Highly accreting quasars: The SDSS low-redshift catalog

Abstract

Context. The most highly accreting quasars are of special interest in studies of the physics of active galactic nuclei (AGNs) and host galaxy evolution. Quasars accreting at high rates (L/L Edd ∼ 1) hold promise for use as 'standard candles': distance indicators detectable at very high redshift. However, their observational properties are still largely unknown. Aims. We seek to identify a significant number of extreme accretors. A large sample can clarify the main properties of quasars radiating near L/L Edd ∼ 1 (in this paper they are designated as extreme Population A quasars or simply as extreme accretors) in the Hβ spectral range for redshift 0.8. Methods. We use selection criteria derived from four-dimensional Eigenvector 1 (4DE1) studies to identify and analyze spectra for a sample of 334 candidate sources identified from the SDSS DR7 database. The source spectra were chosen to show a ratio R FeII between the FeII emission blend at λ4570 and Hβ, R FeII > 1. Composite spectra were analyzed for systematic trends as a function of Feii strength, line width, and [Oiii] strength. We introduced tighter constraints on the signal-to-noise ratio (S/N) and R FeII values that allowed us to isolate sources most likely to be extreme accretors. Results. We provide a database of detailed measurements. Analysis of the data allows us to confirm that Hβ shows a Lorentzian function with a full width at half maximum (FWHM) of Hβ ≤ 4000 km s −1 . We find no evidence for a discontinuity at 2000 km s −1 in the 4DE1, which could mean that the sources below this FWHM value do not belong to a different AGN class. Systematic [Oiii] blue shifts, as well as a blueshifted component in Hβ are revealed. We interpret the blueshifts as related to the signature of outflowing gas from the quasar central engine. The FWHM of Hβ is still affected by the blueshifted emission; however, the effect is non-negligible if the FWHM Hβ is used as a "virial broadening estimator" (VBE). We emphasize a strong effect of the viewing angle on Hβ broadening, deriving a correction for those sources that shows major disagreement between virial and concordance cosmology luminosity values. Conclusions. The relatively large scatter between concordance cosmology and virial luminosity estimates can be reduced (by an order of magnitude) if a correction for orientation effects is included in the FWHM Hβ value; outflow and sample definition yield relatively minor effects.

Unveiling the monster heart: unbeamed properties of blazar 4C 71.07

“…A similar effect was found in quasars at both low and high redshifts (e.g. Negrete et al 2018;Vietri et al 2018). However, as far as we know, this is the first time that the correlation is found for a blazar.…”

Extreme Quasars as Distance Indicators in Cosmology

“…An elementary error budget suggests that the main uncertainty is associated with FWHM measurement errors and with uncertainty in the structure factor (Marziani and Sulentic, 2014a;Negrete et al, 2018). The broad profile of both LILs and HILs in each quasar spectrum can be modeled by considering two main components, the Hβ BC and the blueshifted component BLUE ( §2).…”

“…Vetting the sample on strongest FeII and weakest [OIII]λλ4959,5007 emitters reduces the scatter but only slightly . Negrete et al (2018) have convincingly shown that orientation effects are at the origin of a large fraction of the scatter if lines are emitted in a flattened system (κ 0.2). The difference between virial and concordance luminosity estimates can be zeroed if the structure factor is assumed to be dependent on angle θ in the form given by Eq.…”

“…The resulting distribution of θ values ranges from 0 to 50 with a peak around θ ≈ 18. The range of viewing angles in the sample of Negrete et al (2018) is actually modest. The effect of anisotropy from a geometrically and optically thick disk on the SED is not extremely strong within θ 30, approximately around 0.2 dex, following the models of anisotropic emission of Wang et al (2014c).…”

“…Hβ BC profiles whose FWHM has been corrected for the effect of BLUE via a multi-component fit, as described in Negrete et al (2018). The Hβ BLUE affects however the Hβ FWHM only at ≈ 10% level, with an effect that should be 0.3 dex.…”