19 research outputs found
A High Resolution Survey of the Galactic Plane at 408 MHz
The interstellar medium is a complex 'ecosystem' with gas constituents in the
atomic, molecular, and ionized states, dust, magnetic fields, and relativistic
particles. The Canadian Galactic Plane Survey has imaged these constituents
with angular resolution of the order of arcminutes. This paper presents radio
continuum data at 408 MHz over the area 52 degrees < longitude < 193 degrees,
-6.5 degrees < latitude < 8.5 degrees, with an extension to latitude = 21
degrees in the range 97 degrees < longitude < 120 degrees, with angular
resolution 2.8' x 2.8' cosec(declination). Observations were made with the
Synthesis Telescope at the Dominion Radio Astrophysical Observatory as part of
the Canadian Galactic Plane Survey. The calibration of the survey using
existing radio source catalogs is described. The accuracy of 408-MHz flux
densities from the data is 6%. Information on large structures has been
incorporated into the data using the single-antenna survey of Haslam (1982).
The paper presents the data, describes how it can be accessed electronically,
and gives examples of applications of the data to ISM research.Comment: Accepted for publication in the Astronomical Journa
A New Distance to the Supernova Remnant DA 530 Based on HI Absorption of Polarized Emission
Supernova remnants (SNRs) are significant contributors of matter and energy
to the interstellar medium. Understanding the impact and the mechanism of this
contribution requires knowledge of the physical size, energy, and expansion
rate of individual SNRs, which can only come if reliable distances can be
obtained. We aim to determine the distance to the SNR DA 530 (G93.3+6.9), an
object of low surface brightness. To achieve this, we used the Dominion Radio
Astrophysical Observatory Synthesis Telescope and the National Radio Astronomy
Observatory Very Large Array to observe the absorption by intervening HI of the
polarized emission from DA 530. Significant absorption was detected at
velocities and -67 km/s (relative to the local standard of rest),
corresponding to distances of 4.4 and 8.3 kpc, respectively. Based on the radio
and X-ray characteristics of DA 530, we conclude that the minimum distance is
4.4 kpc. At this minimum distance, the diameter of the SNR is
34 pc, and the elevation above the Galactic plane is
537 pc. The km/s absorption likely occurs in gas whose
velocity is not determined by Galactic rotation. We present a new data
processing method for combining Stokes and observations of the emission
from an SNR into a single HI absorption spectrum, which avoids the difficulties
of the noise-bias subtraction required for the calculation of polarized
intensity. The polarized absorption technique can be applied to determine
distances to many more SNRs
Measuring magnetism in the Milky Way with the Square Kilometre Array
Magnetic fields in the Milky Way are present on a wide variety of sizes and
strengths, influencing many processes in the Galactic ecosystem such as star
formation, gas dynamics, jets, and evolution of supernova remnants or pulsar
wind nebulae. Observation methods are complex and indirect; the most used of
these are a grid of rotation measures of unresolved polarized extragalactic
sources, and broadband polarimetry of diffuse emission. Current studies of
magnetic fields in the Milky Way reveal a global spiral magnetic field with a
significant turbulent component; the limited sample of magnetic field
measurements in discrete objects such as supernova remnants and HII regions
shows a wide variety in field configurations; a few detections of magnetic
fields in Young Stellar Object jets have been published; and the magnetic field
structure in the Galactic Center is still under debate.
The SKA will unravel the 3D structure and configurations of magnetic fields
in the Milky Way on sub-parsec to galaxy scales, including field structure in
the Galactic Center. The global configuration of the Milky Way disk magnetic
field, probed through pulsar RMs, will resolve controversy about reversals in
the Galactic plane. Characteristics of interstellar turbulence can be
determined from the grid of background RMs. We expect to learn to understand
magnetic field structures in protostellar jets, supernova remnants, and other
discrete sources, due to the vast increase in sample sizes possible with the
SKA. This knowledge of magnetic fields in the Milky Way will not only be
crucial in understanding of the evolution and interaction of Galactic
structures, but will also help to define and remove Galactic foregrounds for a
multitude of extragalactic and cosmological studies.Comment: 19 pages, 2 figures; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)09
Calibrating CHIME, A New Radio Interferometer to Probe Dark Energy
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit
interferometer currently being built at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral
hydrogen in the frequency range 400 -- 800\,MHz over half of the sky, producing
a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 --
2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that
will yield constraints on the BAO power spectrum and provide a test-bed for our
calibration scheme. I will discuss the CHIME calibration requirements and
describe instrumentation we are developing to meet these requirements
Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder
A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping
Experiment) is currently being commissioned at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical
interferometer designed to measure the large scale neutral hydrogen power
spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used
to measure the baryon acoustic oscillation (BAO) scale across this poorly
probed redshift range where dark energy becomes a significant contributor to
the evolution of the Universe. The instrument revives the cylinder design in
radio astronomy with a wide field survey as a primary goal. Modern low-noise
amplifiers and digital processing remove the necessity for the analog
beamforming that characterized previous designs. The Pathfinder consists of two
cylinders 37\,m long by 20\,m wide oriented north-south for a total collecting
area of 1,500 square meters. The cylinders are stationary with no moving parts,
and form a transit instrument with an instantaneous field of view of
100\,degrees by 1-2\,degrees. Each CHIME Pathfinder cylinder has a
feedline with 64 dual polarization feeds placed every 30\,cm which
Nyquist sample the north-south sky over much of the frequency band. The signals
from each dual-polarization feed are independently amplified, filtered to
400-800\,MHz, and directly sampled at 800\,MSps using 8 bits. The correlator is
an FX design, where the Fourier transform channelization is performed in FPGAs,
which are interfaced to a set of GPUs that compute the correlation matrix. The
CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed
to detect the BAO feature and constrain the distance-redshift relation.Comment: 20 pages, 12 figures. submitted to Proc. SPIE, Astronomical
Telescopes + Instrumentation (2014