The "Maggie" filament: Physical properties of a giant atomic cloud
Journal article, 2022

Context. The atomic phase of the interstellar medium plays a key role in the formation process of molecular clouds. Due to the line-of-sight confusion in the Galactic plane that is associated with its ubiquity, atomic hydrogen emission has been challenging to study. Aims. We investigate the physical properties of the "Maggie" filament, a large-scale filament identified in H I emission at line-of-sight velocities, upsilon(LSR) similar to -54 km s(-1). Methods. Employing the high-angular resolution data from The H I/OH Recombination line survey of the inner Milky Way (THOR), we have been able to study H I emission features at negative upsilon(LSR) velocities without any line-of-sight confusion due to the kinematic distance ambiguity in the first Galactic quadrant. In order to investigate the kinematic structure, we decomposed the emission spectra using the automated Gaussian fitting algorithm GAUSSPY+. Results. We identify one of the largest, coherent, mostly atomic H I filaments in the Milky Way. The giant atomic filament Maggie, with a total length of 1.2 +/- 0.1 kpc, is not detected in most other tracers, and it does not show signs of active star formation. At a kinematic distance of 17 kpc, Maggie is situated below (by approximate to 500 pc), but parallel to, the Galactic H I disk and is trailing the predicted location of the Outer Arm by 5-10 km s(-1) in longitude-velocity space. The centroid velocity exhibits a smooth gradient of less than +/- 3 km s(-1) (10 pc)(-1) and a coherent structure to within +/- 6 km s(-1). The line widths of similar to 10 km s(-1) along the spine of the filament are dominated by nonthermal effects. After correcting for optical depth effects, the mass of Maggie's dense spine is estimated to be 7.2(-1.9)(+2.5) x 10(5) M-circle dot. The mean number density of the filament is similar to 4 cm(-3), which is best explained by the filament being a mix of cold and warm neutral gas. In contrast to molecular filaments, the turbulent Mach number and velocity structure function suggest that Maggie is driven by transonic to moderately supersonic velocities that are likely associated with the Galactic potential rather than being subject to the effects of self-gravity or stellar feedback. The probability density function of the column density displays a log-normal shape around a mean of < N-HI > = 4.8 x 10(20) cm(-2), thus reflecting the absence of dominating effects of gravitational contraction. Conclusions. While Maggie's origin remains unclear, we hypothesize that Maggie could be the first in a class of atomic clouds that are the precursors of giant molecular filaments.

ISM: clouds

ISM: structure

ISM: kinematics and dynamics

ISM: atoms

radio lines: ISM

Author

J. Syed

Max Planck Society

J. D. Soler

Max Planck Society

H. Beuther

Max Planck Society

Y. Wang

Max Planck Society

S. Suri

University of Vienna

Max Planck Society

J. D. Henshaw

Max Planck Society

M. Riener

Max Planck Society

S. Bialy

Harvard-Smithsonian Center for Astrophysics

Sara Rezaeikhoshbakht

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Max Planck Society

J. M. Stil

University of Calgary

P. F. Goldsmith

California Institute of Technology (Caltech)

M. R. Rugel

Max Planck Society

S. C. O. Glover

Heidelberg University

R. S. Klessen

Heidelberg University

J. Kerp

Argelander-Institut für Astronomie

J. S. Urquhart

University Of Kent

J. Ott

National Radio Astronomy Observatory Socorro

N. Roy

Indian Institute of Science

N. Schneider

University of Cologne

R. J. Smith

University of Manchester

S. N. Longmore

Liverpool John Moores University

H. Linz

Max Planck Society

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 657 A1

Subject Categories

Astronomy, Astrophysics and Cosmology

Geophysics

Theoretical Chemistry

DOI

10.1051/0004-6361/202141265

More information

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8/9/2024 9