Richard Barvainis

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 innermost dusty structure in active galactic nuclei as probed by the Keck interferometer

We are now exploring the inner region of type 1 active galactic nuclei (AGNs) with the Keck interferometer in the near-infrared. Adding to the four targets previously studied, we report measurements of the K-band (2.2 μm) visibilities for four more targets, namely AKN120, IC 4329A, Mrk6, and the radio-loud QSO 3C 273 at z = 0.158. The observed visibilities are quite high for all the targets, which we interpret as an indication of the partial resolution of the dust sublimation region. The effective ring radii derived from the observed visibilities scale approximately with L 1/2 , where L is the AGN luminosity. Comparing the radii with those from independent optical-infrared reverberation measurements, these data support our previous claim that the interferometric ring radius is either roughly equal to or slightly larger than the reverberation radius. We interpret the ratio of these two radii for a given L as an approximate probe of the radial distribution of the inner accreting material. We show tentative evidence that this inner radial structure might be closely related to the radio-loudness of the central engine. Finally, we re-observed the brightest Seyfert 1 galaxy NGC 4151. Its marginally higher visibility at a shorter projected baseline, compared to our previous measurements obtained one year before, further supports the partial resolution of the inner structure. We did not detect any significant change in the implied emission size when the K-band flux was brightened by a factor of 1.5 over a time interval of one year.

RADIO VARIABILITY OF RADIO-QUIET AND RADIO-LOUD QUASARS

The majority of quasars are weak in their radio emission, with flux densities comparable to those in the optical, and energies far lower. A small fraction, about 10%, are hundreds to thousands of times stronger in the radio. Conventional wisdom holds that there are two classes of quasars, the radio-quiets and radio-louds, with a deficit of sources having intermediate power. Are there really two separate populations, and if so, is the physics of the radio emission fundamentally different between them? This paper addresses the second question, through a study of radio variability across the full range of radio power, from quiet to loud. The VLA was used during 10 epochs to study three carefully selected samples of 11 radio-quiet quasars, 11 radio-intermediate quasars, and 8 radio-loud quasars. A fourth sample consists of 20 VLA calibrators used for phase correction during the observations, all of which are radio-loud. The basic findings are that the root mean square amplitude of variability is independent of radio luminosity or radio-to-optical flux density ratio and that fractionally large variations can occur on timescales of months or less in both radio-quiet and radio-loud quasars. Combining this with similarities in other indicators, such as radio spectral index and the presence of VLBI-scale components, leads to the suggestion that the physics of radio emission in the inner regions of all quasars is essentially the same, involving a compact, partially opaque core together with a beamed jet. It is possible that differences in large-scale radio structures between radio-loud and radio-quiet quasars could stem from disruption of the jets in low-power sources before they can escape their host galaxies.

VLBA imaging of central engines in radio-quiet quasars

We have used the Very Long Baseline Array (VLBA) to image five radio-quiet quasars (RQQs) at milliarcsecond resolution, at frequencies between 1.4 and 5 GHz. These quasars have typical total flux densities of a few millijanskys at gigahertz frequencies and are compact on arcsecond scales. The VLBA images reveal that four of the quasars are dominated by unresolved radio cores, while the fifth has an apparent two-sided jet. Typical core brightness temperatures range from 108 to at least 109 K. The compact radio morphologies and X-ray luminosities of many objects in the RQQ sample seem to indicate classical accretion onto black holes as massive as 109 M☉, with emission physics in many ways similar to their radio-loud counterparts. Therefore, the relatively small amount of radiative energy emerging at radio wavelengths in the RQQs may simply be due to the presence of less powerful radio jets.

A Submillimeter Survey of Gravitationally Lensed Quasars

Submillimeter (and in some cases millimeter) wavelength continuum measurements are presented for a sample of 40 active galactic nuclei (probably all quasars) lensed by foreground galaxies. The object of this study is to use the lensing boost, anywhere from ~3 to 20 times, to detect dust emission from more typical active galactic nuclei (AGNs) than the extremely luminous ones currently accessible without lensing. The sources are a mix of radio-loud and radio-quiet quasars, and after correction for synchrotron radiation (in the few cases where necessary), 23 of the 40 (58%) are detected in dust emission at 850 μm; 11 are also detected at 450 μm. Dust luminosities and masses are derived after correction for lensing magnification, and luminosities are plotted against redshift from z = 1 to z = 4.4, the redshift range of the sample. The main conclusions are (1) monochromatic submillimeter luminosities of quasars are, on average, only a few times greater than those of local IRAS galaxies; (2) radio-quiet and radio-loud quasars do not differ significantly in their dust luminosity; (3) mean dust luminosities of quasars and radio galaxies over the same redshift range are comparable; and (4) quasars and radio galaxies alike show evidence for more luminous and massive dust sources toward higher redshift, consistent with an early epoch of formation and possibly indicating that the percentage of obscured AGNs increases with redshift.

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.

Detection of CO(3 − 2) Emission at z = 2.64 from the Gravitationally Lensed Quasar MG 0414+0534

We have detected CO (3-2) line emission from the gravitationally lensed quasar MG 0414+0534 at redshift 2.64, using the IRAM Plateau de Bure Interferometer. The line is broad, with ΔvFWHM = 580 km s−1. The velocity-integrated CO flux is comparable to, but somewhat smaller than, that of IRAS F10214+4724 and the Cloverleaf quasar (H1413+117), both of which are at similar redshifts. The lensed components A1 + A2 and B were resolved, and separate spectra are presented for each. We also observed the unlensed radio-quiet quasar PG 1634+706 at z = 1.33, finding no significant CO emission.

EVIDENCE FOR A RECEDING DUST SUBLIMATION REGION AROUND A SUPERMASSIVE BLACK HOLE

The near-IR emission in Type 1 active galactic nuclei (AGNs) is thought to be dominated by the thermal radiation from dust grains that are heated by the central engine in the UV/optical and are almost at the sublimation temperature. A brightening of the central source can thus further sublimate the innermost dust, leading to an increase in the radius of the near-IR emitting region. Such changes in radius have been indirectly probed by the measurements of the changes in the time lag between the near-IR and UV/optical light variation. Here we report direct evidence for such a receding sublimation region through the near-IR interferometry of the brightest Type 1 AGN in NGC 4151. The increase in radius follows a significant brightening of the central engine with a delay of at least a few years, which is thus the implied destruction timescale of the innermost dust distribution. Compiling historic flux variations and radius measurements, we also infer the reformation timescale for the inner dust distribution to be several years in this galactic nucleus. More specifically and quantitatively, we find that the radius at a given time seems to be correlated with a long-term average of the flux over the previous several (~6) years, instead of the instantaneous flux. Finally, we also report measurements of three more Type 1 AGNs newly observed with the Keck interferometer, as well as the second epoch measurements for three other AGNs.

Extremely Luminous Water Vapor Emission from a Type 2 Quasar at Redshift z = 0.66

A search for water masers in 47 Sloan Digital Sky Survey type 2 quasars using the Green Bank Telescope has yielded a detection at a redshift of z = 0.660. This maser is more than an order of magnitude higher in redshift than any previously known and, with a total isotropic luminosity of 23,000 L☉, also the most powerful. The presence and detectability of water masers in quasars at z ~ 0.3-0.8 may provide a better understanding of quasar molecular tori and disks, as well as fundamental quasar and galaxy properties such as black hole masses. Water masers at cosmologically interesting distances may also eventually provide, via direct distance determinations, a new cosmological observable for testing the reality and properties of dark energy, currently inferred primarily through Type 1a supernova measurements.

ISOCAM 15 Micron Search for Distant Infrared Galaxies Lensed by Clusters

In a search for lensed infrared galaxies, ISOCAM images have been obtained toward the rich clusters Abell 2218 and Abell 2219 at 15 μm. Nine galaxies (four in Abell 2218 and five in Abell 2219) were detected with flux levels in the range 530–1100 μJy. Three of the galaxies detected in Abell 2218 have previously known redshifts; of these one is a foreground galaxy, and the other two are lensed background galaxies at z = 0.474 and z = 1.032. One of the objects detected in the field of Abell 2219 is a faint, optically red, extreme infrared-dominated galaxy with a probable redshift of 1.048.