Figure 1: Background. From Blain et al, astro-ph/020228, to be published in Physics Reports

The mm-wave instrumentation under development by our group can be used not only to make measurements of the cosmic microwave background, but also to observe thermal emission from dust in nearby and distant galaxies. Such emission connects intimately with the history of energy production in the universe. When the first stars to form after the "Dark Ages" end their lives as supernovae, the explosions eject metals (elements heavier than hydrogen and helium) from the stellar cores into the interstellar medium. These elements undergo chemical reactions to form complex compounds, usually involving carbon or silicon, that then can condense into "dust" grains. Such dust grains absorb optical and infrared photons, heat up to tens of Kelvin, and emit a modified blackbody spectrum. This process continues to occur over the entire history of the universe as stars form, live, and die, further enriching the interstellar medium via the metals they have produced. Observationally, the dust thus plays two roles.

Figure 2: SED lines. From Blain et al, astro-ph/020228, to be published in Physics Reports

As an absorber of short wavelengths, it prevents us from seeing directly the full complement of energy emitted by stars. As a reemitter at long wavelengths, it provides access to this absorbed energy via longer-wavelength observations. Thus, to make a full accounting of the history of energy production in the universe, it is necessary to make observations in both optical/near-infrared and submillimeter/millimeter-wave bands. The importance of such observations has become quite clear in recent years thanks to observations from the DIRBE and FIRAS instruments on the COBE satellite. These observations (see Figure 1) indicate that of order half of the energy produced by stars over the history of the universe has been reprocessed into long-wavelength emission. Thus, number, redshift distribution, and clustering properties of galaxies at submillimeter and millimeter wavelengths have become important unanswered questions.

Figure 3: Svz. From Blain et al, astro-ph/020228, to be published in Physics Reports

In some cases, long-wavelength emission may be the only way to observe distant, dust-obscured galaxies. In some cases, the dust obscuration is so complete that the galaxy's total luminosity is dominated by emission at long wavelenghts. Generically, one can look at the spectral energy distribution of a typical luminous dusty infrared galaxy and see the usefulness of submillimeter and millimeter-wave observations. Figure 2 shows such a spectrum. As such a galaxy is moved to higher redshift, the emission at a given observed wavelength on the Rayleigh-Jeans tail of the dust spectrum increases because the dust emission spectrum is steeply rising at such frequencies. This is in contrast to the emission at optical/near-IR wavelengths (< 1 um wavelength), where the starlight component (not shown in Figure 2) at a given observed wavelength typically drops as the galaxy is redshifted.