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Abstract:
We present images of the Sagittarius (Sgr) B giant molecular cloud at 1384 and
2368 MHz obtained using new, multi-configuration Australia Telescope Compact Array
observations. We have combined these observations with archival single-dish observations
yielding images at resolutions of 47'' × 14'' and 27'' × 8'' at 1384 and 2368 MHz, respectively.
These observations were motivated by our theoretical work indicating the possibility that
synchrotron emission from secondary electrons and positrons created in hadronic cosmic ray
(CR) collisions with the ambient matter of the Sgr B2 cloud could provide a detectable (and
possibly linearly polarized) non-thermal radio signal. We find that the only detectable nonthermal
emission from the Sgr B region is from a strong source to the south of Sgr B2, which
we label Sgr B2 Southern Complex (SC). We find Sgr B2(SC) integrated flux densities of 1.2
± 0.2 Jy at 1384 MHz and 0.7 ± 0.1 Jy at 2368 MHz for a source of FWHM size at 1384 MHz
of ~54''. Despite its non-thermal nature, the synchrotron emission from this source is unlikely
to be dominated due to secondary electrons and positrons. Failing to find clear evidence of
non-thermal emission due to secondary electrons and positrons, we use polarization data to
place 5σ upper limits on the level of polarized intensity from the Sgr B2 cloud of 3.5 and 3
mJybeam-1 at 1384 and 2368 MHz, respectively. We also use the angular distribution of the
total intensity of archival 330 MHz Very Large Array and the total intensity and polarized
emission of our new 1384 and 2368 MHz data to constrain the diffusion coefficient for
transport of the parent hadronic CRs into the dense core of Sgr B2 to be no larger than about
1% of that in the Galactic disk. Finally, we have also used the data to perform a spectral and
morphological study of the features of the Sgr B cloud and compare and contrast these to
previous studies.
