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-Pt. A Research Results
-Pt. B Comparison with project programme
-Pt. C Training
-Pt. D Sketches of the young researchers

MID-TERM REVIEW
TMR Research Network Contract No. ERBFMRX--CT96--0086

"Galaxy Formation"

PART A - RESEARCH RESULTS

A.1 Scientific Highlights

The work programme of this project is divided into six major areas. We summarise the scientific highlights in these areas in turn, although in some cases there are clear overlaps. Activity overall has been very high, leading to 112 joint publications submitted to refereed journals and 39 contributions to conference proceedings.

1 Radio Galaxy Evolution

High redshift radio galaxies (HzRGs, z>2) are fundamental probes of galaxy and cluster formation. There is strong evidence that they are amongst the oldest and most massive galaxies in the early Universe and located in dense cluster environments. As such they place important constraints upon the epoch at which the first generation of stars was formed.
During the last two years we have carried out fruitful multi-wavelength imaging and spectroscopic campaigns. Scientific highlights include:

• Demonstrating, using powerful radio galaxies from a Cambridge survey, that distant radio galaxies lie at the centre of the most massive structures in the early Universe.
• A detection of powerful extended X-ray emission from a very distant radio galaxy, indicating an extremely large mass of material.
• The use of the Westerbork radio survey to show that the comoving number density of radio galaxies falls beyond a redshift of two, thus defining the extent of the `quasar epoch'.
• Obtaining the first two solid detections of CO emission from distant radio galaxies.
• Establishing, using sub-millimetre studies, that the most distant radio galaxies contain more dust than their low redshift counterparts.
• Deep HST infrared imaging of the highest redshift radio galaxies showing that they are not associated with well formed ellipticals, unlike their lower redshift counterparts.
• Deep spectroscopy of powerful redshift one radio galaxies demonstrates that the interstellar medium is dramatically affected by the passage of the radio source shocks.
• The discovery of the most distant radio galaxy known known to date at z=5.2.

Many of the most interesting targets uncovered by radio surveys are optically faint, and as such, ESO's VLT (available from April 1999), with its huge collecting area and diverse battery of instrumentation offers a great opportunity for European astronomers. Therefore, we have concentrated the last year on preparing samples of radio galaxies for VLT studies. We have obtained and reduced completely data for half of the 92~cm ``Westerbork survey In the Southern Hemisphere'' (WISH), the first deep large sky radio survey at low frequencies in the southern hemisphere. In addition, spectroscopic redshifts have been obtained for the first large complete sample of the most powerful southern radio galaxies.

2 Evolution of Field and Cluster Evolution

A key objective in the network programme is the understanding of how galaxies form and evolve in different environments, from low/average density regions (`field') to dense groups and clusters. It is now understood that the environment plays an essential role in galaxy evolution.
Our studies of galaxies in clusters have produced very significant progress towards understanding how the morphologies, luminosities and star formation histories of the galaxies evolve in dense environments.

• Comparing the morphological and stellar population properties of cluster galaxies at high and low redshift, we have found a strong morphological evolution for the S0 and spiral populations, as well as for the morphology-density relation in irregular clusters.
• The colour-magnitude relation for early-type galaxies in rich clusters up to redshifts $\simeq1$ indicates that the bulk of the stellar populations of these galaxies are very old, and were formed at redshifts greater than 2.
• The properties of the luminous ellipticals exhibit remarkably small cluster-to-cluster variations, indicating that these galaxies are highly homogeneous between cluster environments. However, at fainter magnitudes we observe a marked increase in the range of mid-UV colours, suggesting the presence of younger populations.
• We have found convincing evidence of evolutionary brightening of the cluster elliptical galaxies consistent with the passive evolution of stellar populations.
• The brightest cluster galaxies have increased their mass in stars by factors $\simeq2$-$4$ in the last $\simeq8\,$billion years, in accordance with the predictions of our semi-analytic galaxy formation models built within the context of the hierarchical scenario of structure formation.
• Using spectro-photometry of distant cluster galaxies, we have carried out detailed studies of the star formation histories of galaxies, quantifying how interactions with other galaxies and with the cluster medium affect the starburst phenomenon.
• We have found that galaxies in high X-ray luminosity clusters are affected by the properties of the intra-cluster gas: the integrated luminosity of the redder cluster galaxies is well correlated with the cluster's X-ray luminosity.
  Our studies of field galaxies aim at understanding the strong evolution found at high redshift, particularly in star-formation activity.
• We have set up the major programme in Europe to prepare for and to follow-up the Hubble Space Telescope observation of a Southern Deep Field. Five nights of successful observations were carried out on ESO's NTT, leading to the first large set of publicly available redshifts in the field. The group has also successfully proposed for VLT time in 1999 for two follow-up programmes.
• In low redshift star-forming galaxies, we have found Lyman alpha to be destroyed by multiple scattering. Lyman alpha photons can only escape in the line wings. This finding solves the long-standing problem of why Lyman-alpha emission is weak or absent in the UV spectrum of such galaxies.
• Using the new SCUBA bolometer array at the James Clerk Maxwell Telescope (JCMT), we have opened a new window on galaxy formation and evolution by observing star formation hidden by dust in extremely distant galaxies. The galaxies detected contribute significantly to the global star formation history of the Universe.
• Interacting and disturbed galaxies constitute the largest class amongst the sub-millimetre galaxies, suggesting that interactions remain an important mechanism for triggering star formation and the formation of ultraluminous galaxies in the distant Universe.
• Our team has also obtained the deepest sub-mm number counts published so far.
• The evolution of elliptical galaxies in the field has been studied using data from the Hubble Deep Field. Even at redshifts as high as 2-3, these galaxies lie on the fundamental plane, in apparently virial equilibrium. However, at such redshifts a significant deficiency of large galaxies is observed, indicating that an important fraction of the field ellipticals formed later.
• Our group has made the first unambiguous detection of the host galaxy of a normal radio-quiet high-redshift QSO at 2.2 microns. The host emits about 35\% of the total luminosity, being about 100 times brighter than an unevolved L* galaxy placed at the QSO redshift (z=2).
  

3 QSO Absorption Lines

An invaluable and complementary point of view on the processes governing the formation and evolution of galaxies is provided by the study of the gaseous component of the universe as seen in quasar absorption lines.
Their study has progressed in the direction of understanding the extent, structure, metallicity and physical conditions of the absorbing structures at high redshift.
In particular the following key results have been achieved:

• Studies of galaxies and identification of absorbers in the Hubble Deep Field South. Spectroscopic observations of galaxies close to the line of sight to the QSO J2233-606 in the HDF-S have been carried out. Several are found to be coincident in redshift with absorption line systems seen in the HST spectrum of the QSO. A new quasar with z=1.3351 at only 45'' angular separation from this QSO has been detected, an ideal target for QSO environment studies.
• QSO pairs and groups. The observations of several closely separated QSO pairs and gravitationally lensed QSOs, providing two or more adjacent lines of sight, have made it possible to sample the size and clustering of the absorbers.
• Simulations. Hydrodynamic simulations of galaxy formation in a cosmological context have been used to investigate the nature of the physical structures giving rise to damped Lyman-alpha absorption systems, the spatial distribution and absorption properties of metal enriched gas in regions of ongoing galaxy formation, the thermal history of the Intergalactic Medium and the dependencies of QSO Lyman-alpha absorption line statistics on cosmological parameters.
• Reconstruction of density fields. Methods for the recovery of the real space line-of-sight mass density field from Lyman absorption in QSO spectra have been developed. The matter density is inferred from the HI density assuming that the absorption is due to a photoionized intergalactic medium which traces the mass distribution as suggested by recent numerical simulations. Redshift distortions are corrected iteratively from a simultaneous estimate of the peculiar velocity. This approach is an excellent tool to study the density probability distribution and clustering properties of the mass density in the (mildly) non-linear regime.

Molecules dominate the cooling function of neutral metal-poor gas at high density. Observation of molecules at high redshift provide thus an important tool toward understanding the physical conditions prevailing in collapsing gas.

4 Stellar Population Modelling

The primary objectives in this area are to expand population synthesis models to the full observed ranges of wavelengths and metallicities. By combining the models with dynamical prescriptions for galaxy evolution, theories of galaxy formation can then be tested against observations.

• Stellar evolution models for a full range of metallicities developped in Padova have been used to build new, metallicity-dependent synthesis programmes by the Paris and Padova groups.
• The new synthesis programmes were implemented into the Munich and Durham semi-analytic models of galaxy formation to compute the chemical enrichment, colors, and line indices of galaxies as a function of redshift. Comparisons with observations have revealed, for example, that the evolution of the K-band luminosity function is a powerful way to constrain galaxy formation theories (other main results are described in the section on phenomenological galaxy formation models).
• The Padova and Paris groups have also developed new models of the near- to mid-IR emission from galaxies including the emission from dust in the interstellar medium and around evolved stars. These models have been combined with the Durham models of galaxy formation to obtain predictions of galaxy counts and redshift distributions at IR/submm wavelengths. These agree well with available data. The Padova and Paris groups are also developing a model of QSO and AGN formation in a hierarchical universe, with particular attention to the modelling of the IR/submm emission.

The achievements so far in population synthesis modelling are extremely encouraging, as the results more than match the milestones that were envisioned at the beginning of the network. It is worthwhile to mention that the state-of-the-art models developed within the network have already been made available to the general astronomical community.

5 Semianalytic modelling

This work aims to produce phenomenological models which can be used to interpret observational data directly in the context of the current theoretical picture for the evolution of structure.

• Current data on the luminosities, colours and redshifts of faint galaxies were shown to be inconsistent with the standard model in which massive galaxies were assembled primarily at high redshift.
• The properties of the newly discovered high value of population of Lyman Break galaxies were shown to be consistent with hierarchical assembly models.
• The clustering of these Lyman Break Galaxies was predicted to be strong, a result later confirmed by observation.
• Semi-analytic models of galaxy formation in a hierarchical universe were combined with new metallicity-dependent spectral synthesis models to compute the chemical enrichment, colors, line indices and mass-to-light ratios of early-type galaxies as a function of redshift. These models reproduce the slope and scatter of the color-magnitude and Mg$_2-\sigma$ relations of elliptical galaxies, challenging the traditional view that luminous early-type galaxies form in a single monolithic collapse at high redshift.
• New models were made for the formation and evolution of galaxy disks. In a Lambda CDM model, the predicted present-day distribution of disk scalelengths agrees very well with the observational one derived by De Jong \& Lacey (1998). The evolution z=1 is predicted to be quite weak at given luminosity, in qualitative agreement with what is found from the CFRS redshift survey. The same models give a good fit to the present-day H-alpha luminosity function of galaxies and can reproduce the observed evolution.

6 Simulations of Galaxies and Clusters

Numerical simulations are one of the most powerful tools for studying galaxy formation and evolution. The network has access to some of the best computing hardware and cosmological software in the world, since it overlaps a broad collaboration known as the Virgo consortium which includes colleagues in the US, Canada and non-network universities in the UK. This collaboration is arguably the strongest numerical cosmology group anywhere. Some of the simulations carried out within the network have redefined the state-of-the art in the subject.
Activity in the simulation area took place at Durham, Munich, Paris and Padova, resulting in 42 joint publications during the first two years of the network involving researchers in the first two of these locations. For the most part the milestones were achieved and, in several instances, exceeded. Highlights include:

• The discovery that the radial density profiles of dark matter halos formed in hierarchical clustering cosmologies have a universal form, independent of mass and cosmological parameters. The characteristic density (or radial scale) of a halo correlates with its total mass, reflecting the later formation epochs of halos of increasing mass.
• The most accurate supercomputer simulations of the dark matter distribution in representative volumes of the universe. These simulations were the first to resolve individual galactic halos in volumes large enough to follow their clustering properties reliably. They have led to the most accurate studies to date of the clustering statistics and topology of the dark matter distribution, and to detailed analyses of the internal structure, velocity distributions, formation history, large-scale environment, and gravitational lensing properties of galaxy cluster halos. Taken together, these studies represent the most comprehensive analysis ever of a high precision set of cold dark matter simulations.
• The execution of the 1-billion particle ``Hubble volume'' simulations, the largest calculations ever done of the formation of structure in the expanding Universe. These follow the growth of clusters and larger scale structures over virtually the entire observable universe, allowing study, for the first time, of a variety of fundamental statistical properties. This work attracted considerable media attention in Europe and the USA.
• The first simulations of the formation of galaxies in cosmological volumes. These include the effects both of the clustering evolution of the dark matter and of the thermodynamic evolution of the gas which eventually turns into stars. For the first time, it is now possible to calculate numerically the formation histories of galaxies and their spatial distribution.

A.2 Joint Publications and Patents

The following joint publications have resulted from Network Activities to date. The names of network young researchers are printed bold-face so that they can be identified. There are 112 articles published in or submitted to refereed journals and 39 contributions to conference proceedings.

THE JOINT PUBLICATIONS ARE LISTED SEPARATELY

PART B: COMPARISON WITH THE PROJECT PROGRAMME

B.1 Research Objectives
The original objectives of our network remain relevant. Indeed, the level of research in these areas has increased substantially since our proposal was submitted as a result of new data from the Hubble Space Telescope and the Keck Telescopes. This is probably the single most active and most rapidly developing field in current astronomy. Certainly it is providing much of the justification for future major programmes such as the Next Generation Space Telescope and the Large Southern Array, as well as for the second generation of instruments planned for the Very Large Telescope. Theoretical work in these areas is also increasing rapidly, in significant part as a result of work associated with the network.

B.2 Methodological Approach and Work Plan
Our methodology has not changed significantly from that described in the contract. We are actively pursuing all six of the scientific areas in which we proposed. Some parts of the detailed research plan have changed in response to new discoveries and opportunities, but the basic structure has been followed almost exactly.
Radio Galaxies
(C, L)
Observational
Aspects Evolution in
Cluster + Field
(C,D,M,P,Pd)
Quasar Absorbers
(C, P, Pd)
Galaxy Formation
and Evolution
Stellar Population Synthesis
(C, P, Pd)
Theoretical
Aspects Semi-analytic Modeling
(C, D, M, P, Pd)
Numerical Simulations
(D, M, P)

B.3 Schedule and Milestones
All milestones in the original contract with expected completion date less than 2.5 years after beginning of the contract have been achieved with the following exceptions:

Field Galaxy Evolution: Completion of the COHSI instrument has been delayed by technical problems.
Evolution of Cluster Galaxies: Comparison of optical and X-ray images to measure infall rates has been displaced by other related projects.
Phenomenological Models: The modelling of QSO absorbers by semi-analytic methods has been replaced by simulation studies.

Additional Major activities added to the programme include:

Field Galaxy Evolution: Preparation and follow-up in the Hubble Deep Field South.
Gas in Young Galaxies: Preparation and follow-up in the Hubble Deep Field South.
Phenomenological Models: Modelling of the evolution of the quasar population.
Simulations: Very large-scale simulations of the evolution of galaxy clusters.
Substantial results are expected in all areas before the programme ends.

B.4 Research Effort of the Participants
Team Research effort from
internal and EC resources
1/10/96 - 31/1/99
in person-months total effort foreseen
in contract:
Garching 150 288
Cambridge 130 240
Durham 170 260
Leiden 170 188
Padova 136 216
Paris 80 300

B.5 Cohesion with Less Favoured Regions

There are no partners from less favoured regions

B.6 Network Organisation and Management

Network organisation and management follows very closely the model in the contract.
The network is coordinated from Munich by S. White; all other partners are associated contractors. The level of activity is, however, quite similar in all six nodes.
In each node the Responsible Scientist is the point of contact for all administrative matters. These are:
Cambridge: A. Aragon-Salamanca
Durham: C. Frenk
Leiden: G. Miley
Munich: S. White
Padova: A. Bressan
Paris: F. Bouchet

In addition, a Task Leader is responsible for monitoring, coordinating and reporting on activity in each of our six primary areas. A seventh Task Leader coordinates work associated with the Hubble Deep Field South. These are:
Radio Galaxies: H. Rottgering (Leiden)
Galaxy Evolution: A. Aragon-Salamanca (Cambridge)
Quasar absorbers: S. Cristiani (Padova/Munich)
Stellar Populations: S. Charlot (Paris)
Semi-analytic Models: G. Kauffmann (Munich)
Simulations: C. Frenk (Durham)
HDF-South: M. Dennefeld (Paris)

In each of the two Network hiring exercises (end of 1995 and 1997) evaluation of postdoctoral applications in the common pool was carried out on each site by senior scientists involved in network programmes and was coordinated by the Responsible Scientist. Conflicts among the choices were few and were resolved by the Coordinator in discussion with the Responsible Scientists.
The major network meeting is held once per year: in Germany in 1997, in Holland in 1998, and in Italy in 1999. The two meetings so far each lasted 4.5 days and attracted 60-70 people from the network sites. In addition a substantial number of more specialised meetings have been held. Details, including participant lists and programmes can be found on the network web-site.
http://www.MPA-Garching.MPG.DE/galform/euronet/index.shtml

B.7 Connections to Industry

There is no involvement of industry in network activities.

PART C - TRAINING

C.1 Employment of Young Researchers

C.2 Training Programme
The rationale of the network's training programme remains as set out in the contract. Each young researcher is fully integrated into all local activites connected with network research. In addition, they all participate in (and speak at) each of the Annual Meetings, as well as in smaller network workshops in areas close to their primary research topic. The Responsible Scientists and Task Leaders at each node are responsible for ensuring full integration of the local young scientists.
The training programme appears to have been successful so far. Of the six young scientists employed in the first phase of the programme, five have now moved on to permanent or long-term positions in astronomy, four of those back in the young scientist's native country. The sixth remains employed within the network and is collaborating very actively with several other nodes.

PART D - SKETCHES OF THE YOUNG RESEARCHERS

Dr Herve Aussel:
I have completed a PhD at the "Service d'Astrophysique" (Saclay, France) with L. Vigroux as thesis advisor. I have worked particularly on deep mid-infrared surveys of galaxies. To analyse these data, I have designed specific tools based on wavelet analysis. I have finally worked on the interpretation of the counts of galaxies.
We find that a large amount of galaxy evolution is required to explain the number counts at the faint flux levels that we probe (i.e. distant [z=0.5 to 1] infrared galaxies undergo strong phases of star formation with respect to the ones observed in the local universe). Moreover, I have shown that this evolving population of galaxies is different from the faint blue galaxies responsible for the evolution observed in deep surveys in the visible. The behavior of the number counts observed in the mid-infrared is therefore different from the one predicted by the models at this wavelength.
The general target of my activities in Padova is the investigation of distant high-redshift galaxies detected in the infrared, to provide a complementary view on galaxy formation and evolution with respect to what optical surveys have offered. Basic questions to be answered will be: what is the nature of the strongly evolving IR galaxy population? Are they starbursts or AGNs? What is the global energetics associated with galaxy IR activity? How do spheroidal galaxies form?
More specifically, I am working with Alberto Franceschini who has already produced models for the galaxies counts at infrared wavelength. We aim together at improving the models and explain my results at 15 microns. We plan to do a detailed study of the spectroscopic properties of these galaxies in cooperation with Bianca Poggianti, formerly at Cambridge with the TMR network. We also are working with the team of IAS (France) and IAP (Paris) on the interpretation of galaxy counts at 175 microns. The mid-infrared surveys provide a good sample of elliptical galaxies. With Alessandro Bressan (Padova), we will compare the observed emission at 7 and 15 microns by these galaxies to the predictions of his model. Finally, I am in charge for maintaining the web page of the TMR network at Padova for which we have already made a brush-up.

Dr Philip Best:
From 1993 to 1996 I studied in Cambridge for my PhD in `Astrophysics and Cosmology', specialising in the study of radio galaxies at very large distances. A combination of imaging at infrared and optical (using the Hubble Space Telescope) wavelengths together with interferometric mapping at radio frequencies allowed a number of properties concerning the nature and evolution of these objects to be discerned.
In November 1996 I was employed by the Sterrewacht Leiden as part of the TMR Network. Here I have been able to continue my research into distant radio galaxies working closely with the Leiden group who have a wealth of expertise in this field. These collaborations have led to further discoveries about the radio galaxy population, such as the fact that the most powerful distant radio galaxies appear to lie at the centres of clusters of galaxies, and have helped to connect these active galaxies to the evolution of the more normal galaxy population. In addition to learning from those more experienced than myself, I have also been given the opportunity to help guide undergraduate and postgraduate students in their own research.
Frequent meetings at the different institutes within the Network have enabled me to learn about other research fields related to my own, and to meet and begin working with scientists from these fields on joint projects. Following these network meetings I am now actively collaborating with researchers in Cambridge, Paris and Munich.
My experience of the Network has been almost entirely positive. I have gained experience of living and working in a foreign country, the opportunity to work within one of the world's leading groups in my research field, and the chance to come into contact with, and travel to continue working with, other leading researchers. My only negative experience is that more time has to be spent on Network- administrative matters than might be wished.

Dr Malcolm Bremer:
(1) Distant radio galaxies. Main result: Showed that there is a decline in the comoving number density of powerful radio galaxies at z>2, Links evolution of radio sources with that of ordinary galaxies. Network collaboration Paris, Leiden and Cambridge.
(2) Adaptive optics imaging of Quasars. Main result: Discovery of quasars close to bright stars, ideal for follow-up with new generation of telescopes. Will be able to study the effect of powerful AGN on their host galaxies up to z=4.5, redshift of the highest object in the sample. Network collaboration Paris and Leiden.
(3) Searching for high redshift structures. Main result: Ongoing, successful search for groups/clus\-ters at z=1-3. Most efficient way of finding key cosmological structures. Now poised to carry out multi-wavelength studies with new generation of telescopes to give viral cosmological information. Network collaboration Paris, Leiden and Cambridge.
(4) Searching for cool material in cooling flows. Main result: Discovery of cool material out to 50 kpc from the centre of most cooling flows at surface brightness levels not before achieved. Network collaboration Paris, Leiden.
All of above are being continued and expanded as participants move from network institutions to other posts. Network has proved invaluable at fostering such collaborations.
Other points about network: As well as obvious benefits from collaborations, the network has enabled me to think far more "internationally" than I perhaps would have otherwise. This is especially apparent on my return to the UK, I think in broader terms than my contemporaries who have not left Britain. It is no coincidence that many of the young scientists (myself included) who took part in the first 2~years of the network secured tenure/good long term posts in their next job.

Dr Pierre-Alain Duc:
As a Ph-D student and then as a post-doctoral researcher, I have studied the environmental effects on the formation and evolution of galaxies. The main laboratories I have used for these studies are: 1) interacting galaxies where collisions trigger in the nuclear regions strong starbursts and where at the same time star-forming dwarf galaxies may form in the outer regions out of debris of collisions expelled in the intergalactic medium; 2) gas-rich dwarf galaxies in nearby clusters of galaxies that, because of their low mass, should be largely affected by the cluster environment; and 3) galaxies in distant clusters that host obscured dust-embedded starbursts revealed by their infrared emission.
These studies are based on multi-wavelength observations and involve several international collaborations in which the network plays a major role. Just hired as a TMR young scientist, I have gathered a team of researchers from Cambridge, Paris and Padova that will carry out the ground-based follow-up of ISO space observations of strong infrared galaxies in clusters. The team involves scientists with observational and theoretical backgrounds whose skills will be especially useful for interpreting the data. From my own experience, the TMR is particularly useful in triggering collaborations among scientists working in a same field but having different technical expertises. As an example, a direct result of our last TMR general meeting in September is the beginning of a collaboration with a young theoretician who will model with numerical simulations some of the interacting systems I had studied so far. The TMR has offered to my research new perspectives that I hope will last after the end of my contract.

Dr Fabio Governato:
The general thrust of my research work concerns the formation and evolution of galaxies and galaxy clusters in a cosmological framework. Understanding the formation and evolution of galaxies is a fundamental astrophysical problem, with implications in almost all branches of astrophysics and cosmology, being a necessary step to understand morphologies and properties of galaxies and their relationship with the local environment. My primary tool are numerical simulations and semi-analytical methods. Starting from 1990 I have used a variety of N-body techniques: direct, tree and cosmological codes (both P3M and a treecode with periodic boundary conditions) on both scalar and parallel machines. I have a good experience in using N-body codes which include the description of a dissipative gaseous component with smoothed particle hydrodynamics techniques (SPH). I'm also experienced in using semi-analytical methods. My duties inside the network were to carry independent research on the formation of galaxies and the structure of dark matter halos. The two years appointment at Durham University as a member of the TMR Network was a very positive experience. It helped me to enlarge my scientific background and enabled me to start many fruitful collaborations inside that will continue in the future. ``Durham's stamp of approval'' gave me a much wider personal recognition in my field and definitely helped me finding a permanent academic job (at the Osservatorio Astronomico di Brera, Milan). My updated CV and research plan may be found on my web page http://star-www.dur.ac.uk/~fabio/index.html.

Simone Marri:
Simone Marri was an undergraduate student at University of Florence (Italy) where I acquired some general specialization skills on general theoretical physics, cosmology and numerical calculation methods. Particularly, the last part of my studies were dedicated to investigate some aspects, and most of all the interconnections, between cosmological models of the hierarchical clustering family, high energy astrophysical sources at high redshift (Pop III SNe) and gravitational lensing. This work was done under the supervision of Dr. Andrea Ferrara of the Astronomy Department of Arcetri, in Florence. This activity ended with the discussion of my Laurea Thesis in September 1997.
Since 1/11/1998 I am a PhD student at the Max-Plank-Institut fur Astrophysik (MPA) in Garching where I work under the supervision of Prof. Simon D.M. White. My task is to study the problem of Galaxy Formation mainly for what concern the effects of SNe explosion: the so called feedback effect. This problem requires an improved understanding of gas processes which occur in the interstellar medium and are believed to be of great importance not only in the steady state of a galaxy but also during its evolution, as constrained by hierarchical cosmological models. In studying such problems, I will collaborate also with Dr. Guinevere Kauffmann (MPA) and Dr. Andrea Ferrara (Arcetri Dep.) contributing in this way to an effective collaboration between two different European institutes.
My first experiences at MPA are quite positive. I have acquired a lot of basic information, on topics relevant for my PhD projects, through the Global ISM workshop (Garching 18-20 November, 1998) and I have started to be more familiar with the important experiences and skills acquired on the field of galaxy formation by the MPA galaxy formation sector both for the theoretical part and for the numerical. I anticipate that interactions with other network nodes, particularly Durham and Paris, will increase as my project progresses.

Dr Yuen Keong Ng:
I started my Ph.D. research on the analysis of the photometric photometry of a great many stars (>> 1 million **) in Field \#3 of the Palomar- Groningen Survey. I continued with the development of a Galactic model based on the Padova stellar population synthesis tool to study the formation, structure and evolution of our Milky Way from star counts.
After my Ph.D. I did my first post-doc at the IAP. I dedicated about 50\% of my time to the analysis of the quality of the data obtained by the Denis survey. The remaining 50\% of my time was spent on the improvement of the Galactic model and on studies with the stellar population synthesis tool.
My second post-doc was done at Padova. I started with the study of population boxes in order to link the stellar population synthesis tool with the Padova spectro-photometric code. However, the integration required a more rigorous and objective method to analyse data with both the stellar population synthesis and the spectro-photometric tool. I started with the development of an automated analysis tool AMORE (Auto-Matic Observation REndering) for stellar applications which should be linked afterwards with the spectro- photometric tool. The spectro-photometric information was subsequently intended to be used as input for AMORE to obtain a self-consistent calibration. In the mean time I tested the stellar evolutionary tracks with the F and G stars in the local Solar neighbourhood. I further profitted from the knowledge about galacto-chemical evolution and carbon star evolution. This was applied to the so-called bulge carbon star mystery and I argued that the bulge C-stars are actually related to the newly discovered Sagittarius dwarf galaxy.

Dr Bianca Maria Poggianti:
My main field of research is the evolution of cluster and field galaxies as a function of environment and redshift, both from the theoretical (spectrophotometric modeling) and the observational point of view (acquisition and interpretation of astronomical data). As part of my responsibilities in the Network, I have contributed to the organization of the EU-TMR Meeting on ``Evolution of Field and Cluster Galaxies'' in Cambridge (28/2-1/3 1997). I have presented oral communications at two site meetings in Cambridge (28 Feb - 1 Mar 1997) and in Paris (7-8 Feb 1997) and at the two annual meetings in Ringberg (19-24 May 1997) and in Leiden (31 Aug-4 Sep 1998). The fellowship in Cambridge gave me the possibility to spend two years at one of the most stimulating astronomical institutes in the world, and this period has been very important for my professional and personal development and for my next career steps. The Network experience offered me the possibility to get in touch, through personal and regular contacts, with the forefront research in different and complementary fields (Radio galaxies, Quasar Absorption lines, Semi-analytic modelling, Numerical simulations\dots), which helped me acquiring a more comprehensive view of my own research field. At the end of September 1998 I have completed my EU-TMR fellowship and I am now an established astronomer at the Osservatorio Astronomico di Padova, Italy. I am still involved in various collaborations together with researchers from different network sites and these collaborations are likely to continue during the coming years.

Dr Tom Theuns:
Tom Theuns has been involved in high-resolution hydrodynamical simulations of the Lyman-alpha forest. The motivation for this project is that the physical picture of the forest is sufficiently simple that current state-of-the-art simulation tools such as used by the Virgo consortium can hope to resolve the structures producing the Lyman-alpha forest. These simulations are then analysed in terms of Voigt profiles and comparison is made against Voigt profile statistics of the Lyman-alpha forest as measured in observed quasar spectra. The results so far are very promising. The simple physical picture where the Lyman-alpha forest is produced by the neutral fraction of the highly ionized gas that traces midly non-linear, filamentary structures, describes remarkably well the observed evolution of the number of absorption lines as a function of redshfit, from low redshifts, as observed by the Hubble Space Telescope, to high redshifts, as obserbed by the Keck telescope. The distribution of line widths is a probe of the temperature of the intergalactic medium, and comparison with observations suggest the temperature is high. Such high temperatures can be obtained in the standard model if the Universe has a high baryon density but a low total matter density. A new method based on the observed correlation of column density with line width turns out to be extremely suited to measuring the temperature-density relation of the intergalactic medium (work in progress).
This investigation is in close collaboration with people in Cambridge (G. Efstathiou, J. Schaye \& B. Carswell), Durham (F. Pearce) and Garching (M. Haehnelt). The travel funds provided by TMR have enabled and facilitated necessary visits to collaborators as well as conferences.

Comments to: Naoki naoki@mpa-garching.mpg.de