1. DETECTING MOLECULAR LINES IN THE 1 - 10 GHz FREQUENCY RANGE
Chris Salter
(NAIC, Arecibo Observatory)‏

2. What are Molecules, and Why do they Radiate Radio Emission?
A molecule is the smallest particle in a chemical compound and is made up of atoms held together by chemical bonds.
Methanol Hydrogen-Cyanide Propenal Acetaldehyde Formaldehyde Carbon-Monoxide
(CH3OH) (HCN) (CH2CHCHO) (CH3CHO) (H2CO) (CO)‏
When a molecule changes its rotation, vibration or bending state to one of lower energy,
it radiates a photon. If the change of energy is very small, the photon is a radio photon.

3. Where are Molecules found in Space?
Generally, in regions of high density in the interstellar medium of galaxies, where star formation is taking place. High density would typically be > 104 particles/cm3. (The atmosphere we breathe has about 2.4 × 1019 particles/cm3.)‏
Star-burst Galaxies
(Luminous Infra-Red Galaxies)
Star Formation Regions in Our Milky Way
(The Orion Nebula)‏
HST Optical Image
Carbon Monoxide (CO)‏
115 GHz

4. Where Else are Molecules found in Space?
Some Old Red Stars (Mira Variables)‏

5. How do we detect Molecules?
Molecules are detected as narrow, spectral features showing emission and/or absorption
WAPP spectrometer
Will analyze 800-MHz bandwidth at a time
Arecibo 305-m Telescope
Covers 1.1 – 10 GHz via 6 receivers

6. A Spectral Scan of Arp 220: 1.1 – 10 GHz
Arp 220 is a star-burst galaxy at a distance of 250 Mly.
It is forming stars at 100-times the rate of the Milky Way.
It is the result of a collision between 2 galaxies now in the final stages of merging.
(VLA:Radio
Wavlength 6cm)‏
(HST:Optical)‏

7. Sharing the Spectrum with Others
Radio Astronomy has primary rights to very little of the radio spectrum.
Elsewhere in the spectrum we have to do the best we can.
Data editing can be reasonably effective against spoadic RFI.
Observing a “Control Source” allows one to distinquish RFI from spectral lines in the target.
However, any spectral scan will be only partially complete.

8. The Spectrum of Arp 220 – Prebiotic Molecules
Methanimine (CH2NH) observed for the first time outside of the Milky Way (where it has only been observed in one source!)‏
This is probably a maser emitter.
“Bending” transitions of HCN observed for the very first time in the radio region.
These lines are at L-, C-, C-Hi & X-band.
STOP PRESS:
HCN at S-band.

9. The Spectrum of Arp 220 – OH&CH
OH Absorption (5 cm)‏
18OH or Formic Acid? (18 cm)‏
OH Absorption (6 cm)‏
CH emission (9 cm) – and look they have two friends!
OH rAbsorption (4 cm)‏

10. Is Arp 220 Unique? -- NO!
IC 860