1,632 research outputs found
The central parsecs of active galactic nuclei: challenges to the torus
Type 2 AGN are by definition nuclei in which the broad-line region and
continuum light are hidden at optical/UV wavelengths by dust. Via accurate
registration of infrared (IR) Very Large Telescope adaptive optics images with
optical \textit{Hubble Space Telescope} images we unambiguously identify the
precise location of the nucleus of a sample of nearby, type 2 AGN. Dust
extinction maps of the central few kpc of these galaxies are constructed from
optical-IR colour images, which allow tracing the dust morphology at scales of
few pc. In almost all cases, the IR nucleus is shifted by several tens of pc
from the optical peak and its location is behind a dust filament, prompting to
this being a major, if not the only, cause of the nucleus obscuration. These
nuclear dust lanes have extinctions mag, sufficient to at least
hide the low-luminosity AGN class, and in some cases are observed to connect
with kpc-scale dust structures, suggesting that these are the nuclear fueling
channels. A precise location of the ionised gas H and
[\textsc{Si\,vii}] 2.48 m coronal emission lines relative to those of the
IR nucleus and dust is determined. The H peak emission is often shifted
from the nucleus location and its sometimes conical morphology appears not to
be caused by a nuclear --torus-- collimation but to be strictly defined by the
morphology of the nuclear dust lanes. Conversely, [\textsc{Si\,vii}] 2.48
m emission, less subjected to dust extinction, reflects the truly, rather
isotropic, distribution of the ionised gas. All together, the precise location
of the dust, ionised gas and nucleus is found compelling enough to cast doubts
on the universality of the pc-scale torus and supports its vanishing in
low-luminosity AGN. Finally, we provide the most accurate position of the NGC
1068 nucleus, located at the South vertex of cloud B.Comment: 23 pages, 10 figures, accepted for publication in MNRA
Generalized S-space-forms
We introduce and study generalized S-space-forms. Moreover, we
investigate generalized S-space-forms endowed with an additional structure
and we obtain some obstructions for them to be S-manifold
Introducción a la Cerámica Prehistórica y Protohistórica en Galicia
Traballos de ArqueoloxÃa e Patrimonio (TAPA)[EN] The intention of these works is to show, in a didactic
way, what are the properties of Bronze Age and Iron
Age pottery in Galicia, done through the chracterization
of their production processes.[ES] La intención de estos trabajos es exponer de manera
didáctica cómo es la cerámica de la Edad del Bronce y
de la Edad del Hierro en Galicia mediante la caracterización
de los procesos de producción.Financiación de la edición: Laboratorio de ArqueoloxÃa
e Formas Culturais.Peer reviewe
The central parsecs of M87: jet emission and an elusive accretion disc
We present the first simultaneous spectral energy distribution (SED) of M87
core at a scale of 0.4 arcsec () across the electromagnetic
spectrum. Two separate, quiescent, and active states are sampled that are
characterized by a similar featureless SED of power-law form, and that are thus
remarkably different from that of a canonical active galactic nuclei (AGN) or a
radiatively inefficient accretion source. We show that the emission from a jet
gives an excellent representation of the core of M87 core covering ten orders
of magnitude in frequency for both the active and the quiescent phases. The
inferred total jet power is, however, one to two orders of magnitude lower than
the jet mechanical power reported in the literature. The maximum luminosity of
a thin accretion disc allowed by the data yields an accretion rate of , assuming 10% efficiency. This power
suffices to explain M87 radiative luminosity at the jet-frame, it is however
two to three order of magnitude below that required to account for the jet's
kinetic power. The simplest explanation is variability, which requires the core
power of M87 to have been two to three orders of magnitude higher in the last
200 yr. Alternatively, an extra source of power may derive from black hole
spin. Based on the strict upper limit on the accretion rate, such spin power
extraction requires an efficiency an order of magnitude higher than predicted
from magnetohydrodynamic simulations, currently in the few hundred per cent
range.Comment: 18 pages, 6 figures. Accepted for publication in MNRA
Effects of fire and three fire-fighting chemicals on main soil properties, plant nutrient content and vegetation growth and cover after 10 years.
The study addresses a knowledge-gap in the long-term ecological consequences of fire and fire-fighting
chemicals. Ten years after a prescribed fire and the application of three fire-fighting chemicals, their effects
on the soil-plant system were evaluated. Five treatments were established: unburnt soils (US) and burnt
soils treated with water alone (BS), foaming agent (BS+Fo), Firesorb (BS+Fi) and ammonium polyphosphate
(BS+Ap). Soils (0-2 cm depth) and foliar material of shrubs (Erica umbellata, Pterospartum tridentatum and
Ulex micranthus) and trees (Pinus pinaster) were analysed for total N, 15N, and soil-available and plant total
macronutrients and trace elements. Soil pH, NH4
+-N and NO3
--N; pine basal diameter and height; and shrub
cover and height were also measured. Compared with US plots, burnt soils had less nitrates and more Mo.
Although differences were not always significant, BS+Ap had the highest levels of soil available P, Na and
Al. Plants from BS+Ap plots had higher values of 15N (P. pinaster and E. umbellata), P (all species), Na (P.
tridentatum and U. micranthus) and Mg (E. umbellata and P. tridentatum) than other treatments; while K in
plants from BS+Ap plots was the highest among treatments for P. pinaster and the lowest for the shrubs.
Pines in US plots were higher and wider than in burnt treatments, except for BS+Ap, where the tallest and
widest trees were found, although half of them were either death (the second highest mortality after BS+Fi)
or had a distorted trunk. BS+Ap was the treatment with strongest effects on plants, showing E. umbellata
the lowest coverage and height, P. tridentatum the highest coverage, U. micranthus one of the lowest
coverages and being the only treatment where Genista triacanthos was absent. Consequently, it is concluded
that both fire and ammonium polyphosphate application had significant effects on the soil-plant system
after 10 years.Peer reviewe
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