Radiative Shock-Induced Collapse of Intergalactic Clouds

Accumulating observational evidence for a number of radio galaxies suggests an association between their jets and regions of active star formation. The standard picture is that shocks generated by the jet propagate through an inhomogeneous medium and trigger the collapse of overdense clouds, which then become active star-forming regions. In this contribution, we report on recent hydrodynamic simulations of radiative shock-cloud interactions using two different cooling models: an equilibrium cooling-curve model assuming solar metallicities and a non-equilibrium chemistry model appropriate for primordial gas clouds. We consider a range of initial cloud densities and shock speeds in order to quantify the role of cooling in the evolution. Our results indicate that for moderate cloud densities (>1 cm^{-3}) and shock Mach numbers (<20), cooling processes can be highly efficient and result in more than 50% of the initial cloud mass cooling to below 100 K. We also use our results to estimate the final H_2 mass fraction for the simulations that use the non-equilibrium chemistry package. This is an important measurement, since H_2 is the dominant coolant for a primordial gas cloud. We find peak H_2 mass fractions of >0.01 and total H_2 mass fractions of >10^{-5} for the cloud gas. Finally, we compare our results with the observations of jet-induced star formation in ``Minkowski's Object.'' We conclude that its morphology, star formation rate (~ 0.3M_solar/yr) and stellar mass (~ 1.2 x 10^7 M_solar) can be explained by the interaction of a 90,000 km/s jet with an ensemble of moderately dense (~ 10 cm^{-3}), warm (10^4 K) intergalactic clouds in the vicinity of its associated radio galaxy at the center of the galaxy cluster.Comment: 30 pages, 7 figures, submitted to Astrophysical Journa

A hundred years Pedagogische Studiën: a century of educational science in service of educational reform

Pedagogische Studiën (PS) heeft de afgelopen honderd jaar gefunctioneerd als een belangrijk platform voor de Nederlandstalige opvoedings- en onderwijswetenschappen. Vanaf de oprichting in 1920 stelde PS zich ten doel onderwijs en opvoeding niet slechts beter te begrijpen, maar door middel van onderzoek en reflectie ook beter te maken. Uitgangspunt was daarbij dat PS zou moeten functioneren als een ‘gemeenschappelijke studeerkamer’ waar een nationaal gesprek over onderwijs en opvoeding zou moeten plaatsvinden. Dit historische overzicht gaat na welke gemeenschap in PS bijeenkwam, waar het gesprek in deze kamer over ging, en hoe beide zich ontwikkelden in de loop van de tijd. Daarbij wordt gekeken naar de verhouding tussen ontwikkelingen in de onderwijswetenschappen en het onderwijsbeleid rond het thema onderwijs- vernieuwing. De geschiedenis van PS wordt verteld in vier perioden, waarin iedere keer een nieuwe groep pedagogen en onderwijswetenschappers aan het roer stond van de ‘gemeenschappelijke studeerkamer’. De analyse laat zien dat er in iedere periode een dominante groep binnen PS was die streefde naar onderwijsvernieuwing aan de hand van wetenschappelijk inzicht, maar dat de richting van die vernieuwing en de wetenschappelijke onderbouwing in iedere periode anders was. Ook wordt duidelijk dat tegenspraak nodig is voor een levendig wetenschappelijk debat.Since its founding in 1920, Pedagogische Studiën(PS) has been an important platform for theeducational sciences in the Netherlands. Aconstant aim was to better understand andimprove the practice of education and upbringingby means of scientific study. PS was meant to bea ‘communal scientific forum’ for a nationaldebate on upbringing and education. This articleprovides a history of the journal in four periods,looking at the community that came together inPS and the debate that took place in it, focusingon the theme of educational reform. For each ofthe four periods, the article shows that a newgroup of academic educationalists dominatedthe debate in PS, each time striving foreducational reform based on scientific insights.In each period, however, the direction of theproposed educational reforms as well as thescientific support for them were markedlydifferent

Triggered Star Formation in a Massive Galaxy at z=3.8: 4C41.17

Spectropolarimetric observations obtained with the W. M. Keck Telescope of the z=3.8 radio galaxy 4C41.17 show that the UV continuum emission from this galaxy, which is aligned with the radio axis, is unpolarized (P[2sigma] < 2.4%). This implies that scattered AGN light, which is generally the dominant contributor to the rest-frame UV emission in z~1 radio galaxies, is unlikely to be a major component of the UV flux from 4C41.17. The spectrum shows absorption lines that are similar to those detected in the spectra of the recently discovered population of star forming galaxies at z~2-3. A galaxian outflow may contribute partially to the low ionization absorption lines; however, the high velocity wings of the high ionization lines are unlikely to be dominated by a galaxian wind since the implied outflow mass is very large. The detection of stellar absorption lines, the shape of the SiIV profile, the unpolarized continuum, the inability of any AGN-related processes to account for the UV flux, and the similarity of the UV continuum spectra of 4C41.17 and the nearby starburst region NGC 1741B1 suggest that the UV light in 4C41.17 is dominated by young stars. If so, the implied star-formation rate is roughly 140-1100Msun/yr. We discuss the possibility that star formation in 4C41.17 was triggered by the radio source. Our data are consistent with the hypothesis that 4C41.17 is undergoing its major epoch of star formation at z~4, and that by z~1 it will have evolved to have spectral and morphological properties similar to those observed in known z~1 powerful radio galaxies.Comment: 28 pages (Latex text + figures); Accepted for publication in The Astrophysical Journal (Dec 1, 1997 issue

Internal Migration and Regional Population Dynamics in Europe: Netherlands Case Study

This report summarises the presentations made and discussions held at the Second of the ESRC/JISC Workshops Planning for the 2001 Census. The report presents views of expert census users and summarises the recommendations to ESRC and JISC about what kinds of data from the 2001 Census should be requested from the UK Census Offices. The Workshops are supported by ESRC Award H507265031. The Census of Population is a very large exercise in data collection and processing. In 2001 some 25 million households in the United Kingdom will be contacted and asked to provide answers to a simple questionnaire of 25 to 30 questions. Such a task is likely to cost £125-150 millions to the Census Offices. Purchase of the data for academic research purposes is likely to cost ESRC and JISC some £1.5 to £2 millions directly and an equivalent amount indirectly on support over the following decade. It is therefore essential that the Population Census is very carefully planned beforehand and that the greatest possible value is extracted from the data collected. This edited collection of papers reports on presentations and discussions in the Fourth and Final Workshop in the series Workshops Planning for the 2001 Census - Determining Academic Community Needs and Strategy. The Fourth Workshop was entitled The 2001 Census: What do we really really want?. The aim was to gather together and summarise the principal recommendations of the First (Geography), Second (Interfaces) and Third (Special Data Sets) Workshops. The Workshop was twinned with another on The One Number Census: A Research Workshop, organised by Ludi Simpson. The One Number Census project is a major undertaking by the Census Offices to deal with anticipated underenumeration by estimating how many households and people are missed by the standard enumeration. Part 1 of the report on Look Up Tables and Area Statistics contains chapters by David Martin on the output geography proposals for 2001, by Seraphim Alvanides and Stan Openshaw on further developments to the methods being used to define output areas and by Bob Barr on what the Look Up Tables associated with the 2001 Census should be like. These chapters contain key recommendations on census output geography. Part 2 of the report puts forward recommendations for the preparation of Microdata - Samples of Anonymised Records and Longitudinal Data from the 2001 Census. Angela Dale summarises the conclusions of the SARs Sub-Group of the Census Offices' Output Working Group. Brian Dodgeon and Heather Joshi document the essential features of the 2001 Census Link to the Longitudinal Study and make a final plea for some new questions. Part 3 of the report reviews proposals for the improvement of Interaction Statistics from the 2001 UK Census. Paul Boyle and Phil Rees make radical proposals for revamping the provision of Migration Statistics. Martin Frost concentrates on ways of improving the accuracy of the Workplace Statistics. The fourth part of the report gathers together recommendations about information technology interfaces to census data, arguing that the tools and infrastructure are now in place to make networked and standalone access to the different types of data so much easier for the new user. Donald Morse and Alistair Towers review what interfaces to boundary data should look like. James Harris argues for the development of interfaces based on general data standards and the Web to access census statistics. Oliver Duke-Williams outlines how complex migration statistics can be presented for access in a simpler and easier to use interface. Ian Turton identifies how current software developments in Java programming will make possible delivering easy to use interfaces to microdata very simple. Finally, Paul Williamson describes a design of a data dictionary for all census data sets. In Part 5, recommendations are summarised. Phil Rees reports on the views of 140 respondents drawn from the different corners of the academic community. The final pages try to draw out some general points from the very large number of recommendations made in the Fourth Workshop

Forming Galaxies with MOND

Beginning with a simple model for the growth of structure, I consider the dissipationless evolution of a MOND-dominated region in an expanding Universe by means of a spherically symmetric N-body code. I demonstrate that the final virialized objects resemble elliptical galaxies with well-defined relationships between the mass, radius, and velocity dispersion. These calculations suggest that, in the context of MOND, massive elliptical galaxies may be formed early (z > 10) as a result of monolithic dissipationless collapse. Then I reconsider the classic argument that a galaxy of stars results from cooling and fragmentation of a gas cloud on a time scale shorter than that of dynamical collapse. Qualitatively, the results are similar to that of the traditional picture; moreover, the existence, in MOND, of a density-temperature relation for virialized, near isothermal objects as well as a mass-temperature relation implies that there is a definite limit to the mass of a gas cloud where this condition can be met-- an upper limit corresponding to that of presently observed massive galaxies.Comment: 9 pages, 9 figures, revised in response to comments of referee. Table added, extended discussion, accepted MNRA

Scalar radiation emitted from a source rotating around a black hole

We analyze the scalar radiation emitted from a source rotating around a Schwarzschild black hole using the framework of quantum field theory at the tree level. We show that for relativistic circular orbits the emitted power is about 20% to 30% smaller than what would be obtained in Minkowski spacetime. We also show that most of the emitted energy escapes to infinity. Our formalism can readily be adapted to investigate similar processes.Comment: 19 pages (REVTEX), 5 figures, title slightly changed, extra demonstration and minor improvements included. To appear in Class. Quant. Gra

HST Imaging of the Host Galaxies of High Redshift Radio-Loud Quasars

We present rest-frame UV and Ly-alpha images of spatially-resolved structures around five high-redshift radio-loud quasars obtained with the WFPC2 camera on the Hubble Space Telescope. We find that all five quasars are extended and this "fuzz" contains ~5-40% of the total continuum flux and 15-65% of the Ly-alpha flux within a radius of about 1.5 arcsec. The rest-frame UV luminosities of the hosts are log lambda P_lambda = 11.9 to 12.5 solar luminosities (assuming no internal dust extinction), comparable to the luminous radio galaxies at similar redshifts and a factor 10 higher than both radio-quiet field galaxies at z~2-3 and the most UV-luminous low redshift starburst galaxies. The Ly-alpha luminosities of the hosts are (in the log) approximately 44.3-44.9 erg/s which are also similar to the those of luminous high redshift radio galaxies and considerably larger than the Ly-alpha luminosities of high redshift field galaxies. To generate the Ly-alpha luminosities of the hosts would require roughly a few percent of the total observed ionizing luminosity of the quasar. We find good alignment between the extended Ly-alpha and the radio sources, strong evidence for jet-cloud interactions in two cases, again resembling radio galaxies, and what is possibly the most luminous radio-UV synchrotron jet in one of the hosts at z=2.110.Comment: 36 pages (latex, aas macros), 3 figures (3 gif and 10 postscript files), accepted for publication in the the Astrophysical Journal Supplement Serie