Energizing Star Formation: The Cosmic-Ray Ionization Rate in NGC 253 Derived from ALCHEMI Measurements of H3O+ and SO
Artikel i vetenskaplig tidskrift, 2022

The cosmic-ray ionization rate (CRIR) is a key parameter in understanding the physical and chemical processes in the interstellar medium. Cosmic rays are a significant source of energy in star formation regions, impacting the physical and chemical processes that drive the formation of stars. Previous studies of the circum-molecular zone of the starburst galaxy NGC 253 have found evidence for a high CRIR value: 10(3)-10(6) times the average CRIR within the Milky Way. This is a broad constraint, and one goal of this study is to determine this value with much higher precision. We exploit ALMA observations toward the central molecular zone of NGC 253 to measure the CRIR. We first demonstrate that the abundance ratio of H3O+ and SO is strongly sensitive to the CRIR. We then combine chemical and radiative transfer models with nested sampling to infer the gas properties and CRIR of several star-forming regions in NGC 253 from emission from their transitions. We find that each of the four regions modeled has a CRIR in the range (1-80) x 10(-14) s(-1) and that this result adequately fits the abundances of other species that are believed to be sensitive to cosmic rays, including C2H, HCO+, HOC+, and CO. From shock and photon-dominated/X-ray dominated region models, we further find that neither UV-/X-ray-driven nor shock-dominated chemistry is a viable single alternative as none of these processes can adequately fit the abundances of all of these species.

Författare

Jonathan Holdship

University College London (UCL)

Universiteit Leiden

Jeffrey G. Mangum

National Radio Astronomy Observatory

Serena Viti

Universiteit Leiden

University College London (UCL)

Erica Behrens

University of Virginia

Nanase Harada

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

Sergio Martin

European Southern Observatory Santiago

Atacama Large Millimeter-submillimeter Array (ALMA)

Kazushi Sakamoto

National Astronomical Observatory of Japan

Sebastien Muller

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

Kunihiko Tanaka

Keio University

Kouichiro Nakanishi

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

Ruben Herrero-Illana

Consejo Superior de Investigaciones Científicas (CSIC)

European Southern Observatory Santiago

Yuki Yoshimura

University of Tokyo

Rebeca Aladro

Max-Planck-Gesellschaft

Laura Colzi

Consejo Superior de Investigaciones Científicas (CSIC)

Istituto nazionale di astrofisica (INAF)

Kimberly L. Emig

National Radio Astronomy Observatory

Christian Henkel

Max-Planck-Gesellschaft

King Abdulaziz University

Yuri Nishimura

National Astronomical Observatory of Japan

University of Tokyo

Victor M. Rivilla

Consejo Superior de Investigaciones Científicas (CSIC)

Istituto nazionale di astrofisica (INAF)

Paul P. van der Werf

Universiteit Leiden

Astrophysical Journal

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

Vol. 931 2 89

Ämneskategorier

Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik

Annan fysik

DOI

10.3847/1538-4357/ac6753

Mer information

Senast uppdaterat

2022-06-10