Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI
Journal article, 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.

Author

Nanase Harada

National Astronomical Observatory of Japan

Academia Sinica

The Graduate University for Advanced Studies (SOKENDAI)

Sergio Martin

European Southern Observatory Santiago

Atacama Large Millimeter-submillimeter Array (ALMA)

Jeffrey G. Mangum

National Radio Astronomy Observatory

Kazushi Sakamoto

Academia Sinica

Sebastien Muller

Chalmers, Space, Earth and Environment, Onsala Space Observatory

Kunihiko Tanaka

Keio University

Kouichiro Nakanishi

The Graduate University for Advanced Studies (SOKENDAI)

National Astronomical Observatory of Japan

Ruben Herrero-Illana

Spanish National Research Council (CSIC)

European Southern Observatory Santiago

Yuki Yoshimura

University of Tokyo

Stefanie Muhle

University of Bonn

Rebeca Aladro

Max Planck Society

Laura Colzi

Istituto nazionale di astrofisica (INAF)

Spanish National Research Council (CSIC)

Victor M. Rivilla

Spanish National Research Council (CSIC)

Istituto nazionale di astrofisica (INAF)

Susanne Aalto

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Erica Behrens

University of Virginia

Christian Henkel

Max Planck Society

Chinese Academy of Sciences

King Abdulaziz University

Jonathan Holdship

Leiden University

University College London (UCL)

P. K. Humire

Max Planck Society

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

Leiden University

Serena Viti

University College London (UCL)

Leiden University

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 923 1 24

Subject Categories (SSIF 2011)

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

DOI

10.3847/1538-4357/ac26b8

More information

Latest update

3/9/2025 1