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|The Narrow-Line Region of the Seyfert 2 Galaxy Mrk 78: An Infrared View|
We report near-infrared spectroscopic data for the Seyfert 2 galaxy Mrk78, taken with the LIRIS near-infrared camera/spectrometer at theWilliam Herschel Telescope (WHT). The long-slit spectra clearly showextended emission. The resolution and depth of the near-infrared spectraallow the examination of its morphology and ionization regions, and adirect comparison with similarly deep visible spectra. The emission-lineratios obtained are used to derive the extinction toward the nucleus.The detection of strong features such as [Fe II], H2,hydrogen recombination lines, and the coronal [Si VI] λ1.962 lineis used to study the kinematics and excitation mechanisms occurring inMrk 78, revealing that despite the strong radio-jet interaction presentin this object, photoionization from the active nucleus dominates thenarrow-line region emission, while UV fluorescence is the source of theH2 emission. Lines with extended emission yield velocitydistributions with an amplitude of about 600 km s-1, theconsequence of an eastern lobe moving away from us plus a western lobewith the opposite contribution. We used the photoionization code CLOUDYto recreate a typical narrow-line region, to derive the ionizationparameter, and to compare our spectral data with diagnostic diagrams.
|Mid-Infrared All-Sky Survey with the Infrared Camera (IRC) on Board the ASTRO-F Satellite|
An all-sky survey in two mid-infrared bands covering wavelengths from 6to 12 and 14 to 26 μm, with a spatial resolution of ~9.4"-10", willbe performed with the Infrared Camera (IRC) on board the ASTRO-Finfrared astronomical satellite. The expected detection limit for pointsources is 80-130 mJy (5 σ). The all-sky survey will provide datawith a detection limit and a spatial resolution an order of magnitudedeeper and higher, respectively, than those of the Infrared AstronomicalSatellite survey. The IRC is optimally designed for deep imaging instaring observations. It employs 256 × 256 Si:As IBC infraredfocal plane arrays for the two mid-infrared channels. In order to makeobservations with the IRC during the scanning observations for theall-sky survey, a new method of operation for the arrays has beendeveloped-``scan mode'' operation. In the scan mode, only 256 pixels ina single row aligned in the cross-scan direction on the array are usedas the scan detector, and they are sampled every 44 ms. Special care hasbeen taken to stabilize the temperature of the array in scan mode, whichenables the user to achieve a low readout noise, comparable to that inthe imaging mode (20-30 e-). The accuracy of the positiondetermination and the flux measurement for point sources is examinedboth in computer simulations and laboratory tests with the flight modelcamera and moving artificial point sources. In this paper we present thescan mode operation of the array, the results of the computer simulationand the laboratory performance test, and the expected performance of theIRC all-sky survey observations.
|A scientific overview of requirements for IFU data reduction and analysis|
Today’s integral field units are opening up 3D imagingspectroscopy as a mainstream observing capability, facilitating studiesof varied astronomical phenomena in unprecedented detail, whilst aidingthe efficient use of large telescopes. With this capability come newrequirements for data reduction and analysis tools, both as a result ofthe way IFUs map information to a 2D detector and in order to exploitthe full scientific potential of their comprehensive 3D datasets. Here Igive a general overview of science requirements for reducing andanalyzing integral field spectroscopy data. Details of existing softwareand processes are covered separately by other speakers.
|3D NIR spectroscopy at subarcsecond resolution|
We present a scientific case approached through high quality 3D NIRspectroscopy performed with CIRPASS, attached to the Gemini Southtelescope. A binary mass concentration at the nucleus of the galaxy M 83was suggested by Thatte et al. [A&A 364 (2000) L47] and Mast et al.[BAAA 45 (2002) 98. Astroph#0505264] determined the possible position ofthe hidden secondary mass concentration with 2D H-alpha kinematics. Thepreliminary results of the NIR study presented here are based in almost1500 spectra centered in the wavelength 1.3 μm, with a spectralresolving power of 3200. They allow us to unveil, with 0.36″ (6.4pc) sampling and subarcsecond resolution, the velocity field in a regionof 13″ × 9″ around the optical nucleus. We confirmthat the optical nucleus is not located at the most important center ofsymmetry of the ionized gas velocity field. The largest black hole thatcould fit to the circular motion in this kinematic center should have amass not larger than 3 × 106(sin i)‑1Mȯ solar masses.
|Lifetime of nuclear velocity dispersion drops in barred galaxies|
We have made hydro/N-body simulations with and without star formation toshed some light on the conditions under which a central kinematicallycold stellar component (characterized by a velocity dispersion drop orσ-drop) could be created in a hot medium (e.g. a bulge) andsurvive enough time to be observed. We found that the time-scale for aσ-drop formation could be short (less than 500 Myr), whereas itslifetime could be long (more than 1 Gyr) provided that the centralregion is continuously or regularly fed by fresh gas which leads to acontinuous star formation activity. Star formation in the centralregion, even at a low rate as 1Msolaryr-1, ismandatory to sustain a permanent σ-drop by replacing heatedparticles by new low-σ ones. We moreover show that as soon as starformation is switched off, the σ-drop begins to disappear.
|Evolutionary unification in composite active galactic nuclei|
In this paper, we present an evolutionary unification scenario,involving supermassive black holes (SMBHs) and starbursts (SBs) withoutflow (OF), that seems capable of explaining most of the observationalproperties (of at least part) of active galactic nuclei (AGN).The scenario includes a nuclear/circumnuclear SB closely associated withthe AGN where the narrow-line region (NLR), broad-line region (BLR) andbroad absorption line (BAL) region are produced in part by the OFprocess with shells and in compact supernova remnants (cSNRs).The OF process in BAL quasi-stellar objects (QSOs) with extreme infrared(IR) and FeII emission is studied. In addition, the FeII problemregarding the BLR of AGN is analysed. The correlations between the BAL,IR emission, FeII intensity and the intrinsic properties of the AGN arenot clearly understood. We suggest here that the behaviour of the BAL,IR and FeII emission in AGN can be understood within an evolutionary andcomposite model for AGN.In our model, strong BAL systems and FeII emission are present (andintense) in young IR objects. Parameters like the BALs, IR emission,FeII/Hβ intensity ratio, FeII equivalent width (EW), broad-linewidth, [OIII]λ5007-Å intensity and width, NLR size, X-rayspectral slope in radio quiet (RQ) AGN plus lobe separation, and lobe tocore intensity ratio in radio loud (RL) AGN are proposed to befundamentally time-dependent variables inside time-scales of the orderof 108 yr. Orientation/obscuration effects take the role of asecond parameter providing the segregation between Seyfert 1/Seyfert 2galaxies (Sy1/Sy2) and broad-/narrow-line radio galaxies (BLRG/NLRG).
|X-ray reflection in the nearby Seyfert 2 galaxy NGC 1068|
We use the full broad-band XMM-Newton European Photon Imaging Camera(EPIC) data to examine the X-ray spectrum of the nearby Seyfert 2 galaxyNGC 1068, previously shown to be complex with the X-ray continuum beinga sum of components reflected/scattered from cold (neutral) and warm(ionized) matter, together with associated emission-line spectra. Wequantify the neutral and ionized reflectors in terms of the luminosityof the hidden nucleus. Both are relatively weak, a result we interpreton the unified Seyfert model by a near side-on view to the putativetorus, reducing the visibility of the illuminated inner surface of thetorus (the cold reflector), and part of the ionized outflow. A highinclination in NGC 1068 also provides a natural explanation for thelarge (Compton-thick) absorbing column in the line-of-sight to thenucleus. The emission line fluxes are consistent with the strength ofthe neutral and ionized continuum components, supporting the robustnessof the spectral model.
|The near-infrared spectrum of Mrk 1239: direct evidence of the dusty torus?|
We report 0.8-4.5 μm SpeX spectroscopy of the narrow-line Seyfert 1galaxy Mrk 1239. The spectrum is outstanding because the nuclearcontinuum emission in the near-infrared (NIR) is dominated by a strongbump of emission peaking at 2.2 μm, with a strength not reportedbefore in an active galactic nucleus. A comparison of the Mrk 1239spectrum to that of Ark 564 allowed us to conclude that the continuum isstrongly reddened by E(B-V) = 0.54. The excess of emission, confirmed byaperture photometry and additional NIR spectroscopy, follows a simpleblackbody curve at T~ 1200 K. This suggests that we may be observingdirect evidence of dust heated to near to the sublimation temperature,likely produced by the putative torus of the unification model. Althoughother alternatives are also plausible, the lack of star formation, thestrong polarization and low extinction derived for the emission linessupport the scenario where the hot dust is located between the narrowline region and the broad line region.
|The lifetime of grand design|
The lifetime of the structure in grand design spiral galaxies isobservationally ill-determined, but is essentially set by how accuratelythe rotation of the pattern can be characterized by a single angularpattern speed. This paper derives a generalized version of theTremaine-Weinberg method for observationally determining pattern speeds,in which the pattern speed is allowed to vary arbitrarily with radius.The departures of the derived pattern speed from a constant then providea simple metric of the lifetime of the spiral structure. Application ofthis method to CO observations of NGC 1068 reveals that the patternspeed of the spiral structure in this galaxy varies rapidly with radius,and that the lifetime of the spiral structure is correspondingly veryshort. If this result turns out to be common in grand-design spiralgalaxies, then these features will have to be viewed as highly transientphenomena.
|Revisiting the infrared spectra of active galactic nuclei with a new torus emission model|
We describe improved modelling of the emission by dust in atoroidal-like structure heated by a central illuminating source withinactive galactic nuclei (AGNs). We have chosen a simple but realistictorus geometry, a flared disc, and a dust grain distribution functionincluding a full range of grain sizes. The optical depth within thetorus is computed in detail taking into account the differentsublimation temperatures of the silicate and graphite grains, whichsolves previously reported inconsistencies in the silicate emissionfeature in type 1 AGNs. We exploit this model to study the spectralenergy distributions (SEDs) of 58 extragalactic (both type 1 and type 2)sources using archival optical and infrared data. We find that both AGNand starburst contributions are often required to reproduce the observedSEDs, although in a few cases they are very well fitted by a pure AGNcomponent. The AGN contribution to the far-infrared luminosity is foundto be higher in type 1 sources, with all the type 2 requiring asubstantial contribution from a circumnuclear starburst. Our resultsappear in agreement with the AGN unified scheme, because thedistributions of key parameters of the torus models turn out to becompatible for type 1 and type 2 AGNs. Further support to theunification concept comes from comparison with medium-resolutioninfrared spectra of type 1 AGNs by the Spitzer observatory, showingevidence for a moderate silicate emission around 10 μm, which ourcode reproduces. From our analysis we infer accretion flows in the innernucleus of local AGNs characterized by high equatorial optical depths(AV~= 100), moderate sizes (Rmax < 100 pc) andvery high covering factors (f~= 80 per cent) on average.
|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.
|Gas and stellar dynamics in NGC 1068: probing the galactic gravitational potential|
We present SAURON integral field spectrography of the central 1.5 kpc ofthe nearby Seyfert 2 galaxy NGC 1068, encompassing the well-knownnear-infrared (NIR) inner bar observed in the K band. We havesuccessively disentangled the respective contributions of the ionizedgas and stars, thus deriving their two-dimensional distribution andkinematics. The [OIII] and Hβ emission lines exhibit a verydifferent spatial distribution and kinematics, the latter followinginner spiral arms with clumps associated with star formation. Stronginward streaming motions are observed in both the Hβ and [OIII]kinematics. The stellar kinematics also exhibit clear signatures of anon-axisymmetric tumbling potential, with a twist in both the velocityand Gauss-Hermite h3 fields. We re-examined the long-slitdata of Shapiro, Gerssen & van der Marel using a pPXF: a strongdecoupling of the Gauss-Hermite term h3 is revealed, and thecentral decrease of Gauss-Hermite term h4 hinted in theSAURON data is confirmed. These data also suggest that NGC 1068 is agood candidate for a so-called σ drop. We confirm the possiblepresence of two separate pattern speeds applying the Tremaine-Weinbergmethod to the Fabry-Perot Hα map. We also examine the stellarkinematics of bars formed in N-body+smoothed particle hydrodynamics(SPH) simulations built from axisymmetric initial conditionsapproximating the luminosity distribution of NGC 1068. The resultingvelocity, dispersion and higher order Gauss-Hermite moments successfullyreproduce a number of properties observed in the two-dimensionalkinematics of NGC 1068 and the long-slit data, showing that thekinematic signature of the NIR bar is imprinted in the stellarkinematics. The remaining differences between the models and theobserved properties are likely mostly due to the exclusion of starformation and the lack of the primary large-scale oval/bar in thesimulations. These models nevertheless suggest that the inner bar coulddrive a significant amount of gas down to a scale of ~ 300 pc. Thiswould be consistent with the interpretation of the σ drop in NGC1068 being the result of central gas accretion followed by an episode ofstar formation.
|GMOS IFU observations of the stellar and gaseous kinematics in the centre of NGC 1068|
We present a data cube covering the central 10 arcsec of the archetypalactive galaxy NGC 1068 over a wavelength range 4200-5400 Åobtainedduring the commissioning of the integral field unit (IFU) of the GeminiMulti-object Spectrograph (GMOS) installed on the Gemini-Northtelescope. The data cube shows a complex emission line morphology in the[OIII] doublet and Hβ line. To describe this structurephenomenologically we construct an atlas of velocity components derivedfrom multiple Gaussian component fits to the emission lines. The atlascontains many features which cannot be readily associated with distinctphysical structures. While some components are likely to be associatedwith the expected biconical outflow, others are suggestive of highvelocity flows or disc-like structures. As a first step towardsinterpretation, we seek to identify the stellar disc using kinematicalmaps derived from the Mgb absorption line feature at 5170 Åandmake associations between this and gaseous components in the atlas ofemission line components.
|Optical Counterparts of Ultraluminous X-Ray Sources Identified from Archival HST WFPC2 Images|
We present a systematic analysis of archival HST WFPC2 ``Association''data sets that correlate with the Chandra positions of a set of 44ultraluminous X-ray sources (ULXs) of nearby galaxies. The mainmotivation is to address the nature of ULXs by searching for opticalcounterparts. Sixteen of the ULXs are found in early-type galaxies (RC3Hubble type <3). We have improved the Chandra/HST relative astrometrywhenever possible, resulting in errors circles of 0.3"-1.7" in size.Disparate numbers of potential ULX counterparts are found, and in somecases none are found. The lack of or low number of counterparts in somecases may be due to insufficient depth in the WFPC2 images. Particularlyin late-type galaxies, the HST image in the ULX region was often complexor crowded, requiring source detection to be performed manually. Wetherefore address various scenarios for the nature of the ULX since itis not known which, if any, of the sources found are true counterparts.The optical luminosities of the sources are typically in the range104-106 Lsolar, with (effective) Vmagnitudes typically in the range 22-24. In several cases colorinformation is available, with the colors roughly tending to be more redin early-type galaxies. This suggests that, in general, the (potential)counterparts found in early-type galaxies are likely to be older stellarpopulations and are probably globular clusters. Several early-typegalaxy counterparts have blue colors, which may be due to youngerstellar populations in the host galaxies, however, these could also bebackground sources. In spiral galaxies the sources may also be due tolocalized structure in the disks rather than bound stellar systems.Alternatively, some of the counterparts in late-type galaxies may beisolated supergiant stars. The observed X-ray/optical flux ratio isdiluted by the optical emission of the cluster in cases where the systemis an X-ray binary in a cluster, particularly in the case of a low-massX-ray binaries in an old cluster. If any of the counterparts are boundsystems with ~104-106 stars and are the truecounterparts to the ULX sources, then the X-ray luminosities of the ULXare generally well below the Eddington limit for a black hole with mass~0.1% of the cluster mass. Finally, we find that the optical flux of thecounterparts is consistent with being dominated by emission from anaccretion disk around an intermediate-mass black hole if the black holehappens to have a mass >~102 Msolar and isaccreting at close to the Eddington rate, unless the accretion disk isirradiated (which would result in high optical disk luminosities atlower black hole masses).Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. This project isassociated with Archival proposal 9545.
|A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds|
We present a Far Ultraviolet Spectroscopic Explorer survey of highlyionized high-velocity clouds (HVCs) in 66 extragalactic sight lines with(S/N)1030>8. We search the spectra for high-velocity (100km s-1<|vLSR|<400 km s-1) O VIabsorption and find a total of 63 absorbers, 16 with 21 cm emitting H Icounterparts and 47 ``highly ionized'' absorbers without 21 cm emission.The highly ionized HVC population is characterized by =38+/-10 km s-1 and =13.83+/-0.36, with negative-velocity clouds generally found atl<180deg and positive-velocity clouds found atl>180deg. Eleven of these highly ionized HVCs arepositive-velocity wings (broad O VI features extending asymmetrically tovelocities of up to 300 km s-1). We find that 81% (30 of 37)of highly ionized HVCs have clear accompanying C III absorption, and 76%(29 of 38) have accompanying H I absorption in the Lyman series. Wepresent the first (O VI selected) sample of C III and H I absorptionline HVCs and find =30+/-8 km s-1,logNa(C III) ranges from <12.5 to >14.4, =22+/-5 km s-1, and log Na(H I) ranges from<14.7 to >16.9. The lower average width of the high-velocity H Iabsorbers implies the H I lines arise in a separate, lower temperaturephase than the O VI. The ratio Na(C III)/Na(O VI)is generally constant with velocity in highly ionized HVCs, suggestingthat at least some C III resides in the same gas as the O VI.Collisional ionization equilibrium models with solar abundances canexplain the O VI/C III ratios for temperatures near1.7×105 K; nonequilibrium models with the O VI ``frozenin'' at lower temperatures are also possible. Photoionization models arenot viable since they underpredict O VI by several orders of magnitude.The presence of associated C III and H I strongly suggests the highlyionized HVCs are not formed in the hotter plasma that gives rise to OVII and O VIII X-ray absorption. We find that the shape of the O VIpositive-velocity wing profiles is well reproduced by a radiativelycooling, vertical outflow moving with ballistic dynamics, withT0=106 K, n0~2×10-3cm-3, and v0~250 km s-1. However, theoutflow has to be patchy and out of ionization equilibrium to explainthe sky distribution and the simultaneous presence of O VI, C III, and HI. We found that a spherical outflow can produce high-velocity O VIcomponents (as opposed to the wings), showing that the possible range ofoutflow model results is too broad to conclusively identify whether ornot an outflow has left its signature in the data. An alternative model,supported by the similar multiphase structure and similar O VIproperties of highly ionized and 21 cm HVCs, is one where the highlyionized HVCs represent the low N(H I) tail of the HVC population, withthe O VI formed at the interfaces around the embedded H I cores.Although we cannot rule out the possibility that some highly ionizedHVCs exist in the Local Group or beyond, we favor a Galactic origin.This is based on the recent evidence that both H I HVCs and themillion-degree gas detected in X-ray absorption are Galactic phenomena.Since the highly ionized HVCs appear to trace the interface betweenthese two Galactic phases, it follows that highly ionized HVCs areGalactic themselves. However, the nondetection of high-velocity O VI inhalo star spectra implies that any Galactic high-velocity O VI exists atz distances beyond a few kpc.
|A FUSE Survey of High-Latitude Galactic Molecular Hydrogen|
Measurements of molecular hydrogen (H2) column densities arepresented for the first six rotational levels (J=0-5) for 73extragalactic targets observed with the Far Ultraviolet SpectroscopicExplorer (FUSE). All of these have a final signal-to-noise ratio largerthan 10 and are located at Galactic latitude |b|>20deg.The individual observations were calibrated with the FUSE calibrationpipeline CalFUSE version 2.1 or higher and then carefully aligned invelocity. The final velocity shifts for all the FUSE segments arelisted. H2 column densities or limits are determined for thesix lowest rotational (J) levels for each H I component in the line ofsight, using a curve-of-growth approach at low column densities(<16.5) and Voigt-profile fitting at higher column densities.Detections include 65 measurements of low-velocity H2 in theGalactic disk and lower halo. Eight sight lines yield nondetections forGalactic H2. The measured column densities range fromlogN(H2)=14 to 20. Strong correlations are found betweenlogN(H2) and T01, the excitation temperature ofthe H2, as well as between logN(H2) and the levelpopulation ratios (log[N(J')/N(J)]). The average fraction ofnuclei in molecular hydrogen [f(H2)] in each sight line iscalculated; however, because there are many H I clouds in each sightline, the physics of the transition from H I to H2 cannot bestudied. Detections also include H2 in 16intermediate-velocity clouds in the Galactic halo (out of 35 IVCs).Molecular hydrogen is seen in one high-velocity cloud (the Leading Armof the Magellanic Stream), although 19 high-velocity clouds areintersected; this strongly suggests that dust is rare or absent in theseobjects. Finally, there are five detections of H2 in externalgalaxies.
|Penetrating the Deep Cover of Compton-thick Active Galactic Nuclei|
We analyze observations obtained with the Chandra X-Ray Observatory ofbright Compton-thick active galactic nuclei (AGNs), those with columndensities in excess of 1.5×1024 cm-2 alongthe lines of sight. We therefore view the powerful central engines onlyindirectly, even at X-ray energies. Using high spatial resolution andconsidering only galaxies that do not contain circumnuclear starbursts,we reveal the variety of emission AGNs alone may produce. Approximately1% of the continuum's intrinsic flux is detected in reflection in eachcase. The only hard X-ray feature is the prominent Fe Kαfluorescence line, with equivalent width greater than 1 keV in allsources. The Fe line luminosity provides the best X-ray indicator of theunseen intrinsic AGN luminosity. In detail, the morphologies of theextended soft X-ray emission and optical line emission are similar, andline emission dominates the soft X-ray spectra. Thus, we attribute thesoft X-ray emission to material that the central engines photoionize.Because the resulting spectra are complex and do not reveal the AGNsdirectly, crude analysis techniques, such as hardness ratios, wouldmisclassify these galaxies as hosts of intrinsically weak, unabsorbedAGNs and would fail to identify the luminous, absorbed nuclei that arepresent. We demonstrate that a three-band X-ray diagnostic can correctlyclassify Compton-thick AGNs, even when significant soft X-ray lineemission is present. The active nuclei produce most of the galaxies'total observed emission over a broad spectral range, and much of theirlight emerges at far-infrared wavelengths. Stellar contamination of theinfrared emission can be severe, however, making long-wavelength dataalone unreliable indicators of the buried AGN luminosity.
|An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium|
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
|Spitzer Reveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies|
We present a Spitzer mid-infrared survey of 42 Fanaroff-Riley class IIradio galaxies and quasars from the 3CRR catalog at redshift z<1. Allof the quasars and 45%+/-12% of the narrow-line radio galaxies have amid-IR luminosity of νLν(15μm)>8×1043 ergs s-1, indicating strongthermal emission from hot dust in the active galactic nucleus. Ourresults demonstrate the power of Spitzer to unveil dust-obscuredquasars. The ratio of ``mid-IR luminous'' narrow-line radio galaxies toquasars indicates a mean dust covering fraction of 0.56+/-0.15, assumingrelatively isotropic emission. We analyze Spitzer spectra of the 14mid-IR luminous narrow-line radio galaxies thought to host hidden quasarnuclei. Dust temperatures of 210-660 K are estimated fromsingle-temperature blackbody fits to the low- and high-frequency ends ofthe mid-IR bump. Most of the mid-IR luminous radio galaxies have a 9.7μm silicate absorption trough with optical depth <0.2, attributedto dust in a molecular torus. Forbidden emission lines fromhigh-ionization oxygen, neon, and sulfur indicate a source of far-UVphotons in the hidden nucleus. However, we find that the other 55%+/-13%of narrow-line FR II radio galaxies are weak at 15 μm, contrary tosingle-population unification schemes. Most of these galaxies are alsoweak at 30 μm. Mid-IR weak radio galaxies may constitute a separatepopulation of nonthermal, jet-dominated sources with low accretionpower.
|On the Fraction of X-Ray-obscured Quasars in the Local Universe|
Recent wide-area hard X-ray and soft gamma-ray surveys have shown thatthe fraction of X-ray-obscured active galactic nuclei (AGNs) in thelocal universe significantly decreases with intrinsic luminosity. Inthis Letter we point out that two corrections have to be made to thesamples: (1) radio-loud AGNs have to be excluded, since their X-rayemission might be dominated by the jet component, and (2) Compton-thicksources have to be excluded too, since their hard X-ray and softgamma-ray emission are also strongly attenuated by Compton scattering.The soft gamma-ray-selected AGN samples obtained by Swift and INTEGRALprovide the best opportunity to study the fraction of obscured AGNs inthe local universe in the least biased way. We choose these samples tocheck if the corrections could alter the above result on the fraction ofobscured AGNs. We find that before the corrections both samples showsignificant anticorrelation between LX and NH,indicating an obvious decrease in the fraction of obscured AGNs withluminosity. However, after the corrections, we find only marginalevidence of anticorrelation (at the 98% confidence level) in the Swiftsample and no evidence at all in the INTEGRAL sample, which consists ofa comparable number of objects. We conclude that current samples onlyshow a marginal decrease in the fraction of obscured AGNs in the localuniverse and that much larger samples are required in order to reach amore robust conclusion.
|Distribution of Dust Clouds around the Central Engine of NGC 1068|
We studied the distribution of dust clouds around the central engine ofNGC 1068 based on shifted and added 8.8-12.3 μm (MIR) multifilterimages and 3.0-3.9 μm (L-band) spectra obtained with the SubaruTelescope. In a region of 100 pc (1.4") around the central peak, wesuccessfully constructed maps of color temperatures and emissivities ofthe MIR and L-band continua as well as the 9.7 and 3.4 μm dustfeatures with spatial resolutions of 26 pc (0.37") in the MIR and 22 pc(0.3") in the L band. Our main results are the following: (1) The colortemperature of the MIR continuum scatters around the thermal equilibriumtemperature with the central engine as the heat source, while that ofthe L-band continuum is higher and independent of distance from thecentral engine. (2) The peak of the 9.7 μm silicate absorptionfeature is shifted to a longer wavelength at some locations. (3) Theratio of the optical depths of the dust features is different from theGalactic values and shows a complicated spatial distribution. (4) Thereis a pie-shaped warm dust cloud as an enhancement in the emissivity ofthe MIR continuum extending about 50 pc to the north from the centralengine. We speculate that material falls into the central engine throughthis cloud.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.
|The Star-forming Torus and Stellar Dynamical Black Hole Mass in the Seyfert 1 Nucleus of NGC 3227|
We report R~4300 VLT SINFONI adaptive optics integral field K-bandspectroscopy of the nucleus of the Seyfert 1 galaxy NGC 3227 at aspatial resolution of 0.085" (7 pc). We present the morphologies andkinematics of emission lines and absorption features and give the firstderivation of a black hole mass in a Seyfert 1 nucleus from stellardynamics (marginally resolving the black hole's sphere of influence). Weshow that the gas in the nucleus has a mean column density of order1024 cm-2 and that it is geometrically thick, inagreement with the standard ``molecular torus'' scenario. We discusspossible heating processes responsible for maintaining the verticalheight of the torus. We also resolve the nuclear stellar distributionand find that within a few parsecs of the AGN there has been an intensestarburst, the most recent episode of which began ~40 Myr ago but hasnow ceased. The current luminosity of stars within 30 pc of the AGN,~3×109 Lsolar, is comparable to that of theAGN. We argue that the star formation has been occurring in theobscuring material. Finally, we apply Schwarzschild orbit superpositionmodels to our full two-dimensional data and derive the mass of the blackhole, paying careful attention to the input parameters, which are oftenuncertain. Our models yield a 1 σ range for the black hole mass ofMBH=7×106-2×107Msolar.Based on observations at the European Southern Observatory VLT(074.B-9012).
|O VI Asymmetry and an Accelerated Outflow in an Obscured Seyfert: FUSE and HST STIS Spectroscopy of Mrk 533|
We present far-ultraviolet spectra of the Seyfert 2 galaxy Mrk 533obtained with FUSE. These spectra show narrow asymmetrical O VIλλ1032,1038 emission lines with stronger wings shortwardof the peak wavelength, but the degree of asymmetry of these wings invelocity is much lower than that of the wings of the lines of lowerionization. In the combined O VI profile there are marginal indicationsof local absorptions in the outflow. The C III λ977 line is seenweakly with a similar profile, but with very low signal-to-noise ratio(S/N). These FUV spectra are among the first for a Seyfert of type 2,i.e., a purportedly obscured Seyfert. The HST STIS spectral image of Mrk533 allows delineation of the various components of the outflow, and weinfer that the outflow is accelerated. We discuss the results in termsof nuclear geometry and kinematics.
|A New Probe of Dense Gas at High Redshift: Detection of HCO+ (5-4) Line Emission in APM 08279+5255|
We report the detection of HCO+ (5-4) emission from the broadabsorption line quasar APM 08279+5255 at z=3.911 based on observationsconducted with the IRAM Plateau de Bure Interferometer. This representsthe first detection of this molecular ion at such a high redshift. Theinferred line luminosity, uncorrected for lensing, isL'HCO+=(3.5+/-0.6)×1010K km s-1 pc2. The HCO+ J=5-4 sourceposition coincides within the errors with that reported from previousHCN J=5-4 and high-J CO line observations of this quasar. TheHCO+ line profile central velocity and width are consistentwith those derived from HCN. This result suggests that HCO+(5-4) emission comes roughly from the same circumnuclear region probedby HCN. However, the HCN (5-4)/HCO+ (5-4) intensity ratiomeasured in APM 08279+5255 is significantly larger than that predictedby simple radiative transfer models, which assume collisional excitationand equal molecular abundances. This could imply that the[HCN]/[HCO+] abundance ratio is particularly large in thissource, or that the J=5 rotational levels are predominantly excited byinfrared fluorescent radiation.Based on observations carried out with the IRAM Plateau de BureInterferometer. IRAM is supported by the Institut National des Sciencesde l'Univers du CNRS (France), the Max-Planck-Gesellschaft (Germany),and the Instituto Geográfico Nacional (Spain).
|Variability Study of Seyfert 2 Galaxies with XMM-Newton|
We present the results of timing analysis of XMM-Newton observations ofSeyfert 2 galaxies in order to search for differences in the meanproperties of Seyfert 1 galaxies and Seyfert 2 galaxies. We selected 13Seyfert 2 galaxies from the XMM-Newton archive that have hard X-raycomponents in their spectra and calculated the excess variance(σ2rms) in the 2-10 keV band. We found thatsix Seyfert 2 galaxies (3C 98, IRAS 05189-2524, MCG -5-23-16, NGC 6300,UGC 4203, and PKS 1814-637) have buried luminous nuclei and that thenuclei have timing properties similar to those of Seyfert 1 nuclei. Thisindicates that these galaxies are candidates for having buried Seyfert 1nuclei as expected by the unified Seyfert model. The first five galaxiesshow significant time variability. The amplitude of the time variabilityof IRAS 05189-2524 is similar to that of narrow-line Seyfert 1 galaxies.In contrast, the amplitude of variability of the seven other galaxies isquite small, much smaller than that of Seyfert 1 galaxies with similarX-ray luminosity. The lack of short time variability in these objects isexplained by the dominance of the reflection component in three galaxies(Mrk 3, Mrk 463, and NGC 7582), and by the presence of very massiveblack holes and an inferred low accretion rate in the other threegalaxies (NGC 1052, NGC 4507, and NGC 7172). For Mrk 348, thesignificant time variability that is expected based on the estimate ofthe central black hole mass was not detected.
|Cosmic Evolution of Black Holes and Spheroids. I. The MBH-σ Relation at z = 0.36|
We test the evolution of the correlation between black hole mass andbulge velocity dispersion (MBH-σ), using a carefullyselected sample of 14 Seyfert 1 galaxies at z=0.36+/-0.01. We measurevelocity dispersion from stellar absorption lines around Mg b (5175Å) and Fe (5270 Å) using high-S/N Keck spectra and estimateblack hole mass from the Hβ line width and the optical luminosityat 5100 Å, based on the empirically calibrated photoionizationmethod. We find a significant offset from the local relation, in thesense that velocity dispersions were smaller for given black hole massesat z=0.36 than locally. We investigate various sources of systematicuncertainties and find that those cannot account for the observedoffset. The measured offset isΔlogMBH=0.62+/-0.10+/-0.25 i.e.,Δlogσ=0.15+/-0.03+/-0.06, where the error bars include arandom component and an upper limit to the systematics. At face value,this result implies a substantial growth of bulges in the last 4 Gyr,assuming that the local MBH-σ relation is the universalevolutionary endpoint. Along with two samples of active galaxies withconsistently determined black hole mass and stellar velocity dispersiontaken from the literature, we quantify the observed evolution with thebest-fit linear relation:ΔlogMBH=(1.66+/-0.43)z+(0.04+/-0.09) with respect tothe local relationship of Tremaine and coworkers, andΔlogMBH=(1.55+/-0.46)z+(0.01+/-0.12) with respect tothat of Ferrarese. This result is consistent with the growth of blackholes predating the final growth of bulges at these mass scales(<σ>=170 km s-1).
|The Active Galactic Nuclei Contribution to the Mid-Infrared Emission of Luminous Infrared Galaxies|
We determine the contribution of AGN to the mid-IR emission of luminousinfrared galaxies (LIRGs) at z>0.6 by measuring the mid-IR dustcontinuum slope of 20,039 mid-IR sources. The 24 μm sources areselected from a Spitzer MIPS survey of the NOAO Deep Wide-Field SurveyBoötes field and have corresponding 8 μm data from the IRACShallow Survey. There is a clear bimodal distribution in the 24 to 8μm flux ratio. The X-ray-detected sources fall within the peakcorresponding to a flat spectrum in νfν, implying thatit is populated by AGN-dominated LIRGs, whereas the peak correspondingto a higher 24 to 8 μm flux ratio is likely due to LIRGs whose IRemission is powered by starbursts. The 24 μm emission is increasinglydominated by AGN at higher 24 μm flux densities (f24): theAGN fraction of the z>0.6 sources increases from 9% atf24~0.35 mJy to 74%+/-20% at f24~3 mJy, in goodagreement with model predictions. Deep 24 μm, small-area surveys,like GOODS, will be strongly dominated by starburst galaxies. AGN areresponsible for ~3%-7% of the total 24 μm background.
|How Much Mass Do Supermassive Black Holes Eat in Their Old Age?|
We consider the distribution of local supermassive black hole Eddingtonratios and accretion rates, accounting for the dependence of radiativeefficiency and bolometric corrections on the accretion rate. We findthat black hole mass growth, both of the integrated mass density and themasses of most individual objects, must be dominated by an earlier,radiatively efficient, high accretion rate stage, and not by theradiatively inefficient low accretion rate phase in which most localsupermassive black holes are currently observed. This conclusion isparticularly true of supermassive black holes in elliptical hostgalaxies, as expected if they have undergone merger activity in the pastthat would fuel quasar activity and rapid growth. We discuss models ofthe time evolution of accretion rates and show that they all predictsignificant mass growth in a prior radiatively efficient state. The onlyway to avoid this conclusion is through careful fine-tuning of theaccretion/quasar timescale to a value that is inconsistent withobservations. Our results agree with a wide range of observationalinferences drawn from the quasar luminosity function and X-raybackground synthesis models, but our approach has the virtue of beingindependent of the modeling of source populations. Models in which blackholes spend the great majority of their time in low accretion ratephases are thus completely consistent both with observations implyingmass gain in relatively short, high accretion rate phases and with thelocal distribution of accretion rates.
|Chandra and Spitzer Unveil Heavily Obscured Quasars in the Chandra/SWIRE Survey|
Using the large multiwavelength data set in the Chandra/SWIRE Survey(0.6 deg2 in the Lockman Hole), we show evidence for theexistence of highly obscured (Compton-thick) AGNs, estimate a lowerlimit to their surface density, and characterize their multiwavelengthproperties. Two independent selection methods based on the X-ray andinfrared spectral properties are presented. The two selected samplescontain (1) five X-ray sources with hard X-ray spectra and columndensities >~1024 cm-2 and (2) 120 infraredsources with red and AGN-dominated infrared SEDs. We estimate a surfacedensity of at least 25 Compton-thick AGNs deg-2 detected inthe infrared in the Chandra/SWIRE field, of which ~40% show distinct AGNsignatures in their optical/near-infrared SEDs, the remaining beingdominated by the host galaxy emission. Only ~33% of all Compton-thickAGNs are detected in the X-rays at our depth [F(0.3-8keV)>10-15 ergs cm-2 s-1]. We reportthe discovery of two sources in our sample of Compton-thick AGNs, SWIREJ104409.95+585224.8 (z=2.54) and SWIRE J104406.30+583954.1 (z=2.43),which are the most luminous Compton-thick AGNs at high z currentlyknown. The properties of these two sources are discussed in detail withan analysis of their spectra, SEDs, luminosities, and black hole masses.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation. Based on observations at the Kitt Peak National Observatory,National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation. The NationalRadio Astronomy Observatory is a facility of the National ScienceFoundation operated under a cooperative agreement by AssociatedUniversities, Inc.
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