Gas shells and magnetic fields in the Orion-Eridanus superbubble

Abstract

Aims. The Orion-Eridanus superbubble has been blown by supernovae and supersonic winds of the massive stars in the Orion OB associations. It is the nearest site at which stellar feedback on the interstellar medium that surrounds young massive clusters can be studied. The formation history and current structure of the superbubble are still poorly understood, however. It has been pointed out that the picture of a single expanding object should be replaced by a combination of nested shells that are superimposed along the line of sight. We have investigated the composite structure of the Eridanus side of the superbubble in the light of a new decomposition of the atomic and molecular gas. Methods. We used H i 21 cm and CO (J=1−0) emission lines to separate coherent gas shells in space and velocity, and we studied their relation to the warm ionised gas probed in H α emission, the hot plasma emitting X-rays, and the magnetic fields traced by dust polarised emission. We also constrained the relative distances to the clouds using dust reddening maps and X-ray absorption. We applied the Davis-Chandrasekhar-Fermi method to the dust polarisation data to estimate the plane-of-sky components of the magnetic field in several clouds and along the outer rim of the superbubble. Results. Our gas decomposition has revealed several shells inside the superbubble that span distances from about 150 pc to 250 pc. One of these shells forms a nearly complete ring filled with hot plasma. Other shells likely correspond to the layers of swept-up gas that is compressed behind the expanding outer shock wave. We used the gas and magnetic field data downstream of the shock to derive the shock expansion velocity, which is close to ∼20 km s −1 . Taking the X-ray absorption by the gas into account, we find that the hot plasma inside the superbubble is over-pressured compared to plasma in the Local Bubble. The plasma comprises a mix of hotter and cooler gas along the lines of sight, with temperatures of (3-9) and (0.3 − 1.2) × 10 6 K, respectively. The magnetic field along the western and southern rims and in the approaching wall of the superbubble appears to be shaped and compressed by the ongoing expansion. We find plane-of-sky magnetic field strengths from 3 to 15 µG along the rim.

3D dynamics of the Orion cloud complex -- Discovery of coherent radial gas motions at the 100-pc scale

“…The idea that the Orion clouds were and are being affected by the feedback of massive stars is not new (e.g., Bally et al 1987;Bally 2008). It has been proposed that several nested shells are superimposed along the line-of-sight, forming the so called Orion-Eridanus superbubble, a less than 10 Myr old relic shell of several Supernovae remnants, spatially encircling the main Orion clouds (e.g., Lee & Chen 2009;Pon et al 2014bPon et al ,a, 2016Ochsendorf et al 2015;Soler et al 2018;Joubaud et al 2019). The progenitors of the superbubble are likely related, at least partially, with the Orion−6 event presented in this paper.…”

“…However, a clear determination of such a central point of origin is not straightforward due to different reasons: (a) There is likely not a single point of origin in the first place. Several massive stars formed in the region and produced feedback (radiation, SNe, winds), as indicated by the nested shells in the Orion-Eridanus superbubble (Ochsendorf et al 2015;Joubaud et al 2019, see also the Discussion in Sect. 5.2).…”

Compressed magnetized shells of atomic gas and the formation of the Corona Australis molecular cloud

“…(Dawson et al 2015) have shown a strong association between molecular gas formation and superbubbles. Close-by molecular clouds in the Gould Belt -at a distance from the Sun of d < 500 pc -such as Orion (Soler et al 2018;Joubaud et al 2019;Könyves et al 2020), Taurus, Perseus (Shimajiri et al 2019), and Ophiuchus (Ladjelate et al 2020), were also found to be shaped by large-scale compression from expanding shells and bubbles in their magnetized surroundings.…”

The cosmic-ray content of the Orion-Eridanus superbubble

“…Conversely, CR that are produced internally can remain confined in the superbubble medium for typically 300 kyr for 100 GeV particles in a 25-50 pc superbubble if the diffusion lengths are 100 times shorter than in the Article number, page 1 of 20 arXiv:2001.10139v1 [astro-ph.HE] 28 Jan 2020 the key H α features towards Orion. In the analysis region, the black contours delineate the main H i shells related to the superbubble, i.e the North Rim (N), South Loop (S), East Shell (E), and West Rim (W), and the Eridu cirrus (C) lying outside the superbubble (Joubaud et al 2019). The molecular MBM 20 cloud in front of the superbubble edge is outlined in white.…”