Magnetic field and ISM in the local Galactic disc

Sofue, Yoshiaki; Nakanishi, Hiroyuki; Ichiki, Kiyotomo

doi:10.1093/mnras/stz407

Cited by 9 publications

(14 citation statements)

References 31 publications

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“…The different directions are noted with their truncated right ascension, and the letters N, W, or S for the north rim, west rim, and south loop rims, respectively. sample where B tot is available, we obtain values of 8.2±1.2 and 12.3±1.5 µG, in good agreement with the 12 µG value found at these locations in the Sofue et al (2019) map. We further discuss magnetic compression along the outer shell of the superbubble in the next section.…”

Section: B Sky Estimatessupporting

confidence: 87%

“…We find that the fields along the outer shell of the superbubble (along the west rim and the south loop) span B sky values from 5 to about 15 µG, which means that the total field downstream of the expanding shock wave exceeds the mean total field B tot = 7 µG that prevails outside the superbubble, at high Galactic latitudes (Sofue et al 2019). Xu & Han (2019) reported a similar enhancement by a factor of 2 in the shell of the Gum nebula, using rotation measures from pulsars.…”

Section: Outer Shock Velocity and Compression Ratiomentioning

confidence: 78%

“…We obtain B sky strengths ranging from ∼ 3 to ∼ 15 µG towards the superbubble clouds. We can compare these values with the Sofue et al (2019) results, which are based on synchrotron emission and Faraday rotation measures. They have derived all-sky maps of B los and B tot = (B 2 sky + B 2 los ) 1/2 , assuming equipartition between the magnetic and cosmic-ray energy densities.…”

Section: B Sky Estimatesmentioning

confidence: 99%

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Gas shells and magnetic fields in the Orion-Eridanus superbubble

Joubaud

Grenier

Ballet

et al. 2019

A&A

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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.

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Section: B Sky Estimatessupporting

confidence: 87%

Section: Outer Shock Velocity and Compression Ratiomentioning

confidence: 78%

Section: B Sky Estimatesmentioning

confidence: 99%

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Gas shells and magnetic fields in the Orion-Eridanus superbubble

Joubaud

Grenier

Ballet

et al. 2019

A&A

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“…Far-infrared observations of dust polarization (Planck collaboration 2016) reveal that magnetic lines of force penetrate the clouds without particular change of flux. In larger scale, magnetic field in the local Galactic disc within a few kpc is shown to be about constant at strength of B ∼ 5 − 10 µG (Sofue et al 2019). Figure 1 shows Alfvén velocities in MCs calculated for observed values of B = √ 2Bz plotted against the gas density using the data from Crutcher et al (2010), where √ 2 is a correction from line-of-sight to total strength.…”

Section: Magnetic Field and Alfvén Velocitymentioning

confidence: 98%

Focusing magnetohydrodynamic waves as a trigger of star formation

Sofue

2020

Publications of the Astronomical Society of Japan

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Propagation of fast-mode magnetohydrodynamic (MHD) waves in the interstellar space is simulated, and focusing MHD wave (FMW) model is proposed for triggered star formation (SF). Waves from an SF region are trapped by nearby molecular clouds and converge onto their focal points, causing implosive compression. Even an isolated cloud suffers from long-distance invasion of waves from remote sources. Echoing SF occurs inside a cloud as well as between clouds. Repetitive refocusing in a filamentary cloud suggests spatial periodicity in SF sites along the filament. The model is applied to the SF regions M16 and M17, where MHD waves produced by M16 are shown to converge onto the focal point of nearby GMC and trigger the SF in M17.

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“…If cosmic rays (CR) are produced by turbulent acceleration in the compression site of magnetic fields, we may assume equipartition between CR and magnetic energy densities. Then, the magnetic strength can be estimated using the relation (Sofue et al 2019), where ν [in GHz] is the radio frequency and ǫ = 4π Σν dν/L ∼ 4πνΣν /L [in erg cm −3 s −1 ] is the radio emissivity for line-of-sight depth L of the emission region. Here, Σν = 2kTB ν /λ 2 is radio surface brightness at ν, TB ν the brightness temperature, and λ the wavelength.…”

Section: Magnetic Fieldsmentioning

confidence: 99%

Interaction of the Galactic-Centre Super Bubbles with the Gaseous Disc

Sofue,

Kataoka

2021

Preprint

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The interaction of Galactic-Centre (GC) super bubbles (GSB) with the gaseous disc and halo of the Milky Way is investigated using radio continuum, X-ray, HI and CO line surveys. The radio North Polar Spur (NPS) constitutes the brightest eastern ridge of GSB, brightening towards the galactic plane and reaching l = 22 • , b = +2 • at the sharpest end, where it intersects the tangential direction of the 3-kpc expanding ring and crater. Examination of the spur ridges reveals that the entire GSB, including the NPS and its counter spurs, constitutes a GC-symmetrical Ω/ Ω shape. The thickness and gas density of the HI and CO discs are shown to increase sharply from the inside (lower longitude) to the outside of the 3-kpc crater. Formation of crater is explained by the sweeping of the upper layer of disc gas by the shock wave from the GC by the explosion ∼ 10 My ago with the emitted energy of several 10 55 ergs. Based on the discussion, a unified view on the structure and formation mechanism of GSB is presented.

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Magnetic field and ISM in the local Galactic disc

Cited by 9 publications

References 31 publications

Gas shells and magnetic fields in the Orion-Eridanus superbubble

Gas shells and magnetic fields in the Orion-Eridanus superbubble

Focusing magnetohydrodynamic waves as a trigger of star formation

Interaction of the Galactic-Centre Super Bubbles with the Gaseous Disc

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