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First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151
We have recently completed a 64 night spectroscopic monitoring campaignat the Lick Observatory 3 m Shane telescope with the aim of measuringthe masses of the black holes in 13 nearby (z<0.05) Seyfert 1galaxies with expected masses in the range~106-107 Msolar. We present here thefirst results from this project-the mass of the central black hole inArp 151. Strong variability throughout the campaign led to anexceptionally clean Hβ lag measurement in this object of4.25+0.68-0.66 days in the observed frame. Coupledwith the width of the Hβ emission line in the variable spectrum, wedetermine a black hole mass of (7.1+/-1.2)×106Msolar, assuming the Onken et al. normalization forreverberation-based virial masses. We also find velocity-resolved laginformation within the Hβ emission line which clearly showsinfalling gas in the Hβ-emitting region. Further detailed analysismay lead to a full model of the geometry and kinematics of broad lineregion gas around the central black hole in Arp 151.
| A New H I Survey of Active Galaxies
We have conducted a new Arecibo survey for H I emission for 113 galaxieswith broad-line (type 1) active galactic nuclei (AGNs) out to recessionvelocities as high as ~35,000 km s-1. The primary aim of thestudy is to obtain sensitive H I spectra for a well-defined, uniformlyselected sample of active galaxies that have estimates of their blackhole masses in order to investigate correlations between H I propertiesand the characteristics of the AGNs. H I emission was detected in 66out of the 101 (65%) objects with spectra uncorrupted by radio frequencyinterference, among which 45 (68%) have line profiles with adequatesignal-to-noise ratio and sufficiently reliable inclination correctionsto yield robust deprojected rotational velocities. This paper presentsthe basic survey products, including an atlas of H I spectra,measurements of H I flux, line width, profile asymmetry, optical images,optical spectroscopic parameters, as well as a summary of a number ofderived properties pertaining to the host galaxies. To enlarge ourprimary sample, we also assemble all previously published H Imeasurements of type 1 AGNs for which we can estimate black hole masses,which total an additional 53 objects. The final comprehensivecompilation of 154 broad-line active galaxies, by far the largest sampleever studied, forms the basis of our companion paper, which uses the H Idatabase to explore a number of properties of the AGN host galaxies.
| The Steep Balmer Decrement of Quasars and Seyfert I Galaxies and its Origin
Observations of QSOs and Seyfert I galaxies show an anomalously steepBalmer decrement, which is in contradiction to the prediction of thetraditional recombination theory. This is a long standing puzzle in pastthree decades in the study of AGNs. In this paper, we provide analternative approach to solve this puzzle by using a newly recognizedline emission mechanism, namely, the “Cerenkov line-likeradiation”. For this purpose, we collected about a hundred of QSOsand Seyfert I galaxies, whose Balmer decrements have been measured andpublished in the past 30 years, and make the theoretical calculations onthe observed Balmer decrements using an improved formula for theCerenkov line intensity. The agreement between the calculations andobservations is excellent. Therefore, we argue that the broad hydrogenlines of the QSOs and Seyfert I galaxies mainly originate from theCerenkov line-like radiation of relativistic electrons. If thissuggestion is further confirmed, our knowledge about the physics of AGNswill be greatly changed.
| An Atlas of the Circumnuclear Regions of 75 Seyfert Galaxies in the Near-Ultraviolet with the Hubble Space Telescope Advanced Camera for Surveys
We present an atlas of the central regions of 75 Seyfert galaxies imagedin the near-UV with the Advanced Camera for Surveys of the Hubble SpaceTelescope at an average resolution of ~10 pc. These data complementarchival high-resolution data from the Hubble Space Telescope at opticaland near-IR wavelengths, creating an extremely valuable data set forastronomers with a broad range of scientific interests. Our goal is toinvestigate the nature of the near-UV light in these objects, itsrelation to the circumnuclear starburst phenomenon, and the connectionof this to the evolution and growth of the galaxy bulge and centralblack hole. In this paper we describe the near-UV morphology of theobjects and characterize the near-UV emission. We estimate the size andthe luminosity of the emitting regions and extract the luminosityprofile. We also determine the presence of unresolved compact nuclei. Inaddition, the circumnuclear stellar cluster population is identified,and the contribution of the stellar clusters to the total light, at thiswavelength, is estimated. The size of the sample allows us to drawrobust statistical conclusions. We find that Seyfert 1 galaxies (Sy1's)are completely dominated by their bright and compact nuclei, whichremains pointlike at this resolution, while we find almost no unresolvednuclei in Seyfert 2 galaxies (Sy2's). The Seyfert types 1 and 2 arequite segregated in an asymmetry versus compactness plot. Stellarclusters are found somewhat more frequently in Sy2's (in ~70% of thegalaxies) than in Sy1's (~57%), and contribute more to the total lightin Sy2's, but these two differences seem to be mostly due to the largecontribution of the compact nuclei in Sy1's, as the luminositydistribution of the clusters is similar in both Seyfert types.
| Sloan Digital Sky Survey Active Galactic Nuclei with X-Ray Emission from ROSAT PSPC Pointed Observations
We present a sample of 1744 type 1 active galactic nuclei (AGNs) fromthe Sloan Digital Sky Survey Data Release 4 (SDSS DR4) spectroscopiccatalog with X-ray counterparts in the White-Giommi-Angelini Catalog(WGACAT) of ROSAT PSPC pointed observations. Of 1744 X-ray sources, 1410(80.9%) are new AGN identifications. Of 4574 SDSS DR4 AGNs for which wefound radio matches in the catalog of radio sources from the FaintImages of the Radio Sky at Twenty cm survey, 224 turned up in our sampleof SDSS X-ray AGNs. The sample objects are given in a catalog thatcontains optical and X-ray parameters and supporting data, includingredshifts; it also contains radio emission parameters where available.We illustrate the content of our catalog and its potential for AGNscience by providing statistical relationships for the catalog data. Thepotential of the morphological information is emphasized by confrontingthe statistics of optically resolved, mostly low-redshift AGNs withunresolved AGNs that occupy a much wider redshift range. The immediateproperties of the catalog objects include significant correlation ofX-ray and optical fluxes, which is consistent with expectations. Alsoexpected is the decrease of X-ray flux toward higher redshifts. TheX-ray-to-optical flux ratio for the unresolved AGNs exhibits a declinetoward higher redshifts, in agreement with previous results. Theresolved AGNs, however, display the opposite trend. The X-ray hardnessratio shows a downward trend with increasing low-energy X-ray flux andno obvious dependence on redshift. At a given optical brightness, X-rayfluxes of radio-loud AGNs are, on average, higher than those ofradio-quiet AGNs by a factor of 2. We caution, however, that because ofthe variety of selection effects present in both the WGACAT and theSDSS, the interpretation of any relationships based on our sample ofX-ray AGNs requires a careful analysis of these effects.
| A catalogue of quasars and active nuclei: 12th edition
Aims.This catalogue is aimed at presenting a compilation of all knownAGN in a compact and convenient form and we hope that it will be usefulto all workers in this field.Methods.Like the eleventh edition, itincludes position and redshift as well as photometry (U, B, V) and 6 cmflux densities when available. We now give 20 cm rather than 11 cm fluxdensities.Results.The present version contains 85 221 quasars,1122 BL Lac objects and 21 737 active galaxies (including 9628 Seyfert1s), almost doubling the number listed in the 11th edition. We also givea list of all known lensed and double quasars.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| The MBH-σ* Relation in Local Active Galaxies
We examine whether active galaxies obey the same relation between blackhole mass and stellar velocity dispersion as inactive systems, using thelargest published sample of velocity dispersions for active nuclei todate. The combination of 56 original measurements with objects from theliterature not only increases the sample from the 15 consideredpreviously to 88 objects but allows us to cover an unprecedented rangein both stellar velocity dispersion (30-268 km s-1) and blackhole mass (105-108.6 Msolar). In theMBH-σ* relation of active galaxies, we finda lower zero point than the best-fit relation of Tremaine et al. forinactive galaxies, and an upper limit on the intrinsic scatter of 0.4dex. There is also evidence of a flatter slope at low black hole masses.We discuss potential contributors to the observed offsets, includingvariations in the geometry of the broad-line region, evolution in theMBH-σ* relation, and differential growthbetween black holes and galaxy bulges.
| Measuring Stellar Velocity Dispersions in Active Galaxies
We present stellar velocity dispersion (σ*)measurements for a significant sample of 40 broad-line (type 1) activegalaxies for use in testing the well-known relation black hole mass andstellar velocity dispersion. The objects are selected to contain Ca IItriplet, Mg I b triplet, and Ca H+K stellar absorption features in theiroptical spectra so that we may use them to perform extensive tests ofthe systematic biases introduced by both template mismatch andcontamination from the active galactic nucleus (AGN). We use the Ca IItriplet as a benchmark to evaluate the utility of the other spectralregions in the presence of AGN contamination. Broad Fe II emission,extending from ~5050 to 5520 Å, in combination with narrow coronalemission lines, can seriously bias σ* measurements fromthe Mg I b region, highlighting the need for extreme caution in its use.However, we argue that at luminosities constituting a moderate fractionof the Eddington limit, when the Fe II lines are both weak and smoothrelative to the stellar lines, it is possible to derive meaningfulmeasurements with careful selection of the fitting region. Inparticular, to avoid the contamination of coronal lines, we advocate theuse of the region 5250-5820 Å, which is rich in Fe absorptionfeatures. At higher AGN contaminations, the Ca H+K region may providethe only recourse for estimating σ*. These features arenotoriously unreliable, due to a strong dependence on spectral type, asteep local continuum, and large intrinsic broadening. Indeed, we find astrong systematic trend in comparisons of Ca H+K with other spectralregions. Luckily the offset is well described by a simple linear fit asa function of σ*, which enables us to remove the biasand thus extract unbiased σ* measurements from thisregion. We lay the groundwork for an extensive comparison between blackhole mass and bulge velocity dispersion in active galaxies, as describedin a companion paper by Greene & Ho.
| An atlas of calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering theregion around the λλ8498, 8542, 8662 calcium triplet(CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26Seyfert 1s, three starburst and six normal galaxies. The spectra pertainto the inner ~300 pc in radius, and thus sample the central kinematicsand stellar populations of active galaxies. The data are used to measurestellar velocity dispersions (σ*) with bothcross-correlation and direct fitting methods. These measurements arefound to be in good agreement with each other and with those in previousstudies for objects in common. The CaT equivalent width is alsomeasured. We find average values and sample dispersions ofWCaT of 4.6 +/- 2.0, 7.0 +/- 1.0 and 7.7 +/- 1.0 Å forSeyfert 1s, Seyfert 2s and normal galaxies, respectively. We furtherpresent an atlas of [SIII]λ9069 emission-line profiles for asubset of 40 galaxies. These data are analysed in a companion paperwhich addresses the connection between stellar and narrow-line regionkinematics, the behaviour of the CaT equivalent width as a function ofσ*, activity type and stellar population properties.
| The Second Byurakan Survey. General Catalogue
The Second Byurakan Survey (SBS) General Catalogue is presented. TheSBS, a continuation of the Markarian survey reaching fainter limitingmagnitudes, is the first survey which combines the search of galaxiesand QSOs. A total area of 991OS#square;degrees of the Northern sky wascovered with the use of three objective prisms in combination withSchott filters. The limited magnitude on the best plates reached B ~19.5.The General Catalogue consists of 3563 objects presented in two parts: aCatalogue of galaxies (1863 objects) and one of stellar objects (1700objects). The Catalogue of SBS AGN consists of 761 objects (155 SyG, 596QSOs, and 10 BLLac). Multi-wavelength data are presented for 1438 SBSobjects identified with X-ray, IRAS and FIRST sources.Spectrophotometric observations obtained over 26 years are available for3132 objects. Redshifts were measured for ~ 2100 extragalactic objects.Spectral classification is presented for ~ 2970 objects. The majority ofthe data is presented here for the first time. The Catalogue presentsnew large homogeneous deep representative complete samples of brightQSOs, AGNs, and faint UVX galaxies in the Northern sky. The SBS sampleis found to be complete at 70% for galaxies and ~ 85% for AGN/QSOs withB ≤ 17.5.
| 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.
| The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.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/422/941
| 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.
| Chain Galaxies in the Tadpole Advanced Camera for Surveys Field
Colors and magnitudes were determined for 69 chain galaxies, 58 otherlinear structures, 32 normal edge-on galaxies, and all of their largestar formation clumps in the Hubble Space Telescope Advanced Camera forSurveys field of the Tadpole galaxy. Redshifts of 0.5-2 are inferredfrom comparisons with published color-evolution models. The lineargalaxies have no red nuclear bulges like the normal disk galaxies in ourfield, but the star formation clumps in each have about the same colorsand magnitudes. Light profiles along the linear galaxies tend to beflat, unlike the exponential profiles of normal galaxies. Although themost extreme of the linear objects look like beaded filaments, they areall probably edge-on disks that will evolve to late Hubble typegalaxies. The lack of an exponential profile is the result of either adust scale height that is comparable to the stellar scale height or anintrinsically irregular structure. Examples of galaxies that could beface-on versions of linear galaxies are shown. They have an irregularclumpy structure with no central bulge and with clump colors andmagnitudes that are comparable to those in the linear galaxies.Radiative transfer solutions to the magnitudes and surface brightnessesof inclined dusty galaxies suggest that edge-on disks should become moreprominent near the detection limit for surface brightness. The surfacebrightness distribution of the edge-on galaxies in this field confirmthis selection effect. The star formation regions are much more massivethan in modern galaxies, averaging up to ~109Msolar for kiloparsec scales.
| Constraints on the Very High Energy Emission from BL Lacertae Objects
We present results from observations of 29 BL Lacertae objects, takenwith the Whipple Observatory 10 m gamma-ray telescope between 1995 and2000. The observed objects are mostly at low redshift (z<0.2), butobservations of objects of up to z=0.444 are also reported. Five of theobjects are EGRET sources and two are unconfirmed TeV sources. Three ofthe confirmed sources of extragalactic TeV gamma rays were originallyobserved as part of this survey and have been reported elsewhere. Nosignificant excesses are detected from any of the other objectsobserved, on timescales of days, months, or years. We report 99.9%confidence level flux upper limits for the objects for each observingseason. The flux upper limits are typically 20% of the Crab flux,although for some sources, limits as sensitive as 6% of the Crab fluxwere derived. The results are consistent with the synchrotronself-Compton model predictions considered in this work.
| 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
| Exploring the selection of galaxy clusters and groups: an optical survey for X-ray dark clusters
Data from a new, wide-field, coincident optical and X-ray survey, theX-ray Dark Cluster Survey (XDCS), are presented. This survey comprisessimultaneous and independent searches for clusters of galaxies in theoptical and X-ray passbands. Optical cluster detection algorithmsimplemented on the data are detailed. Two distinct optically selectedcatalogues are constructed, one based on I-band overdensity, the otheron overdensities of colour-selected galaxies. The superior accuracy ofthe colour-selection technique over that of the single-passband methodis demonstrated, via internal consistency checks and comparison withexternal spectroscopic redshift information. This is compared with anX-ray-selected cluster catalogue. In terms of gross numbers, the surveyyields 185 I-band-selected, 290 colour-selected and 15 X-ray-selectedsystems, residing in ~11 deg2 of optical + X-ray imaging.The relationship between optical richness/luminosity and X-rayluminosity is examined, by measuring X-ray luminosities at the positionsof our 290 colour-selected systems. Power-law correlations between theoptical richness/luminosity and X-ray luminosity are fitted, bothexhibiting approximately 0.2 dex of intrinsic scatter. Interestingoutliers in these correlations are discussed in greater detail.Spectroscopic follow-up of a subsample of X-ray underluminous systemsconfirms their reality.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Evidence for Bar-Driven Fueling
We present a study of the host galaxy morphologies of narrow- andbroad-line Seyfert 1 galaxies (NLS1's and BLS1's) based on broadbandoptical images from the Hubble Space Telescope archives. We find thatlarge-scale stellar bars, starting at ~1 kpc from the nucleus, are muchmore common in NLS1's than BLS1's. Furthermore, the fraction of NLS1spirals that have bars increases with decreasing full width athalf-maximum of the broad component of Hβ. These results suggest alink between the large-scale bars, which can support high fueling ratesto the inner kiloparsecs, and the high mass accretion rates associatedwith the supermassive black holes in NLS1's.
| 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.
| Spectroscopic study of blue compact galaxies. II. Spectral analysis and correlations
This is the second paper in a series studying the star formation rates,stellar components, metallicities, and star formation histories andevolution of a sample of blue compact galaxies. We analyzed spectralproperties of 97 blue compact galaxies, obtained with the BeijingAstronomical Observatory (China) 2.16 m telescope, with spectral range3580 Å-7400 Å. We classify the spectra according to theiremission lines: 13 of the total 97 BCG sample are non-emission linegalaxies (non-ELGs); 10 have AGN-like emission (AGNs), and 74 of themare star-forming galaxies (SFGs). Emission line fluxes and equivalentwidths, continuum fluxes, the 4000 Å Balmer break index andequivalent widths of absorption lines are measured from the spectra. Weinvestigate the emission line trends in the integrated spectra of thestar-forming galaxies in our sample, and find that: 1) The equivalentwidths of emission lines are correlated with the galaxy absolute bluemagnitude MB; lower luminosity systems tend to have largerequivalent widths. 2) The equivalent width ratio [N II]6583/Hα isanti-correlated with equivalent width Hα; a relationship is giventhat can be used to remove the [N II] contribution from blendedHα+ [N II]6548, 6583. 3) The [O II], Hβ , Hγ andHα fluxes are correlated; those can be used as star formationtracers in the blue. 4) The metallicity indices show trends with galaxyabsolute magnitude and attenuation by dust, faint, low-mass BCGs havelower metallicity and color excess. Tables 1-4, and 6 are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/396/503
| X-Ray versus Optical Observations of Active Galactic Nuclei: Evidence for Large Grains?
Recently, Maiolino et al. constructed a sample of active galactic nucleifor which both the reddening E(B-V) and the column density NHto the nucleus could be determined. For most of the galaxies in theirsample, they found that E(B-V)/NH is substantially smallerthan for the diffuse interstellar medium of our Galaxy. They assertedthat either the dust-to-gas ratio is lower than in the Galaxy or thegrains are so large that they do not extinct or redden efficiently inthe optical. We show that there is no systematic increase in E(B-V) withNH for the Maiolino et al. galaxies, which suggests that theX-ray absorption and optical extinction occur in distinct media. In alater paper, Maiolino et al. suggested that the observed lines of sightfor the previous Maiolino et al. galaxies pass through the ``torus''that obscures the broad-line region and nuclear continuum in Seyfert 2galaxies and argued that the torus grains are larger than Galacticgrains. There is no reason to believe that the lines of sight for thesegalaxies pass through the torus, since the observed column densities arelower than those typically observed in Seyfert 2 galaxies. We suggestinstead that the X-ray absorption occurs in material located off thetorus and/or accretion disk, while the optical extinction occurs inmaterial located beyond the torus. The X-ray absorbing material couldeither be dust-free or contain large grains that do not extinctefficiently in the optical. There is no conclusive evidence that thegrains in active galactic nuclei are systematically larger than those inthe diffuse interstellar medium of our Galaxy. We discuss an alternativeway to probe the properties of dust in Seyfert tori but find thatobservations of Seyfert 2 nuclei with higher resolution than currentlyavailable will be needed in order to place stringent limits on the dust.
| Spectroscopic study of blue compact galaxies. I. The spectra
Blue compact galaxies are compact objects that are dominated by intensestar formation. Most of them have dramatically different propertiescompared to the Milky Way and many other nearby galaxies. Using theIRAS, H I data, and optical spectra, we wanted to measure the currentstar formation rates, stellar components, metallicities, and starformation histories and evolution of a large blue compact galaxy sample.We anticipate that our study will be useful as a benchmark for studiesof emission line galaxies at high redshift. In the first paper of thisseries, we describe the selection, spectroscopic observation, datareduction and calibration, and spectrophotometric accuracy of a sampleof 97 luminous blue compact galaxies. We present a spectrophotometricatlas of rest-frame spectra, as well as tables of the recessionvelocities and the signal-to-noise ratios. The recession velocities ofthese galaxies are measured with an accuracy of delta V< 67 kms-1. The average signal-to-noise ratio of sample spectra is ~51. The spectral line strengths, equivalent widths and continuum fluxesare also measured for the same galaxies and will be analyzed in the nextpaper of this series. The atlas and tables of measurements will be madeavailable electronically. Table 3 and Fig. 4 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/389/845
| Where is the[O III] λ4363 Emitting Region in Active Galactic Nuclei?
The emission-line flux ratio of [O III] λ4363/[O III]λ5007 (RO III) is a useful diagnostic for theionization mechanism and physical properties of emission-line regions inactive galactic nuclei (AGNs). However, it is known that simplephotoionization models underpredict the [O III] λ4363 intensity,being inconsistent with observations. In this paper we report on severalpieces of evidence that a large fraction of the [O III] λ4363emission arises from the dense gas obscured by putative tori: (1) thevisibility of high-RO III regions is correlated to that ofbroad-line regions, (2) higher RO III objects show hottermid-infrared colors, (3) higher RO III objects show strongerhighly ionized emission lines such as [Fe VII] λ6087 and [Fe X]λ6374, and (4) higher RO III objects have broader linewidth of [O III] λ4363 normalized by that of [O III]λ5007. To estimate how such a dense component contributes to thetotal emission-line flux, dual-component photoionization modelcalculations are performed. It is shown that the observed values ofRO III of type 1 AGNs may be explained by introducing a5%-20% contribution from the dense component, while those of type 2 AGNsmay be explained by introducing a 0%-2% contribution. We also discussthe [O III] λ4363 emitting regions in LINERs in the framework ofour dual-component model.
| Soft X-ray properties of a spectroscopically selected sample of interacting and isolated Seyfert galaxies
We present a catalogue of ROSAT detected sources in the sample ofspectroscopically selected Seyfert 1 and Seyfert 2 galaxies of Rafanelliet al. (\cite{Rafanelli95}). The catalogue contains 102 Seyfert 1 and 36Seyfert 2 galaxies. The identification is based on X-ray contour mapsoverlaid on optical images taken from the Digitized Sky Survey. We havederived the basic spectral and timing properties of the X-ray detectedSeyfert galaxies. For Seyfert 1 galaxies a strong correlation betweenphoton index and X-ray luminosity is detected. We confirm the presenceof generally steeper X-ray continua in narrow-line Seyfert 1 galaxies(NLS1s) compared to broad-line Seyfert 1 galaxies. Seyfert 2 galaxiesshow photon indices similar to those of NLS1s. Whereas a tendency for anincreasing X-ray luminosity with increasing interaction strength isfound for Seyfert 1 galaxies, such a correlation is not found forSeyfert 2 galaxies. For Seyfert 1 galaxies we found also a strongcorrelation for increasing far-infrared luminosity with increasinginteraction strength. Both NLS1s and Seyfert 2 galaxies show the highestvalues of far-infrared luminosity compared to Seyfert 1 galaxies,suggesting that NLS1s and Seyfert 2 galaxies host strong (circumnuclear)star formation. For variable Seyfert galaxies we present the X-ray lightcurves obtained from the ROSAT All-Sky Survey and from ROSAT PSPC andHRI pointed observations. Besides the expected strong short- andlong-term X-ray variability in Seyfert 1 galaxies, we find indicationsfor X-ray flux variations in Seyfert 2 galaxies. All overlays can beretrieved via CDS anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)}or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/368/797
| The Multitude of Unresolved Continuum Sources at 1.6 Microns in Hubble Space Telescope Images of Seyfert Galaxies
We examine 112 Seyfert galaxies observed by the Hubble Space Telescopeat 1.6 μm. We find that ~50% of the Seyfert 2.0 galaxies which arepart of the Revised Shapely-Ames (RSA) Catalog or the CfA redshiftsample contain unresolved continuum sources at 1.6 μm. All but acouple of the Seyfert 1.0-1.9 galaxies display unresolved continuumsources. The unresolved sources have fluxes of order 1 mJy,near-infrared luminosities of order 1041 ergs s-1,and absolute magnitudes MH~-16. Comparison non-Seyfertgalaxies from the RSA Catalog display significantly fewer (~20%),somewhat lower luminosity nuclear sources, which could be due to compactstar clusters. We find that the luminosities of the unresolved Seyfert1.0-1.9 sources at 1.6 μm are correlated with [O III] λ5007and hard X-ray luminosities, implying that these sources are nonstellar.Assuming a spectral energy distribution similar to that of a Seyfert 2galaxy, we estimate that a few percent of local spiral galaxies containblack holes emitting as Seyferts at a moderate fraction,~10-1-10-4, of their Eddington luminosities. Wefind no strong correlation between 1.6 μm fluxes and hard X-ray or [OIII] λ5007 fluxes for the pure Seyfert 2.0 galaxies. Thesegalaxies also tend to have lower 1.6 μm luminosities compared to theSeyfert 1.0-1.9 galaxies of similar [O III] luminosity. Either largeextinctions (AV~20-40) are present toward theircontinuum-emitting regions or some fraction of the unresolved sources at1.6 μm are compact star clusters. With increasing Seyfert type thefraction of unresolved sources detected at 1.6 μm and the ratio of1.6 μm to [O III] fluxes tend to decrease. These trends areconsistent with the unification model for Seyfert 1 and 2 galaxies.
| The Narrow-Line Region of Seyfert Galaxies: Narrow-Line Seyfert 1 Galaxies versus Broad-Line Seyfert 1 Galaxies
It is known that the spectral energy distribution (SED) of the nuclearradiation of narrow-line Seyfert 1 galaxies (NLS1's) has differentshapes with respect to that of ordinary broad-line Seyfert 1 galaxies(BLS1's) particularly in X-ray wavelengths. This may cause somedifferences in the ionization degree and the temperature of gas innarrow-line regions (NLRs) between NLS1's and BLS1's This paper aims toexamine whether or not there are such differences in the physicalconditions of NLR gas between them. For this purpose, we have compiledthe emission-line ratios of 36 NLS1's and 83 BLS1's from the literature.Comparing these two samples, we have found that the line ratios of [O I]λ6300/[O III] λ5007 and [O III] λ4363/[O III]λ5007, which represent the ionization degree and the gastemperature respectively, are statistically indistinguishable betweenNLS1's and BLS1's. Based on new photoionization model calculations, weshow that these results are not inconsistent with the difference of theSED between them. The influence of the difference of SEDs on the highlyionized emission lines is also briefly discussed.
| Accurate optical positions for 2978 objects from the Second Byurakan Survey (SBS) with the Digitized Sky Survey
Optical positions of 2978 objects listed in the Second Byurakan Survey(SBS) were obtained using the Digitized Sky Survey (DSS), and are givenwith an rms uncertainty ~ 1 arcsec in each coordinate. Tables 1 and 2are only available in electronic form at the CDS via anonymous ftp130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| High-Ionization Nuclear Emission-Line Region of Seyfert Galaxies
Recently, Murayama & Taniguchi proposed that a significant part ofthe high-ionization nuclear emission-line region (HINER) in Seyfertnuclei arises from the inner wall of dusty tori because type 1 Seyfertnuclei (S1s) show excess HINER emission with respect to type 2 Seyfertnuclei (S2s). This means that the radiation from the HINER isanisotropic, and thus statistical properties of the HINER emission canbe used to investigate the viewing angle toward dusty tori for varioustypes of Seyfert nuclei. In order to investigate viewing angles towardnarrow-line Seyfert 1 galaxies (NLS1s) and intermediate types of Seyfertgalaxies (i.e., type 1.5, 1.8, and 1.9 Seyfert galaxies, hereafter S1.5,S1.8, and S1.9, respectively), we apply this HINER test to them. We alsoapply the same test for S2s with and without the hidden broad-lineregion. The sample of Seyfert nuclei analyzed here consists of 124Seyfert nuclei compiled from the literature. Our main results andsuggestions are as follows: (1) The NLS1s are viewed more face-on towarddusty tori than the S2s. However, the HINER properties of the NLS1s areindistinguishable from those of the S1s. (2) The S1.5s appear to composeheterogeneous populations; e.g., (a) some of them may be seen from anintermediate viewing angle between S1s and S2s, (b) some S1.5s arebasically S1s but a significant part of the broad-line region (BLR)emission is accidentally obscured by dense, clumpy gas clouds, or (c)some S1.5s are basically S2s, but a part of the BLR emission can be seenfrom some optically thin regions of the dusty torus. (3) The S1.8s, theS1.9s, and the objects showing either a broad Paβ line or polarizedbroad Balmer lines are seen from a large inclination angle, and theemission from the BLRs of such objects reaches us through optically thinparts of dusty tori. These three results support strongly the currentunified model of Seyfert nuclei. Finally, (4) the line ratios of [Fe X]λ6374 to the low-ionization emission lines are rather moreisotropic than those of [Fe VII] λ6087. Therefore, it issuggested that the [Fe X] λ6374 emission is not useful forinvestigating the viewing angle toward the dusty torus in Seyfertnuclei. The most plausible reason seems to be that the [Fe X]λ6374 emission is spatially extended, and thus its strength tendsto show less viewing-angle dependence.
| The Asiago-ESO/RASS QSO Survey. I. The Catalog and the Local QSO Luminosity Function
This paper presents the first results of a survey for bright quasars(V<14.5 and R<15.4) covering the northern hemisphere at Galacticlatitudes |b|>30°. The photometric database is derived from theGuide Star and USNO catalogs. Quasars are identified on the basis oftheir X-ray emission measured in the ROSAT All-Sky Survey. The surfacedensity of quasars brighter than 15.5 mag turns out to be(10+/-2)×10-3 deg-2, about 3 times higherthan that estimated by the PG survey. The quasar optical luminosityfunction (LF) at 0.04
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