, respectively. Predicted concentrations were usually highest in July
The Circumstellar Disk of HD 141569 Imaged with NICMOS
Coronagraphic imaging with the Near Infrared Camera and Multi Object
Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'')
radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected
light image at 1.1 micron shows the disk oriented at a position angle of 356
+/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic
scattering function of the dust in the disk makes the side inclined toward us,
the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from
the star and falls off to both larger and smaller radii. A region of depleted
material, or a gap, in the disk is centered 250 AU from the star. The dynamical
effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript
figures, Accepted to ApJ Letter
X-ray enabled MOCASSIN: a 3D code for photoionized media
We present a new version of the fully 3D photoionization and dust radiative
transfer code, MOCASSIN, that uses a Monte Carlo approach for the transfer of
radiation. The X-ray enabled MOCASSIN allows a fully geometry independent
description of low-density gaseous environments strongly photoionized by a
radiation field extending from radio to gamma rays. The code has been
thoroughly benchmarked against other established codes routinely used in the
literature, using simple plane parallel models designed to test performance
under standard conditions. We show the results of our benchmarking exercise and
discuss applicability and limitations of the new code, which should be of
guidance for future astrophysical studies with MOCASSIN.Comment: Accepted for publication in ApJS 9 pages, 5 figure
Union économique et mobilité des facteurs; le cas de l'Union Économique et Monétaire Ouest Africain (UEMOA)
L'objet de ce papier est d'analyser les conséquences de la mise en place d'une Union économique entre les pays d'Afrique de l'Ouest (UEMOA), dans le cadre d'un modèle d'équilibre général calculable multi-pays avec mobilité des facteurs de production. On s'interroge sur les facteurs de convergence ou de divergence de développement, consécutifs à la réallocation des ressources et du commerce engendrés par la création de l'Union entre les pays membres qui, même s'ils ont des niveaux de revenus uniformément faibles, sont d'une configuration assez asymétrique. Tout d'abord, dans la mesure où l'Union économique signifie pour certains une forte ouverture internationale et pour d'autres un léger réarmement douanier, ses effets, de faible ampleur, sont contrastés. Par ailleurs, en dépit de l'asymétrie du choc, nos résultats sont conformes à ceux développés par Venables (1999): la Côte d'Ivoire qui possède le rapport des facteurs de production le moins éloigné du rapport mondial est le pays qui bénéficie le plus du processus d'intégration régionale. A l'inverse, le Burkina Faso voit sa situation se dégrader. La mobilité du travail et du capital industriel accentue le phénomène de divergence entre les pays de la zone. C'est ainsi que le Sénégal, et dans une moindre mesure le Togo, verraient à long terme leurs situations se dégrader par rapport au scénario de référence du fait de la fuite des capitaux industriels et donc leur écart de développement avec la Côte d'Ivoire croître. A contrario, la question migratoire, qui est parfois mise en exergue dans ce contexte, compte tenu des niveaux des flux et de l'ampleur somme toute modérée du choc macro-économique n'apparaît pas avec acuité. Enfin, on montre que la question de la transition fiscalo-douanière est centrale. En effet, selon le mode de financement des pertes fiscales choisi, l'impact des réformes douanières peut aller en sens opposé notamment sur la croissance des secteurs industriels dans des pays comme le Sénégal. Tant de problème du "creusement" du fossé entre la Côte d'Ivoire et ses partenaires régionaux et ses effets en terme de migration et de localisation du capital industriel dans la région, que le traitement du problème de la transition fiscalo-douanière doivent inciter la communauté internationale à envisager les politiques d'aide dans une stratégie régionale et non pas nationale comme cela l'est malheureusement encore.Intégration régionale, UEMOA, migration, FDI, MEGC
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