Quasars from the 7C survey – I. Sample selection and radio maps |
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| Authors: | Julia M Riley Steve Rawlings Richard G McMahon Katherine M Blundell Philip Miller Mark Lacy Elizabeth M Waldram |
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| Institution: | Mullard Radio Astronomy Observatory, Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE; Astrophysics, Department of Physics, Keble Road, Oxford OX1 3RH Institute of Astronomy, Madingley Road, Cambridge CB3 0HA |
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| Abstract: | We describe the selection of candidate radio-loud quasars obtained by cross-matching radio source positions from the low-frequency (151-MHz) 7C survey with optical positions from five pairs of EO POSS-I plates scanned with the Cambridge Automatic Plate-measuring Machine (APM). The sky region studied is centred at RA 10h 28m, Dec.+41° and covers ≈0.057 sr. We present VLA observations of the quasar candidates, and tabulate various properties derived from the radio maps. We discuss the selection criteria of the resulting '7CQ' sample of radio-loud quasars. The 70 confirmed quasars, and some fraction of the 36 unconfirmed candidates, constitute a filtered sample with the following selection criteria: 151-MHz flux density S 151>100 mJy; POSS-I E -plate magnitude E ≈ R <20; POSS-I colour ( O E )<1.8; the effective area of the survey drops significantly below S 151≈200 mJy. We argue that the colour criterion excludes few if any quasars, but note, on the basis of recent work by Willott et al., that the E magnitude limit probably excludes more than 50 per cent of the radio-loud quasars. |
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| Keywords: | galaxies: active quasars: general radio continuum: galaxies |
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