Whether I shall turn out to be the hero of my own life,
or whether that station will be held by anybody else,
these pages must show.
Charles Dickens, from "David Copperfield", 1850
The atmosphere has always been a formidable barrier to astronomers.
The efforts of casual star gazers are often frustrated by clouds, and
for professional astronomers the atmospehere is a serious handicap
because, even on a clear night, the air above our heads blocks most of
the radiation which arrives from space and distorts what little information
does reach the ground. To overcome these difficulties astronomers have moved
their instruments steadily higher, first to observatories located on
mountains, then to cages suspended below balloons, and then, albeit briefly,
above the atmosphere on rockets. The discoveries which flowed from these
short rocket flights led to the development of automatic observatories
in orbit around the Earth, and these instruments opened new windows on the
sky and revolutionized the way in which mankind views the Universe. Like
the primitive telescopes of Galileo, satellites have propelled astronomy
into a new age of discovery.
The infrared portion of the electromagnetic spectrum has been a major player
in this revolution. Even if narrow spectral "windows" allow astronomers
to observe infrared emission from celestial bodies from the ground,
both absorption and emission from the atmosphere hopelessly hamper deep
infrared ground-based observations to the extent that it is perhaps fair to
say that infrared astronomy has only reached maturity when it first became
possible to carry it out from space.
A few decades after its birth, we now live in what may well be called the
"Golden Age" of space astronomy, and this is particularly true as far as
infrared observations are concerned.
Never has a decade been so full of promises for infrared observers, with
a mission already delivering the most detailed images and spectra ever
of the infrared sky and with three comparably revolutionary missions planned
for launch within the next ten years.
Such an emphasis on the infrared range of the electromagnetic spectrum
is by no means casual. Even if it was largely due to the intervened
technological developments that we are now able for the first time
to produce high-quality and large-size infrared detectors for use in space,
the interest the scientific community is showing towards exploring the
Universe using infrared light could not be higher.
Astronomers find the infrared to be a valuable tool as it opens an important
window into otherwise hidden regions of the Universe.
Research into the origin and composition of planets hinges on infrared
observations which can reveal the composition of objects within our solar
system as well as detect the material that may be forming worlds around other
stars. Likewise, in the infrared spectral range astronomers can study stars
throughout their
lives, from the earliest stages of formation in the hearts of dust clouds
to their final years as they sputter and die. On larger scales, astronomers
can probe distant galaxies individually or collectively, expanding our picture
of the Universe as a whole, and it is this latter end of an ideal voyage from
the very near to the very far space surrounding us that this work is concerned
with.
Due to the very strong interest of the international astronomical community
towards infrared astronomy, it is of the uttermost importance to provide on
one side state-of-the-art technical tools to process the upcoming data in an
efficient and accurate manner and on the other side to exploit current data
to better understand infrared astronomical sources and thus help and guide
the design and operation of future missions. Accordingly, this Thesis deals
with the use of space infrared extragalactic surveys as a powerful tool for
astronomical investigation.
Its main aim was to develop techniques and tools for the efficient
exploitation of infrared datasets, to demonstrate their value by applying
such tools to a massive dataset and discuss the early scientific results
arising from data analysis.
While from a purely technical point of view this work has mostly involved
the detection of the faintest possible sources imaged by a given space
telescope in the most reliable, complete and accurate way, the background
one has to draw upon to understand and solve related issues is vast
and the significance of the obtained results is far-reaching.
Thus, the Thesis begins by dwelling on the importance of infrared observations
of extragalactic sources and on the coordinated set of investigations carried
out in this respect with the Infrared Space Observatory (ISO), whose design,
operation and instrumentation are also described. Then it goes on to deal
with the specific issues involved in ISO data reduction and describes a
powerful new method to deal with them, now known as LARI Method.
The application of the LARI Method to a dataset obtained as part of the
most ambitious extragalactic survey project undertaken by ISO, namely the
European Large ISO Survey (ELAIS), is then described together with the early
scientific results arising from the combination of infrared data with
observations obtained at different wavelengths. Finally, the future prospects
for the exploitation of the developed technical tools and the obtained
scientific results are outlined with reference to the already operating
Spitzer satellite.