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.

ISM: atoms

ISM: clouds

radio lines: ISM

galaxies: ISM

ISM: structure

ISM: molecules

Författare

J. D. Soler

Max Planck-institutet

H. Beuther

Max Planck-institutet

M. Rugel

Max Planck-institutet

Y. Wang

Max Planck-institutet

P. C. Clark

Cardiff University

S. C. O. Glover

Universität Heidelberg

P. F. Goldsmith

California Institute of Technology (Caltech)

M. Heyer

Univ Massachusetts, Dept Astron

L. D. Anderson

West Virginia University

A. Goodman

Harvard-Smithsonian Center for Astrophysics

Th. Henning

Max Planck-institutet

J. Kainulainen

Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium

R. S. Klessen

Universität Heidelberg

S. N. Longmore

Liverpool John Moores University

N. M. McClure-Griffiths

Australian National University

K. M. Menten

Max Planck-institutet

J. C. Mottram

Max Planck-institutet

J. Ott

Natl Radio Astron Observ, POB O, 1003 Lopezville Rd

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 Inst Sci

P. Schilke

Universität zu Köln

Astronomy and Astrophysics

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

Vol. 622 A166

Ämneskategorier

Meteorologi och atmosfärforskning

Astronomi, astrofysik och kosmologi

Geofysik

DOI

10.1051/0004-6361/201834300

Mer information

Senast uppdaterat

2019-07-20