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|Gas in early-type galaxies: cross-fuelling in late-type-early-type pairs?|
We present 12CO (J= 1-0) and 12CO (J= 2-1)observations of eight early-type galaxies, forming part of a sample ofinteracting galaxies, each consisting of one late- and one early-typesystem. All of the early-type galaxies observed are undetected in CO tolow levels, allowing us to place tight constraints on their moleculargas content. Additionally, we present HI absorption data for one system.The implications for possible gas transfer from the late- to theearly-type galaxy during the interaction are discussed.
|Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/1410|
I present two-band Hubble Space Telescope (HST) STIS imaging and WIYNspectral mapping of ongoing mass transfer in the interacting galaxy pairNGC 1409/1410 (where NGC 1410 is the Seyfert galaxy also cataloged asIII Zw 55). Archival snapshot WFPC2 imaging from the survey by Malkanand coworkers showed a dust feature stretching between the galaxies,apparently being captured by NGC 1409. The new images allow estimates ofthe mass being transferred and the rate of transfer. An absorption lanetypically 0.25" (100 pc) wide, with a representative optical depthτB=0.2, cuts across the spiral structure of NGC 1410,crosses the 7 kpc projected space between the nuclei, wraps in front ofand, at the limits of detection, behind NGC 1409 and becomes a denser(τB=0.4) polar feature around the core of NGC 1409. Thecombination of extinction data in two passbands allows a crudethree-dimensional recovery of the dust structure, supporting thefront/back geometry derived from colors and extinction estimates. Thewhole feature contains on the order of 2×106Msolar in dust, implying about 3×108Msolar of gas and requiring a mass transfer rate averaging ~1Msolar yr-1, unless we are particularly unlucky inviewing angle. Curiously, this demonstrable case of mass transfer seemsto be independent of the occurrence of a Seyfert nucleus, since theSeyfert galaxy in this pair is the donor of the material. Likewise, therecipient shows no signs of recent star formation from incoming gas,although NGC 1410 has numerous luminous young star clusters andwidespread Hα emission.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555.
|Massive Star Clusters in Ongoing Galaxy Interactions: Clues to Cluster Formation|
We present HST WFPC2 observations, supplemented by ground-based Hαdata, of the star-cluster populations in two pairs of interactinggalaxies selected for being in very different kinds of encounters seenat different stages. Dynamical information and n-body simulationsprovide the details of encounter geometry, mass ratio, and timing. InNGC 5752/4 we are seeing a weak encounter, well past closest approach,after about 2.5×108 yr. The large spiral NGC 5754 has anormal population of disk clusters, while the fainter companion NGC 5752exhibits a rich population of luminous clusters with a flatterluminosity function. The strong, ongoing encounter in NGC 6621/2, seenabout 1.0×108 yr past closest approach between roughlyequal-mass galaxies, has produced an extensive population of luminousclusters, particularly young and luminous in a small region between thetwo nuclei. This region is dynamically interesting, with such a strongperturbation in the velocity field that the rotation curve reversessign. From these results, in comparison with other strongly interactingsystems discussed in the literature, cluster formation requires athreshold level of perturbation, with stage of the interaction a lessimportant factor. The location of the most active star formation in NGC6621/2 draws attention to a possible role for the Toomre stabilitythreshold in shaping star formation in interacting galaxies. The richcluster populations in NGC 5752 and NGC 6621 show that direct contactbetween gas-rich galaxy disks is not a requirement to form luminousclusters and that they can be triggered by processes happening within asingle galaxy disk (albeit triggered by external perturbations).Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
|High and Low Surface Brightness Galaxies in the Local Universe. V. Optical and H I Properties|
Using optical spectra of the nuclei of 250 galaxies chosen from theAutomated Plate Measuring Facility (APM) survey of UK Schmidt plates, wederive synthetic B-V and V-R colors, estimates of reddening from Balmerdecrements, metallicity via oxygen abundance, and star formation ratefrom the Hα luminosity. We also present mass-to-light ratios andgas mass fractions from 21 cm H I measurements of 238 APM surveygalaxies, 101 of which also have optical spectra. This sample ofgalaxies spans a large range in surface brightness, from high surfacebrightness irregular galaxies down to the kind of low surface brightness(LSB) galaxies that are missing from most magnitude-limited catalogs.The generally blue global colors are best explained by a combination oflow metallicity and active star formation, primarily because of thetremendous scatter in metallicity versus B-V. Optical spectra show thepresence of G and K main-sequence stars in the nuclei of these galaxies,and the stellar mass-to-light ratios and gas mass fractions show thegalaxies as a whole to be gas-rich. LSB galaxies are most likely toexperience sporadic low levels of star formation over gigayeartimescales.
|Stellar indices and kinematics in Seyfert 1 nuclei|
We present spectra of six type 1 and two type 2 Seyfert galaxies, astarburst galaxy and a compact narrow-line radio galaxy, taken in twospectral ranges centred around the near-infrared Caii triplet(~8600Å), and the Mgb stellar feature at 5180Å. We measuredthe equivalent widths (EWs) of these features and the Fe52and Fe53 spectral indices. We found that the strength of theinfrared Caii triplet (CaT) in type 1 Seyfert galaxies with prominentcentral point sources is larger than what would be expected from theobserved strength of the blue indices. This could be explained by thepresence of red supergiants in the nuclei of Seyfert 1 galaxies. On theother hand, the blue indices of these galaxies could also be diluted bythe strong Feii multiplets that can be seen in their spectra. We havealso measured the stellar- and gas-velocity dispersions of the galaxiesin the sample. The stellar velocity dispersions were measured using boththe Mgb and CaT stellar features. The velocity dispersion of the gas inthe narrow-line region (NLR) was measured using the strong emissionlines [Oiii] λλ5007, 4959 and [Siii] λ9069. Wecompare the gas- and star-velocity dispersions and find that themagnitudes of both are correlated in Seyfert galaxies. Most of theSeyfert 1 galaxies that we observe have stellar-velocity dispersionssomewhat greater than that of the gas in the NLR.
|Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/10|
I present two-band HST STIS imaging of ongoing mass transfer in theinteracting galaxy pair NGC 1409/10 (where NGC 1410 is the Seyfertgalaxy often listed as III Zw 55). Archival snapshot WFPC2 imaging fromthe survey by Malkan et al. showed a dust feature stretching between thegalaxies, apparently being captured by NGC 1409. The new images allowestimates of the mass being transferred and rate of transfer. Anabsorption lane typically 0.25" (100 pc) wide with a representativeoptical depth τ B = 0.2 cuts across the spiral structureof NGC 1410, crosses the 7-kpc projected space between the nuclei, wrapsin front of and, at the limits of detection, behind NGC 1409, andbecomes a denser (τ B = 0.4) polar ring around the coreof NGC 1409. Models for the light distribution in the two galaxies allowa crude three-dimensional recovery of the dust structure, supporting thefront/back geometry derived from colors and extinction estimates. Thewhole feature contains of order 5000 solar masses in dust, implyingabout 8 x 105 solar masses of gas. Incorporating theprojected velocity difference between nuclei for a timescale, thissuggests a very modest mass transfer rate averaging about 0.02 solarmasses per year unless we are particularly unlucky in viewing angle.Curiously, this demonstrable case of mass transfer seems to beindependent of the occurrence of a Seyfert nucleus, since the Seyfertgalaxy in this pair is the donor of the material. This work was supportby NASA through STScI grant GO-8147.01-97A.
|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.
|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.
|A Survey for H 2O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies|
A survey for H2O megamaser emission from 354 active galaxies hasresulted in the detection of 10 new sources, making 16 known altogether.The galaxies surveyed include a distance-limited sample (coveringSeyferts and LINERs with recession velocities less than 7000 km s-1) anda magnitude-limited sample (covering Seyferts and LINERs with mB <=14.5). In order to determine whether the H2O-detected galaxies are"typical" active galactic nuclei (AGNs) or have special properties thatfacilitate the production of powerful masers, we have accumulated adatabase of physical, morphological, and spectroscopic properties of theobserved galaxies. The most significant finding is that H2O megamasersare detected only in Seyfert 2 and LINER galaxies, not Seyfert 1's. Thislack of detection in Seyfert 1's indicates either that they do not havemolecular gas in their nuclei with physical conditions appropriate toproduce 1.3 cm H2O masers or that the masers are beamed away from Earth,presumably in the plane of the putative molecular torus that hides theSeyfert 1 nucleus in Seyfert 2's. LINERs are detected at a similar rateto Seyfert 2's, which constitutes a strong argument that at least somenuclear LINERs are AGNs rather than starbursts, since starbursts havenot been detected as H2O megamasers. We preferentially detect H2Oemission from the nearer galaxies and from those that are apparentlybrighter at mid- and far-infrared and centimeter radio wavelengths.There is also a possible trend for the H2O-detected galaxies to be moreintrinsically luminous in nuclear 6 cm radio emission than theundetected ones, though these data are incomplete. We find evidence thatSeyfert 2's with very high (NH > 1024 cm-2) X-ray--absorbing columnsof gas are more often detected as H2O maser emitters than Seyfert 2'swith lower columns. It may be that the probability of detecting H2Omaser emission in Seyfert galaxies increases with increasing column ofcool gas to the nucleus, from Seyfert 1's through narrow-line X-raygalaxies to Seyfert 2's.
|Optical and Far-Infrared Emission of IRAS Seyfert Galaxies|
This paper presents an analysis of moderately large samples of type 1and 2 Seyfert galaxies through optical observations and far-infraredIRAS data, also taking into account theoretical color indices derivedfrom dust emission models. The galaxies in the samples cover a ratherlarge interval in far-infrared luminosity, i.e., 7.6 <= log(LIR/Lȯ) <= 12.6. We show that both types of Seyferts haveapproximately the same distribution of number of objects with a givenLIR. Galaxies with similar far-infrared color indices alpha (100, 60)are grouped together, and the corresponding average color indices areinterpreted in terms of a simple model in which the observed colorsresult from the combination of dust directly heated by the activegalactic nucleus with a component from the host galaxy represented bythe emission of cool dust. On the basis of the average IRAS colors ofthe derived groups, we show that type 1 and 2 Seyfert galaxies areundistinguishable from each other. From the luminosity ratios LIR/LHalpha and LIR/L[O III], we show that basically the same model can beapplied to both types of Seyfert, only allowing for the variation ofmodel conditions: type 2 Seyferts would be like type 1 Seyferts but withthe Seyfert nucleus and broad line region more effectively "hidden" bydust.
|Determination of the atmospheric point spread function by a parameter search|
The result of blind deconvolution is a reconstructed image that has nonpositive intensities. The number of these non positive pixels has beenused as an estimator for the departure from a perfect reconstruction.Simulations of reconstruction of objects convolved with a kernel havingone or two parameters are shown to demonstrate the efficiency of theestimator. We thus present a technique of determining the unknownparameters of the point spread function by searching for the point inparameter space with the lowest number of nonpositive pixels. It is alsoshown that the parameters of the convolving kernel can be obtained evenin the presence of noise. This method was validated using a longexposure image of NGC 1409.
|Interpretation of the emission line spectra of Seyfert 2 galaxies by multi-component photoionization models.|
We present multi-component photoionization models allowing for localdensity inhomogeneities in the NLR to interpret the emission linespectra of Seyfert2 galaxies. This approach leads to a successful matchof a large set of line intensities from the UV to the NIR. Inparticular, the hitherto elusive NIR features[SIII]λ9062+λ9531 as well as high-ionization lines like[FeVII]λ6087 are consistently fitted. The predictions ofCIII]λ1909 and CIVλ1549 are considerably improved. Fromthe detailed analysis of single-component photoionization models wederive the minimal radial extent of the NLR and the necessary span indensity. Furthermore, we determine constraints on suggestions made aboutthe role of matter-bounded clouds, and on proposed explanations forlarge [OIII]λ4363/λ5007 ratios (the so-called `temperatureproblem'), and assess the usability of some emission-line ratios asindicators of the ionization parameter. We find that a systematicvariation of the cloud column densities in a population ofmatter-bounded clouds is inconsistent with the trends and correlationsexhibited by the emission lines in the diagnostic diagrams. Concerningthe temperature problem, the only possibility that leads to an overallconsistency with the strengths of all other observed emission lines issubsolar metal abundances (as compared to e.g. the presence of dust, theexistence of a high-density component, or matter-bounded clouds). Inaddition, the consequences of the presence of (Galactic-ISM-like) dustinternal to the clouds were investigated. These models alleviate the[OIII]-ratio problem but did not lead to overall consistent fits. Themost conspicuous fallacy lies in the extreme underprediction ofFe-lines, which is mainly due to the strong depletion of the Feabundance. In our final model series, the NLR is composed of a mixtureof metal-depleted (~0.5xsolar) clouds with a radius-independent range indensities (10^2^ to 10^5^cm^-3^) distributed over a range of distancesfrom the nucleus (galactocentric radii from at least ~10^20^cm to10^21.5^cm, for Q_tot_=10^54^s^-1^). In order to encompass the observedrange of each line intensity relative to Hβ, it turns out to benecessary to vary the spectral energy distribution incident on theclouds, qualitatively confirming the findings of Ho et al.(1993ApJ...410..567H). We found a successful continuum sequence byadding an increasing contribution of a hot black body (T=~200000K) to asteep powerlaw (α_uv-x_=~-2). These continua imply that low andhigh-excitation objects differ in the strength but not in the basicshape of the EUV bump.
|Rotation Curves and Velocity Measures for Spiral Galaxies in Pairs|
Rotation curves have been obtained for 76 spiral galaxies in pairs,including a geometrically selected subset from the Karachentsev catalogand a set of Seyfert galaxies with close companions. Derived parametersof the rotation curves and the galaxies light distributions are alsopresented. The rotation curves are classified broadly by shape, withspecial emphasis on kinematic disturbances and regions of solid-bodybehavior that may lead to bar development. Broadband images of thegalaxies allow assessments of their degree of symmetry or disturbance.These velocity slices afford an empirical basis for evaluating theaccuracy of radial velocity measures for spiral galaxies in pairs, andthe dynamically important radial velocity differences. Specifically, thedisagreement among several plausible ways of estimating the centralvelocity from these rotation data is used to estimate how closely any ofthese might approximate the nuclear or center-of-mass values. From sevenindicators of central velocity, the internal scatter is σ_vv_ = 34km s^-1^. Of these, the velocity weighted by Hα intensity alongthe slit shows a systematic offset of about 20 km s^-1^ with respect tothe others for the Karachentsev pairs, in the sense that this measure isredshifted with respect to the other indicators. This is in the sense(but not of the total magnitude) required to account for statisticalasymmetries in pair velocity differences. Individual scatter between thevelocity indicators taken pairwise ranges from σ = 20 to 52 km s^-1^. These results imply that emission-line data such as these cannotspecify the center of mass or nuclear redshift at a level more accuratethan this, even for arbitrarily precise velocity measurements, becauseit is not clear how the observed quantities relate to the desiredmeasurement in a physical sense. No useful predictor of which galaxieshave large or small scatter among velocity measures was found, exceptthat the scatter is small for the class of "nonrotating" galaxies withsmall overall velocity amplitudes. Projected separation, separationnormalized to disk scale length, and morphological disturbance do notcorrelate with the velocity scatter.
|Low Surface Brightness Galaxies in the Local Universe. I. The Catalog|
Data are presented for 693 galaxies identified in a large new survey forlow surface brightness galaxies in the nearby universe (z <~ 0.1).The survey covers 786 square degrees centered on the equator, and itextends significantly the surface brightness range of galaxy surveys inwhich there are a substantial number of galaxies with redshifts. Thedata are derived from the Automated Plate Measuring machine scans ofsurvey plates from the UK Schmidt Telescope and from follow-upobservations at radio and optical wavelengths. Accurate positions, totalB magnitudes, surface brightness parameters, and angular sizes aretabulated for each galaxy. Radial velocities, optical luminosities, andneutral hydrogen masses are listed for a subset of the sample. Findingcharts are also presented for those objects having a large enoughangular size that the scans from survey plates provide somemorphological information. The selection function and the luminosityfunction that can be derived from the survey are discussed in twocompanion papers.
|Seyfert Galaxies. IV. Nuclear Profiles of Markarian Seyfert Galaxies from Hubble Space Telescope Images|
We have examined the nuclear profiles of the Seyfert and non-SeyfertMarkarian galaxies in our near-infrared Hubble Space Telescope WF/PC-1snapshot survey. We find that nuclei of types 1-1.5 Seyfert galaxies aredominated by strong point sources, while those of Seyfert 2 and non-Seyfert Markarian galaxies tend to be resolved, less distinguished, andsimilar in shape to normal galaxy luminosity profiles. Two possibleinterpretations of this result for type 2 Seyfert galaxies are thattheir nuclear continuum sources are undetected in our bandpass,contributing less than 10% of the nuclear light (within 0.5 radius) inall cases or that their nuclear components are resolved and blend insmoothly with the brightness profile of the host galaxy's bulge. Sincespectroscopic studies support typical nuclear continuum fractionsdistinctly greater than 10%, the latter conclusion is clearlypreferable. If the continua observed in Seyfert 2 galaxies originate asnuclear light that is redirected into the line of sight by scattering,as predicted by unified models of active galactic nuclei, then thescattering regions must be extended. Simple simulations suggest thatthese regions must cover several tens of parsecs or more, in agreementwith estimates of the sizes of the scattering "mirrors" in other Seyfert2 galaxies. However, the similarity of the profiles of non-SeyfertMarkarian and type 2 Seyfert nuclei suggests that circumnuclear starformation may also be an important component in the nuclear profiles ofthe latter.
|Seyfert Galaxies With Companions: Orbital and Kinematic Clues to AGN Triggering|
This paper presents imaging and optical spectroscopy of paired Seyfertgalaxies and their companions. The aim is to seek common properties ofSeyfert galaxies in interacting systems, which might provide evidence ofAGN triggering in a way independent of the usual two-sample statisticswhich have proven ambiguous on this issue. Three kinds of comparisonhave been made-the kinds of interactions involving Seyfert galaxies, therelative luminosities of the Seyferts and their companions, and thelevel of kinematic disturbance as measured from rotation curves. (1)Dynamics and tidal features have been used to determine (or at leastlimit) the sense of orbital motion (direct/retrograde/polar with respectto the Seyfert galaxy's disk) for many of these pairs. There is noobviously preferred kind of interaction-direct, polar, and retrogradeencounters are all well represented, despite the gross differences indynamical response of a disk to these various kinds of encounter. To theextent that triggering of Seyfert nuclei occurs due to tidal encounters,the existence of a perturbation seems more important than its exactduration or detailed effects on the disk. However, the ratio of mergingto paired Seyferts is higher than for disk galaxies in general,consistent with more effective triggering of AGN in this specific phase;the implied time scale for enhanced occurrence during mergers is thesame as the timescape for merger remnants to appear as such, a fewdisk-edge crossing times (typically several times 10^8^ yr). (2) Seyfertnuclei occur preferentially in the brighter members of galaxy pairs, bya median of 0.93 mag after making the maximal correction forcontaminating nonstellar light in the nuclei. Only about 1/3 of thiseffect can be accounted for by the known tendency of Seyfert nuclei tooccur in more luminous galaxies. Enhancement of AGN by interactions isevidently more effective for more luminous galaxies (though this willalso be the case if both star formation and AGN occurrence are enhancedin the same galaxies). (3) The rotation curves of the paired Seyfertsshow systematically small regions of rising or solid-body rotationcompared to the disk radius, as a group comparable to Sa but verydifferent from Sb or Sc galaxies (even for Seyfert galaxies with Hubbletype later than Sa). There is weak evidence that this difference is alsopresent with respect to more isolated Seyfert galaxies. Despite theobvious utility of a dynamically disturbed disk for transport of angularmomentum and "feeding the monster," Seyfert galaxies in pairs actuallyhave smaller kinematic disturbances (measured by the maximum departurefrom a symmetric rotation curve, normalized to the full rotationamplitude) than found in a complete sample of non-Seyfert spirals inpairs.
|Stellar and Gaseous Kinematics of Seyfert Galaxies. I. Spectroscopic Data|
In order to study the relationship between the gravitational potentialand the properties of active galaxies, we have measured nuclear stellarand gaseous kinematics for a large sample of Seyfert galaxies. In thispaper we present moderate-resolution data (80-230 km s^-1^ FWHM) fromtwo spectral regions, one in the near-infrared containing the Ca IItriplet absorption features at ~8550 A and the [S III] 9069 A emissionline, and the other in the visual including the Mg b absorption lines at~5175 A and the [O III] 5007 A emission line. Nuclear stellarvelocities, V_*_,and velocity dispersions, σ_*_, were measuredusing the cross- correlation method. Complications for the kinematicanalysis associated with the featureless continua and strong emissionlines in Seyfert galaxies are briefly discussed. Emission-linevelocities and widths were also measured from our spectra. The finalsample contains 85 objects (22 type 1 Seyfert galaxies, 51 type 2Seyferts, nine LINERs, and three normal galaxies). We provide asupplement to the database of narrow-line region and host galaxyproperties compiled by Whittle (1992a) for 20 Seyfert galaxies notoriginally included. We plan to use our measurements in conjunction withthis database to investigate the relationship between the nucleargravitational potential and other properties of Seyfert galaxies.
|The CA II triplet lines in starburst and AGN|
In the frame of the Starburst Model for AGN, we show that the evolutionof a massive stellar cluster in a high metallicity environment canreproduce the observed equivalent widths of Ca II triplet lines inabsorption in Starburst and AGN. In the case of Starburst galaxies, thisstrength, together with the emission-line ratio (O II)/(O III), can beused to determine the age of the cluster. The strength of the Ca IIlines is mainly governed by the age of the stellar cluster through thepresence of red supergiant stars.
|Photometric properties of some AGNs|
The absolute spectrophotometry of 67 AGNs (de Bruyn and Sargent 1978) isused for Seyfert type classification and for computation of syntheticmagnitudes, colors and K-correction for the UBV system. Syntheticspectra for Sy 1, Sy 1.5 and Sy 2 galaxies are constructed and meancolors and K-corrections are derived. Their variation with redshift arepresented with polynomial fittings. The photometric properties of AGNssuppose a further development of more refined Seyfert types.
|Models and observations of starbursts. II - Starbursts in interacting galaxies|
Evolutionary models are applied here to starburst galaxies in a sampleof 30 interacting or merged systems in order to determine the durationof the starbursts. The time delay between bursts in both components ofinteracting pairs of disk galaxies is investigated and it is found thatstarbursts in the minor galaxies of these pairs started earlier thanthose in the major galaxies. While strong starbursts are found to beactive for only about 2 x 10 exp 7 yrs, the time delay between thebursts in both components of the interacting pairs can be significantlylarger. Delays of up to 2 x 10 exp 8 yrs are found in the sample. Modelfits show that the mass-to-luminosity ratios of strong centralstarbursts indicate a deficiency of low-mass stars in the starburstinitial mass function. The required low-mass-star deficiency is smallerthan previously believed.
|A compilation of active and normal galaxies observed in both infrared and X-rays|
Infrared and X-ray data from the IRAS and Einstein satellites have beencompiled for a total of 269 quasars, Seyferts, emission-line and normalgalaxies. It is found that galaxies with soft X-ray to infrared fluxratios greater than about 0.01 are almost certain to show broad-lineoptical emission. For the full IRAS/Einstein ensemble, a significantcorrelation between luminosities is found in the 60-micron and 0.5-4.5keV bands. A strong offset separates broad line from normal andnarrow-line galaxies. The jump toward higher X-ray emission inbroad-line galaxies is interpreted as evidence for the increasingimportance of a nonthermal nuclear source. The analysis of the empiricalrelationship between LX and L60 microns for normaland narrow optical emission-line galaxies makes it possible to convert60-micron IRAS luminosity functions into estimates of the 2-keV X-rayluminosity function of IR-emitting galaxies.
|Virial and jet-induced velocities in Seyfert galaxies. I - A compilation of narrow line region and host galaxy properties|
Data for a sample of 140 Seyfert galaxies have been compiled with theaim of studying the dependence of nuclear gas velocities on propertiesof the host galaxy and properties of the nuclear activity. Parameterswhich characterize these three basic qualities include (1) forbidden OIII 5007 emission line widths measured at various levels in the profile,(2) galaxy luminosity, morphology, inclination, disturbance, androtation amplitude, and (3) H-beta luminosity, forbidden III 5007luminosity, radio luminosity, radio morphology, and Seyfert type.Because compilations of this type draw on a wide range of data quality,each value has been assigned a simple yet well-defined quality rating(a, b, c, r = reject). These indicate the relative data reliability andmake it possible to monitor the influence of poor data on correlationanalyses. Simple descriptions of the parameter distributions are given.
|On the behaviour of the IR CA II triplet in normal and active galaxies|
The strength of the Ca II triplet in absorption at 8498/8542/8662 A hasbeen found to serve as a good luminosity indicator for metal-richstellar populations; high S/N near-IR spectroscopic data are presentedfor the nuclear regions of 42 normal and active galaxies. The normalgalaxies' Ca II triplet strengths exhibit a small spread around a meanvalue of 7 A. The large equivalent width of the IR Ca II triplet inSeyfert nuclei furnishes a unique means for probing the gravitationalpotential close to the central engine. Nuclear velocity dispersions in'active' galaxies are comparable to those in normal ones of similarluminosity.
|A survey of the profiles of narrow emission lines in Seyfert galaxies|
An atlas of the nuclear spectra of 58 Seyfert galaxies and six galaxieswith nuclear H II regions is presented. For all but three galaxies, therange of rest wavelengths covered is about 6000-6800 A, with spectralresolution at H-alpha either 45 km/s or 130 km/s. Widths are given forthe emission lines forbidden Fe VII 6086 A, forbidden O I 6300 A,H-alpha, forbidden N II 6584, and forbidden S II 6717,6731 A. In all,widths for some 210 lines in 53 galaxies are listed. A comparison ismade between the present and previous line width measurements.
|Seyfert galaxies. I - Morphologies, magnitudes, and disks|
CCD images of a volume- and luminosity-limited sample of 51 Markarianand NGC Seyfert galaxies show that Seyfert galaxies nearly alwayspossess mechanisms for transporting material into their nuclei. A subsetof Seyfert galaxies with amorphous morphologies, some of which may beremnants of past interactions, constitutes approximately one-fifth ofthe sample. The colors and exponential disk parameters of Seyfertgalaxies are generally similar to those of spiral galaxies withoutactive nuclei. Images of the galaxies are presented along with aperturemagnitudes.
|X-ray and infrared selected active galactic nuclei. I - The missing edge-on galaxies|
Morphological classification and axial ratio measurements for a sampleof 288 Seyfert Galaxies (SGs) are presented. Seyferts are predominantlyspirals, and a deficiency of edge-on objects is found of both classesSeyfert 1 and 2 in comparison with a sample of 1600 normal spirals. Thedata suggest that obscuration extends beyond line region, and that thedistribution of dust is flattened and coplanar with the disk of theparent galaxy. A way to find the missing edge-on SGs on the basis oftheir infrared and X-ray emission is proposed. A sample of 144 IRASgalaxies lying inside or close to unidentified hard X-ray HEAO-1 sourcesis selected. Most of the target galaxies are in fact seen edge-on, andit is estimated that at least about 34 of them are obscured activegalactic nuclei (AGN) associated with the X-ray sources.
|Spectroscopic study of non-cluster early-type galaxies|
Data from long-slit spectroscopic observations of eight binary, triple,or merging groups containing early-type galaxies (Laurikainen and Moles,1989) are compiled in tables and graphs and analyzed in detail, with afocus on the older stellar populations. A clear distinction is foundbetween elliptical galaxies interacting in clusters and isolatedellipticals: the latter are redder and have lower surface brightness andstronger metal lines, suggesting a formation process involving mergers.A high degree of variation is found in the MgH and CN band strengths ofmetal-rich interacting galaxies, with strong values for 'metals'attributed to high Fe I (+ CN) values and increased CN abundance.
|Star formation in a sample of interacting galaxies|
The star formation properties are analyzed for a sample of interactinggalaxies based on long-slit optical spectroscopy observations, and theresults are reported. A high frequency of LINERs is detected among thesample galaxies, many of which show only low-level activity and are notassociated with high infrared flux LINERs. Their global star-formationrates are higher than for field galaxies in most of the systems. Thestar-formation activity is mainly concentrated toward the central partsof the strongly interacting galaxies. Extended emission can appear ingalaxies of very spectral type when the activity level is very high, butit is not a general feature. The star formation in a galaxy in everygeneration of its 'ecologic cycle' of molecular cloud and star formationis found to be essentially produced with the same spatial distribution.
|Seyfert galaxies. II - Environments and IRAS colors|
The environments of Seyfert galaxies are compared to the environments ofnon-Seyfert Markarian galaxies using galaxy counts obtained from thePalomar Observaory Sky Survey prints. While previous work by Dahari,confirmed here, indicates that Seyfert galaxies are more likely to haveclose companion galaxies than field galaxies, the Seyfert galaxiesexamined here have essentially the same environments as the comparisonsample of non-Seyfert Markarian galaxies. The IRAS colors of the Seyfertand non-Seyfert Markarian galaxies are used to distinguish betweenSeyfert activity and bursts of star formation. The results suggest thatclose companion galaxies enhance star formation rather than directlyenhancing Seyfert-like activity.
|A catalogue of Seyfert galaxies.|
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