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 from the systemic velocity. Images with submilliarcsecond angular resolution show that the red-shifted emission lies along an arc to the northwest of the systemic emission. (The blue-shifted 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 about 1e7 Msun 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 (T_B< 5e6 K on size scales of about 0.1 pc), so that the observed flat-spectrum core cannot be direct self-absorbed synchrotron radiation.Comment: 12 pages, 4 figures. To appear in ApJ Part 2. Also available at http://www.physics.ucsb.edu/~vlbiweb

Galaxies Inside Stromgren Spheres of Luminous Quasars at z>6: Detection of The First Galaxies

The intrinsic Lyman-alpha emission lines of normal galaxies before reionization are much absorbed by the damping wing of the Gunn-Peterson trough, rendering their direct detection nearly impossible, if their intrinsic line widths are less than ~100km/s. High redshift luminous quasars prior to the completion of cosmological reionization at z~6, on the other hand, are capable of producing large HII regions around them (Stromgren spheres) to allow their intrinsic Lyman-alpha emission lines to be transmitted without overwhelming absorption (Cen & Haiman 2000). We suggest that targeted observations at the Stromgren spheres of known luminous quasars at z >= 6 would be able to detect Lyman-alpha emission lines of galaxies inside the Stromgren spheres largely unattenuated. A tunable, very narrowband filter of \Delta\lambda\over \lambda ~ 0.1% or a narrowband filter of \Delta\lambda\over \lambda ~1% with follow-up spectroscopic identifications will be required. Such observations could directly observe the sources of cosmological reionization including possibly the Pop III galaxies at z=6-20 by JWST. Possible applications include determinations of the ionization state of the intergalactic medium, the sizes of the Stromgren spheres, the ages of the quasars, the luminosity function of high redshift galaxies and its evolution, the spatial distribution of galaxies and its evolution, the biased distribution of galaxies around quasars and the anisotropy of quasar emission. Observations using Keck-class telescopes may already be made to enable a differentiation between a fully neutral and a 10% neutral intergalactic medium at z>6.Comment: Submitted to ApJ Letters, 10 page

Mid Infrared Spectra of Radio Galaxies and Quasars

Spitzer Infrared Spectrograph (IRS) observations of 3C radio galaxies and quasars shed new light on the nature of the central engines of AGN. Emission from silicate dust obscuring the central engine can be used to estimate the bolometric luminosity of an AGN. Emission lines from ions such as O IV and Ne V give another indication of the presence or lack of a hidden source of far-UV photons in the nucleus. Radio-loud AGN with relative-to-Eddington luminosity ratios of L/L_Edd < 3E-3 do not appear to have broad optical emission lines, though some do have strong silicate emission. Aromatic emission features from star formation activity are common in low-luminosity radio galaxies. Strong molecular hydrogen pure-rotational emission lines are also seen in some mid-IR weak radio galaxies, caused by either merger shocks or jet shocks in the interstellar medium.Comment: Conference proceedings to appear in "The Central Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP

Constraining the size of the narrow line region in distant quasars

We propose a proper method to measure the size of the narrow line region (NLR) in distant quasars. The apparent angular size of the NLR is, in general, too small to resolve technically. However, it is possible to map the NLR if with gravitational lensing. In our method, we directly compare the observed image of the NLR with the expected lensed images of the NLR for various source sizes and lens models. Seeking the best fit image via the comparison procedures, we can obtain the best-fit size and the best-fit lens model. We apply this method to the two-dimensional spectroscopic data of a famous lensed quasar, Q2237+0305. If the lens galaxy resembles the applied lens model, an upper limit to the NLR size can be set 750 pc. Further, we examine how the fitting results will be improved by future observations, taking into account the realistic observational effects, such as seeing. Future observations will provide us more stringent constraints on the size of the NLR and on the density profile of the lens galaxy.Comment: 17 pages including 4 figures, accepted to Ap

AGN Obscuring Tori Supported by Infrared Radiation Pressure

Explicit 2-d axisymmetric solutions are found to the hydrostatic equilibrium, energy balance, and photon diffusion equations within obscuring tori around active galactic nuclei. These solutions demonstrate that infrared radiation pressure can support geometrically thick structures in AGN environments subject to certain constraints: the bolometric luminosity must be roughly 0.03--1 times the Eddington luminosity; and the Compton optical depth of matter in the equatorial plane should be order unity, with a tolerance of about an order of magnitude up or down. Both of these constraints are at least roughly consistent with observations. In addition, angular momentum must be redistributed so that the fractional rotational support against gravity rises from the inner edge of the torus to the outer in a manner specific to the detailed shape of the gravitational potential. This model also predicts that the column densities observed in obscured AGN should range from about 10^{22} to about 10^{24} cm^{-2}.Comment: ApJ, in pres

Spectropolarimetry of 3CR 68.1: A Highly Inclined Quasar

We present Keck spectropolarimetry of the highly polarized radio-loud quasar 3CR 68.1 (z=1.228, V=19). The polarization increases from 5 in the red (4000 A rest-frame) to >10% in the blue (1900 A rest-frame). The broad emission lines are polarized the same as the continuum, which shows that 3CR 68.1 is not a blazar as it has sometimes been regarded in the past. We also present measurements of the emission lines and a strong, blueshifted, associated absorption line system, as well as a detection at the emission-line redshift of Ca II K absorption, presumably from stars in the host galaxy. 3CR 68.1 belongs to an observationally rare class of highly polarized quasars that are neither blazars nor partially obscured radio-quiet QSOs. Taking into account 3CR 68.1's other unusual properties, such as its extremely red spectral energy distribution and its extreme lobe dominance, we explain our spectropolarimetric results in terms of unified models. We argue that we have a dusty, highly inclined view of 3CR 68.1, with reddened scattered (polarized) quasar light diluted by even more dust-reddened quasar light reaching us directly from the nucleus.Comment: 20 pages, includes 3 tables, 6 figures. Accepted by Ap

3C 216: A Powerful FRII Seyfert 1 Galaxy

3C 216 has a weak accretion flow luminosity, well below the Seyfert1/QSO dividing line, weak broad emission lines (BELs) and powerful radio lobes. As a consequence of the extreme properties of 3C 216, it is the most convincing example known of an FR II radio source that is kinetically dominated: the jet kinetic luminosity, $Q$, is larger than the total thermal luminosity (IR to X-ray) of the accretion flow, $L_{bol}$. Using three independent estimators for the central black hole mass, we find that the jet in 3C 216 is very super-Eddington, $3.3 L_{Edd}<\bar{Q}< 10 L_{Edd}$, where $\bar{Q}$ is the long term time averaged $Q(t)$, calculated at 151 MHz. It is argued that 3C 216 satisfies the contemporaneous kinetically dominated condition, $R(t)\equiv Q(t)/L_{bol}(t)>1$, either presently or in the past based on the rarity of $L_{bol}>L_{Edd}$ quasars. The existence of $R(t)>1$ AGN is a strong constraint on the theory of the central engine of FRII radio sources

Physical Conditions in the Inner Narrow-Line Region of the Seyfert 2 Galaxy NGC 1068

The physical conditions in the inner narrow line region (NLR) of the Seyfert 2 galaxy, NGC 1068, are examined using ultraviolet and optical spectra and photoionization models. The spectra are Hubble Space Telescope (HST) Harchive data obtained with the Faint Object Spectrograph (FOS). We selected spectra of four regions, taken through the 0.3" FOS aperture, covering the full FOS 1200A to 6800A waveband. Each region is approximately 20 pc in extent, and all are within 100 pc of the apparent nucleus of NGC 1068. The spectra show similar emission-line ratios from wide range of ionization states for the most abundant elements. After extensive photoionization modeling, we interpret this result as an indication that each region includes a range of gas densities, which we included in the models as separate components. Supersolar abundances were required for several elements to fit the observed emission line ratios. Dust was included in the models but apparently dust to gas fraction varies within these regions. The low ionization lines in these spectra can be best explained as arising in gas that is partially shielded from the ionizing continuum. Although the predicted line ratios from the photoionization models provide a good fit to the observed ratios, it is apparent that the model predictions of electron temperatures in the ionized gas are too low. We interpret this as an indication of additional collisional heating due to shocks and/or energetic particles associated with the radio jet that traverses the NLR of NGC 1068. The density structure within each region may also be the result of compression by the jet.Comment: 38 pages, Latex, includes 5 figures (postscript), to appear in Ap