• When and how did the first galaxies form?
• Were the first galaxies just like new (current) ones?
• What are the most critical elements in the star formation process?
  • What determines stellar masses?
  • How important is interstellar chemistry?
  • Has the star formation process changed over time?

FIRST is well suited to address these questions.  It is a large (3.5m), cold, low emissivity telescope  working in an environment which is completely free of atmospheric contamination. This allows a complete spectral coverage over the entire range of the telescope.  It will contain three cryogenic instruments, one operating at low spectral resolution (SPIRE),one medium (PACS) and one at very high resolution (HIFI), each of which is extraordinarily sensitive. The expected improvement in sensitivity is illustrated by comparison with the best existing and proposed instruments across the the FIRST wavelength band.At low resolving power FIRST will be 3 to 10 times more sensitive than SCUBA is. At modest spectral resolution FIRST will be 5 times more sensitive than Sofia, and at a spectral resolution of one part in a milion FIRST will be three times more sensitive than Sofia and two orders of magnitude more sensitive than SWAS or ODIN!

FIRST is a truly major  satellite observatory on a similar level to NASA's "Great Observatories", which are  the Hubble Space Telescope, HST (and its "replacement" NGST),  AXAF ( an X-ray observatory due for launch this year), the Gamma Ray Observatory, GRO (launched in 1991), and SIRTF ( a 0.85m cryogenic Infra-red telescope due for launch December 2001). Like these other space observatories,  FIRST is expected to open a major new window  on the universe and provide results which are exciting for scientists and the general public as well.  Access to this facility will be crucial for scientists wishing to study the topics FIRST is designed to address.

The specific observing program will depend, partially, on proposals. However, one can identify key scientific projects which are likely to be near the top of FIRST's priorities. These include

• Investigation of the statistics and physics of galaxy and structure formation at high redshift. Galaxies emit a large fraction of their total energy (30% to 100%) in the Infra-red, and at redshifts greater than 1 much of this energy is shifted into the SPIRE passband. FIRST will measure the transition from smooth initial conditions to the present clumpy galactic distribution.

• Deep broadband photometric surveys aimed at studying galaxy bulges and elliptical galaxies in the first third of the age of the Universe. We know from studying gravitationally lensed Infra Red luminous galaxies that many of the most distant galaxies undergoing rapid bursts of star formation are very dusty. Because of this, optical studies alone can not reveal the rate of star formation. FIRST will be able to measure processes at the cores of these galaxies.

  The picture below illustrates  the usefulness of long wavelength measurements of  dusty regions. It is an image of the center of our Galaxy measured at a wavelength of 240 microns by the DIRBE instrument on COBE. This same region of the sky appears as a slightly dark band in the Milky Way at optical wavelengths because the starlight is obscurred by dust whereas here  the re-emission by the heated dust provides a very clear picture of the dynamics of the Galactic center.

  

• Follow-up spectroscopy of especially interesting objects discovered in the surveys above. The brightest  cooling lines  of interstellar gas fall in the HIFI passband and this study will reveal a wealth of new information on energy production mechanisms in galaxies.

• Observational astrochemistry of gas and dust as a quantitative tool for understanding the stellar-interstellar life cycle. Virtually all components of this cycle, e.g. cloud collapse, freeze-out,  disk formation, dust coagulation and planetesimal formation, ie all stages except the stars themselves, can be studied with FIRST.  See the figure.   HIFI will have the sensitivity to observe many of these processes at high redshift as well as nearby. SPIRE will enable astronomers, for the first time, to observe the physical and chemical processes  in the cold phases of the interstellar medium at high spatial resolution.

  

• Detailed high resolution spectroscopy of  a number of comets and high resolution spectroscopy of the cool outer planets, which will help us to understand the origin and evolution of our planetary system.

These key projects will form a major part of the FIRST observing programme early in the mission. The formation of large observer collaborations collectively addressing these topics will be actively encouraged. The call for proposals in this phase will be open, but the instrument teams themselves are expected to compete strongly for this time. Only when these programmes have been established will the first call for "normal" observing proposals be entertained.

It is likely that SPIRE and to some extent PACS will be heavily used in the earliest surveys because of their broadband sensitivity and that HIFI will eventually become the primary instrument, since virtually all the surveys will require high spectral resolution follow-up.