DISCOVERY OF A LUMINOUS QUASAR IN THE NEARBY UNIVERSE

In the course of the Pico dos Dias survey (PDS), we identified the ste llar-like object PDS 456 at coordinates alpha = 17(h)28(m)19(s).796, d elta = -14 degrees 15'55.'' 87 (epoch 2000), with a relatively nearby (z = 0.184) and bright (B = 14.69) quasar. Its position at Galactic co ordinates I = 10.4 degrees, b = +11.2 degrees, near the bulge of the G alaxy, may explain why it was not detected before. The optical spectru m of PDS 456 is typical of a luminous quasar, showing a broad (FWHM si milar to 4000 km s(-1)) H beta line, very intense Fe II lines, and a w eak [O III] lambda 5007 line. PDS 456 is associated to the infrared so urce IRAS 17254-1413 with a 60 mu m infrared luminosity L-60 = 3.8 x 1 0(45) ergs s(-1). The relatively flat slopes in the infrared [alpha(25 , 60) = -0.33 and alpha(12, 25) = -0.78] and a flat power index in the optical (F(nu)proportional to nu(-0.72)) may indicate a low dust cont ent. A good match between the position of PDS 456 and the position of the X-ray source RXS J172819.3-141600 implies an X-ray luminosity L-X = 2.8 x 10(44) ergs s(-1). The good correlation between the strength o f the emission lines in the optical and the X-ray luminosity, as well as the steep optical to X-ray index estimated (alpha(OX) = -1.64), sug gests that PDS 456 is radio quiet. A radio survey previously performed in this region yields an upper limit for radio power at about 5 GHz o f approximately 2.6 x 10(30) ergs(-1) Hz(-1). We estimate the Galactic reddening in this line of sight to be A(B) similar or equal to 2.0, i mplying an absolute magnitude M-B = -26.7 (using H-0 = 75 km s(-1) Mpc (-1) and q(0) = 0). In the optical, PDS 456 is therefore 1.3 times mor e luminous than 3C 273 and the most luminous quasar in the nearby (z l ess than or equal to 0.3) universe.