G. Orban de Xivry

The role of secular evolution in the black hole growth of narrow-line Seyfert 1 galaxies

Narrow-line Seyfert 1 (NLS1) galaxies show extreme properties with respect to the other Seyfert galaxies. Indeed, they are thought to be accreting at Eddington rates and to possess low-mass black holes. Therefore, they may represent a key class of objects for understanding the co-evolution of black holes and their host galaxies. We propose that NLS1s represent a class of active galactic nucleus in which the black hole growth is, and has always been, dominated by secular evolution. First, by looking at the NLS1 host galaxy properties in the literature, we show that the evolution of NLS1s is presently driven by secular processes, much more so than for broad-line Seyfert 1s (BLS1s). Secondly, we study the bulges of NLS1 and BLS1 galaxies. Our results demonstrate that NLS1 host bulges are pseudo-bulges and are statistically different from BLS1 bulges. This difference points to the particular importance of secular processes in the past evolution of their hosts. We build on this result to understand the implications on their evolution and the duration of their duty cycle. We show that NLS1s are not necessarily in a special phase of black hole growth and that several Gyr are required for their black hole masses to become similar to BLS1s. Finally, in the light of our results, we discuss the location of NLS1 galaxies on the MBH–σ plane and speculate about the connection between the NLS1 galaxy properties and their black hole spin.

Physical properties of dense molecular gas in centres of Seyfert galaxies

We present new ∼1 arcsec resolution data of the dense molecular gas in the central 50–100 pc of four nearby Seyfert galaxies. Plateau de Bure Interferometer (PdBI) observations of HCN and, in two of the four sources, simultaneously HCO + allow us to carefully constrain the dynamical state of the dense gas surrounding the active galactic nuclei (AGN). The analysis of the kinematics shows large line widths of 100–200 km s −1 full width at half-maximum (FWHM) that can only partially arise from beam smearing of the velocity gradient. The observed morphological and kinematic parameters (dimensions, major axis position angle, red and blue channel separation, and integrated line width) are well reproduced by a thick disc, where the emitting dense gas has a large intrinsic dispersion (20–40 km s −1 ), implying that it exists at significant scale heights (25–30 per cent of the disc radius). To put the observed kinematics in the context of the starburst and AGN evolution, we estimate the Toomre Q parameter. We find this is always greater than the critical value, i.e. Q is above the limit such that the gas is stable against rapid star formation. This is supported by the lack of direct evidence, in these four Seyfert galaxies, for on-going star formation close around the AGN. Instead, any current star formation tends to be located in a circumnuclear ring. We conclude that the physical conditions are indeed not suited to star formation within the central ∼100 pc.

Insights on the Dusty Torus and Neutral Torus from Optical and X-Ray Obscuration in a Complete Volume Limited Hard X-Ray AGN Sample

We describe a complete volume limited sample of nearby active galaxies selected by their 14?195 keV luminosity, and outline its rationale for studying the mechanisms regulating gas inflow and outflow. We also describe a complementary sample of inactive galaxies, selected to match the host galaxy properties. The active sample appears to have no bias in terms of active galactic nucleus (AGN) type, the only difference being the neutral absorbing column, which is two orders of magnitude greater for the Seyfert 2s. In the luminosity range spanned by the sample, ?43.7, the optically obscured and X-ray absorbed fractions are 50%?65%. The similarity of these fractions to more distant spectroscopic AGN samples, although over a limited luminosity range, suggests that the torus does not strongly evolve with redshift. Our sample confirms that X-ray unabsorbed Seyfert 2s are rare, comprising not more than a few percent of the Seyfert 2 population. At higher luminosities, the optically obscured fraction decreases (as expected for the increasing dust sublimation radius), but the X-ray absorbed fraction changes little. We argue that the cold X-ray absorption in these Seyfert 1s can be accounted for by neutral gas in clouds that also contribute to the broad-line region (BLR) emission, and suggest that a geometrically thick neutral gas torus co-exists with the BLR and bridges the gap to the dusty torus.

Obscuration in active galactic nuclei: near-infrared luminosity relations and dust colors

We combine two approaches to isolate the AGN luminosity at near-IR wavelengths and relate the near-IR pure AGN luminosity to other tracers of the AGN. Using integral-field spectroscopic data of an archival sample of 51 local AGNs, we estimate the fraction of non-stellar light by comparing the nuclear equivalent width of the stellar 2.3 m CO absorption feature with the intrinsic value for each galaxy. We compare this fraction to that derived from a spectral decomposition of the integrated light in the central arcsecond and find them to be consistent with each other. Using our estimates of the near-IR AGN light, we find a strong correlation with presumably isotropic AGN tracers. We show that a significant o set exists between type 1 and type 2 sources in the sense that type 1 sources are 7 (10) times brighter in the near-IR at logL MIR = 42.5 (logL X = 42.5). These o sets only become clear when treating infrared type 1 sources as type 1 AGNs. All AGNs have very red near- to mid-IR dust colors. This, as well as the range of observed near-IR temperatures, can be explained with a simple model with only two free parameters: the obscuration to the hot dust and the ratio between the warm and hot dust areas. We find obscurations of A hot = 5::: 15 mag for infrared type 1 sources and A hot = 15::: 35 mag for type 2 sources. The ratio of hot dust to warm dust areas of about 1000 is nicely consistent with the ratio of radii of the respective regions as found by infrared interferometry.

Thick discs, and an outflow, of dense gas in the nuclei of nearby Seyfert galaxies

We discuss the dense molecular gas in central regions of nearby Seyfert galaxies, and report new arcsec resolution observations of HCN(1-0) and HCO

The path towards high-contrast imaging with the VLTI: the Hi-5 project

^+

Constraints on the broad-line region properties and extinction in local Seyferts

(1-0) for 3 objects. In NGC 3079 the lines show complex profiles as a result of self-absorption and saturated continuum absorption. H

Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758

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LLAMA : normal star formation efficiencies of molecular gas in the centres of luminous Seyfert galaxies

CN reveals the continuum absorption profile, with a peak close to the galaxys systemic velocity that traces disk rotation, and a second feature with a blue wing extending to

The role of host galaxy for the environmental dependence of active nuclei in local galaxies

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