ULTRALUMINOUS INFRARED GALAXIES AND THE RADIOOPTICAL CORRELATION FOR QUASARS

Through analysis of available optical spectrophotometric data and radi o flux density measurements in the literature, it is demonstrated that a good correlation exists between the radio power and bolometric lumi nosity of the optically-selected QSOs in the Bright Quasar Sample (BQS ) of Schmidt and Green (1983). This correlation, noted previously by o thers as a correlation with absolute B-magnitude, is shown to be robus t, and to be independent of a variety of assumptions used in the calcu lation of the bolometric luminosity. The correlation is present for th e entire BQS sample, but is improved when QSOs with high values of rad io-to-optical flux density (radio-loud) are excluded. Using this corre lation, radio measurements can therefore be used to predict the bolome tric luminosity of quasars even if their optical and UV continua are n ot directly observable. We have recently used VLBI meausurements of a sample of ultraluminous infrared galaxies to infer the likely existenc e of radio-quiet AGNs deeply enshrouded in dust within their nuclei (L onsdale, Smith, and Lonsdale 1993). We employ the radio-bolometric lum inosity correlation for the BQS quasars to test whether these hypothet ical buried AGNs can be energetically responsible for the observed far -infrared luminosities of the ultraluminous infrared galaxies. The ult raluminous infrared galaxies are shown to follow the same relation bet ween radio core power and bolometric luminosity as the radio-quiet QSO s, suggesting that buried AGNs can account for essentially all the obs erved infrared luminosity, and raising the possibility that any starbu rst which may be in progress may not be energetically dominant. The br oader implications of the radio-optical correlation in quasars for AGN s and luminous infrared galaxy models and the use of radio astronomy a s a probe of the central powerhouse in radio quiet AGNs and luminous i nfrared galaxies are briefly discussed.