M. J. A. Oort’s research while affiliated with National Radio Astronomy Observatory and other places

A deep 21 cm survey, carried out with the Westerbork Synthesis Radio Telescope (WSRT), of two fields in the constellation of Hercules is presented. These areas were observed previously at 21 cm in the Leiden-Berkeley Deep Survey (LBDS), (Windhorst et al., 1984), but with a factor of three higher noise level. A complete sample is defined, containing 116 radio sources with a peak flux above 5 sigma, within the -7dB attenuation radius (0.464 deg). This complete sample is used to determine the 1412 MHz source counts down to 0.45 mJy. The counts from the current sample show the same small scale structure at about 1 mJy, as was found in previous surveys. A direct comparison is made with the LBDS observations of the same fields. It is shown that the 5 sigma peak flux cut-off in the complete sample is not stringent enough to sufficiently avoid contamination by spurious sources, especially when strong (S of not less than 100 mJy) sources are present in the field. Finally, a search was made for the variable sources.

A redshift dependence of the maximum distance out to which active galactic nuclei (AGN) can transport their relativistic particles was first found for radio quasars by Miley1. He demonstrated that this distance was, on average, smaller in the past than it is at present, Analysing the run of median angular size with flux density for the entire extragalactic radio source population, Kapahi2 concluded that the radio galaxy population probably shares this property with the extended radio quasars. By using samples of radio ellipticals complete to vastly different flux limits, we can, for the first time, separate redshift- and luminosity-dependences of their linear sizes. Ram pressure in a medium with cosmologically varying density will naturally cause a dependence on redshift3, but this cannot explain so steep a dependence as that implied here. It may be expected if galaxy haloes influence the outward energy transport4.

The majority of the 1-arcsec resolution snapshot maps of 133 radio sources presented from the Leiden-Berkeley Deep Survey (LBDS) indicate that the sources have flux densities in the 1-100 mJy range at 1.4 GHz, with a median flux density of 5 mJy. A combination of all radio-morphological data available for the LBDS, the median angular size of a complete radio sample is found to decrease with decreasing flux density to a value as low as about 2 arcsec between 1 and 10 mJy. Definite indications are found for a decrease of intrinsic size with increasing redshift, with a relation that results in a size decrease of factor 4 with respect to the local value at the same radio power.

A progress report is presented on the ongoing project to chart the populations and luminosities of faint radio galaxies. The primary samples used in the project derive from deep, complete flux-limited samples defined at 1.4 GHz. Optical identification on deep optical material is followed by colorimetry, spectroscopy, and high-resolution radio mapping. The current status of the radio and optical work is reported, and information on the nature of the radio and optically faint galaxies is presented. The population evolution described by the redshift dependence of the radio luminosity function is discussed.

The authors present a deep 21 cm radio survey of the Lynx 2 field selected from the Leiden-Berkeley Deep Survey areas. In the main part of the paper the authors give a review of the data reduction techniques that were used and present a complete radio sample which they used to determine the 1412 MHz source counts and the median angular size at the mJy level. A comparison of this survey with a survey of the same field with the Very Large Array is performed. A systematic position difference as a function of distance to the field center is found. The absolute uncertainties in the coordinate frame and flux scale are determined, as well as the signal-to-noise dependent error distribution. Corrections for systematic influence of the flux determining algorithm are discussed. Finally, a search was made for variable sources in the maps.

The current data base developed from surveys of radio galaxies is assessed. It is suggested that most objects with high radio flux densities within the range of current instrumentation have already been detected, while those at lower flux densities must still be scanned as well as characterized for their spectroscopic redshifts. Conditions under which photometric redshift determinations are accurate are discussed, as are large dynamic range radio-optical surveys at Westerbork and Kitts Peak. It is noted that at redshifts above 1.5 all the radio galaxies appear as quasars. Progress in radio surveys of evolving blue galaxies is also reviewed, particularly for evidence of a parent population. Printing Options Send high resolution image to Level 2 Postscript Printer Send low resolution image to Level 2 Postscript Printer Send low resolution image to Level 1 Postscript Printer Get high resolution PDF image Get low resolution PDF Send 300 dpi image to PCL Printer Send 150 dpi image to PCL Printer More Article Retrieval Options HELP for Article Retrieval Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints