Isaac Shlosman

The agn-obscuring torus : The end of the doughnut paradigm?

Unified schemes of active galactic nuclei (AGNs) require an obscuring dusty torus around the central engine. The compact sizes (only a few parsecs) determined in recent high-resolution observations require that the obscuring matter be clumpy and located inside the region where the black hole gravity dominates over the galactic bulge. This location is in line with the scenario depicting the torus as the region of the clumpy wind coming off the accretion disk in which the clouds are dusty and optically thick. We study here the outflow scenario within the framework of hydromagnetic disk winds, incorporating the cloud properties determined from detailed modeling of the IR emission from clumpy tori. We find that torus clouds were likely detected in recent water maser observations of NGC 3079. In the wind scenario, the AGN main dynamic channel for release of accreted mass seems to be switching at low luminosities from torus outflow to radio jets. The torus disappears when the bolometric luminosity decreases below ~1042 ergs s-1 because the accretion onto the central black hole can no longer sustain the required cloud outflow rate. This disappearance seems to have been observed in both LINERs and radio galaxies. With further luminosity decrease, suppression of cloud outflow spreads radially inward from the disks dusty, molecular region into its atomic, ionized zone, resulting in the disappearance of the broad emission-line region at lower luminosities yet to be determined.

Evolution of Stellar Bars in Live Axisymmetric Halos: Recurrent Buckling and Secular Growth

Evolution of stellar bars in disk galaxies is accompanied by dynamical instabilities and secular changes. Following the vertical buckling instability, the bars are known to weaken dramatically and develop a pronounced boxy/peanut shape when observed edge-on. Using high-resolution N-body simulations of stellar disks embedded in live axisymmetric dark matter halos, we have investigated the long-term changes in the bar morphology, specifically the evolution of the bar size, its vertical structure, and the exchange of angular momentum. We find that following the initial buckling, the bar resumes its growth from deep inside the corotation radius and follows the ultraharmonic resonance thereafter. We also find that this secular bar growth triggers a spectacular secondary vertical buckling instability that leads to the appearance of characteristic boxy/peanut/X-shaped bulges. The secular bar growth is crucial for the recurrent buckling to develop. Furthermore, the secondary buckling is milder, persists over a substantial period of time, ~3 Gyr, and can have observational counterparts. Overall, the stellar bars show recurrent behavior in their properties and evolve by increasing their linear and vertical extents, both dynamically and secularly. We also demonstrate explicitly that the prolonged growth of the bar is mediated by continuous angular momentum transfer from the disk to the surrounding halo and that this angular momentum redistribution is resonant in nature: a large number of lower resonances trap disk and halo particles, and this trapping is robust, in broad agreement with the earlier results in the literature.

NESTED AND SINGLE BARS IN SEYFERT AND NON-SEYFERT GALAXIES

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert versus non-Seyfert galaxy sample of nearby galaxies with complete near-infrared or optical imaging sensitive to length scales ranging from tens of parsecs to tens of kiloparsecs. The presence of bars is deduced by —tting ellipses to isophotes in Hubble Space Telescope (HST ) H-band images up to 10A radius and in ground-based near-infrared and optical images outside the H-band images. This is a conservative approach that is likely to result in an underestimate of the true bar fraction. We —nd that a signi—cant fraction of the sample galaxies, 17% ^ 4%, have more than one bar, and that 28% ^ 5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For the nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, in both absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of disk resonances, speci—cally the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches eUectively from three-dimensional to two-dimensional. This conclusion is further strengthened by the observed distribution of the sizes of nuclear rings which are dynamically associated with the ILRs. While primary bar sizes are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we —nd that secondary bars diUer morphologically from single bars. Our matched Seyfert and non-Seyfert samples show a statistically signi—cant excess of bars among the Seyfert galaxies at practically all length scales. We con—rm our previous results that bars are more abundant in Seyfert hosts than in non-Seyfert galaxies and that Seyfert galaxies always show a preponderance of ii thick ˇˇ bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones. Overall, since star formation and dust extinction can be signi—cant even in the H band, the stellar dynamics of the central kiloparsec cannot always be revealed reliably by the use of near-infrared surface photometry alone. (%) (%)

A Subarcsecond Resolution Near-infrared Study of Seyfert and Normal Galaxies II. Morphology

We present a detailed study of the bar fraction in the CfA sample of Seyfert galaxies and in a carefully selected control sample of nonactive galaxies to investigate the relation between the presence of bars and of nuclear activity. To avoid the problems related to bar classification in the Third Reference Catalogue (RC3), e.g., subjectivity, low resolution, and contamination by dust, we have developed an objective bar classification method, which we conservatively apply to our new subarcsecond resolution near-infrared (NIR) imaging data set discussed in the first paper in this series. We are able to use stringent criteria based on radial profiles of ellipticity and major axis position angle to determine the presence of a bar and its axial ratio. Concentrating on noninteracting galaxies in our sample for which morphological information can be obtained, we find that Seyfert hosts are barred more often (79% ± 7.5%) than the nonactive galaxies in our control sample (59% ± 9%), a result which is at the ~2.5 σ significance level. The fraction of nonaxisymmetric hosts becomes even larger when interacting galaxies are taken into account. We discuss the implications of this result for the fueling of central activity by large-scale bars. This paper improves on previous work by means of imaging at higher spatial resolution and by the use of a set of stringent criteria for bar presence and confirms that the use of NIR is superior to optical imaging for detection of bars in disk galaxies.

Magnetic acceleration of broad emission-line clouds in active galactic nuclei

It is proposed that broad emission lines in active galactic nuclei are formed by dense clouds in a molecular, hydromagnetic wind accelerated radiatively and centrifugally away from an accretion disk orbiting a massive black hole. These clouds are supposed to be photoionized by the UV continuum produced in the innermost radii of the accretion disk where the radiation flux is sufficient to evaporate the dust grains, that is, at a radius ∼0.2L 1/2 ion,46 pc

Mass-transfer induced activity in galaxies

Part 1. Introduction Part 2. The inner parsec Part 3. The circumnuclear region Part 4. Gas dynamics and star formation in barred and normal galaxies Part 5. Nuclear gas and large-scale properties of AGN and starburst hosts Part 6. Host galaxy-AGN-nuclear starburst connection Part 7. Galaxy interactions and induced activity Part 8. Gas dynamics in ellipticals Part 9. AGN and starbursts at large redshifts Part 10. Summary Subject index Object index Author index.

The Central Kiloparsec of Starbursts and Active Galactic Nuclei: The La Palma Connection*

Original article can be found at :--http://www.journals.uchicago.edu/--Copyright The Astronomical Society of the Pacific

FLAT-CORED DARK MATTER IN CUSPY CLUSTERS OF GALAXIES

Sand and coworkers have measured the central density profile of cluster MS 213723 with gravitational lensing and velocity dispersion and removed the stellar contribution with a reasonable M/L. The resulting dark matter (DM) distribution within was fitted by a density cusp of with , in an apparent 1 b r ! 50 h kpc r b p 0.35 contradiction to the cold dark matter prediction of . The disagreement worsens if adiabatic compression of b ∼ 1 the DM by the infalling baryons is considered. Following El-Zant, Shlosman, & Hoffman, we argue that dynamical friction acting on galaxies moving within the DM background counters the effect of adiabatic compression by transfering their orbital energy to the DM, thus heating up and softening the cusp. Using N-body simulations we show that indeed the inner DM distribution flattens (with for a cluster like MS 2137 23) when the b ≈ 0.35 galaxies spiral inward. We find as a robust result that while the DM distribution becomes core-like, the overall mass distribution preserves its cuspy nature, in agreement with X-ray and lensing observations of clusters. Subject heading: dark matter — galaxies: clusters: general — galaxies: formation — galaxies: halos

Bar Evolution over the Last 8 Billion Years: A Constant Fraction of Strong Bars in the GEMS Survey

Original article can be found at: --http://www.journals.uchicago.edu/--Copyright The American Astronomical Society

Evolution of self-gravitating accretion disks in active galactic nuclei

The evolution of self-gravitating gaseous disks in active galactic nuclei on scales of about 10-1000 pc is investigated. Star formation is a plausible outcome of the Jeans instability operating in a disk which violates the criterion for local stability. Even a low efficiency of star formation would deplete the gaseous disk on a short time scale and create a flat stellar system. These systems can evolve (sphericalize) secularly by means of stellar encounters but this process appears to be too slow to be important. Such flattened stellar systems may be common in the circumnuclear regions of disk galaxies. Conventional viscosities are inefficient in building anew the accretion process even in a cosmological time. Strongly self-gravitating disks are unstable to global nonaxisymmetric modes, which can induce radial inflow of gas in a short dynamical time. The latter effect is studied in a separate paper. 56 refs.