The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules

Abstract

An on-going Arecibo line search between 1.1 and 10 GHz of the prototypical starburst/megamaser galaxy, Arp 220, has revealed a spectrum rich in molecular transitions. These include the ``pre-biotic'' molecules: methanimine (CH${}_2$NH) in emission, three $v_2=1$ direct l-type absorption lines of HCN, and an absorption feature likely to be from either ${}^{18}$OH or formic acid (HCOOH). In addition, we report the detection of two, possibly three, transitions of $\lambda$4-cm excited OH not previously detected in Arp~220 which are seen in absorption, and a possible absorption feature from the 6.668-GHz line of methanol. This marks the first distant extragalactic detection of methanimine, a pre-biotic molecule. Also, if confirmed, the possible methanol absorption line presented here would represent the first extragalactic detection of methanol at a distance further than 10 Mpc. In addition, the strong, previously undetected, cm-wave HCN $v_2=1$ direct l-type lines will aid the study of dense molecular gas and active star-forming regions in this starburst galaxy.

25 pages, 10 figures. Accepted for publication in AJ

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• High-resolution HNC 3-2 SMA observations of Arp220
• Detection of a methanol megamaser in a major-merger galaxy
• Methanol masers in NGC 253 with ALCHEMI
• Low Pressure EUV Photochemical Experiments: Insight on the Ion-Chemistry Occurring in Titan's Atmosphere
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• High Resolution Observations of Molecular Lines in Arp 220: Kinematics, Morphology, and Limits on the Applicability of the Ammonia Thermometer
• The Opaque Heart of the Galaxy IC 860: Analogous Protostellar, Kinematics, Morphology, and Chemistry
• Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei
• 36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?
• High-Sensitivity Observations of Molecular Lines with the Arecibo Telescope
• The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk
• FAST Observations of Four Comets to Search for the Molecular Line Emissions between 1.0 and 1.5 GHz Frequencies