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Register a new userA low-luminosity type-1 QSO sample - A morphological study of nearby AGN hosts
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Gerold Busch
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There is growing evidence that every galaxy with a considerable spheroidal component hosts a supermassive black hole (SMBH) at its center. Strong correlations between the SMBH and the spheroidal component suggest a physical connection through a coevolutionary scenario. For very massive galaxies a merger-driven scenario is preferred, resulting in elliptical galaxies. In the nearby universe, we find many disk galaxies, showing no signs of recent interaction. Alternative secular evolutionary scenarios for such galaxies involve internal triggers like bars and spiral arms or minor mergers. We analyze a sample of 99 nearby galaxies (0.02 < z < 0.06) from the Hamburg/ESO survey in order to get insight into structural and dynamical properties of the hosts to trace the origin of the bulge-SMBH correlation. In this work, we first collect images of sample members to get an impression of the morphological distribution in the sample. In a second step, we start to analyze sensitive, high resolution near-infrared images of 20 galaxies, performing aperture photometry and bulge-disk decomposition with the BUDDA code. We find an unexpected high fraction of barred galaxies and many other structural peculiarities.
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Recognizing the properties of the host galaxies of quasi-stellar objects (QSOs) is essential to understand the suspected coevolution of central supermassive black holes (BHs) and their host galaxies. We selected a subsample of the Hamburg/ESO survey for bright UV-excess QSOs, containing only the 99 nearest QSOs with redshift z<=0.06, that are close enough to allow detailed structural analysis. From this low-luminosity type-1 QSO sample, we observed 20 galaxies and performed aperture photometry and bulge-disk-bar-AGN-decomposition with BUDDA on near-infrared J, H, K band images. 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 2x10^9 M_sun to 2x10^11 M_sun. Black hole masses measured from single epoch spectroscopy range from 1x10^6 M_sun to 5x10^8 M_sun. In comparison to higher luminosity QSO samples, LLQSOs tend to have lower stellar and BH masses. Also, 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 further evidence that they can be pictured as a bridge between the local Seyfert population and luminous QSOs at higher redshift. Eleven low-luminosity QSOs 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 could be partially explained by bulges of active galaxies containing much younger stellar populations than bulges of inactive galaxies. Also, one could suspect that their BHs are undermassive. This might hint at the growth of the host spheroid to precede that of the BH.
We present near-infrared (NIR) $H+K$-band longslit spectra of eleven galaxies which are 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 ($zleq 0.06$) 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, since they show much stronger AGN activity compared to local objects but are still close enough for a detailed structural analysis. We fit hydrogen recombination, molecular hydrogen, and [FeII] lines after carefully subtracting the continuum emission. From the broad Pa$alpha$ components, we estimate black hole masses and enlarge the sample of LLQSOs that show a deviation from the $M_mathrm{BH}-L_mathrm{bulge}$ relations of inactive galaxies from 12 to 16 objects. All objects show emission from hot dust ($Tsim 1200,mathrm{K}$) as well as stellar contribution. However, the particular fractions vary a lot between the objects. More than half of the objects show H$_2$ emission lines that are indicating a large reservoir of molecular gas which 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 $M_mathrm{BH}-L_mathrm{bulge}$ relations of inactive galaxies may be a consequence of overluminous bulges.
Circumnuclear star formation and AGN feedback is believed to play a critical role in the context of galaxy evolution. The low-luminosity QSO (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 near-infrared H+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 BUDDA 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 rather caused by young stellar populations and not by an undermassive black hole.
We present ground-based high-spatial resolution mid-infrared (MIR) observations of 20 nearby low-luminosity AGN (LLAGN) with VLT/VISIR and the preliminary analysis of a new sample of 10 low-luminosity Seyferts observed with Gemini/Michelle. LLAGN are of great interest because these objects are the most common among active galaxies, especially in the nearby universe. Studying them in great detail makes it possible to investigate the AGN evolution over cosmic timescale. Indeed, many LLAGN likely represent the final stage of an AGNs lifetime. We show that even at low luminosities and accretion rates nuclear unresolved MIR emission is present in most objects. Compared to lower spatial resolution Spitzer/IRS spectra, the high-resolution MIR photometry exhibits significantly lower fluxes and different PAH emission feature properties in many cases. By using scaled Spitzer/IRS spectra of typical starburst galaxies, we show that the star formation contribution to the 12 micron emission is minor in the central parsecs of most LLAGN. Therefore, the observed MIR emission in the VISIR and Michelle data is most likely emitted by the AGN itself, which, for higher luminosity AGN, is interpreted as thermal emission from a dusty torus. Furthermore, the 12 micron emission of the LLAGN is strongly correlated with the absorption corrected 2-10 keV luminosity and the MIR--X-ray correlation found previously for AGN is extended to a range from 10^40 to 10^45 erg/s. This correlation is independent of the object type, and in particular the low-luminosity Seyferts observed with Michelle fall exactly on the power-law fit valid for brighter AGN. In addition, no dependency of the MIR--X-ray ratio on the accretion rate is found. These results are consistent with the unification model being applicable even in the probed low-luminosity regime.
We analyse a sample of 69 QSOs which have been randomly selected in a complete sample of 104 QSOs (R<18, 0.142 < z < 0.198). 60 have been observed with the NTT/SUSI2 at La Silla, through two filters in the optical band (WB#655 and V#812), and the remaining 9 are taken from archive databases. The filter V#812 contains the redshifted Hbeta and forbidden [OIII] emission lines, while WB#655 covers a spectral region devoid of emission lines, thus measuring the QSO and stellar continua. The contributions of the QSO and the host are separated thanks to the MCS deconvolution algorithm, allowing a morphological classification of the host, and the computation of several parameters such as the host and nucleus absolute V-magnitude, distance between the luminosity center of the host and the QSO, and colour of the host and nucleus. We define a new asymmetry coefficient, independent of any galaxy models and well suited for QSO host studies. The main results from this study are: (i) 25% of the total number of QSO hosts are spirals, 51% are ellipticals and 60% show signs of interaction; (ii) Highly asymmetric systems tend to have a higher gas ionization level (iii) Elliptical hosts contain a substantial amount of ionized gas, and some show off-nuclear activity. These results agree with hierarchical models merger driven evolution.
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