F. Lafranca et al., DEEP VLA OBSERVATIONS OF AN OPTICALLY SELECTED SAMPLE OF INTERMEDIATEREDSHIFT QSOS AND THE OPTICAL LUMINOSITY FUNCTION OF THE RADIO-LOUD QSOS, The Astronomical journal, 108(5), 1994, pp. 1548-1556
We present deep VLA observations of a complete sample of 23 optically
selected QSOs with B <19.4 at intermediate redshift (0.8<z<3.4). The o
bservations were carried out at 5 and 1.4 GHz in the C array configura
tion. 4 of our 23 QSOs were detected (2 radio loud and 2 radio quiet),
confirming the decrease of the radio loud (alpha(10)>0.19) fraction o
f QSOs with increasing redshift. Stronger constraints are obtained for
the radio luminosity of the radio quiet population at 2<z<3 with L(5)
(GHz)<10(24.2) W HZ(-1). Combining our observations with other existi
ng radio data on optically selected samples (a total of 357 QSOs), we
derive the evolutionary functional form of the optical luminosity func
tion of the radio loud QSOs in the redshift range 0<z<2.9. The data ar
e consistent with a radio loud optical luminosity function having lowe
r densities but a similar shape with respect to the total (radio quiet
plus radio loud) population, i.e., Phi(L)proportional to gamma LY wit
h -3.5>gamma>-4.1 at bright luminosities, and -1.7>gamma>-2.4 at faint
luminosities. The evolution is slower (2.7<k<3.1), and the ''break ma
gnitude'' is brighter (-24>M(B)>-25 at z=0) than in the parent total
optical luminosity function. It results that the differential evolutio
n between the radio loud and radio quiet QSOs population could account
for the recent claims of a steepening with redshift of the total QSO
luminosity function.