The history of dynamics and stellar feedback revealed by the H I filamentary structure in the disk of the Milky Way

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: soler@mpia.de
² Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
³ Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
⁴ Laboratoire AIM, Paris-Saclay, CEA/IRFU/SAp – CNRS – Université Paris Diderot, 91191 Gif-sur-Yvette Cedex, France
⁵ Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305, USA
⁶ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁷ ESO, Karl Schwarzschild str. 2, 85748 Garching bei München, Germany
⁸ Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT, Australia
⁹ National Radio Astronomy Observatory, PO Box O, 1003 Lopezville Road, Socorro, NM 87801, USA
¹⁰ School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA, UK
¹¹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹² I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937, Köln, Germany
¹³ Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
¹⁴ Centre for Astrophysics and Planetary Science, University of Kent, Canterbury CT2 7NH, UK

Received: 9 July 2020
Accepted: 9 September 2020

Abstract

We present a study of the filamentary structure in the emission from the neutral atomic hydrogen (HI) at 21 cm across velocity channels in the 40′′ and 1.5-km s⁻¹ resolution position-position-velocity cube, resulting from the combination of the single-dish and interferometric observations in The HI/OH/recombination-line survey of the inner Milky Way. Using the Hessian matrix method in combination with tools from circular statistics, we find that the majority of the filamentary structures in the HI emission are aligned with the Galactic plane. Part of this trend can be assigned to long filamentary structures that are coherent across several velocity channels. However, we also find ranges of Galactic longitude and radial velocity where the HI filamentary structures are preferentially oriented perpendicular to the Galactic plane. These are located (i) around the tangent point of the Scutum spiral arm and the terminal velocities of the Molecular Ring, around l ≈ 28° and v_LSR ≈ 100 km s⁻¹, (ii) toward l ≈ 45° and v_LSR ≈ 50 km s⁻¹, (iii) around the Riegel-Crutcher cloud, and (iv) toward the positive and negative terminal velocities. A comparison with numerical simulations indicates that the prevalence of horizontal filamentary structures is most likely the result of large-scale Galactic dynamics and that vertical structures identified in (i) and (ii) may arise from the combined effect of supernova (SN) feedback and strong magnetic fields. The vertical filamentary structures in (iv) can be related to the presence of clouds from extra-planar HI gas falling back into the Galactic plane after being expelled by SNe. Our results indicate that a systematic characterization of the emission morphology toward the Galactic plane provides an unexplored link between the observations and the dynamical behavior of the interstellar medium, from the effect of large-scale Galactic dynamics to the Galactic fountains driven by SNe.