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Annual Report 1999 | |
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ANNUAL REPORT The network continued to be very active in its third year with 43 additional joint publications submitted to the refereed scientific literature over the period 1/10/98 to 30/9/99. In addition 8 jointly authored contributions to conference proceedings were submitted. (See attached publications list.) Personnel changes within the Network were relatively minor over this
year with most of the Network's postdoctoral fellows remaining in post.
The third Annual Meeting of the network was held over the period 30 August - 4 September 1999 in Asiago, Italy. Although attendance was strictly limited to scientists from the participating sites, almost 80 scientists took part. The meeting was very successful in reporting on existing activity and in generating new collaborations. Other smaller meetings are detailed in the following scientific report.
The main event in 1999 was that the first 8.2-m VLT Unit Telescope (ANTU) was "handed over'' to the scientists on April 1, 1999; its first "visiting astronomers'' at Paranal were astronomers from Leiden carrying out a network programme. One of VLT's major asset is its excellent instrumentation. A number of collaborative projects have been started to use these facilities to study various classes of distant galaxies, including very red galaxies, young and starforming galaxies, dusty galaxies and galaxies that are good candidates for being in extremely distant clusters. The aim is to obtain a good census and understanding of the distant galaxy population. Within this context, a large VLT programme has recently been approved to obtain the deepest infrared images ever taken. Scientific highlights
Network activities The Sterrewacht Leiden organised a TMR workshop on hydrodynamic aspects
of galaxy formation and evolution at the Lorentz Center at the Universiteit
Leiden from March 8 to 10 1999. The workshop was visited mainly by advanced
graduate students and young postdocs from the network. A significant fraction
of the workshop was devoted to a series of extended review talks by senior
researchers on hydrodynamics in general, certain aspects of its numerical
implementation, and the application to galaxy formation and evolution.
Progress with appointment of young researchers The young researcher being employed by the network in Leiden is Philip
Best (a number of other PhD students and post-docs are also involved in
network activities). Dr Best, originally from Cambridge, was employed
following the network's initial advertisement. He has traveled to meetings
at other sites of the network, and is now involved in active collaborations
with researchers in Leiden, Cambridge, Paris and Munich. Carlos de Breuck,
a Belgium PhD student, has also been employed for a period of one year.
2a Evolution of cluster galaxies: A group of Network researchers from Cambridge, Durham and Padova have completed an extensive spectroscopic catalogue of galaxies in 10 distant rich clusters for which Hubble Space Telescope imaging was obtained earlier. The clusters span the redshift range z=0.37-0.56 and are the subject of a detailed ground- and space-based study to investigate the evolution of galaxies as a function of environment and epoch. A direct comparison of the spectral properties of the high-redshift cluster and field populations suggests that the abundance of galaxies that formed stars in the recent past decreased in cluster environments by more than one order of magnitude in the last 5 billion years, while such evolution is much more modest in the field. This suggests that the process or processes involved in producing such galaxies are either substantially more effective in the cluster environment or that this environment prolongs the visibility of the post-star-formation phase. These data have also been used to investigate the nature of the different cluster galaxy types, including star-forming, poststarburst, and passive galaxy populations, and to reproduce their basic properties using spectral synthesis models developed within the Network. The comparison of the spectra of the distant galaxy populations with samples drawn from the local universe leads us to identify a significant population of dust-enshrouded starburst galaxies. The spectral and morphological properties of the distant cluster galaxies indicate that either two different timescales and/or two different physical processes are responsible for the spectral and morphological transformation of galaxies in clusters. Finally, researchers in Durham and Cambridge have detected dust in the central galaxies of distant cooling-flow clusters. Although the sample is still small, the detections have important implications for the interpretation of star formation in cooling-flow galaxies. 2b Evolution of field galaxies: The pioneering study of star formation hidden by dust in extremely distant galaxies using the SCUBA bolometer array at the UK James Clerk Maxwell Telescope (JCMT) has continued to be a very active field of research within the network. Reliable redshifts for 20 galaxies have been obtained, suggesting that the majority of the extragalactic background light in the submillimeter is emitted by sources at z$<$3 and hence that the peak activity in highly obscured sources (both Active Galactic Nuclei and starbursts) lies at relatively modest redshifts. For some of these galaxies, molecular gas has been detected for the first time. The large molecular gas mass found in some of the galaxies and their radio emission are consistent with the interpretation that massive starbursts are taking place, and that massive reservoirs of molecular gas are available to fuel the very high rates of star formation detected. Two of the systems appear to be associated with merger events which may evolve into present-day luminous elliptical galaxies. At low redshift, Network researchers in Cambridge and Munich have completed an optical and near-infrared study of a large and representative sample of nearby star-forming galaxies. The new data has been used to characterize the star-formation properties of the galaxies, including the strength and age of their current (or most recent) burst of star formation, their star-formation rate and their total stellar mass. The Institute of Astronomy of the University of Cambridge has hosted several visits of researchers from other network institutions (Munich, Paris, Durham, Leiden and Padova), to carry out collaborative research. In addition, several IoA members have visited other nodes (Padova, Durham, Paris, Munich) to work on various collaborations an plan future research. Dr Pierre-Alain Duc continued working at the IoA during this period as
a research fellow, funded by the Network. He terminated his contract on
September 30th, and moved to the D\'epartement d'Astrophysique of the
Commissariat \`a l'\'Energie Atomique, (CEA) in Saclay, France, where
he has secured a permanent research post. His main research activities
were related to the observational study of interacting and star-forming
galaxies, and the role of the environment in their formation and evolution.
He actively collaborated with researchers in Cambridge, Paris and Padova
within the Network.
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 absorbing halos at high redshift. In particular the following key results have been achieved:
Semi-analytic techniques have been extended this year in a number of new ways.
6 Simulations of galaxies and clusters Scientific results: A considerable amount of effort was expended analysing the"Hubble volume''simulations, which were described in last year's report. Two network papers analysing the statistical properties of the clustering pattern in the simulations were completed and several more are in progress. These cover topics such as the properties and distribution of rich clusters (tens of thousands of which formed in each simulation), the mass function of dark matter halos over an unprecedented range of scales, and the construction of realistic mock catalogues of galaxies ideal for analysing data from galaxy surveys (such as the ``PSCz'' and ``2dF'' surveys in which the network is involved). We recently completed the first large N-body/gasdynamical simulations capable of resolving the formation of galaxies in representative volumes of the Universe. These simulations contained 2097152 dark matter particles and the same number of gas particles, with a gas mass per particle of $\sim 2\times10^9 M_\odot$, and a gravitational softening of 10 kpc. The simulations followed the formation of galaxies by gas cooling within dark halos of mass a few times $10^{11}M_\odot$ and above. This is a calculation that we had been struggling to perform for several years. The breakthrough that made it possible was a novel treatment of the intergalactic medium in which cool galactic gas is partially decoupled from the hot cooling flow around it. Over 2200 galaxies formed in our simulation, with a distribution of K-band luminosities (obtained from a spectral population synthesis model) in excellent agreement with observations. We are currently investigating the demographics and clustering properties of these galaxies as a function of time. Our preliminary results show that the two-point correlation function of bright galaxies in the model evolves rather little since $z=3$. At the present day, it has a shape close to a power-law over four orders of magnitude in amplitude, in good agreement with observations. The galaxies in a flat model with a cosmological constant are antibiased relative to the mass on small scales. These early results point to a remarkable success of these models in matching the trends seen in the data. Encouraging as our first results are, this is only a start. Apart from the ongoing detailed analysis of these simulations, we are exploring further the validity of the assumptions we have made in the treatment of the intergalactic medium. This requires extensive testing via suites of small-scale simulations which we have recently began. Beyond that, we are focussing on an increasingly realistic treatment of the astrophysics of galaxy formation, particularly star formation and feedback. Our codes already include crude treatments of these processes but, at present, we have little idea of how the simulation results are affected by different parameterizations. We have recently began a systematic study of this problem. This is a long-term programme that will occupy a substantial fraction of our computing resources in the near future. The simulations we have carried out this year represent substantial progress towards our year-4 milestone (``compiling the largest available suite of simulations of galaxy formation in differing environments and in a variety of cosmogonies.'') By contrast, we have not yet been able to achieve our year 2 milestone (understanding the requirements for disk galaxies to form with the observed properties) which proved to be more difficult than anticipated. We are continuing work in this problem. Scientific highlights: Networking and coordinating activities: Appointment of young researchers:
Three network proposals for VLT time to study galaxies in the Huble Deep
Field South were successful: \parindent=10pt
Comments to: Naoki |
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