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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.
| XMM-Newton observations of the interacting galaxy pairs NGC 7771/0 and NGC 2342/1
We present XMM-Newton X-ray observations of the interacting galaxy pairsNGC 7771/7770 and NGC 2342/2341. In NGC 7771, for the first time we areable to resolve the X-ray emission into a bright central source plus twobright (LX > 1040 erg s-1)ultraluminous X-ray sources (ULXs) located either end of the bar. In thebright central source (LX~ 1041 ergs-1), the soft emission is well-modelled by a two-temperaturethermal plasma with kT= 0.4/0.7 keV. The hard emission is modelled witha flat absorbed power-law (Γ~ 1.7, NH~ 1022cm-2), and this together with a low-significance (1.7σ)~ 300 eV equivalent width emission line at ~6 keV are the firstindications that NGC 7771 may host a low-luminosity AGN. For the barULXs, a power-law fit to X-1 is improved at the 2.5σ level withthe addition of a thermal plasma component (kT~ 0.3 keV), while X-2 isimproved only at the 1.3σ level with the addition of a discblackbody component with Tin~ 0.2 keV. Both sources arevariable on short time-scales implying that their emission is dominatedby single accreting X-ray binaries (XRBs). The three remaining galaxies,NGC 7770, NGC 2342 and NGC 2341, have observed X-ray luminosities of0.2, 1.8 and 0.9 × 1041 erg s-1,respectively (0.3-10 keV). Their integrated spectra are alsowell-modelled by multi-temperature thermal plasma components with kT=0.2-0.7 keV, plus power-law continua with slopes of Γ= 1.8-2.3that are likely to represent the integrated emission of populations ofXRBs as observed in other nearby merger systems. A comparison with otherisolated, interacting and merging systems shows that all four galaxiesfollow the established correlations for starburst galaxies betweenX-ray, far-infrared and radio luminosities, demonstrating that theirX-ray outputs are dominated by their starburst components.
| Ultraviolet Emission from Stellar Populations within Tidal Tails: Catching the Youngest Galaxies in Formation?
New Galaxy Evolution Explorer (GALEX) observations have detectedsignificant far-UV (FUV; 1530 Å) and near-UV (NUV; 2310 Å)emission from stellar substructures within the tidal tails of fourongoing galaxy mergers. The UV-bright regions are optically faint andare coincident with H I density enhancements. FUV emission is detectedat any location where the H I surface density exceeds ~2Msolar pc-2, and it is often detected in theabsence of visible wavelength emission. UV luminosities of the brighterregions of the tidal tails imply masses of 106 to~109 Msolar in young stars in the tails, and H Iluminosities imply similar H I masses. UV-optical colors of the tidaltails indicate stellar populations as young as a few megayears, and inall cases ages under 400 Myr. Most of the young stars in the tailsformed in single bursts, rather than resulting from continuous starformation, and they formed in situ as the tails evolved. Star formationappears to be older near the parent galaxies and younger at increasingdistances from the parent galaxy. This could be because the starformation occurs progressively along the tails, or because the starformation has been inhibited near the galaxy/tail interface. Theyoungest stellar concentrations, usually near the ends of long tidaltails, have masses comparable to confirmed tidal dwarf galaxies and maybe newly forming galaxies undergoing their first burst of starformation.
| The Westerbork HI survey of spiral and irregular galaxies. III. HI observations of early-type disk galaxies
We present Hi observations of 68 early-type disk galaxies from the WHISPsurvey. They have morphological types between S0 and Sab and absoluteB-band magnitudes between -14 and -22. These galaxies form the massive,high surface-brightness extreme of the disk galaxy population, few ofwhich have been imaged in Hi before. The Hi properties of the galaxiesin our sample span a large range; the average values of MHI/LB and DH I/D25 are comparableto the ones found in later-type spirals, but the dispersions around themean are larger. No significant differences are found between the S0/S0aand the Sa/Sab galaxies. Our early-type disk galaxies follow the same Himass-diameter relation as later-type spiral galaxies, but theireffective Hi surface densities are slightly lower than those found inlater-type systems. In some galaxies, distinct rings of Hi emissioncoincide with regions of enhanced star formation, even though theaverage gas densities are far below the threshold of star formationderived by Kennicutt (1989, ApJ, 344, 685). Apparently, additionalmechanisms, as yet unknown, regulate star formation at low surfacedensities. Many of the galaxies in our sample have lopsided gasmorphologies; in most cases this can be linked to recent or ongoinginteractions or merger events. Asymmetries are rare in quiescentgalaxies. Kinematic lopsidedness is rare, both in interacting andisolated systems. In the appendix, we present an atlas of the Hiobservations: for all galaxies we show Hi surface density maps, globalprofiles, velocity fields and radial surface density profiles.
| 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.
| A Study of the Distribution of Star-forming Regions in Luminous Infrared Galaxies by Means of Hα Imaging Observations
We performed Hα imaging observations of 22 luminous infraredgalaxies to investigate how the distribution of star-forming regions inthese galaxies is related to galaxy interactions. Based on correlationdiagrams between Hα flux and continuum emission for individualgalaxies, a sequence for the distribution of star-forming regions wasfound: very compact (~100 pc) nuclear starbursts with almost nostar-forming activity in the outer regions (type 1), dominant nuclearstarbursts <~1 kpc in size with a negligible contribution from theouter regions (type 2), nuclear starbursts >~1 kpc in size with asignificant contribution from the outer regions (type 3), and extendedstarbursts with relatively faint nuclei (type 4). These classes ofstar-forming regions were found to be strongly related to globalstar-forming properties, such as star formation efficiency, far-infraredcolor, and dust extinction. There was a clear tendency for the objectswith more compact distributions of star-forming regions to show a higherstar formation efficiency and hotter far-infrared color. An appreciablefraction of the sample objects were dominated by extended starbursts(type 4), which is unexpected in the standard scenario ofinteraction-induced starburst galaxies. We also found that thedistribution of star-forming regions was weakly but clearly related togalaxy morphology: severely disturbed objects had a more concentrateddistribution of star-forming regions. This suggests that the propertiesof galaxy interactions, such as dynamical phase and orbital parameters,play a more important role than the internal properties of progenitorgalaxies, such as dynamical structure or gas mass fraction. We alsodiscuss the evolution of the distribution of star-forming regions ininteracting galaxies.
| Kinematics of tidal tails in interacting galaxies: Tidal dwarf galaxies and projection effects
The kinematics of tidal tails in colliding galaxies has been studied viaFabry-Pérot observations of the Hα emission. With theirlarge field of view and high spatial resolution, the Fabry-Pérotdata allow us to probe simultaneously, in 2D, two kinematical featuresof the tidal ionized gas: large-scale velocity gradients due tostreaming motions along the tails, and small-scale motions related tothe internal dynamics of giant HII regions within the tails. In severalinteracting systems, massive (109 Mȯ)condensations of HI, CO and stars are observed in the outer regions oftails. Whether they are genuine accumulations of matter or not is stilldebated. Indeed a part of the tidal tail may be aligned with theline-of-sight, and the associated projection effect may result inapparent accumulations of matter that does not exist in the 3D space.Using numerical simulations, we show that studying the large-scalekinematics of tails, it is possible to know whether these accumulationsof matter are the result of projection effects or not. We conclude thatseveral ones (Arp 105-South, Arp 242, NGC 7252, and NGC 5291-North) aregenuine accumulations of matter. We also study the small-scale motionsinside these regions: several small-scale velocity gradients areidentified with projected values as large as 50-100 km s-1accross the observed HII regions. In the case of NGC 5291-North, thespatial resolution of our observations is sufficient to detail thevelocity field; we show that this system is rotating andself-gravitating, and discuss its dark matter content. TheFabry-Pérot observations have thus enabled us to prove that some109 Mȯ condensations of matter are realstructures, and are kinematically decoupled from the rest of the tail.Such massive and self-gravitating objects are the progenitors of theso-called ``Tidal Dwarf Galaxies''.Based on observations collected at the European Southern Observatory, LaSilla, Chile and at the Canada-France-Hawaii Observatory, Hawaii, USA.Appendix is only available in electronic form athttp://www.edpsciences.org
| Seyfert galaxies in UZC-Compact Groups
We present results concerning the occurrence of Seyfert galaxies in anew automatically selected sample of nearby Compact Groups of galaxies(UZC-CGs). Seventeen Seyferts are found, constituting 3% of theUZC-CG galaxy population. CGs hosting and non-hosting a Seyfert memberexhibit no significant differences, except that a relevant number of Sy2is found in unusual CGs, all presenting large velocity dispersion(σ>400 km s-1), many neighbours and a high number ofellipticals. We also find that the fraction of Seyferts in CGs is 3times as large as that among UZC-single-galaxies, and results from anexcess of Sy2s. CG-Seyferts are not more likely than other CG galaxiesto present major interaction patterns, nor to display a bar. Our resultsindirectly support the minor-merging fueling mechanism.
| Physical Coupling of Kazarian Galaxies with Surrounding Galaxies
Results from a statistical study of Kazarian galaxies and the objectssurrounding them are presented. It is shown that: (1) the sample ofKazarian galaxies up to 16m.0 is complete. (2) Roughly 35.7% of theKazarian galaxies are members of clusters, 14.0% of groups, and 13.6% ofbinary systems, while 36.7% are single galaxies. (3) Of the 580 Kazariangalaxies, roughly 61.2% are infrared, 8.8% radio, and 2.8% x-raysources. (4) The relative numbers of Kazarian galaxies for completesamples of I, R, and X in the different groups are systematically higherthan the corresponding numbers for samples of all Kazarian galaxies.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Mass-to-light ratios from the fundamental plane of spiral galaxy discs
The best-fitting two-dimensional plane within the three-dimensionalspace of spiral galaxy disc observables (rotational velocityvrot, central disc surface brightnessμ0=-2.5logI0 and disc scalelength h) has beenconstructed. Applying the three-dimensional bisector method ofregression analysis to a sample of ~100 spiral galaxy discs that spanmore than 4magarcsec-2 in central disc surface brightnessyields vrot\proptoI0.50\pm0.050\,h0.77\pm 0.07 (B band)and vrot\proptoI0.43\pm0.040\,h0.69\pm 0.07 (R band).Contrary to popular belief, these results suggest that in the B band,the dynamical mass-to-light ratio (within four disc scalelengths) islargely independent of the surface brightness, varying as I0.00\pm0.100\,h0.54\pm 0.14. Consistentresults were obtained when the range of the analysis was truncated byexcluding the low-surface-brightness galaxies. Previous claims thatM/LBvaries withI-1/20,Bareshown to be misleading and/or caused by galaxy selection effects - notall low-surface-brightness disc galaxies are dark matter dominated. Thesituation is, however, different in the near-infrared whereLK'~v4 and M/LK' is shown to vary asI-1/20,K\prime. Theoretical studies ofspiral galaxy discs should therefore not assume a constant M/L ratiowithin any given passband. The B-band dynamical mass-to-light ratio(within four disc scalelengths) has no obvious correlation with (B-R)disc colour, while in the K' band it varies as -1.25+/-0.28(B-R).Combining the present observational data with recent galaxy modelpredictions implies that the logarithm of the stellar-to-dynamical massratio is not a constant value, but increases as discs become redder,varying as 1.70+/-0.28(B-R).
| A Hubble Space Telescope Survey of the Mid-Ultraviolet Morphology of Nearby Galaxies
We present a systematic imaging survey of 37 nearby galaxies observedwith the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2(WFPC2) in the mid-UV F300W filter, centered at 2930 Å, as well asin the I-band (F814W) filter at 8230 Å. Eleven of these galaxieswere also imaged in the F255W filter, centered at 2550 Å. Oursample is carefully selected to include galaxies of sufficiently smallradius and high predicted mid-UV surface brightness to be detectablewith WFPC2 in one orbit and covers a wide range of Hubble types andinclinations. The mid-UV (2000-3200 Å) spans the gap betweenground-based UBVR(IJHK) images, which are available or were acquired forthe current study, and far-UV images available from the Astro/UITmissions for 15 galaxies in our sample. The first qualitative resultsfrom our study are as follows:1. Early-type galaxies show a significantdecrease in surface brightness going from the red to the mid-UV,reflecting the absence of a dominant young stellar population and insome cases the presence of significant (central) dust lanes. Galaxiesthat are early types in the optical show a variety of morphologies inthe mid-UV that can lead to a different morphological classification,although not necessarily as later type. Some early-type galaxies becomedominated by a blue nuclear feature or a point source in the mid-UV,e.g., as a result of the presence of a Seyfert nucleus or a LINER. Thisis in part due to our mid-UV surface brightness selection, but it alsosuggests that part of the strong apparent evolution of weak AGNs inearly-type galaxies may be due to surface brightness dimming of theirUV-faint stellar population, which renders the early-type host galaxiesinvisible at intermediate to higher redshifts.2. About half of themid-type spiral and star-forming galaxies appear as a latermorphological type in the mid-UV, as Astro/UIT also found primarily inthe far-UV. Sometimes these differences are dramatic (e.g., NGC 6782shows a spectacular ring of hot stars in the mid-UV). However, not allmid-type spiral galaxies look significantly different in the mid-UV.Their mid-UV images show a considerable range in the scale and surfacebrightness of individual star-forming regions. Almost without exception,the mid-type spirals in our sample have their small bulges bisected by adust lane, which often appears to be connected to the inner spiral armstructure.3. The majority of the heterogeneous subset of late-type,irregular, peculiar, and merging galaxies display F300W morphologiesthat are similar to those seen in F814W, but with important differencesdue to recognizable dust features absorbing the bluer light and to hotstars, star clusters, and star formation ``ridges'' that are bright inthe mid-UV. Less than one-third of the galaxies classified as late typein the optical appear sufficiently different in the mid-UV to result ina different classification.Our HST mid-UV survey of nearby galaxiesshows that, when observed in the rest-frame mid-UV, early- to mid-typegalaxies are more likely to be misclassified as later types thanlate-type galaxies are to be misclassified as earlier types. This isbecause the later type galaxies are dominated by the same young and hotstars in all filters from the mid-UV to the red and so have a smaller``morphological K-correction'' than true earlier type galaxies. Themorphological K-correction can thus explain part, but certainly not all,of the excess faint blue late-type galaxies seen in deep HST fields.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute (STScI), which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS 5-26555. Also based in part onobservations made with the Vatican Advanced Technology Telescope: theAlice P. Lennon Telescope and the Thomas J. Bannan AstrophysicsFacility.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| An Investigation into the Prominence of Spiral Galaxy Bulges
From a diameter-limited sample of 86 low-inclination (face-on) spiralgalaxies, the bulge-to-disk size and luminosity ratios and otherquantitative measurements for the prominence of the bulge are derived.The bulge and disk parameters have been estimated using aseeing-convolved Sérsic r1/n bulge and aseeing-convolved exponential disk that were fitted to the optical (B, R,and I) and near-infrared (K) galaxy light profiles. In general,early-type spiral galaxy bulges have Sérsic values of n>1, andlate-type spiral galaxy bulges have values of n<1. In the B band,only eight galaxies have a bulge shape parameter n consistent with theexponential value 1, and only five galaxies do in the K band. Use of theexponential bulge model is shown to restrict the range ofre/h and B/D values by more than a factor of 2. Applicationof the r1/n bulge models, unlike exponential bulge models,results in a larger mean re/h ratio for the early-type spiralgalaxies than for the late-type spiral galaxies, although this result isshown not to be statistically significant. The mean B/D luminosity ratiois, however, significantly larger (>3 σ) for the early-typespirals than for the late-type spirals. Two new parameters areintroduced to measure the prominence of the bulge. The first is thedifference between the central surface brightness of the galaxy and thesurface brightness level at which the bulge and disk contribute equally.The other test uses the radius at which the contribution from the diskand bulge light are equal, normalized for the effect of intrinsicallydifferent galaxy sizes. Both of these parameters reveal that theearly-type spiral galaxies ``appear'' to have significantly (more than 2σ in all passbands) bigger and brighter bulges than late-typespiral galaxies. This apparent contradiction with the re/hvalues can be explained with an iceberg-like scenario, in which thebulges in late-type spiral galaxies are relatively submerged in theirdisk. This can be achieved by varying the relative stellar density whilemaintaining the same effective bulge-to-disk ratio. The B/D luminosityratio and the concentration index C31, in agreement with paststudies, are positively correlated and decrease as one moves along thespiral Hubble sequence toward later spiral galaxy types, although forgalaxies with large extended bulges the concentration index no longertraces the B/D luminosity ratio in a one-to-one fashion. A strong(Spearman's rank-order correlation coefficient, rs=0.80) andhighly significant positive correlation exists between the shape, n, ofthe bulge light profile and the bulge-to-disk luminosity ratio. Theabsolute bulge magnitude-logn diagram is used as a diagnostic tool forcomparative studies with dwarf elliptical and ordinary ellipticalgalaxies. At least in the B band these objects occupy distinctlydifferent regions of this parameter space. While the dwarf ellipticalgalaxies appear to be the faint extension to the brighter ellipticalgalaxies, the bulges of spiral galaxies do not; for a given luminositythey have a noticeably smaller shape parameter and hence a more dramaticdecline of stellar density at large radii.
| 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.
| 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.
| Optical Long-Slit Spectroscopy of a Sample of Spiral Galaxies
We have analyzed long-slit spectra of a sample of 11 spiral galaxies. Weidentify several disk H II regions in each galaxy and provideclassifications for the nuclear spectra. We find seven nuclear H IIregion galaxies, including four starburst nucleus galaxies, and fourLINERs.
| 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.
| The Luminous Starburst Ring in NGC 7771: Sequential Star Formation?
Only two of the 20 highly luminous starburst galaxies analyzed by Smithet al. exhibit circumnuclear rings of star formation. These galaxiesprovide a link between ~10^11 L_solar luminosity class systems andclassical, less-luminous ringed systems. In this paper, we report thediscovery of a near-infrared counterpart to the 1.6 kpc diameter nuclearring of radio emission in NGC 7771 (UGC 12815). The ring contains ~10radio-bright clumps and ~10 near-infrared-bright clumps. A displacementbetween the peaks of the radio and the near-infrared emission indicatesthe presence of multiple generations of star formation. The estimatedthermal emission from each radio source is equivalent to that of ~35,000O6 stars. Each near-infrared-bright knot contains ~5000 red supergiants,on average. In the case that the radio-bright knots are 4 Myr old andthe near-infrared-bright knots are ~10 Myr old, each knot ischaracterized by a stellar mass of 10^7 M_solar, and the impliedtime-averaged star formation rate is ~40 M_solar yr^-1. Severalsimilarities are found between the properties of this system and otherringed and nonringed starbursts. Morphological differences between NGC7771 and the starburst+Seyfert 1 galaxy NGC 7469 (UGC 12332) suggestthat NGC 7771 may not be old enough to fuel an active galactic nucleus(AGN), or may not be capable of fueling an AGN. Alternatively, thedifferences may be unrelated to the presence or absence of an AGN andmay simply reflect the possibility that star formation in rings isepisodic.
| Near-infrared observations of galaxies in Pisces-Perseus. I. vec H-band surface photometry of 174 spiral
We present near-infrared, H-band (1.65 $() μm), surface photometry of174 spiral galaxies in the area of the Pisces-Perseus supercluster. Theimages, acquired with the ARNICA camera mounted on various telescopes,are used to derive radial profiles of surface brightness, ellipticities,and position angles, together with global parameters such as H-bandmagnitudes and diameters Radial profiles in tabular form and images FITSfiles are also available upon request from gmorio@arcetri.astro.it.}.The mean relation between H-band isophotal diameter D_{21.5} and theB-band D25 implies a B-H color of the outer disk bluer than3.5; moreover, D_{21.5}/D25 depends on (global) color andabsolute luminosity. The correlations among the various photometricparameters suggest a ratio between isophotal radius D_{21.5}/2 and diskscale length of ~ m3.5 and a mean disk central brightness ~ meq 17.5H-mag arcsec^{-2}. We confirm the trend of the concentration indexC31$ with absolute luminosity and, to a lesser degree, withmorphological type. We also assess the influence of non-axisymmetricstructures on the radial profiles and on the derived parameters. Basedon observations at the TIRGO, NOT, and VATT telescopes. TIRGO(Gornergrat, CH) is operated by CAISMI-CNR, Arcetri, Firenze. NOT (LaPalma, Canary Islands) is operated by NOTSA, the Nordic ObservatoryScientific Association. VATT (Mt. Graham, Az) is operated by VORG, theVatican Observatory Research Group Table 3 and Fig. 4 are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.
| Very Wide Galaxy Pairs of the Northern and Southern Sky
We present highly accurate observations of the 21 cm line of hydrogen ingalaxies made at the Arecibo and Parkes Observatories. The galaxiesobserved have been identified, through rigorous selection criteriaapplied to the CfA and SSRS catalogs, as being members of pairs withprojected separations of up to 1.5 Mpc (H0 = 75 km s-1 Mpc-1). Theseobservations form the completion of the Chengalur-Nordgren galaxy pairsample with data previously published by Chengalur, Nordgren andcolleagues. The new selection criteria used in this paper are anextension to larger projected separations of the criteria usedpreviously. Forty-nine new galaxies are observed, while H I is detectedin 41 of them. With the addition of these galaxies, the completed samplehas highly accurate H I velocities for a total of 219 galaxies.
| Extensive Spiral Structure and Corotation Resonance
Spiral density wave theories demand that grand-design spiral structurebe bounded, at most, between the inner and outer Lindblad resonances ofthe spiral pattern. The corotation resonance lies between the outer andthe inner Lindblad resonances. The locations of the resonances are atradii whose ratios to each other are rather independent of the shape ofthe rotation curve. The measured ratio of outer to inner extent ofspiral structure for a given spiral galaxy can be compared to thestandard ratio of corotation to inner Lindblad resonance radius. In thecase that the measured ratio far exceeds the standard ratio, it islikely that the corotation resonance is within the bright optical disk.Studying such galaxies can teach us how the action of resonances sculptsthe appearance of spiral disks. This paper reports observations of 140disk galaxies, leading to resonance ratio tests for 109 qualified spiralgalaxies. It lists candidates that have a good chance of having thecorotation resonance radius within the bright optical 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.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
| 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
| 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 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
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