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The Unified Model of Active Galactic Nuclei. I. Non-Hidden Broad-Line Region Seyfert 2 and Narrow-Line Seyfert 1 Galaxies
The unified model of Seyfert galaxies suggests that there are hiddenbroad-line regions (HBLRs) in Seyfert 2 galaxies (S2s). However, thereis increasing evidence for the appearance of a subclass of S2s lackingHBLRs (non-HBLR S2s). An interesting issue arises as to the relations ofnon-HBLR S2s with other types of Seyfert galaxies and whether or notthey can be included in the unified model. We assemble two subsamplesconsisting of 42 non-HBLR S2s and 44 narrow-line Seyfert 1 galaxies(NLS1s) with redshift z<=0.05 from published literatures to explorethis issue. We compare black hole masses in the galactic centers,accretion rates, and infrared color ratio(f60μm/f25μm) as a potential indicator ofthe dusty torus orientation, [O III] λ5007, radio, andfar-infrared luminosities. We find that non-HBLR S2s and NLS1s have (1)similar distributions of black hole masses [(0.1-3)×107Msolar] and Eddington ratios(LBol/LEdd~1) (2) significantly differentdistributions of f60μm/f25μm ratios; and (3)similar distributions of bulge magnitudes and luminosities of [O III],radio, and far-infrared emission. The similarities and differences canbe understood naturally if they are intrinsically the same, but non-HBLRS2s are viewed at larger angles of the observer's sight than NLS1s. Wethus suggest that non-HBLR S2s only have ``narrower'' broad-line regionsand that they are the counterparts of NLS1s viewed at high inclinationangles. The absence of the polarized emission line in non-HBLR S2s iscaused by the less massive black holes and high accretion rate similarto NLS1s. The implications of the unification scheme of non-HBLR S2s andNLS1s are discussed.
| X-ray surveys and wide-field optical/near-infrared imaging with JDEM
I briefly describe a few important scientific issues that could beaddressed effectively via the combination of data from JDEM and X-raymissions. The topics covered are largely focused on active galacticnuclei (AGN) and include (1) the selection of AGN via X-ray emission andoptical variability, (2) nuclear outbursts in galaxies due to transientfueling of their supermassive black holes, (3) moderate-luminosity AGNat high redshift (z > 4) found via application of“dropout” techniques to X-ray sources, and (4) thehost-galaxy morphologies of X-ray selected AGN. I also describe thesubstantial challenges to obtaining wide-field X-ray data withsufficient sensitivity to complement JDEM properly.
| Stellar velocity dispersion in narrow-line Seyfert 1 galaxies
Several authors have recently explored, for narrow-line Seyfert 1galaxies (NLS1s), the relationship between black hole mass(MBH) and stellar velocity dispersion (σ*).Their results are more or less in agreement and seem to indicate thatNLS1s fill the region below the fit obtained by Tremaine et al., showinga range of σ* similar to that of Seyfert 1 galaxies,and a lower MBH. Until now, the [OIII] width has been used inplace of the stellar velocity dispersion, but some indications havebegun to arise against the effectiveness of the gaseous kinematics inrepresenting the bulge potential, at least in NLS1s. Bian & Zhaohave stressed the urgency of producing true σ*measurements. Here, we present new stellar velocity dispersions obtainedthrough direct measurements of the CaII absorption triplet (~8550Å) in the nuclei of eight NLS1 galaxies. The resultingσ* values and a comparison withσ[OIII] confirm our suspicion that [OIII] typicallyoverestimates the stellar velocity dispersion. We demonstrate that NLS1sfollow the MBH-σ* relation as Seyfert 1,quasars and non-active galaxies.
| Chandra observations of five X-ray transient galactic nuclei
We report on exploratory Chandra observations of five galactic nucleithat were found to be X-ray bright during the ROSAT All-Sky Survey (withLX>~ 1043 erg s-1) but subsequentlyexhibited a dramatic decline in X-ray luminosity. Very little is knownabout the post-outburst X-ray properties of these enigmatic sources. Inall five cases Chandra detects an X-ray source positionally coincidentwith the nucleus of the host galaxy. The spectrum of the brightestsource (IC 3599) appears consistent with a steep power law (Γ~3.6). The other sources have too few counts to extract individual,well-determined spectra, but their X-ray spectra appear flatter(Γ~ 2) on average. The Chandra fluxes are~102-103 fainter than was observed during theoutburst (up to 12 yr previously). That all post-outburst X-rayobservations have seen a similarly low X-ray luminosities is consistentwith these sources having `switched' to a persistent low-luminositystate. Unfortunately the relative dearth of long-term monitoring andother data mean that the physical mechanism responsible for thisspectacular behaviour is still highly unconstrained.
| Chandra Observations of the Narrow-Line Seyfert 1 Galaxy RX J2217.9-5941
We report the results of two Chandra ACIS-S observations from 2003February and August of the highly X-ray variable narrow-line Seyfert 1galaxy RX J2217.9-5941. Observations spanning the time from the ROSATAll-Sky Survey (RASS) through an ASCA observation in 1998 indicateapparently monotonically decreasing flux by a factor of 30. The Chandraobservations reveal increased emission over that seen with ASCA,supporting a persistent variability rather than an X-ray outburst event.However, the cause of the strong X-ray variability remains unclear. OurChandra observations confirm the steep soft X-ray spectrum in the0.2-2.0 keV band found during the RASS observation(αX=2.7). The spectral shape of the source appears tobe variable, with the spectrum becoming softer when the source becomesfainter. Best-fitting models to the data include an absorbed brokenpower law, a blackbody plus a power law, and a power law with partialcovering absorption. The latter model suggests a variable partialcovering absorber in the line of sight, which can explain in part thevariability seen in RX J2217.9-5941. We suggest that there might be apopulation of narrow-line Seyfert 1 galaxies that are, at least attimes, highly absorbed.
| Exploring Narrow-Line Seyfert 1 Galaxies through the Physical Properties of Their Hosts
In this work we address the still open question of the nature ofnarrow-line Seyfert 1 galaxies (NLS1s): are they really active nucleiwith lower mass black holes (BHs) than Seyfert 1 galaxies (S1s) andquasars? Our approach is based on the recently discovered physicalconnections between nuclear supermassive BHs and their hosting spheroids(spiral bulges or elliptical galaxies). In particular, we compare BHmasses of NLS1s and S1s, analyzing the properties of their hosts bymeans of spectroscopic and photometric data in the optical wavelengthdomain. We find that NLS1s fill the low BH mass and bulge luminosityvalues of the MBH-MB relation, a result stronglysuggesting that NLS1s are active nuclei in which less massive BHs arehosted by less massive bulges. The correlation is good, with arelatively small scatter fitting simultaneously NLS1s, S1s, and quasars.On the other hand, NLS1s seem to share the same stellar velocitydispersion range as S1s in the MBH-σ*relation, indicating that NLS1s have a smaller BH/bulge mass ratio thanS1s. These two conflicting results support in any case the idea thatNLS1s could be young S1s. Finally, we do not confirm the significantlynonlinear BH-bulge relation claimed by some authors.Partially based on observations made with the Asiago 1.82 m telescope ofthe Padova Astronomical Observatory.
| A Complete Sample of Soft X-Ray-selected AGNs. II. Statistical Analysis
Direct correlations and a principal component analysis (PCA) arepresented for a complete sample of 110 soft X-ray-selected AGNs, ofwhich about half are narrow-line Seyfert 1 galaxies (NLS1's). The directcorrelation analyses show that narrower FWHM(Hβ) correlates withsteeper X-ray spectrum, stronger optical Fe II emission, weaker [O III]emission and stronger short-term X-ray variability. This directcorrelation analysis and the PCA confirm the Boroson & Green (1992)eigenvector 1 relationship for AGNs: Fe II strength anticorrelates with[O III] line strength. Eigenvector 1 is well correlated with theEddington luminosity ratio L/LEdd, while eigenvector 2 showsa very good correlation with the mass of the central black holeMBH and the mass accretion rate M. The Eddington ratioL/LEdd correlates with the X-ray spectral indexαX and the black home mass MBHanticorrelates with the X-ray variability χ2/ν. TheEddington ratio L/LEdd may be interpreted as the age of anAGN: AGNs with steep X-ray spectra, strong Fe II, and weak [O III] areAGNs in an early phase of their evolution. In this hypothesis, NLS1'sare young AGNs.Based in part on observations at the European Southern Observatory LaSilla (Chile) with the 2.2 m telescope of the Max Planck Society duringMPI and ESO time and the ESO 1.52 m telescope during ESO time in 1995September and 1999 September.
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| Comptonization in Super-Eddington Accretion Flow and Growth Timescale of Supermassive Black Holes
Super-Eddington accretion onto black holes (BHs) may occur atultraluminous compact X-ray sources in nearby galaxies, Galacticmicroquasars, and narrow-line Seyfert 1 galaxies (NLS1s). Effects ofelectron scattering (opacity and Comptonization) and the relativisticcorrection (gravitational redshift and transverse Doppler effect) on theemergent spectra from super-Eddington accretion flows onto nonrotatingBHs are examined for 101.5 and 106.5Msolar BH masses (MBH). Withm[≡M/(LEdd/c2)]>=100 (where M is theaccretion rate), the spectral hardening factor via electron scatteringis <~2.3-6.5. As a result of the m-sensitive hardening factor, thecolor temperature of the innermost radiation is not proportional toL0.25, differing from the simplest standard accretion disk.The model is applied to optical-soft X-ray emission from NLS1s. We pickup one NLS1, namely, PG 1448+273 with an inferred MBH of106.4 Msolar, among the highest m candidates. Thebroadband spectral distribution is successfully reproduced by the modelwith an extremely high m (=1000) and the viscosity parameter α of0.01. This implies that this object, as well as some other highest msystems, is really young: the inferred age, MBH/M, is about106 yr. We also briefly discuss the distribution of m fortransient and highly variable NLS1s, finding that those are located at3<~m<~300. Such a moderately high accretion rate is indicative ofthermal instability. Furthermore, m for a possible type 2 counterpart ofNLS1s, NGC 1068, is found to be similar to m for NLS1s.
| Follow-Up Hubble Space Telescope/Space Telescope Imaging Spectroscopy of Three Candidate Tidal Disruption Events
Large-amplitude, high-luminosity, soft X-ray flares were detected by theROSAT All-Sky Survey in several galaxies with no evidence for Seyfertactivity in their ground-based optical spectra. These flares had theproperties predicted for a tidal disruption event by a centralsupermassive black hole: soft X-ray spectrum, timescale of months, andlarge X-ray luminosity (1042-1044 ergss-1). In order to evaluate the alternative hypothesis thatthese flares could have been some form of extreme active galacticnucleus variability, we obtained follow-up optical spectroscopy of threeof the flaring galaxies a decade later with the Space Telescope ImagingSpectrograph and a narrow slit to search for or place stringent limitson the presence of any persistent Seyfert-like emission in their nuclei.Two of the galaxies, RX J1624.9+7554 and RX J1242.6-1119, show neitherevidence for emission lines nor a nonstellar continuum in their HubbleSpace Telescope nuclear spectra, consistent with their ground-basedclassification as inactive galaxies. They remain the most convincing ashosts of tidal disruption events. NGC 5905, previously known as astarburst H II galaxy due to its strong emission lines, has in its inner0.1" a nucleus with narrow emission line ratios requiring a Seyfert 2classification. This weak Seyfert 2 nucleus in NGC 5905, which wasmasked by the many surrounding H II regions in ground-based spectra,requires a low level of prior nonstellar photoionization, thus raisingsome uncertainty about the nature of its X-ray flare, which may or maynot have been a tidal disruption event. The absence of both broademission lines and nuclear X-ray absorption in NGC 5905 alsocharacterizes it as a true Seyfert 2 galaxy, yet one that has varied bymore than a factor of 100 in X-rays.On the basis of observations with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555. These observations are associated withproposal 9177.
| X-Ray-Luminous Galaxies. I. Chandra Observations of IRAS 00317-2142
We present Chandra observations of the enigmatic galaxy IRAS 00317-2142,which is classified as a star-forming galaxy on the basis of theionization level of its emission lines. However, a weak broad Hαwing and a high X-ray luminosity give away the presence of an activenucleus. The Chandra image reveals a nuclear point source(L(2-10keV)~6×1041ergss-1),contributing over 80% of the galaxy X-ray counts in the 0.3-8 keV band.This is surrounded by some fainter nebulosity extending up to 6 kpc. Thenucleus does not show evidence for short-term variability. However, wedetect long-term variations between the ROSAT, ASCA, and Chandra epochs.Indeed, the source has decreased its flux by over a factor of 25 in aperiod of about 10 yr. The nuclear X-ray spectrum is well represented bya power law with a photon index ofΓ=1.91+0.17-0.15, while the extendedemission is represented by a Raymond-Smith component with a temperatureof ~0.6 keV. We find no evidence for the presence of an Fe line. Thenucleus is absorbed by an intrinsic column density ofNH~8×1020cm-2. Thus, the Chandraobservations suggest that at least the X-ray emission is dominated by atype 1 active galactic nucleus (AGN). Then the observed optical spectrumcan be explained by the masking of the nucleus by the powerfulstar-forming component. These, together with previous X-ray observationsof galaxies with no clear signs of AGN activity in the optical (e.g.,NGC 6240), cast doubt on the optical classification scheme and haveimplications for the nature of the ``normal'' galaxies detected in deepChandra X-ray surveys.
| Frequency of X-ray transients in galactic nuclei
Not Available
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| Properties of Broad Band Continuum of Narrow Line Seyfert 1 Galaxies
We have performed a statistical study of the properties of the broadband continuum of Narrow Line Seyfert 1 galaxies (NLS1s) by collectingratio, infrared, optical and X-ray continuum data from various databasesand compared the results with control samples of Broad Line Seyfert 1galaxies (BLS1s). We find that the fraction ( 6%) of Radio Loud(RL) NLS1s is significantly less than that of BLS1s ( 13%), whichis caused by the lack of radio-very-loud sources in the former. Therarity of RL NLS1s, especially radio-very-loud ones, is consistent withthe scenario of small black hole and high accretion rate for NLS1s. Sixnew radio loud NLS1s are found and five RL NLS1 candidates arepresented. In comparison with the BLS1s, the NLS1s tend to havestronger far infrared emission, cooler infrared colors and redder B-Kcolor, which suggests that NLS1s are hosted by dust-richer nuclei. TheNLS1s also show steeper soft X-ray spectrum and large soft X-ray tooptical flux ratio, while a significant fraction show flat soft X-ray spectra. At least two factors can account for this, absorption andspectral variability. We also perform a correlation analysis betweenvarious broad band data. It is found that most correlations identifiedfor NLS1s are also valid for radio quiet BLS1s: (1) the optical colorsare anti-correlated with X-ray spectral index; (2) higher optical, X-rayand NIR luminosity objects show bluer optical colors and red H-K color;(3) higher luminosity objects show warmer IRAS color; (4) the radioloudness correlates with B-K and X-ray to optical flux ratio. Radio loudobjects behave somewhat differently in a few correlations.
| Large-Amplitude X-Ray Outbursts from Galactic Nuclei: A Systematic Survey using ROSAT Archival Data
In recent years, luminous X-ray outbursts with variability amplitudes ashigh as ~400 have been serendipitously detected from a small number ofactive and inactive galaxies. These outbursts may result from the tidaldisruptions of stars by supermassive black holes, as well as accretiondisk instabilities. In order to place the first reliable constraints onthe rate of such outbursts in the universe and to test the stellar tidaldisruption hypothesis, we have performed a systematic and completesurvey for them by cross-correlating ROSAT All-Sky Survey (RASS) andpointed Position Sensitive Proportional Counter data. We have detectedfive galaxies that were in outburst during the RASS, three of which showno signs of nuclear activity; these objects had been reported onindividually in previous studies. After making reasonable correctionsfor the complicated selection effects, we conclude that the rate oflarge-amplitude X-ray outbursts from inactive galaxies in the localuniverse is ~9.1×10-6 galaxy-1yr-1. This rate is consistent with the predicted rate ofstellar tidal disruption events in such galaxies. When only the twoactive galaxies are considered, we find a rate for active galaxies of~8.5×10-4 galaxy-1 yr-1. In orderto place tighter constraints on these rates, additional outbursts mustbe detected.
| Near infrared observations of soft X-ray selected AGN
We report the results of near infrared observations of 19 soft X-rayselected AGN. The goal of the observations was to search for strong,narrow Paalpha or Brgamma emission lines, as a sign of nuclearstarbursts. We found Paalpha emission in the spectra of 11 sources andBrgamma in at least five. Strong NIR emission has been found in twosources, CBS 126 and Mkn 766, both objects with strong [OIII]lambda 5007emission, weak Fe II emission and wavelength dependent degree ofpolarization in the optical. Classical Narrow Line Seyfert 1 galaxies donot show exceptionally strong NIR emission lines. We present the resultsof our study and discuss how our findings fit into an evolutionaryscheme of AGN. Based on observations performed at the 2.7 m telescope ofthe McDonald Observatory, Texas.
| A complete sample of Seyfert galaxies selected at 0.25 keV
We have used the ROSAT Bright Source Catalogue to extract a completesample of sources selected in the band from 0.1-0.4keV. This0.25keV-selected sample is composed of 54 Seyfert galaxies, 25 BLLacertae objects, 4 clusters and 27 Galactic stars or binaries.Seyfert-type galaxies with `ultrasoft' X-ray spectra can very often beclassed optically as narrow-line Seyfert 1s (NLS1s). Such objects arereadily detected in 0.25keV surveys; the sample reported here contains20 NLS1s, corresponding to a 40 per cent fraction of the Seyferts.Optical spectra of the Seyfert galaxies were gathered for correlativeanalysis, which confirmed the well-known relations between X-ray slopeand optical spectral properties (e.g. [Oiii]/Hβ ratio; Feiistrength, Hβ width). The various intercorrelations are most likelydriven, fundamentally, by the shape of the photoionizing continuum inSeyfert nuclei. We argue that a steep X-ray spectrum is a betterindicator of an `extreme' set of physical properties in Seyfert galaxiesthan is the narrowness of the optical Hβ line. The correlationstudies were also used to isolate a number of Seyfert galaxies withapparently `anomalous' properties. Of particular interest are the sixobjects with relatively weak permitted line emission (Hβ and Feii)and weak optical continua. Such objects are rare in most surveys, buttwo of these (IC 3599 and NGC 5905) are known to be transient activegalactic nuclei in which the X-ray flux has faded by factors ~100. Ifthe other four objects also turn out to be transient, this woulddemonstrate that 0.25keV surveys provide an efficient way of finding aninteresting class of object. Finally, the luminosity function of the0.25keV-selected Seyfert galaxies was determined and broken down intosubsamples to investigate the relative space densities of Seyferts whenseparated on the basis of either X-ray slope or Hβ linewidth.
| RE J2248-511: not all variable, ultrasoft, X-ray AGN have narrow Balmer lines
We present ASCA data on RE J2248-511, extending existing optical andsoft X-ray coverage to 10keV, and monitoring the soft component. Thesedata show that, despite a very strong ultrasoft X-ray excess below0.3keV and a soft 0.3-2keV spectral index in earlier ROSAT data, thehard X-ray spectrum (α~-0.8 0.6-10keV) is typical of type 1 activegalactic nuclei (AGN), and the soft component has since disappeared.Optical data taken at two different epochs show that the big blue bumpis also highly variable. The strength of the ultrasoft X-ray componentand the extreme variability in RE J2248-511 are reminiscent of thebehaviour observed in many narrow line Seyfert 1s (NLS1s). However, thehigh-energy end of the ROSAT spectrum, the ASCA spectrum and the Balmerline full widths at half maximum of ~3000kms-1 in REJ2248-511 are typical of normal Seyfert 1 AGN. The change in the softX-ray spectrum as observed in the ROSAT and ASCA data is consistent withthe behaviour of Galactic Black Hole Candidates (GBHCs) as they movefrom a high to a low state, i.e. a fall in the ultrasoft component and ahardening of the X-ray continuum. This GBHC analogy has also beenproposed for NLS1s. Alternatively, the variability may be caused byopacity changes in a hot, optically thin corona which surrounds a cold,dense accretion disc; this was first suggested by Guainazzi et al. for1H 0419-577, an object which shows remarkably similar properties to REJ2248-511.
| Host Galaxies and Circumgalactic Environment of ``Narrow Line'' Seyfert 1 Nuclei
This paper presents a statistical study of the host galaxies andenvironment for a sample of 27 ``narrow line'' Seyfert 1 (NLSy1) nuclei,based on a computer-aided search of companions in the Digitized SkySurvey. The sample includes all objects listed as NLSy1 in theVéron-Cetty & Véron catalog (8th edition) withredshift in the range 0.010<=z<=0.061 and Galactic latitude|b|>=30deg. We compared the environments of NLSy1's withthose of Seyfert 1 and Seyfert 2 galaxies using the method and theSeyfert samples employed in 1999 by Dultzin-Hacyan et al. The frequencyof ``physical'' companions was measured within a search radius equal to3 times the diameter DS of each NLSy1 and up to a projectedlinear distance of ~100 kpc. No statistical difference was found betweenthe environments of NLSy1's and those of Seyfert 1 galaxies. Our resultsfurther suggest that NLSy1 hosts may show fewer companions and may bepreferentially farther away from bright companion galaxies than normalgalaxies with similar morphological type, diameter, and redshiftdistribution. The results for host galaxies and environments help todisprove the hypothesis that NLSy1 objects have characteristics similarto those of Seyfert 2 galaxies: whereas Seyfert 2 galaxies show a highlysignificant excess of bright companions, Seyfert 1's and NLSy1's do not.The morphological distribution of NLSy1's and Seyfert 1 objects issimilar, but NLSy1 nuclei are hosted in galaxies smaller than Seyfert 1and nonactive galaxies, to a statistical confidence level of 95%. Theseresults support the interpretation of NLSy1 nuclei (suggested by X-rayobservations) as Seyfert 1 nuclei with higher Eddington ratio, sincesmaller diameter galaxies may host central black holes of lower mass.
| The harmonic power spectrum of the soft X-ray background. I. The data analysis
Fluctuations of the soft X-ray background are investigated usingharmonic analysis. A section of the ROSAT All-Sky Survey around thenorth galactic pole is used. The flux distribution is expanded into aset of harmonic functions and the power spectrum is determined. Severalsubsamples of the RASS have been used and the spectra for differentregions and energies are presented. The effects of the data binning inpixels are assessed and taken into account. The spectra of the analyzedsamples reflect both small scale effects generated by strong discretesources and the large scale gradients of the XRB distribution. Ourresults show that the power spectrum technique can be effectively usedto investigate anisotropy of the XRB at various scales. This statisticswill become a useful tool in the investigation of various XRBcomponents.
| Black hole mass and velocity dispersion of narrow line region in active galactic nuclei and narrow line Seyfert 1 galaxies
Controversy regarding whether Narrow Line Seyfert 1 galaxies (NLS1s)follow the same black hole - galactic bulge relation as normal galaxieshas been raised by Mathur et al. (\cite{Mathur01}) and Ferrarese et al.(\cite{Ferrarese01}). In this paper, the correlation between the blackhole mass and the velocity dispersion of the narrow line region,indicated by the [OIII] line width for a heterogeneous sample of NLS1s,is examined. We show that the non-virial component subtracted [OIII]width, which may well represent the stellar velocity dispersion (sigma), correlates with the estimated black hole mass MBH, madeusing the empirical law for the size of the broad line region from thereverberation mapping measurements. Considering measurement errors, wefind that the relation between MBH and the [OIII] width inactive galactic nuclei (both NLS1s in this paper and normal Seyferts inNelson \cite{Nelson00}) is consistent with that defined in nearby hotgalaxies (ellipticals and spiral bulge) but with more scatter. It seemsthat there is no clear difference in the relation between MBHand sigma (represented by the [OIII] width for AGN) in both NLS1s andnormal broad line active galactic nuclei from the same relation definedby nearby hot galaxies.
| A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies
We have compiled a list of 83 objects classified as Narrow-Line Seyfert1 galaxies (NLS1s) or known to have a broad Balmer component narrowerthan 2 000 km s-1. Of these, 19 turned out to have beenspectroscopically misidentified in previous studies; only 64 of theselected objects are genuine NLS1s. We have spectroscopically observed59 of them and tried to characterize their Narrow and Broad-Line Regions(NLR and BLR) by fitting the emission-lines with Gaussian and/orLorentzian profiles. In most cases, the broad Balmer components are wellfitted by a single Lorentzian profile, confirming previous claims thatLorentzian rather than Gaussian profiles are better suited to reproducethe shape of the NLS1s broad emission lines. This has consequencesconcerning their FWHMs and line ratios: when the broad Balmer componentsare fitted with a Lorentzian, most narrow line regions have line ratiostypical of Seyfert 2s while, when a Gaussian profile is used for fittingthe broad Balmer components, the line ratios are widely scattered in theusual diagnostic diagrams (Veilleux & Osterbrock \cite{vei87});moreover, the FWHM of the best fitting Lorentzian is systematicallysmaller than the FWHM of the Gaussian. We find that, in general, the [OIII] lines have a relatively narrow Gaussian profile ( ~ 200-500 kms-1 FWHM) with often, in addition, a second broad ( ~ 500-1800 km s-1 FWHM), blueshifted Gaussian component. We do notconfirm that the [O III] lines are weak in NLS1s. As previouslysuggested, there is a continuous transition of all properties betweenNLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limitof 2000 km s-1 used to separate the two species is arbitrary;R4570, the ratio of the Fe II to the Hβ fluxes, could bea physically more meaningful parameter to distinguish them.
| RX J2217.9-5941: A highly X-ray variable Narrow-Line Seyfert1 galaxy
We report the discovery of a highly X-ray variable AGN, RX J2217.9-5941.This object was bright during the ROSAT All-Sky Survey (RASS), duringwhich a decrease in the count rate by a factor of 12 was observed. Itwas found to be much fainter in follow-up HRI observations and istherefore an X-ray transient AGN candidate. On long time scales ofyears, its count rate decreased by a factor of about 30 between the RASSand the ROSAT HRI and ASCA observations in 1998. Analysis of the ASCAdata, complicated by source confusion and poor statistics, tentativelyindicates a steep spectrum in the faint state. There is no evidence forvariability among 5 optical observations of the object obtained between1992 and 1998. We discuss the variability of RX J2217.9-5941 and itspossible X-ray transient nature. Bases in part on observations at theEuropean Southern Observatory La Silla (Chile) with the ESO/MPG 2.2~mtelescope, the ESO 1.52~m telescope in August 1992 and September 1995,and the ESO 3.6~m in January 2001.
| X-ray variability in a complete sample of Soft X-ray selected AGN
We present ROSAT All-Sky Survey and ROSAT pointed observations (PSPC andHRI) of a complete sample of 113 bright soft X-ray AGN selected from theROSAT Bright Source Catalog. We compare these observations in order tosearch for extreme cases of flux and spectral X-ray variability - X-raytransient AGN. Three definite transients and one transient candidate arefound. The other sources show amplitude variations typically by factorsof 2-3 on timescales of years. We found that the variability strength ontimescales of days is a function of the steepness of the X-ray spectrum:steeper X-ray objects show stronger variability than flat X-ray spectrumsources. We also present new HRI measurements of our extreme X-raytransients IC 3599 and WPVS007. We discuss possible models to explainthe X-ray transience and the variabilities observed in the non-transientsources. Based in part on observations at the European SouthernObservatory La Silla (Chile) with the 2.2~m telescope of theMax-Planck-Society during MPG and ESO time and the ESO 1.52~m telescope.
| Statistical properties of narrow-line Seyfert 1 galaxies
The number of publications considering Narrow-Line Seyfert 1 galaxieshas increased dramatically in recent years. Especially after the launchof the X-ray missions ROSAT and ASCA, Narrow-Line Seyfert 1s have becomevery popular. In these proceedings I will give an overview of how theyare distributed over the electromagnetic spectrum. I will describe whatwe know about them at radio, infrared, optical, and X-ray bands, and howthey differ and how they are similar to Broad-Line Seyfert 1s. Finally Iwill introduce a method to find them with high probability.
| Tidal Disruption of a Solar-Type Star by a Supermassive Black Hole
We study the long-term evolution of a solar-type star that is beingdisrupted by a supermassive (106 Msolar) blackhole. The evolution is followed from the disruption event, which turnsthe star into a long, thin stream of gas, to the point at which some ofthis gas returns to pericenter and begins its second orbit around theblack hole. Following the evolution for this long allows us to determinethe amount of mass that is accreted by the black hole. We find thatapproximately 75% of the returning mass is not accreted but insteadbecomes unbound, following the large compression characterizing thereturn to pericenter. The impact of a tidal disruption on thesurrounding gas may therefore be like that of two consecutivesupernova-type events.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| A Search for X-ray Transient AGN
We present ROSAT All-Sky Survey and ROSAT pointed observations (PSPC andHRI) of a complete sample of 113 bright soft X-ray selected AGN. Wecompare these observations in order to search for extreme cases of fluxand spectral X-ray variability - X-ray transient AGN. Among the objectsof our sample we found three secure sources to be transients and onepossible transient candidate. The other sources show amplitudevariations typically by factors of 2-3 on timescales of days. We found atrend that sources that have become fainter in X-rays show harder X-rayspectra. We also present new HRI measurements of our extreme X-raytransients IC 3599 and WPVS007. We discuss possible models that canexplain the X-ray transience and the variabilities observed in the morecalmer sources.
| 1.65 μm (H-band) surface photometry of galaxies. III. observations of 558 galaxies with the TIRGO 1.5 m telescope
We present near-infrared H-band (1.65 μm ) surface photometry of 558galaxies in the Coma Supercluster and in the Virgo cluster. This dataset, obtained with the Arcetri NICMOS3 camera ARNICA mounted on theGornergrat Infrared Telescope, is aimed at complementing, withobservations of mostly early-type objects, our NIR survey of spiralgalaxies in these regions, presented in previous papers of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derived. We confirm the existence of apositive correlation between the near-infrared concentration index andthe galaxy H-band luminosity Based on observations taken at TIRGO(Gornergrat, Switzerland). TIRGO is operated by CAISMI-CNR, Arcetri,Firenze, Italy. Tables 1 and 2 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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