8,049 research outputs found
Ly-alpha excess in high redshift radio galaxies: a signature of star formation
About 54% of radio galaxies at z>3 and 8% of radio galaxies at 2<z<3 show
unusually strong Ly-alpha emission, compared with the general population of
high redshift (z>2) radio galaxies. These Ly-alpha excess objects (LAEs) show
Ly-alpha/HeII values consistent with or above standard photoionization model
predictions.
We show that the most successful explanation is the presence of a young
stellar population which provides the extra supply of ionizing photons required
to explain the Ly-alpha excess in at least the most extreme LAEs (probably in
all of them).
The measurement of unusually high Ly-alpha ratios in the extended gas of some
high redshift radio galaxies suggests that star formation activity occurs in
spatial scales of tens of kpc.
We argue that, although the fraction of LAEs may be incompletely determined,
both at 23, the much larger fraction of LAEs found at z>3 is a
genuine redshift evolution and not due to selection effects. Therefore, our
results suggest that the radio galaxy phenomenon is more often associated with
a massive starburst at z>3 than at z<3.Comment: 14 pages, 5 figures, accepted for publication in MNRA
Global controllability tests for geometric hybrid control systems
Hybrid systems are characterized by having an interaction between continuous
dynamics and discrete events. The contribution of this paper is to provide
hybrid systems with a novel geometric formulation so that controls can be
added. Using this framework we describe some new global controllability tests
for hybrid control systems exploiting the geometry and the topology of the set
of jump points, where the instantaneous change of dynamics take place.
Controllability is understood as the existence of a feasible trajectory for the
system joining any two given points. As a result we describe examples where
none of the continuous control systems are controllable, but the associated
hybrid system is controllable because of the characteristics of the jump set.Comment: 27 pages, 5 figure
Hamilton-Jacobi Theory in k-Symplectic Field Theories
In this paper we extend the geometric formalism of Hamilton-Jacobi theory for
Mechanics to the case of classical field theories in the k-symplectic
framework
Xystreurys rasilis
This demersal species is distributed from southern Brazil to Argentina. It is taken in commercial fisheries in Uruguay and northern Argentina, which is where its largest global abundance exists. According to stock assessment and fisheries data, there is no decline detected in the demersal stock in Argentina and Uruguay and abundance indices show an increase in recent years (since 2014). Conservation measures in Argentina and Uruguay include a total allowable catch limit and regular monitoring of stock status.Fishing is not expected to be driving declines approaching a threatened or Near Threatened level at this time; therefore, it is listed as Least Concern.Fil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin
High volume-per-dose and low resistivity of cobalt nanowires grown by Ga+ focused ion beam induced deposition
The growth of ferromagnetic nanostructures by means of focused-Ga+-beam-induced deposition (Ga+-FIBID) using the Co2(CO)8 precursor has been systematically investigated. The work aimed to obtain growth conditions allowing for the simultaneous occurrence of high growth speed, good lateral resolution, low electrical resistivity, and ferromagnetic behavior. As a first result, it has been found that the competition between deposition and milling that is produced by the Ga+ beam is a limiting factor. In our working conditions, with the maximum available precursor flux, the maximum deposit thickness has been found to be 65 nm. The obtained volumetric growth rate is at least 50 times higher than in the case of deposition by focused-electron-beam-induced deposition. The lateral resolution of the deposits can be as good as 50 nm while using Ga+-beam currents lower than 10 pA. The high metallic content of the as-grown deposits gives rise to a low electrical resistivity, within the range 20-40 µ¿cm. Magnetic measurements confirm the ferromagnetic nature of the deposits at room temperature. In conclusion, the set of obtained results indicates that the growth of functional ferromagnetic nanostructures by Ga+-FIBID while using the Co2(CO)8 precursor is a viable and competitive technique when compared to related nanofabrication techniques
Compact radio sources and jet-driven AGN feedback in the early Universe: Constraints from integral-field spectroscopy
To investigate the impact of radio jets during the formation epoch of their
massive host galaxies, we present an analysis of two massive, log(M_stel/
M_sun)~10.6 and 11.3, compact radio galaxies at z=3.5, TNJ0205+2242 and
TNJ0121+1320. Their small radio sizes (R<= 10 kpc) are most likely a sign of
youth. We compare their radio properties and gas dynamics with those in well
extended radio galaxies at high redshift, which show strong evidence for
powerful, jet-driven outflows of significant gas masses (M 10^9-10 M_sun). Our
analysis combines rest-frame optical integral-field spectroscopy with existing
radio imaging, CO emission line spectra, and rest-frame UV spectroscopy.
[OIII]5007 line emission is compact in both galaxies and lies within the region
defined by the radio lobes. For TNJ0205+2242, the Ly-alpha profile narrows
significantly outside the jet radius, indicating the presence of a quiescent
halo. TNJ0121+1320 has two components separated by ~10 kpc and a velocity
offset of ~300 km s^-1. If motions are gravitational, this implies a dynamical
mass of 2x10^11 M_sun for the more massive, radio-loud component. The dynamical
mass, molecular gas mass measured from the CO line emission, and radio
luminosity of these two compact radio galaxies imply that compact radio sources
may well develop large-scale, energetic outflows as observed in extended radio
galaxies, with the potential of removing significant fractions of the ISM from
the host galaxy. The absence of luminous emission line gas extending beyond the
radio emission in these sources agrees with the observed timescales and outflow
rates in extended radio galaxies, and adds further evidence that the energetic,
large-scale outflows observed in extended radio sources (Nesvadba et al. 2006)
are indeed the result of influence of the radio jet.Comment: A&A accepte
CO line emission in the halo of a radio galaxy at z=2.6
We report the detection of luminous CO(3-2) line emission in the halo of the
z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at
optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun
and relatively low star-formation rates. With the IRAM PdBI we find two CO
emission line components at the same position at ~80 kpc distance from the HzRG
along the axis of the radio jet, with different blueshifts of few 100 km s^-1
relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected
at 8 sigma significance. HzRGs have significant galaxy overdensities and
extended halos of metal-enriched gas often with embedded clouds or filaments of
denser material, and likely trace very massive dark-matter halos. The CO
emission may be associated with a gas-rich, low-mass satellite galaxy with
little on-going star formation, in contrast to all previous CO detections of
galaxies at similar redshifts. Alternatively, the CO may be related to a gas
cloud or filament and perhaps jet-induced gas cooling in the outer halo,
somewhat in analogy with extended CO emission found in low-redshift galaxy
clusters.Comment: MNRAS Letters, accepte
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