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The Narrow-Line Region of the Seyfert 2 Galaxy Mrk 78: An Infrared View
We report near-infrared spectroscopic data for the Seyfert 2 galaxy Mrk78, taken with the LIRIS near-infrared camera/spectrometer at theWilliam Herschel Telescope (WHT). The long-slit spectra clearly showextended emission. The resolution and depth of the near-infrared spectraallow the examination of its morphology and ionization regions, and adirect comparison with similarly deep visible spectra. The emission-lineratios obtained are used to derive the extinction toward the nucleus.The detection of strong features such as [Fe II], H2,hydrogen recombination lines, and the coronal [Si VI] λ1.962 lineis used to study the kinematics and excitation mechanisms occurring inMrk 78, revealing that despite the strong radio-jet interaction presentin this object, photoionization from the active nucleus dominates thenarrow-line region emission, while UV fluorescence is the source of theH2 emission. Lines with extended emission yield velocitydistributions with an amplitude of about 600 km s-1, theconsequence of an eastern lobe moving away from us plus a western lobewith the opposite contribution. We used the photoionization code CLOUDYto recreate a typical narrow-line region, to derive the ionizationparameter, and to compare our spectral data with diagnostic diagrams.
| Lifetime of nuclear velocity dispersion drops in barred galaxies
We have made hydro/N-body simulations with and without star formation toshed some light on the conditions under which a central kinematicallycold stellar component (characterized by a velocity dispersion drop orσ-drop) could be created in a hot medium (e.g. a bulge) andsurvive enough time to be observed. We found that the time-scale for aσ-drop formation could be short (less than 500 Myr), whereas itslifetime could be long (more than 1 Gyr) provided that the centralregion is continuously or regularly fed by fresh gas which leads to acontinuous star formation activity. Star formation in the centralregion, even at a low rate as 1Msolaryr-1, ismandatory to sustain a permanent σ-drop by replacing heatedparticles by new low-σ ones. We moreover show that as soon as starformation is switched off, the σ-drop begins to disappear.
| On the Fraction of X-Ray-obscured Quasars in the Local Universe
Recent wide-area hard X-ray and soft gamma-ray surveys have shown thatthe fraction of X-ray-obscured active galactic nuclei (AGNs) in thelocal universe significantly decreases with intrinsic luminosity. Inthis Letter we point out that two corrections have to be made to thesamples: (1) radio-loud AGNs have to be excluded, since their X-rayemission might be dominated by the jet component, and (2) Compton-thicksources have to be excluded too, since their hard X-ray and softgamma-ray emission are also strongly attenuated by Compton scattering.The soft gamma-ray-selected AGN samples obtained by Swift and INTEGRALprovide the best opportunity to study the fraction of obscured AGNs inthe local universe in the least biased way. We choose these samples tocheck if the corrections could alter the above result on the fraction ofobscured AGNs. We find that before the corrections both samples showsignificant anticorrelation between LX and NH,indicating an obvious decrease in the fraction of obscured AGNs withluminosity. However, after the corrections, we find only marginalevidence of anticorrelation (at the 98% confidence level) in the Swiftsample and no evidence at all in the INTEGRAL sample, which consists ofa comparable number of objects. We conclude that current samples onlyshow a marginal decrease in the fraction of obscured AGNs in the localuniverse and that much larger samples are required in order to reach amore robust conclusion.
| The K-band properties of Seyfert 2 galaxies
Aims. It is well known that the [O iii]λ5007 emission line andhard X-ray (2-10 keV) luminosities are good indicators of AGN activitiesand that the near and mid-infrared emission of AGN originates fromre-radiation of dusty clouds heated by the UV/optical radiation from theaccretion disk. In this paper we present a study of the near-infraredK-band (2.2 μm) properties for a sample of 65 Seyfert 2 galaxies. Methods: .By using the AGN/Bulge/Disk decomposition technique, weanalyzed the 2MASS K_S-band images for Seyfert 2 galaxies in order toderive the K_S-band magnitudes for the central engine, bulge, and diskcomponents. Results: .We find that the K_S-band magnitudes of thecentral AGN component in Seyfert 2 galaxies are tightly correlated withthe [O iii]λ5007 and the hard X-ray luminosities, which suggeststhat the AGN K-band emission is also an excellent indicator of thenuclear activities at least for Seyfert 2 galaxies. We also confirm thegood relation between the central black hole masses and bulge's K-bandmagnitudes for Seyfert 2s.
| Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the λ 1.3 cm (22 GHz) water vaporline towards galaxies with nuclear activity, large nuclear columndensities or high infrared luminosities, we present H2O spectra for NGC2273, UGC 5101, and NGC 3393 with isotropic luminosities of 7, 1500, and400 Lȯ. The H2O maser in UGC 5101 is by far the mostluminous yet found in an ultraluminous infrared galaxy. NGC 3393 revealsthe classic spectrum of a "disk maser", represented by three distinctgroups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below1000 km s-1. Based on the literature and archive data, X-rayabsorbing column densities are compiled for the 64 galaxies withreported maser sources beyond the Magellanic Clouds. For NGC 2782 andNGC 5728, we present Chandra archive data that indicate the presence ofan active galactic nucleus in both galaxies. Modeling the hard nuclearX-ray emission, NGC 2782 is best fit by a high energy reflectionspectrum with NH 1024 cm-2. ForNGC 5728, partial absorption with a power law spectrum indicatesNH 8 × 1023 cm-2. Thecorrelation between absorbing column and H2O emission is analyzed. Thereis a striking difference between kilo- and megamasers with megamasersbeing associated with higher column densities. All kilomasers (L_H_2O< 10 Lȯ) except NGC 2273 and NGC 5194 areCompton-thin, i.e. their absorbing columns are <1024cm-2. Among the H{2}O megamasers, 50% arise fromCompton-thick and 85% from heavily obscured (>1023cm-2) active galactic nuclei. These values are not larger butconsistent with those from samples of Seyfert 2 galaxies not selected onthe basis of maser emission. The similarity in column densities can beexplained by small deviations in position between maser spots andnuclear X-ray source and a high degree of clumpiness in thecircumnuclear interstellar medium.
| Massive star formation in the central regions of spiral galaxies
Context: . The morphology of massive star formation in the centralregions of galaxies is an important tracer of the dynamical processesthat govern the evolution of disk, bulge, and nuclear activity. Aims. Wepresent optical imaging of the central regions of a sample of 73 spiralgalaxies in the Hα line and in optical broad bands, and deriveinformation on the morphology of massive star formation. Methods. Weobtained images with the William Herschel Telescope, mostly at a spatialresolution of below one second of arc. For most galaxies, no Hαimaging is available in the literature. We outline the observing anddata reduction procedures, list basic properties, and present the I-bandand continuum-subtracted Hα images. We classify the morphology ofthe nuclear and circumnuclear Hα emission and explore trends withhost galaxy parameters. Results. We confirm that late-type galaxies havea patchy circumnuclear appearance in Hα, and that nuclear ringsoccur primarily in spiral types Sa-Sbc. We identify a number ofpreviously unknown nuclear rings, and confirm that nuclear rings arepredominantly hosted by barred galaxies. Conclusions. Other than instimulating nuclear rings, bars do not influence the relative strengthof the nuclear Hα peak, nor the circumnuclear Hα morphology.Even considering that our selection criteria led to an over-abundance ofgalaxies with close massive companions, we do not find any significantinfluence of the presence or absence of a close companion on therelative strength of the nuclear Hα peak, nor on the Hαmorphology around the nucleus.
| Molecular hydrogen and [FeII] in active galactic nuclei - II. Results for Seyfert 2 galaxies
Near-infrared spectroscopy is used to study the kinematics andexcitation mechanisms of H2 and [FeII] lines in a sampledominated by Seyfert 2 galaxies. The spectra simultaneously cover theJHK bands, allowing us to compare line fluxes emitted in the interval0.8-2.4 μm and avoiding aperture and seeing effects. TheH2 lines are systematically narrower than the narrow-lineregion lines, suggesting that, very likely, the H2 does notoriginate from the same parcel of gas that forms the narrow-line region.Emission-line ratios between H2 lines favour thermalexcitation mechanisms for the molecular gas in active galactic nuclei.It was found that non-thermal excitation contributes, at most, 30 percent of the observed H2. Thermal excitation is also confirmedby the rather similar vibrational and rotational temperatures in theobjects (~2000 K). The mass of hot H2 ranges from102 to 103Msolar, with nearly half ofobjects showing values of <500 Msolar. It shows that thefraction of molecular mass present in the nuclear region and emitting inthe near-infrared is a very small fraction of the warm molecular masspresent in the centre. A diagnostic diagram composed of the line ratiosH2/Brγ and [FeII]/Paβ proves to be a useful toolin the near-infrared for separating emission-line objects by theirdegree of nuclear activity. We found that active galactic nuclei arecharacterized by H2 2.121 μm/Brγ and [FeII] 1.257μm/Paβ flux ratios between 0.6 and 2. Starburst/HII galaxiesdisplay line ratios <0.6 while low-ionization nuclear emission-lineregions are characterized by values larger than 2 in either ratio.
| The Relationship of Hard X-Ray and Optical Line Emission in Low-Redshift Active Galactic Nuclei
In this paper we assess the relationship of the population of activegalactic nuclei (AGNs) selected by hard X-rays to the traditionalpopulation of AGNs with strong optical emission lines. First, we studythe emission-line properties of a new hard-X-ray-selected sample of 47local AGNs (classified optically as Type 1 and 2 AGNs). We find that thehard X-ray (3-20 keV) and [O III] λ5007 optical emission-lineluminosities are well-correlated over a range of about 4 orders ofmagnitude in luminosity (mean luminosity ratio 2.15 dex with a standarddeviation of σ=0.51 dex). Second, we study the hard X-rayproperties of a sample of 55 local AGNs selected from the literature onthe basis of the flux in the [O III] line. The correlation between thehard X-ray (2-10 keV) and [O III] luminosity for the Type 1 AGNs isconsistent with what is seen in the hard-X-ray-selected sample. However,the Type 2 AGNs have a much larger range in the luminosity ratio, andmany are very weak in hard X-rays (as expected for heavily absorbedAGNs). We then compare the hard X-ray (3-20 keV) and [O III] luminosityfunctions of AGNs in the local universe. These have similar faint-endslopes, with a luminosity ratio of 1.60 dex (0.55 dex smaller than themean value for individual hard-X-ray-selected AGNs). We conclude that atlow redshift, selection by narrow optical emission lines will recovermost AGNs selected by hard X-rays (with the exception of BL Lacobjects). However, selection by hard X-rays misses a significantfraction of the local AGN population with strong emission lines.
| The Swift/BAT High-Latitude Survey: First Results
We present preliminary results from the first 3 months of the SwiftBurst Alert Telescope (BAT) high Galactic latitude survey in the 14-195keV band. The survey reaches a flux of ~10-11 ergscm-2 s-1 and has ~2.7 arcmin (90% confidence)positional uncertainties for the faintest sources. This represents themost sensitive survey to date in this energy band. These data confirmthe conjectures that a high-energy-selected active galactic nucleus(AGN) sample would have very different properties from those selected inother bands and that it represents a ``true'' sample of the AGNpopulation. We have identified 86% of the 66 high-latitude sources.Twelve are Galactic-type sources, and 44 can be identified withpreviously known AGNs. All but five of the AGNs have archival X-rayspectra, enabling us to estimate the line-of-sight column densities andother spectral properties. Both of the z>0.11 objects are blazars.The median redshift of the others (excluding radio-loud objects) is0.012. We find that the column density distribution of these AGNs isbimodal, with 64% of the nonblazar sources having column densitiesNH>=1022 cm-2. None of the sourceswith logLX>43.5 (cgs units) show high column densities,and very few of the lower LX sources have low columndensities. Based on these data, we expect the final BAT catalog to have>200 AGNs and reach fluxes of less than ~10-11 ergscm-2 s-1 over the entire sky.
| The Connection between the Narrow-Line Region and the UV Absorbers in Seyfert Galaxies
We present evidence that the outflowing UV absorbers in Seyfert 1galaxies arise primarily in their inner narrow- (emission-) line regions(NLRs), based on similarities in their locations, kinematics, andphysical conditions. Hubble Space Telescope observations show thatnearly all Seyfert galaxies have bright, central knots of [O III]emission in their NLRs with radii of tens of parsecs. These sizes areconsistent with most previous estimates of the distances of UV (andX-ray) absorbers from their central continuum sources and a recentlyobtained reliable distance of ~25 pc for a UV absorber in the Seyfert 1galaxy NGC 3783. The nuclear emission-line knots in a sample of 10Seyfert galaxies have velocity widths of 300-1100 km s-1(half-width at zero intensity), similar to the radial velocities of mostUV absorbers. The highest radial velocity for a Seyfert UV absorber todate is only -2100 km s-1, which is much lower than typicalbroad-line region (BLR) velocities. There is also mounting evidence thatthe NLR clouds are outflowing from the nucleus, like the UV absorbers.If our hypothesis is correct, then the NLR should have a component witha high global covering factor (Cg) of the continuum sourceand a BLR to match that found from previous surveys of UV absorbers(Cg=0.5-1.0). Using Space Telescope Imaging Spectrographspectra of NGC 4151, obtained when the continuum and BLR fluxes werelow, we find evidence for optically thin gas in its nuclearemission-line knot. We are able to match the line ratios from this gaswith photoionization models that include a component withCg~1 and an ionization parameter and hydrogen column densitythat are typical of UV absorbers.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| Rotational Widths for Use in the Tully-Fisher Relation. I. Long-Slit Spectroscopic Data
We present new long-slit Hα spectroscopy for 403 noninteractingspiral galaxies, obtained at the Palomar Observatory 5 m Hale telescope,which is used to derive well-sampled optical rotation curves. Becausemany of the galaxies show optical emission features that aresignificantly extended along the spectrograph slit, a technique wasdevised to separate and subtract the night sky lines from the galaxyemission. We exploit a functional fit to the rotation curve to identifyits center of symmetry; this method minimizes the asymmetry in thefinal, folded rotation curve. We derive rotational widths using bothvelocity histograms and the Polyex model fit. The final rotational widthis measured at a radius containing 83% of the total light as derivedfrom I-band images. In addition to presenting the new data, we use alarge sample of 742 galaxies for which both optical long-slit and radioH I line spectroscopy are available to investigate the relation betweenthe H I content of the disks and the extent of their rotation curves.Our results show that the correlation between those quantities, which iswell established in the case of H I-poor galaxies in clusters, ispresent also in H I-normal objects: for a given optical size, starformation can be traced farther out in the disks of galaxies with largerH I mass.
| Hα Imaging of Early-Type Sa-Sab Spiral Galaxies. II. Global Properties
New results, based on one of the most comprehensive Hα imagingsurveys of nearby Sa-Sab spirals completed to date, reveals early-typespirals to be a diverse group of galaxies that span a wide range inmassive star formation rates. While the majority of Sa-Sab galaxies inour sample are forming stars at a modest rate, a significant fraction(~29%) exhibit star formation rates greater than 1 Msolaryr-1, rivaling the most prolifically star-forming late-typespirals. A similar diversity is apparent in the star formation historyof Sa-Sab spirals as measured by their Hα equivalent widths.Consistent with our preliminary results presented in the first paper inthis series, we find giant H II regions [L(Hα)>=1039ergs s-1] in the disks of ~37% of early-type spirals. Wesuspect that recent minor mergers or past interactions are responsiblefor the elevated levels of Hα emission and, perhaps, for thepresence of giant H II regions in these galaxies. Our results, however,are not in total agreement with the Hα study of Kennicutt &Kent, who did not find any early-type spirals with Hα equivalentwidths >14 Å. A close examination of the morphologicalclassification of galaxies, however, suggests that systematicdifferences between the Revised Shapley-Ames Catalog and the SecondReference Catalogue may be responsible for the contrasting results.Based on observations obtained with the 3.5 m telescope at Apache PointObservatory (APO) and the 0.9 m telescope at Kitt Peak NationalObservatory (KPNO). The APO 3.5 m telescope is owned and operated by theAstrophysical Research Consortium.
| Probing the Kinematics of the Narrow-Line Region in Seyfert Galaxies with Slitless Spectroscopy: Observational Results
We present slitless spectra of 10 Seyfert galaxies observed with theSpace Telescope Imaging Spectrograph on the Hubble Space Telescope(HST). The spectra cover the [O III] λλ4959, 5007 emissionlines at a spectral resolving power of λ/Δλ~9000 anda spatial resolution of ~0.1". We compare the slitless spectra withprevious HST narrowband images to determine the velocity shifts anddispersions of the bright emission-line knots in the narrow-line regions(NLRs) of these Seyfert galaxies, which extend out to at least severalhundred parsecs from their nuclei. Many knots are spatially resolvedwith sizes of tenths of arcseconds, corresponding to tens of parsecs,and yet they appear to move coherently with radial velocities betweenzero and +/-1200 km s-1 with respect to the systemicvelocities of their host galaxies. The knots also show a broad range invelocity dispersion, ranging from ~30 km s-1 (the velocityresolution) to ~1000 km s-1 FWHM. Most of the Seyfertgalaxies in this sample show an organized flow pattern, with radialvelocities near zero at the nucleus (defined by the optical continuumpeak) and increasing to maximum blueshifts and redshifts within ~1" ofthe nucleus, followed by a decline to the systemic velocity. However,there are large local variations around this pattern, and in one case(NGC 7212), the radial velocities are nearly chaotic. The emission-lineknots also follow a general trend of decreasing velocity dispersion withincreasing distance from the nucleus. In the Seyfert 2 galaxies, thepresence of blueshifts and redshifts on either side of the nucleusindicates that rotation alone cannot explain the observed radialvelocities. The most straightforward interpretation is that radialoutflow plays an important role in the NLR kinematics. Each of theSeyfert galaxies in this sample (with the exception of Mrk 3) shows abright, compact (FWHM<=0.5") [O III] knot at the position of itsoptical nucleus. These nuclear emission-line knots have radial velocitycentroids near zero, but they typically have the highest velocitydispersions. Their similar properties suggest that they may be a common,distinct component of the NLR.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute (STScI), which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS5-26555. These observations areassociated with proposal GO-8340.
| Dark matter in the inner parts of barred galaxies: The data
This paper presents surface photometry (B,V,I,J,H,K) and Hαrotation curves of 27 isolated spiral galaxies. The final goal is toobtain the mass distribution of a sample of isolated spiral galaxies inorder to model their gas kinematics. This is then compared to theobserved rotation curve, to determine the necessity of a dark halo inthe inner parts (Perez et al. 2004, A&A, 424, 799). The azimuthallyaveraged radial surface brightness profiles and the integratedmagnitudes obtained from ellipse fitting are given for each of thesample galaxies. The ellipse fitting technique applied to the lightdistribution also allowed us to obtain the size of the bar, and theinclination and position angle of the outer isophotes that allow thegalaxy deprojection. Using these profiles, 1-D disk-bulge decompositionwas performed to obtain the disk scale-length and the bulge effectiveradius for the different bands. Through the fitting of a parametricfunction to the observed rotation curve, the maximum rotational velocityand the corresponding radius was obtained. The correlation between thebulge and disk parameters is in agreement with previous studies (de Jong1996a, A&A, 313, 45; Márquez & Moles 1999, A&A, 344,421; Baggett et al. 1998, AJ, 116, 1626). Regarding the Kormendyrelation (Kormendy 1977, ApJ, 218, 333), in agreement with de Jong, nocorrelation between the bulge effective radius and its surfacebrightness is found, possibly due to the small range of bulge magnitudescovered. We find a smaller scatter in the structural relations whencompared to non-isolated samples in agreement with Márquez &Moles (1999). Finally, a correlation between the disk scale-length andthe bar size is observed, possibly reflecting the rapid growth of a bar.
| 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.
| Asymmetrical structure of ionization and kinematics in the Seyfert galaxy NGC 5033
We present integral field spectroscopy of NGC 5033, a low luminositySeyfert galaxy. The observations were made with INTEGRAL, a fiber basedsystem operating at the WHT. The intensity map of the Hβ emissionline represents a spiral or ring-like pattern of HII regions. On thecontrary, the [OIII] intensity map morphology is markedly anisotropic.The strong morphological differences imply that the [OIII] emittersrepresent highly ionized gas illuminated by the central source. The[OIII] map morphology is compatible with a biconical structure ofionization induced by strong extinction in the galaxy disc that alsoobscures half of the spheroidal stellar bulge. We identify the spectrumcorresponding to the Seyfert 1 nucleus from the presence of Hβbroad emission lines. This spectrum is located in a region where strongextinction is expected but exhibits the bluest spectral energydistribution. The Seyfert 1 nucleus seems to be offcenter with respectto the stellar rotation center. This result has been also found in otherSeyfert galaxies and interpreted in terms of a past merger. Theoffcentering could indicate the presence of nonsymmetric departures inthe gravitational potential which could be fueling the active nucleus.The kinematics of the [OIII] emitters show important deviations at a kpcscale with respect to the stellar velocity field and show featuresrelated to the asymmetrical morphology of the high ionization region.
| The star formation history of Seyfert 2 nuclei
We present a study of the stellar populations in the central ~200 pc ofa large and homogeneous sample comprising 79 nearby galaxies, most ofwhich are Seyfert 2s. The star formation history of these nuclei isreconstructed by means of state-of-the-art population synthesismodelling of their spectra in the 3500-5200 Åinterval. Aquasar-like featureless continuum (FC) is added to the models to accountfor possible scattered light from a hidden active galactic nucleus(AGN).We find the following. (1) The star formation history of Seyfert 2nuclei is remarkably heterogeneous: young starbursts, intermediate-ageand old stellar populations all appear in significant and widely varyingproportions. (2) A significant fraction of the nuclei show a strong FCcomponent, but this FC is not always an indication of a hidden AGN: itcan also betray the presence of a young, dusty starburst. (3) We detectweak broad Hβ emission in several Seyfert 2s after cleaning theobserved spectrum by subtracting the synthesis model. These are mostlikely the weak scattered lines from the hidden broad-line regionenvisaged in the unified model, given that in most of these casesindependent spectropolarimetry data find a hidden Seyfert 1. (4) The FCstrengths obtained by the spectral decomposition are substantiallylarger for the Seyfert 2s which present evidence of broad lines,implying that the scattered non-stellar continuum is also detected. (5)There is no correlation between the star formation in the nucleus andeither the central or overall morphology of the parent galaxies.
| Dusty, Radiation Pressure-Dominated Photoionization. II. Multiwavelength Emission Line Diagnostics for Narrow-Line Regions
Seyfert narrow-line region (NLR) emission line ratios are remarkablyuniform, displaying only ~0.5 dex variation between galaxies, and evenless within an individual object. Previous photoionization and shockmodels of this region were unable to explain this observation withoutthe introduction of arbitrary assumptions or additional parameters.Dusty, radiation pressure-dominated photoionization models provide asimple physical mechanism that can reproduce this spectral uniformitybetween different objects. In the first paper of this series, wedescribed this model and its implementation in detail, as well aspresenting grids of model emission lines and examining the modelstructures. Here we explore these models further, demonstrating theirability to reproduce the observed Seyfert line ratios on standard linediagnostic diagrams in both the optical and UV. We also investigate theeffects that the variation of metallicity, density, and ionizingspectrum have upon both the new paradigm and the standardphotoionization models used hitherto. Along with the standard diagnosticdiagrams we provide several new diagnostic diagrams in the UV, optical,and IR. These new diagrams can provide further tests of the dusty,radiation pressure photoionization paradigm as well as being used asdiagnostics of the metallicity, density, and ionizing spectrum of theemission line clouds.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Emission Line Properties of Active Galactic Nuclei from a Post-COSTAR Hubble Space Telescope Faint Object Spectrograph Spectral Atlas
We present consistent emission-line measurements for active galacticnuclei (AGNs), useful for reliable statistical studies of emission lineproperties. This paper joins a series including similar measurements of993 spectra from the Large Bright Quasar Survey and 174 spectra of AGNsobtained from the Faint Object Spectrograph (FOS) on the Hubble SpaceTelescope (HST) prior to the installation of COSTAR. This time weconcentrate on 220 spectra obtained with the FOS after the installationof COSTAR, completing the emission line analysis of all FOS archivalspectra. We use the same automated technique as in previous papers,which accounts for Galactic extinction, models blended optical and UViron emission, includes Galactic and intrinsic absorption lines, andmodels emission lines using multiple Gaussians. We present UV andoptical emission line parameters (equivalent widths, fluxes, FWHM, andline positions) for a large number (28) of emission lines includingupper limits for undetected lines. Further scientific analyses will bepresented in subsequent papers.
| 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.
| Molecular Gas in Candidate Double-Barred Galaxies. III. A Lack of Molecular Gas?
Most models of double-barred galaxies suggest that a molecular gascomponent is crucial for maintaining long-lived nuclear bars. We haveundertaken a CO survey in an attempt to determine the gas content ofthese systems and to locate double-barred galaxies with strong COemission that could be candidates for high-resolution mapping. Weobserved 10 galaxies in CO J=2-1 and J=3-2 and did not detect anygalaxies that had not already been detected in previous CO surveys. Wepreferentially detect emission from galaxies containing some form ofnuclear activity. Simulations of these galaxies require that theycontain 2%-10% gas by mass in order to maintain long-lived nuclear bars.The fluxes for the galaxies for which we have detections suggest thatthe gas mass fraction is in agreement with these models requirements.The lack of emission in the other galaxies suggests that they contain aslittle as 7×106 Msolar of molecularmaterial, which corresponds to <~0.1% gas by mass. This resultcombined with the wide variety of CO distributions observed indouble-barred galaxies suggests the need for models of double-barredgalaxies that do not require a large, well-ordered molecular gascomponent.
| Stellar Kinematics of Boxy Bulges: Large-Scale Bars and Inner Disks
Long-slit stellar kinematic observations were obtained along the majoraxis of 30 edge-on spiral galaxies, 24 with a boxy or peanut-shaped(B/PS) bulge and six with other bulge types for comparison. Such B/PSbulges are identified in at least 45% of highly inclined systems, and agrowing body of theoretical and observational work suggests that theyare the edge-on projection of thickened bars. Profiles of the meanstellar velocity V, the velocity dispersion σ, as well as theasymmetric (h3) and symmetric (h4) deviations froma pure Gaussian are presented for all objects. Comparing these profileswith stellar kinematic bar diagnostics developed from N-bodysimulations, we find bar signatures in 24 of our sample galaxies (80%).Galaxies with a B/PS bulge typically show a double-humped rotation curvewith an intermediate dip or plateau. They also frequently show a ratherflat central velocity dispersion profile accompanied by a secondary peakor plateau, and numerous galaxies have a local central σ minimum(>~40%). The h3 profiles display up to three slopereversals. Most importantly, h3 is normally correlated with Vover the presumed bar length, contrary to expectations from axisymmetricdisks. These characteristic bar signatures strengthen the case for aclose relationship between B/PS bulges and bars and leave little roomfor other explanations of the bulges' shape. We also find thath3 is anticorrelated with V in the very center of mostgalaxies (>~60%), indicating that these objects additionally harborcold and dense decoupled (quasi-) axisymmetric central stellar disks,which may be related to the central light peaks. These central diskscoincide with previously identified star-forming ionized-gas disks(nuclear spirals) in gas-rich systems, and we argue that they formed outof gas accumulated by the bar at its center through inflow. As suggestedby N-body models, the asymmetry of the velocity profile (h3)appears to be a reliable tracer of asymmetries in disks, allowing us todiscriminate between axisymmetric and barred disks seen in projection.B/PS bulges (and thus a large fraction of all bulges) appear to be madeup mostly of disk material, which has acquired a large vertical extentthrough bar-driven vertical instabilities. Their formation is thusprobably dominated by secular evolution processes rather than merging.
| Molecular hydrogen and [Fe II] in Active Galactic Nuclei
Near-infrared spectroscopy is used to study the kinematics andexcitation mechanisms of H2 and [Fe II] lines in a sample ofmostly Seyfert 1 galaxies. The spectral coverage allows simultaneousobservation of the JHK bands, thus eliminating the aperture and seeingeffects that have usually plagued previous works. The H2lines are unresolved in all objects in which they were detected whilethe [Fe II] lines have widths implying gas velocities of up to 650 ~kms-1. This suggests that, very likely, the H2 and[Fe II] emission does not originate from the same parcel of gas.Molecular H2 lines were detected in 90% of the sample,including PG objects, indicating detectable amounts of molecularmaterial even in objects with low levels of circumnuclear starburstactivity. Analysis of the observations favors thermal excitationmechanisms for the H2 lines. Indeed, in NGC 3227, Mrk 766,NGC 4051 and NGC 4151, the molecular emission is found to be purelythermal but with heating processes that vary between the objects.Thermal excitation is also confirmed by the rather similar vibrationaland rotational temperatures in the objects for which data wereavailable. [Fe II] lines are detected in all of the sample AGN. The [FeII] 1.254 μm/Paβ ratio is compatible with excitation of the [FeII] lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk766 the ratio implies a stellar origin. A correlation betweenH2/Brγ and [Fe II]/Paβ is found for our sampleobjects supplemented by data from the literature. The correlation ofthese line ratios is a useful diagnostic tool in the NIR to separateemitting line objects by their level of nuclear activity. X-rayexcitation models are able to explain the observed H2 andpart of the [Fe II] emission but fail to explain the observations inSeyfert 2 galaxies. Most likely, a combination of X-ray heating, shocksdriven by the radio jet and circumnuclear star formation contributes, indifferent proportions, to the H2 and [Fe II] lines observed.In most of our sample objects, the [Fe II] 1.257 μm/1.644 μm ratiois found to be 30% lower than the intrinsic value based on currentatomic data. This implies either that the extinction towards the [FeII]-emitting clouds is very similar in most objects or there arepossible inaccuracies in the A-values in the Fe II transitions.Based on observations taken at the Infrared Telescope Facility, which isoperated by the University of Hawaii under Cooperative Agreement no. NCC5-538 with the National Aeronautics and Space Administration, Office ofSpace Science, Planetary Astronomy Program.
| Gas flow and dark matter in the inner parts of early-type barred galaxies. I. SPH simulations and comparison with the observed kinematics
This paper presents the dynamical simulations run in the potentialderived from the light distribution of 5 late-type barred spiralgalaxies (IC 5186, NGC 5728,NGC 7267, NGC 7483 and NGC 5505). The aim is to determine whether the massdistribution together with the hydrodynamical simulations can reproducethe observed line-of-sight velocity curves and the gas morphology in theinner regions of these barred galaxies. The light distribution isobtained from the H-band and the I-band combined. The M/L is determinedusing population synthesis models. The observations and the methodologyof the mass distribution modelling are presented in a companion paper.The SPH models using the stellar mass models obtained directly from theH-band light distributions give a good representation of the gasdistribution and dynamics of the modelled galaxies, supporting themaximum disk assumption. This result indicates that the gravitationalfield in the inner region is mostly provided by the stellar luminouscomponent. When 40% of the total mass is transferred to an axisymmetricdark halo, the modelled kinematics clearly depart from the observedkinematics, whereas the departures are negligible for dark mass halos of5% and 20% of the total mass. This result sets a lower limit for thecontribution of the luminous component of about 80%, which is inagreement with the maximum disk definition of the stellar masscontribution to the rotation curve (about 85% ± 10). This resultis in agreement with the results found by \citet{weiner01} forNGC 4123 using a similar methodology. For twogalaxies, NGC 7483 and IC 5186, a very good agreement with the observeddata is found. In these cases the non-circular motions can help to breakthe disk-halo degeneracy. For the other three galaxies (NGC 5728, NGC7267 and NGC 5505) no definite results are found: for NGC 7267 and NGC5505 no steady state is reached in the simulations and for NGC 5728there is no good agreement with the observed kinematics, possibly due tothe presence of a secondary bar decoupled from the primary. However, forthis latter galaxy the M/L ratio used gives the right amplitude of therotation curve, in further support of the M/L calculation method usedthroughout this work. Fast bars give the best fit to the observedkinematics for NGC 7483 and IC 5186 with corotation at the end of thebar for NGC 7483 and at 1.4× Rbar for IC 5186. For NGC5505 for which no steady state configuration is found, the addition of arigid halo stabilises the gas flows but the derived kinematics does notfit well the observations.Figures \ref{fig:vel1}-\ref{fig:Lz_IC5186}, \ref{fig:mask_height},\ref{fig:height_rc}, \ref{fig:rc_NGC5728}, \ref{fig:pv_NGC7483},\ref{fig:substract_NGC7483}, \ref{fig:mask_dm}, \ref{fig:dm_rc} and\ref{fig:ngc5505_dm_rc} are only available in electronic form athttp://www.edpsciences.org}
| Structure and kinematics of candidatedouble-barred galaxies
Results of optical and NIR spectral and photometric observations of asample of candidate double-barred galaxies are presented. Velocityfields and velocity dispersion maps of stars and ionized gas, continuumand emission-line images were constructed from integral-fieldspectroscopy observations carried out at the 6 m telescope (BTA) of SAORAS, with the MPFS spectrograph and the scanning Fabry-PerotInterferometer. NGC 2681 was also observed with thelong-slit spectrograph of the BTA. Optical and NIR images were obtainedat the BTA and at the 2.1 m telescope (OAN, México).High-resolution images were retrieved from the HST data archive.Morphological and kinematic features of all 13 sample objects aredescribed in detail. Attention is focused on the interpretation ofobserved non-circular motions of gas and stars in circumnuclear (onekiloparsec-scale) regions. We have shown first of all that these motionsare caused by the gravitational potential of a large-scale bar.NGC 3368 and NGC 3786 have nuclearbars only, their isophotal twist at larger radii being connected withthe bright spiral arms. Three cases of inner polar disks in our sample(NGC 2681, NGC 3368 andNGC 5850) are considered. We found ionized-gascounter-rotation in the central kiloparsec of the lenticular galaxyNGC 3945. Seven galaxies (NGC 470,NGC 2273, NGC 2681, NGC3945, NGC 5566, NGC5905, and NGC 6951) have inner mini-disksnested in large-scale bars. Minispiral structures occur often in thesenuclear disks. It is interesting that the majority of the observed,morphological and kinematical, features in the sample galaxies can beexplained without the secondary bar hypothesis. Thus we suggest that adynamically independent secondary bar is a rarer phenomenon than followsfrom isophotal analysis of the images only.Based on observations carried out at the 6 m telescope of the SpecialAstrophysical Observatory of the Russian Academy of Sciences, operatedunder the financial support of the Science Department of Russia(registration number 01-43), at the 2.1 m telescope of the ObservatorioAstronónico Nacional, San Pedro Martir, México, and fromthe data archive of the NASA/ESA Hubble Space Telescope at the SpaceTelescope Science Institute. STScI is operated by the association ofUniversities for Research in Astronomy, Inc. under NASA contract NAS5-26555.Tables 1 to 6 and Figures 2-13 and 15-18 are only available inelectronic form at http://www.edpsciences.org
| Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4spiral galaxies which are characterized by a zero-velocity plateau alongthe major axis and a velocity gradient along the minor axis,respectively. By combining these new kinematical data with thoseavailable in the literature for the ionized-gas component of the S0s andspirals listed in the Revised Shapley-Ames Catalog of Bright Galaxies werealized that about 50% of unbarred galaxies show a remarkable gasvelocity gradient along the optical minor axis. This fraction rises toabout 60% if we include unbarred galaxies with an irregular velocityprofile along the minor axis. This phenomenon is observed all along theHubble sequence of disk galaxies, and it is particularly frequent inearly-type spirals. Since minor-axis velocity gradients are unexpectedif the gas is moving onto circular orbits in a disk coplanar to thestellar one, we conclude that non-circular and off-plane gas motions arenot rare in the inner regions of disk galaxies.Based on observations carried out at the European Southern Observatoryin La Silla (Chile) (ESO 69.B-0706 and 70.B-0338), with the MultipleMirror Telescope which is a joint facility of the SmithsonianInstitution and the University of Arizona, and with the ItalianTelescopio Nazionale Galileo (AOT-5, 3-18) at the Observatorio del Roquede los Muchachos in La Palma (Spain).Table 1 is only available in electronic form athttp://www.edpsciences.org. Table 5 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/507
| Long slit spectroscopy of a sample of isolated spirals with and without an AGN
We present the kinematical data obtained for a sample of active(Seyfert) and non active isolated spiral galaxies, based on long slitspectra along several position angles in the Hα line region and,in some cases, in the Ca triplet region as well. Gas velocitydistributions are presented, together with a simple circular rotationmodel that allows us to determine the kinematical major axes. Stellarvelocity distributions are also shown. The main result is that activeand control galaxies seem to be equivalent in all kinematical aspects.For both subsamples, the departure from pure circular rotation in somegalaxies can be explained by the presence of a bar and/or of a spiralarm. They also present the same kind of peculiarities, in particular,S-shape structures are quite common near the nuclear regions. Theydefine very similar Tully-Fisher relations. Emission line ratios aregiven for all the detected HII regions; the analysis of the[NII]/Hα metallicity indicator shows that active and non-activegalaxies have indistinguishable disk metallicities. These results arguein favour of active and non-active isolated spiral galaxies havingessentially the same properties, in agreement with our previous resultsbased on the analysis of near infrared images. It appears now necessaryto confirm these results on a larger sample.Based on observations made with WHT operated on the island of La Palmaby ING in the Spanish Observatorio del Roque de Los Muchachos of theInstituto de Astrofísica de Canarias, the European SouthernObservatory (La Silla), Calar Alto Observatory (Almería, Spain)and Las Campanas Observatories (Chile).Table 3 and Figs. \ref{res_cen_u1395}, 5, 7, 9, 11, 13, 15, 17, 19, 21,23, 25, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50 and 52 are onlyavailable in electronic form at http://www.edpsciences.orgTable 5 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/416/475
| Double-barred galaxies. I. A catalog of barred galaxies with stellar secondary bars and inner disks
I present a catalog of 67 barred galaxies which contain distinct,elliptical stellar structures inside their bars. Fifty of these aredouble-barred galaxies: a small-scale, inner or secondary bar isembedded within a large-scale, outer or primary bar. I providehomogenized measurements of the sizes, ellipticities, and orientationsof both inner and outer bars, along with global parameters for thegalaxies. The other 17 are classified as inner-disk galaxies, where alarge-scale bar harbors an inner elliptical structure which is alignedwith the galaxy's outer disk. Four of the double-barred galaxies alsopossess inner disks, located in between the inner and outer bars. Whilethe inner-disk classification is ad-hoc - and undoubtedly includes someinner bars with chance alignments (five such probable cases areidentified) - there is good evidence that inner disks form astatistically distinct population, and that at least some are indeeddisks rather than bars. In addition, I list 36 galaxies which may bedouble-barred, but for which current observations are ambiguous orincomplete, and another 23 galaxies which have been previously suggestedas potentially being double-barred, but which are probably not. Falsedouble-bar identifications are usually due to features such as nuclearrings and spirals being misclassified as bars; I provide someillustrated examples of how this can happen.A detailed statistical analysis of the general population of double-barand inner-disk galaxies, as represented by this catalog, will bepresented in a companion paper.Tables \ref{tab:measured} and \ref{tab:deproj} are only available inelectronic form at http://www.edpsciences.org
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