15,419 research outputs found
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
Deactivation and regeneration of activated carbon-supported Rh and Ru catalysts in the hydrodechlorination of chloromethanes into light olefins
This work analyses the deactivation of activated carbon-supported Rh and Ru (both at 1 wt%) catalysts (Rh/C and Ru/C) in the hydrodechlorination (HDC) of dichloromethane (DCM) and chloroform (TCM). The deactivation can be mainly attributed to the coverage of active metal centres by organometallic species resulting from the chemisorption of reaction products, such as olefins, at the electro-deficient metal sites. With DCM, the activity of Ru/C decreased by more than 80% after 90 h on stream at 250 °C and with a space time of 1.7 kg h mol−1. Under the same conditions, with TCM, the Rh/C and Ru/C catalysts lost 75% of activity after 84 and 54 h on stream, respectively. A regeneration treatment with air at 250 °C allowed complete recovery of the catalytic activity. After each deactivation-regeneration cycle, the selectivity to olefins increased. Therefore, HDC with the catalysts tested provides a promising way for the upgrading of chloromethanes from waste gas streams into light olefinshe authors gratefully acknowledge financial support from FEDER/
Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de
Investigación/CTM2017-85498-R. M. Martín Martínez acknowledges a
postdoctoral grant, 2017-T2/AMB-5668, from the Comunidad de
Madrid “Atracción de talento investigador” programm
Lateral patterning of multilayer InAs/GaAs(001) quantum dot structures by in-vacuo focused ion beam
We report on the effects of patterning and layering on multilayer InAs/GaAs(001) quantum dot structures laterally ordered using an in vacuo focused ion beam. The patterned hole size and lateral pattern spacing affected the quantum dot size and the fidelity of the quantum dots with respect to the lateral patterns. 100% pattern fidelity was retained after six layers of dots for a 9.0 ms focused ion beam dwell time and 2.0 µm lateral pattern spacing. Analysis of the change in quantum dot size as a function of pattern spacing provided a means of estimating the maximum average adatom surface diffusion length to be approximately 500 nm, and demonstrated the ability to alter the wetting layer thickness via pattern spacing. Increasing the number of layers from six to 26 resulted in mound formation, which destroyed the pattern fidelity at close pattern spacings and led to a bimodal quantum dot size distribution as measured by atomic force microscopy. The bimodal size distribution also affected the optical properties of the dots, causing a split quantum dot photoluminescence peak where the separation between the split peaks increased with increasing pattern spacing.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98602/1/0957-4484_23_13_135401.pd
Near-Infrared Polarimetric Adaptive Optics Observations of NGC 1068: A torus created by a hydromagnetic outflow wind
We present J' and K' imaging linear polarimetric adaptive optics observations
of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to
study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5" (30 pc)
aperture at K', we find that polarisation arising from the passage of radiation
from the inner edge of the torus through magnetically aligned dust grains in
the clumps is the dominant polarisation mechanism, with an intrinsic
polarisation of 7.0%2.2%. This result yields a torus magnetic field
strength in the range of 482 mG through paramagnetic alignment, and
139 mG through the Chandrasekhar-Fermi method. The measured
position angle (P.A.) of polarisation at K is found to be similar to the
P.A. of the obscuring dusty component at few parsec scales using infrared
interferometric techniques. We show that the constant component of the magnetic
field is responsible for the alignment of the dust grains, and aligned with the
torus axis onto the plane of the sky. Adopting this magnetic field
configuration and the physical conditions of the clumps in the MHD outflow wind
model, we estimate a mass outflow rate 0.17 M yr at 0.4
pc from the central engine for those clumps showing near-infrared dichroism.
The models used were able to create the torus in a timescale of 10
yr with a rotational velocity of 1228 km s at 0.4 pc. We conclude
that the evolution, morphology and kinematics of the torus in NGC 1068 can be
explained within a MHD framework.Comment: 14 pages, 4 figures, Accepted by MNRA
- …