174 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
The highly polarized dusty emission core of Cygnus A
We report the detection of linearly polarized emission at 53 and 89 m,
from the radio-loud active galactic nucleus (AGN) Cygnus A using HAWC+ onboard
SOFIA. We measure a highly polarized core of % and % with a
position angle (P.A.) of polarization of and
at 53 and 89 m, respectively. We find (1) a synchrotron dominated core
with a flat spectrum () and a turn-over at m,
which implies synchrotron emission is insignificant in the infrared (IR), and
(2) a m bump peaking at m described by a blackbody
component with color temperature of K. The polarized SED has the same
shape as the IR bump of the total flux SED. We observe a change in the P.A. of
polarization of from 2 to 89 m, which suggests a change
of polarization mechanisms. The ultraviolet, optical and near-IR polarization
has been convincingly attributed to scattering by polar dust, consistent with
the usual torus scenario, though this scattered component can only be directly
observed from the core in the near-IR. By contrast, the gradual rotation by
towards the far-IR, and the near-perfect match between the
total and polarized IR bumps, indicate that dust emission from aligned dust
grains becomes dominant at m, with a large polarization of 10% at
a nearly constant P.A. This result suggests that a coherent dusty and magnetic
field structure dominates the m emission around the AGN.Comment: 9 pages, 4 figures. accepted for publication in ApJ
GTC/CanariCam Mid-IR Polarimetry of Magnetic Fields in Star-Forming Region W51 IRS2
We present 0.4 arcsec-resolution imaging polarimetry at 8.7, 10.3, and 12.5
microns, obtained with CanariCam at the Gran Telescopio Canarias, of the
central region of W51 IRS2. The polarization, as high as 14 percent, arises
from silicate particles aligned by the interstellar magnetic field. We
separate, or unfold, the polarization of each sightline into emission and
absorption components, from which we infer the morphologies of the
corresponding projected magnetic fields that thread the emitting and
foreground-absorbing regions. We conclude that the projected magnetic field in
the foreground material is part of the larger-scale ambient field. The
morphology of the projected magnetic field in the mid-IR emitting region
spanning the cometary HII region W51 IRS2W is similar to that in the absorbing
region. Elsewhere, the two magnetic fields differ significantly with no clear
relationship between them. The magnetic field across the W51 IRS2W cometary
core appears to be an integral part of a champagne outflow of gas originating
in the core and dominating the energetics there. The bipolar outflow, W51north
jet, that appears to originate at or near SMA1/N1 coincides almost exactly with
a clearly demarcated north-south swath of lower polarization. While
speculative, comparison of mid-IR and submm polarimetry on two different scales
may support a picture in which SMA1/N1 plays a major role in the magnetic field
structure across W51 IRS2.Comment: To be published in the Astrophysical Journa
Magnetic field structures in star-forming regions : mid-infrared imaging polarimetry of K3-50
We report new imaging polarimetry observations of the Galactic compact H ii region K3-50 using CanariCam at the Gran Telescopio Canarias. We use a standard polarimetric analysis technique, first outlined by Aitken, to decompose the observed polarization images centred at 8.7, 10.3, and 12.5 μm into the emissive and absorptive components from silicate grains that are aligned with the local magnetic field. These components reveal the spatially resolved magnetic field structures across the mid-infrared emission area of K3-50. We examine these structures and show that they are consistent with previously observed features and physical models of K3-50, such as the molecular torus and the ionized outflow. We propose a 3D geometry for all the structures seen at different wavelengths. We also compute relevant physical quantities in order to estimate the associated magnetic field strengths that would be implied under various physical assumptions. We compare these results with magnetohydrodynamic simulations of protostar formation that predict the magnetic field strength and configuration. We find that the magnetic field may be dynamically important in the innermost 0.2 pc of the molecular torus, but that the torus is more likely to be rotationally supported against gravity outside this radius. Similarly, magnetic fields are unlikely to dominate the global physics of the ionized outflow, but they may be important in helping confine the flow near the cavity wall in some locations. Ours is the first application of the Aitken technique to spatially resolved magnetic field structures in multiple layers along the line of sight, effectively a method of ‘polarization tomography’Peer reviewe
Broadband circularly-polarized infrared emission from multilayer metamaterials
Development of a 2D metamaterial that preferentially emits broadband circularly-polarized (CP) infrared radiation is hindered by the fact that orthogonal electric-field components are uncorrelated at the surface of the thermal emitter, a consequence of the fluctuation-dissipation theorem. We achieve broadband CP thermal emission by fabricating a meanderline quarter-wave retarder on a transparent thermal-isolation layer. Behind this isolation layer, in thermal contact with the emitter, is a wire-grid polarizer. Along with an unavoidable linear polarized radiation characteristic from the meanderline, we measured a degree of circular polarization (DOCP) of 28%, averaged over the 8- to 12 mu m band
The Magnetic Field in the central parsec of the Galaxy
We present a polarisation map of the warm dust emission from the minispiral
in the central parsec of the Galactic centre. The observations were made at a
wavelength of 12.5 microns with CanariCam mounted on the 10.4-m Gran Telescopio
Canarias. The magnetic field traced by the polarised emission from aligned dust
grains is consistent with previous observations, but the increased resolution
of the present data reveals considerably more information on the detailed
structure of the B field and its correspondence with the filamentary emission
seen in both mid-infrared continuum emission and free-free emission at cm
wavelengths. The magnetic field appears to be compressed and pushed by the
outflows from luminous stars in the Northern Arm, but it is not disordered by
them. We identify some magnetically coherent filaments that cross the Northern
Arm at a Position Angle of ~45 degrees, and which may trace orbits inclined to
the primary orientation of the Northern Arm and circumnuclear disk. In the
East-West bar, the magnetic fields implied by the polarization in the lower
intensity regions lie predominantly along the bar at a Position Angle of 130 -
140 degrees. In contrast to the Northern Arm, the brighter regions of the bar
tend to have lower degrees of polarization with a greater divergence in
position angle compared to the local diffuse emission. It appears that the
diffuse emission in the East-West bar traces the underlying field and that the
bright compact sources are unrelated objects presumably projected onto the bar
and with different field orientationsComment: 12 Pages, 5 figures, 1 Table. To be published in MNRA
- …