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\subsection{Star 
Formation in the Early Universe}\label{bertoldi} %Please give
                                                        %title here

{\bf{
{Dr. Frank Bertoldi}\\
{Max-Planck-Institut f\"ur Radioastronomie}\\
{Auf dem H\"ugel 69}\\
{D-53121 BONN}\\
{Telefon: 0228/525377}\\
{Fax: 0228/525435}\\
{Email: bertoldi@mpifr-bonn.mpg.de}\\}}


\subsubsection{Abstract}

The rapid development of millimeter and sub-millimeter bolometer array
technology has recently lead to the detections of abundant thermal dust
emission from galaxies and quasars at high redshifts, at epochs where
the first galaxies and black holes formed. In this project we propose to
utilize present and upcoming sensitive bolometer arrays to study the
nature of these submillimeter and millimeter background objects.  We
plan to perform unbiased searches for such objects in square degree
blank fields, and to study the uncovered sources in detail through
follow-up radio, optical, near-infrared, and X-ray observations, in
order to clarify their relation to known classes of objects, and to
examine their redshift and spatial distribution.  We supplement the
unbiased surveys with deep pointed observations of know galaxies and
quasars. Our aim is to trace the star and black hole formation history
of the Early Universe.

\subsubsection{Current status of research}

Among the fundamental cosmological questions being asked today are: when
did galaxies and massive black holes form in the early Universe, and how
did they subsequently evolve?  Modern telescopes, operating from radio
through optical wavelengths are now detecting galaxies out to redshifts
beyond 6, thereby probing the ``dark ages'' where the first stars and
black holes may have formed (Rees 1999).

The most luminous starburst galaxies in the universe are
difficult to observe at optical wavelengths, since much
of the stellar light is typically obscured by dust, which absorbs the
radiation and reradiates the energy at infrared wavelengths.  The
emission from galaxies at large distances is redshifted, so that the
far-infrared (FIR) to millimeter (mm) 
wavelength region is best suited to
detect and study such galaxies.  This has motivated deep searches at
submm and mm wavelengths with existing ground-based instruments
such as SCUBA and MAMBO, and in the future with the 
space observatories SIRTF (to 160$\mu$m) and FIRST.

A most puzzling discoveries in high-redshift
astronomy was the recent identification of compact (sub)mm
background sources, objects that are
estimated to be at redshifts 1 to $>5$.  
The bolometric luminosities of
these sources are similar to those of quasars, but the ratio of (sub)mm to
optica/IR flux shows that at least 99\% of the emission is coming from
dust. The relation between metal production and background radiation
(Eales et al. 1999) then implies that roughly 25\% of all the stars ever
formed have formed in extreme objects like this.  Apparently high
obscuration makes these sources inconspicious at optical and
near-IR wavelengths, although many of them can be detected in deep
VLA radio images (Barger et al. 1999; Carilli et al. 2000).
The lack of clear optical identifications leaves unclear to what class
of objects these sources belong.  It is not yet clear whether they
represent the bright end of star-bursting Lyman break galaxies (Chapman
et al.  1999; Adelberger \& Steidel 2000), or whether they correspond to
dust-obscured quasars (Guilloteau et al. 1999; Carilli et al. 2000), to
spirals or ellipticals in their formation phase, to lensed galaxies, or
a composite of the above.  The small number of current identifications
does not yet permit firm conclusions about their nature.

The high luminosities and star formation suggest
that these objects might be ellipticals seen
during their formation phase, in which a significant fraction of their
stars are forming (Smail et al. 2000; Tan et al. 1999; Blain et al.
1999).  If so, then (sub)mm surveys would have found a population
which has been looked for in vain at optical wavelengths for several
decades.
If the (sub)mm sources are ``proto-ellipticals'', then the basic question
one would like to answer is whether ellipticals form at very
high redshift by the collapse of individual primordial clouds, as the
ages of stellar populations in low-redshift ellipticals suggest (Bower
et al.  1992), or whether they form over a range of redshift by the
gradual hierarchical merging of smaller systems (Baugh et al. 1998).


%Far-IR and sub-mm observations are the key to a better understanding,
%because they trace the peak of the rest frame spectral energy
%distribution of the thermal dust emission from dusty galaxies and thus
%constrain their bolometric luminosities and star formation rates.

To address this question, (sub)mm 
observations have proven to be powerful probes of early
galaxy formation because the dramatic ``negative K-correction'' enables
very deep and essentially distance-independent surveys of thermal
sources.  Because the rest frame SED peaks at 60-100 $\mu$m, the colors
derived from (sub)mm measurements also provide a rough redshift
discrimination, which is important since for nearly all the (sub)mm
sources found so far, a spectroscopic 
redshift cannot be determined
because of their optical/near-IR faintness.

A new generation of bolometer arrays now build at the MPIfR for the IRAM
30~m telescope and for the upcoming MPIfR/ESO {\it Atacama Submillimeter
  Telescope} (AST) will vastly improve the sensitivity of deep and wide
field mapping surveys to detect galaxies and quasars at the earliest
epochs of galaxy formation.
One major goal of deep, large-area (sub)mm surveys is the determination of
extragalactic source counts as a function of flux density.  These
measurements can be compared with theoretical model predictions.
Depending on the evolutionary model used (e.g., monolithic collapse vs.
hierarchical merging), the number counts can be quite different. SCUBA
and MAMBO surveys have take the first steps in establishing statistics
on the (sub)mm background sources. Detailed comparisons with model
predictions are however limited by the small number of sources 
detected, by the small areas surveyed (typically 4 arcmin$^2$ for SCUBA
and 100 arcmin$^2$ for MAMBO maps), and by
the lack of accurate redshifts.

One important result from the SCUBA and MAMBO surveys was the appearance
of a turnover in the (sub)mm background source number counts above $\sim
5$ mJy at 850~$\mu$m.  The cause of this turnover is unclear, but one
could envision several interesting possibilities. The prodigious star
formation rates implied by the luminosities of the brightest background
sources suggest correspondingly large gas supplies, and a limit to the
star formation rate could be due to the limited gas supply within the
galaxy. A turnover in the luminosity function of these galaxies might
then trace the spectrum of density fluctuations in the early Universe.
Alternatively, a limit to the starburst luminosity may be due to an
internal feedback mechanism that inhibits stronger starbursts.

SCUBA and MAMBO can only map a limited area to adequate
depth; the statistical significance of the apparent turnover in the
luminosity function therefore remains marginal. In the near future, wider
field surveys --initially with the 117-element MAMBO at the IRAM 30~m
telescope, and in two years with a large 850$\mu$m bolometer array
on the AST (and at shorter wavelengths with SIRTF)-- will vastly
improve the significance of the source brightness distribution.
Detailed follow-up radio and optical/near-IR studies of the luminous
(sub)mm background sources will also clarify the effect of lensing on
the count statistic.

Wide field imaging will also reveal source clustering.
If the (sub)mm background sources are indeed the precursors of present
day elliptical galaxies, then
they should cluster on typically 10 arcminute scales, which would
be detectable with future mapping capabilities.  Large-scale
mapping surveys have already shown hints of
variations in the source brightness distribution from field to field.
However, considering the still large systematic uncertainties, this
evidence remains marginal, but does point at 
noticable large-scale structure due to ``cosmic variance.''
 
At present an interesting puzzle is 
the connection between high-redshift AGN
and the thermal (sub)mm 
sources, which are thought to be powered by starbursts.
It was noticed in nearby galaxies that the mass of galactic
bulges correlates well with the mass of supermassive black holes
(Magorrian et al. 1998). This indicates that the growth of black holes
and the formation of the first stellar populations are closely linked.
The discovery of strong thermal dust emission in
high-redshift quasars (McMahon et al. 1994; Omont et al. 1996, 2000;
Carilli et al. 2000), and the recent 
observation that a large fraction of the X-ray
background sources are obscured by high columns of
dust and gas, indicate that
galaxies with active nuclei could contribute noticably to the FIR to mm
background.  In fact, two of the three SCUBA submm sources for which optical
emission lines were detected show signs of an active nucleus, and
the two brightest sources in recent blank field surveys with MAMBO
(Bertoldi et al. 2001) and SCUBA (Knudsen et al. 2000) are
intermediate-redshift quasars. On the other hand, recent Chandra
observations failed to detect most of the targeted SCUBA sources (Bautz
et al. 2000; Fabian et al. 2000; Hornschemeier et al. 2000). Right now,
a connection between starbursts and AGN is evident but unclear.

\subsubsection{Own experience}

During the past three years, Dr. Bertoldi has coordinated the
bolometer scientific programs, observing campagnes, and the bolometer
data processing development at the MPIfR. Before joining the MPIfR, he
has worked on the theory and observations regarding the physics and
chemistry of the interstellar medium in star forming regions. Recently,
he has coordinated numerous international collaborative efforts for
observations of star forming galaxies and of AGN using MAMBO at the IRAM
30~m telescope, the VLA, and SCUBA.  This includes deep blank field
surveys to resolve the millimeter background, high-redshift quasar
surveys, the study of radio galaxies and gamma-ray bursts, and also of
comets and asteroids.


\subsubsection{Goals of the project}

To further our understanding of dust-obscured high-redshift starburst
galaxies and AGN seen at mm and submm wavelengths, to establish how they
fit into the broader picture of galaxy evolution, we propose the following
strategy.
\begin{itemize}
\item Using the new MAMBO 117-element array
  at the IRAM 30~m, conduct square degree blank
  field 1.2 mm surveys to obtain statistically significant source counts of
  the rare, bright $(>5 mJy)$ 
   population, to study their nature, redshifts, and
  clustering in contiguous fields.
\item With the new generation bolometers at the AST extend wide field
  surveys to 870~$\mu$m and 350~$\mu$m, thereby optimizing the survey
  sensitivity for high-redshift thermal sources,
  and determine the source spectral energy distributions and
  photometric redshifts.
\item Target specific samples of objects detected at other wavelengths,
  such as optically selected high-redshift galaxies and quasars, radio
  galaxies, X-ray sources, and galaxy clusters.  MAMBO is the currently
  most sensitive ($5\sigma$ detection limit $\approx 1.0$ mJy)
  instrument for pointed observations of high-redshift thermal sources.
\end{itemize}
For operation in early 2003 at the AST, a $\approx 1000$-element
bolometer array at will be available for the 870 $\mu$m window, and a
smaller array for the 350~$\mu$m window.  The AST will surpass any other
ground-based instrument in its capability to detect thermal emission at
high redshift.  Operating at the best (readily accessible) terrestrial
site for year-round submm astronomy, the AST bolometers may even surpass
the mapping capabilities of SIRTF, and in any case, will be the choice
instrument for obtaining photometric redshifts of SIRFT-detected
sources.

With the data obtained through our observations we will try to constrain
structure and galaxy formation models which consistently account for the
formation of stars and massive black holes throughout the history of the
Universe. Such models are constrained mainly by the AGN and starburst
source luminosity functions and redshift distributions, and the spectral
energy distribution of the X-ray to radio background, which is now well
determined.

\subsubsection{Estimate of resources expected from DFG}
Two doctoral students and one postdoc. (???)

\subsubsection{Members of research group relevant for the project}
Dr. Frank Bertoldi, Dr. Karl M. Menten, Dr. E. Kreysa 

\subsubsection{Connections to other projects of current SFB proposal}

This project is closely related to that of E. Kreysa, which
proposes the development of bolometer arrays through which much of the
research proposed here will be possible. It also relates to the project
of P. Schneider, which investigates the large scale matter distribution
in the Universe. (MORE?)

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