The Orion-Taurus ridge: a synchrotron radio loop at the edge of the Orion-Eridanus superbubble - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2023

The Orion-Taurus ridge: a synchrotron radio loop at the edge of the Orion-Eridanus superbubble

Résumé

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.

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hal-04211200 , version 1 (19-09-2023)

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Andrea Bracco, Marco Padovani, Juan D Soler. The Orion-Taurus ridge: a synchrotron radio loop at the edge of the Orion-Eridanus superbubble. Astronomy and Astrophysics - A&A, 2023, 677, pp.L11. ⟨10.1051/0004-6361/202347283⟩. ⟨hal-04211200⟩
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