New insights on the QSO radio-loud/radio-quiet dichotomy: SDSS spectra in the context of the 4D eigenvector1 parameter space

Abstract

We search for a dichotomy/bimodality between radio-loud (RL) and radio-quiet (RQ) type 1 active galactic nuclei (AGN). We examine several samples of Slogan Digital Sky Survey (SDSS) quasi-stellar objects (QSOs) with high signal-to-noise ratio optical spectra and matching Faint Images of the Radio Sky at Twenty-cm/NRAO VLA Sky Survey (FIRST/NVSS) radio observations. We use the radio data to identify the weakest RL sources with a Fanaroff-Riley type II (FR II) structure to define a RL/RQ boundary which corresponds to log L 1.4 GHz = 31.6 erg s −1 Hz −1 . We measure the properties of broad-line Hβ and Fe II emission to define the optical plane of a 4DE1 spectroscopic diagnostic space. The RL quasars occupy a much more restricted domain in this optical plane compared to the RQ sources, which a 2D Kolmogorov-Smirnov test finds to be highly significant. This tells us that the range of broad-line region kinematics and structure for RL sources is more restricted than for the RQ QSOs, which supports the notion of dichotomy. FR II and CD RL sources also show significant 4DE1 domain differences that likely reflect differences in line-of-sight orientation (inclined versus face-on, respectively) for these two classes. The possibility of a distinct radio-intermediate (RI) population between RQ and RL source is disfavoured because a 4DE1 diagnostic space comparison shows no difference between RI and RQ sources. We show that searches for dichotomy in radio versus bolometric luminosity diagrams will yield ambiguous results mainly because in a reasonably complete sample, the radio brightest RQ sources will be numerous enough to blur the gap between RQ and RL sources. Within resolution constraints of NVSS and FIRST, we find no FR I sources among the broad-line quasar population.

Radio-faint AGN: a tale of two populations

“…Goldschmidt et al 1999), which artificially increases their fraction; b) RL AGN are on average more powerful than RQ ones in the optical band (e.g. Zamfir, Sulentic & Marziani 2008). When one reaches the very faint end of the optical LF only RQ AGN will be present and therefore the integrated, intrinsic RL fraction will be quite small.…”

Is MgIIλ2800 a reliable virial broadening estimator for quasars?

“…B1 ++ sources, however, constitute less than 3% of our sample. They are nonetheless relevant if for no other reason that bin B1 ++ shows the largest RL fraction in the 4DE1 sequence (Zamfir et al 2008 and Table 1). This is also the domain of some of the best known sources that show doublepeaked profiles (Eracleous & Halpern 2003), although most do not.…”

“…The radio morphology defines the classical RL phenomenon with the weakest FRII sources that provide an empirical lower limit for this activity. Compact sources were considered core-dominated (CD) RL if their rest frame specific emission was above the FRII lower limit, as in Zamfir et al (2008). This corresponds roughly to R K = 70 as defined in Kellermann et al (1989).…”

“…The majority of RL sources belong to Pop. B (Sulentic et al 2003;Zamfir et al 2008). Most radio-detected RQ sources show core-dominated (CD), sometimes core-jet morphology.…”

“…A-B formalism. Population A involves a largely radioquiet quasar population because few radio-loud quasars (especially with double-lobe Fanaroff-Riley II (FRII) radio morphology) show FWHM Hβ < 4000 km s −1 (Zamfir et al 2008). Those active galactic nuclei (AGN) with FWHM Hβ ≤ 2000 km s −1 are often referred to as narrow-line Seyfert 1 (NLSy1) sources but there is continuity in source properties over the full Pop.…”