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. ONeil, 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 CH2NH and 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 v21, J4 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 15070724 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 v21)
The ?6-cm lines of the excited-OH Transitions
2?½,,J1/2,F0-1,1-1 and 1-0 have intensity
ratios close to 121, 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 v21 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.