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|The SAURON project - VII. Integral-field absorption and emission-line kinematics of 24 spiral galaxy bulges|
We present observations of the stellar and gas kinematics for arepresentative sample of 24 Sa galaxies obtained with our custom-builtintegral-field spectrograph SAURON operating on the William HerschelTelescope. The data have been homogeneously reduced and analysed bymeans of a dedicated pipeline. All resulting data cubes were spatiallybinned to a minimum mean signal-to-noise ratio of 60 per spatial andspectral resolution element. Our maps typically cover thebulge-dominated region. We find a significant fraction of kinematicallydecoupled components (12/24), many of them displaying central velocitydispersion minima. They are mostly aligned and co-rotating with the mainbody of the galaxies, and are usually associated with dust discs andrings detected in unsharp-masked images. Almost all the galaxies in thesample (22/24) contain significant amounts of ionized gas which, ingeneral, is accompanied by the presence of dust. The kinematics of theionized gas are consistent with circular rotation in a disc co-rotatingwith respect to the stars. The distribution of mean misalignmentsbetween the stellar and gaseous angular momenta in the sample suggeststhat the gas has an internal origin. The [OIII]/Hβ ratio is usuallyvery low, indicative of current star formation, and shows variousmorphologies (ring-like structures, alignments with dust lanes oramorphous shapes). The star formation rates (SFRs) in the sample arecomparable with that of normal disc galaxies. Low gas velocitydispersion values appear to be linked to regions of intense starformation activity. We interpret this result as stars being formed fromdynamically cold gas in those regions. In the case of NGC5953, the datasuggest that we are witnessing the formation of a kinematicallydecoupled component from cold gas being acquired during the ongoinginteraction with NGC5954.
|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.
|The SCUBA Local Universe Galaxy Survey - III. Dust along the Hubble sequence|
We present new results from the Submillimetre Common-User BolometerArray (SCUBA) Local Universe Galaxy Survey (SLUGS), the first largesystematic submillimetre (submm) survey of the local Universe. Since ourinitial survey of a sample of 104 IRAS-selected galaxies we have nowcompleted a survey of a sample of 81 optically selected galaxies,observed with the SCUBA camera on the James Clerk Maxwell Telescope.Since SCUBA is sensitive to the 90 per cent of dust too cold to radiatesignificantly in the IRAS bands our new sample represents the firstunbiased SCUBA survey of dust in galaxies along the whole length of theHubble sequence.We find little change in the properties of dust in galaxies along theHubble sequence, except a marginally significant trend for early-typegalaxies to be less-luminous submm sources than late types. Wenevertheless detected six out of 11 elliptical galaxies, although someof the emission may possibly be synchrotron rather than dust emission.As in our earlier work on IRAS galaxies we find that the IRAS and submmfluxes are well fitted by a two-component dust model with dustemissivity index β= 2. The major difference from our earlier workis that we find the ratio of the mass of cold dust to the mass of warmdust is much higher for our optically selected galaxies and can reachvalues of ~1000. Comparison of the results for the IRAS and opticallyselected samples shows that there is a population of galaxies containinga large proportion of cold dust that is unrepresented in the IRASsample.We derive local submm luminosity and dust mass functions, both directlyfrom our optically selected SLUGS sample, and by extrapolation from theIRAS Point Source Catalogue Redshift Survey (PSCz) survey using themethod of Serjeant and Harrison (by extrapolating the spectral energydistributions of the IRAS PSCz survey galaxies out to 850μm we probea wider range of luminosities than probed directly by the SLUGSsamples), and find excellent agreement between the two. We find them tobe well fitted by Schechter functions except at the highestluminosities. We find that as a consequence of the omission of coldgalaxies from the IRAS sample the luminosity function presented in ourearlier work is too low by a factor of 2, reducing the amount of cosmicevolution required between the low-z and high-z Universe.
|Atomic and Molecular Gas in Colliding Galaxy Systems. I. The Data|
We present H I and CO (1-0) interferometric observations of 10comparable-mass interacting systems obtained at the Very Large Array(VLA) and the Owens Valley Radio Observatory (OVRO) millimeter array.The primary intent of this study is to investigate the response of coldgas during the early stages of collision of massive disk galaxies. Thesample sources are selected based on their luminosity(MB<=-19), projected separation (5-40 kpc), andsingle-dish CO (1-0) content (SCO>=20 Jy kms-1). These selection criteria result in a sample thatprimarily consists of systems in the early stages of an interaction or amerger. Despite this sample selection, 50% of the systems show long H Itidal tails indicative of a tidal disruption in a prograde orbit. Inaddition, all (4/4) of the infrared luminous pairs (LIRGs) in the sampleshow long H I tails, suggesting that the presence of a long H I tail canbe a possible signature of enhanced star formation activity in acollision of gas-rich galaxies. More than half of the groups show adisplacement of H I peaks from the stellar disks. The CO (1-0)distribution is generally clumpy and widely distributed, unlike in mostIR-selected late stage mergers-in fact, CO peaks are displaced from thestellar nucleus in 20% (4/18) of the galaxies with robust CO detection.H I and CO (1-0) position-velocity diagrams (PVDs) and rotation curvesare also presented, and their comparison with the numerical simulationanalyzed in Paper I show evidence for radial inflow and wide occurrencesof nuclear molecular rings. These results are further quantified byexamining physical and structural parameters derived in comparison withisolated systems in the BIMA SONG sample in our forthcoming paper.
|Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis|
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
|Gas and Stars in an H I-Selected Galaxy Sample|
We present the results of a J-band study of the H I-selected AreciboDual-Beam Survey and Arecibo Slice Survey galaxy samples using TwoMicron All Sky Survey data. We find that these galaxies span a widerange of stellar and gas properties. However, despite the diversitywithin the samples, we find a very tight correlation between luminosityand size in the J band, similar to that found in a previous paper byRosenberg & Schneider between the H I mass and size. We also findthat the correlation between the baryonic mass and the J-band diameteris even tighter than that between the baryonic mass and the rotationalvelocity.
|The distribution of atomic gas and dust in nearby galaxies - II. Further matched-resolution Very Large Array H I and SCUBA 850-μm images|
We present Very Large Array (VLA) C-array 21-cm HI images of galaxiesfrom the SCUBA Local Universe Galaxy Survey which have been observed at850 μm with the James Clerk Maxwell Telescope. Matched-resolution (~25 arcsec) HI images of 17 galaxies are presented and compared with850-μm images. HI or 850-μm images of an additional six galaxieswhich were detected at only one wavelength are presented. Additionally,lower resolution H I observations of nine galaxies are presented. Theobservations of these galaxies, along with results previously presented,do not show any obvious trends in the HI/dust or H2/dust massratios with morphological type.
|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.
|CO Molecular Gas in Infrared-luminous Galaxies|
We present the first statistical survey of the properties of the12CO(1-0) and 12CO(3-2) line emission from thenuclei of a nearly complete subsample of 60 infrared (IR) luminousgalaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). Thissubsample is flux limited at S60μm>=5.24 Jy with far-IR(FIR) luminosities mostly at LFIR>1010Lsolar. We compare the emission line strengths of12CO(1-0) and (3-2) transitions at a common resolution of~15". The measured 12CO(3-2) to (1-0) line intensity ratiosr31 vary from 0.22 to 1.72, with a mean value of 0.66 for thesources observed, indicating a large spread of the degree of excitationof CO in the sample. These CO data, together with a wide range of dataat different wavelengths obtained from the literature, allow us to studythe relationship between the CO excitation conditions and the physicalproperties of gas/dust and star formation in the central regions ofgalaxies. Our analysis shows that there is a nonlinear relation betweenCO and FIR luminosities, such that their ratioLCO/LFIR decreases linearly with increasingLFIR. This behavior was found to be consistent with theSchmidt law relating star formation rate to molecular gas content, withan index N=1.4+/-0.3. We also find a possible dependence of the degreeof CO gas excitation on the efficiency of star-forming activity. Usingthe large velocity gradient (LVG) approximation to model the observeddata, we investigate the CO-to-H2 conversion factor X for theSLUGS sample. The results show that the mean value of X for the SLUGSsample is lower by a factor of 10 compared to the conventional valuederived for the Galaxy, if we assume the abundance of CO relative toH2, ZCO=10-4. For a subset of 12galaxies with H I maps, we derive a mean total face-on surface densityof H2+HI of about 42 Msolar pc-2 withinabout 2 kpc of the nucleus. This value is intermediate between that ingalaxies like our own and those with strong star formation.
|NGC 5953/54: BVRIHαJK photometry and [N II] Fabry-Perot interferometry. I. The data|
We present new BVRIHαJK imaging and [N II] scanning Fabry-Perotobservations for the interacting galaxy pair NGC 5953/54. Morphology isreviewed using a combination of contrast-enhanced images, color-indexmaps, and geometric (radial μ ɛ = 1 - b/a, PA anda4/a) profile parameters. Our data are complemented byarchived V/R/H images from HST. The Seyfert 2 NGC 5953 shows anunderlying featureless disk (>=1.5 kpc) in all the observed bands andtraces of faint external fan-like features in Hα and [N II]. Acompact flocculent spiral pattern (<=1.5 kpc), and a ~ 60 pcbar-like central structure are also observed. The Liner galaxy NGC 5954is an inclined and distorted spiral with a strong circumnuclearstarburst region and star-forming regions throughout the disk. A tidalbridge or distorted arm appears to link the two galaxies, extending tothe northwest as a linear feature (plume). NGC 5954 also shows bluefilaments delineating bubble-like features on the north side of thenucleus where our Fabry-Perot observations reveal double emission lineprofiles. We derive BVRIJK magnitudes and surface brightness profilesfor the galaxies. HST V/R and H-band surface brightness profiles arealso presented for NGC 5953. Fabry-Perot observations yield an [N II]velocity field and rotation curves for the components. The observationscoupled with results from a simulation atlas of tidal features allow us1) to suggest a tentative geometry of the encounter in NGC 5953/54, and2) to comment about a suspected secular transformation in NGC 5953/54via the interaction process. A forthcoming paper is devoted to a moredetailed analysis of our observations including HI synthesisobservations and n-body numerical simulations.Based on data obtained at the 1.5-m and 2.1-m telescopes of theObservatorio Astronomico Nacional, San Pedro Mártir, BajaCalifornia, México, operated by the Instituto deAstronomía, UNAM.Figures 5, 7, 10 and 13 are only available in electronic form athttp://www.edpsciences.org
|SCUBA observations of galaxies with metallicity measurements: a new method for determining the relation between submillimetre luminosity and dust mass|
Using a new technique, we have determined a value for the constant ofproportionality between submillimetre emission and dust mass, the dustmass-absorption coefficient (κd) at 850μm. Ourmethod has an advantage over previous methods in that we avoidassumptions about the properties of dust in the interstellar medium. Ouronly assumption is that the fraction of metals incorporated in the dust(ɛ) in galaxies is a universal constant. To implement ourmethod, we require objects that have submillimetre and far-infrared fluxmeasurements as well as gas mass and metallicity estimates. We presentdata for all the galaxies with suitable measurements, including newsubmillimetre maps for five galaxies. We find κ850=0.07 +/- 0.02 m2 kg-1. We have also been able touse our sample to investigate our assumption that ɛ is auniversal constant. We find no evidence that ɛ is different fordwarf and giant galaxies, and show that the scatter in ɛ fromgalaxy to galaxy is apparently quite small.
|HI observations of loose galaxy groups. I. Data and global properties|
At Nançay, 21-cm H I line observations were made of 15spiral-dominated loose groups of galaxies, divided into two samples: an``interacting'' sample containing at least one pair of interactinggalaxies, and a ``control'' sample having no optical evidence ofinteractions or morphological disturbances among the group members. Theinteracting sample consists of 62 galaxies representing 9 differentgroups, and the control sample contains 40 galaxies representing 6groups. Of the 91 galaxy and galaxy pairs observed, 74 were detected,while upper limits were placed on the remaining 17 objects. Thesehomogeneous H I data, which will be used in future analyses, providecomparative information on the H I content of groups and serve as aprobe of the vicinity of the target spirals for H I clouds or very lowsurface brightness gas-rich galaxies.
|Cold gas and star formation in a merging galaxy sequence|
We explore the evolution of the cold gas (molecular and neutralhydrogen) and star formation activity during galaxy interactions, usinga merging galaxy sequence comprising both pre- and post-mergercandidates. Data for this study come from the literature, but aresupplemented by some new radio observations presented here. First, weconfirm that the ratio of far-infrared luminosity to molecular hydrogenmass (LFIRM(H2); star formation efficiency)increases close to nuclear coalescence. After the merging of the twonuclei there is evidence that the star formation efficiency declinesagain to values typical of ellipticals. This trend can be attributed toM(H2) depletion arising from interaction induced starformation. However, there is significant scatter, likely to arise fromdifferences in the interaction details (e.g., disc-to-bulge ratio,geometry) of individual systems. Secondly, we find that the centralmolecular hydrogen surface density, ΣH2,increases close to the final stages of the merging of the two nuclei.Such a trend, indicating gas inflows caused by gravitationalinstabilities during the interaction, is also predicted by numericalsimulations. Furthermore, there is evidence for a decreasing fraction ofcold gas mass from early interacting systems to merger remnants,attributed to neutral hydrogen conversion into other forms (e.g., stars,hot gas) and molecular hydrogen depletion resulting from ongoing starformation. The evolution of the total-radio to blue-band luminosityratio, reflecting the total (disc and nucleus) star formation activity,is also investigated. Although this ratio is on average higher than thatfor isolated spirals, we find a marginal increase along the mergingsequence, attributed to the relative insensitivity of disc starformation to interactions. However, a similar result is also obtainedfor the nuclear radio emission, although galaxy interactions arebelieved to significantly affect the activity (star formation, AGN) inthe central galaxy regions. Nevertheless, the nuclear-radio to blue-bandluminosity ratio is significantly elevated compared with that forisolated spirals. Finally, we find that the FIR-radio flux ratiodistribution of interacting galaxies is consistent with star formationbeing the main energizing source.
|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 Arecibo Dual-Beam Survey: Arecibo and VLA Observations|
The Arecibo Dual-Beam Survey is a ``blind'' 21 cm search for galaxiescovering ~430 deg2 of sky. We present the data from thedetection survey as well as from the follow-up observations to confirmdetections and improve positions and flux measurements. We find 265galaxies, many of which are extremely low surface brightness. Some ofthese previously uncataloged galaxies lie within the zone of avoidance,where they are obscured by the gas and dust in our Galaxy. Eighty-one ofthese sources are not previously cataloged optically, and there are 11galaxies that have no associated optical counterpart or are onlytentatively associated with faint wisps of nebulosity on the DigitizedSky Survey images. We discuss the properties of the survey, and inparticular we make direct determinations of the completeness andreliability of the sample. The behavior of the completeness and itsdependencies is essential for determining the H I mass function. Weleave the discussion of the mass function for a later paper, but do notethat we find many low surface brightness galaxies and seven sources withMHI<108 Msolar. The AreciboObservatory is part of the National Astronomy and Ionosphere Center,which is operated by Cornell University under cooperative agreement withthe National Science Foundation. in Puerto Rico.
|The 1.0 Megaparsec Galaxy Pair Sample in Low-Density Regions|
Using complete redshift catalogs, we have compiled a list of galaxypairs based solely on a pair's projected separation, rp, andvelocity difference, ΔV. We have made high-velocity precision H Iobservations of each galaxy in the sample and have reported these in theliterature. Due to the nature of the redshift catalogs, we are able toquantitatively evaluate the effects of isolation and number density ofsurrounding galaxies on each pair in the sample. For the close galaxypairs (rp<100 kpc), the degree of isolation (a measure ofthe number of near neighbors) has little effect on the median ΔV.This median is about 55 km s-1 for the 25 close pairs (ifmedium-density close pairs are omitted ΔV is even smaller, but thedifference is not statistically significant). The effect of isolation isstrong for the entire sample of galaxy pairs with separations as largeas 1.0 Mpc. For these larger separation pairs, relaxation of strictisolation requirements introduces small groups into the sample, whichdramatically increases the median ΔV. We find little evidence ofan increase in the median ΔV with decreasing rp, norwith increasing total luminosity. For our isolated pairs in low-densityregions, the overall median ΔV is only 30 km s-1. Forsimilar separations and isolation criteria, galaxy satellites withlarger luminosity ratios (i.e., less dynamical friction) in higherdensity regions have ΔV approximately twice as large. Weconjecture that our orbits are highly eccentric, so that the indirecteffect of dynamical friction leads to predominantly small ΔV.However, the halos of our galaxies may also be of low density (althoughhighly extended).
|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.
|The Nature of LINERS|
We present J-band (1.15-1.35 μm) spectroscopy of a sample of ninegalaxies showing some degree of LINER activity (classical LINERs,weak-[O I] LINERs, and transition objects), together with H-bandspectroscopy for some of them. A careful subtraction of the stellarcontinuum allows us to obtain reliable [Fe II] 1.2567 μm/Paβline ratios. We conclude that different types of LINERs (i.e.,photoionized by a stellar continuum or by an active galactic nucleus)cannot be easily distinguished based solely on the [Fe II] 1.2567μm/Paβ line ratio. The emission-line properties of many LINERscan be explained in terms of an aging starburst. The optical line ratiosof these LINERs are reproduced by a model with a metal-rich H II regioncomponent photoionized with a single stellar temperatureT*=38,000 K, plus a supernova remnant (SNR) component. The[Fe II] line is predominantly excited by shocks produced by SNRs instarbursts and starburst-dominated LINERs, while Paβ tracks H IIregions ionized by massive young stars. The contribution from SNRs tothe overall emission-line spectrum is constrained by the [Fe II] 1.2567μm/Paβ line ratio. Although our models for aging starbursts areconstrained only by these infrared lines, they consistently explain theoptical spectra of the galaxies also. The LINER-starburst connection istested by predicting the time dependence of the ratio of the ionizingluminosity (Lion) to the supernova rate (SNr),Lion/(SNr). We predict the relative number of starbursts tostarburst-dominated LINERs (aging starbursts) and show that it is inapproximate agreement with survey findings for nearby galaxies.Observations reported in this paper were obtained with the MultipleMirror Telescope, which is operated jointly by the SmithsonianAstrophysical Observatory and the University of Arizona.
|The Peculiar System ESO 244-G012|
We present spectroscopic and photometric observations of the peculiargalaxy ESO 244-G012, the most prominent features of which are twodistinct nuclei and a long asymmetric tail visible up to about 40 kpcfrom the center of the main body. The spectral characteristics of allthe observed zones are typical of H II regions of low excitation; theirN(N)/N(O) ratios indicate a comparative overabundance of nitrogen withrespect to the oxygen. Around the northern nucleus, the internalreddenings, the excitations, the equivalent widths, and the derivedabundances are systematically different from those of the southern one,suggesting they have had different evolutions. The equivalent width ofthe Hα+[N II] lines of the northern nucleus indicates it is astarburst; that of the southern one is compatible with a Sb galaxy. TheHα+[N II] equivalent width of the integrated spectrum iscomparable with those observed in mergers of two disk galaxies. Thestarburst nature of the northern nucleus, observed in the optical range,is in agreement with the properties of ESO 244-G012 detected in the farIR and with the CO and radio observations. In this object, one of thenuclei dominates the IR emission, and the enhancement of the starformation activity is observed in only one of them. The integrated totalcolor B-V corresponds to an Sa-Sab galaxy. The integrated colorsB-V,V-R,R-I, and B-I do not show big radial variations reflecting arather uniform population, on average, which would be between G8 and K0types. Indicative B-V colors of the nuclei, corrected for internalabsorption, give very different results, and that of the northernnucleus suggests it is an active star-forming region as found from thespectroscopic data. The velocity distribution of ESO 244-G012 has twobranches, being similar to that of other system which also has twonuclei. The derived data would indicate that ESO 244-G012 is a mergersystem; the two distinct visible nuclei suggest that the components arestill interacting.
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|Investigation of Barred Galaxies. V. Surroundings of SB and SA Galaxies|
|Molecular Gas in Strongly Interacting Galaxies. I. CO (1-0) Observations|
We present observations of the CO (1-0) line in 80 interacting galaxiesas part of a program to study the role of interactions and mergers intriggering starbursts. The sample, which only includes obviouslyinteracting pairs of galaxies, is the largest such sample observed inCO. The observations were carried out at the NRAO 12 m and IRAM 30 mtelescopes. CO emission was detected in 56 galaxies (of which 32 are newdetections), corresponding to a detection rate of 70%. Because mostgalaxies are slightly larger than the telescope beam, correction factorswere applied to include CO emission outside the beam. The correctionfactors were derived by fitting a Gaussian function or an exponential CObrightness distribution to galaxies with multiple pointings and byassuming an exponential model for galaxies with single pointing. Wecompared the global CO fluxes of 10 galaxies observed by us at bothtelescopes. We also compared the measured fluxes for another 10 galaxiesobserved by us with those by other authors using the NRAO 12 m and FCRAO14 m telescopes. These comparisons provide an estimate of the accuracyof our derived global fluxes, which is ~40%. Mapping observations of twoclose pairs of galaxies, UGC 594 (NGC 317) and UGC 11175 (NGC 6621), arealso presented. In subsequent papers we will report the statisticalanalyses of the molecular properties in our sample galaxies and makecomparisons between isolated spirals and interacting galaxies.
|Near-Infrared Spectroscopy of ARP Interacting Galaxies|
We discuss near-infrared spectra of 20 interacting galaxies from the ArpCatalog and analyze the properties of similar galaxies for which onlyoptical spectra are available. We find excellent agreement between thetypes of activity determined from the infrared and optical,demonstrating that obscuration does not seriously bias the opticalresults. None of the 20 galaxies show infrared spectral characteristicsthat differ from expectations for isolated galaxies; the very strongshock-excited lines seen in a few interacting systems must be uncommon.Most of the galaxies in our infrared sample are the sites of starburststhat appear to have had durations of 1 to 5 Myr and to be observed 3 to10 Myr after the peak star-forming episode. Four of the 20 galaxies haveLINER or composite starburst/LINER spectra that are likely to arise fromshocks due to supernovae in late phase starbursts. In the fullinteracting galaxy sample, there is a substantial excess of Seyfert 2nuclei, supporting previous indications that this type of activity tendsto occur in interacting host galaxies.
|Groups of galaxies. III. Some empirical characteristics.|
|Optical colour maps of Seyfert galaxies. II. More Seyfert 2s|
We present optical broad band B-I colour maps of a further sample of 10Seyfert 2 galaxies. In these bands, the contribution from emission linesto the total flux is small, and hence the images predominantly trace thecontinuum distribution. As in our earlier colour maps of a sample ofSeyferts type 1 and 2, we detect extended blue continuum components inthe circumnuclear region of several galaxies. These components areeither elongated (in Mkn 533, Mkn 607, Mkn 1066, NGC 5347, NGC 5953 andNGC 7319) or form a double structure across the nucleus (in NGC 5929).They are closely aligned with the radio and emission line axes of thesegalaxies and probably arise from scattering of nuclear continuum lightby extranuclear mirrors. Similar blue elongations (in Mkn 1 and NGC7212) and double structures (in NGC 788) are less well aligned with theradio and line emission, and their relationship with scattering regionsmust be considered uncertain. The colours of the blue maxima areconsistent with those expected from scattering off dust or electrons, aconclusion strengthened by the combined sample of the two papers in thisseries. Our findings thus strongly support the current unified models ofAGN. Based on observations made with the Nordic Optical Telescope,operated on the island of La Palma jointly by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.
|Catalogue of HI maps of galaxies. I.|
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 18.104.22.168 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|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 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 (to22.214.171.124) or via http://cdsweb.u-strasbg.fr/Abstract.html
|H II Region Population in a Sample of Nearby Galaxies with Nuclear Activity. II. Luminosity Function, Size, and Radial Distributions|
This paper presents the second part of an extensive study of theproperties of the H II region population in a sample of spiral galaxieswith active nucleus. This study comprises some 2000 H II regions,distributed in 27 out of the 55 galaxies in the original sample,observed in narrow-band H alpha CCD imaging. About 70% of these H IIregions are calibrated in absolute flux. We present the luminosityfunction, size distribution, the relationship between the H alpha fluxand the size, the emission measure, and the radial distribution of the HII regions in each galaxy. We analyze the main properties of the H IIregions attending to the Hubble type and to the level of nuclearactivity of the host galaxy.
|H II Region Population in a Sample of Nearby Galaxies with Nuclear Activity. I. Data and General Results|
This paper presents the distribution of ionized gas in the disk andcircumnuclear region of a sample of 55 galaxies with active nuclei,Seyfert galaxies of type 1 and 2, and low-ionization nuclear emissionline regions (LINERs). We use CCD narrow-band H alpha + [N II] images tomap the distribution of H II regions and the morphology of thecircumnuclear extended emission associated with the active nucleus. Wealso present [O III] images for a few of the galaxies. An analysis ofthe presence of extended emission and of H II regions is carried outtwofold, as a function of the level of nuclear activity and of theHubble type. In this sample, the extended emission is more common inSeyfert type 1 than in type 2; however, disk star formation is morecommon in Seyfert type 2. One-third of the galaxies have circumnuclear HII regions, but only 8% of these are Seyfert 1. The number surfacedensity of H II regions and the location of the brightest H II regionindicate that in Seyfert 2 the star formation is more important in theinner disk, as defined by the radius that contains half the total blueluminosity. In Seyfert 1 the distribution of H II regions is moreuniform with distance, and the H II regions are farther away from thenucleus than in Seyfert 2. We discuss the possible connection betweenthe dynamical properties of the galaxy, particularly in the inner parts,and the differences found in Seyfert types 1 and 2.
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