186 research outputs found
An Imprint of Molecular Cloud Magnetization in the Morphology of the Dust Polarized Emission
We describe a morphological imprint of magnetization found when considering
the relative orientation of the magnetic field direction with respect to the
density structures in simulated turbulent molecular clouds. This imprint was
found using the Histogram of Relative Orientations (HRO): a new technique that
utilizes the gradient to characterize the directionality of density and column
density structures on multiple scales. We present results of the HRO analysis
in three models of molecular clouds in which the initial magnetic field
strength is varied, but an identical initial turbulent velocity field is
introduced, which subsequently decays. The HRO analysis was applied to the
simulated data cubes and mock-observations of the simulations produced by
integrating the data cube along particular lines of sight. In the 3D analysis
we describe the relative orientation of the magnetic field with
respect to the density structures, showing that: 1.The magnetic field shows a
preferential orientation parallel to most of the density structures in the
three simulated cubes. 2.The relative orientation changes from parallel to
perpendicular in regions with density over a critical density in the
highest magnetization case. 3.The change of relative orientation is largest for
the highest magnetization and decreases in lower magnetization cases. This
change in the relative orientation is also present in the projected maps. In
conjunction with simulations HROs can be used to establish a link between the
observed morphology in polarization maps and the physics included in
simulations of molecular clouds.Comment: (16 pages, 11 figures, submitted to ApJ 05MAR2013, accepted
07JUL2013
Tracing H2 column density with atomic carbon (CI) and CO isotopologues
We present first results of neutral carbon ([CI], 3P1 - 3P0 at 492 GHz) and
carbon monoxide (13CO, J = 1 - 0) mapping in the Vela Molecular Ridge cloud C
(VMR-C) and G333 giant molecular cloud complexes with the NANTEN2 and Mopra
telescopes. For the four regions mapped in this work, we find that [CI] has
very similar spectral emission profiles to 13CO, with comparable line widths.
We find that [CI] has opacity of 0.1 - 1.3 across the mapped region while the
[CI]/13CO peak brightness temperature ratio is between 0.2 to 0.8. The [CI]
column density is an order of magnitude lower than that of 13CO. The H2 column
density derived from [CI] is comparable to values obtained from 12CO. Our maps
show CI is preferentially detected in gas with low temperatures (below 20 K),
which possibly explains the comparable H2 column density calculated from both
tracers (both CI and 12CO underestimate column density), as a significant
amount of the CI in the warmer gas is likely in the higher energy state
transition ([CI], 3P2 - 3P1 at 810 GHz), and thus it is likely that
observations of both the above [CI] transitions are needed in order to recover
the total H2 column density.Comment: accepted for publication in ApJ Letter
SOFIA and ALMA Investigate Magnetic Fields and Gas Structures in Massive Star Formation: The Case of the Masquerading Monster in BYF 73
We present SOFIA+ALMA continuum and spectral-line polarisation data on the
massive molecular cloud BYF 73, revealing important details about the magnetic
field morphology, gas structures, and energetics in this unusual massive star
formation laboratory. The 154m HAWC+ polarisation map finds a highly
organised magnetic field in the densest, inner 0.550.40 pc portion of
the cloud, compared to an unremarkable morphology in the cloud's outer layers.
The 3mm continuum ALMA polarisation data reveal several more structures in the
inner domain, including a pc-long, 500 M "Streamer" around the
central massive protostellar object MIR 2, with magnetic fields mostly parallel
to the east-west Streamer but oriented north-south across MIR 2. The magnetic
field orientation changes from mostly parallel to the column density structures
to mostly perpendicular, at thresholds = 6.610
m, = 2.510 m, and =
427 nT. ALMA also mapped Goldreich-Kylafis polarisation in CO
across the cloud, which traces in both total intensity and polarised flux, a
powerful bipolar outflow from MIR 2 that interacts strongly with the Streamer.
The magnetic field is also strongly aligned along the outflow direction;
energetically, it may dominate the outflow near MIR 2, comprising rare evidence
for a magnetocentrifugal origin to such outflows. A portion of the Streamer may
be in Keplerian rotation around MIR 2, implying a gravitating mass 135050
M for the protostar+disk+envelope; alternatively, these kinematics
can be explained by gas in free fall towards a 95035 M object.
The high accretion rate onto MIR 2 apparently occurs through the Streamer/disk,
and could account for 33% of MIR 2's total luminosity via gravitational
energy release.Comment: 33 pages, 32 figures, accepted by ApJ. Line-Integral Convolution
(LIC) images and movie versions of Figures 3b, 7, and 29 are available at
https://gemelli.spacescience.org/~pbarnes/research/champ/papers
Spider Optimization: Probing the Systematics of a Large Scale B-Mode Experiment
Spider is a long-duration, balloon-borne polarimeter designed to measure
large scale Cosmic Microwave Background (CMB) polarization with very high
sensitivity and control of systematics. The instrument will map over half the
sky with degree angular resolution in I, Q and U Stokes parameters, in four
frequency bands from 96 to 275 GHz. Spider's ultimate goal is to detect the
primordial gravity wave signal imprinted on the CMB B-mode polarization. One of
the challenges in achieving this goal is the minimization of the contamination
of B-modes by systematic effects. This paper explores a number of instrument
systematics and observing strategies in order to optimize B-mode sensitivity.
This is done by injecting realistic-amplitude, time-varying systematics in a
set of simulated time-streams. Tests of the impact of detector noise
characteristics, pointing jitter, payload pendulations, polarization angle
offsets, beam systematics and receiver gain drifts are shown. Spider's default
observing strategy is to spin continuously in azimuth, with polarization
modulation achieved by either a rapidly spinning half-wave plate or a rapidly
spinning gondola and a slowly stepped half-wave plate. Although the latter is
more susceptible to systematics, results shown here indicate that either mode
of operation can be used by Spider.Comment: 15 pages, 12 figs, version with full resolution figs available here
http://www.astro.caltech.edu/~lgg/spider_front.ht
Design and construction of a carbon fiber gondola for the SPIDER balloon-borne telescope
We introduce the light-weight carbon fiber and aluminum gondola designed for
the SPIDER balloon-borne telescope. SPIDER is designed to measure the
polarization of the Cosmic Microwave Background radiation with unprecedented
sensitivity and control of systematics in search of the imprint of inflation: a
period of exponential expansion in the early Universe. The requirements of this
balloon-borne instrument put tight constrains on the mass budget of the
payload. The SPIDER gondola is designed to house the experiment and guarantee
its operational and structural integrity during its balloon-borne flight, while
using less than 10% of the total mass of the payload. We present a construction
method for the gondola based on carbon fiber reinforced polymer tubes with
aluminum inserts and aluminum multi-tube joints. We describe the validation of
the model through Finite Element Analysis and mechanical tests.Comment: 16 pages, 11 figures. Presented at SPIE Ground-based and Airborne
Telescopes V, June 23, 2014. To be published in Proceedings of SPIE Volume
914
The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry
(BLAST-Pol) is a suborbital mapping experiment designed to study the role
played by magnetic fields in the star formation process. BLAST-Pol is the
reconstructed BLAST telescope, with the addition of linear polarization
capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a
focal plane that consists of 280 bolometric detectors in three arrays,
observing simultaneously at 250, 350, and 500 um. The diffraction-limited
optical system provides a resolution of 30'' at 250 um. The polarimeter
consists of photolithographic polarizing grids mounted in front of each
bolometer/detector array. A rotating 4 K achromatic half-wave plate provides
additional polarization modulation. With its unprecedented mapping speed and
resolution, BLAST-Pol will produce three-color polarization maps for a large
number of molecular clouds. The instrument provides a much needed bridge in
spatial coverage between larger-scale, coarse resolution surveys and narrow
field of view, and high resolution observations of substructure within
molecular cloud cores. The first science flight will be from McMurdo Station,
Antarctica in December 2010.Comment: 14 pages, 9 figures Submitted to SPIE Astronomical Telescopes and
Instrumentation Conference 201
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