Three-dimensional Aquila Rift: magnetized H I arch anchored by molecular complex

Abstract

Three-dimensional structure of the Aquila Rift of magnetized neutral gas is investigated by analysing H I and CO line data. The projected distance on the Galactic plane of the H I arch of the Aquila Rift is r_⊥ ∼ 250 pc from the Sun. The H I arch emerges at l ∼ 30°, reaches to altitudes as high as ∼500 pc above the plane at l ∼ 350°, and returns to the disc at l ∼ 270°. The extent of arch at positive latitudes is ∼1 kpc and the width is ∼100 pc. The eastern root is associated with the giant molecular cloud complex, which is the main body of the optically defined Aquila Rift. The H I and molecular masses of the Rift are estimated to be M_{H I}∼ 1.4{×} 10^5 M_{⊙} and M_H_2∼ 3{×} 10^5 M_{⊙}. Gravitational energies to lift the gases to their heights are E_{grav: H I}∼ 1.4{×} 10^{51} erg and E_{grav: H_2}∼ 0.3{×} 10^{51} erg, respectively. Magnetic field is aligned along the H I arch of the Rift, and the strength is measured to be B ∼ 10 μG using Faraday rotation measures of extragalactic radio sources. The magnetic energy is estimated to be E_mag ∼ 1.2 × 10⁵¹ erg. A possible mechanism of formation of the Aquila Rift is proposed in terms of interstellar magnetic inflation by a sinusoidal Parker instability of wavelength of ∼2.5 kpc and amplitude ∼500 pc.