The evolution of the coastal aquifer of Belgium

In the unconfined aquifer below the coastal area of Belgium salt water Occurs under a fresh-water layer at depths that vary from 2 to more than 25 m. Radiocarbon dating of groundwater samples set the seawater encroachment in the deep parts of the aquifer back at least in the Sub boreal period. A working hypothesis concerning the evolution of the aquifer is formulated

Hydrogeologie van het duingebied tussen Koksijde en Oostduinkerke

The lithology of the unconfined aquifer between Koksijde and Oostduinkerke have been deduced from well logs. From a pumping test a value of 340 m2/d was obtained for the transmissivity and 3.10-3 for the elastic storage coefficient. Analyses of water samples indicated that the groundwater contains more salt near the water catchment than to north of it. Geo-electric well logging has shown the presence of fresh water over the entire thickness of the aquifer at the high-tide line. The groundwater currents have been computed by means of a mathematical model for two cases of a groundwater extraction of 1,5 million m3 per year

Litostratigrafie van de kwartaire sedimenten in het Oostelijk Kustgebied (België)

The composition of the Quaternary surface sediments in the Coastal Area is known in detail since the making of the geological map and especially since the systematic soil survey. The knowledge of the deeper Quaternary sediments however remains still fragmentary .Field work by the Center for Hydrogeological Research at the State University of Ghent has provided new data about the relief of the Tertiary substratum and the lithostratigraphy of the Pleistocene and Holocene sediments of the eastern part of the Coastal Area. A south-north section indicates the existence, in the burried surface of the Tertiary substratum, of two degradation levels (between -17 and -22 and between -8 and -6). Several lithostratigraphic units have been distinguished. The deepest deposit is the gravel-sand Ostend formation of Eemian age. This deposit is covered by the sandy Uitkerke formation of Weichselian age. The Wenduine formation on top of this sand is very heterogeneous; it has been formed during the transition between Pleistocene and Holocene. Along the edge of Inner Flanders the -8 level is overlain by the clayey Meetkerke formation with Hydrobia. In seaward direction this formation becomes sandy when passing laterally into the Houtave formation. The chronostratigraphic relationship between the two formations is not clear although the latter was probably deposited during the Atlantic. They are covered by the sands of the Zuienkerke formation, of which the northern part is also of Atlantic age. During this period and the Subboreal the Nieuwmunster peat was formed. This peat has been covered by the Dunkirk formation, except in the "Moere" of Meetkerke

Compact radio sources and jet-driven AGN feedback in the early Universe: Constraints from integral-field spectroscopy

To investigate the impact of radio jets during the formation epoch of their massive host galaxies, we present an analysis of two massive, log(M_stel/ M_sun)~10.6 and 11.3, compact radio galaxies at z=3.5, TNJ0205+2242 and TNJ0121+1320. Their small radio sizes (R<= 10 kpc) are most likely a sign of youth. We compare their radio properties and gas dynamics with those in well extended radio galaxies at high redshift, which show strong evidence for powerful, jet-driven outflows of significant gas masses (M 10^9-10 M_sun). Our analysis combines rest-frame optical integral-field spectroscopy with existing radio imaging, CO emission line spectra, and rest-frame UV spectroscopy. [OIII]5007 line emission is compact in both galaxies and lies within the region defined by the radio lobes. For TNJ0205+2242, the Ly-alpha profile narrows significantly outside the jet radius, indicating the presence of a quiescent halo. TNJ0121+1320 has two components separated by ~10 kpc and a velocity offset of ~300 km s^-1. If motions are gravitational, this implies a dynamical mass of 2x10^11 M_sun for the more massive, radio-loud component. The dynamical mass, molecular gas mass measured from the CO line emission, and radio luminosity of these two compact radio galaxies imply that compact radio sources may well develop large-scale, energetic outflows as observed in extended radio galaxies, with the potential of removing significant fractions of the ISM from the host galaxy. The absence of luminous emission line gas extending beyond the radio emission in these sources agrees with the observed timescales and outflow rates in extended radio galaxies, and adds further evidence that the energetic, large-scale outflows observed in extended radio sources (Nesvadba et al. 2006) are indeed the result of influence of the radio jet.Comment: A&A accepte

Geo-elektrische profielen bij de geologische en hydrologische detailkartering

Geoelectric traverses have been made in several regions of the F1anders, in order to test their usefulness for mapping purposes. The three regions selected had previously been covered by a grid of resistivity soundings mostly in Wenner arrangement.In the Beernem area different arrays have been used along the same line. These multiple traverses have provided data which allowed a comparison of the different arrays as well as a detailed subdivision in geoelectrical homogeneous zones coinciding with lithological units.Along traverse 136 GP/EE axial dipole measurements have been made over a distance of 2,7 km. For every point two values were determined : one for an array 2-20-2 and another for a 5-20-5 array. The first number stands for the length in meters of the current electrode separation, the third for the length of the voltage electrode separation, and the second for the distance between the two inner electrodes of bath dipoles.On the traverse 136-212 GP / AA Wenner arrangement perpendicular to the line has been used over a distance of 9,6 km to determine at each spot Q20' Q40' and Q80. Along the same line apparent resistivities have been measured with axial dipole arrays 2-20-2, 5-20-5, 5-40-5 and 10-40-10, parallel with the line.In the Westhoek area, a part of the coastal plain with salt-water encroachment in the unconfined aquifer, 21 traverses (194 GPW to 194 GPW21) have been run in the vicinity of Veurne (Furnes). The resistivities Q10 were measured by a longitudinal Wenner array. Since the traverses had been confined to a geoelectric homogeneous zone a quantitative interpretation could be performed. A relationship between Q10 and the depth of the saltwater - fresh water interface was computed from previous soundings. This relationship has been used to convert the apparent-resistivity data along the traverses into depth to interface values.The polder area of the F1emish Valley north of Ghent also has an unconfined aquifer with brackish water at variable depths. The situation is very similar to the one in the coastal plain although the variations here may not so readily find an explanation. One single traverse 142 GPW1 of 3550 m length has been run with a Wenner array for Q10. A relationship based upon former soundings has been used to convert resistivity data into interface depths.Resistivity traversing proves to be a very accurate and speedy tool for detailed mapping. Even a qualitative interpretation of a traverse, multiple if possible, can be sufficient to outline the boundaries between lithological or hydrogeological units. Quantitative interpretation is possible when in conjunction with a sounding grid, previously established, a relationship between the fixed electrode array and the unknown factor is found.Once a relationship is established, fixed-electrode separations allow a more detailed survey than resistivity soundings. These have to be long enough to obtain a reliable curve and hence average depth or resistivity data over longer a distance than fixed-electrode measurements which tend to be as short as possible. When traversing for qualitative purpose dipole arrangements have an advantage over Wenner arrangement in being speedier

An extreme rotation measure in the high-redshift radio galaxy PKS B0529-549

We present the results of a radio polarimetric study of the high-redshift radio galaxy PKS B0529-549 (z=2.575), based on high-resolution 12 mm and 3 cm images obtained with the Australia Telescope Compact Array (ATCA). The source is found to have a rest-frame Faraday rotation measure of -9600 rad m^{-2}, the largest seen thus far in the environment of a z > 2 radio galaxy. In addition, the rest-frame Faraday dispersion in the screen responsible for the rotation is calculated to be 5800 rad m^{-2}, implying rotation measures as large as -15400 rad m^{-2}. Using supporting near-IR imaging from the Very Large Telescope (VLT), we suggest that the rotation measure originates in the Ly-alpha halo surrounding the host galaxy, and estimate the magnetic field strength to be ~10 microGauss. We also present a new optical spectrum of PKS B0529-549 obtained with the New Technology Telescope (NTT), and propose that the emission-line ratios are best described by a photoionization model. Furthermore, the host galaxy is found to exhibit both hot dust emission at 8.0 microns and significant internal visual extinction (~1.6 mag), as inferred from Spitzer Space Telescope near/mid-IR imaging.Comment: 12 pages, 6 figures, accepted for publication in MNRA

A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In the Southern Hemisphere (WISH) survey

The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the observations, the survey has a much lower resolution in declination than in right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS shows that the positional accuracy is less constrained in declination than in right ascension, but there is no significant systematic error. We present a source list containing 73570 sources. We correlate this WISH catalogue with the NVSS to construct a sample of faint Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies with large optical telescopes in the southern hemisphere. This sample is aimed at increasing the number of known high redshift radio galaxies to allow detailed follow-up studies of these massive galaxies and their environments in the early Universe.Comment: 12 Pages, including 5 PostScript figures. Accepted for publication in Astronomy & Astrophysics. The full WISH catalog with 73570 sources is available from http://www.strw.leidenuniv.nl/wenss

A new search for distant radio galaxies in the southern hemisphere - I. Sample definition and radio properties

This paper introduces a new program to find high-redshift radio galaxies in the southern hemisphere through ultra-steep spectrum (USS) selection. We define a sample of 234 USS radio sources with spectral indices alpha_408^843 < -1.0 and flux densities S_408 > 200 mJy in a region of 0.35 sr, chosen by cross-correlating the revised 408 MHz Molonglo Reference Catalogue, the 843 MHz Sydney University Molonglo Sky Survey and the 1400 MHz NRAO VLA Sky Survey in the overlap region -40 deg < delta < -30 deg. We present Australia Telescope Compact Array (ATCA) high-resolution 1384 and 2368 MHz radio data for each source, which we use to analyse the morphological, spectral index and polarization properties of our sample. We find that 85 per cent of the sources have observed-frame spectral energy distributions that are straight over the frequency range 408-2368 MHz, and that, on average, sources with smaller angular sizes have slightly steeper spectral indices and lower fractional linear polarization. Fractional polarization is anti-correlated with flux density at both 1400 and 2368 MHz. We also use the ATCA data to determine observed-frame Faraday rotation measures for half of the sample.Comment: 28 pages, 9 figures, 10 tables, accepted for publication in MNRAS. Correct version of SUMSS catalogue now noted in Section 2.1.2; analysis and conclusions unchanged. A higher-resolution version of Figure 1 is available at http://www.physics.usyd.edu.au/~jess/papers.htm