ALCHEMI Finds a “Shocking” Carbon Footprint in the Starburst Galaxy NGC 253
Journal article, 2022
The centers of starburst galaxies may be characterized by a specific gas and ice chemistry due to their gas dynamics and the presence of various ice desorption mechanisms. This may result in a peculiar observable composition. We analyse the abundances of CO2, a reliable tracer of ice chemistry, from data collected as part of the Atacama Large Millimeter/submillimeter Array large program ALCHEMI, a wide-frequency spectral scan toward the starburst galaxy NGC 253 with an angular resolution of 1.″6. We constrain the CO2 abundances in the gas phase using its protonated form HOCO+. The distribution of HOCO+ is similar to that of methanol, which suggests that HOCO+ is indeed produced from the protonation of CO2 sublimated from ice. The HOCO+ fractional abundances are found to be (1-2) × 10−9 at the outer part of the central molecular zone (CMZ), while they are lower (∼10−10) near the kinematic center. This peak fractional abundance at the outer CMZ is comparable to that in the Milky Way CMZ, and orders of magnitude higher than that in Galactic disk, star-forming regions. From the range of HOCO+/CO2 ratios suggested from chemical models, the gas-phase CO2 fractional abundance is estimated to be (1-20) × 10−7 at the outer CMZ, and orders of magnitude lower near the center. We estimate the CO2 ice fractional abundances at the outer CMZ to be (2-5) × 10−6 from the literature. A comparison between the ice and gas CO2 abundances suggests an efficient sublimation mechanism. This sublimation is attributed to large-scale shocks at the orbital intersections of the bar and CMZ.
Author
N. Harada
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
J. G. Mangum
National Radio Astronomy Observatory
K. Sakamoto
Academia Sinica
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Víctor M. Rivilla
Centro de Astrobiologia (CAB)
C. Henkel
Xinjiang Astronomical Observatory
King Abdulaziz University
Max Planck Society
D. S. Meier
New Mexico Institute of Mining and Technology
National Radio Astronomy Observatory
L. Colzi
Centro de Astrobiologia (CAB)
Mitsuyoshi Yamagishi
University of Tokyo
Kunihiko Tanaka
Keio University
Kouichiro Nakanishi
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
R. Herrero-Illana
European Southern Observatory Santiago
Spanish National Research Council (CSIC)
Y. Yoshimura
University of Tokyo
Pedro Humire
Max Planck Society
Rebeca Aladro
Max Planck Society
P. van der Werf
Leiden University
K.L. Emig
National Radio Astronomy Observatory
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 938 1 80Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Geology
Geochemistry
DOI
10.3847/1538-4357/ac8dfc