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Evidence for Interactions in H I Imaging of Seyfert Galaxies
We still do not know the primary trigger of local active galacticnuclei. Tidal torques and nuclear bars are often invoked to explain gasinfall onto the central supermassive black hole, but as yet neither hasdefinitive observational support. Here we exploit the sensitivity andendurance of H I to trace the strength and prevalence of tidalinteractions among Seyfert galaxies. To minimize selection biases, wesurvey the 27 northern Seyferts compiled in the comprehensive opticalcatalog of Véron-Cetty & Véron lying in the narrowredshift range 0.015-0.017. This paper is a detailed presentation of asubsample, including channel maps for all systems. In addition to theprogram objects, we also investigate galaxies imaged in the field.
| Galaxy Interaction and the Starburst-Seyfert Connection
Galaxy interactions are studied in terms of the starburst-Seyfertconnection. The starburst requires a high rate of gas supply. Since theefficiency for supplying the gas is high in a galaxy interaction,although the companion is not necessarily discernible, Seyfert galaxieswith circumnuclear starbursts are expected to be interacting. Since thelarge amounts of circumnuclear gas and dust obscure the broad-lineregion, they are expected to be observed as Seyfert 2 galaxies. Theactive galactic nucleus itself does not require a high rate of gassupply. Seyfert galaxies without circumnuclear starbursts are notnecessarily expected to be interacting even at the highest luminosities.They are not necessarily expected to evolve from Seyfert galaxies withcircumnuclear starbursts. We derive these and other theoreticalexpectations and confirm them with statistics on observational data ofmagnitude-limited samples of Seyfert galaxies.
| An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
| VLBI Imaging of Luminous Infrared Galaxies: Active Galactic Nucleus Cores in Markarian 231, UGC 5101, and NGC 7469
We report 18 cm VLBI continuum imaging observations at ~5 mas resolutionfor UGC 5101, NGC 7469, and Mrk 231, all part of a sample of luminousinfrared galaxies that were shown to have strong VLBI radio cores in aprevious 18 cm VLBI survey. Mrk 231, generally considered to be adust-enshrouded quasi-stellar object (QSO), shares many characteristicswith quasars, including a broad Sy1 optical emission spectrum, opticaland radio variability, and a broad absorption line spectrum. NGC 7469 isa classical Sy1 galaxy, and UGC 5101 is a LINER system. The radiomorphology of these three systems on VLBI scales is like that of anactive galactic nucleus (AGN), with well-defined ridgelines andhigh-brightness yet spatially resolved components. The structure andflux densities of these VLBI components are not consistent withstarburst-generated radio supernovae of the type found in Arp 220. Onscales of ~100 pc and perhaps beyond, the radio continuum in all threeobjects appears to be dominated by an AGN, not a starburst. Radioemission on larger scales may well originate, in part or in total, in aless compact circumnuclear star-forming region. This is in contrast tothe situation thought to prevail in many luminous infrared galaxies(LIGs), which involves a very compact and dense nuclear star-formingregion. By placing a lower limit on the AGN-related radio emission, itis possible to shed light on the relative luminosities of the AGN andstarburst in these objects. Using the far-infrared-radio correlation forstarburst-related radio emission, we show that, despite the unambiguousevidence for AGN activity in these systems, the AGN luminosity, althoughenergetically important, may be exceeded by the extended starburstluminosity in all three cases, unless the bolometric luminosity of theentire system has been underestimated. The lower limits on AGN-relatedradio emission indicate that these AGNs are somewhat overluminous in theradio compared with radio-quiet Palomar-Green (PG) QSOs and thus thatthe AGN radio luminosity cannot be used to estimate the bolometricluminosity of the AGN. However, comparing near- and mid-IR luminositiesof the LIGs to those of PG QSOs, we find evidence that a significantfraction of the bolometric luminosity of the AGN in Mrk 231 and to alesser extent UGC 5101 may be radiated away from Earth and thus notdetected at any wavelength. The VLBI structure observed in Mrk 231allows additional interpretation. Confirming and extending VLBI imagingby Ulvestad, Wrobel, and Carilli, our continuum image shows a triplestructure, with a core and two lobes, causing it to be classied as acompact symmetric object. It has been suggested that these sources areyoung, τ<<106 yr, with the hot spots representingthe working surface of a relativistic jet on the ambient medium. If thesouthern (primary) lobe/hot-spot in Mrk 231 is confined by ram pressure,we estimate a lobe advance speed, va~10-4c, and anage for the jet/compact source, τ<106 yr. We have alsoimaged the 1667 MHz OH maser emission in Mrk 231, which is extended onscales of 50-100 mas (40-80 pc) and probably coincides with the innerregion of the disk, which is seen in CO emission and H I absorption.Among OH megamaser sources studied at high sensitivity withmilliarcsecond resolution, Mrk 231 is unique in the stringent upperlimits placed on the flux density of compact OH structures of the typefound in Arp 220 and other LIGs. It is possible that the circumnuclearenvironment of Mrk 231 has been sufficiently disrupted by the emergentQSO that the cool dense clouds necessary for such compact masers nolonger exist.Based on observations from the VLBA of the National Radio AstronomyObservatory, which is a facility of the National Science Foundation,operated under cooperative agreement by Associated Universities, Inc.
| Tridimensional Spectroscopic Observation of the Interacting System NGC 7592
We performed a tridimensional spectroscopic study of NGC 7592, aninfrared-luminous interacting system of three galaxies, one of whichcontains a Seyfert 2 nucleus. Narrow-band images of Hα and [O III] were obtained using an imaging Fabry-Perot interferometer with atunable filter. An area-spectroscopic observation was also made by aslit scan in a direction perpendicular to the slit. The Seyfert nucleuswas found to be surrounded by a knotty star-forming region of disk- orring-shape. Along the axis of the disk or ring, a highly-ionized bipolargaseous region was identified. From kinematical analyses, it has beensuggested that this system is composed of two galaxies; one apparentnucleus is considered to be a giant H II region belonging to one galaxy.This result is supported by the morphological properties innear-infrared. Further, it has been suggested that one galaxy is anearly-type spiral, whereas the other is a late-type one, and the twogalaxies show a marked difference in the distribution of thestar-forming regions within each. The cause of the difference was arguedin relation with the dynamical perturbation between the two galaxies.
| Sub-arcsecond atomic hydrogen absorption in the Seyfert galaxies NGC 7674 and NGC 7469
Neutral hydrogen has been studied on sub-arcsecond scales in two Seyfertgalaxies, NGC 7469 and NGC 7674. The 1.4-GHz continuum emission fromthese sources agree with higher frequency measurements and shows linear,triple source in NGC 7674 and a compact source surrounded by a weak ringof radio emission in NGC 7469. In both of these sources we detect deeplocalized H I absorption in front of a single continuum component. Inthe case of NGC 7674 the H I absorption is only seen against the centralcomponent and has a peak optical depth of 0.21 +/- 0.03, a linewidth of114 +/- 7 km s-1 and a heliocentric velocity of 8623 +/- 5 kms-1. The integrated H I absorption against the centralcomponent corresponds to a column density of 5.0 +/- 0.7 ×1021 atom cm-2. We interpret the lack of H Iabsorption against the east and west components (τ < 0.07 and0.06) as evidence that the H I is localized within the central fewhundred pc, similar to the H I observed against the nucleus of NGC 4151,and has an upper mass limit of ~4 × 105Msolar. We speculate that this H I may be associated with adusty torus. Giant Meterwavelength Radio Telescope (GMRT) results showextended emission and give a rest velocity of 8699 +/- 20 kms-1. The H I absorption against NGC 7469 shows a single deepfeature against the strong central component. The line has a peakoptical depth 0.25, a linewidth of 65 +/- 6 km s-1 and aheliocentric velocity of 4843 +/- 5 km s-1. The integratedcolumn density is 3.6 +/- 0.4 × 1021 atomcm-2. Unfortunately the other components in NGC 7469 are tooweak to set significant limits to the H I optical depth, and hence,unlike NGC 7674, it is not possible to constrain the size of theabsorbing gas.
| Star Formation Rates in Interacting Starburst Galaxies
By narrowband imaging in Hα and in the adjacent red stellarcontinuum we have studied the rate and distribution of star formation in43 systems of luminous and ultraluminous IR galaxies currentlyundergoing interaction and merging. These galaxies are amongst the mostluminous at 60 μm and range in distance from ~50 up to 100 Mpc. Herewe present the Hα and the adjacent red-continuum narrowbandimages, and we compare the star formation rates derived from Hαwith those estimated from the IR luminosity. We find clear evidence forsubstantial extinction and obscuration of star-forming regions in theoptical. Without correction for reddening in the host galaxy orcorrection for [N II] contamination, the star formation rates derivedfor Hα are typically 0.5-1.0 dex lower than those estimated fromthe IR flux, and the scatter in the correlation is very large. However,an unexpected result is that when spectroscopic data are used toeliminate objects dominated by an active nucleus, to determine thegalaxian extinction, and to correct the Hα flux for both reddeningand for the contamination by the [N II] emission, a remarkably goodcorrelation emerges between the star formation rates estimated from theHα flux and those derived from the FIR continuum. In addition, astrong correlation is found between the extinction in the line-emittingregion, AHα, and the rate of star formation. Ourresults invalidate the use of Hα imaging as a reliable indicatorof star formation in starburst galaxies unless spectroscopic data arealso available. This has important implications for the determination ofstar formation rates in high-redshift galaxies. Finally, we find nocorrelation between the measured star formation rates, and theinteraction class, suggesting that the enhanced star formation ratestriggered by the interaction continue throughout the whole of themerging sequence.
| Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of Hαemission line of a sample of 111 spiral galaxies with recognizable andwell defined spiral morphology and with a well determined environmentalstatus, ranging from isolation to non-disruptive interaction withsatellites or companions. The form and properties of the rotation curvesare considered as a function of the isolation degree, morphological typeand luminosity. The line ratios are used to estimate the metallicity ofall the detected HII regions, thus producing a composite metallicityprofile for different types of spirals. We have found that isolatedgalaxies tend to be of later types and lower luminosity than theinteracting galaxies. The outer parts of the rotation curves of isolatedgalaxies tend to be flatter than in interacting galaxies, but they showsimilar relations between global parameters. The scatter of theTully-Fisher relation defined by isolated galaxies is significantlylower than that of interacting galaxies. The [NII]/Hα ratios, usedas a metallicity indicator, show a clear trend between Z andmorphological type, t, with earlier spirals showing higher ratios; thistrend is tighter when instead of t the gradient of the inner rotationcurve, G, is used; no trend is found with the change in interactionstatus. The Z-gradient of the disks depends on the type, being almostflat for early spirals, and increasing for later types. The[NII]/Hα ratios measured for disk HII regions of interactinggalaxies are higher than for normal/isolated objects, even if all thegalaxy families present similar distributions of Hα EquivalentWidth. Tables 3 and 4 and Figs. 6, 7 and 21 are only available inelectronic form at http://www.edpsciences.org. Table 5 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/389 Based on dataobtained Asiago/Ekar Observatory. Also based on observations made withINT operated on the island of La Palma by ING in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias.
| The SCUBA Local Universe Galaxy Survey - I. First measurements of the submillimetre luminosity and dust mass functions
This is the first of a series of papers presenting results from theSCUBA Local Universe Galaxy Survey (SLUGS), the first statistical surveyof the submillimetre properties of the local Universe. As the initialpart of this survey, we have used the SCUBA camera on the James ClerkMaxwell Telescope to observe 104 galaxies from the IRAS Bright GalaxySample. We present here the 850-μm flux measurements. The 60-, 100-,and 850-μm flux densities are well fitted by single-temperature dustspectral energy distributions, with the sample mean and standarddeviation for the best-fitting temperature beingTd=35.6+/-4.9K and for the dust emissivity indexβ=1.3+/-0.2. The dust temperature was found to correlate with60-μm luminosity. The low value of β may simply mean that thesegalaxies contain a significant amount of dust that is colder than thesetemperatures. We have estimated dust masses from the 850-μm fluxesand from the fitted temperature, although if a colder component ataround 20K is present (assuming a β of 2), then the estimated dustmasses are a factor of 1.5-3 too low. We have made the first directmeasurements of the submillimetre luminosity function (LF) and of thedust mass function. Unlike the IRAS 60-μm LF, these are well fittedby Schechter functions. The slope of the 850-μm LF at lowluminosities is steeper than -2, implying that the LF must flatten atluminosities lower than we probe here. We show that extrapolating the60-μm LF to 850μm using a single temperature and β does notreproduce the measured submillimetre LF. A population of `cold' galaxies(Td<25K) emitting strongly at submillimetre wavelengthswould have been excluded from the 60-μm-selected sample. If suchgalaxies do exist, then this estimate of the 850-μm flux is biased(it is underestimated). Whether such a population does exist is unknownat present. We correlate many of the global galaxy properties with theFIR/submillimetre properties. We find that there is a tendency for lessluminous galaxies to contain hotter dust and to have a greater starformation efficiency (cf. Young). The average gas-to-dust ratio for thesample is 581+/-43 (using both the atomic and molecular hydrogen), whichis significantly higher than the Galactic value of 160. We believe thatthis discrepancy is probably due to a `cold dust' component atTd<=20K in our galaxies. There is a surprisingly tightcorrelation between dust mass and the mass of molecular hydrogen,estimated from CO measurements, with an intrinsic scatter of ~=50percent.
| The Structure of Infrared-luminous Galaxies at 100 Microns
We have observed 22 galaxies at 100 μm with the Kuiper AirborneObservatory in order to determine the angular size of their FIR-emittingregions. This one-dimensional array data constitutes the highest spatialresolution ever achieved on luminous galaxies in the far-infrared. Mostof these galaxies are very luminous far-infrared sources, withLFIR>1011 Lsolar. We clearlyresolved six of these galaxies at 100 μm and have some evidence forextension in seven others. Those galaxies that we have resolved can havelittle of their 100 μm flux directly emitted by a pointlike activegalactic nucleus. Dust heated to ~40 K by recent bursts of nonnuclearstar formation provides the best explanation for their extreme FIRluminosity. In a few cases, heating of an extended region by a compactcentral source is also a plausible option.
| 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.
| Optical Spectral Signatures of Dusty Starburst Galaxies
We analyze the optical spectral properties of the complete sample ofVery Luminous Infrared Galaxies presented by Wu et al., and we find ahigh fraction (~50%) of spectra showing both a strong Hδ line inabsorption and relatively modest [O II] emission [e(a) spectra]. Thee(a) signature has been proposed as an efficient method to identifydusty starburst galaxies, and we study the star formation activity andthe nature of these galaxies, as well as the effects of dust on theirobserved properties. We examine their emission-line characteristics, inparticular their [O II]/Hα ratio, and we find this to be greatlyaffected by reddening. A search for AGN spectral signatures reveals thatthe e(a) galaxies are typically H II/LINER galaxies. We compare the starformation rates derived from the FIR luminosities with the estimatesbased on the Hα line and find that the values obtained from theoptical emission lines are a factor of 10-70 (Hα) and 20-140 ([OII]) lower than the FIR estimates (50-300 Msolaryr-1). We then study the morphological properties of the e(a)galaxies, looking for a near companion or signs of a merger/interaction.In order to explore the evolution of the e(a) population, we present anoverview of the available observations of e(a) galaxies in differentenvironments both at low and high redshift. Finally, we discuss the roleof dust in determining the e(a) spectral properties and we propose ascenario of selective obscuration in which the extinction decreases withthe stellar age.
| NICMOS Imaging of Infrared-Luminous Galaxies
We present near-infrared images obtained with the Hubble Space TelescopeNICMOS camera for a sample of nine luminous [LIGs: LIR(8-1000μm)>=1011 Lsolar] and 15 ultraluminous(ULIGS: LIR>=1012 Lsolar) infraredgalaxies. The sample includes representative systems classified as warm(f25μm/f60μm>0.2) and cold(f25μm/f60μm<=0.2) based on themid-infrared colors and systems with nuclear emission lines classifiedas H II (i.e., starburst), QSO, Seyfert, and LINER. The morphologies ofthe sample galaxies are diverse and provide further support for the ideathat they are created by the collision or interactions of spiralgalaxies. Although no new nuclei are seen in the NICMOS images, theNICMOS images do reveal new spiral structures, bridges, andcircumnuclear star clusters. The colors and the luminosities of theobserved clusters are consistent with them being young(107-108 yr), formed as a result of galacticinteractions, and having masses much greater than those of Galacticglobular clusters. In NGC 6090 and VV 114, they are preferentiallysituated along the area of overlap of the two galactic disks. With theexception of IR 17208-0018, all of the ULIGs have at least one compact(2.2 μm FWHM<=200 pc) nucleus. Analysis of the near-infraredcolors (i.e., m1.1-1.6 vs. m1.6-2.2) derived from1.1" diameter apertures suggests that the warm galaxies havenear-infrared colors consistent with QSO+hot dust emission and the coldgalaxies, as a group, have near-infrared colors consistent with reddenedstarlight. In addition, the cold ULIG UGC 5101 (and possibly threeothers) have near-infrared colors suggesting additional active galacticnucleus-like near-infrared components in their nuclei. In a 2 kpcdiameter aperture measurement, the global colors of all of the coldgalaxies except UGC 5101 are consistent with starlight with a fewmagnitudes of visual extinction. The general dichotomy of thenear-infrared properties of the warm and the cold galaxies are furthersupported by the light distributions: seven of the eight warm galaxieshave unresolved nuclear emission that contributes significantly (i.e.,>=30%-40%) to the total near-infrared luminosity. The smooth, moreextended light observed in all of the galaxies is most likely composedof giant and supergiant stars, but evidence at longer wavelengthssuggests that these stars contribute little to the high 8-1000 μmluminosity of these galaxies. Finally, light profiles of nine of the 24systems were fitted well by an r1/4 law (and not so well byan exponential disk profile). Whether these star systems eventuallybecome massive central bulges or giant elliptical galaxies will dependon how efficiently the present ISM is converted into stars.
| UBVRI Light Curves of the Seyfert Galaxy NGC 7469 During 1990-1998: Microvariability
Observations of the nuclear region of the Seyfert galaxy NGC 7469obtained at Crimean Astrophysical Observatory with the 1.25 m telescopeare presented. During 64 nights on nine observational runs between 1990September 24 and 1998 October 22 in each spectral band of the JohnsonUBVRI system, about 1500 measurements have been performed simultaneouslythrough the round aperture 20" in diameter using differential photometrytechniques. The estimated accuracy of each measurement is about 0.01mag. During the observing period 1990-1996 the mean luminosity of thenucleus was almost constant; only overlapping brightness fluctuationswere observed. The mean luminosity level has been raised in 1996October. The peak amplitude (maximum flux/minimum flux)Fmax/Fmin=2.09 on the light curves was observed inthe U band, while the minimum amplitudeFmax/Fmin=1.32 was in the I band for the entireobservation period. Using structure function (SF) analysis, thefollowing conclusions have been made: (1) Long-term variability iscaused by the same processes in the optical, because the slope b of theSF is approximately equal for all wave bands, except for the I band theslope is appreciably distinguished from the others. This would be anindication of the presence of an independent IR energy source in NGC7469. (2) Considering the same time interval (from 6 minutes to 2 hr)for intranight variability on SFs at different wave bands, one canconclude that flicker noise causes variations observed on the lightcurve at the UV region (U and B bands), while at the near-IR region thelight curve is formed by mixed shot noise and flicker noise-the greaterthe wavelength, the more the contribution of shot noise processes. (3)On intranight light curves of the NGC 7469 there exist rapid flares withdurations ~25 minutes at U band, ~55 minutes at B, V bands, and ~2 hr atR, I bands-a typical timescale of intranight variability increasing withthe increasing wavelength. In order to examine the intranight variationsof the nucleus of NGC 7469, standard deviations (SDs) of the nightlyaveraged flux, F, and a measure of intranight variability, SD/F, werecalculated for each night of observations. The ratiosP=Ni/Ntot of number of nights with SD/F>=1%,2%, 3%, and so forth (Ni) to all 64 observational nights(Ntot) were expressed as a percentage of probability todetect variability at a given level; they were plotted versus theappropriate parameter SD/F. It is interesting that a probability todetect intranight variability at a level given by a parameter SD/F maybe fitted well by a ``probability curve'' for a given galaxy. Thehomogeneity of data obtained with the same telescope using the sametechnique has made statistical comparisons possible among differentgalaxies and different wave bands. Therefore, analogous curves for theSeyfert galaxies NGC 1275 and NGC 4151 were plotted and were averaged bybands. Probability curves for the two galaxies of the same type (Seyfert1; NGC 4151 and NGC 7469) coincided well. The probability curve for thegalaxy NGC 1275 of BL Lacertae type shows more nights with variations ofamplitude less than 7%. The probability to observe intranight variationswith an amplitude of more than 7% is approximately equal for both typesof objects. An excess of nights with intranight variability parameterSD/F in the range of ~4%-8% is a common characteristic of the twoSeyfert 1 galaxies (NGC 4151 and NGC 7469) and of the BL Lac object (NGC1275) studied in this paper. This excess may be connected with aspecific type of intranight galaxy variability. All probability curvesare fitted best by the second-order exponential decay. As a result, onecan conclude that intranight variability is really transient incharacter and has manifested itself with different probabilities fordifferent galaxies. The efficiency of the energy source for every galaxyto produce intranight variability on a given level (duty cycle of thecentral energy engine) was estimated using these probability curves. Fora given threshold of detection estimated as an error of a giventechnique (for instance, 1% for observations presented in this paper),one can conclude that duty cycle of NGC 1275 is about 100%. Vice versa,NGC 4151 has a more quiet energy source: only ~60% of nights showintranight variability on a level greater than 1%. The efficiency of theenergy source producing the near-IR radiation of NGC 7469 is more than0.9, while at the optical bands it is equal to ~0.7+/-0.1. It may be anindication of the presence of an independent IR energy source, too.
| High-Resolution CO Observations of Luminous Infrared Galaxies
We have performed a high-resolution imaging survey of the CO J=1-->0emission in seven galaxies with infrared (IR) luminosities exceeding3x10^11 L_solar-five of which are mergers. The resultant maps show thatthe molecular gas is very highly concentrated towards the cores of themergers, with gas surface densities approaching or exceeding 10^4M_ȯ pc^-2 within 300-400 pc of the nuclei in three cases. Thisresult supports earlier findings based on data from a smaller sample ofluminous mergers. In the two mergers that show closely spaced double IR(stellar) nuclei, CO emission peaks between the nuclei and shows anextent roughly equal to the nuclear separation. The gas cores of theindividual merging galaxies appear to be coalescing, while the stellarcores remain distinct. In the three single nucleus mergers, the CO peaksare coincident with the stellar nuclei, consistent with the hypothesisthat these are relatively evolved merger remnants. In two of the threemergers with the most compact CO emission (Mrk 231 and NGC 6240), theempirical Galactic conversion factor from CO luminosity to molecular gasmass appears to overestimate the nuclear gas mass by a factor of morethan 2 (3.6 in the case of Mrk 231). For Mrk 231, the high brightnesstemperature of the CO emission (T_b>34 K) is the likeliestexplanation for this overestimate. In the third such merger (NGC 2623),however, the geometry and kinematics suggest that the molecular gas massis within a factor of 2 of the value given by using the Galacticconversion factor. Nonetheless, in all three of these objects, themolecular gas probably dominates the nuclear gravitational potential. Wesuggest that the molecular gas in objects with such high gas masssurface densities (~10^4 M_ȯ pc^-2) is distributed in nuclear disks.These disks must be thin because of their self-gravity, with a fullwidth of 30-40 pc (compared to radii of 300-400 pc) for a verticalvelocity dispersion of 90 km s^-1. The mean volume density of molecularhydrogen in such disks must be over 10^4 cm^-3. The trend of increasingL_FIR/L_CO with increasing CO surface brightness is confirmed. The highconcentrations of molecular gas thus appear intimately related to thehigh luminosities of these systems and probably serve as the fuel.
| A Search for Ultrarapid Microvariability in the Seyfert Galaxy NGC 7469 with the Hubble Space Telescope
The Faint Object Spectrograph on the Hubble Space Telescope (HST) wasused to obtain spectrophotometric observations of the Seyfert 1 galaxyNGC 7469. The spectra were obtained with a 90 s time resolution in orderto resolve the fastest expected variability and to search for rapidcharacteristic timescales (e.g., quasi-periodic oscillations or breaksin the power spectrum). The sensitivity of the observations is such thata ~1% spectral variation, or a ~0.1% photometric variation, aredetectable. The observations were taken through a 0.86" square apertureand do not suffer contamination from the host galaxy and nearby brightstarburst ring. During the 11.5 hr spanned by the observations, a 4%rise in the 1315 Å continuum was seen, with a correspondingsmaller rise at longer wavelengths. Variations on timescales of hours orless are of very low amplitude, at or below the Poisson noise level-therms amplitude of the fluctuations is ~1% in the UV and 0.2% in the G160Lzero-order photometric bandpass. No periodicities or characteristictimescales are present, nor do we see any evidence for delays betweenvariations at different wavelengths. The HST observations were madeduring an intense monitoring campaign using IUE, RXTE, and ground-basedobservatories, and a comparison with the results of those observationsis presented. The 4% rise seen in the HST data agrees well with the IUElight curve. The very small amplitude, rapid fluctuations are roughlyconsistent with a power-law extrapolation of the power spectrum of themuch longer timescale IUE observations. We were unable to determine theamount of correlated variability between the HST and RXTE light curvesbecause the amplitude of the fluctuations are extremely small at thesevery rapid timescales.
| Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XIV. Intensive Optical Spectrophotometric Observations of NGC 7469
We present results of an intensive 2 month campaign of ground-basedspectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with atemporal resolution <~ 1 day. The broad H alpha and H beta emissionlines respond to ~35% ultraviolet continuum variations with an amplitudeof ~10% and time delays of 5.6 +/- 1.3 days and 5.4 +/- 0.8 days,respectively. We interpret this as evidence of variable Balmer line gas~5-6 light days from the central source in this object, widely believedto be a supermassive black hole. The virial mass of the central sourceimplied by line widths and time delays is ~106-107 Mȯ.Concomitantly, we find evidence for wavelength-dependent continuum timedelays: optical continuum variations lag those at 1315 Angstroms by 1.0+/- 0.3 days at 4865 Angstroms to 1.5 +/- 0.7 days at 6962 Angstroms.This suggests a stratified continuum reprocessing region extendingseveral light days from the central source, possibly an accretion disk.
| Starburst Galaxies. III. Properties of a Radio-selected Sample
We have analyzed the properties of the 20 most radio-luminous UGCstarburst galaxies from Condon, Frayer, & Broderick. Near-infraredimages, spectra, and optical rotation curves were presented in Smith etal. In this paper, we use these data and published radio data to assessthe stellar populations, dust contents, ionizing conditions, anddynamics of the starbursts. Certain properties of the star formationoccurring in these galaxies differ from those observed locally. Theinfrared excesses (IREs) are lower than and span a narrower range ofvalues than those of Galactic H II regions. The starbursts appear toproduce a higher proportion of ionizing photons than most Galactic H IIregions. Consequently, the initial mass functions (IMFs) of thestarbursts may be more strongly biased toward high-mass star formation.The starbursts may also contain fewer old H II regions than the MilkyWay. Furthermore, the starburst IRE is likely to be influenced by thepresence of large reservoirs of gas that absorb a larger fraction of theLyman continuum photons. The OB stellar and far-infrared luminositiesimply that the upper mass range of the starburst IMF (M > 10 Mȯ)is characterized by a slope of 2.7 +/- 0.2. The starburst IMF thus bearsa strong similarity to that observed in Magellanic OB associations.Optical line ratios indicate that a range of excitation conditions arepresent. We conclude that the near-infrared light from many of thestarbursts is dominated by a heavily obscured mixture of emission fromevolved red stars and young blue stars with small contributions (~5%)from thermal gas and hot dust, under the assumptions that a Galactic orSMC extinction law can be applied to these systems and that the truereddening curve follows one of the models currently existing in theliterature. In some cases, larger amounts of emission from blue stars orhot dust may be required to explain the observed near-infrared colors.The amount of dust emission exceeds that predicted from comparisons withGalactic H II regions. The near-infrared colors of some of the systemsmay also be influenced by the presence of a low-luminosity activegalactic nucleus (AGN). Emission from blue stars and hot dust, ifpresent, dilutes the observed CO index. The activity in the redder, moreluminous systems is strongly peaked. The galaxies hosting the starburstsexhibit a wide range of morphological and star-forming properties. Whileall of the host galaxies are interacting systems, the nuclearseparations of the interacting nuclei range from <1 kpc to >1 Mpc.The dynamical behavior ranges from relaxed to strongly perturbed. Theoff-nuclear regions of the galaxies are sites of active star formationand are characterized by a range of excitation conditions. Spatiallyextended LINER emission is consistent with shock excitation produced bysuperwinds or galaxy-galaxy collisions. Violent star formation activityoccurs over a larger physical scale in the most active starbursts.Systems containing mergers and widely separated nuclei possess similarcolors and luminosities. The burst properties are most likely regulatedby the internal structures of the interacting galaxies and not theseparations of the interacting galaxies.
| A statistical study of the spectra of very luminous IRAS galaxies. II. Spectral and environmental analysis
Spectroscopic observations of a sample of 73 very luminous IRAS galaxies(log(LIR/Lsun)>=11.5 for H0=50 km\s(-1) ; Mpc(-1) ,q0=0.5) from the 2 Jy redshift surveycatalogue were carried out using the 2.16 m telescope at the BeijingAstronomical Observatory. The observational data, including the opticalimages (extracted from Digital Sky Survey) and spectra for thesegalaxies, are presented in Paper I \cite[(Wu et al. 1998)]{wu98}. Inthis paper, we give the spectral and morphological classifications forthese very luminous IRAS galaxies (VLIRGs). We show that about 60% ofVLIRGs exhibit AGN-like spectra (Seyfert 1s, Seyfert 2s, LINER-likegalaxies). This fraction goes up to 82% for the ultraluminous IRASgalaxies (ULIRGs) subsample (Log(LIR/Lsun) >=12.0). 56% of the VLIRGs show strong interaction or merging signatures;this fraction rises to 91% for the ULIRGs. These statistical resultsstrongly suggest that interaction triggers nuclear activities andenhances the infrared luminosity. We find that LINER and a mixture typewhich have optical properties of both HII galaxies and LINERs could beat the transition stage from infrared luminous HII galaxies to AGNs;their main energy production is from starbursts as well as AGNs. Bothinfrared luminosities and Hα equivalent widths increasedramatically as nuclear separations between VLIRGs and their nearestneighbors decrease. There is little doubt that strong starbursts happenin the nuclei of VLIRGs. Assuming class 0 as advanced merger, weconstruct a simple merger sequence, from morphological classes 1 to 4(with near or far companions), to class 5 and 6 (interacting pairs andmergers) and then to class 0 (isolated galaxies). Along this sequence,VLIRGs evolve from HII galaxies to AGNs. Table 1 is only available atthe CDS via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr
| BVRI imaging of M51-type interacting galaxy pairs. I. Data reductions
Deep broad-band BVRI photometry of a sample of 22 closely interactingisolated galaxy pairs is presented. The sample consists of pairs with alarge variety of orbital geometries, but most of them are M51-typepairs: a small companion in the vicinity of a prominent two-armedspiral. This subsample will be later modelled in detail with N-bodysimulations. Nine of the thirteen M51-type pairs show enhanced starformation in the central regions of the companions, detected in B-V orR-I color maps, and only one pair in the nucleus of the main galaxy.This is expected if there is mass transfer from the main galaxy to thecompanion. Some pairs with larger separation, and with more massivecompanions show global instabilities manifesting as strong colorgradients at least in one of the members.
| Morphology transformation in pairs of galaxies - the local sample
We present photometric analysis of a local sample of 14 isolated pairsof galaxies. The photometric properties analyzed in the local pairs are:colors, morphology, tidal effects and activity. We verify that closepairs have an excess of early-type galaxies and many elliptical galaxiesin this pairs are, in fact, lenticular galaxies. Many late-pairs in oursample show strong tidal damage and blue star formation regions. Weconclude that pairs of different morphologies may have passed throughdifferent evolution processes which violently transformed theirmorphology. Pairs with at least one early-type component may bedescendents of groups of galaxies. However, late-type pairs are probablylong-lived showing clearly signs of interaction. Some of them could beseen as an early stage of mergers. These photometric databases will beused for future comparison with more distant pairs in order to studygalaxy evolution.
| 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 statistical study of the spectra of very luminous IRAS galaxies. I. Data
This paper presents the results of spectral observations for the largestcomplete sample of very luminous IRAS galaxies obtained to date. Thesample consists of those 73 objects for which log(L_IR/Lsun)>= 11.5 (H0=50;km; s(-1) Mpc(-1) , q0=0.5) andmag <= 15.5 , and was extracted from the 2 Jy IRAS redshift catalog.All the spectra were obtained using the 2.16 m telescope of BeijingAstronomical Observatory during the years 1994-1996. A total of 123galaxy spectra were obtained with spectral ranges of 4400;Angstroms to7100;Angstroms and 3500;Angstroms to 8100;Angstroms at resolutions of11.2;Angstroms and 9.3;Angstroms respectively. In addition to the 73spectra for sample galaxies, we also present spectra for ten non-samplegalaxies and a further 40 for the companions of sample galaxies. Thedata presented include nuclear spectrum and the parameters describingthe emission lines, absorption lines and continua as well as DSS imagesand environmental parameters. Table 1 is also available in electricform, Table 2-4 are only available in electronic form form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130. 79.128.5) or via http:cdsweb.u-strasbg.fr/Abstract.html. Figures 4 and 9 are published in theon-line version of A&A..
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Millimetre line CO (2->1) observations of a complete sample of AGN.
We report on observations of the CO (2->1) transition of a completesubset of 11/39 of the Piccinotti (1982ApJ...253..485P) hard X-rayselected AGN sample. All of the 11 galaxies were clearly detected. Allthe galaxies in our sample are strong hard-X ray sources and thus thesample is unbiased with respect to obscuring material. Six of thegalaxies are Seyfert 1 type objects with the rest five being reddenedSeyfert 1s, or the so called ``Narrow Line Galaxies''. Based on our highS/N detections we investigate the relation between CO and far-infraredluminosities. A strong correlation is found to exist for both Seyfert 1sand Narrow Line Galaxies similar to the one seen in normal and brightinfrared galaxies. Our data also suggest that the FIR emission inSeyferts galaxies is of thermal origin, an argument which is supportedby three different lines of evidence, the CO-FIR correlation, theFIR/M(H_2_) dependence on dust temperature and the similarities in theshapes of the CO and HI profiles. The relation between CO emission andnon-thermal radio power was examined next. Seyferts were found to showan excess radio non-thermal power for a given CO luminosity (whencompared to starburst galaxies) while no differences were found betweenSeyfert 1s and 2s in their CO and radio properties (Seyfert 2s wereselected from the literature). We conclude that Seyfert 1s and NarrowLine Galaxies have very similar properties with respect to theirmolecular gas reservoir. By comparing our CO observations with publishedoptical data we explore the distribution of the molecular clouds in thesample galaxies. We find that in most cases the spatial distribution ofCO clouds is confined within 1-1.4kpc around the nucleus.
| Hickson 96: a physical compact group.
We analyze the morphology and dynamics of the galaxies of the Hickson 96compact group by means of deep CCD images in the B, V and R photometricbands and long-slit spectroscopy. The four galaxies of this spiral richgroup show signs of gravitational interaction. Two long tails come outfrom the contact region of the close pair H96ac. It is also there whereboth galaxies, bi-symmetrical in their inner parts, loose one of theirarms. Moreover, both the photometric and kinematical center of H96a aredisplaced relative to the center of the disk. H96b, a giant ellipticalgalaxy, shows significant deviations from a r^1/4^ law at the innerparts and small rotation along its major axis. We find at the centre ofthe galaxy an elongated component which is kinematically decoupled. Awide faint plume seems to emerge from this galaxy. H96d, the smallestgalaxy of the group, seems to be influenced by the bigger members, asindicated by three prominent knots of recent bursts of star formation inits blue disk, and by hints of optical bridges joining H96d with H96aand b. Finally the group has a low velocity dispersion (160km/s) and iswell isolated - no galaxies with comparable magnitude to H96a or H96bare found in its neighborhood. All these results lead us to concludethat Hickson 96 constitutes a real physical system.
| Kinematics and distribution of dense gas in Seyfert nuclei
We report on high spatial and spectral resolution observations of thedistribution, physical parameters and kinematics of the molecularinterstellar medium toward the nuclei of three nearby active galaxies.The data consist of high resolution interferometric observations of theHCN and CO J = 1 0 lines, single dish observations of severalmm/submm isotopic lines of HCN and CO, and subarcsecond resolutionimaging spectroscopy of the near-IR K-band.
| 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.
| 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.
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