812 research outputs found
The subarcsecond mid-infrared view of local active galactic nuclei: III. Polar dust emission
Recent mid-infrared (MIR) interferometric observations showed in few active
galactic nuclei (AGN) that the bulk of the infrared emission originates from
the polar region above the putative torus, where only little dust should be
present. Here, we investigate whether such strong polar dust emission is common
in AGN. Out of 149 Seyferts in the MIR atlas of local AGN (Asmus et al.), 21
show extended MIR emission on single dish images. In 18 objects, the extended
MIR emission aligns with the system axis position angle, established by [OIII],
radio, polarisation and maser based position angle measurements. The relative
amount of resolved MIR emission is at least 40 per cent and scales with the
[OIV] fluxes implying a strong connection between the extended continuum and
[OIV] emitters. These results together with the radio-quiet nature of the
Seyferts support the scenario that the bulk of MIR emission is emitted by dust
in the polar region and not by the torus, which would demand a new paradigm for
the infrared emission structure in AGN. The current low detection rate of polar
dust in the AGN of the MIR atlas is explained by the lack of sufficient high
quality MIR data and the requirement for the orientation, NLR strength and
distance of the AGN. The James-Webb Space Telescope will enable much deeper
nuclear MIR studies with comparable angular resolution, allowing us to resolve
the polar emission and surroundings in most of the nearby AGN.Comment: Accepted for publication in ApJ on Mar 08 (submitted Dec 22
The subarcsecond mid-infrared view of local active galactic nuclei: II. The mid-infrared--X-ray correlation
We present an updated mid-infrared (MIR) versus X-ray correlation for the
local active galactic nuclei (AGN) population based on the high angular
resolution 12 and 18um continuum fluxes from the AGN subarcsecond MIR atlas and
2-10 keV and 14-195 keV data collected from the literature. We isolate a sample
of 152 objects with reliable AGN nature and multi-epoch X-ray data and minimal
MIR contribution from star formation. Although the sample is not homogeneous or
complete, we show that our results are unlikely to be affected by biases. The
MIR--X-ray correlation is nearly linear and within a factor of two independent
of the AGN type and the wavebands used. The observed scatter is <0.4 dex. A
possible flattening of the correlation slope at the highest luminosities probed
(~ 10^45 erg/s) is indicated but not significant. Unobscured objects have, on
average, an MIR--X-ray ratio that is only <= 0.15 dex higher than that of
obscured objects. Objects with intermediate X-ray column densities (22 < log
N_H < 23) actually show the highest MIR--X-ray ratio on average. Radio-loud
objects show a higher mean MIR--X-ray ratio at low luminosities, while the
ratio is lower than average at high luminosities. This may be explained by
synchrotron emission from the jet contributing to the MIR at low-luminosities
and additional X-ray emission at high luminosities. True Seyfert 2 candidates
and double AGN do not show any deviation from the general behaviour. Finally,
we show that the MIR--X-ray correlation can be used to verify the AGN nature of
uncertain objects. Specifically, we give equations that allow to determine the
intrinsic 2-10 keV luminosities and column densities for objects with complex
X-ray properties to within 0.34 dex. These techniques are applied to the
uncertain objects of the remaining AGN MIR atlas, demonstrating the usefulness
of the MIR--X-ray correlation as an empirical tool.Comment: Accepted for publication in MNRAS, 40 pages, 25 figure
Evolution of field spiral galaxies up to redshifts z=1
We have gained VLT/FORS spectra and HST/ACS images of a sample of 220 distant
field spiral galaxies. Spatially resolved rotation curves were extracted and
fitted with synthetic velocity fields that take into account all geometric and
observational effects, like blurring due to the slit width and seeing
influence. The maximum rotation velocity Vmax could be determined for 124
galaxies that cover the redshift range 0.1<z<1.0. The luminosity-rotation
velocity distribution of this sample is offset from the Tully-Fisher relation
(TFR) of local low-mass spirals, whereas the distant high-mass spirals are
compatible with the local TFR. We show that the slope of the local and the
intermediate-z TFR would be in compliance if its scatter decreased by more than
a factor of 3 between z~0.5 and z~0. On the other hand, the distant
low-luminosity disks have much lower stellar M/L ratios than their local
counterparts, while high-luminosity disks barely evolved in M/L over the
covered redshift range. This could be the manifestation of the "downsizing"
effect, i.e. the succesive shift of the peak of star formation from high-mass
to low-mass galaxies towards lower redshifts. This trend might be canceled out
in the TF diagram due to the simultaneous evolution of multiple parameters. We
also estimate the ratios between stellar and total masses, finding that these
remained constant since z=1, as would be expected in the context of
hierarchically growing structure. (Abridged)Comment: 20 pages, 5 figures, ApJ, accepte
Níveis de danos do nematóide de cisto da soja.
bitstream/item/24729/1/COT200269.pdfDocumento on-line
Reprodução do nematoide de galhas em plantas forrageiras utilizadas em sistemas integrados de produção agropecuária.
bitstream/item/39450/1/Cot28-98.pd
Reprodução de Meloidogyne javanica em algumas plantas daninhas de ocorrência freqüente na Regiao Oeste do Brasil.
bitstream/item/39434/1/Cot19-97.pd
Efeito de duas concentrações de cama de aviário sobre a reprodução de Meloidogyne javanica e o crescimento de plantas de tomateiro.
bitstream/item/39648/1/PA-5-1998.pd
Reprodução do nematóide das galhas (Meloidogyne javanica) em algumas plantas alternativas para uso em sucessão à cultura da soja.
bitstream/item/62572/1/COT-37-2001.pd
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