Hydrodynamical evolution of AGN driven by radiation from circumnuclear starbursts

We explore the hydrodynamical evolution of dusty gas around active galactic nuclei (AGN) driven by the radiation from circumnuclear starbursts. For this purpose, we calculate the temporal equilibrium states between the radiation force by starburst regions and the gravity in galactic nuclei. As a result, we find that the equilibrium patterns between the radiation force and the gravity are roughly characterized by three types. The first is the situation where the starburst luminosity is larger than the Eddington luminosity. In this case, the dusty gas is blown out like a wind. We may detect intense infrared (IR) radiation from the starburst regions screened by blown-out dusty gas. The second is the situation when the radiation force is comparable to the gravity. In this case, the equilibrium surface surrounds the nuclear regions as well as starburst regions. Since the dusty gas absorbs UV or soft X-rays from the center and re-emits IR radiation, we may recognize it as a Seyfert 2 galaxy. The last is the situation where the starburst luminosity is small. In this case, the dusty wall of equilibrium would be built up only in the vicinity of starburst regions. The radiation from central regions is rarely obscured, because the dusty regions have only small angular extension. So, it would look like a Seyfert 1 galaxy which is characterized by intense soft X-rays. When we consider the stellar evolution in starburst regions, the starburst luminosity decreases with time. Therefore, we can recognize the above three types as time evolution; a starburst galaxy (first stage), a Seyfert 2 galaxy (second stage), and a Seyfert 1 galaxy (third stage). Note that we present here an alternative scenario for explaining the relation between Sy 1's and Sy 2's to the standard “Unified Scheme”.     

High energy emission from AGN

The recent detection of radio loud quasars with a large high energy γ-ray luminosity is discussed, in the framework of non-thermal synchrotron self Compton models. These observations are strong evidence of relativistic beaming of the radiation, due to the absence of strong photon-photon opacity. If γ-rays are self Compton emission, these sources can be the first observed example of a Compton catastrophe, resulting from the dominance of the radiation over the magnetic energy density. Inhomogeneous and relativistic jet models can in this case explain the observed spectrum from the far infrared to the γ-rays. If, on the other hand, the magnetic energy density is dominant, then the γ-rays must be due to direct synchrotron emission, implying very large particle energies. Pure synchrotron models which take into account electron-positron pair production are then discussed. Multifrequency simultaneous observations are a powerful test of the models.     

Star formation and AGN fuelling

We present new observational data that tackle the issues of the star formation in Seyfert galaxies, the obscuration and fuelling mechanisms of active galactic nuclei, and the connection between these phenomena. New ISOCAM mid-IR images of nearby Seyfert 2 galaxies confirm that these systems are characterized by enhanced star forming activity. In barred systems the star forming activity occurs preferentially along the bar, indicating that these bars have formed recently and are still in the process of transporting gas towards the center. New X-ray data indicate that the gaseous column density absorbing Sy2 nuclei is a function of the bar strength, therefore indicating that stellar bars play an important role in obscuring AGNs. We speculate that non-axisymmetric disturbances (interaction/bars) both enhance the star forming activity in host galaxy and drive gas into the nuclear region to obscure the AGN, thus making the observed starburst-Sy2 connection. On smaller scales (10–100 pc), we report the discovery of a nuclear gaseous bar in the nearby Sy2 Circinus galaxy. The molecular gas kinematics indicates that this bar causes the gas to flow into the nuclear 10 pc. In the nuclear 10 pc we detect a young nuclear stellar cluster. We show that the post-main-sequence mass loss of this young nuclear stellar population could account for the fuelling of the active nucleus.     

Obscured AGN and the X-ray background

There is growing evidence that the hard X-ray background (XRB) can be explained by a large population of obscured AGN. I review some of the results of recent deep X-ray surveys, and in particular I discuss the nature of the X-ray luminous emission-line galaxies which have emerged at the faintest X-ray fluxes. If obscured AGN do explain the XRB, a direct implication is that the majority of the energy produced by accretion in the universe is absorbed and not emitted directly. Deep submillimetre surveys with SCUBA have recently attracted a lot of attention, with the potential to allow us an unobscured view dust-enshrouded starformation at high redshift. It has generally been assumed that these sources are purely high redshift starforming galaxies, but if models for the XRB are correct then a significant fraction (∼20%) could contain a luminous AGN.     

BBXRT and Ginga observations of AGN

The X-ray properties of Active Galactic Nuclei (AGN) support recent theories which unify the Seyfert 1 nuclei with the Seyfert 2's and radio-quiet quasars. In these objects the underlying spectrum is strongly distorted by the effects of reflection from the accretion flow and by absorption in partially ionised material. These obscure any intrinsic changes in the spectrum, making it difficult (though not impossible) to constrain the nature of the emission process. Conversely, there is no evidence for either of these spectral distortions in the radio-loud AGN, supporting the hypothesis that the X-rays are dominated by beamed emission from the relativistic jet.     

Simultaneous COMPTON GRO and optical monitoring of AGN

During two 14-day periods in January 1992 and March 1992, several AGN which have been in the wide field of view of COMPTEL and EGRET at that time were monitored optically for variations in intensity and polarization. We report on first results of this correlated optical and CGRO observations.     

Ultraluminous infrared galaxies: Starburst vs. AGN

We have obtained ISOPHOT-S low resolution mid-infrared spectra of a sample of 60 Ultraluminous Infrared Galaxies (ULIRGs). We use the strength of the ‘PAH’ mid-infrared features as a discriminator between starburst and AGN activity, and to probe for evolutionary effects. Observed ratios of PAH features in ULIRGs differ slightly from those in lower luminosity starbursts. We suggest that such PAH ratio changes relate to the conditions in the interstellar medium in these galaxies, and in particular to extinction.     

The AGN/normal galaxy connection: Summary

The connection between normal and active galaxies is reviewed, by summarizing our progress on answering nine key questions. (1) Do all galaxies contain massive dark objects (MDOs)? (2) Are these MDOs actually supermassive black holes? (3) Why are the dark objects so dark? (4) Do all galaxies contain an Active Galactic Nucleus (AGN)? (5) Are the “dwarf AGN” really AGN? (6) Does AGN activity correlate with host galaxy properties? (7) How are AGN fuelled? (8) Is AGN activity related to starburst activity? (9) How do quasars relate to galaxy formation?     

MLR events and associated triggered emissions observed by DEMETER

This paper gives an overview of different sets of new Magnetospheric Line Radiation (MLR) observed by the satellite DEMETER. Different types of emissions have been observed: emissions called Power Line Harmonic Radiation (PLHR) with frequency lines exactly separated by 50/100 or 60/120 Hz, emissions with frequency lines not exactly separated by 50/100 or 60/120 Hz and drifting in frequency (MLR). By comparison with past observations one can say that some MLR events are due to man-made PLHR which may suffer a non-linear gyro-resonant interaction at the magnetic equator. It is also shown that periodic emissions are very often associated with the MLR. In this case the origin of these waves is natural. The lines are produced by the periodicity and the frequency band limits of the individual elements which causes the appearance of lines on the spectrograms. Finally the paper shows that MLR can trigger emissions.     

Catalogue of ionized emission line spectra in obscured AGN

High-energy, high-resolution in the spatial and energy domains is crucial to derive the geometrical distribution and the physical properties of gas and dust surrounding Active Galactic Nuclei (AGN). These are, in turn, basic ingredients of any serious attempt to build an AGN structure model. We present in this paper CIELO-AGN, the first catalogue of ionized emission lines detected in the soft X-ray spectra of a sample of 69 nearby obscured AGN. This catalogue has been implemented according to an IVOA data model, and can be accessed through VO-compatible applications.     

Interstellar scintillation,ISS, and intrinsic variability of radio AGN

We investigate the relationship between the 5 GHz interstellar scintillation (ISS) and the 15 GHz intrinsic variability of the compact, radio-selected active galactic nuclei (AGN) common to the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory blazar flux density monitoring program. As part of this investigation, we also re-examine the reported intrinsic nature of the February 1990 VLA observations of the blazar S5 0716+714. We are also examining the presence of IDV/ISS in the Owens Valley 15 GHz flux density monitoring data. We find a significant relationship between the Owens Valley 15 GHz modulation index and the MASIV modulation index. We also discuss the implications of these findings for RadioAstron.     

Polarization VLBI observations of AGN jets now and into the future

The history of Very Long Baseline Interferometry (VLBI) observations has been characterized predominantly by an ongoing quest for increasingly high resolution and sensitivity. VLBI monitoring of relatively large samples of Active Galactic Nuclei (AGNs) with uniform quality and linear polarization sensitivity are now available at the moderately high frequencies of 15 and 43 GHz. This has enabled considerable advances in our understanding of the relativistic jets of AGNs, but gaps in the available observational material remain, which must be addressed in future VLBI polarization observations. Linear polarization observations at frequencies above 43 GHz remain non-routine, and the availability of multi-frequency and circular polarization measurements is still limited. It is of interest both to push inward toward the jet base and to study details of the jets themselves on parsec scales, such as magnetic field structures along and across the jets, which are intrinsically related to their formation, launching and propagation. Requirements for future VLBI polarization observations are considered, highlighting the key role that can be played by space VLBI observations. Unique opportunities are offered by relatively low-frequency space VLBI observations that are sensitive to effects such as Faraday rotation, opacity, and low-frequency absorption.     

A study of a complete soft X-ray selected sample of AGN

We present preliminary results from analyses of hard X-ray and optical observations of a soft X-ray selected sample. We created a small but complete sample with 20 of the softest and brightest objects with low Galactic absorption from the ROSAT bright soft X-ray selected radio-quiet AGN sample. This sample consists of 10 narrow-line Seyfert 1 galaxies and 10 broad-line Seyfert galaxies. We analyze ASCA data in the 0.6–10 keV band and optical spectra from ground-based telescopes. We investigate the photon indices in the hard X-ray band, soft excesses in the ASCA band, and optical emission line properties. The photon indices in the 2–10 keV band are nominal for both narrow-line Seyfert 1 galaxies and broad-line Seyfert 1 galaxies in each class compared with other heterogeneous samples. All of the narrow-line Seyfert 1 galaxies show soft excesses, but this component seems to be less significant for broad-line Seyfert 1 galaxies. There seems to be a trend of steeper X-ray spectra to be accompanied by narrower Hβ for narrow-line Seyfert 1 galaxies, but this is not extended to the larger velocity width regime of broad-line Seyfert 1 galaxies, and no clear trend is seen among them.     

High-density and high-temperature molecular gas around the AGN in M51

We investigated the physical properties of molecular gas in the nuclear region of M51 (Seyfert 2). We obtained an aperture synthesis ¹³CO(J = 1 − 0) image using the Nobeyama Millimeter Array (NMA), and compared it with NMA ¹²CO(J = 1 − 0) and HCN(J = 1 − 0) maps at similar spatial resolutions. Within a radius of 180 pc from the center, the ¹³CO(1 − 0) integrated intensity was found to be 3 times weaker than that of HCN(1 − 0). Large-Velocity-Gradient (LVG) calculations suggest that the observed high HCN(1 − 0)/¹³CO(1 − 0) intensity ratio would arise from dense (n_H2 ∼ 10⁵ cm⁻³) and hot (T_kin ≳ 300 K) molecular clouds in the nuclear molecular disk. We also observed in the ¹²CO(1 − 0), (3 − 2), ¹³CO(1 − 0), and (3 − 2) lines using the Nobeyama 45m and JCMT 15m telescopes. We detected weak ¹³CO lines as well as strong ¹²CO lines. The LVG calculations assuming a two-component model suggest that there is a large amount of low-density (n_H2 ∼ 3 − 6 × 10² cm⁻³), low-temperature (T_kin ∼ 20 – 50 K) gas, and a small amount of high-density (n_H2 ≳ 10⁴ cm⁻³), high-temperature (T_kin ≳ 500 K) gas. The existence of the high-density and high-temperature component, although having a quite small beam filling factor, supports the aperture synthesis observation results mentioned above. Since this dense, hot gas is located in the nuclear molecular disk around the Active Galactic Nucleus (AGN), it may be heated by the strong X-ray radiation and/or by the shock induced by the radio jet.     

On ultra-high energy cosmic rays: Origin in AGN jets and transport in expanding universe

The cosmic ray source spectrum produced by AGN (active galactic nucleus) jets is calculated. A distinctive feature of these calculations is the account for the jet distribution on kinetic energy. The expected cosmic ray spectrum at the Earth is determined with the use of a simple numerical code which takes into account interactions of ultra-high energy protons and nuclei with the background radiation in an expanding universe.     

The optical to X-ray spectrum of the broad-line ultrasoft AGN RE J2248-511

We present a series of monitoring observations of the ultrasoft broad-line Seyfert galaxy RE J2248-511 with XMM-Newton. Previous X-ray observations showed a transition from a very soft state to a harder state five years later. We find that the ultrasoft X-ray excess has re-emerged, yet there is no change in the hard power-law. Reflection models with a reflection fraction of 15, and Comptonisation models with two components of different temperatures and optical depths (kT₁ = 83 keV, T₁ = 30 eV, τ₁ = 0.8; KT₂ = 3.5 keV, T₂ = 60 eV, τ₂ = 2.8) can be fit to the spectrum, but cannot be constrained. The best representation of the spectrum is a model consisting of two blackbodies (kT₁ = 0.09 ± 0.01 keV, kT₂ = 0.21 ± 0.03 keV) plus a power-law (Γ = 1.8 ± 0.08). We also present simultaneous optical and infrared data showing that the optical spectral slope also changes dramatically on timescales of years. If the optical to X-ray flux comes primarily from a Comptonised accretion disk we obtain estimates for the black hole mass , accretion rate and inclination cos(i)  0.8 of the disk.     

X-ray spectroscopy and variability of AGN detected in the 2 Ms Chandra Deep Field-North Survey

We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 active galactic nuclei (AGN) detected in the 2 Ms Chandra Deep Field-North Survey with >200 background-subtracted 0.5–8.0 keV counts [F_{0.5–8.0 keV} = (1.4−200) × 10⁻¹⁵ erg cm⁻² s⁻¹]. Our preliminary spectral analyses yield median spectral parameters of Γ = 1.61 and intrinsic N_H = 6.2 × 10²¹ cm⁻² (z = 1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived JVH distribution and, to a lesser extent, the X-ray luminosity distribution. We also find that among the 136 AGN, 10 (≈7%) show significant Fe K emission-line features with equivalent widths in the range 0.1–1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Γ < 1.0 and large Fe K equivalent width). Finally, we find that 81 (≈60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (≈80–90%) when better photon statistics are available.     

ISEE-1 observations in the magnetosphere of VLF emissions triggered by nonducted coherent VLF waves during VLF waveinjection experiments

Recent data from the ISEE-1 spacecraft indicates that VLF emissions triggered by nonducted coherent VLF waves can differ in important aspects from VLF emissions triggered by ducted VLF waves.     

Geomagnetic activity driven by solar wind turbulence

Within the framework of the solar wind—magnetosphere coupled system, intense perturbations in the solar wind, causing geomagnetic storms and substorms, have been widely studied by means of the so-called coupling parameters. However, remarkable variations in the geomagnetic field occur even in absence of such perturbations. In those conditions, solar wind MHD turbulence might have a role. Recent results have shown that solar wind turbulence can be described not only as a mixture of inward and outward stochastic Alfvénic fluctuations, but includes also advected structures, dominated by an excess of magnetic energy.