2023ApJ...943..161V

λ-21 cm HI4PI survey data are used to study the anomalous-velocity hydrogen gas associated with high-velocity cloud Complex M. These high-sensitivity, high-resolution, high-dynamic-range data show that many of the individual features, including MI, MIIa, and MIIb, are components of a long, arched filament that extends from about (l, b) = (105°, 53°) to (l, b) = (196°, 55°). Maps at different velocities, results from Gaussian analysis, and observations of associated high-energy emission make a compelling case that the MI cloud and the arched filament are physically interacting. If this is the case, we can use the distance to MI, 150 pc as reported by Schmelz & Verschuur, to set the distance to Complex M. The estimated mass of Complex M is then about 120 M_⊙, and the energy implied using the observed line-of-sight velocity, -85 km s^–1, is 8.4 × 10⁴⁸ erg. Integrating over 4π sr, the total energy for a spherically symmetrical explosion is estimated to be 1.9 × 10⁵⁰ erg, well within the energy budget of a typical supernova.