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XMM-Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption
We present a sample of 21 ROSAT bright active galactic nuclei (AGNs),representing a range of spectral classes, and selected for follow-upsnapshot observations with XMM-Newton. The typical exposure was between5 and 10ks. The objects were primarily selected on the bases of X-raybrightness and not on hardness ratio; thus the sample cannot be strictlydefined as a `soft'sample. One of the main outcomes from the XMM-Newtonobservations was that all of the AGN, including 11 type 1.8-2 objects,required low levels of intrinsic absorption (NH<~1021cm-2). The low absorption in type 2 systems isa challenge to account for in the standard orientation-based unificationmodel, and we discuss possible physical and geometrical models whichcould elucidate the problem. Moreover, there does not appear to be anyrelation between the strength and shape of the soft excess, and thespectral classification of the AGN in this sample. We further identify anumber of AGN which deserve deeper observations or further analysis: forexample, the low-ionization nuclear emission regions (LINERs) NGC 5005and NGC 7331, where optically thin thermal and extended emission isdetected, and the narrow-line Seyfert 1 II Zw 177, which shows a broademission feature at ~ 5.8keV.
| 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.
| Size and properties of the narrow-line region in Seyfert-2 galaxies from spatially-resolved optical spectroscopy
Context: .While [O III] narrow-band imaging is commonly used to measurethe size of the narrow-line regions (NLRs) in active galactic nuclei(AGNs), it can be contaminated by emission from surrounding starbursts.Recently, we have shown that long-slit spectroscopy provides a valuablealternative approach to probe the size in terms of AGN photoionisation.Moreover, several parameters of the NLR can be directly accessed.Aims: .We here apply the same methods developed and described for theSeyfert-2 galaxy NGC 1386 to study the NLR of five other Seyfert-2galaxies by using high-sensitivity spatially-resolved opticalspectroscopy obtained at the VLT and the NTT. Methods: .We probethe AGN-photoionisation of the NLR and thus, its "real" size usingdiagnostic line-ratio diagrams. We derive physical properties of the NLRsuch as reddening, ionisation parameter, electron density, and velocityas a function of distance from the nucleus. Results: .For NGC5643, the diagnostic diagrams unveil a similar transition between lineratios falling in the AGN regime and those typical for H II regions asfound for NGC 1386, thus determining the size of the NLR. For the otherfour objects, all measured line ratios fall in the AGN regime. In almostall cases, both electron density and ionisation parameter decrease withradius. Deviations from this general behaviour (such as a secondarypeak) seen in both the ionisation parameter and electron density can beinterpreted as signs of shocks from the interaction of a radio jet andthe NLR gas. In several objects, the gaseous velocity distribution ischaracteristic for rotational motion in an (inclined) emission-line diskin the centre. We compare our results to those of NGC 1386 and show thatthe latter can be considered as prototypical also for this largersample. We discuss our findings in detail for each object.
| The radio structure of radio-quiet quasars
Aims.We investigate the radio emitting structures of radio-quiet activegalactic nuclei with an emphasis on radio-quiet quasars to study theirconnection to Seyfert galaxies. Methods: .We present and analysehigh-sensitivity VLA radio continuum images of 14 radio-quiet quasarsand six Seyfert galaxies. Results: .Many of the low redshiftradio-quiet quasars show radio structures that can be interpreted asjet-like outflows. However, the detection rate of extended radiostructures on arcsecond scales among our sample decreases withincreasing redshift and luminosity, most likely due to a lack ofresolution. The morphologies of the detected radio emission indicatestrong interactions of the jets with the surrounding medium. We alsocompare the radio data of seven quasars with corresponding HST images ofthe [O III] emitting narrow-line region (NLR). We find that the scenarioof interaction between the radio jet and the NLR gas is confirmed in twosources by structures in the NLR gas distribution as previously knownfor Seyfert galaxies. The extended radio structures of radio-quietquasars at sub-arcsecond resolution are by no means different from thatof Seyferts. Among the luminosities studied here, the morphologicalfeatures found are similar in both types of objects while the overallsize of the radio structures increases with luminosity. This supportsthe picture where radio-quiet quasars are the scaled-up versions ofSeyfert galaxies. In addition to known luminosity relations we find acorrelation of the NLR size and the radio size shared by quasars andSeyferts.
| The K-band properties of Seyfert 2 galaxies
Aims. It is well known that the [O iii]λ5007 emission line andhard X-ray (2-10 keV) luminosities are good indicators of AGN activitiesand that the near and mid-infrared emission of AGN originates fromre-radiation of dusty clouds heated by the UV/optical radiation from theaccretion disk. In this paper we present a study of the near-infraredK-band (2.2 μm) properties for a sample of 65 Seyfert 2 galaxies. Methods: .By using the AGN/Bulge/Disk decomposition technique, weanalyzed the 2MASS K_S-band images for Seyfert 2 galaxies in order toderive the K_S-band magnitudes for the central engine, bulge, and diskcomponents. Results: .We find that the K_S-band magnitudes of thecentral AGN component in Seyfert 2 galaxies are tightly correlated withthe [O iii]λ5007 and the hard X-ray luminosities, which suggeststhat the AGN K-band emission is also an excellent indicator of thenuclear activities at least for Seyfert 2 galaxies. We also confirm thegood relation between the central black hole masses and bulge's K-bandmagnitudes for Seyfert 2s.
| Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the λ 1.3 cm (22 GHz) water vaporline towards galaxies with nuclear activity, large nuclear columndensities or high infrared luminosities, we present H2O spectra for NGC2273, UGC 5101, and NGC 3393 with isotropic luminosities of 7, 1500, and400 Lȯ. The H2O maser in UGC 5101 is by far the mostluminous yet found in an ultraluminous infrared galaxy. NGC 3393 revealsthe classic spectrum of a "disk maser", represented by three distinctgroups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below1000 km s-1. Based on the literature and archive data, X-rayabsorbing column densities are compiled for the 64 galaxies withreported maser sources beyond the Magellanic Clouds. For NGC 2782 andNGC 5728, we present Chandra archive data that indicate the presence ofan active galactic nucleus in both galaxies. Modeling the hard nuclearX-ray emission, NGC 2782 is best fit by a high energy reflectionspectrum with NH 1024 cm-2. ForNGC 5728, partial absorption with a power law spectrum indicatesNH 8 × 1023 cm-2. Thecorrelation between absorbing column and H2O emission is analyzed. Thereis a striking difference between kilo- and megamasers with megamasersbeing associated with higher column densities. All kilomasers (L_H_2O< 10 Lȯ) except NGC 2273 and NGC 5194 areCompton-thin, i.e. their absorbing columns are <1024cm-2. Among the H{2}O megamasers, 50% arise fromCompton-thick and 85% from heavily obscured (>1023cm-2) active galactic nuclei. These values are not larger butconsistent with those from samples of Seyfert 2 galaxies not selected onthe basis of maser emission. The similarity in column densities can beexplained by small deviations in position between maser spots andnuclear X-ray source and a high degree of clumpiness in thecircumnuclear interstellar medium.
| The soft X-ray/NLR connection: a single photoionized medium?
We present a sample of 8 nearby Seyfert 2 galaxies observed by HST andChandra. All of the sources present soft X-ray emission which iscoincident in extension and overall morphology with the [O iii]emission. The spectral analysis reveals that the soft X-ray emission ofall the objects is likely to be dominated by a photoionized gas. This isstrongly supported by the 190 ks combined XMM-Newton/RGS spectrum of Mrk3, which different diagnostic tools confirm as being produced in a gasin photoionization equilibrium with an important contribution fromresonant scattering. We tested with the code cloudy a simple scenariowhere the same gas photoionized by the nuclear continuum produces boththe soft X-ray and the [O iii] emission. Solutions satisfying theobserved ratio between the two components exist, and require the densityto decrease with radius roughly like r-2, similarly to whatoften found for the Narrow Line Region.
| Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black holeresearch, as seen from a purely observational standpoint. Since theearly ‘90s, rapid technological advances, most notably the launchof the Hubble Space Telescope, the commissioning of the VLBA andimprovements in near-infrared speckle imaging techniques, have not onlygiven us incontrovertible proof of the existence of supermassive blackholes, but have unveiled fundamental connections between the mass of thecentral singularity and the global properties of the host galaxy. It isthanks to these observations that we are now, for the first time, in aposition to understand the origin, evolution and cosmic relevance ofthese fascinating objects.
| On the transmission-dominated to reprocessing-dominated spectral state transitions in Seyfert 2 galaxies
We present Chandra and XMM-Newton observations of a small sample (11objects) of optically selected Seyfert 2 galaxies, for which ASCA andBeppoSAX had suggested Compton-thick obscuration of the active galacticnucleus (AGN). The main goal of this study is to estimate the rate oftransitions between `transmission-dominated' and`reprocessing-dominated' states. We discover one new transition in NGC4939, with a possible additional candidate in NGC 5643. This indicates atypical occurrence rate of at least ~0.02yr-1. Thesetransitions could be due to large changes of the obscuring gas columndensity, or to a transient dimming of the AGN activity, the latterscenario being supported by detailed analysis of the best-studiedevents. Independently of the ultimate mechanism, comparison of theobserved spectral dynamics with Monte Carlo simulations demonstratesthat the obscuring gas is largely inhomogeneous, with multiple absorbingcomponents possibly spread through the whole range of distances from thenucleus between a fraction of parsecs up to several hundred parsecs. Asa by-product of this study, we report the first measurement ever of thecolumn density covering the AGN in NGC 3393 (NH~= 4.4 ×1024cm-2), and the discovery of soft X-rayextended emission, apparently aligned along the host galaxy main axis inNGC 5005. The latter object most likely hosts an historicallymisclassified low-luminosity Compton-thin AGN.
| The Relationship of Hard X-Ray and Optical Line Emission in Low-Redshift Active Galactic Nuclei
In this paper we assess the relationship of the population of activegalactic nuclei (AGNs) selected by hard X-rays to the traditionalpopulation of AGNs with strong optical emission lines. First, we studythe emission-line properties of a new hard-X-ray-selected sample of 47local AGNs (classified optically as Type 1 and 2 AGNs). We find that thehard X-ray (3-20 keV) and [O III] λ5007 optical emission-lineluminosities are well-correlated over a range of about 4 orders ofmagnitude in luminosity (mean luminosity ratio 2.15 dex with a standarddeviation of σ=0.51 dex). Second, we study the hard X-rayproperties of a sample of 55 local AGNs selected from the literature onthe basis of the flux in the [O III] line. The correlation between thehard X-ray (2-10 keV) and [O III] luminosity for the Type 1 AGNs isconsistent with what is seen in the hard-X-ray-selected sample. However,the Type 2 AGNs have a much larger range in the luminosity ratio, andmany are very weak in hard X-rays (as expected for heavily absorbedAGNs). We then compare the hard X-ray (3-20 keV) and [O III] luminosityfunctions of AGNs in the local universe. These have similar faint-endslopes, with a luminosity ratio of 1.60 dex (0.55 dex smaller than themean value for individual hard-X-ray-selected AGNs). We conclude that atlow redshift, selection by narrow optical emission lines will recovermost AGNs selected by hard X-rays (with the exception of BL Lacobjects). However, selection by hard X-rays misses a significantfraction of the local AGN population with strong emission lines.
| The Connection between the Narrow-Line Region and the UV Absorbers in Seyfert Galaxies
We present evidence that the outflowing UV absorbers in Seyfert 1galaxies arise primarily in their inner narrow- (emission-) line regions(NLRs), based on similarities in their locations, kinematics, andphysical conditions. Hubble Space Telescope observations show thatnearly all Seyfert galaxies have bright, central knots of [O III]emission in their NLRs with radii of tens of parsecs. These sizes areconsistent with most previous estimates of the distances of UV (andX-ray) absorbers from their central continuum sources and a recentlyobtained reliable distance of ~25 pc for a UV absorber in the Seyfert 1galaxy NGC 3783. The nuclear emission-line knots in a sample of 10Seyfert galaxies have velocity widths of 300-1100 km s-1(half-width at zero intensity), similar to the radial velocities of mostUV absorbers. The highest radial velocity for a Seyfert UV absorber todate is only -2100 km s-1, which is much lower than typicalbroad-line region (BLR) velocities. There is also mounting evidence thatthe NLR clouds are outflowing from the nucleus, like the UV absorbers.If our hypothesis is correct, then the NLR should have a component witha high global covering factor (Cg) of the continuum sourceand a BLR to match that found from previous surveys of UV absorbers(Cg=0.5-1.0). Using Space Telescope Imaging Spectrographspectra of NGC 4151, obtained when the continuum and BLR fluxes werelow, we find evidence for optically thin gas in its nuclearemission-line knot. We are able to match the line ratios from this gaswith photoionization models that include a component withCg~1 and an ionization parameter and hydrogen column densitythat are typical of UV absorbers.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| Size and properties of AGN narrow-line regions from emission-line diagnostics.
Not Available
| The Distribution of Bar and Spiral Arm Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamentalproperty of the galaxy population that has only begun to be explored. Wehave applied the bar-spiral separation method of Buta and coworkers toderive the distribution of maximum relative gravitational bar torques,Qb, for 147 spiral galaxies in the statistically well-definedOhio State University Bright Galaxy Survey (OSUBGS) sample. Our goal isto examine the properties of bars as independently as possible of theirassociated spirals. We find that the distribution of bar strengthdeclines smoothly with increasing Qb, with more than 40% ofthe sample having Qb<=0.1. In the context of recurrent barformation, this suggests that strongly barred states are relativelyshort-lived compared to weakly barred or nonbarred states. We do notfind compelling evidence for a bimodal distribution of bar strengths.Instead, the distribution is fairly smooth in the range0.0<=Qb<0.8. Our analysis also provides a first look atspiral strengths Qs in the OSUBGS sample, based on the sametorque indicator. We are able to verify a possible weak correlationbetween Qs and Qb, in the sense that galaxies withthe strongest bars tend to also have strong spirals.
| CO in the Bipolar Radio Continuum Galaxy NGC 3367
CO(1-0) emission has been imaged at 2" resolution in the central 10 kpcof the barred spiral galaxy NGC 3367. This galaxy has bipolarsynchrotron lobes out to a radius of 6 kpc, straddling the compactnucleus. The peak molecular emission is in a source of radius 2" (425pc) centered on the galaxy nucleus. The molecular gas mass is~3×108 Msolar in this peak and~5.9×108 Msolar within a radius of 4.5" (950pc). The very large gas masses in the central source imply extinctionssufficiently high to completely obscure optical emission lines (e.g.,broad-line region) associated with the nuclear radio source. Theobserved Balmer lines probably originate in the narrow-line region a fewhundred parsecs from the nucleus. The CO emission in the central regionis elongated northeast-southwest, very similar to the position angle ofthe large-scale synchrotron lobes. This elongation is likely due to thenonaxisymmetric gravitational potential of the stellar bar. We inferthat the northeast radio continuum lobe is on the far side of the galaxyand the southwest lobe is on the near side. The central mass ofmolecular gas is of sufficient mass to power the active galactic nucleusaccretion luminosity for over 108 yr at 3 Msolaryr-1.
| Probing the Kinematics of the Narrow-Line Region in Seyfert Galaxies with Slitless Spectroscopy: Observational Results
We present slitless spectra of 10 Seyfert galaxies observed with theSpace Telescope Imaging Spectrograph on the Hubble Space Telescope(HST). The spectra cover the [O III] λλ4959, 5007 emissionlines at a spectral resolving power of λ/Δλ~9000 anda spatial resolution of ~0.1". We compare the slitless spectra withprevious HST narrowband images to determine the velocity shifts anddispersions of the bright emission-line knots in the narrow-line regions(NLRs) of these Seyfert galaxies, which extend out to at least severalhundred parsecs from their nuclei. Many knots are spatially resolvedwith sizes of tenths of arcseconds, corresponding to tens of parsecs,and yet they appear to move coherently with radial velocities betweenzero and +/-1200 km s-1 with respect to the systemicvelocities of their host galaxies. The knots also show a broad range invelocity dispersion, ranging from ~30 km s-1 (the velocityresolution) to ~1000 km s-1 FWHM. Most of the Seyfertgalaxies in this sample show an organized flow pattern, with radialvelocities near zero at the nucleus (defined by the optical continuumpeak) and increasing to maximum blueshifts and redshifts within ~1" ofthe nucleus, followed by a decline to the systemic velocity. However,there are large local variations around this pattern, and in one case(NGC 7212), the radial velocities are nearly chaotic. The emission-lineknots also follow a general trend of decreasing velocity dispersion withincreasing distance from the nucleus. In the Seyfert 2 galaxies, thepresence of blueshifts and redshifts on either side of the nucleusindicates that rotation alone cannot explain the observed radialvelocities. The most straightforward interpretation is that radialoutflow plays an important role in the NLR kinematics. Each of theSeyfert galaxies in this sample (with the exception of Mrk 3) shows abright, compact (FWHM<=0.5") [O III] knot at the position of itsoptical nucleus. These nuclear emission-line knots have radial velocitycentroids near zero, but they typically have the highest velocitydispersions. Their similar properties suggest that they may be a common,distinct component of the NLR.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute (STScI), which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS5-26555. These observations areassociated with proposal GO-8340.
| New H2O masers in Seyfert and FIR bright galaxies
Using the Effelsberg 100-m telescope, detections of four extragalacticwater vapor masers are reported. Isotropic luminosities are ~50, 1000, 1and 230 Lȯ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 andArp 299, respectively. Mrk 34 contains by far the most distant and oneof the most luminous water vapor megamasers so far reported in a Seyfertgalaxy. The interacting system Arp 299 appears to show two maserhotspots separated by approximately 20´´. With these newresults and even more recent data from Braatz et al. (2004, ApJ, 617,L29), the detection rate in our sample of Seyferts with known jet-NarrowLine Region interactions becomes 50% (7/14), while in star forminggalaxies with high (S100~μ m>50 Jy) far infrared fluxesthe detection rate is 22% (10/45). The jet-NLR interaction sample maynot only contain “jet-masers” but also a significant numberof accretion “disk-masers” like those seen in NGC 4258. Astatistical analysis of 53 extragalactic H2O sources (excluding theGalaxy and the Magellanic Clouds) indicates (1) that the correlationbetween IRAS Point Source and H2O luminosities, established forindividual star forming regions in the galactic disk, also holds forAGN-dominated megamaser galaxies; (2) that maser luminosities are notcorrelated with 60 μm/100 μm color temperatures; and (3) that onlya small fraction of the luminous megamasers (L_H_2O > 100Lȯ) detectable with 100-m sized telescopes have so farbeen identified. The H2O luminosity function (LF) suggests that thenumber of galaxies with 1 Lȯ < L_H_2O < 10Lȯ, the transition range between“kilomasers” (mostly star formation) and“megamasers” (active galactic nuclei), is small. The overallslope of the LF, ~-1.5, indicates that the number of detectable masersis almost independent of their luminosity. If the LF is not steepeningat very high maser luminosities and if it is possible to find suitablecandidate sources, H2O megamasers at significant redshifts should bedetectable even with present day state-of-the-art facilities.
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| Unveiling the nature of the highly obscured active galactic nucleus in NGC 5643 with XMM-Newton
We present results from an XMM-Newton observation of the nearby Seyfert2 galaxy NGC 5643. The nucleus exhibits a very flat X-ray continuumabove 2 keV, together with a prominent Kα fluorescent iron line.This indicates heavy obscuration. We measure an absorbing column densityNH in the range 6-10 × 1023 cm-2,either directly covering the nuclear emission, or covering its Comptonreflection. In the latter case, we might be observing a rather unusualgeometry for the absorber, whereby reflection from the inner far side ofa torus is in turn obscured by its near side outer atmosphere. Thenuclear emission might be then either covered by a Compton-thickabsorber, or undergoing a transient state of low activity. A secondsource (christened `X-1' in this paper) at the outskirts of the NGC 5643optical surface outshines the nucleus in X-rays. If belonging to NGC5643, it is the third brightest (LX~ 4 ×1040 erg s-1) known ultraluminous X-ray source.Comparison with past large aperture spectra of NGC 5643 unveils dramaticX-ray spectral changes above 1 keV. We interpret these as due tovariability of the active nucleus and of source X-1 intrinsic X-raypowers by factors of >=10 and 5, respectively.
| The star formation history of Seyfert 2 nuclei
We present a study of the stellar populations in the central ~200 pc ofa large and homogeneous sample comprising 79 nearby galaxies, most ofwhich are Seyfert 2s. The star formation history of these nuclei isreconstructed by means of state-of-the-art population synthesismodelling of their spectra in the 3500-5200 Åinterval. Aquasar-like featureless continuum (FC) is added to the models to accountfor possible scattered light from a hidden active galactic nucleus(AGN).We find the following. (1) The star formation history of Seyfert 2nuclei is remarkably heterogeneous: young starbursts, intermediate-ageand old stellar populations all appear in significant and widely varyingproportions. (2) A significant fraction of the nuclei show a strong FCcomponent, but this FC is not always an indication of a hidden AGN: itcan also betray the presence of a young, dusty starburst. (3) We detectweak broad Hβ emission in several Seyfert 2s after cleaning theobserved spectrum by subtracting the synthesis model. These are mostlikely the weak scattered lines from the hidden broad-line regionenvisaged in the unified model, given that in most of these casesindependent spectropolarimetry data find a hidden Seyfert 1. (4) The FCstrengths obtained by the spectral decomposition are substantiallylarger for the Seyfert 2s which present evidence of broad lines,implying that the scattered non-stellar continuum is also detected. (5)There is no correlation between the star formation in the nucleus andeither the central or overall morphology of the parent galaxies.
| Dusty, Radiation Pressure-Dominated Photoionization. II. Multiwavelength Emission Line Diagnostics for Narrow-Line Regions
Seyfert narrow-line region (NLR) emission line ratios are remarkablyuniform, displaying only ~0.5 dex variation between galaxies, and evenless within an individual object. Previous photoionization and shockmodels of this region were unable to explain this observation withoutthe introduction of arbitrary assumptions or additional parameters.Dusty, radiation pressure-dominated photoionization models provide asimple physical mechanism that can reproduce this spectral uniformitybetween different objects. In the first paper of this series, wedescribed this model and its implementation in detail, as well aspresenting grids of model emission lines and examining the modelstructures. Here we explore these models further, demonstrating theirability to reproduce the observed Seyfert line ratios on standard linediagnostic diagrams in both the optical and UV. We also investigate theeffects that the variation of metallicity, density, and ionizingspectrum have upon both the new paradigm and the standardphotoionization models used hitherto. Along with the standard diagnosticdiagrams we provide several new diagnostic diagrams in the UV, optical,and IR. These new diagrams can provide further tests of the dusty,radiation pressure photoionization paradigm as well as being used asdiagnostics of the metallicity, density, and ionizing spectrum of theemission line clouds.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Emission Line Properties of Active Galactic Nuclei from a Post-COSTAR Hubble Space Telescope Faint Object Spectrograph Spectral Atlas
We present consistent emission-line measurements for active galacticnuclei (AGNs), useful for reliable statistical studies of emission lineproperties. This paper joins a series including similar measurements of993 spectra from the Large Bright Quasar Survey and 174 spectra of AGNsobtained from the Faint Object Spectrograph (FOS) on the Hubble SpaceTelescope (HST) prior to the installation of COSTAR. This time weconcentrate on 220 spectra obtained with the FOS after the installationof COSTAR, completing the emission line analysis of all FOS archivalspectra. We use the same automated technique as in previous papers,which accounts for Galactic extinction, models blended optical and UViron emission, includes Galactic and intrinsic absorption lines, andmodels emission lines using multiple Gaussians. We present UV andoptical emission line parameters (equivalent widths, fluxes, FWHM, andline positions) for a large number (28) of emission lines includingupper limits for undetected lines. Further scientific analyses will bepresented in subsequent papers.
| Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
| Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?
Infrared (IR) emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 μmare generally attributed to IR fluorescence from (mainly)far-ultraviolet (FUV) pumped large polycyclic aromatic hydrocarbon (PAH)molecules. As such, these features trace the FUV stellar flux and arethus a measure of star formation. We examined the IR spectralcharacteristics of Galactic massive star-forming regions and of normaland starburst galaxies, as well as active galactic nuclei (AGNs) andultraluminous infrared galaxies (ULIRGs). The goal of this study is toanalyze whether PAH features are a good qualitative and/or quantitativetracer of star formation, and hence to evaluate the application of PAHemission as a diagnostic tool in order to identify the dominantprocesses contributing to the infrared emission from Seyfert galaxiesand ULIRGs. We develop a new mid-infrared (MIR)/far-infrared (FIR)diagnostic diagram based on our Galactic sample and compare it to thediagnostic tools of Genzel and coworkers and Laurent and coworkers, withthese diagnostic tools also applied to our Galactic sample. This MIR/FIRdiagnostic is derived from the FIR normalized 6.2 μm PAH flux and theFIR normalized 6.2 μm continuum flux. Within this diagram, theGalactic sources form a sequence spanning a range of 3 orders ofmagnitude in these ratios, ranging from embedded compact H II regions toexposed photodissociation regions (PDRs) and the (diffuse) interstellarmedium (ISM). However, the variation in the 6.2 μm PAHfeature-to-continuum ratio is relative small. Comparison of ourextragalactic sample with our Galactic sources revealed an excellentresemblance of normal and starburst galaxies to exposed PDRs. WhileSeyfert 2 galaxies coincide with the starburst trend, Seyfert 1 galaxiesare displaced by at least a factor of 10 in 6.2 μm continuum flux, inaccordance with general orientation-dependent unification schemes forAGNs. ULIRGs show a diverse spectral appearance. Some show a typical AGNhot dust continuum. More, however, either are starburst-like or showsigns of strong dust obscuration in the nucleus. One characteristic ofthe ULIRGs also seems to be the presence of more prominent FIR emissionthan either starburst galaxies or AGNs. We discuss the observedvariation in the Galactic sample in view of the evolutionary state andthe PAH/dust abundance and discuss the use of PAHs as quantitativetracers of star formation activity. Based on these investigations, wefind that PAHs may be better suited as a tracer of B stars, whichdominate the Galactic stellar energy budget, than as a tracer of massivestar formation (O stars).
| Spiral galaxies observed in the near-infrared K band. I. Data analysis and structural parameters
Deep surface photometry in the K band was obtained for 54 normal spiralgalaxies, with the aim of quantifying the percentage of faint bars andstudying the morphology of spiral arms. The sample was chosen to cover awider range of morphological types while inclination angles anddistances were limited to allow a detailed investigation of the internalstructure of their disks and future observations and studies of the diskkinematics. An additional constraint for a well defined subsample wasthat no bar structure was seen on images in the visual bands. Accuratesky projection parameters were determined from the K maps comparingseveral different methods. The surface brightness distribution wasdecomposed into axisymmetric components while bars and spiral structureswere analyzed using Fourier techniques.Bulges were best represented by a Sérsic r1/n law withan index in the typical range of 1-2. The central surface brightness ofthe exponential disk and bulge-to-disk ratio only showed weakcorrelation with Hubble type. Indications of a central point source werefound in many of the galaxies. An additional central, steep, exponentialdisk improved the fit for more than 80% of the galaxies suggesting thatmany of the bulges are oblate.Bars down to the detection level at a relative amplitude of 3% weredetected in 26 of 30 galaxies in a subsample classified as ordinary SAspirals. This would correspond to only 5% of all spiral galaxies beingnon-barred at this level. In several cases, bars are significantlyoffset compared to the starting points of the main spiral pattern whichindicates that bar and spiral have different pattern speeds. A smallfraction (10%) of the sample has complex central structuresconsisting of several sets of bars, arcs or spirals.A majority of the galaxies (60%) displays a two-armed, grand-designspiral pattern in their inner parts which often breaks up into multiplearms in their outer regions. Phase shifts between the inner and outerpatterns suggest in some cases that they belong to different spiralmodes. The pitch angles of the main two-armed symmetric spiral patternin the galaxies have a typical range of 5-30 °. The sample shows alack of strong, tight spirals which could indicate that such patternsare damped by non-linear, dynamical effects due to their high radialforce perturbations.Based on observations collected at the European Southern Observatory, LaSilla, Chile; programs: ESO 63.N-0343, 65.N-0287, 66.N-0257.Table 2 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/849Appendix A is only available in electronic form athttp://www.edpsciences.org
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Deprojecting spiral galaxies using Fourier analysis. Application to the Ohio sample
We use two new methods developed recently (Barberàet al.\cite{bar03}, A&A, 415, 849), as well as information obtained fromthe literature, to calculate the orientation parameters of the spiralgalaxies in the Ohio State University Bright Galaxy Survey. We comparethe results of these methods with data from the literature, and find ingeneral good agreement. We provide a homogeneous set of mean orientationparameters which can be used to approximately deproject the disks of thegalaxies and facilitate a number of statistical studies of galaxyproperties.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/421/595
| The relation between AGN hard X-ray emission and mid-infrared continuum from ISO spectra: Scatter and unification aspects
We use mid-infrared spectral decomposition to separate the 6 μmmid-infrared AGN continuum from the host emission in the ISO lowresolution spectra of 71 active galaxies and compare the results toobserved and intrinsic 2-10 keV hard X-ray fluxes from the literature.We find a correlation between mid-infrared luminosity and absorptioncorrected hard X-ray luminosity, but the scatter is about an order ofmagnitude, significantly larger than previously found with smallerstatistics. Main contributors to this scatter are likely variations inthe geometry of absorbing dust, and AGN variability in combination withnon-simultaneous observations. There is no significant differencebetween type 1 and type 2 objects in the average ratio of mid-infraredand hard X-ray emission, a result which is not consistent with the mostsimple version of a unified scheme in which an optically andgeometrically thick torus dominates the mid-infrared AGN continuum. Mostprobably, significant non-torus contributions to the AGN mid-IRcontinuum are masking the expected difference between the two types ofAGN.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/465Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries: France, Germany, TheNetherlands, and the UK) with the participation of ISAS and NASA.
| A joint mid-infrared spectroscopic and X-ray imaging investigation of LINER galaxies
We present a comprehensive comparative high resolution mid-IRspectroscopic and X-ray imaging investigation of LINERs using archivalobservations from the ISO-SWS and the Chandra Advanced CCD ImagingSpectrometer. Although the sample is heterogenous and incomplete, thisis the first comprehensive study of the mid-infrared fine structure lineemission of LINERs. These results have been compared with similarobservations of starburst galaxies and AGN. We find that LINERs veryclearly fall between starbursts and AGN in their mid-IR fine structureline spectra, showing L[OIV]26 μm/LFIR andL[OIV]26 μm/L[NeII]12.8 μm ratios, bothmeasures of the dominant nuclear energy source in dust-enshroudedgalaxies, intermediate between those of AGN and starbursts. Chandraimaging observations of the LINERs reveal hard nuclear point sourcesmorphologically consistent with AGN in most (67%) of the sample, with aclear trend with IR-brightness. Most LINERs that show a single dominanthard compact X-ray core are IR-faint (LFIR/LB <1), whereas most LINERs that show scattered X-ray sources are IR-bright.A comparative X-ray/mid-IR spectroscopic investigation of LINERs revealssome puzzling results. Objects that display strong hard nuclear X-raycores should also display high excitation lines in the IR. However, wefind two LINERs disagree with this expectation. The galaxy NGC 404 showsweak soft X-ray emission consistent with a starburst but has the mostprominent highest excitation mid-IR spectrum of our entire sample. UsingIR emission line diagnostics alone, this galaxy would be classified ashosting a dominant AGN. Conversely, the IR luminous LINER NGC 6240 hasan extremely luminous binary AGN as revealed by the X-rays but showsweak IR emission lines. With the advent of SIRTF, and future IR missionssuch as Herschel and JWST, it is increasingly critical to determine theorigin of these multiwavelength anomalies.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/825Table 3 is only available in electronic form athttp://www.edpsciences.org
| Mid-infrared emission of galactic nuclei. TIMMI2 versus ISO observations and models
We investigate the mid-infrared radiation of galaxies that are poweredby a starburst or by an AGN. For this end, we compare the spectraobtained at different spatial scales in a sample of infrared brightgalaxies. ISO observations which include emission of the nucleus as wellas most of the host galaxy are compared with TIMMI2 spectra of thenuclear region. We find that ISO spectra are generally dominated bystrong PAH bands. However, this is no longer true when inspecting themid-infrared emission of the pure nucleus. Here PAH emission is detectedin starbursts whereas it is significantly reduced or completely absentin AGNs. A physical explanation of these new observational results ispresented by examining the temperature fluctuation of a PAH afterinteraction with a photon. It turns out that the hardness of theradiation field is a key parameter for quantifying the photo-destructionof small grains. Our theoretical study predicts PAH evaporation in softX-ray environments. Radiative transfer calculations of clumpy starburstsand AGN corroborate the observational fact that PAH emission isconnected to starburst activity whereas PAHs are destroyed near an AGN.The radiative transfer models predict for starbursts a much largermid-infrared size than for AGN. This is confirmed by our TIMMI2acquisition images: We find that the mid-infrared emission of Seyfertsis dominated by a compact core while most of the starbursts arespatially resolved.Based on ESO: 68.B-0066(A) and observations with ISO, an ESA projectwith instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) with theparticipation of ISAS and NASA.}
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