63 research outputs found
A Thorough Investigation of Distance and Age of the Pulsar Wind Nebula 3C58
A growing number of researchers present evidence that the pulsar wind nebula
3C58 is much older than predicted by its proposed connection to the historical
supernova of A.D. 1181. There is also a great diversity of arguments. The
strongest of these arguments rely heavily on the assumed distance of 3.2 kpc
determined with HI absorption measurements. This publication aims at
determining a more accurate distance for 3C58 and re-evaluating the arguments
for a larger age. I have re-visited the distance determination of 3C58 based on
new HI data from the Canadian Galactic Plane Survey and our recent improvements
in the knowledge of the rotation curve of the outer Milky Way Galaxy. I have
also used newly determined distances to objects in the neighbourhood, which are
based on direct measurements by trigonometric parallax. I have derived a new
more reliable distance estimate of 2 kpc for 3C58. This makes the connection
between the pulsar wind nebula and the historical event from A.D. 1181 once
again much more viable.Comment: 11 pages, 6 figures, 1 table, accepted for publication in Astronomy &
Astrophysic
A Case Study of Triggered Star Formation in Cygnus X
Radiative feedback from massive stars can potentially trigger star formation
in the surrounding molecular gas. Inspired by the case of radiatively driven
implosion in M16 or Eagle Nebula, we analyze a similar case of star formation
observed in the Cygnus X region. We present new JCMT observations of
CO(3-2) and CO(3-2) molecular lines of a cometary feature located
at 50 pc north of the Cyg OB2 complex that was previously identified in
CO(3-2) mapping. These data are combined with archival H,
infrared, and radio continuum emission data, from which we measure the mass to
be 110 M. We identify Cyg OB2 as the ionizing source. We measure the
properties of two highly energetic molecular outflows and the photoionized rim.
From this analysis, we argue the external gas pressure and gravitational energy
dominate the internal pressure. The force balance along with previous
simulation results and a close comparison with the case of Eagle Nebula favours
a triggering scenario
A Relation Between the Warm Neutral and Ionized Media Observed in the Canadian Galactic Plane Survey
We report on a comparison between 21 cm rotation measure (RM) and the
optically-thin atomic hydrogen column density (N_HI) measured towards
unresolved extragalactic sources in the Galactic plane of the northern sky. HI
column densities integrated to the Galactic edge are measured immediately
surrounding each of nearly 2000 sources in 1-arcminute 21 cm line data, and are
compared to RMs observed from polarized emission of each source. RM data are
binned in column-density bins 4x10^20 cm^-2 wide, and one observes a strong
relationship between the number of hydrogen atoms in a 1 cm^2 column through
the plane and the mean RM along the same line-of-sight and path length. The
relationship is linear over one order of magnitude (from 0.8-14x10^21 atoms
cm^-2) of column densities, with a constant RM/N_HI -23.2+/-2.3 rad m^-2/10^21
atoms cm^-2, and a positive RM of 45.0+/-13.8 rad m^-2 in the presence of no
atomic hydrogen. This slope is used to calculate a mean volume-averaged
magnetic field in the 2nd quadrant of ~1.0+/-0.1 micro-Gauss directed
away from the Sun, assuming an ionization fraction of 8% (consistent with the
WNM). The remarkable consistency between this field and =1.2 micro-Gauss
found with the same RM sources and a Galactic model of dispersion measures
suggests that electrons in the partially ionized WNM are mainly responsible for
pulsar dispersion measures, and thus the partially-ionized WNM is the dominant
form of the magneto-ionic interstellar medium.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letters, July 15, 201
Probing ISM Magnetic Fields With SNRs
As supernova remnants expand, their shock waves are freezing in and
compressing the magnetic field lines they encounter; consequently we can use
supernova remnants as magnifying glasses for their ambient magnetic fields. We
will describe a simple model to determine emission, polarization, and rotation
measure characteristics of adiabatically expanding supernova remnants and how
we can exploit this model to gain information about the large scale magnetic
field in our Galaxy. We will give two examples: The SNR DA530, which is located
high above the Galactic plane, reveals information about the magnetic field in
the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre
of our Galaxy and reveals the most probable direction where the large-scale
magnetic field is perpendicular to the line of sight. This may help to decide
on the large-scale magnetic field configuration of our Galaxy.Comment: 6 pages, IAU 259 Conference Proceedings, in pres
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
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