Abstract:
The magnetic universe can be unveiled by measurements of Rotation
Measure (RM) of polarised extragalactic sources in radio
wavelengths. Such RM-grid experiments have allowed studies of magnetic
fields in a wide range of astrophysical objects such as Galactic HII
regions, the Milky Way, nearby galaxies like the Magellanic Clouds and
M31, and distant galaxies. As the largest RM catalogue to date with
measurements towards 37,543 sightlines, the Taylor RM catalogue is a
powerful dataset for cosmic magnetism studies. Their RM values were
derived from polarisation measurements at two frequencies only, hence
susceptible to npi-ambiguity. Despite efforts to minimise this effect,
some sources in the catalogue could still have their RM values deviate
from the true values by +/- 652.9 rad m-2. In this talk, I will present
our work using new broadband spectro-polarimetric observations of 23
n pi-ambiguity candidates in the Taylor catalogue with the Jansky VLA
at L-band (1-2 GHz). We revealed 9 sources suffering from
npi-ambiguity. From this, we estimated the number of sources in the
entire catalogue which may suffer from the same RM ambiguity. Our
study further revealed that off-axis polarisation leakage affects the
Taylor catalogue, leading to unpolarised sources mistakenly listed as
polarised, as well as deviations of their RM values from ours even
after correcting for the npi-ambiguity. We also exploited the
broadband capability of the Jansky VLA to investigate Faraday
complexities of our sample, including preliminary study of broadband
polarisation time variabilities.
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