ALCHEMI finds a "shocking" carbon footprint in the starburst galaxy NGC~253

Abstract

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 analyze abundances of $C{O}_2$, a reliable tracer of ice chemistry, from data collected as part of the ALMA large program ALCHEMI, a wide-frequency spectral scan toward the starburst galaxy NGC~253 with an angular resolution of 1.6${}^{\prime \prime }$. We constrain the $C{O}_2$ abundances in the gas phase using its protonated form $HOC{O}^{+}$. The distribution of $HOC{O}^{+}$ is similar to that of methanol, which suggests that $HOC{O}^{+}$ is indeed produced from the protonation of $C{O}_2$ sublimated from ice. The $HOC{O}^{+}$ fractional abundances are found to be $(1-2)\times 10^{-9}$ at the outer part of the central molecular zone (CMZ), while they are lower ($\sim 10^{-10}$) 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 $HOC{O}^{+}/C{O}_2$ ratios suggested from chemical models, the gas-phase $C{O}_2$ fractional abundance is estimated to be $(1-20)\times 10^{-7}$ at the outer CMZ, and orders of magnitude lower near the center. We estimate the $C{O}_2$ ice fractional abundances at the outer CMZ to be $(2-5)\times 10^{-6}$ from the literature. A comparison between the ice and gas $C{O}_2$ abundances suggests an efficient sublimation mechanism. This sublimation is attributed to large-scale shocks at the orbital intersections of the bar and CMZ.

22 pages, 9 figures. Accepted for publication in the Astrophysical Journal

References in corpus (19)

• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Binding energies: new values and impact on the efficiency of chemical desorption
• A 2 mm spectral line survey of the starburst galaxy NGC 253
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• Parametrization of C-shocks. Evolution of the Sputtering of Grains
• Lambda = 3 mm line survey of nearby active galaxies
• ALCHEMI: an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory. Survey presentation and first results from the ACA array
• ALMA observations of 99 GHz free-free and H40$\alpha$ line emission from star formation in the centre of NGC 253
• HIFI Spectroscopy of ${\mathrm{H}}_2\mathrm{O}$ submm Lines in Nuclei of Actively Star Forming Galaxies
• The Distribution and Origin of C${}_2$H in NGC 253 from ALCHEMI
• 3 mm spectral line survey of two lines of sight toward two typical cloud complexes in the Galactic Center
• First extragalactic detection of a phosphorus-bearing molecule with ALCHEMI: phosphorus nitride (PN)
• Starburst Energy Feedback Seen Through HCO${}^{+}$/HOC${}^{+}$ Emission in NGC 253 from ALCHEMI
• The Morpho-Kinematic Architecture of Super Star Clusters in the Center of NGC253
• Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of H${}_3$O${}^{+}$ and SO
• Methanol masers in NGC 253 with ALCHEMI
• Do nuclear rings in barred galaxies form at the shear minimum of the rotation curve?
• Evaporative cooling of icy interstellar grains. I. Basic characterization
• Unveiling Kinematic Structure in the Starburst Heart of NGC 253

Cited by in corpus (7)

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• Reconstructing the shock history in the CMZ of NGC 253 with ALCHEMI
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• Molecular isotopologue measurements toward super star clusters and the relation to their ages in NGC253 with ALCHEMI
• Shock-induced HCNH+ abundance enhancement in the heart of the starburst galaxy NGC 253 unveiled by ALCHEMI
• Tracing the chemical footprint of shocks in AGN-host and starburst galaxies with ALMA multi-line molecular studies
• Complex Organic Molecules towards the central molecular zone of NGC 253