Relations between optical spectral parameters and the (far-)infrared continuum in Type~1 active galactic nuclei

Abstract

This study combines multi-wavelength continuum data with optical spectral properties for a far-infrared (FIR)-selected sample of Type 1 active galactic nuclei (AGNs) from AKARI data. We explore the relation between AGN physics and concomitant star formation processes using empirical correlations of optical and multiwavelength data. We measured spectral parameters including full widths at half maximum (FWHMs) and velocity shifts of broad and narrow optical emission lines, as well as continuum luminosities from GALEX FUV to AKARI 160 microns. The sample contains 88 AGNs observed at both optical and FIR wavelengths. About 50% are Seyfert 1s with both broad H$β$ and H$α$ lines; almost all remaining objects are S1.9s with only broad H$α$. The FWHMs of broad H$β$ and H$α$ are anti-correlated with luminosity in most bands. Shifts of narrow H$β$, H$α$, and [O III] 5007 lines and FWHM of [O III] 5007 correlate with optical and IR luminosities. Luminosities at 65 and 90 microns are more strongly connected with optical and other spectral properties than those at 140 and 160 microns. These trends extend the well-known Eigenvector 1 (EV1) correlations into the MIR and FIR domain. The anti-correlation between broad-line FWHMs and NIR and MIR luminosities is probably caused by the inclination of the torus and accretion disc: higher inclinations see less AGN radiation. However, most objects fall into Population A along the quasar EV1 main sequence, where narrower broad H$β$ profiles and FIR excess emission are commonly linked to higher Eddington ratios.