TY - JOUR
T1 - Tracing Interstellar Heating
T2 - An ALCHEMI Measurement of the HCN Isomers in NGC 253
AU - Behrens, Erica
AU - Mangum, Jeffrey G.
AU - Holdship, Jonathan
AU - Viti, Serena
AU - Harada, Nanase
AU - Martín, Sergio
AU - Sakamoto, Kazushi
AU - Muller, Sebastien
AU - Tanaka, Kunihiko
AU - Nakanishi, Kouichiro
AU - Herrero-Illana, Rubén
AU - Yoshimura, Yuki
AU - Aladro, Rebeca
AU - Colzi, Laura
AU - Emig, Kimberly L.
AU - Henkel, Christian
AU - Huang, Ko Yun
AU - Humire, P. K.
AU - Meier, David S.
AU - Rivilla, Víctor M.
AU - van der Werf, Paul P.
N1 - Funding Information:
We thank the anonymous referee for providing an extremely thorough and constructive review of the original version of this article. The referee’s comments and suggestions resulted in numerous improvements to the research presented in this article, for which we are grateful. We thank Jack Warfield for his technical expertize in getting this project off the ground. We also thank Heihei Behrens for his crucial support to the authors throughout this process. This work is part of a project that has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program MOPPEX 833460. V.M.R. acknowledges support from the Comunidad de Madrid through the Atracción de Talento Investigador Modalidad 1 (Doctores con experiencia) grant (COOL:Cosmic Origins of Life; 2019-T1/TIC-15379). L.C. has received partial support from the Spanish State Research Agency (AEI; project number PID2019-105552RB-C41). N.H. acknowledges support from JSPS KAKENHI grant No. JP21K03634. P.H. is a member of and received financial support for this research from the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. K.S. acknowledges the grant MOST 111-2112-M-001-039 from the Ministry of Science and Technology in Taiwan.
Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/11/1
Y1 - 2022/11/1
N2 - We analyze HCN and HNC emission in the nearby starburst galaxy NGC 253 to investigate its effectiveness in tracing heating processes associated with star formation. This study uses multiple HCN and HNC rotational transitions observed using the Atacama Large Millimeter/submillimeter Array via the ALCHEMI Large Program. To understand the conditions and associated heating mechanisms within NGC 253's dense gas, we employ Bayesian nested sampling techniques applied to chemical and radiative transfer models, which are constrained using our HCN and HNC measurements. We find that the volume density n H 2 and cosmic-ray ionization rate (CRIR) ζ are enhanced by about an order of magnitude in the galaxy’s central regions as compared to those further from the nucleus. In NGC 253's central giant molecular clouds (GMCs), where observed HCN/HNC abundance ratios are the lowest, n ∼ 105.5 cm−3 and ζ ∼ 10−12 s−1 (greater than 104 times the average Galactic rate). We find a positive correlation in the association of both density and CRIR with the number of star formation-related heating sources (supernova remnants, H ii regions, and super hot cores) located in each GMC, as well as a correlation between CRIRs and supernova rates. Additionally, we see an anticorrelation between the HCN/HNC ratio and CRIR, indicating that this ratio will be lower in regions where ζ is higher. Though previous studies suggested HCN and HNC may reveal strong mechanical heating processes in NGC 253's CMZ, we find cosmic-ray heating dominates the heating budget, and mechanical heating does not play a significant role in the HCN and HNC chemistry.
AB - We analyze HCN and HNC emission in the nearby starburst galaxy NGC 253 to investigate its effectiveness in tracing heating processes associated with star formation. This study uses multiple HCN and HNC rotational transitions observed using the Atacama Large Millimeter/submillimeter Array via the ALCHEMI Large Program. To understand the conditions and associated heating mechanisms within NGC 253's dense gas, we employ Bayesian nested sampling techniques applied to chemical and radiative transfer models, which are constrained using our HCN and HNC measurements. We find that the volume density n H 2 and cosmic-ray ionization rate (CRIR) ζ are enhanced by about an order of magnitude in the galaxy’s central regions as compared to those further from the nucleus. In NGC 253's central giant molecular clouds (GMCs), where observed HCN/HNC abundance ratios are the lowest, n ∼ 105.5 cm−3 and ζ ∼ 10−12 s−1 (greater than 104 times the average Galactic rate). We find a positive correlation in the association of both density and CRIR with the number of star formation-related heating sources (supernova remnants, H ii regions, and super hot cores) located in each GMC, as well as a correlation between CRIRs and supernova rates. Additionally, we see an anticorrelation between the HCN/HNC ratio and CRIR, indicating that this ratio will be lower in regions where ζ is higher. Though previous studies suggested HCN and HNC may reveal strong mechanical heating processes in NGC 253's CMZ, we find cosmic-ray heating dominates the heating budget, and mechanical heating does not play a significant role in the HCN and HNC chemistry.
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U2 - 10.3847/1538-4357/ac91ce
DO - 10.3847/1538-4357/ac91ce
M3 - Article
AN - SCOPUS:85142444186
SN - 0004-637X
VL - 939
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 119
ER -