A low-luminosity type-1 QSO sample; III. Optical spectroscopic properties and activity classification

TL;DR

This study analyzes optical spectra of 99 low-luminosity QSOs to understand their properties, activity types, and classifications, revealing diversity in emission features and potential differences due to observational effects.

Contribution

It provides a detailed optical spectroscopic characterization of a large sample of low-luminosity QSOs, highlighting their activity classifications and the impact of observational biases.

Findings

50% of sources with broad Hβ are radio-quiet

AGN/Seyfert activity detected in 50-60% of sources

Variability and aperture effects influence classification results

Abstract

We report on the optical spectroscopic analysis of a sample of 99 low-luminosity quasi-stellar objects (LLQSOs) at $z\leq 0.06$ base the Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility of studying the faint end of the QSO population at smaller cosmological distances and, therefore, in greater detail. A small number of our LLQSO present no broad component. Two sources show double broad components, whereas six comply with the classic NLS1 requirements. As expected in NLR of broad line AGNs, the [S{\sc{ii}}]$-$based electron density values range between 100 and 1000 N$_{e}$/cm$^{3}$. Using the optical characteristics of Populations A and B, we find that 50\% of our sources with H$\beta$ broad emission are consistent with the radio-quiet sources definition. The remaining sources could be interpreted as low-luminosity radio-loud quasar. The BPT-based classification renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources, the possible star burst contribution might control the LINER and HII classification. Finally, we discuss the aperture effect as responsible for the differences found between data sets, although variability in the BLR could play a significant role as well.