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On the origin of the iron Kα line cores in active galactic nuclei
X-ray observations made with Chandra and XMM-Newton have shown thatthere are relatively narrow cores to the iron Kα emission lines inactive galactic nuclei (AGN). Plausible origins for this core emissioninclude the outer regions of an accretion disc, a parsec-scale moleculartorus, and the optical broad-line region (BLR). Using data from theliterature it is shown that no correlation exists between the FeKα core width and the BLR (specifically Hβ) line width. Thisshows that in general the iron Kα core emission does not arisefrom the BLR. There is a similar lack of correlation between the widthof the Fe Kα core and black hole mass. The average Kα widthis about a factor of 2 lower than the Hβ width. It therefore seemslikely that, in many cases, the narrow core arises in the torus. Thereis a very wide range of observed Fe Kα core widths, however, andthis argues for multiple origins. The simplest explanation for theobserved line profiles in AGN is that they are due to a mixing of verynarrow emission from the inner edge of the torus, and broadened emissionfrom the accretion disc, in varying proportions from object to object.
| XMM-Newton study of the complex and variable spectrum of NGC 4051
We study the X-ray spectral variability of the narrow line Seyfert 1galaxy NGC 4051 as observed during two XMM-Newton observations. To gaininsight on the general behaviour, we first apply model-independenttechniques such as rms spectra and flux-flux plots. We then performtime-resolved spectral analysis by splitting the observations into 68spectra (2 ks each). The data show evidence for a neutral andconstant-reflection component and for constant emission fromphotoionized gas, which are included in all spectral models. The nuclearemission can be modelled both in terms of a `standard model' [pivotingpower-law plus a blackbody (BB) component for the soft excess] and of atwo-component one (power law plus ionized reflection from the accretiondisc). Both the models reproduce the source spectral variability andcannot be distinguished on a statistical ground. The distinction hasthus to be made on a physical basis. The standard model results indicatethat the soft excess does not follow the standard BB law (LBB~ T4), despite a variation in luminosity by about one orderof magnitude. The resulting temperature is consistent with beingconstant and has the same value as observed in the PG quasars. Moreover,although the spectral slope is correlated with flux, which is consistentwith spectral pivoting, the hardest photon indices are so flat (Γ~ 1.3-1.4) as to require rather unusual scenarios. Furthermore, the verylow flux states exhibit an inverted Γ-flux behaviour whichdisagrees with a simple pivoting interpretation. These problems can besolved in terms of the two-component model in which the soft excess isnot thermal, but due to the ionized reflection component. In thiscontext, the power law has a constant slope (about 2.2) and theslope-flux correlation is explained in terms of the relativecontribution of the power-law and reflection components which alsoexplains the shape of the flux-flux plot relationship. The variabilityof the reflection component from the inner disc closely follows thepredictions of the light-bending model, suggesting that most of theprimary nuclear emission is produced in the very innermost regions, onlya few gravitational radii (rg) from the central black hole.
| Investigating the nature of narrow-line Seyfert 1 galaxies with high-energy spectral complexity
With the commissioning of XMM-Newton came the discovery of 2.5-10keVspectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). Thishigh-energy complexity can be manifested as sharp, spectral drops orgradual curvature in the spectrum. Models which are normally consideredare ionized reflection and partial covering. In this work, we define twosamples of NLS1: a complex sample whose members exhibit high-energycomplexity (C sample), and a general sample of NLS1 whose 2.5-10keVspectra do not strongly deviate from a simple power law (S sample). Wethan compare multiwavelength parameters of these two samples todetermine if there are any distinguishing characteristics in the complexNLS1. Considering historical light curves of each object, we find thatthe C sample is representative of NLS1 in a low X-ray flux state,whereas the members of the S sample appear to be in a typical fluxstate. Moreover, from measurements of αox withcontemporaneous ultraviolet (UV)/X-ray data, we find that the C sampleof NLS1 appear X-ray weaker at the time of the observation. For two NLS1in the C sample multi-epoch measurements of αox areavailable and suggest that αox approaches more normalvalues as the complexity between 2.5 and 10keV diminishes. This impliesthat a source could transit from one sample to the other as its X-rayflux varies. Secondly, there are indications that the C sample sources,on average, exhibit stronger optical FeII emission, with the three mostextreme (FeII/Hβ > 1.8) FeII emitters all displaying complexityin the 2.5-10keV band. It is an intriguing possibility that we may beable to identify X-ray complex NLS1 based on the extreme strength of themore easily observable optical FeII emission. However, it is not clearif the possible connection between FeII strength and spectral complexityis due to the FeII producing mechanism or because strong FeII emittersmay exhibit the greatest variability and consequently more likely to becaught in an extreme (low) flux state. Based on the current analysis, wecannot straightforwardly dismiss absorption or reflection as the causeof the X-ray complexity; by considering the multiple UV/X-rayobservations of 1H 0707-495 (a C sample member), we discuss a possiblemethod of distinguishing the two models provided further UV/X-rayobservations.
| Investigating a fluctuating-accretion model for the spectral-timing properties of accreting black hole systems
The fluctuating-accretion model of Lyubarskii and its extension byKotov, Churazov & Gilfanov seek to explain the spectral-timingproperties of the X-ray variability of accreting black holes in terms ofinward-propagating mass accretion fluctuations produced at a broad rangeof radii. The fluctuations modulate the X-ray emitting region as theymove inwards and can produce temporal-frequency-dependent lags betweenenergy bands, and energy-dependent power spectral densities (PSDs) as aresult of the different emissivity profiles, which may be expected atdifferent X-ray energies. Here, we use a simple numerical implementationto investigate in detail the X-ray spectral-timing properties of themodel and their relation to several physically interesting parameters,namely the emissivity profile in different energy bands, the geometricalthickness and viscosity parameter of the accretion flow, the strength ofdamping on the fluctuations and the temporal coherence (measured by the`quality factor', Q) of the fluctuations introduced at each radius. Wefind that a geometrically thick flow with large viscosity parameter isfavoured, and we confirm that the predicted lags are quite robust tochanges in the emissivity profile and physical parameters of theaccretion flow, which may help to explain the similarity of the lagspectra in the low/hard and high/soft states of Cyg X-1. We alsodemonstrate the model regime where the light curves in different energybands are highly spectrally coherent. We compare model predictionsdirectly to X-ray data from the narrow line Seyfert 1 galaxy NGC 4051and the black hole X-ray binary (BHXRB) Cyg X-1 in its high/soft state,and we show that this general scheme can reproduce simultaneously thetime lags and energy-dependence of the PSD.
| XMM-Newton observations of the Seyfert 1 AGN H0557-385
We present XMM-Newton observations of the Seyfert 1 active galacticnucleus (AGN) H0557-385. We have conducted a study into the warmabsorber present in this source, and using high-resolution ReflectionGrating Spectrometer (RGS) data we find that the absorption can becharacterized by two phases: a phase with log ionization parameter ξof 0.50 (where ξ is in units of ergcms-1) and a column of0.2 × 1021cm-2, and a phase with log ξ of1.62 and a column of 1.3 × 1022cm-2. An ironKα line is detected. Neutral absorption is also present in thesource, and we discuss possible origins for this. On the assumption thatthe ionized absorbers originate as an outflow from the inner edge of thetorus, we use a new method for finding the volume filling factor. Bothphases of H0557-385 have small volume filling factors (<=1 per cent).We also derive the volume filling factors for a sample of 23 AGN usingthis assumption and for the absorbers with logξ > 0.7, we findreasonable agreement with the filling factors obtained through thealternative method of equating the momentum flow of the absorbers to themomentum loss of the radiation field. By comparing the filling factorsobtained by the two methods, we infer that some absorbers with logξ< 0.7 occur at significantly larger distances from the nucleus thanthe inner edge of the torus.
| An explanation for the soft X-ray excess in active galactic nuclei
We present a large sample of type 1 active galactic nuclei (AGN) spectrataken with XMM-Newton, and fit them with both the conventional model (apower law and blackbody) and the relativistically blurred photoionizeddisc reflection model of Ross & Fabian. We find that the discreflection model is a better fit. The disc reflection model successfullyreproduces the continuum shape, including the soft excess, of all thesources. The model also reproduces many features that wouldconventionally be interpreted as absorption edges. We are able to usethe model to infer the properties of the sources, specifically that themajority of black holes in the sample are strongly rotating, and thatthere is a deficit in sources with an inclination >70°. Weconclude that the disc reflection model is an important tool in thestudy of AGN X-ray spectra.
| A deep XMM-Newton observation of the ultraluminous X-ray source Holmberg II X-1: the case against a 1000-Msolar black hole
We present results from a 112-ks long look by XMM-Newton at theultraluminous X-ray source (ULX) Holmberg II X-1 (Ho II X-1), longthought to be the one of best candidates for the missing class ofintermediate-mass black holes (IMBHs). Our data comprises the firsthigh-quality XMM-Newton/RGS (reflection grating spectrometer) spectrumof an ULX, and an XMM-Newton/EPIC (European Photo Imaging Camera)spectrum with unprecedented signal-to-noise ratio. A detailed timinganalysis shows that any variability on time-scales of minutes to hoursis very weak (less than a few per cent fractional rms), though largeramplitude variations on much shorter time-scales could be hidden byphoton counting statistics. This result suggests that if Ho II X-1harbours an IMBH, then we are observing this source in a highly unusualand atypical state when compared with the known variability behaviour ofother accreting systems of large mass. Moreover, unlike galactic X-raybinaries, our spectral analysis indicates the possible presence of anoptically thick low-temperature corona. Taken together our timing andspectral analysis suggests that the compact companion is most likely ahigh-luminosity analogue of black hole binary systems similar to GRS1915+105, the galactic microquasar, harbouring a compact object of massno greater than 100 Msolar.
| Comptonization and Reprocessing Processes in Accretion Disks: Applications to the Seyfert 1 Galaxies NGC 5548 and NGC 4051
Simultaneous multi-wavelength observations have revealed complexvariability in AGNs. To explain the variability we considered atheoretical model consisting of an inner hot comptonizing corona and anouter thin accretion disk, with interactions between the two componentsin the form of comptonization and reprocessing. We found that thevariability of AGNs is strongly affected by the parameters of the model,namely, the truncated disk radius rmin, the corona radiusrs, the temperature KTe and the optical depthτ0 of the corona. We applied this model to the two bestobserved Seyfert 1 galaxies, NGC 5548 and NGC 4051. Our model canreproduce satisfactory the observed SEDs. Our fits indicate that NGC5548 may have experienced dramatic changes in physical parametersbetween 19891990 and 1998, and that NGC 4051 has a much largertruncated disk radius (700 Schwarzschild radii) than NGC 5548 (severaltens of Schwarzschild radii). Since we adopted a more refined treatmentof the comptonization process rather than simply assuming a cut-offpower law, our results should be more reasonable than the previous ones.
| Dark and Baryonic Matter in Bright Spiral Galaxies. I. Near-Infrared and Optical Broadband Surface Photometry of 30 Galaxies
We present photometrically calibrated images and surface photometry inthe B, V, R, J, H, and K bands of 25, and in the g, r, and K bands offive nearby bright (B0T<12.5 mag) spiralgalaxies with inclinations of 30°-65° spanning the Hubblesequence from Sa to Scd. Data are from The Ohio State University BrightSpiral Galaxy Survey, the Two Micron All Sky Survey, and the SloanDigital Sky Survey Second Data Release. Radial surface brightnessprofiles are extracted, and integrated magnitudes are measured from theprofiles. Axis ratios, position angles, and scale lengths are measuredfrom the near-infrared images. A one-dimensional bulge/diskdecomposition is performed on the near-infrared images of galaxies witha nonnegligible bulge component, and an exponential disk is fit to theradial surface brightness profiles of the remaining galaxies.Based in part on observations obtained at the Cerro TololoInter-American Observatory, operated by the Association of Universitiesfor Research in Astronomy, Inc., under a cooperative agreement with theNational Science Foundation.
| Constraining Dark Matter Halo Profiles and Galaxy Formation Models Using Spiral Arm Morphology. I. Method Outline
We investigate the use of spiral arm pitch angles as a probe of diskgalaxy mass profiles. We confirm our previous result that spiral armpitch angles (P) are well correlated with the rate of shear (S) in diskgalaxy rotation curves by using a much larger sample (51 galaxies) thanused previously (17 galaxies). We use this correlation to argue thatimaging data alone can provide a powerful probe of galactic massdistributions out to large look-back times. In contrast to previouswork, we show that observed spiral arm pitch angles are similar whenmeasured in the optical (at 0.4 μm) and the near-infrared (at 2.1μm) with a mean difference of 2.3d+/-2.7d. This is then used tostrengthen the known correlation between P and S using B-band images. Wethen use two example galaxies to demonstrate how an inferred shear ratecoupled with a bulge-disk decomposition model and a Tully-Fisher-derivedvelocity normalization can be used to place constraints on a galaxy'sbaryon fraction and dark matter halo profile. We show that ESO 582-G12,a galaxy with a high shear rate (slightly declining rotation curve) at~10 kpc, favors an adiabatically contracted halo, with high initial NFWconcentration (cvir>16) and a high fraction of halobaryons in the form of stars (~15%-40%). In contrast, IC 2522 has a lowshear rate (rising rotation curve) at ~10 kpc and favorsnonadiabatically contracted models with low NFW concentrations(cvir~=2-8) and a low stellar baryon fraction <10%.
| Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. II. X-Ray and Ultraviolet Continuum Variability
We report on two Chandra observations, and a simultaneous Hubble SpaceTelescope ultraviolet observation, of the dwarf Seyfert 1 galaxy NGC4395. Each Chandra observation had a duration of ~30 ks, with aseparation of ~50 ks. The spectrum was observed to harden between theseobservations via a scaling down of the soft-band flux. Theinterobservation variability is in a different sense from the observedvariability within each observation and is most likely the result ofincreased absorption. Spectral variations were seen during the firstobservation suggesting that the X-ray emission is produced in more thanone disconnected region. We have also reanalyzed a ~17 ks Chandraobservation conducted in 2000. During the three Chandra observations the2-10 keV flux is about a factor of 2 lower than seen during anXMM-Newton observation conducted in 2003. Moreover, the fractionalvariability amplitude exhibited during the XMM-Newton observation issignificantly softer than seen during the Chandra observations. A powerspectral analysis of the first of the two new Chandra observationsrevealed a peak at 341 s with a formal detection significance of 99%. Asimilar peak was seen previously in the 2000 Chandra data. However, thedetection of this feature is tentative given that it was found inneither the second of our two new Chandra observations nor theXMM-Newton data, and it is much narrower than expected. The Hubble SpaceTelescope observation was conducted during part of the second Chandravisit. A zero-lag correlation between the ultraviolet and X-ray fluxeswas detected with a significance of ~99.5%, consistent with thepredictions of the two-phase model for the X-ray emission from activegalactic nuclei.
| On the X-Ray Baldwin Effect for Narrow Fe Kα Emission Lines
Most active galactic nuclei (AGNs) exhibit a narrow Fe Kα line at~6.4 keV in the X-ray spectra, due to the fluorescent emission from coldmaterial far from the inner accretion disk. Using XMM-Newtonobservations, Page et al. found that the equivalent width (EW) of thenarrow Fe Kα line decreases with increasing luminosity(EW~L-0.17+/-0.08), suggesting a decrease in the coveringfactor of the material emitting the line (presumably the torus). Bycombining the archival Chandra HETG observations of 34 type 1 AGNs withXMM observations in the literature, we build a much larger sample with101 AGNs. We find a similar X-ray Baldwin effect in the sample(EW~L-0.2015+/-0.0426) however, we note that theanticorrelation is dominated by the radio-loud AGNs in the sample, whoseX-ray spectra might be contaminated by the relativistic jet. Excludingthe radio-loud AGNs, we find a much weaker anticorrelation(EW~L-0.1019+/-0.0524). We present Monte Carlo simulationsshowing that such a weak anticorrelation can be attributed to therelative short timescale variations of the X-ray continuum.
| The Optical/Near-Infrared Light Curves of SN 2002ap for the First 1.5 Years after Discovery
Late-time BVRIJHK photometry of the peculiar Type Ic SN 2002ap, takenbetween 2002 June 12 and 2003 August 29 with the MAGNUM Telescope, ispresented. The light-curve decline rate is derived in each band, and thecolor evolution is studied through comparison with nebular spectra andwith SN 1998bw. Using the photometry, the OIR bolometric light curve isbuilt, extending from before light maximum to day 580 after explosion.The light curve has a late-time shape strikingly similar to that of thehypernova SN 1998bw. The decline rate changes from 0.018 magday-1 between days 130 and 230 to 0.014 mag day-1between days 270 and 580. To reproduce the late-time light curve, adense core must be added to the one-dimensional hypernova model thatbest fits the early-time observations, bringing the ejecta mass from 2.5to 3 Msolar without much change in the kinetic energy, whichis 4×1051 ergs. This is similar to the case of otherhypernovae and suggests asymmetry. A large H-band bump developed in thespectral energy distribution after ~day 300, probably caused by strong[Si I] 1.646 and 1.608 μm emissions. The near-infrared fluxcontribution increased simultaneously from <30% to >50% at day580. The near-infrared light curves were compared with those of otherType Ib/c supernovae, among which SN 1983I seems similar to SN 2002apboth in the near-infrared and in the optical.
| A Galactic Origin for the Local Ionized X-Ray Absorbers
Recent Chandra and XMM-Newton observations of distant quasars have shownstrong local (z~0) X-ray absorption lines from highly ionized gas,primarily He-like oxygen. The nature of these X-ray absorbers, i.e.,whether they are part of the hot gas associated with the Milky Way orpart of the intragroup medium in the Local Group, remains a puzzle dueto the uncertainties in the distance. We present in this paper a surveyof 20 AGNs with Chandra and XMM-Newton archival data. About 40% of thetargets show local O VII He α absorption with column densitiesaround 1016 cm-2; in particular, O VII absorptionis present in all the high-quality spectra. We estimate that the skycovering fraction of this O VII-absorbing gas is at least 63%, at 90%confidence, and likely to be unity given enough high-quality spectra. Onthe basis of (1) the expected number of absorbers along sight linestoward distant AGNs, (2) joint analysis with X-ray emissionmeasurements, and (3) mass estimation, we argue that the observed X-rayabsorbers are part of the hot gas associated with our Galaxy. Futureobservations will significantly improve our understanding of thecovering fraction and provide robust tests of this result.
| The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
We have obtained high-resolution images of the central regions of 14reverberation-mapped active galactic nuclei (AGNs) using the HubbleSpace Telescope Advanced Camera for Surveys High Resolution Camera toaccount for host-galaxy starlight contamination of measured AGNluminosities. We measure the host-galaxy starlight contribution to thecontinuum luminosity at 5100 Å through the typical ground-basedslit position and geometry used in the reverberation-mapping campaigns.We find that removing the starlight contribution results in asignificant correction to the luminosity of each AGN both for lowerluminosity sources, as expected, but also for the higher luminositysources such as the PG quasars. After accounting for the host galaxystarlight, we revisit the well-known broad-line region radius-luminosityrelationship for nearby AGNs. We find the power-law slope of therelationship for the Hβ line to be 0.518+/-0.039, shallower thanwhat was previously reported and consistent with the slope of 0.5expected from the naive theoretical assumption that all AGNs have, onaverage, the same ionizing spectrum and the same ionization parameterand gas density in the Hβ line-emitting region.
| The Nonlinear Behavior of the Black Hole System GRS 1915+105
Using nonlinear time series analysis, along with surrogate dataanalysis, it is shown that the various types of long-term variabilityexhibited by the black hole system GRS 1915+105 can be explained interms of a deterministic nonlinear system with some inherent stochasticnoise. Evidence is provided for a nonlinear limit cycle origin of one ofthe low-frequency QPOs detected in the source, while some other types ofvariability could be due to an underlying low-dimensional chaoticsystem. These results imply that the partial differential equations thatgovern the magnetohydrodynamic flow of the inner accretion disk can beapproximated by a small number (~3-5) of nonlinear but ordinarydifferential equations. While this analysis does not reveal the exactnature of these approximate equations, they may be obtained in thefuture, after results of magnetohydrodynamic simulation of realisticaccretion disks become available.
| Dark and Baryonic Matter in Bright Spiral Galaxies. II. Radial Distributions for 34 Galaxies
We decompose the rotation curves of 34 bright spiral galaxies intobaryonic and dark matter components. Stellar mass profiles are createdby applying color-M/L relations to near-infrared and optical photometry.We find that the radial profile of the baryonic-to-dark-matter ratio isself-similar for all galaxies, when scaled to the radius at which thecontribution of the baryonic mass to the rotation curve equals that ofthe dark matter (RX). We argue that this is due to thequasi-exponential nature of disks and rotation curves that are nearlyflat after an initial rise. The radius RX is found tocorrelate most strongly with baryonic rotation speed, such that galaxieswith RX measurements that lie further out in their disksrotate faster. This quantity also correlates very strongly with stellarmass, Hubble type, and observed rotation speed; B-band central surfacebrightness is less related to RX than these other galaxyproperties. Most of the galaxies in our sample appear to be close tomaximal disk. For these galaxies, we find that maximum observed rotationspeeds are tightly correlated with maximum rotation speeds predictedfrom the baryon distributions, such that one can create a Tully-Fisherrelation based on surface photometry and redshifts alone. Finally, wecompare our data to the NFW parameterization for dark matter profileswith and without including adiabatic contraction as it is most commonlyimplemented. Fits are generally poor, and all but two galaxies arebetter fit if adiabatic contraction is not performed. In order to havebetter fits, and especially to accommodate adiabatic contraction,baryons would need to contribute very little to the total mass in theinner parts of galaxies, seemingly in contrast with other observationalconstraints.
| The MBH-σ* Relation in Local Active Galaxies
We examine whether active galaxies obey the same relation between blackhole mass and stellar velocity dispersion as inactive systems, using thelargest published sample of velocity dispersions for active nuclei todate. The combination of 56 original measurements with objects from theliterature not only increases the sample from the 15 consideredpreviously to 88 objects but allows us to cover an unprecedented rangein both stellar velocity dispersion (30-268 km s-1) and blackhole mass (105-108.6 Msolar). In theMBH-σ* relation of active galaxies, we finda lower zero point than the best-fit relation of Tremaine et al. forinactive galaxies, and an upper limit on the intrinsic scatter of 0.4dex. There is also evidence of a flatter slope at low black hole masses.We discuss potential contributors to the observed offsets, includingvariations in the geometry of the broad-line region, evolution in theMBH-σ* relation, and differential growthbetween black holes and galaxy bulges.
| Determining Central Black Hole Masses in Distant Active Galaxies and Quasars. II. Improved Optical and UV Scaling Relationships
We present four improved empirical relationships useful for estimatingthe central black hole mass in nearby AGNs and distant luminous quasarsalike using either optical or UV single-epoch spectroscopy. These massscaling relationships between line widths and luminosity are based onrecently improved empirical relationships between the broad-line regionsize and luminosities in various energy bands and are calibrated to theimproved mass measurements of nearby AGNs based on emission-linereverberation mapping. The mass scaling relationship based on theHβ line luminosity allows mass estimates for low-redshift sourceswith strong contamination of the optical continuum luminosity by stellaror nonthermal emission, while that based on the C IV λ1549 linedispersion allows mass estimates in cases where only the line dispersion(as opposed to the FWHM) can be reliably determined. We estimate thatthe absolute uncertainties in masses given by these mass scalingrelationships are typically around a factor of 4. We include in anappendix mass estimates for all of the Bright Quasar Survey (PG) quasarsfor which direct reverberation-based mass measurements are notavailable.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained from the Data Archive at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| The Radio-Loud Narrow-Line Quasar SDSS J172206.03+565451.6
We report identification of the radio-loud narrow-line quasar SDSSJ172206.03+565451.6, which we found in the course of a search forradio-loud narrow-line active galactic nuclei (AGNs). SDSSJ172206.03+565451.6 is only about the fourth securely identifiedradio-loud narrow-line quasar and the second-most radio loud, with aradio index R1.4~100-700. Its black hole mass,MBH~=(2-3)×107 Msolar estimatedfrom Hβ line width and 5100 Å luminosity, is unusually smallgiven its radio loudness, and the combination of mass and radio indexputs SDSS J172206.03+565451.6 in a scarcely populated region ofMBH-R diagrams. SDSS J172206.03+565451.6 is a classicalnarrow-line Seyfert 1-type object with FWHMHβ~=1490 kms-1, an intensity ratio of [O III]/Hβ~=0.7, and Fe IIemission complexes with Fe II λ4570/Hβ~=0.7. The ionizationparameter of its narrow-line region, estimated from the line ratio [OII]/[O III], is similar to Seyferts, and its high ratio of [Ne V]/[NeIII] indicates a strong EUV-to-soft X-ray excess. We advertise thecombined usage of [O II]/[O III] and [Ne V]/[Ne III] diagrams as auseful diagnostic tool to estimate ionization parameters and toconstrain the EUV-soft X-ray continuum shape relatively independentlyfrom other parameters.
| Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies
The most intense monitoring observations yet made in the optical andnear-infrared wave bands were carried out for Seyfert 1 galaxies NGC5548, NGC 4051, NGC 3227, and NGC 7469 by the MAGNUM telescope, andclear time-delayed responses of the K-band flux variations to the V-bandflux variations were found for all of these galaxies. Their H-K colortemperatures of 1500-1800 K, estimated from their observed fluxvariation gradients, support a view that the bulk of the K flux shouldoriginate in the thermal radiation of hot dust surrounding the centralengine and that the lag time should correspond to light-travel distancebetween them. Cross-correlation analysis measures their lag times to be47-53 (NGC 5548), 11-18 (NGC 4051), about 20 (NGC 3227), and 65-87 (NGC7469) days. The lag times are tightly correlated with the opticalluminosities, as expected from dust reverberation(Δt~L0.5), while weakly with the central virial masses,which suggests that the inner radii of the dust tori around activenuclei have one-to-one correspondences with their central luminosities.In the lag time versus central luminosity diagram, the K-band lag timesplace an upper boundary on the similar lag times of broad emission linesin the literature, which not only supports the unified scheme of AGNsbut also implies a physical transition from the BLR out to the dusttorus that encircles the BLR. Correlated short-term V-band and X-rayflux variations in NGC 5548 are also found with a delay of 1 or 2 days,indicating the thermal reprocessing of X-ray emission by the centralaccretion flow.
| The First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observationsperformed from launch of the mission in 2002 October until 2004 January.The catalog includes 42 AGNs, of which 10 are Seyfert 1, 17 are Seyfert2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rathersmall, with five detected objects, and only one galaxy cluster and nostarburst galaxies have been detected so far. A complete subset consistsof 32 AGNs with a significance limit of 7 σ in the INTEGRAL ISGRI20-40 keV data. Although the sample is not flux limited, thedistribution of sources shows a ratio of obscured to unobscured AGNs of1.5-2.0, consistent with luminosity-dependent unified models for AGNs.Only four Compton-thick AGNs are found in the sample. Based on theINTEGRAL data presented here, the Seyfert 2 spectra are slightly harder(Γ=1.95+/-0.01) than Seyfert 1.5 (Γ=2.10+/-0.02) and Seyfert1 (Γ=2.11+/-0.05).
| Discovery of Water Maser Emission in Eight AGNs with 70 m Antennas of NASA's Deep Space Network
We report the discovery of water maser emission in eight active galacticnuclei (AGNs) with the 70 m NASA Deep Space Network (DSN) antennas atTidbinbilla, Australia, and Robledo, Spain. The positions of the newlydiscovered masers, measured with the VLA, are consistent with theoptical positions of the host nuclei to within 1 σ (0.3" radio and1.3" optical) and most likely mark the locations of the embedded centralengines. The spectra of two sources, NGC 3393 and NGC 5495, display thecharacteristic spectral signature of emission from an edge-on accretiondisk, with orbital velocities of ~600 and ~400 km s-1,respectively. In a survey with DSN facilities of 630 AGNs selected fromthe NASA Extragalactic Database, we have discovered a total of 15 watermaser sources. The resulting incidence rate of maser emission amongnearby (vsys<7000 km s-1) Seyfert 1.8-2.0 andLINER systems is ~10% for a typical rms noise level of ~14 mJy over 1.3km s-1 spectral channels. As a result of this work, thenumber of nearby AGNs (vsys<7000 km s-1)observed with <20 mJy rms noise has increased from 130 to 449.
| The High-Velocity Outflow of PG 1211+143 May Not Be That Fast
We analyze the X-ray spectrum of the quasar PG 1211+143 observed withthe CCD and grating spectrometers on board XMM-Newton. Using anion-by-ion fitting model, we find an outflow component of about 3000 kms-1, which includes absorption lines of K and L shell ions ofthe astrophysically abundant elements. We also identify and include inour model broad (FWHM=6000 km s-1) emission lines from H-likeions of C, N, O, and Ne, and He-like ions of O, Ne, and Mg. The outflowvelocity we find is an alternative interpretation of the data and is incontrast with the ultra high velocity of ~24,000 km s-1reported previously for this object. Nevertheless, we cannot completelyrule out the presence of a high-velocity component due to the poorsignal-to-noise ratio of the data.
| Spatially Resolved Narrow-Line Region Kinematics in Active Galactic Nuclei
We have analyzed Hubble Space Telescope spectroscopy of 24 nearby activegalactic nuclei (AGNs) to investigate spatially resolved gas kinematicsin the narrow-line region (NLR). These observations effectively isolatethe nuclear line profiles on less than 100 pc scales and are used toinvestigate the origin of the substantial scatter between the widths ofstrong NLR lines and the stellar velocity dispersion σ*of the host galaxy, a quantity that relates with substantially lessscatter to the mass of the central, supermassive black hole and moregenerally characterize variations in the NLR velocity field with radius.We find that line widths measured with STIS at a range of spatial scalessystematically underestimate both σ* and the line widthmeasured from ground-based observations, although they do havecomparably large scatter to the relation between ground-based NLR linewidth and σ*. There are no obvious trends in theresiduals when compared with a range of host galaxy and nuclearproperties. The widths and asymmetries of [O III] λ5007 and [SII] λλ6716, 6731 as a function of radius exhibit a widerange of behavior. Some of the most common phenomena are substantialwidth increases from the STIS to the large-scale, ground-based apertureand almost no change in line profile between the unresolved nuclearspectrum and ground-based measurements. We identify asymmetries in asurprisingly large fraction of low-ionization [S II] line profiles andseveral examples of substantial red asymmetries in both [O III] and [SII]. These results underscore the complexity of the circumnuclearmaterial that constitutes the NLR and suggest that the scatter in theNLR width and σ* correlation cannot be substantiallyreduced with a simple set of empirical relations.
| X-Ray Emission from Megamaser Galaxy IC 2560
An observation of the H2O megamaser galaxy IC 2560 with theChandra X-Ray Observatory reveals a complex spectrum composed of softX-ray emission due to multitemperature thermal plasma and a hardcontinuum with strong emission lines. The continuum is most likely aCompton reflection (reprocessing) of primary emission that is completelyabsorbed at least up to 7 keV. The lines can be identified withfluorescence from Si, S, and Fe in the lowest ionization stages. Theequivalent widths of the Si and S lines are broadly compatible withthose anticipated for reprocessing by optically thick cold plasma ofsolar abundances, while the large equivalent width of the Fe linerequires some overabundance of iron. A contribution to the line from atransmitted component cannot be ruled out, but the limits on thestrength of the Compton shoulder make it less likely. From thebolometric luminosity of the nuclear region, we infer that the sourceradiates at 1%-10% of its Eddington luminosity for an adopted centralmass of 3×106 Msolar. The overall spectrumis consistent with the hypotheses that the central engines powering thedetected megamasers in accretion disks are obscured from direct view bythe associated accretion disk material itself and that there is acorrelation between the occurrence of megamaser emission andCompton-thick absorption columns. For the 11 known galaxies with bothcolumn density measurements and maser emission believed to arise fromaccretion disks, eight AGNs are Compton thick.
| AGN in deep radio/X-ray surveys: Hunting the earliest massive galaxies
Despite the plethora of deep (sub-mJy) radio surveys there remainsconsiderable doubt as to the exact nature of the galaxies contributingto the source counts. Current evidence suggests that star formation inmoderately luminous normal galaxies is responsible for the bulk of theemission below 1 mJy. However given the sensitivities of these surveyswe would expect a fraction of these sources to be distant radiogalaxies. Using deep VLA and GMRT data we have found 20 high-zcandidate radio galaxies in two fields using the classical ultra-steepradio spectrum technique (De Breuck {et al. } 2000) and selectinggalaxies with faint (i'>25) optical counterparts. Several of thesesources have X-ray detections in our deep XMM/Chandra observations andhave fluxes high enough to put them in the quasar regime if they lieabove redshift 3. Recently performed Spitzer GTO observations andupcoming near-infrared observations will help reveal the nature of thesesources.
| A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei
Seyfert galaxies commonly host compact jets spanning 10-100 pc scales,but larger structures are resolved out in long-baseline aperturesynthesis surveys. Previous, targeted studies showed thatkiloparsec-scale radio structures (KSRs) may be a common feature ofSeyfert and LINER galaxies, and the origin of KSRs may be starbursts oractive galactic nuclei (AGNs). We report a new Very Large Array surveyof a complete sample of Seyfert and LINER galaxies. Out of all of thesurveyed radio-quiet sources, we find that 44% (19 out of 43) showextended radio structures at least 1 kpc in total extent that do notmatch the morphology of the disk or its associated star-forming regions.The detection rate is a lower limit owing to the combined effects ofprojection and resolution. The infrared colors of the KSR host galaxiesare unremarkable compared to other Seyfert galaxies, and the large-scaleoutflows orient randomly with respect to the host galaxy axes. The KSRSeyfert galaxies instead stand out by deviating significantly from thefar-infrared-radio correlation for star-forming galaxies, with tendencytoward radio excess, and they are more likely to have a relativelyluminous, compact radio source in the nucleus; these results argue thatKSRs are powered by the AGNs rather than starbursts. The high detectionrate indicates that Seyfert galaxies generate radio outflows over asignificant fraction of their lifetime, which is much longer than thedynamical timescale of an AGN-powered jet but is comparable instead tothe buoyancy timescale. The likely explanation is that the KSRsoriginate from jet plasma that has been decelerated by interaction withthe nuclear interstellar medium (ISM). Based on a simple ram pressureargument, the kinetic power of the jet on kiloparsec scales is about 3orders of magnitude weaker than the power of the jet on 10-100 pcscales. This result is consistent with the interaction model, in whichcase virtually all of the jet power must be lost to the ISM within theinner kiloparsec.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| Absolute Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib, and 13Type Ic supernovae (collectively known as stripped-envelope supernovae)are studied by collecting data on the apparent magnitude, distance, andinterstellar extinction of each event. Weighted and unweighted meanabsolute magnitudes of the combined sample, as well as various subsetsof the sample, are reported. The limited sample size and theconsiderable uncertainties, especially those associated with extinctionin the host galaxies, prevent firm conclusions regarding differencesbetween the absolute magnitudes of supernovae of Types Ib and Ic, andregarding the existence of separate groups of overluminous andnormal-luminosity stripped-envelope supernovae. The spectroscopiccharacteristics of the events of the sample are considered. Three of thefour overluminous events are known to have had unusual spectra. Most butnot all of the normal-luminosity events have had typical spectra. Thelight curves of stripped-envelope supernovae are collected and compared.Because SN 1994I in M51 was very well observed, it often is regarded asthe prototypical Type Ic supernova, but it has the fastest light curvein the sample. Light curves are modeled by means of a simple analyticaltechnique that, combined with a constraint on E/M from spectroscopy,yields internally consistent values of ejected mass, kinetic energy, andnickel mass.
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