The B3-VLA quasar sample

Astron. Astrophys. Suppl. Ser. The B3-VLA quasar sample? M. Vigotti G. Vettolani R. Merighi J.F. Lahulla M. Pedani Istituto di Radioastronomia del CNR Bologna Italy Osservatorio Astronomico di Bologna Italy A new low frequency radio selected Sample of 125 Quasars complete down to 100 mJy at 408 MHz is presented in this paper. The sample is a part of the B3-VLA sample: 1050 radiosources selected from the B3 catalogue at 408 MHz and observed at the VLA (1465 MHz, C and A con gurations). Out of the 352 sources, identi ed on the POSS-I down to mr 20:0, 172 are quasar candidates. In this paper we give the nal assessment of the quasar sample from spectroscopic observations of the candidates. The nal complete quasar sample consists of 125 objects. Furthermore 3 Bl Lac objects have been identi ed and two Bl Lac candidates. galaxies; active | quasars; general | radio continuum; general 1. Introduction Quasars were rst discovered through the optical identication of radio sources. Optical searches, based on different criteria from multicolor selection to grism searches, have produced a large number of optically selected quasar and have shown that radio loud quasars are really a fraction of the quasar population. However, optical multicolor searches have their own problems in completeness if, for instance, a large fraction of obscured quasars exists (Webster et al. 1995) . In principle radio quasars samples do not su er from a bias of this kind and, therefore, studying their color distribution, they should provide a direct test on the number of obscured quasars. In the last years, a renewed interest is also raising in radio samples selected at low frequency because they provide an e ective way to test the Uni ed Schemes (US) for Send o print requests to: M. Vigotti ? Tables 4, 5, 6 and Figs. 1, 2, 3, 4, 6 are also available in electronic form at the CDS via anonymous ftp to: cdsarc.ustrasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/ Abstract.html extragalactic radiosources (Barthel 1989) through, for instance, a direct comparison of the observed angular sizes of radiogalaxies and quasars in the same redshift range. Quasar samples selected at meter-wavelength are preferable with respect to high frequency selected samples because the source selection is largely based on their lobe emission. On the contrary flat spectrum sources, predominant in high frequency selected samples, are mostly core-dominated cases where the relativistic beaming might introduce serious selection e ects. Although US are generally accepted, some authors found observational evidences which cannot be explained by this scheme and that require a more complex treatment of the AGN phenomenon. Using 3CR, MQS, 1JY samples and an earlier version of the present B3−VLA quasar sample (see Singal 1993 and references therein) , Singal nds several discrepancies between the predictions of US and the observational data. For instance, the observed number of quasars versus total source number, namely the quasar fraction (fq) changes with the limiting flux of the sample. In the MQS sample, Kapahi et al. (1996) show that apparent sizes of radiogalaxies and quasars have almost an equal distribution at any redshift in contradiction with the US prediction. A similar result has been found by Blundell et al. (1996) , using 3CR, 5C, 6C and 8C samples. In a future paper, using all the available parameters of radiogalaxies and quasars of the B3−VLA sample (apparent diameters, flux, power, redshifts), we will verify the predictions of the US. In Sect. 2 we present the nal QSO sample based on spectroscopic observations reported in Vigotti et al. (1990) , Lahulla et al. (1991) and further observations of the remaining candidates described in Sect. 3 of the present paper. Section 4 contains comments on some individual sources, and nally Sect. 5 summarizes the present data. 2. The B3-VLA quasar sample placement greater than 20:05. A posteriori looking the Acon guration maps we understand why the distribution is 2.1. The radio sample not gaussian. In all the four cases the quasar was coinciThe B3 radiosource catalogue (Ficarra et al. 1985) , lists dent with the faint component of a double radiosource of 13354 sources brighter than 100 mJy at 408 MHz and 4 − 5 arcseconds diameter, and with a very high flux ratio covers 0.78 steradians in a sky strip from 37 to 47 , all between the two radio components. hour angles. Furthermore, we obtained CCD images with the 1.5 From the B3, down to the catalogue limit of 0.1 Jy, meters Loiano Telescope of Bologna Observatory or with Vigotti et al. (1989) selected ve complete subsamples 3.5 meters telescope at Calar Alto of all the identi ed separated by equal increments in logarithmic flux density objects with uncertain optical classi cation from plates in and containing approximately the same number of sources, the original sample, in order to be sure not to have missed through the choice of di erent decli (...truncated)