REST-FRAME UV SINGLE-EPOCH BLACK HOLE MASS ESTIMATES OF LOW-LUMINOSITY AGNs AT INTERMEDIATE REDSHIFTS

Abstract

The ability to accurately derive black hole (BH) masses at progressively higher redshifts and over a wide range of continuum luminosities has become indispensable in the era of large-area extragalactic spectroscopic surveys. In this paper we present an extension of existing comparisons between restframe UV and optical virial BH mass estimators to intermediate redshifts and luminosities comparable to the local Hβ reverberation mapped active galactic nuclei (AGN). We focus on the MgII, CIV, and CIII] broad emission lines and compare them to both Hα and Hβ. We use newly acquired near-infrared spectra from the FMOS instrument on the Subaru telescope for 89 broad-lined AGN at redshifts between 0.3 and 3.5, complemented by data from the AGES survey. We employ two different prescriptions for measuring the emission line widths and compare the results. We confirm that MgII shows a tight correlation with Hα and Hβ, with a scatter of ∼ 0.25 dex. The CIV and CIII] estimators, while showing larger scatter, are viable virial mass estimators after accounting for a trend with the UV-to-optical luminosity ratio. We find an intrinsic scatter of ∼ 0.37 dex between Balmer and carbon virial estimators by combining our dataset with previous high redshift measurements. This updated comparison spans a total of 3 decades in BH mass. We calculate a virial factor for CIV/CIII] log f CIV/CIII] = 0.87 with an estimated systematic uncertainty of ∼ 0.4 dex and find excellent agreement between the local reverberation mapped AGN sample and our high-z sample.

An FMOS Survey of Moderate-luminosity, Broad-line AGNs in COSMOS, SXDS, and E-CDF-S

“…Our FMOS study is unique in that it robustly tests these relationships and the reliability of current calibrations of the virial method for an unprecedentedly large sample of moderate-luminosity AGN at high redshift, that is probing the bulk of the (unobscured) AGN population at the epoch of peak SMBH mass assembly. As shown in section 4.3, the empirical relationships in FWHM and luminosity between Hα, Hβ and Mg II hold for moderate-luminosity AGN at z 1, consistent with previous work based on smaller samples (M13 Karouzos et al 2015;Suh et al 2015). Furthermore, the virial M BH estimators presented in section 4.2 provide consistent results.…”

“…The scatter in the measured line properties originates in ambiguities in the line fit for low S/N data, including the contribution of a narrow component or the choice of parametric model for the broad component, e.g. number of Gaussian components (Denney et al 2009;Shen et al 2011;Karouzos et al 2015;Denney et al 2016). We note that for the vast majority of our sources the continuum S/N for at least one of the spectra is < 5.…”

The Infrared Medium-deep Survey. IV. The Low Eddington Ratio of A Faint Quasar at z ∼ 6: Not Every Supermassive Black Hole is Growing Fast in the Early Universe

“…C IV Line Measurement After subtracting the best-fit continuum model obtained from Section 3.1, we fitted the C IV emission line and measured its spectral properties. It is well-known that the C IV emission line of quasars often shows asymmetric line shapes that cannot be well modeled by a single Gaussian function (Shen et al 2011;Tang et al 2012;Runnoe et al 2013;Park et al 2013Park et al , 2017De Rosa et al 2014;Karouzos et al 2015;Coatman et al 2016). While this asymmetric line shape of C IV can be seen in high S/N spectra (S/N 10 for continuum), it is not discernible in the spectrum with low S/N of 10 (De Rosa et al 2014) like our case.…”

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

“…Our sample is too small to improve on the emission line correlations extensively studied by e.g. Shen & Liu (2012), Denney et al (2013), and Karouzos et al (2015); however, since such studies generally use power-law continuum models, it is desirable to have a better understanding of the true continuum, especially as this continuum forms the basis of many virial M BH estimators. In particular, the Balmer continuum lies underneath the Mg II feature, but due to additional contamination by Fe II, this can be difficult to deconvolve, particularly when considering only a limited wavelength range on either side of the Mg II lines.…”