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Robert Minchin - Arecibo Observatory/NAIC

Thursday, May 28 – 3:45-4:30PM

 

“A cm-wavelength search for molecular lines with Arecibo and the GBT”

 

An Arecibo spectral 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 molecule methanimine (CH2NH) in emission, formaldehyde (H2CO) also in emission, a number of previously-undetected HCN (v2=1) absorption lines, excited OH transitions in absorption, and possible methanol absorption at 6.7 GHz. Following on from this, we have initiated a C-band survey of 40 'Arp 220-like' galaxies using both the Arecibo and Green Bank Telescopes. These were selected on the basis of published data on OH megamasers, formaldehyde emission (for Arecibo only), optical emission lines in FIR luminous galaxies, or compact starbursts in ULIRGs. To date, almost a half of the galaxies observed at Arecibo have been fully analysed, of which two (IC 860 and Zw 049.057) show very similar, equally rich, spectra to Arp 220, including detections of methanimine, HCN (v2=1), and excited OH. Both of these galaxies were selected with the prior knowledge that they contained OH megamasers and formaldehyde, which may point to a close similarity between them and Arp 220, and help understand the conditions that give rise to the lines of HCN and methanimine.

 

Related Reference(s):

C. J. Salter, T. Ghosh, B. Catinella, M. Lebron, M. S. Lerner, R. Minchin, and E. Momjian, “The Arecibo Arp 220 Spectral Census. I. Discovery of the Pre-Biotic Molecule Methanimine and New cm-Wavelength Transitions of Other Molecules,” AJ, 136, 389-399 (2008).

P. S. Chen, H. G. Shan, and Y. F. Gao, “Photometric Study of Galaxies with OH Megamasers in the Infrared,” AJ, 133, 496-503 (2007).

E. Araya , W. A. Baan, and P. Hofner, “Studies of Extragalactic Formaldehyde and Radio Recombination Lines,” ApJS, 154, 541-552 (2004).

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Condon et al., ApJ, 378, 65 (1991).