48 research outputs found
Polarized Radio Sources: A Study of Luminosity, Redshift and Infrared Colors
The Dominion Radio Astrophysical Observatory Deep Field polarization study
has been matched with the Spitzer Wide-Area Infrared Extragalactic survey of
the European Large Area Infrared Space Observatory Survey North 1 field. We
have used VLA observations with a total intensity rms of 87 microJy beam^-1 to
match SWIRE counterparts to the radio sources. Infrared color analysis of our
radio sample shows that the majority of polarized sources are elliptical
galaxies with an embedded active galactic nucleus. Using available redshift
catalogs, we found 429 radio sources of which 69 are polarized with redshifts
in the range of 0.04 < z <3.2. We find no correlation between redshift and
percentage polarization for our sample. However, for polarized radio sources,
we find a weak correlation between increasing percentage polarization and
decreasing luminosity.Comment: 35 pages, 12 figures, accepted for publication in The Astrophysical
Journa
Three-Dimensional Simulations of Magnetized Superbubbles: New Insights into the Importance of MHD Effects on Observed Quantities
We present three-dimensional magnetohydrodynamic (MHD) simulations of
superbubbles, to study the importance of MHD effects in the interpretation of
images from recent surveys of the Galactic plane. These simulations focus
mainly on atmospheres defined by an exponential density distribution and the
Dickey & Lockman (1990) density distribution. In each case, the magnetic field
is parallel to the Galactic plane and we investigate cases with either infinite
scale height (constant magnetic field) or a constant ratio of gas pressure to
magnetic pressure. The three-dimensional structure of superbubbles in these
simulations is discussed with emphasis on the axial ratio of the cavity as a
function of magnetic field strength and the age of the bubble. We investigate
systematic errors in the age of the bubble and scale height of the surrounding
medium that may be introduced by modeling the data with purely hydrodynamic
models. Age estimates derived with symmetric hydrodynamic models fitted to an
asymmetric magnetized superbubble can differ by up to a factor of four,
depending on the direction of the line of sight. The scale height of the
surrounding medium based on the Kompaneets model may be up to 50% lower than
the actual scale height. We also present the first ever predictions of Faraday
rotation by a magnetized superbubble based on three-dimensional MHD
simulations. We emphasize the importance of MHD effects in the interpretation
of observations of superbubbles.Comment: 21 journal pages. 17 figures. 5 tables (added extensive discussion on
the effect of cooling on the bubbles); Accepted for publications in the
Astrophysical Journal. Related animations can be accessed via
http://www.capca.ucalgary.c
Detection Thresholds and Bias Correction in Polarized Intensity
Detection thresholds in polarized intensity and polarization bias correction
are investigated for surveys where the polarization information is obtained
from RM synthesis. Considering unresolved sources with a single rotation
measure, a detection threshold of applied to the Faraday
spectrum will retrieve the RM with a false detection rate less than ,
but polarized intensity is more strongly biased than Ricean statistics suggest.
For a detection threshold of , the false detection rate
increases to ~4%, depending also on coverage and the extent of the
Faraday spectrum. Non-Gaussian noise in Stokes Q and U due to imperfect imaging
and calibration can be represented by a distribution that is the sum of a
Gaussian and an exponential. The non-Gaussian wings of the noise distribution
increase the false detection rate in polarized intensity by orders of
magnitude. Monte-Carlo simulations assuming non-Gaussian noise in Q and U, give
false detection rates at similar to Ricean false detection
rates at .Comment: 8 pages, 8 figures, accepted for publication in Publications of the
Astronomical Society of Australi
CHANG-ES XXVII: A Radio/X-ray Catalogue of Compact Sources in and around Edge-on Galaxies
We present catalogues of discrete, compact radio sources in and around the
discs of 35 edge-on galaxies in the Continuum Halos in Nearby Galaxies -- an
EVLA Survey (CHANG-ES). The sources were extracted using the PyBDSF program at
both 1.6 GHz (L-band) and 6.0 GHz (C-band) from matching resolution (
3 arcsec) data. We also present catalogues of X-ray sources from Chandra data
sets for 27 of the galaxies. The sources at the two radio frequency bands were
positionally cross-correlated with each other, and the result cross-correlated
with the X-ray sources. All catalogues are included for download with this
paper. We detect a total of 2507 sources at L-band and 1413 sources at C-band.
Seventy-five sources have been successfully cross-correlated in both radio
bands plus X-ray. Three new nuclear sources are candidates for Low Luminosity
Active Galactic Nuclei in NGC~3877, NGC~4192, and NGC~5792; the one in NGC~3877
also appears to be variable. We also find new nuclear sources in two companion
galaxies: NGC~4435 (companion to NGC~4438) and NGC~4298 (companion to
NGC~4302). We have also discovered what appears to be a foreground double-star;
each star has X-ray emission and there is radio emission at both L-band and
C-band in between them. This could be a colliding wind binary system.
Suggestions for follow-up studies are offered.Comment: Accepted to MNRAS, 57 pages of which pages 30 to 57 are figures. 5
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