Aims. This paper addresses the global molecular gas properties of a representative sample of galaxies hosting low-luminosity quasistellar objects. An abundant supply of gas is necessary to fuel both the active galactic nucleus and any circum-nuclear starburst activity of QSOs. The connection between ultraluminous infrared galaxies and the host properties of QSOs is still subject to a controversial debate. Nearby low-luminosity QSOs are ideally suited to study the properties of their host galaxies because of their higher frequency of occurrence compared to high-luminosity QSOs in the same comoving volume and because of their small cosmological distance. Methods. We selected a sample of nearby low-luminosity QSO host galaxies that is free of infrared excess biases. All objects are drawn from the Hamburg-ESO survey for bright UV-excess QSOs, have δ > −30• and redshifts that do not exceed z = 0.06. The IRAM 30 m telescope was used to measure the 12 CO(1−0) and 12 CO(2−1) transition in parallel. Results. 27 out of 39 galaxies in the sample have been detected. The molecular gas masses of the detected sources range from 0.4 × 10 9 M to 9.7 × 10 9 M . The upper limits of the non-detected sources correspond to molecular gas masses between 0.3 × 10 9 M and 1.2 × 10 9 M . We can confirm that the majority of galaxies hosting low-luminosity QSOs are rich in molecular gas. The properties of galaxies hosting brighter type I AGN and circumnuclear starformation regions differ from the properties of galaxies with fainter central regions. The overall supply of molecular gas and the spread of the line width distribution is larger. When comparing the farinfrared with the CO luminosities, the distribution can be separated into two different power-laws: one describing the lower activity Seyfert I population and the second describing the luminous QSO population. The separation in the L FIR /L CO behavior may be explainable with differing degrees of compactness of the emission regions. We provide a simple model to describe the two power-laws. The sample studied in this paper is located in a transition region between the two populations.

The galaxy SDSSJ095209.56+214313.3 (SDSSJ0952+2143 hereafter) showed remarkable emission-line and continuum properties and strong emission-line variability first reported in 2008 (Paper I). The spectral properties and low-energy variability are the consequence of a powerful high-energy flare which was itself not observed directly. Here we report follow-up optical, near-infrared (NIR), mid-infrared (MIR), and X-ray observations of SDSSJ0952+2143. We discuss outburst scenarios in terms of stellar tidal disruption by a supermassive black hole, peculiar variability of an active galactic nucleus (AGN), and a supernova (SN) explosion, and possible links between these scenarios and mechanisms. The optical spectrum of SDSSJ0952+2143 exhibits several peculiarities: an exceptionally high ratio of [Fe vii] transitions over [O iii], a dramatic decrease by a factor of 10 of the highestionization coronal lines, a very unusual and variable Balmer line profile including a triple-peaked narrow component with two unresolved horns, and a large Balmer decrement. The MIR emission measured with the Spitzer IRS in the narrow 10-20 μm band is extraordinarily luminous and amounts to L 10−20 μm = 3.5 × 10 43 erg s −1 . The IRS spectrum shows a bump around ∼11 μm and an increase toward longer wavelengths, reminiscent of silicate emission. The strong MIR excess over the NIR implies the dominance of relatively cold dust. The pre-and postflare NIR host galaxy colors indicate a nonactive galaxy. The X-ray luminosity of L x,0.1−10 keV = 10 41 erg s −1 measured with Chandra is below that typically observed in AGNs. Similarities of SDSSJ0952+2143 with some extreme SNe suggest the explosion of a SN of Type IIn. However, an extreme accretion event in a low-luminosity AGN or inactive galaxy, especially stellar tidal disruption, remain possibilities, which could potentially produce a very similar emission-line response. If indeed a SN, SDSSJ0952+2143 is one of the most distant X-ray-and MIR-detected SNe known so far, the most MIR luminous, and one of the most X-ray luminous. It is also by far the most luminous (> 10 40 erg s −1 ) in high-ionization coronal lines, exceeding previous SNe by at least a factor of 100.

Recognizing the properties of the host galaxies of quasi-stellar objects (QSOs) is essential for understanding the suspected coevolution of central supermassive black holes (BHs) and their host galaxies. Low-luminosity type-1 QSOs (LLQSOs) are ideal targets because of their small cosmological distance, which allows for a detailed structural analysis. We selected a subsample of the Hamburg/ESO survey for bright UV-excess QSOs that contains only the 99 nearest QSOs with redshift z ≤ 0.06. From this LLQSO sample, we observed 20 galaxies and performed aperture photometry and bulge-disk-decomposition with BUDDA on near-infrared J-, H-, and K-band images to separate disk, bulge, bar, and nuclear component. From the photometric decomposition of these 20 objects and visual inspection of images of another 26, we find that ∼50% of the hosts are disk galaxies and most of them (86%) are barred. Stellar masses, calculated from parametric models based on inactive galaxy colors, range from 2 × 10 9 M to 2 × 10 11 M with an average mass of 7 × 10 10 M . Black hole masses measured from single-epoch spectroscopy range from 1 × 10 6 M to 5 × 10 8 M with a median mass of 3 × 10 7 M . In comparison with higher-luminosity QSO samples, LLQSOs tend to have lower stellar and BH masses. Moreover, in the effective radius vs. mean surface-brightness projection of the fundamental plane, they lie in the transition area between luminous QSOs and normal galaxies. This can be seen as additional evidence that they populate a region intermediate between the local Seyfert population and luminous QSOs at higher redshift. This region has not been well studied so far. Eleven LLQSOs, for which we have reliable morphological decompositions and BH mass estimations, lie below the published BH mass vs. bulge luminosity relations for inactive galaxies. This can partially be explained if one assumes that the bulges of active galaxies contain much younger stellar populations than the bulges of inactive galaxies. Another possibility would be that their BHs are undermassive. This might indicate that the growth of the host spheroid precedes that of the BH.

We present near infrared ISAAC VLT observations of nine nearby (0.01 ≤ z ≤ 0.06) Active Galactic Nuclei selected from the Hamburg/ESO Survey and the Véron-Cetty & Véron catalog. Hydrogen recombination lines Paα and Brγ are observed in seven of the nine sources of which five show a broad component. In three sources, extended 1-0S(1) rotational-vibrational molecular hydrogen emission is detected. Stellar CO absorption is seen in four sources. In one of these objects, an upper limit of the central mass can be determined from the stellar velocity field. H-and Ks-band imaging allow us to determine the morphology class of the host galaxies. Colors (with supplementary J-band 2MASS images) show that the four galaxies with detected CO absorption are characterized by an overall strong stellar contribution. One galaxy shows an increased extinction towards the nucleus. After removal of the nuclear point source, the host galaxies show colors typical for non-active spiral galaxies.

Circumnuclear star formation and active galactic nucleus (AGN) feedback is believed to play a critical role in galaxy evolution. The low-luminosity quasi-stellar object (LLQSO) sample that contains 99 of the closest AGN with redshift z ≤ 0.06 fills the gap between the local AGN population and high-redshift QSOs that is essential to understand the AGN evolution with redshift. In this paper, we present the results of the near-infrared H-and K-integral field spectroscopy of the inner kiloparsecs of the LLQSO HE 1029-1831 with SINFONI. Line maps show that ionized hydrogen gas is located in spiral arms within the stellar bar and in a circumnuclear ring. Line fluxes and diagnostic line ratios indicate recent or ongoing star formation in the circumnuclear region and the presence of young and intermediate-age stellar populations in the bulge. In particular, we find traces of an intense starburst in the circumnuclear region that has begun around 100 Myr ago but has declined to a fraction of the maximum intensity now. We estimate the dynamical bulge mass and find that the galaxy follows published M BH −M bulge relations. However, bulge-disk decomposition of the K-band image with B reveals that HE 1029-1831 does not follow the M BH −L bulge relations of inactive galaxies. We conclude that the deviation from M BH −L bulge relations of inactive galaxies in this source is instead caused by young stellar populations and not by an undermassive black hole.