Todd Hurt

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We present a compilation of emission properties for a sample of 116 Seyfert galaxies based on both previously unpublished data and measurements available in the literature.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.

The Quadruple Gravitational Lens PG 1115+080: Time Delays and Models

Optical photometry is presented for the quadruple gravitational lens PG 1115+080. A preliminary reduction of data taken from 1995 November to 1996 June gives component C leading component B by 23.7 ? 3.4 days and components A1 and A2 by 9.4 days. A range of models has been fitted to the image positions, none of which gives an adequate fit. The best-fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km s-1 Mpc-1 for ? = 1, with an observational uncertainty of 14%, as computed from the B - C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0 = 64 km s-1 Mpc-1, while taking the galaxy to be a point mass gives H0 = 84 km s-1 Mpc-1. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned Hubble Space Telescope observations.

The intrinsic nuclear spectrum of NGC 1068

We have inferred the intrinsic optical, UV and X-ray continuum of the obscured Seyfert nucleus of NGC 1068, using small aperture and polarized flux data to separate host galaxy contamination from reflected nuclear light. In support of popular unification models, we find it to be similar to typical type 1 Seyfert galaxy and quasar continua. The bolometric luminosity of the active nucleus is 2.2 x 10(exp 11) (f(sub refl)/0.01)(exp -1)(D/22Mpc)(exp 2) L(sub sun), where f(sub refl) is the fraction of nuclear flux reflected into our line of sight and D is the distance to NGC 1068.

HST ultraviolet spectropolarimetry of NGC 1068

We present multiaperture spectropolarimetric observations of the Seyfert 2 galaxy NGC 1068. The nuclear region of NGC 1068 was observed with three apertures (4.3 sec x 1.4 sec., 1.0 sec., and 0.3 sec.) by the Hubble Space Telescope (HST). These ultraviolet data allow us to study the scattered, nuclear light without the complication of polarization dilution caused by strong unpolarized starlight. In particular, we can determine the mechanism of the scattering and the size scale of the scattering region. Our data confirm the findings of Antonicci & Miller (1985) and Code et al. (1993). Shortward of 2700 A, the continuum polarization is constant, P is approximately 16%, at a position angle of 97 deg, indicating electron scattering as the mechanism for the polarization. In addition, the narrow-line emission is much less polarized than the continuum, and two broad lines, Mg II lambda lambda 2796, 2804 and C III lambda 1909, are seen in polarized flux Ly-alpha and C IV are not included in our spectral region). The total flux data also indicate that from approximately 2200 A to approximately 3000 A, the spectrum of NGC 1068 is strongly affected by blended Fe II emission. These polarimetry data are explained by the occulation/reflection model proposed by Antonucci & Miller (1985). According to this model, NGC 1068 harbors a Seyfert 1 nucleus which is obscured along the line of sight by an opaque torus. The symmetry axis of the torus is alinged with the radio axis. Radiation from the broad-line region and feature continuum source can escape along the poles of the torus where it is scattered to us. This scattered light receives a partial linear polarization, perpendicular to the symmetry axis of the torus. Our measurements of the relative fluxes and polarized fluxes in the three apertures indicated that the scattering region is spatially extended on a scale of approximatley 1 sec. Also, in the 0.3 sec aperture, and to a lesser extent in the 1.0 sec aperture, the polarization is is somewhat higher, and the position angle somewhat lower, than in largest aperture. Presumably, isolating the central part of the relecting region results in less geometrical cancellation of the polarization and an angle indicative of the location of the innermost scattering paricles.

Keck Spectropolarimetry of Two High-z Radio Galaxies: Discerning the Components of the Alignment Effect

We present the first results of optical spectropolarimetry of high z radio galaxies performed at the W.M. Keck 10m telescope, and discuss the main implications about the components of the UV continuum and the relation to the Unified Model of radio—loud AGN.

The Broadband Spectral Energy Distributions of the Cloverleaf Quasar and IRAS F10214+4724

We have constructed broadband spectral energy distributions for the Cloverleaf quasar (z = 2.56) and the luminous infrared galaxy IRAS F10214+4724 (z = 2.28). These are to date the only two high-redshift objects known with measured thermal far-infrared spectra and the only two with solid millimeter-wave detections of molecular gas. The continuum data are assembled from the literature, from a new analysis of IRAS measurements, and from new measurements in the near-infrared, optical, and at 1.25 mm. The spectral shapes and luminosities of the two objects are nearly identical from the rest submillimeter to 20 μm, but they diverge dramatically in the optical/ultraviolet. A simple unifying obscuration/reflection model is presented that may explain the differences. Considering their very similar molecular gas content, together with evidence based on the continuum energy distributions and optical spectropolarimetry, it appears quite plausible that the Cloverleaf and F10214+4724 in fact differ for the most part only in their orientations with respect to Earth.

Ultraviolet Spectropolarimetry of Narrow-Line Radio Galaxies*

We present the results of UV spectropolarimetry (λrest 2000-3000 A) and far-UV spectroscopy (λrest 1500-2000 A) of two low-redshift narrow-line radio galaxies (NLRGs) taken with the Faint Object Spectrograph on board the Hubble Space Telescope (HST). Spectropolarimetry of several NLRGs has shown that, by the presence of broad permitted lines in polarized flux spectrum, they have hidden quasars seen through scattered light. Imaging polarimetry has shown that NLRGs including our targets often have large scattering regions of a few to 10 kpc scale. This has posed a problem concerning the nature of the scatterers in these radio galaxies. Their polarized continuum has the spectral index similar to or no bluer than that of quasars, which favors electrons as the dominant scattering particles. The large scattering region size, however, favors dust scattering because of its higher scattering efficiency compared to electrons. In this paper we investigate the polarized flux spectrum over a wide wavelength range, combining our UV data with previous optical/infrared polarimetry data. We infer that the scattering would be often caused by opaque dust clouds in the NLRGs and this would be part of the reason for the apparently gray scattering. In the high-redshift radio galaxies, these opaque clouds could be the protogalactic subunits inferred to be seen in the HST images. However, we still cannot rule out the possibility of electron scattering, which could imply the existence of a large gas mass surrounding these radio galaxies.

Ultraviolet Imaging Polarimetry of Narrow-Line Radio Galaxies

In an examination of the unification of radio galaxies and quasars, we obtained UV polarization images of eight narrow-line radio galaxies (NLRGs) with the Faint Object Camera on board the Hubble Space Telescope (HST). By observing in the rest ultraviolet, we can measure the polarization of the active nucleus with little contamination from unpolarized host-galaxy starlight. If, as the unified model predicts, NLRGs are really quasars with their jets lying in the sky plane, we expect to find elongated continua and large polarizations, with the E-vector perpendicular to the UV extent. The observations presented in this paper confirm both of these predictions.

Ultraviolet Imaging Polarimetry of the Seyfert 2 Galaxy Markarian 3

We present ultraviolet (UV) imaging polarimetry data of the Seyfert 2 galaxy Mrk 3, taken by the Hubble Space Telescope. The polarized flux is found to be extended to ~1 kpc from the nucleus, and the position angles of polarization are centrosymmetric, confirming that the polarization is caused by scattering. We determine the location of the hidden nucleus as the center of this centrosymmetric pattern. From the polarization images taken in two broad bands, we have obtained the color distribution of the polarized flux. Some regions have blue polarized flux, consistent with optically thin dust scattering, but some bright knots have a color similar to that of a Seyfert 1 nucleus. Also, the recent Chandra X-ray observation suggests that the ratio of scattered UV flux to scattered X-ray flux is rather similar to the intrinsic UV/X-ray ratio in a Seyfert 1 nucleus, if the observed extended X-ray continuum is scattered light. While the scattered X-rays would essentially be from electron scattering, the similarity of both the UV slope and UV/X-ray ratio to those of a Seyfert 1 nucleus would lead to two possibilities as to the nature of the UV scatterers. One is that the UV may also be scattered by electrons, in which case the scattering gas is somehow dust free. The other is that the UV is scattered by dust grains, but the wavelength-independent UV scattering with low efficiency, indicated by the UV slope and UV/X-ray ratio, would suggest that the grains reside in UV-opaque clouds, or that the dust might be mainly composed of large grains and lack small-grain population.

Ultraviolet Imaging Polarimetry of the Peculiar Seyfert 2 Galaxy Markarian 477

We present the results of UV imaging polarimetry of the Seyfert 2 galaxy Mrk 477 taken by the Faint Object Camera on board the Hubble Space Telescope (HST). From a previous HST UV image (λ ~ 2180 A), Mrk 477 has been known to have a pointlike bright UV hot spot in the central region, peculiar among nearby Seyfert 2 galaxies. There are also claims of UV/optical variability, unusual for a Seyfert 2 galaxy. Our data show that there is an off-nuclear scattering region ~06 (~500 pc) northeast from the hot spot. The data, after the subtraction of the instrumental effect due to this bright hot spot region, might indicate that the scattered light is also detected in the central 02 radius region and is extended to a very wide angle. The hot spot location is consistent with the symmetric center of the position angle pattern, which represents the location of the hidden nucleus, but our data do not provide a strong upper limit to the distance between the symmetric center and the hot spot. We have obtained a high spatial resolution color map of the continuum that shows that the nuclear spiral arm of 04 scale (~300 pc) is significantly bluer than the off-nuclear mirror and the hot spot region. The nature of the hot spot is briefly discussed.