Starburst Energy Feedback Seen Through HCO${}^{+}$/HOC${}^{+}$ Emission in NGC 253 from ALCHEMI

Abstract

Molecular abundances are sensitive to UV-photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO${}^{+}$ and its metastable isomer HOC${}^{+}$ in the center of the starburst galaxy NGC 253 using data from the ALMA large program ALCHEMI. The distribution of the HOC${}^{+}$(1-0) integrated intensity shows its association with "superbubbles", cavities created either by supernovae or expanding HII regions. The observed HCO${}^{+}$/HOC${}^{+}$ abundance ratios are $\sim 10-150$, and the fractional abundance of HOC${}^{+}$ relative to H${}_2$ is $\sim 1.5\times 10^{-11}-6\times 10^{-10}$, which implies that the HOC${}^{+}$ abundance in the center of NGC 253 is significantly higher than in quiescent spiral-arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of $G_0\gtrsim 10^3$ if the maximum visual extinction is $\gtrsim 5$, or a cosmic-ray ionization rate of $\zeta \gtrsim 10^{-14}$ s${}^{-1}$ (3-4 orders of magnitude higher than that within clouds in the Galactic spiral-arms) to reproduce the observed results. From the difference in formation routes of HOC${}^{+}$, we propose that a low-excitation line of HOC${}^{+}$ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV-photons and cosmic rays, sources of energy feedback.

57 pages, 32 figures, accepted for publication in ApJ

References in corpus (29)

• The 2014 KIDA network for interstellar chemistry
• Diagnostics of irradiated dense gas in galaxy nuclei. II. A grid of XDR and PDR models
• A 2 mm spectral line survey of the starburst galaxy NGC 253
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• Modeling Complex Organic Molecules in dense regions: Eley-Rideal and complex induced reaction
• Molecular line emission in NGC1068 imaged with ALMA: II. The chemistry of the dense molecular gas
• High resolution observations of HCN and HCO+ J=3-2 in the disk and outflow of Mrk231 -Detection of vibrationally excited HCN in the warped nucleus
• Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253
• Lambda = 3 mm line survey of nearby active galaxies
• Cold CO in circumstellar disks: On the effects of photodesorption and vertical mixing
• Multi-molecule ALMA observations towards the Seyfert 1 galaxy NGC 1097
• ALCHEMI: an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory. Survey presentation and first results from the ACA array
• The Central 300 pc of the Galaxy probed by infrared spectra of H${}_3^{+}$ and CO: part I. Predominance of warm and diffuse gas and high H${}_2$ ionization rate
• The nucleus of NGC 253 and its massive stellar clusters at parsec scales
• Carbon isotopic fractionation in molecular clouds
• Distributions of molecules in the circumnuclear disk and surrounding starburst ring in the Seyfert galaxy NGC 1068 observed with ALMA
• On the chemistry and distribution of HOC+ in M82: More evidence for extensive PDRs
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• Outflows from Super Star Clusters in the Central Starburst of NGC253
• OH+ and H2O+ absorption toward PKS1830-211
• The Distribution and Origin of C${}_2$H in NGC 253 from ALCHEMI
• A Multi-Transition Study of Molecules toward NGC 1068 based on High-Resolution Imaging Observations with ALMA
• Spatially resolved carbon and oxygen isotopic ratios in NGC 253 using optically thin tracers
• Diverse nuclear star-forming activities in the heart of NGC 253 resolved with ten-pc scale ALMA images
• CO+ in M 82: A Consequence of Irradiation by X-rays
• The Molecular ISM in the Super Star Clusters of the Starburst NGC 253
• The ionization rates of galactic nuclei and disks from Herschel/HIFI observations of water and its associated ions
• A chemical study of carbon fractionation in external galaxies
• On the effects of UV photons/X-rays on the chemistry of the Sgr B2 cloud

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