A Cm-Wavelength Search for Pre-Biotic Molecules

1. A Cm-Wavelength Search for Pre-Biotic Molecules in Starburst Galaxies: A Case Study for Zw 049.057 Minchin R., Catinella B., Ghosh, T., Lebron M., Lerner M.S., Momjian E. O’Neil, K., Salter, C.J. (NAIC , NRAO, UPR and MPIfA)‏ Interstellar organic species mostly form on the surface of dust grains and are then released into the gas phase by heating events. Organic species known as pre-biotic molecules may combine to form amino acids; one example is the combination of methanimine (CH2NH) and HCN on the path to glycine. Both CH2NHand HCN can be detected at cm-wavelengths, as we have demonstrated in Arp 220 (Salter et al 2008, AJ, 136, 389). Following this discovery, we have initiated observations of 40 Arp 220-like galaxies with Arecibo and the GBT. C-band observations with a frequency range of 4.4 - 5.2 GHz cover both the CH2NH line and the HCN v2=1, J=4 transition. Observations and analysis are ongoing for both telescopes. In the data reduced so far, both CH2NH and HCN have been found in a number of sources, as have other molecules such as H2CO and excited OH, and hydrogen recombination lines. In this poster we present a case study for Zw 049.057. Formaldehyde (H2CO) -cm Excited OH Absorption Lines • The Sample • Our sample of 40 Arp-220-like galaxies were selected from the lists of; • OH Megamaser galaxies as compiled by Chen et al. (2007) • Starbursts with detected H2CO masers or absorption (Araya et al. 2004) • ULIRGS with direct evidence of nuclear starbursts (Armus et al.1990) • FIR-luminous merging galaxies (Condon et al. 1991) Spectra were recorded from 8 × 100-MHz C-band band-passes that included lines either seen in Arp 220, or felt to be good candidates for detection. The objective was to obtain ~1 hr of ON-source integration on each target. The spectra here have ~30 km/s resolution. 4660-MHz satellite line The H2CO line in Zw 049.057 was previously detected by Araya et al. (2004) and Baan et al. (1993). However, our line shape appears somewhat different to that of Araya et al. The possibility of variability needs investigation. a Methanimine (CH2NH) 4750-MHz main line Zw 049.057 Zw 049.057 (IRAS 1507+0724; z = 0.012999) appears as a highly inclined disk with a smooth light distribution at large radii, but a bright arm of star formation ~1“ south of the 2.2-μm peak. ZW 049.057 is classified as both an HII and a Luminous IR Galaxy (LIRG), and is also a strong OH Megamaser emitter. The galaxy was one of the sources included in the Arecibo part of the sample, and 1.25 hr of ON-source data were acquired for the object. 4765-MHz satellite line Hydrogen Cyanide (HCN; v2=1) The λ6-cm lines of the excited-OH Transitions 2П½,,J=1/2,F=0-1,1-1 and 1-0 have intensity ratios close to 1:2:1, the LTE values.The OH lines at 4750 & 4765 MHz were heavily affected by RFI, and only 20 min of good ON-source data was usable. • A Molecular Comparison with Arp 220 • All molecular lines seen in our bands in Arp 220 are also detected in Zw 049.057. • Excited-OH absorptions in both galaxies display LTE, with the Zw 049.057 line integrals ~12% the stronger. The HCN v2=1 absorption in Zw 049.057 is a factor of ~2.5 times the weaker. • In each of the two galaxies, the H2CO and CH2NH emission lines have similar relative strengths, with the absolute integrated luminosities of these lines being ~6 × stronger in Arp 220 than in Zw 049.057.