1,279 research outputs found
The contribution of faint AGN to the hard X-ray background
Hard X-ray selection is the most efficient way to discriminate between
accretion-powered sources, such as AGN, from sources dominated by starlight.
Hard X-rays are also less affected than other bands by obscuration. We have
then carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the
largely unexplored 5-10 keV band, finding 180 sources in ~50 deg^2 of sky with
flux >5E-14 erg cm-2 s-1. After correction for the non uniform sky coverage
this corresponds to resolving about 30 % of the hard Cosmic X-ray Background
(XRB). Here we report on a first optical spectroscopic identification campaign,
finding 12 AGN out of 14 X-ray error-boxes studied. Seven AGN show evidence for
obscuration in X-ray and optical bands, a fraction higher than in previous
ROSAT or ASCA-ROSAT surveys (at a 95-99 % and 90 % confidence level
respectively), thus supporting the scenario in which a significant fraction of
the XRB is made by obscured AGN.Comment: MNRAS, revised version after minor referee comment
AGN counts at 15um. XMM observations of the ELAIS-S1-5 sample
Context: The counts of galaxies and AGN in the mid infra-red (MIR) bands are
important instruments for studying their cosmological evolution. However, the
classic spectral line ratios techniques can become misleading when trying to
properly separate AGN from starbursts or even from apparently normal galaxies.
Aims: We use X-ray band observations to discriminate AGN activity in
previously classified MIR-selected starburst galaxies and to derive updated
AGN1 and (Compton thin) AGN2 counts at 15 um.
Methods: XMM observations of the ELAIS-S1 15um sample down to flux limits
~2x10^-15 erg cm^-2 s^-1 (2-10 keV band) were used. We classified as AGN all
those MIR sources with a unabsorbed 2-10 keV X-ray luminosity higher that
~10^42 erg/s.
Results: We find that at least about 13(+/-6) per cent of the previously
classified starburst galaxies harbor an AGN. According to these figures, we
provide an updated estimate of the counts of AGN1 and (Compton thin) AGN2 at 15
um. It turns out that at least 24% of the extragalactic sources brighter than
0.6 my at 15 um are AGN (~13% contribution to the extragalactic background
produced at fluxes brighter than 0.6 mJy).Comment: Accepted for publication on A&
Importância do tratamento de sementes de soja com fungicidas na safra 2010/2011, ano de "La Nina" - Série Sementes.
Histórico do tratamento de sementes. Sementes devem ser bem armazenadas antes do plantio. Como tratar. Tratamento utilizando tambor giratório ou betoneira. Tratamento realizado diretamente na semeadora. Tratamento utilizando máquinas de tratar sementes. Tratamento industrial.bitstream/item/23533/1/CT-82.indd.pdf; bitstream/item/90483/1/CT82-VE.pd
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