The Orion-Taurus ridge: a synchrotron radio loop at the edge of the Orion-Eridanus superbubble
Journal
Date Issued
2023
Author(s)
Abstract
Large-scale synchrotron loops are recognized as the main source of diffuse
radio-continuum emission in the Galaxy at intermediate and high Galactic
latitudes. Their origin, however, remains rather unexplained. Using a
combination of multi-frequency data in the radio band of total and polarized
intensities, for the first time in this letter, we associate one arc --
hereafter, the Orion-Taurus ridge -- with the wall of the most prominent
stellar-feedback blown shell in the Solar neighborhood, namely the
Orion-Eridanus superbubble. We traced the Orion-Taurus ridge using 3D maps of
interstellar dust extinction and column-density maps of molecular gas, $N_{\rm
H_2}$. We found the Orion-Taurus ridge at a distance of 400\,pc, with a
plane-of-the-sky extent of $180$\,pc. Its median $N_{\rm H_2}$ value is
$(1.4^{+2.6}_{-0.6})\times 10^{21}$ cm$^{-2}$. Thanks to the broadband
observations below 100 MHz of the Long Wavelength Array, we also computed the
low-frequency spectral-index map of synchrotron emissivity, $\beta$, in the
Orion-Taurus ridge. We found a flat distribution of $\beta$ with a median value
of $-2.24^{+0.03}_{-0.02}$ that we interpreted in terms of depletion of
low-energy ($<$ GeV) cosmic-ray electrons in recent supernova remnants ($10^5$
- $10^6$ yrs). Our results are consistent with plane-of-the-sky magnetic-field
strengths in the Orion-Taurus ridge larger than a few tens of $\mu$G ($> 30 -
40 \,\mu$G). We report the first detection of diffuse synchrotron emission from
cold-neutral, partly molecular, gas in the surroundings of the Orion-Eridanus
superbubble. This observation opens a new perspective to study the multiphase
and magnetized interstellar medium with the advent of future high-sensitivity
radio facilities, such as the C-Band All-Sky Survey and the Square Kilometre
Array.
Volume
677
Start page
L11
Issn Identifier
0004-6361
Rights
open.access
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