CO enhancement by magnetohydrodynamic waves. Striations in the Polaris Flare
Artikel i vetenskaplig tidskrift, 2023

Context. The formation of molecular gas in interstellar clouds is a slow process, but can be enhanced by gas compression. Magneto-hydrodynamic (MHD) waves can create compressed quasi-periodic linear structures, referred to as striations. Striations are observed at the column densities at which the transition from atomic to molecular gas takes place.
Aims: We explore the role of MHD waves in the CO chemistry in regions with striations within molecular clouds.
Methods: We targeted a region with striations in the Polaris Flare cloud. We conducted a CO J = 2−1 survey in order to probe the molecular gas properties. We used archival starlight polarization data and dust emission maps in order to probe the magnetic field properties and compare against the CO morphological and kinematic properties. We assessed the interaction of compressible MHD wave modes with CO chemistry by comparing their characteristic timescales.
Results: The estimated magnetic field is 38-76 µG. In the CO integrated intensity map, we observe a dominant quasiperiodic intensity structure that tends to be parallel to the magnetic field orientation and has a wavelength of approximately one parsec. The periodicity axis is ~17° off from the mean magnetic field orientation and is also observed in the dust intensity map. The contrast in the CO integrated intensity map is ~2.4 times higher than the contrast of the column density map, indicating that CO formation is enhanced locally. We suggest that a dominant slow magnetosonic mode with an estimated period of 2.1-3.4 Myr and a propagation speed of 0.30-0.45 km s−1 is likely to have enhanced the formation of CO, hence created the observed periodic pattern. We also suggest that within uncertainties, a fast magnetosonic mode with a period of 0.48 Myr and a velocity of 2.0 km s−1 could have played some role in increasing the CO abundance.
Conclusions: Quasiperiodic CO structures observed in striation regions may be the imprint of MHD wave modes. The Alfvénic speed sets the dynamical timescales of the compressible MHD modes and determines which wave modes are involved in the CO chemistry.

Astrophysics - Astrophysics of Galaxies

polarization

ISM: kinematics and dynamics

ISM: individual objects: Polaris Flare

ISM: clouds

ISM: abundances

ISM: magnetic fields

Författare

Raphael Skalidis

California Institute of Technology (Caltech)

K. Gkimisi

Panepistimio Kritis

Konstantinos Tassis

Panepistimio Kritis

Georgia Panopoulou

University of Cyprus

Vincent Pelgrims

Panepistimio Kritis

Aris Tritsis

Ecole Polytechnique Federale de Lausanne (EPFL)

Paul F. Goldsmith

California Institute of Technology (Caltech)

Astronomy and Astrophysics

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

Vol. 673 A76

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fusion, plasma och rymdfysik

DOI

10.1051/0004-6361/202345880

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Senast uppdaterat

2024-04-05