J. E. Pringle

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.

The Alignment of disk and black hole spins in active galactic nuclei

The inner parts of an accretion disk around a spinning black hole are forced to align with the spin of the hole by the Bardeen-Petterson effect. Assuming that any jet produced by such a system is aligned with the angular momentum of either the hole or the inner disk, this can, in principle, provide a mechanism for producing steady jets in active galactic nuclei (AGNs) whose direction is independent of the angular momentum of the accreted material. However, the torque that aligns the inner disk with the hole, also by Newtons third law, tends to align the spin of the hole with the outer accretion disk. In this Letter, we calculate this alignment timescale, talign, for a black hole powering an AGN, and we show that it is relatively short. This timescale is typically much less than the derived ages for jets in radio-loud AGNs and implies that the jet directions, in general, are not controlled by the spin of the black hole. We speculate that the jet directions are most likely controlled either by the angular momentum of the accreted material or by the gravitational potential of the host galaxy.

The Disk-Jet Connection in Microquasars and Active Galactic Nuclei

We propose a new model for the disk-jet connection in black hole X-ray transients and active galactic nuclei. In our model, the inner part of the accretion disk around the central black hole switches between two states. In one state, the accretion energy is dissipated locally (some within the disk, some within a corona) to produce the observed disk luminosity. In the second state, the accretion energy is deposited into the bulk flow of a relativistic jet. We associate the transition between the two states with the generation of a global, poloidal magnetic field. We show that this model can explain the observed behavior of black hole accretors.

The Orientation of Jets Relative to Dust Disks in Radio Galaxies

We use Hubble Space Telescope broadband images and VLA and VLBI continuum data to study the three-dimensional orientation of jets relative to nuclear dust disks in 20 radio galaxies. The comparison between the position angles of the jets and those of the dust disk major axes shows a wide distribution, suggesting that they are not aligned preferentially perpendicular to each other. We use a statistical technique to determine the three-dimensional distribution of angles between jets and dust disk rotation axes. This analysis shows that the observations are consistent with jets homogeneously distributed over a large region, extending over polar caps of 55°-77° but seeming to avoid lying close to the plane of the dust disks. We argue that the lack of close alignment between jets and dust disks axes is not likely to be caused by feeding the nucleus with gas from mergers originated from random directions. We suggest that the misalignment can be due to a warping mechanism in the accretion disk, such as self-irradiation instability or the Bardeen-Petterson effect, or that the gravitational potential in the inner regions of the galaxy is misaligned with respect to that of the dust disk.

An Investigation into the Geometry of Seyfert Galaxies

We present a new method for the statistical investigation into the distributions of the angle β between the radio axis and the normal to the galactic disk for a sample of Seyfert galaxies. We discuss how further observations of the sample galaxies can strengthen the conclusions. Our data are consistent with the hypothesis that active galactic nuclei (AGNs) jets are oriented randomly in space, independent of the position of the plane of the galaxy. By making the simple assumption that the standard model of AGNs holds, with a universal opening angle of the thick torus of c, we demonstrate a statistical method to obtain an estimate of c. Our data are not consistent with the simple-minded idea that Seyfert 1s and Seyfert 2s are differentiated solely by whether or not our line of sight lies within some fixed angle of the jet axis. Our result is significant on the 2 σ level and can thus be considered only suggestive, not conclusive. A complete sample of Seyfert galaxies selected on an isotropic property is required to obtain a conclusive result.

Evidence for periodic modulation of presupernova mass loss from the progenitor of SN 1979 C

Examination of the short-term deviations from the best-fit model light curves for 10 years of measurements on the radio supernova SN 1979C at 20 and 6 cm shows periodic behavior. With an observed period of ∼1575 days, model interpretations imply an ∼8% modulation of the presupernova stellar wind density on a time scale of ∼4000 yr. These observations therefore provide the first direct evidence for the periodic modulation of stellar winds on long time scales

HUNDRED THOUSAND DEGREE GAS IN THE VIRGO CLUSTER OF GALAXIES

The physical relationship between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of many galaxy clusters is not understood. It is unclear whether the ~104 K filaments have cooled and condensed from the ambient hot (~107 K) medium or have some other origin such as the infall of cold gas in a merger, or the disturbance of an internal cool reservoir of gas by nuclear activity. Observations of gas at intermediate temperatures (~105-106 K) can potentially reveal whether the central massive galaxies are gaining cool gas through condensation or losing it through conductive evaporation and hence identify plausible scenarios for transport processes in galaxy cluster gas. Here we present spectroscopic detection of ~105 K gas spatially associated with the Hα filaments in a central cluster galaxy, M87, in the Virgo Cluster. The measured emission-line fluxes from triply ionized carbon (C IV 1549 A) and singly ionized helium (He II 1640 A) are consistent with a model in which thermal conduction determines the interaction between hot and cold phases.

Discovery of C IV Emission Filaments in M87

ABSTRACTGas at intermediate temperatures between the hot X-ray-emitting coronal gas in galaxies at the centers of galaxyclusters and the much cooler optical line emitting filaments yields information on transport processes and plausiblescenarios for the relationship between X-ray cool cores and other galactic phenomena such as mergers or the onsetof an active galactic nucleus. Hitherto, detection of intermediate temperature gas has proven elusive. Here, wepresent FUV imaging of the “low excitation” emission filaments of M87 and show strong evidence for the presenceof Civ 1549 A emission which arises in gas at temperature ∼10 5 K co-located with H α +[Nii] emission fromcooler ∼10 4 K gas. We infer that the hot and cool phases are in thermal communication, and show that quanti-tatively the emission strength is consistent with thermal conduction, which in turn may account for many of theobserved characteristics of cool-core galaxy clusters. Key words: conduction – galaxies: individual (M87) – galaxies: ISM1. INTRODUCTIONThe close correlation between “cool-core clusters” viewedin X-rays, and optical emission-line nebulae in clusters ofgalaxies has been recognized for many years, but the physicalreason for this connection remains unclear. Optical emission-line filamentary structures have been seen and analyzed inmany cool-core clusters (e.g., Sparks et al. 1989, 2004;Voit& Donahue 1997;Crawfordetal.2005; Conselice et al.2001; Hatch et al. 2006, and references therein). Suggestedformation scenarios for the “optical” filaments have included(1) condensations in cooling intracluster medium (e.g., FabianN Cowie et al. 1980; Fabian et al. 1984; Heckmanetal.1989;DonahueV Revaz et al. 2007),(2)alreadycold interstellar material originating in galaxies falling into thecluster core (e.g., Rubin et al. 1977; Sparks et al. 1989; Sparks1992; Braine et al. 1995; Yagi et al. 2007), and (3) already coldmaterial originating in the central cluster galaxy (e.g., Fabianet al. 2003;Crawfordetal.2005).Many different excitation mechanisms for the filaments havebeen considered. For NGC 1275 (Sabra et al. 2000; Conseliceet al. 2001) and M87 (Sabra et al. 2003) photoionizationby the central active galactic nucleus (AGN) and by theintracluster medium, by shocks, and by hot, young stars were allconsidered. These authors concluded that “neither shocks norphotoionization alone can reproduce the emission-line intensityratios” and that some additional source of heating must bepresent. A study of the optical line ratios in Abell 2597 ledVoit & Donahue (1997) to rule out shocks as an excitationmechanism, and to conclude that although hot stars might bethe best candidate for producing the ionization, even the hotteststars could not power a nebula as hot as the one observed andthat some other non-ionizing source of heat must contribute acomparable amount of power. Similarconclusions were reachedby Hatch et al. (2007) for a number of cool-core clusters.One obvious source of such extra heating comes from the factthat the relatively cool H

Infrared emission from the nearby cool core cluster abell 2597

We observed the brightest central galaxy (BCG) in the nearby (z = 0.0821) cool core galaxy cluster Abell 2597 with the IRAC and MIPS instruments on board the Spitzer Space Telescope. The BCG was clearly detected in all Spitzer bandpasses, including the 70 and 160 μm wave bands. We report aperture photometry of the BCG. The spectral energy distribution exhibits a clear excess in the far-IR over a Rayleigh-Jeans stellar tail, indicating a star formation rate of ~4-5 M☉ yr-1, consistent with the estimates from the UV and its Hα luminosity. This large far-IR luminosity is consistent with that of a starburst or a luminous infrared galaxy, but together with a very massive and old population of stars that dominate the energy output of the galaxy. If the dust is at one temperature, the ratio of 70 to 160 μm fluxes indicates that the dust emitting mid-IR in this source is somewhat hotter than the dust emitting mid-IR in two BCGs at higher redshift (z ~ 0.2-0.3) and higher far-IR luminosities observed earlier by Spitzer in clusters Abell 1835 and Zwicky 3146.

Direct Measurement of the Jet Geometry in Seyfert Galaxies.

We demonstrate that by combining optical, radio, and X-ray observations of a Seyfert galaxy, it is possible to provide a direct measurement of the angle beta between the direction of the radio jet and the normal to the plane of the spiral host galaxy. To do so, we make the assumptions that the inner radio jet is perpendicular to the X-ray observed inner accretion disk and that the observed jet (or the stronger component, if the jet is two-sided) is physically closer to Earth than the plane of the galaxy. We draw attention to the possibility that the measurement will produce a result that is not self-consistent, in which case, for that galaxy, one of the assumptions must fail.