A low-luminosity type-1 QSO sample

V. Overluminous host spheroids and their excitation mechanisms ^⋆,⋆⋆

¹ I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: busch@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ LERMA, Observatoire de Paris, PSL, CNRS, Sorbonne Universités, UPMC, 75014 Paris, France
⁴ Niedersächsische Staats- und Universitätsbibliothek Göttingen, 37070 Göttingen, Germany
⁵ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Königswinterer Str. 522-524, 53227 Bonn, Germany

Received: 15 June 2015
Accepted: 29 October 2015

Abstract

We present near-infrared (NIR) H + K-band long-slit spectra of eleven galaxies that were obtained with SOFI at the NTT (ESO). The galaxies are chosen from the low-luminosity type-1 quasi-stellar object (LLQSO) sample, which comprises the 99 closest (z ≤ 0.06) QSOs from the Hamburg/ESO survey for bright UV-excess QSOs. These objects are ideal targets to study the gap between local Seyfert galaxies and high-redshift quasars because they show much stronger AGN activity than local objects, but are still close enough for a detailed structural analysis. We fit hydrogen recombination, molecular hydrogen, and [Fe ii] lines after carefully subtracting the continuum emission. From the broad Paα components, we estimated black hole masses and enlarged the sample of LLQSOs that deviate from the M_BH − L_bulge relations of inactive galaxies from 12 to 16 objects. All objects show emission from hot dust (T ~ 1200 K) as well as stellar contribution. However, the respective fractions vary strongly among the objects. More than half of the objects show H₂ emission lines, which indicate a large reservoir of molecular gas that is needed to feed the AGN and star formation. In the NIR diagnostic diagram all objects lie in the location of AGN-dominated objects. However, most of the objects show indications of star formation activity, suggesting that their offset location with respect to M_BH–L_bulge relations of inactive galaxies may be a consequence of overluminous bulges.