1,305 research outputs found
A Lack of Resolved Near-Infrared Polarization Across the Face of M51
The galaxy M51 was observed using the Mimir instrument on the Perkins
telescope to constrain the resolved H-band (1.6 m) polarization across the
galaxy. These observations place an upper limit of on the -band
polarization across the face of M51, at 0.6 arcsecond pixel sampling. Even with
smoothing to coarser angular resolutions, to reduce polarization uncertainty,
the -band polarization remains undetected. The polarization upper limit at
-band, when combined with previous resolved optical polarimetry, rules out a
Serkowski-like polarization dependence on wavelength. Other polarization
mechanisms cannot account for the observed polarization ratio () across the face of M51.Comment: 4 pages, 2 figures, Accepted for publication in ApJ
The Magnetic Field of L1544: I. Near-Infrared Polarimetry and the Non-Uniform Envelope
The magnetic field (B-field) of the starless dark cloud L1544 has been
studied using near-infrared (NIR) background starlight polarimetry (BSP) and
archival data in order to characterize the properties of the plane-of-sky
B-field. NIR linear polarization measurements of over 1,700 stars were obtained
in the H-band and 201 of these were also measured in the K-band. The NIR BSP
properties are correlated with reddening, as traced using the RJCE (H-M)
method, and with thermal dust emission from the L1544 cloud and envelope seen
in Herschel maps. The NIR polarization position angles change at the location
of the cloud and exhibit their lowest dispersion of position angles there,
offering strong evidence that NIR polarization traces the plane-of-sky B-field
of L1544. In this paper, the uniformity of the plane-of-sky B-field in the
envelope region of L1544 is quantitatively assessed. This allowed evaluating
the approach of assuming uniform field geometry when measuring relative
mass-to-flux ratios in the cloud envelope and core based on averaging of the
envelope radio Zeeman observations, as in Crutcher et al. (2009). In L1544, the
NIR BSP shows the envelope B-field to be significantly non-uniform and likely
not suitable for averaging Zeeman properties without treating intrinsic
variations. Deeper analyses of the NIR BSP and related data sets, including
estimates of the B-field strength and testing how it varies with position and
gas density, are the subjects of later papers in this series.Comment: 16 pages, 9 figures; accepted for publication in The Astrophysical
Journa
Magnetic Field Uniformity Across the GF 9-2 YSO, L1082C Dense Core, and GF 9 Filamentary Dark Cloud
The orientation of the magnetic field (B-field) in the filamentary dark cloud
GF 9 was traced from the periphery of the cloud into the L1082C dense core that
contains the low-mass, low-luminosity Class 0 young stellar object (YSO) GF 9-2
(IRAS 20503+6006). This was done using SOFIA HAWC+ dust thermal emission
polarimetry (TEP) at 216 um in combination with Mimir near-infrared background
starlight polarimetry (BSP) conducted at H-band (1.6 um) and K-band (2.2 um).
These observations were augmented with published I-band (0.77 um) BSP and
Planck 850 um TEP to probe B-field orientations with offset from the YSO in a
range spanning 6000 AU to 3 pc. No strong B-field orientation change with
offset was found, indicating remarkable uniformity of the B-field from the
cloud edge to the YSO environs. This finding disagrees with weak-field models
of cloud core and YSO formation. The continuity of inferred B-field
orientations for both TEP and BSP probes is strong evidence that both are
sampling a common B-field that uniformly threads the cloud, core, and YSO
region. Bayesian analysis of Gaia DR2 stars matched to the Mimir BSP stars
finds a distance to GF 9 of 270 +/- 10 pc. No strong wavelength dependence of
B-field orientation angle was found, contrary to previous claims.Comment: 18 pages, 6 figures ApJ, accepte
Recent H-alpha results on pulsar B2224+65's bow-shock nebula, the "Guitar"
We used the 4 m Discovery Channel Telescope (DCT) at Lowell observatory in 2014 to observe the Guitar Nebula, an Hα bow-shock nebula around the high-velocity radio pulsar B2224+65. Since the nebula`s discovery in 1992, the structure of the bow-shock has undergone significant dynamical changes. We have observed the limb structure, targeting the "body" and "neck" of the guitar. Comparing the DCT observations to 1995 observations with the Palomar 200-inch Hale telescope, we found changes in both spatial structure and surface brightness in the tip, head, and body of the nebula
Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties
We present optical and near-infrared stellar polarization observations toward
the dark filamentary clouds associated with IC5146. The data allow us to
investigate the dust properties (this paper) and the magnetic field structure
(Paper II). A total of 2022 background stars were detected in -, -,
-, and/or -bands to mag. The ratio of the polarization
percentage at different wavelengths provides an estimate of ,
the wavelength of peak polarization, which is an indicator of the small-size
cutoff of the grain size distribution. The grain size distribution seems to
significantly change at 3 mag, where both the average and dispersion
of decrease. In addition, we found
0.6-0.9 m for mag, which is larger than the 0.55 m
in the general ISM, suggesting that grain growth has already started in low
regions. Our data also reveal that polarization efficiency (PE ) decreases with as a power-law in -, -, and
-bands with indices of -0.710.10, -1.230.10 and -0.530.09.
However, -band data show a power index change; the PE varies with
steeply (index of -0.950.30) when mag but softly
(index of -0.250.06) for greater values. The soft decay of PE in
high regions is consistent with the Radiative Aligned Torque model,
suggesting that our data trace the magnetic field to mag.
Furthermore, the breakpoint found in -band is similar to the where we
found the dispersion significantly decreased. Therefore, the
flat PE- in high regions implies that the power index changes result
from additional grain growth.Comment: 31 pages, 17 figures, and 3 tables; accepted for publication in Ap
Proper Motion of the Faint Star near KIC 8462852 (Boyajian's Star) - Not a Binary System
A faint star located 2 arcsec from KIC 8462852 was discovered in Keck 10 m
adaptive optics imaging in the near-infrared (NIR) in 2014 by Boyajian et
al. (2016). The closeness of the star to KIC 8462852 suggested the two could
constitute a binary, which might have implications for the cause of the
brightness dips seen by {\it Kepler} (Boyajian et al. (2016) and in
ground-based optical studies Boyajian et al. (2018). Here, NIR imaging in 2017
using the Mimir instrument resolved the pair and enabled measuring their
separation. The faint star had moved milliarcsec (mas) relative to
KIC 8462852 since 2014. The relative proper motion of the faint star is mas yr, for a tangential velocity of km s if
it is at the same 390 pc distance as KIC 8462852. Circular velocity at the 750
AU current projected separation is km s, hence the star pair
cannot be bound.Comment: 10 pages, 2 figure
Resolved Magnetic Field Mapping of a Molecular Cloud Using GPIPS
We present the first resolved map of plane-of-sky magnetic field strength for
a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 x 10 pc at a distance
of 1.88 kpc, masses 16,000 M_sun, and exhibits no star formation. Near-infrared
background starlight polarizations were obtained for the Galactic Plane
Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir
instrument. The cloud area of 0.78 deg2 contains 2684 significant starlight
polarizations for Two Micron All Sky Survey matched stars brighter than 12.5
mag in the H band. Polarizations are generally aligned with the cloud's major
axis, showing an average position angle dispersion of 15 \pm 2{\deg} and
polarization of 1.8 \pm 0.6%. The polarizations were combined with Galactic
Ring Survey 13CO spectroscopy and the Chandrasekhar-Fermi method to estimate
plane-of-sky magnetic field strengths, with an angular resolution of 100
arcsec. The average plane-of-sky magnetic field strength across the cloud is
5.40 \pm 0.04 {\mu}G. The magnetic field strength map exhibits seven
enhancements or "magnetic cores." These cores show an average magnetic field
strength of 8.3 \pm 0.9 {\mu}G, radius of 1.2 \pm 0.2 pc, intercore spacing of
5.7 \pm 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their
magnetic fields continue to suppress star formation. The magnetic field
strength shows a power-law dependence on gas volume density, with slope 0.75
\pm 0.02 for n_{H_2} >=10 cm-3. This power-law index is identical to those in
studies at higher densities, but disagrees with predictions for the densities
probed here.Comment: 11 pages, 15 figures, published in ApJ (2012, 755, 130
Expression of the chemokine receptor CCR6 in human renal inflammation
Background. Nodular inflammatory cell infiltrates with defined microarchitecture, i.e. tertiary lymphoid organs, develop in the tubulointerstitium during chronic renal inflammation. CCR6 and the corresponding ligand CCL20 are involved in the formation of gut-associated lymphatic tissue. We hypothesized that CCR6 might be involved in the formation of nodular infiltrates in the kidney. Methods. CCR6- and CD20-positive B cells were localized in renal biopsies with IgA nephropathy (n = 13), membranous nephropathy (n = 12), crescentic glomerulonephritis (cGN, n = 11) and chronic interstitial nephritis (n = 13), and in pre-implantation biopsies as controls (n = 8). The mRNA expression of CCR6 and the ligand CCL20 was quantified by real-time RT-PCR in 51 renal biopsies of the same disease entities. Results. In the pre-transplant biopsies, CCR6 was expressed by endothelial cells of peritubular and glomerular capillaries. In patients with glomerulonephritis, infiltrating cells were positive particularly in areas of nodular inflammatory cell accumulations. A major part of the CCR6-positive cells were CD20-positive B cells, but a part of the CD3-positive T cells were also found to be positive. The constitutive expression of CCR6 on the endothelium of glomerular capillaries was lost in biopsies with progressive injury. Tubular epithelial cells expressed CCR6 in inflamed kidneys, most commonly on the basolateral side. Conclusions. CCR6 and the corresponding ligand CCL20 might therefore be involved in the recruitment of T and B cells to organized nodular infiltrates in chronic renal inflammation. The functional role of endothelial CCR6 needs to be evaluated in further studie
Magnetic fields of the starless core L 1512
We present JCMT POL-2 850 um dust polarization observations and Mimir H band
stellar polarization observations toward the starless core L1512. We detect the
highly-ordered core-scale magnetic field traced by the POL-2 data, of which the
field orientation is consistent with the parsec-scale magnetic fields traced by
Planck data, suggesting the large-scale fields thread from the low-density
region to the dense core region in this cloud. The surrounding magnetic field
traced by the Mimir data shows a wider variation in the field orientation,
suggesting there could be a transition of magnetic field morphology at the
envelope scale. L1512 was suggested to be presumably older than 1.4 Myr in a
previous study via time-dependent chemical analysis, hinting that the magnetic
field could be strong enough to slow the collapse of L1512. In this study, we
use the Davis-Chandrasekhar-Fermi method to derive a plane-of-sky magnetic
field strength () of 187 uG and an observed mass-to-flux ratio
() of 3.52.4, suggesting that L1512 is magnetically
supercritical. However, the absence of significant infall motion and the
presence of an oscillating envelope are inconsistent with the magnetically
supercritical condition. Using a Virial analysis, we suggest the presence of a
hitherto hidden line-of-sight magnetic field strength of ~27 uG with a
mass-to-flux ratio () of ~1.6, in which case both magnetic and
kinetic pressures are important in supporting the L1512 core. On the other
hand, L1512 may have just reached supercriticality and will collapse at any
time.Comment: 25 pages, 10 figures, accepted for publication in Ap
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