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

Max Planck Society

King Abdulaziz University

Xinjiang Astronomical Observatory

D. S. Meier

National Radio Astronomy Observatory Socorro

New Mexico Institute of Mining and Technology

L. Colzi

Centro de Astrobiologia (CAB)

Mitsuyoshi Yamagishi

University of Tokyo

Kunihiko Tanaka

Keio University

Kouichiro Nakanishi

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

R. Herrero-Illana

Institute of Space Sciences (ICE) - CSIC

European Southern Observatory Santiago

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 80

Subject Categories

Astronomy, Astrophysics and Cosmology

Geology

Geochemistry

DOI

10.3847/1538-4357/ac8dfc

More information

Latest update

11/7/2022