The distribution and origin of C2 H in NGC 253 from ALCHEMI
Journal article, 2021
Context. Observations of chemical species can provide insights into the physical conditions of the emitting gas however it is important to understand how their abundances and excitation vary within different heating environments. C2H is a molecule typically found in PDR regions of our own Galaxy but there is evidence to suggest it also traces other regions undergoing energetic processing in extragalactic environments. Aims. As part of the ALCHEMI ALMA large program, we map the emission of C2H in the central molecular zone of the nearby starburst galaxy NGC 253 at 1.6″ (28 pc) resolution and characterize it to understand its chemical origins. Methods. We used spectral modeling of the N = 1-0 through N = 4-3 rotational transitions of C2H to derive the C2H column densities towards the dense clouds in NGC 253. We then use chemical modeling, including photodissociation region (PDR), dense cloud, and shock models to investigate the chemical processes and physical conditions that are producing the molecular emission. Results. We find high C2H column densities of ∼1015 cm-2 detected towards the dense regions of NGC 253. We further find that these column densities cannot be reproduced if it is assumed that the emission arises from the PDR regions at the edge of the clouds. Instead, we find that the C2H abundance remains high even in the high visual extinction interior of these clouds and that this is most likely caused by a high cosmic-ray ionization rate.
Astrochemistry
Galaxies: individual: NGC 253
Submillimeter: galaxies
Radiative transfer
Author
Jonathan Holdship
Leiden University
University College London (UCL)
Serena Viti
University College London (UCL)
Leiden University
S. Martin
Atacama Large Millimeter-submillimeter Array (ALMA)
European Southern Observatory Santiago
N. Harada
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
Academia Sinica
J. G. Mangum
National Radio Astronomy Observatory
K. Sakamoto
Academia Sinica
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Kunihiko Tanaka
Keio University
Y. Yoshimura
University of Tokyo
K. Nakanishi
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
R. Herrero-Illana
European Southern Observatory Santiago
Institute of Space Sciences (ICE) - CSIC
S. Muhle
University of Bonn
Rebeca Aladro
Max Planck Society
L. Colzi
Arcetri Astrophysical Observatory
Centro de Astrobiologia (CAB)
K.L. Emig
National Radio Astronomy Observatory
S. G. Burillo
Spanish National Observatory (OAN)
C. Henkel
King Abdulaziz University
Max Planck Society
Pedro Humire
Max Planck Society
D. S. Meier
New Mexico Institute of Mining and Technology
National Radio Astronomy Observatory Socorro
Víctor M. Rivilla
Centro de Astrobiologia (CAB)
Arcetri Astrophysical Observatory
P. van der Werf
Leiden University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 654 A55Subject Categories
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
DOI
10.1051/0004-6361/202141233