Syed, J, Wang, Y, Beuther, H et al. (15 more authors) (2020) Atomic and molecular gas properties during cloud formation. Astronomy & Astrophysics, 642. A68. ISSN 0004-6361
Abstract
Context. Molecular clouds, which harbor the birthplaces of stars, form out of the atomic phase of the interstellar medium (ISM). To understand this transition process, it is crucial to investigate the spatial and kinematic relationships between atomic and molecular gas.
Aims. We aim to characterize the atomic and molecular phases of the ISM and set their physical properties into the context of cloud formation processes.
Methods. We studied the cold neutral medium (CNM) by means of H I self-absorption (HISA) toward the giant molecular filament GMF20.0-17.9 (distance = 3.5 kpc, length ~170 pc) and compared our results with molecular gas traced by 13CO emission. We fitted baselines of HISA features to H I emission spectra using first and second order polynomial functions.
Results. The CNM identified by this method spatially correlates with the morphology of the molecular gas toward the western region. However, no spatial correlation between HISA and 13CO is evident toward the eastern part of the filament. The distribution of HISA peak velocities and line widths agrees well with 13CO within the whole filament. The column densities of the CNM probed by HISA are on the order of 1020 cm−2 while those of molecular hydrogen traced by 13CO are an order of magnitude higher. The column density probability density functions (N-PDFs) of HISA (CNM) and H I emission (tracing both the CNM and the warm neutral medium, WNM) have a log-normal shape for all parts of the filament, indicative of turbulent motions as the main driver for these structures. The H2 N-PDFs show a broad log-normal distribution with a power-law tail suggesting the onset of gravitational contraction. The saturation of H I column density is observed at ~25 M⊙ pc−2.
Conclusions. We conjecture that different evolutionary stages are evident within the filament. In the eastern region, we witness the onset of molecular cloud formation out of the atomic gas reservoir while the western part is more evolved, as it reveals pronounced H2 column density peaks and signs of active star formation.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © J. Syed et al. 2020. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
Keywords: | ISM: clouds, ISM: atoms, ISM: molecules, ISM: kinematics and dynamics , radio lines: ISM, stars: formation |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds) > Astrophysics (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 10 Nov 2020 12:03 |
Last Modified: | 25 Jun 2023 22:29 |
Status: | Published |
Publisher: | EDP Sciences |
Identification Number: | 10.1051/0004-6361/202038449 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:167794 |