387 research outputs found
2016+112: A Gravitationally Lensed Type-II Quasar
A single-screen model of the gravitational lens system 2016+112 is proposed,
that explains recent Hubble Space Telescope} (HST) infrared (NICMOS-F160W)
observations and new high-resolution European VLBI Network (EVN) 5-GHz radio
observations, presented in this paper. In particular, we find that a massive
`dark' structure at the lens position, previously suggested by X-ray, optical
and spectroscopic observations of the field around 2016+112, is not necessarily
required to accommodate the strong lensing constraints. A massive structure to
the north-west of the lens system, suggested from a weak-lensing analysis of
the field, is included in the model. The lensed source is an X-ray bright
active galaxy at z=3.273 with a central bright optical continuum core and
strong narrow emission lines, suggestive of a type-II quasar. The EVN 5-GHz
radio maps show a radio-jet structure with at least two compact subcomponents.
We propose that the diamond caustic crosses the counter-jet of the radio
source, so that part of the counter-jet, host galaxy and narrow-line emission
regions are quadruply imaged. The remainder of the radio source, including the
core, is doubly imaged. Our lens model predicts a very high magnification
(mu~300) at the bightness peaks of the inner two radio components of complex C.
If the jet exhibits relativistic velocities on micro-arsecond scales, it might
result in apparent hyperluminal motion. However, the lack of strong radio
variability and the peaked radio spectrum imply that these motions need not be
present in the source. Our model furthermore implies that the optical spectrum
of C' can only show features of the AGN and its host galaxy.Comment: 10 pages, 3 figures, accepted by MNRAS; minor change
Radio Astronomy
Contains reports on nine research projects.National Science Foundation (Grant AST 86-17172)National Aeronautics and Space Administration (Contract NAS7-918)Jet Propulsion Laboratory (Contract 958048)U.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)U.S. Navy - Office of Naval Research (Contract N00014-86-C-2114)SM Systems and Research, Inc.National Aeronautics and Space Administration/Goddard Space Flight Center (Grant NAG5-10)Center for Advanced Television StudiesBrazil, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (Grant 300.832-82)National Aeronautics and Space Administration/Goddard Space Flight Center (Grant NAG5-537
Drivers of diversification and pluriactivity among smallholder farmers—evidence from Nigeria
Diversification and pluriactivity have become a norm among farm business owners (FBOs) due to persistent low farm income. This study applies the resource-based theory to examine drivers of diversification and livelihood income-oriented towards a sustainable livelihood. Our framework develops hypotheses about the impact of internal and external resources on livelihood choices at the household level. We use a survey of 480 rural Nigerian farmers (agripreneurs), applying a Multivariate Tobit to test our framework. We find that education plays the most significant role in all types of employment options. The more FBOs are educated, the more the likelihood that they will choose non-farm or wage employment. This study revealed that while the agriculture sector’s share of rural employment is declining, non-farm is on the increase. More so, there is a decline in farming among the young generation, marital status bias and gender influence in resource allocation. The socioeconomic (income and food security) and socio-cultural (employment and rural-urban migration) implications of rural sustainability linked to UN Development Goals have been highlighted and analysed in this article
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