On the dust tori in Palomar-Green quasars

The dust clouds in the torus of the quasar are irradiated by the central source, and the clouds at the inner radius of the torus re-radiate mostly in the near-infrared (NIR) wavebands. The ratio of the near-infrared luminosity to the bolometric luminosity L_NIR/L_bol can therefore reflect the torus geometry to some extent. We find a significant correlation between the ratio of the near-infrared luminosity to the bolometric luminosity L_NIR/L_bol and the central black hole mass M_bh for the Palomar-Green(PG) quasars, whereas no correlation is found between the Eddington ratio L_bol/L_Edd and the ratio L_NIR/L_bol. Similar correlations are found for the mid-infrared and far-infrared cases. It may imply that the torus geometry, i.e., the solid angle subtended by the dust torus as seen from the central source, does not evolve with the accretion rate. The correlation of the solid angle subtended by the torus with the central black hole mass M_bh implies that the formation of the dust torus is likely regulated by the central black hole mass. We find that the torus thickness H increases with quasar bolometric luminosities, which is different from the constant torus thickness H with luminosity assumed in the receding torus model. The mean covering factor of the dust clouds at the inner radius of the torus derived from the IR emission data is ~0.39 for PG quasars. The average relative thickness H/R of the tori in the PG quasars derived from the ratios of the infrared to bolometric luminosities is ~0.9. We suggest that the further IR observations on a larger quasar sample including more fainter quasars by the Spitzer Space Telescope will help understand the physics of the dust tori in quasars.Comment: The incorrect V-magnitude used for 1351+640 is fixed, the main conclusions are not changed, accepted for publication in Ap

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

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

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

Further Evidence that the Redshifts of AGN Galaxies May Contain Intrinsic Components

In the decreasing intrinsic redshift (DIR) model galaxies are assumed to be born as compact objects that have been ejected with large intrinsic redshift components, z_(i), out of the nuclei of mature AGN galaxies. As young AGN (quasars) they are initially several magnitudes sub-luminous to mature galaxies but their luminosity gradually increases over 10^8 yrs, as z_(i) decreases and they evolve into mature AGN (Seyferts and radio galaxies). Evidence presented here that low- and intermediate-redshift AGN are unquestionably sub-luminous to radio galaxies is then strong support for this model and makes it likely that the high-redshift AGN (quasars) are also sub-luminous, having simply been pushed above the radio galaxies on a logz-m_(v) plot by the presence of a large intrinsic component in their redshifts. An increase in luminosity below z = 0.06 is also seen. It is associated in the DIR model with an increase in luminosity as the sources mature but, if real, is difficult to interpret in the cosmological redshift (CR) model since at this low redshift it is unlikely to be associated with a higher star formation rate or an increase in the material used to build galaxies. Whether it might be possible in the CR model to explain these results by selection effects is also examined.Comment: 12 pages, 2 figures. Contains response to referees suggestions. (Accepted for ApJL

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

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

MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. IV. The Parent Luminosity Function of Radio-Loud Blazars

(Abridged) We use a complete sample of active galactic nuclei (AGN) selected on the basis of relativistically beamed 15 GHz radio flux density to derive the parent radio luminosity function (RLF) of bright radio-selected blazar cores. We use a maximum likelihood method to fit a beamed RLF to the observed data and thereby recover the parameters of the intrinsic (unbeamed) RLF. We analyze two subsamples of the MOJAVE sample: the first contains only objects of known FR II class, with a total of 103 sources, and the second subsample adds 24 objects of uncertain FR class for a total of 127 sources. Both subsamples exclude four known FR I radio galaxies and two gigahertz-peaked spectrum sources. We obtain good fits to both subsamples using a single power law intrinsic RLF with pure density evolution function. We find that a previously reported break in the observed MOJAVE RLF actually arises from using incomplete bins (because of the luminosity cutoff) across a steep and strongly evolving RLF, and does not reflect a break in the intrinsic RLF. The derived space density of the parent population of the FR II sources from the MOJAVE sample (with L>1.3e25 W/Hz) is approximately 1600/Gpc^3.Comment: 31 pages, 7 figures and 2 tables. Accepted for publication in ApJ. Changes: classification of sources based on radio morphology instead of optical classes; added the parameters of the RLF of the FR II sources; added more explanations; added a table listing the sample sources; added 2 extra figures related to the observed break in the RLF; updated reference

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