תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Local and Large-Scale Environment of Seyfert Galaxies
We present a three-dimensional study of the local (<=100h-1 kpc) and the large-scale (<=1 h-1 Mpc)environment of the two main types of Seyfert AGN galaxies. For thispurpose we use 48 Seyfert 1 galaxies (with redshifts in the range0.007<=z<=0.036) and 56 Seyfert 2 galaxies (with0.004<=z<=0.020), located at high galactic latitudes, as well astwo control samples of nonactive galaxies having the same morphological,redshift, and diameter size distributions as the corresponding Seyfertsamples. Using the Center for Astrophysics (CfA2) and Southern SkyRedshift Survey (SSRS) galaxy catalogs (mB~15.5) and our ownspectroscopic observations (mB~18.5), we find that within aprojected distance of 100 h-1 kpc and a radial velocityseparation of δv<~600 km s-1 around each of ourAGNs, the fraction of Seyfert 2 galaxies with a close neighbor issignificantly higher than that of their control (especially within 75h-1 kpc) and Seyfert 1 galaxy samples, confirming a previoustwo-dimensional analysis of Dultzin-Hacyan et al. We also find that thelarge-scale environment around the two types of Seyfert galaxies doesnot vary with respect to their control sample galaxies. However, theSeyfert 2 and control galaxy samples do differ significantly whencompared to the corresponding Seyfert 1 samples. Since the maindifference between these samples is their morphological typedistribution, we argue that the large-scale environmental differencecannot be attributed to differences in nuclear activity but rather totheir different type of host galaxies.
| 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.
| Interstellar polarization and the position-angle orientations of type 1 Seyfert galaxies
We comment on recent spectropolarimetric studies that compare theobserved polarization position angles (PAs) of type 1 Seyfert galaxiesnear Hα with the observed orientations of their radio-source axeson the sky. For a Seyfert galaxy in which scattering occurs mainly in anequatorial scattering region, the polarization PA is expected to beparallel to the radio axis, while for a case in which light scatterspredominantly in the polar regions, the Hα polarization PA shouldbe perpendicular to the radio axis. In practice, these correlations aredifficult to establish because a Galactic interstellar polarizationcontribution can introduce a significant uncertainty into thepolarization PA determination, even when the magnitude of interstellarpolarization is small. We show how such uncertainties may affect theanalysis of PA alignments, and present spectropolarimetric observationsof a probe star along the line of sight to the type 1 Seyfert galaxy Mrk871 that allow us to assess the intrinsic Hα polarization and PAof Mrk 871. These results suggest that spectropolarimetric observationsof such probe stars should form an integral part of future polarizationstudies of Seyfert galaxies.
| 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.
| Seyferts on the edge: polar scattering and orientation-dependent polarization in Seyfert 1 nuclei
We have identified 12 Seyfert 1 galaxies that exhibit opticalpolarization spectra similar to those of Seyfert 2 galaxies in whichpolarized broad lines are detected. We present new spectropolarimetricobservations of three of them: Was 45, Mrk 231 and NGC 3227. Theseobjects appear to be polarized as a result of far-field scattering inthe polar illumination cones of the circumnuclear torus. We estimatethat they represent between 10 and 30 per cent of the Seyfert 1population; they are found amongst all the main spectroscopic subtypes,including narrow-line Seyfert 1 galaxies. We have shown elsewhere thatSeyfert 1 nuclei more commonly have polarization characteristics thatcan be attributed to scattering by a compact `equatorial' scatteringregion located inside the torus. We propose that both equatorial andpolar scattering regions are present in all Seyfert galaxies and arguethat the observed range of polarization properties can be broadlyunderstood as an orientation effect. In this scheme, polar-scatteredSeyfert 1 galaxies represent the transition between unobscured (themajority of type 1) and obscured (type 2) Seyferts. They are viewedthrough the upper layers of the torus and are thus subject to moderateextinction (AV~ 1-4 mag) sufficient to suppress polarizedlight from the equatorial scattering region, but not the broad wings ofthe Balmer lines. The orientation of the polarization position anglerelative to the radio source is broadly consistent with thetwo-component scattering model. More generally, we find that amongstSeyfert 1 galaxies, parallel, perpendicular and intermediateorientations of the polarization position angle relative to the radioaxis occur roughly in the proportions 2:1:1.
| A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei
Using the Green Bank Telescope, we have conducted a survey for 1.3 cmwater maser emission toward the nuclei of nearby active galaxies, themost sensitive large survey for H2O masers to date. Among 145galaxies observed, maser emission was newly detected in 11 sources andconfirmed in one other. Our survey targeted nearby (v<12,000 kms-1), mainly type 2 active galactic nuclei (AGNs) north ofδ=-20deg and includes a few additional sources as well.We find that more than one-third of Seyfert 2 galaxies have strong maseremission, although the detection rate declines beyond v~5000 kms-1 because of sensitivity limits. Two of the masersdiscovered during this survey are found in unexpected hosts: NGC 4151(Seyfert 1.5) and NGC 2782 (starburst). We discuss the possiblerelations between the large X-ray column to NGC 4151 and a possiblehidden AGN in NGC 2782 to the detected masers. Four of the masersdiscovered here, NGC 591, NGC 4388, NGC 5728, and NGC 6323, havehigh-velocity lines symmetrically spaced about the systemic velocity, alikely signature of molecular gas in a nuclear accretion disk. The masersource in NGC 6323, in particular, reveals the classic spectrum of a``disk maser'' represented by three distinct groups of Dopplercomponents. Future single-dish and VLBI observations of these fourgalaxies could provide a measurement of the distance to each galaxy andof the Hubble constant, independent of standard candle calibrations.
| 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
| The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey(SSRS2) is used to characterize the properties of galaxies hostingactive galactic nuclei (AGNs). Using emission-line ratios, we identify atotal of 162 (3%) Seyfert galaxies out of the parent sample with 5399galaxies. The sample contains 121 Seyfert 2 galaxies and 41 Seyfert 1galaxies. The SSRS2 Seyfert galaxies are predominantly in spirals oftypes Sb and earlier or in galaxies with perturbed appearance as theresult of strong interactions or mergers. Seyfert galaxies in thissample are twice as common in barred hosts as the non-Seyfert galaxies.By assigning galaxies to groups using a percolation algorithm, we findthat the Seyfert galaxies in the SSRS2 are more likely to be found inbinary systems when compared with galaxies in the SSRS2 parent sample.However, there is no statistically significant difference between theSeyfert and SSRS2 parent sample when systems with more than two galaxiesare considered. The analysis of the present sample suggests that thereis a stronger correlation between the presence of the AGN phenomenonwith internal properties of galaxies (morphology, presence of bar,luminosity) than with environmental effects (local galaxy density, groupvelocity dispersion, nearest neighbor distance).Partly based on observations at European Southern Observatory (ESO),under the ESO-ON agreement to operate the 1.52 m telescope.
| 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.
| Iron Is Not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei
To examine whether or not high-ionization nuclear emission-line regions(HINERs) in narrow-line regions of active galactic nuclei are dusty, wefocus on two high-ionization forbidden emission lines, [Fe VII]λ6087 and [Ne V] λ3426. We perform photoionization modelcalculations to investigate possible dependences of the flux ratio of[Fe VII] λ6087/[Ne V] λ3426 on various gas properties, inorder to investigate how useful this flux ratio is to explore the dustabundances in HINERs. Based on our photoionization model calculations,we show that the observed range of the flux ratio of [Fe VII]λ6087/[Ne V] λ3426 is consistent with the dust-freemodels, while it cannot easily be explained by the dusty models. Thissuggests that iron is not depleted in HINERs, which implies that theHINERs are not dusty. This result is consistent with the idea that theHINERs are located closer than the dust-sublimation radius (i.e., theinner radius of dusty tori) and thus can be hidden by dusty tori whenseen from a edge-on view toward the tori, which is also suggested by theAGN-type dependence of the visibility of high-ionization emission lines.
| Evolution of active galaxies: black-hole mass-bulge relations for narrow line objects
Mathur [MNRAS Letters 314 (2000) L17] has proposed that the narrow lineSeyfert 1 galaxies (NLS1s) are likely to be the active galaxies in theearly stage of evolution. To test this hypothesis, we have calculatedthe black hole (BH) masses and the host galaxy bulge masses for a sampleof NLS1s. We find that the mean BH to bulge mass ratio of NLS1s issignificantly smaller than that for normal Seyfert galaxies. We alsofind that the ratio of BH mass to bulge velocity dispersion is alsosignificantly smaller for NLS1s. A scenario of BH growth is ourpreferred interpretation, though alternative explanations are discussed.Assuming that the BHs grow with accretion with a radiative efficiency of0.1, it will take them t>~3.3×108 years to become asmassive as in normal Seyfert 1s. These timescales are consistent withthe theoretical estimates of quasar timescaletQ<~4.5×108 years calculated by Haehneltet al. [MNRAS 300 (1998) 817]. Studies of low redshift NLS1s thusprovide a powerful, and due to their proximity, relatively easy way tounderstand the high redshift quasars and their evolution.
| The infrared luminosity of the torus and the visibility of scattered broad line emission in Seyfert 2 galaxies
A number of studies have shown that the visibility of scattered broademission lines in Seyfert 2 galaxies is strongly dependent on the IRASf60/f25 flux ratio, where those Seyfert 2 galaxieswith `warm' IRAS colours show polarized broad line emission. It is nowclear that this effect is owing to the increasing dominance of thegalactic rather than the active galactic nucleus (AGN) emission at60μm in less-luminous `cool' Seyfert 2 galaxies. However, we presentevidence that the 25-μm emission is a good measure of the AGNluminosity for most Seyfert 2 galaxies. Using this result, we show thatthe visibility of scattered broad line emission has a dependence on theAGN luminosity. The observations can be interpreted self-consistently ifthe scaleheight of the scattering zone varies with central sourceluminosity whilst the scaleheight of the obscuring torus isapproximately constant.
| H I Gas in the Environment of the Seyfert Galaxies NGC 6764 and Markarian 1126
We present the results of a 21 cm line study of the environment of twoSeyfert galaxies: NGC 6764 and Mrk 1126. Both galaxies are embedded inlarge and slightly distorted gaseous disks that extend 2-4 times fartherthan their optical diameters. The asymmetry of the H I distribution andprofile is indicative of a weak perturbation, although one that is notstrong enough to disturb either the gas or the stars in the inner partsof the galaxies. Whereas Mrk 1126 does have a nearby companion, MCG-02-58-017, the gravitational interaction between the two galaxies isquite weak, and it is unlikely that MCG -02-58-017 is responsible fordriving the nuclear activity in Mrk 1126. NGC 6764 has no companionswithin a radius of 160 kpc. We conclude that the nuclear activity in NGC6764 and Mrk 1126 is unrelated to the galaxies' immediate environment.
| 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.
| 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
| Jet Directions in Seyfert Galaxies: B and I Imaging Data
We present the results of broadband B and I imaging observations for asample of 88 Seyfert galaxies (29 Seyfert 1s and 59 Seyfert 2s),selected from a mostly isotropic property, the flux at 60 μm. We alsopresent the B and I imaging results for an additional sample of 20Seyfert galaxies (7 Seyfert 1s and 13 Seyfert 2s), selected from theliterature and known to have extended radio emission. The I-band imagesare fitted with ellipses to determine the position angle and ellipticityof the host galaxy major axis. This information will be used in a futurepaper, combined with information from radio observations, to study theorientation of radio jets relative to the planes of their host galaxies.Here we present surface brightness profiles and magnitudes in the B andI bands, as well as mean ellipticities and major axis position angles.
| Visible and Near-Infrared Spectroscopy of Seyfert 1 and Narrow-Line Seyfert 1 Galaxies
This paper studies the continuum and emission-line properties of asample composed of 16 normal Seyfert 1 and seven narrow-line Seyfert 1(NLS1) galaxies using optical and near-IR CCD spectroscopy. Thecontinuum emission of the galaxies can be described in terms of acombination of stellar population, a nonstellar continuum of power-lawform, and Fe II emission. A significative difference in the opticalspectral index between NLS1's and normal Seyfert 1's is observed; thelatter is steeper. Most NLS1's show Fe II/Hβ ratios larger thanthose observed in the other Seyfert 1's. In the IRAS band, both groupsof galaxies have very similar properties. We have searched for thepresence of optically thin gas in the broad-line region (BLR) of thegalaxies by comparing the broad O I λ8446 and Hαemission-line profiles. Our analysis show that in the NLS1's, bothprofiles are similar in shape and width. This result contradicts thehypothesis of thin gas emission in the high-velocity part of the BLR toexplain the ``narrowness'' of broad optical permitted lines in theseobjects. Evidence of narrow O I λ8446 emission is found in sixgalaxies of our sample, implying that this line is not restricted to apure BLR phenomenon. In the narrow-line region, we find similarluminosities in the permitted and high-ionization lines of NLS1's andnormal Seyfert 1's. However, low-ionization lines such as [O I]λ6300, [O II] λ3727, and [S II] λλ6717, 6731are intrinsically less luminous in NLS1's. Physical properties derivedfrom density- and temperature-sensitive line ratios suggest that the [OII] and [S II] emitting zones are overlapping in normal Seyfert 1's andseparated in NLS1's. Based on observations made at CASLEO. ComplejoAstronómico El Leoncito (CASLEO) is operated under agreementbetween the Consejo Nacional de Investigaciones Científicas ytécnicas de la República Argentina and the NationalUniversities of La Plata, Córdoba and San Juán.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Jet Directions in Seyfert Galaxies
Here we present the study of the relative angle between the accretiondisk (or radio jet) and the galaxy disk for a sample of Seyfert galaxiesselected from a mostly isotropic property, the 60 μm flux, and warminfrared colors. We used VLA A-array 3.6 cm continuum data andground-based optical imaging, homogeneously observed and reduced tominimize selection effects. For parts of the analysis we enlarged thesample by including galaxies serendipitously selected from theliterature. For each galaxy we have a pair of points (i, δ), whichare the inclination of the galaxy relative to the line of sight and theangle between the jet projected into the plane of the sky and the hostgalaxy major axis, respectively. For some galaxies we also hadinformation about which side of the minor axis is closer to Earth. Thisdata is combined with a statistical technique, developed by us, todetermine the distribution of β angles in three dimensions, theangle between the jet and the host galaxy plane axis. We found from aninitial analysis of the data of the 60 μm sample, where Seyfert 1 and2 galaxies were not differentiated, that the observed distribution of iand δ values can be well represented either by a homogeneoussinβ distribution in the range0deg<=β<=90deg or in0deg<=β<=65deg, but not by anequatorial ring. A more general model, which tested β-distributionsin the range β1<=β<=β2, fordifferent ranges of β1 and β2 values,required β2 to be larger than 65° and gavepreference for β1 smaller than 40°-50°. Animportant result from our analysis was obtained when we determinedwhether the jet was projected against the near or the far side of thegalaxy and differentiated between Seyfert 1 and Seyfert 2 galaxies,which showed that the model could not represent Seyfert 1 galaxiesadequately. We found that the inclusion of viewing angle restrictionsfor Seyfert 1 galaxies, namely, that a galaxy can be recognized as aSeyfert 1 only if the angle between the jet and the line of sight(|φ|) is smaller than a given angle φc and that thegalaxy inclination i is smaller than an angle ic, gave riseto statistically acceptable models. This indication that there is adifference in viewing angle to the central engine between Seyfert 1galaxies and Seyfert 2 galaxies is a direct and independent confirmationof the underlying concepts of the unified model. We discuss possibleexplanations for the misalignment between the accretion disk and thehost galaxy disk: warping of the accretion disk by self-irradiationinstability, by the Bardeen-Petterson effect, or by a misalignedgravitational potential of a nuclear star cluster surrounding the blackhole, as well as feeding of the accretion disk by a misaligned inflow ofgas from minor mergers, capture of individual stars or gas from thenuclear star cluster, and the capture of individual molecular cloudsfrom the host galaxy.
| 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).
| 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 Relative Orientation of Nuclear Accretion and Galaxy Stellar Disks in Seyfert Galaxies
We use the difference (delta) between the position angles of the nuclearradio emission and the host galaxy major axis to investigate thedistribution of the angle (beta) between the axes of the nuclearaccretion disk and the host galaxy disk in Seyfert galaxies. We providea critical appraisal of the quality of all measurements, and find thatthe data are limited by observational uncertainties and biases, such asthe well known deficiency of Seyfert galaxies of high inclination. Thereis weak evidence that the distribution of delta for Seyfert 2 galaxiesmay be different (at the 90% confidence level) from a uniformdistribution, while the Seyfert 1 delta distribution is notsignificantly different from a uniform distribution or from the Seyfert2 delta distribution. The cause of the possible nonuniformity in thedistribution of delta for Seyfert 2 galaxies is discussed. Seyfertnuclei in late-type spiral galaxies may favor large values of delta (atthe ~96% confidence level), while those in early-type galaxies show amore or less random distribution of delta. This may imply that thenuclear accretion disk in noninteracting late-type spirals tends toalign with the stellar disk, while that in early-type galaxies is morerandomly oriented, perhaps as a result of accretion following a galaxymerger. We point out that biases in the distribution of inclinationtranslate to biased estimates of beta in the context of the unifiedscheme. When this effect is taken into account, the distributions ofbeta for all Seyferts together, and of Seyfert 1s and 2s separately,agree with the hypothesis that the radio jets are randomly oriented withrespect to the galaxy disk. The data are consistent with theexpectations of the unified scheme, but do not demand it.
| Radio-loud and Radio-quiet Active Galactic Nuclei
We have generated a sample of 409 active galactic nuclei (AGNs) forwhich both the radio luminosity at 5 GHz and the line luminosity in [OIII] lambda5007 have been measured. The radio luminosity spans a rangeof 10 orders of magnitude, and the [O III] line luminosity spans a rangeof 8 orders of magnitude-both considerably larger than the ranges inprevious studies. We show that these two quantities are correlated in asimilar way for both radio-loud and radio-quiet AGNs. We demonstratethat the observed correlation can be explained in terms of a model inwhich jets are accelerated and collimated by a vertical magnetic field.
| Radio continuum morphology of southern Seyfert galaxies
We present radio observations for 29 southern Seyfert galaxies selectedfrom a volume limited sample with cz<3600 km s(-1) , and declinationdelta <0{(deg} ) r. Objects with declination -30{(deg} }r
| A Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
| The Difference between the Narrow-Line Regions of Seyfert 1 and Seyfert 2 Galaxies
This paper presents a comparative study of emission-line ratios of thenarrow-line regions (NLRs) of Seyfert 1 and Seyfert 2 galaxies. Itincludes a literature compilation of the emission-line fluxes [O II]lambda3727, [Ne III] lambda3869, [O III] lambda5007, and [Ne V]lambda3426 as well as 60 μm continuum flux, for a sample of 52Seyfert 1 and 68 Seyfert 2 galaxies. The distribution of theemission-line ratios [O II]/[Ne III] and [O II]/[Ne V] shows thatSeyfert 1 and Seyfert 2 galaxies are statistically different: Seyfert 1galaxies have smaller values than Seyfert 2 galaxies, indicating ahigher excitation spectrum. These and other emission-line ratios arecompared with sequences of models that combine different proportions ofmatter and ionization-bounded clouds and also with sequences of modelsthat vary only the ionization parameter. This comparison shows that theformer models better reproduce the overall distribution of emission-lineratios, indicating that Seyfert 1 galaxies have a smaller number ofionization-bounded clouds than Seyfert 2 galaxies. This difference,together with other results available in the literature, are interpretedfrom the point of view of four different scenarios. The most likelyscenario assumes that Seyfert 1 galaxies have smaller NLRs than Seyfert2 galaxies, possibly due to a preferential alignment of the torus axisclose to the host galaxy plane axis in Seyfert 1 galaxies.
| CO Survey of a Distance-limited Seyfert Sample. I. The Data
We present the data of ^12CO (J = 1-0) observations of the centralregions of a sample of 43 nearby Seyfert galaxies (cz <= 5000 kms^-1) with the NRO 45 m telescope. The general properties of this sampleare also discussed, but a more detailed analysis is deferred to PaperII. The CO detection rate of this sample (i.e., almost 50%) iscomparable to that of other spiral galaxy surveys in similar redshiftranges made with that telescope. There seems to be no difference in thedetection rates of Seyfert galaxies types 1 and 2. Since we observed asingle point centered at the nucleus, and the average ratio of the beamHPBW of the 45 m telescope to the apparent optical diameter of theseobjects was 0.13, only a small fraction of the total molecular gas isrecovered. However, a clear correlation of the CO contents with the IRASFIR luminosities is also seen, and there seems to be a tendency forSeyfert galaxies to be closer to normal galaxies than to starbursts. Theradial distribution of the molecular gas in these galaxies is compatiblein most cases with a steeply decreasing function. Our high spatialresolution observations trace the interface region between the largescale properties of the disks of the host galaxies and the activenuclear regions. This interface region is the one most directlyassociated to the fuelling of the nuclear energy source in these objectsand can be thus compared with data on samples of nonactive galaxies atsimilar spatial scales to deduce the possible relation of thecircumnuclear gas contents and dynamics with nuclear activity (see PaperII).
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Scattering and absorption in soft X-ray selected AGN: an optical polarization survey
We have surveyed the optical linear polarization of a completelyidentified sample of 43 bright soft-X-ray-selected ROSAT AGN. Most (40)of these AGN show low polarization (~1%), and no clear opticalreddening. This supports the suggestion from rapid X-ray variability,disk-like spectral energy distributions, and lack of cold X-rayabsorption, that we are viewing a bare AGN disk. IRASF12397+3333 andIRAS13349+2438 show high polarization increasing to the UV - clearevidence for scattering. As well as steep, soft-X-ray spectra, they showoptical reddening and rapid X-ray variability, but almost no cold X-rayabsorption - a combination that suggests dusty ionized gas along theline-of-sight. Brandt et al. suggested and found these `warm absorbers'for IRAS13349+2438. IRASF12397+3333 is a new candidate. Combining ourdata with the optical and X-ray spectra of the high polarizationnarrow-line Seyfert 1 nuclei (NLSy1s) investigated by Goodrich revealsstrong correlations among optical reddening indicators (alpha_opt andHα /Hβ ), [OIII]/Hβ_b , and cold intrinsic X-rayabsorption Delta N_H. Optical reddening underpredicts the cold X-rayabsorption, suggesting dusty warm absorbers in all the highly polarizedAGN. The existence of these scattering-polarized and reddened NLSy1ssuggests an orientation Unified Scheme within the class of NLSy1s,analogous to that linking Seyfert 1 and Seyfert 2 nuclei. For somehighly polarized and optically selected AGN we present new analysis ofarchival X-ray data, and for the highly polarized AGN new opticalspectroscopy is presented in an appendix.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
קטלוגים וכינוים:
|
