Histogram of oriented gradients: a technique for the study of molecular cloud formation
Artikel i vetenskaplig tidskrift, 2019
We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of spectral line observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterized HOG using synthetic observations of HI and (CO)-C-13(J = 1 -> 0) emission from numerical simulations of magnetohydrodynamic (MHD) turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We found a significant spatial correlation between the two tracers in velocity channels where v(HI) approximate to v(13CO), almost independent of the orientation of the collision with respect to the line of sight. Subsequently, we used HOG to investigate the spatial correlation of the HI, from The HI/OH/recombination line survey of the inner Milky Way (THOR), and the (CO)-C-13(J = 1 -> 0) emission from the Galactic Ring Survey (GRS), toward the portion of the Galactic plane 33.degrees 75 <= l <= 35.degrees 25 and vertical bar b vertical bar <= 1.degrees 25. We found a significant spatial correlation between the two tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption (HISA) features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results derived for the observational data indicate significant differences between individual regions: some show spatial correlation in channels around v(HI) approximate to v(13CO) while others present spatial correlations in velocity channels separated by a few kilometers per second. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.
radio lines: ISM
ISM: clouds
ISM: molecules
ISM: structure
galaxies: ISM
ISM: atoms
Författare
J. D. Soler
Max-Planck-Gesellschaft
H. Beuther
Max-Planck-Gesellschaft
M. Rugel
Max-Planck-Gesellschaft
Y. Wang
Max-Planck-Gesellschaft
P. C. Clark
Cardiff University
S. C. O. Glover
Universität Heidelberg
P. F. Goldsmith
California Institute of Technology (Caltech)
M. Heyer
University of Massachusetts
L. D. Anderson
West Virginia University
A. Goodman
Harvard-Smithsonian Center for Astrophysics
Th. Henning
Max-Planck-Gesellschaft
Jouni Kainulainen
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
R. S. Klessen
Universität Heidelberg
S. N. Longmore
Liverpool John Moores University
N. M. McClure-Griffiths
Australian National University
K. M. Menten
Max-Planck-Gesellschaft
J. C. Mottram
Max-Planck-Gesellschaft
J. Ott
National Radio Astronomy Observatory Socorro
S. E. Ragan
Cardiff University
R. J. Smith
University of Manchester
J. S. Urquhart
University Of Kent
F. Bigiel
Universität Heidelberg
Universität Bonn
P. Hennebelle
Université Paris Diderot
N. Roy
Indian Institute of Science
P. Schilke
Universität zu Köln
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 622 A166Ämneskategorier
Meteorologi och atmosfärforskning
Astronomi, astrofysik och kosmologi
Geofysik
DOI
10.1051/0004-6361/201834300