1. ASIAA Interferometry Summer School – 2006 Introduction – Radio Astronomy Tatsuhiko Hasegawa (ASIAA) 1. Atmospheric window to the electromagnetic waves 2. Radio wavelengths band – advantages and disadvantages 3. What do we probe with the radio ?

2. Arizona Radio Observatory

3. What is sub-millimeter astronomy ? (http://aro.as.arizona.edu/documentation.htm)http://aro.as.arizona.edu/documentation.htm

4. Advantages and Disadvantages of Radio Astronomy ● No interstellar extinction – You can see through a dark cloud. ● Difficulty in separating radio sources along the same line of sight – It is difficult to separate multiple emission sources if they have the same radial velocity. ● High spectral-resolution – A velocity resolution of 0.1 km/s is readily attained. ● Low angular-resolution – Largest single-dish millimeter telescopes have angular resolutions similar to a human eye (about 20 arcseconds). => This is overcome by combining many radio telescopes – interferometer. ● Detections of low-temperature (low energy) sources – 10 K gas does not emit in IR. Angular resolution ~ beam size (HPBW) ~ / D (radian). Freq=5 10 5 GHz1000 GHz 100 GHz10 GHz = 0.6  m 0.3 mm 3 mm 3 cm D = 6 mm 3 m30 m 300 m  / D = 10 –4 10 –4 10 –4 10 –4 (radian) = 21'' Max Planck D = 100 m Nobeyama D = 45 m IRAM D = 30 m JCMT D = 15 m

6. A  = A V ( 0.55  m / ) + c (0.3  m < < 3  m) Whittet 1981 QJRAS, 22, 3.

7. What do we probe with the radio ? What does the electromagnetic wave in the (sub-)mm band reflect ? What kind of phenomena or material do we see in the radio band ? 1. Continuum emission in the (sub-)mm band. (i) Thermal dust emission. (ii) Free-free emission from ionized gas. 2. Line emission from molecules and atoms. (i) From the line frequency, we identify the molecular species. (ii) From line ratios, we can estimate the density and temperature. (iii) Line emission from cold (10K) gas is most easily observed in the mm band. (iv) Sub-mm lines selectively probe warm molecular gas (protostars, evolved stars, photodissociation regions, active star-forming regions). (v) Kinematics of molecular gas can be studied.

8. log Free-free continuum emission from an HII region at > 1mm ( 300 GHz). Hoare et al. 1992 MNRAS, 258, 257 (right). Knapp et al. 1993 ApJS, 88, 173 (left). <= (  m)

9. Keen et al. 1980 ApJL, 240, L43 Crapsi et al. 2004 A&Ap, 420, 957.

10. Phillips and Vastel 2002 ASPH 0211610

11. (  m) =>