Motivation

Why do we use submillimeter astronomy?
 

  1. Extinction
    1. Energy for most of the radiant light in a galaxy originates in the photospheres of stars, through the visible light.  The stars form in dusty molecular clouds, where the dust is at a radius of 0.1 µm.  This distance is at the same length as the wavelength of visible light.  Therefore, the visible light is scattered and absorbed, and the star formation regions cannot be seen in the visible light.  In order to see these regions, the regions must be observed in a longer wavelength.  In wavelengths larger than 40 µm, over 90% of the visible photons reach us, in comparison to the one visible photon in every 10 billion.

 

  1. Energetics
    1. Much of the electromagnetic radiation in the local Universe arrives in the far-infrared and submillimeter band as thermal radiation from dust.
      1. One example of this is protostars, which glow in the submillimeter band.  Stars form in the dust cores of giant molecular clouds.  Where the core collapses to form a protostar, the protostar’s gravitational energy is converted to kinetic energy (heat) because the core heats up.  The first glow that comes from a protostar is in the submillimeter bands.  

      2. A second example is the starlight from dusty starforming galaxies that is reradiated in the far-infrared and submillimeter bands.  The Milky Way emits about half of its light in this range.  The most luminous galaxies in the local Universe, called Ultraluminous Infrared Galaxies (ULIGS) emit most (up to 99%) of their energy in this range.


Arp 220: Near- IR
Arp 220: Visible




                         Optical                                                               Mid-IR                                                          Submm                             
 

 
  1. Spectral Lines
    1. Interstellar gas clouds are heated by starlight.  When it collapses under gravity, it heat up.  However, the clouds need to cool in order to form the next generation of stars.  The spectral lines that are in the far-infrared and submillimeter bands are the primary coolants for the neutral gas that form stars.  Some of the most important cooling lines include H2O, SO2, and CO rotational lines, [CI] [CII], and [NII] fine structure lines.