Ann Savage

THE PARKES HALF-JANSKY FLAT-SPECTRUM SAMPLE

We present a new sample of Parkes half-jansky flat-spectrum radio sources, having made a particular effort to find any previously unidentified sources. The sample contains 323 sources selected according to a flux limit of 0.5 Jy at 2.7 GHz, a spectral index measured between 2.7 and 5.0 GHz of alpha(2.7/5.0) > -0.5, where S(nu) proportional to nu(alpha), Galactic latitude \b\ > 20 degrees and -45 degrees < declination (B1950) < +10 degrees. The sample was selected from a region 3.90 steradians in area. We have obtained accurate radio positions for all the unresolved sources in this sample, and combined these with accurate optical positions from digitized photographic sky survey data to check all the optical identifications. We report new identifications based on R- and Kn-band imaging and new spectroscopic measurements of many of the sources. We present a catalogue of the 323 sources, of which 321 now have identified optical counterparts and 277 have measured spectral redshifts.

Optical identifications of southern compact radio sources

Optical identifications are presented for 158 radio sources, mostly from the Southern Hemisphere, based on the coincidence between the position of the optical object and the compact milliarcsecond radio nucleus. Radio positions with an accuracy of typically 0.3 arcsec rms were measured from the observed delay and fringe rate of VLBI observations at 2.29 GHz on an Australia-to-South Africa baseline. Optical identifications and positions were measured from the UK Schmidt Telescope deep IIIa-J Southern Sky Survey plates, where available. 16 refs.

2.3-GHz accurate positions and optical identifications for selected Parkes radio sources

Accurate radio positions of 74 extragalactic radio sources contained in the Parkes 2.7-GHz survey were measured at 2.3 GHz with the Tidbinbilla interferometer, located near Canberra, Australia. The radio sources, most of which lie between declinations -30/sup 0/ and -35/sup 0/, were measured to an rms positional accuracy of approx.3 arcsec relative to a grid of previously identified radio sources. Optical identifications have been made on the basis of positional coincidence alone, without regard to color or morphology, using the UK Schmidt telescope deep IIIa-J sky survey plates. Identifications are suggested and accurate optical positions have been measured for 62 objects brighter than magnitude 22.5 on the IIIa-J plates.

Flat-spectrum radio sources from the Parkes 2.7 GHz survey—a study of a complete sample

We describe our complete sample, taken from the Parkes 2·7 GHz catalogue, of flat-spectrum radio sources with flux densities > 0·5 Jy. The sample covers all right ascensions and declinations from +10° to -45°, excluding the galactic plane (lhI < 10°) and contains 403 sources. Attention is drawn to the advantages of radio surveys over optical surveys. The survey is used to highlight some selection effects found in optical surveys. We also discuss how this sample can be used to give us information on the early universe

The Parkes-MIT-NRAO Radio Surveys

During 1990, the Parkes radio telescope made a new, deep survey of the southern sky at 4850 MHz (the PMN Survey: see e.g. Griffith and Wright, 1993; Wright et al., 1994). The declination coverage of the survey was from δ = −87° to +10°. The flux limit of the survey was around 30 mJy, although dependent on declination. This survey increased the number of known, southern radio sources by a factor of about 6 to over 65,000.

The Importance of Schmidt Astrometry for the Optical Identification of Sources detected in other Wavebands

The early optical identifications of radio sources were restricted to bright galaxies and to quasars with ultraviolet excesses, since such objects were rare and unlikely to land by chance within the large radio position error boxes. Other types of objects, such as very high redshift quasars and distant galaxies, were discriminated against because they did not look unusual and so were not readily recognised. Eventually much more accurate interferometric radio positions became available, enabling unambiguous identification of many optically faint objects. Now the internal accuracy of the radio positions can exceed that of the optical positions, requiring optical astrometry to be done to higher precision than ever before. A related problem is the correct registration of the two reference frames, which should be solved soon using a combination of data from the Hipparcos satellite and the Hubble Space Telescope. The digitised data now available from the Schmidt sky surveys make it possible to automate the optical identification of sources, such as those in the IRAS infrared and Rosat X-ray surveys. Very accurate digitised optical surveys are also needed to prepare lists of targets for multi-object spectroscopy using fibre optic systems.

Wild, Woolley and Savage—or how John Bolton and I went hunting for quasars and QSOs

This paper is about how I met John Bolton and includes some highlights of the four years I took compiling my Ph.D. at the Parkes Observatory. It is strongly linked to the discovery of quasars (quasi-stellar radio sources) and QSOs (quasi-stellar objects, not necessarily radio sources)-John being dedicated to discovering quasars and I to discovering QSOs. I hope my perception of John Bolton as a person comes through as it seems I was fortunate in meeting him at a time when, according to some, he had mellowed!

A Homogeneous Bright Quasar Survey

In undertaking a large shallow survey for quasars, we considered especially two issues: (I) On the one hand, the shape of the Luminosity Function and the determination of the form of evolution as L ∝ (1 + z) k or L ∝ e T/τ are uncertain. Trends of this form, potentially telling about the mechanism to fuel the central engine (in principle they can reveal if the QSO phenomenon is driven by the surrounding environment or is determined by its nuclear conditions only), can be spuriously favoured by fits that overlook the observational biases. To probe the real trend, not only the database at faint magnitudes and higher redshifts has to be enlarged, but also the incompleteness at bright magnitudes should be bound or removed with better samples allowing an adequately sophisticated analysis.

Unbiased Searches for Quasars Beyond a Redshift of 3.5

Nearly a decade elapsed between the discovery by Wampler at al. (1973) that the QSO OQ172 has a redshift of 3.53 and the discovery by Peterson et al. (1982) that the QSO Pks 2000–330 has a redshift of 3.78. During that time, radio and optical searches were vigorously pursued to find QSO’s with redshifts greater than 3.5, but none were found. In this paper, we discuss selection effects in optical and radio searches and show how these selection effects have limited the redshift range of previous surveys. We propose a combination of radio and optical techniques that may be used to find high redshift QSO’s and provide us with an undistorted view of the Universe beyond a redshift of 3.5.