<< Sheffield on MSFR >> Node: The University of Sheffield, UK Senior scientists involved: - Dr. Richard de Grijs (UK national coordinator, RTN deputy PI) - RdG - Prof. Clive Tadhunter - CT - Dr. Paul Crowther - PAC 1. science objectives: a) Star cluster formation in the intense environments of interacting and starburst galaxies. Star cluster formation seems to be a (if not the) major mode of star formation in the extreme environments found in interacting and starburst galaxies. As such, they trace the major stages of galaxy formation and evolution. The main objective of our research at Sheffield is to use the young and intermediate-age star clusters as tracers of galaxy evolution and to determine whether they have the potential to evolve into old Galactic globular cluster-type objects by the time they reach similar ages. If so, this implies that globular cluster formation did not only happen at the time of galaxy formation, but continues until the present. If we can establish this scenario beyond a doubt, this will have far-reaching consequences for theories of galaxy formation and evolution. These questions can most easily be addressed using the star cluster luminosity (or mass) functions in conjunction with models for the evolution of star cluster SYSTEMS. Alternatively, we are engaged in a number of projects in which we try to determine the stellar initial mass function (IMF) based on high-resolution spectroscopy (HST/STIS, VLT/UVES). The slope of the IMF is the most crucial ingredient for the evolution and survivability of an individual cluster High-resolution spectroscopy is used to determine dynamical cluster masses, and in combination with HST imaging, their mass-to-light ratios, which are then compared to models using a variety of prescriptions for the evolution of single stellar populations with certain IMF parameters. b) The internal dynamics of star clusters Rich, compact star clusters are the ideal laboratories for the study of stellar evolution. As such, the old globular clusters (GCs) in the Milky Way have been used extensively for this purpose, and their colour-magnitude diagrams (CMDs) are now well understood. However, the evolution of the dynamically important binary population is not yet well understood. Although the Milky Way contains a large population of GCs, they are predominantly old, with ages largely in excess of 10 Gyr. Therefore, we cannot use the Galactic GC population to follow the evolution of binary systems in the dense environments of GC-type objects. Fortunately, however, we have access to a unique data set of deep HST observations of a carefully selected sample of similar star clusters in the Large Magellanic Cloud (LMC). The cluster population in the LMC is characterised by ages spanning the range from ~10^6 to ~10^10 yr. The observations of the young and intermediate-age LMC clusters in our sample are sufficiently deep that we can detect binary systems based on a careful analysis of their CMDs: binary systems consisting of two stars of similar mass and temperature will have the same colour, but twice the luminosity of a single star. Thus, binary systems will appear as a broadening or a secondary main sequence in star cluster CMDs. Using our existing observations of carefully selected star clusters in the LMC, our group is involved in (i) estimating the binary fractions in each of our sample clusters, both overall and as a function of radius, using sophisticated Monte Carlo simulation techniques; (ii) connecting the expected radial dependence of the binary fraction to the effects of dynamical evolution and to the cluster stellar density, and we will thus (iii) constrain the importance of primordial versus dynamical production of binary systems; and (iv) obtain valuable constraints on the dynamical evolution of binary systems in these star clusters, by virtue of the clusters' age range. - Massive stellar evolution: How inidividual massive stars evolve as a function of metallicity, and how this in turn feeds back to the ISM. Do stars behave differently in MW, LMC and SMC clusters ? The IMF of massive stars and blue-red supergiant ratio as a function of metallicity. - Stellar winds from massive stars: their energy input to the ISM and effects on chemical evolution of galaxuies - Fundamental parameters of OB-stars and accurate calculations of theoretical spectra for input into e.g. STARBURST99. - Probing the chemical homogeneity of the Local Group by determining abundances of massive blue stars c) to investigate the link between galaxy evolution and AGN activity in galaxies One of the most important results in extragalactic research in the last decade has been the discovery that AGN activity is linked to galaxy evolution. This link is manifest in two ways: first, the form of the redshift evolution of the population of quasars and powerful radio galaxies is similar to that of evolution of global star formation rate; second there are strong correlations between the masses of the supermassive black holes and the properties of the bulges of the host galaxies. However, a detailed physical understanding of these links is currently lacking, although the former link is thought to be related to the triggeering of AGN activity in major galaxy mergers. Clearly, if we are to truly understand the link between AGN activity and galaxy evolution, it is crucial to investigate the relationship between star formation and activity in the local universe, particularly in the context of galaxy mergers and the triggering of the activity. By measuring the ages and masses of the young stellar populations (YSP) in the AGN host galaxies we can investigate: - The nature of the mergers or galaxy interactions that trigger the activity: are the triggereing interactions always major gas rich mergers, or merely minor accretion events that provide the fuel for the AGN activity? - The time-scales and order-of-events: at what stage in the merger/interaction sequence in the activity triggered? - Relationship to the evolution of galaxies: do all galaxies go through an AGN phase following a galaxy merger/interaction? Detailed analysis of the merger-induced star formation, as embodied in the YSP component detected in the host galaxies, may provide the *only* quantitative means of addressing these issues; the quantitative information that can be derived from morphological or kinematical information alone is limited. We plan to concentrate on well-defined, complete samples of the AGN, for which we are accumulating large, high quality data sets using the new generation of 8m telescopes and instrumentation. Initially we will concentrate on complete samples of powerful radio galaxies and Seyfert galaxies, but will then extend this work to samples of merging galaxies (e.g. ultraluminous infrared galaxies - ULIRGS) which may represent the pre-AGN phase in the evolutionary sequence. This project is extremely timely, because the analysis tools required to separate the YSP and activity-related continuum components have just reached maturity following a decade of development. Moreover, the new generation of large telescopes and associated instrumentation for the first time allow us to obtain spatially resolved, deep spectra for AGN hosts out to moderate redshifts. d) Winds - role of metallicity in energy/chemical enrichment in ISM Feedback, in the form of K.E. and chemical enrichment, is treated very crudely at present in models of galactic evolution. Meanwhile, our knowledge of the role played by metallicity in driving stellar winds has significantly improved, such that an improved prescription for feedback by supernovae and stellar winds needs to be devised and applied to galactic evolution models and tested against observations spanning a wide metallicity range. e) Starbursts - stellar content of regions undergoing violent star formation The integrated rest-frame UV and optical spectrum of starburst galaxies at low and high redshift contain (solely) the direct signature of massive stars via UV P Cyg profiles and emission lines of Wolf-Rayet stars. Evolutionary synthesis models have recently been improved to enable the synthesis of such spectral features, enabling the massive stellar content to be probed in a wide variety of metallicity environments, including that of the early universe. f) Star formation - young massive clusters The formation and early evolution of massive stars remains an open issue in astrophysics. Whilst the majority of massive stars form in clusters, rather than individually, the precise formation mechanism (accretion versus cannibalism) remains untested. Against this background, the question of whether there is an universal upper mass cutoff in clustered star formation is unclear at present, with impact upon a wide variety of applications. Photometric studies alone do not allow one to readily disentangle mass functions for massive stars. Instead, spectroscopy is required, analysis of which will permit the relative mass distribution in the upper main sequence within individual clusters in different environments. 2. potential thesis titles: RdG: - Star cluster formation in the intense environments of interacting and starburst galaxies - Star formation modes in gravitationally disturbed galaxy environments - The evolution and dynamical importance of binary systems in compact star clusters - Spectroscopic determinations of the initial mass function in young massive star clusters - The LMC star cluster systems as an evolutionary benchmark CT: postdoc preferred PAC: Stellar content and early evolution of young massive clusters The mass distribution and properties of individual stars within young massive clusters (science driver a) can be addressed via near- or mid-IR spectroscopic observations (since young clusters are obscured at UV/optical wavelengths). Spectroscopy also provides information on the formation mechanism, i.e. accretion via a disk versus coalesence. PAC: Stellar population studies of nearby to high redshift starbursts It is proposed to apply the latest generation of evolutionary synthesis models to rest-frame UV/optical/near-IR observations of young starbursts including those at redshift z=3 (science driver b). Further, the metallicity dependence of feedback (science driver a) in galactic evolution models will be parameterized via application of population synthesis models. 3. postdoc topics: CT: The link between galaxy evolution and AGN activity in galaxies To be completed in a timely manner this project is best suited to a postdoctoral-level researcher who would start in year 1 on the project. . The postdoctoral researcher will gain considerable experience in spectral synthesis modelling of the spectra of AGN, learning how to distinguish YSP and AGN-related component. The postdoc will also gain experience in the use of large optical telescopes and associated instrumentation. Time-line: - Reduce, analyse, and model the existing data for powerful radio galaxy and Seyfert samples (~1.5yr) - Obtain further time to extend the samples to high redshifts; and also obtain time for similar optical/UV spectroscopic studies of ULIRGs (~1yr) - Reduce, analyse and model the new data (~1.5yr) 4. synergy: RdG: - on-going collaborations with UFvA on stellar population modeling, star cluster formation and evolution in merging and starburst galaxies (Germany) - on-going collaborations with LJS on young cluster IMFs (UK) - on-going collaborations with GG + Cambridge group on mass segregation in and dynamics of LMC clusters (UK) - on-going collaborations with H. Lamers (Netherlands) on cluster disruption CT: - on-going collaborations with E. Perez and R. Gonzalez-Delgado (Spain) on the starburst-AGN connection PAC: - on-going collaborations with LJS on feedback from young clusters and starbursts (UK) - on-going collaborations with SS on massive stars in Local Group (UK) - on-going collaborations with DS on spectral synthesis of Wolf-Rayet galaxies (Switzerland) - on-going collaborations with FN on stellar winds of massive stars (Spain) 5. Recent relevant publications: RdG: - de Grijs R., O'Connell R.W., Gallagher III J.S., 2001, AJ, 121, 768, ``The Fossil Starburst in M82'' - de Grijs R., Johnson R.A., Gilmore G.F., Frayn C.M., 2002, MNRAS, 331, 228, ``Mass segregation in young compact LMC star clusters: I. Data and Luminosity Functions'' - de Grijs R., Gilmore G.F., Johnson R.A., Mackey A.D., 2002, MNRAS, 331, 245, ``Mass segregation in young compact LMC star clusters: II. Mass Functions'' - de Grijs R., Gilmore G.F., Mackey A.D., Wilkinson M.I., Beaulieu S.F., Johnson R.A., Santiago B.X., 2002, MNRAS, 337, 597, ``Mass segregation in rich clusters in the Large Magellanic Cloud: III. Implications for the initial mass function'' - de Grijs R., Lee J.T., Mora Herrera M.C., Fritze-v. Alvensleben U., Anders P., 2003, New Astronomy, 8, 155, ``Stellar Populations and Star Cluster Formation in Interacting Galaxies with the Advanced Camera for Surveys'' - de Grijs R., Bastian N., Lamers, H.J.G.L.M., 2003, ApJ, 583, L17, ``The Missing Link in Star Cluster Evolution'' - de Grijs R., Bastian N., Lamers H.J.G.L.M., 2003, MNRAS, in press (astro-ph/0211420), ``Star Cluster Formation and Disruption Time-Scales - II. Evolution of the Star Cluster System in M82's Fossil Starburst'' CT: Tadhunter, C.N., Dickson, R., Morganti, R., Robinson, T.G., Wills, K., Villar-Martin, M., Hughes, M., 2002, MNRAS, 339, 977: The origin of the UV excess in powerful radio galaxies Wills, K., Tadhunter, C.N., Robinson, T.G., Morganti, R., 2002, MNRAS, 333, 211: The ultraviolet excess in powerful radio galaxies: evidence for a young stellar component Morganti, R., Oosterloo, T.A., Capetti, A., de Ruiter, H.R., Fanti, R., Parma, P., Tadhunter, C.N., Wills, K.A., 2003, A&A, 399, 511: B20648+27: a radio galaxy in a major merger Tadhunter, C., Marconi, A., Axon, D., Wills, K., Robinson, T.G., Jackson, N., 2003, MNRAS, 342, 861: Sepcetroscopy of the near-nuclear regions of Cygnus A: estimating the mass of the supermassive black hole PAC: Crowther P.A., Conti P.S., MSX mid-IR imaging of massive star birth environments I. Ultracompact HII regions MNRAS 343, 143-163 (2003) Smith L.J., Norris R.P.N., Crowther P.A., Realistic ionizing fluxes for young stellar populations from 0.05 to 2Zo, MNRAS 337, 1309-1328 (2002) Crowther P.A., Beck S.C., Willis A.J., Conti P.S., Morris P.W., Sutherland R.S., Properties of hot stars in the Wolf-Rayet galaxy NGC5253 from ISO-SWS spectroscopy, MNRAS 304, 654-668 (1999) Crowther P.A., Dessart L., Quantitative spectroscopy of Wolf-Rayet stars in HD97950 and R136a - the cores of giant HII regions, MNRAS 296, 622-642 (1998) 6. Management: (needs to be polished and added to) Tadhunter has more than 10 years of experience in leading and managing a observational research group in AGN research that has been highly successful at gaining access to major international facilities such as VLT, Keck and HST. Tadhunter is currently the UK representative on the ESO Observing Programmes Committee, and the Chair of the UK Panel for the Allocation of Telescope Time.