Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI
Artikel i vetenskaplig tidskrift, 2021
Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1-0) integrated intensity shows its association with "superbubbles," cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are similar to 10-150, and the fractional abundance of HOC+ relative to H-2 is similar to 1.5 x 10(-11)-6 x 10(-10), which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G (0) greater than or similar to 10(3) if the maximum visual extinction is greater than or similar to 5, or a cosmic-ray ionization rate of zeta greater than or similar to 10(-14) s(-1) (3-4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.
Författare
Nanase Harada
Academia Sinica
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
Sergio Martin
Atacama Large Millimeter-submillimeter Array (ALMA)
European Southern Observatory Santiago
Jeffrey G. Mangum
National Radio Astronomy Observatory
Kazushi Sakamoto
Academia Sinica
Sebastien Muller
Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium
Kunihiko Tanaka
Keio University
Kouichiro Nakanishi
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
Ruben Herrero-Illana
European Southern Observatory Santiago
Consejo Superior de Investigaciones Científicas (CSIC)
Yuki Yoshimura
University of Tokyo
Stefanie Muhle
Universität Bonn
Rebeca Aladro
Max-Planck-Gesellschaft
Laura Colzi
Centro de Astrobiología (INTA-CSIC)
Istituto nazionale di astrofisica (INAF)
Victor M. Rivilla
Istituto nazionale di astrofisica (INAF)
Centro de Astrobiología (INTA-CSIC)
Susanne Aalto
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
Erica Behrens
University of Virginia
Christian Henkel
King Abdulaziz University
Chinese Academy of Sciences
Max-Planck-Gesellschaft
Jonathan Holdship
Universiteit Leiden
University College London (UCL)
P. K. Humire
Max-Planck-Gesellschaft
David S. Meier
National Radio Astronomy Observatory Socorro
New Mexico Institute of Mining and Technology
Yuri Nishimura
National Astronomical Observatory of Japan
University of Tokyo
Paul P. van der Werf
Universiteit Leiden
Serena Viti
Universiteit Leiden
University College London (UCL)
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 923 1 24Ämneskategorier
Meteorologi och atmosfärforskning
Astronomi, astrofysik och kosmologi
Atom- och molekylfysik och optik
DOI
10.3847/1538-4357/ac26b8