Robert Antonucci

Multiwavelength tests of the dusty torus model for Seyfert galaxies

We present a compilation of emission properties for a sample of 116 Seyfert galaxies based on both previously unpublished data and measurements available in the literature. These measurements include fluxes in the emission lines (O III) lambda(5007) and H-beta, as well as the infrared (25-60 microns), ultraviolet (1450 A), soft (0.2-4 keV), and hard (2-10 keV) X-ray continua. These are used to try to distinguish between isotropic and anisotropic emission properties of Seyfert galaxies. The distribution functions of (O III) lambda 5007 infrared, and hard X-ray continuum are similar for Seyfert 1s and Seyfert 2s, consistent with these properties being isotropic. The ultraviolet and soft X-ray continua of Seyfert 2s are underluminous relative to the type 1s suggesting photons at these energies escape from the central source anisotropically. There is a correlation between the ultraviolet continuum and emission-line fluxes in Seyfert 1s consistent with the idea that the central engine is responsible for powering the line emission. No such correlation is found for the Seyfert 2s. Instead, the scatter in the plot of ultraviolet continuum versus line emission suggests the true nuclear continuum luminosity is not seen at Earth in these objects. These properties are consistent with those expected in the dusty torus model.

Jet Directions in Seyfert Galaxies

Here we present the study of the relative angle between the accretion disk (or radio jet) and the galaxy disk for a sample of Seyfert galaxies selected from a mostly isotropic property, the 60 μm flux, and warm infrared colors. We used VLA A-array 3.6 cm continuum data and ground-based optical imaging, homogeneously observed and reduced to minimize selection effects. For parts of the analysis we enlarged the sample by including galaxies serendipitously selected from the literature. For each galaxy we have a pair of points (i, δ), which are the inclination of the galaxy relative to the line of sight and the angle between the jet projected into the plane of the sky and the host galaxy major axis, respectively. For some galaxies we also had information about which side of the minor axis is closer to Earth. This data is combined with a statistical technique, developed by us, to determine the distribution of β angles in three dimensions, the angle between the jet and the host galaxy plane axis. We found from an initial analysis of the data of the 60 μm sample, where Seyfert 1 and 2 galaxies were not differentiated, that the observed distribution of i and δ values can be well represented either by a homogeneous sin β distribution in the range 0° ≤ β ≤ 90° or in 0° ≤ β ≤ 65°, but not by an equatorial ring. A more general model, which tested β-distributions in the range β1 ≤ β ≤ β2, for different ranges of β1 and β2 values, required β2 to be larger than 65° and gave preference for β1 smaller than 40°-50°. An important result from our analysis was obtained when we determined whether the jet was projected against the near or the far side of the galaxy and differentiated between Seyfert 1 and Seyfert 2 galaxies, which showed that the model could not represent Seyfert 1 galaxies adequately. We found that the inclusion of viewing angle restrictions for Seyfert 1 galaxies, namely, that a galaxy can be recognized as a Seyfert 1 only if the angle between the jet and the line of sight (||) is smaller than a given angle c and that the galaxy inclination i is smaller than an angle ic, gave rise to statistically acceptable models. This indication that there is a difference in viewing angle to the central engine between Seyfert 1 galaxies and Seyfert 2 galaxies is a direct and independent confirmation of the underlying concepts of the unified model. We discuss possible explanations for the misalignment between the accretion disk and the host galaxy disk: warping of the accretion disk by self-irradiation instability, by the Bardeen-Petterson effect, or by a misaligned gravitational potential of a nuclear star cluster surrounding the black hole, as well as feeding of the accretion disk by a misaligned inflow of gas from minor mergers, capture of individual stars or gas from the nuclear star cluster, and the capture of individual molecular clouds from the host galaxy.

VLBI Imaging of Water Maser Emission from the Nuclear Torus of NGC 1068

We have made the first VLBI synthesis images of the H2O maser emission associated with the central engine of the Seyfert galaxy NGC 1068. Emission extends about ±300 km s-1 from the systemic velocity. Images with sub-milliarcsecond angular resolution show that the redshifted emission lies along an arc to the northwest of the systemic emission. (The blueshifted emission has not yet been imaged with VLBI.) Based on the maser velocities and the relative orientation of the known radio jet, we propose that the maser emission arises on the surface of a nearly edge-on torus, where physical conditions are conducive to maser action. The visible part of the torus is axially thick, with comparable height and radius. The velocity field indicates sub-Keplerian differential rotation around a central mass of ~1 × 107 M☉ that lies within a cylindrical radius of about 0.65 pc. The estimated luminosity of the central engine is about 0.5 of the Eddington limit. There is no detectable compact radio continuum emission near the proposed center of the torus (TB < 5 × 106 K on size scales of ~0.1 pc), so that the observed flat-spectrum core cannot be direct self-absorbed synchrotron radiation.

A Hubble Space Telescope Survey of Extended [O III] λ5007 Å Emission in a Far-Infrared-Selected Sample of Seyfert Galaxies: Results*

We present the results of a Hubble Space Telescope (HST) survey of extended [O III] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1s and 38 Seyfert 2s), selected by mostly isotropic properties. The comparison between the semimajor axis size of their [O III] emitting regions (Rmaj) shows that Seyfert 1s and Seyfert 2s have similar distributions, which seems to contradict unified model predictions. We discuss possible ways to explain this result, which could be due to either observational limitations or the models used for the comparison with our data. We show that Seyfert 1 narrow-line regions (NLRs) are more circular and concentrated than Seyfert 2s, which can be attributed to foreshortening in the former. We find a good correlation between the NLR size and luminosity, following the relation Rmaj L([O III])0.33 ? 0.04, which is flatter than a previous one found for QSOs and Seyfert 2s. We discuss possible reasons for the different results, and their implications to photoionization models. We confirm previous results that show that the [O III] and radio emission are well aligned and also find no correlation between the orientation of the extended [O III] emission and the host galaxy major axis. This agrees with results showing that the torus axis and radio jet are not aligned with the host galaxy rotation axis, indicating that the orientation of the gas in the torus, and not the spin of the black hole, determines the orientation of the accretion disk, and consequently, the orientation of the radio jet.

VLA Observations of NGC 253: Supernova Remnants and H II Regions at 1 Parsec Resolution

The edge-on starburst galaxy NGC 253 has been imaged with the VLA at wavelengths ranging from 1.3 to 20 cm, with resolutions between 1 and 15 pc. These images reveal a large number of compact radio sources embedded within the diffuse radio structure in the inner 200 pc of the galaxy. We have identified approximately 64 individual compact radio sources in the galaxy. Of the strongest 17 sources, for which the flux densities are high enough to measure spectral indices with moderately low errors, about half have flat spectra and half have steep spectra; this indicates that perhaps half of the individual radio sources are dominated by thermal radio emission from H II regions. Over an 8 yr timescale, few, if any, of the strongest sources have varied in flux density, with limits of 1%-2% yr-1 on the rate of decrease. At the highest resolution of 1 pc, a number of radio sources are beginning to be resolved, and at least 15 different sources can be identified within the innermost 20 pc of the galaxy. Individual radio sources have been explored in more detail. The strongest source, 5.79-39.0 (TH2), assumed to be at the nucleus of the galaxy, has a brightness temperature greater than 20,000 K at 22 GHz and greater than 40,000 K at 15 GHz. It is unresolved at the VLA and may be either an active galactic nucleus or a very compact (nonvariable) supernova remnant. A resolved flat-spectrum source, 5.72-40.1 (TH6), is located ~20 pc to the southwest. It has an apparent size of 2.4 ? 1.2 pc and appears to be an H II region similar to the inner part of 30 Doradus, containing approximately 105 M? in stars, as well as ~600 M? of ionized gas. Source counts, the lack of variability, and the lack of new sources imply that the radio supernova rate is no more than 0.3 yr-1, consistent with estimates made in other wave bands.

A survey for high optical polarization in quasars with core-dominant radio structure - Is there a beamed optical continuum?

129 new optical linear polarization measurements of 84 quasars (defined as starlike on Sky Survey prints) are presented. 23 new highly polarized objects (p > 3%) were discovered, of which 14 are known to have broad emission lines. This represents a significant increase in the numbers of these objects that were known. With the addition of data from the literature, our measurements constitute well-defined samples of flat-spectrum core-dominant radio quasars brighter than about 18 mag, one selected from the list published by Perley (1982, AJ, 87), and another from that by Kuhr et al. (1981)

HST imaging of the inner 3 arcseconds of NGC 1068 in the light of forbidden O III 5007 A

The Planetary Camera aboard HST has been used to obtain a high spatial resolution forbidden O III 5007 A image of the nucleus of the barred spiral galaxy NGC 1068. This image shows more detail than any previously published images and resolves the NLR into several distinct clouds arranged in an apparently conical geometry. The individual emission-line regions appear to be resolved with sizes of 0.1-0.2 arcsec. There is a strong apparent correspondence between the 1.3 cm radio structure and several of the forbidden O III 5007 A clouds, although there are also bright emission-line clouds for which there are no radio counterparts. In particular, the radio triple of Ulvestad et al. (1987) appears to correspond directly to the forbidden O III 5007 A clouds A-D. It is concluded that the distribution of the clouds is consistent with ionization core models. The hidden nucleus is located somewhere in the southern radio component and may be coincident with the H2O megamaser. 33 refs.

Aromatic Features in AGNs: Star-forming Infrared Luminosity Function of AGN Host Galaxies

We describe observations of aromatic features at 7.7 and 11.3 μm in AGNs of three types, including PG, 2MASS, and 3CR objects. The feature has been demonstrated to originate predominantly from star formation. Based on the aromatic-derived star-forming luminosity, we find that the far-IR emission of AGNs can be dominated by either star formation or nuclear emission; the average contribution from star formation is around 25% at 70 and 160 μm. The star-forming infrared luminosity functions of the three types of AGNs are flatter than those of field galaxies, implying that nuclear activity and star formation tend to be enhanced together. The star-forming luminosity function is also a function of the strength of nuclear activity from normal galaxies to the bright quasars, with luminosity functions becoming flatter for more intense nuclear activity. Different types of AGNs show different distributions in the level of star formation activity, with 2MASS > PG > 3CR star formation rates.

JET-POWERED MOLECULAR HYDROGEN EMISSION FROM RADIO GALAXIES

H2 pure-rotational emission lines are detected from warm (100–1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshift z< 0.22 observed with the Spitzer IR Spectrograph. The summed H2 0–0 S(0)–S(3) line luminosities are L(H2) = 7 × 10 38 –2 × 10 42 erg s −1 , yielding warm H2 masses up to 2 × 10 10 M� . These radio galaxies, of both FR radio morphological types, help to firmly establish the new class of radio-selected molecular hydrogen emission galaxies (radio MOHEGs). MOHEGs have extremely large H2 to 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission ratios: L(H2)/L(PAH7.7) = 0.04–4, up to a factor 300 greater than the median value for normal star-forming galaxies. In spite of large H2 masses, MOHEGs appear to be inefficient at forming stars, perhaps because the molecular gas is kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission together with low-ionization emission line spectra indicates low-luminosity active galactic nuclei (AGNs) in all but three radio MOHEGs. The AGN X-ray emission measured with Chandra is not luminous enough to power the H2 emission from MOHEGs. Nearly all radio MOHEGs belong to clusters or close pairs, including four cool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest that the H2 in radio MOHEGs is delivered in galaxy collisions or cooling flows, then heated by radio-jet feedback in the form of kinetic energy dissipation by shocks or cosmic rays.

THE NUCLEAR REDDENING CURVE FOR ACTIVE GALACTIC NUCLEI AND THE SHAPE OF THE INFRARED TO X-RAY SPECTRAL ENERGY DISTRIBUTION

We present extinction curves derived from the broad emission lines and continua of samples of 72 radio-loud and 1018 radio-quiet active galactic nuclei (AGNs). The curves are significantly flatter in the UV than curves for the local interstellar medium. The reddening curves for the radio-quiet Large Bright Quasar Survey quasars are slightly steeper than those of the radio-loud quasars in the UV, probably because of additional reddening by dust farther out in the host galaxies of the former. The UV extinction curves for the radio-loud AGNs are very flat. This is explicable with slight modifications to standard Mathis-Rumpl-Nordsieck dust models: there is a relative lack of small grains in the nuclear dust. Our continuum and broad emission line reddening curves agree in both shape and amplitude, confirming that the continuum shape is indeed profoundly affected by reddening for all but the bluest AGNs. With correction by our generic extinction curve, all of the radio-loud AGNs have optical-UV continuous spectra consistent with a single shape. We show that radio-quiet AGNs have very similar intrinsic UV to optical shape over orders of magnitude in luminosity. We also argue that radio-loud and radio-quiet AGNs probably share the same underlying continuum shape and that most of the systematic differences between their observed continuum shapes are due to higher nuclear reddening in radio-selected AGNs and additional reddening from dust farther out in the host galaxies in radio-quiet AGNs. Our conclusions have important implications for the modeling of quasar continua and the analysis of quasar demographics.