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A Hubble Space Telescope WFPC2 Investigation of the Nuclear Morphology in the Toomre Sequence of Merging Galaxies
We report on the properties of nuclear regions in the Toomre sequence ofmerging galaxies, based on imaging data gathered with the Hubble SpaceTelescope WFPC2 camera. We have imaged the 11 systems in the proposedevolutionary merger sequence in the F555W and F814W broadband filters,and in Hα+[N II] narrowband filters. The broadband morphology ofthe nuclear regions varies from nonnucleated starburst clumps throughdust-covered nuclei to a nucleated morphology. There is no unambiguoustrend in the morphology with merger stage. The emission-line morphologyis extended beyond the nucleus in most cases, but centrally concentrated(within 1 kpc) emission-line gas can be seen in the four latest-stagemerger systems. We have quantified the intrinsic luminosity densitiesand colors within the inner 100 pc and 1 kpc of each identified nucleus.We find little evidence for a clear trend in nuclear properties alongthe merger sequence other than a suggestive rise in the nuclearluminosity density in the most evolved members of the sequence. The lackof clear trends in nuclear properties is likely due both to the effectsof obscuration and geometry, as well as the physical variety of galaxiesincluded in the Toomre sequence.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555. These observations are associated with proposal8669.
| 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.
| Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutralhydrogen) of elliptical galaxies and merger remnants ordered into a timesequence on the basis of spectroscopic age estimates. We find that thefraction of cold gas in early merger remnants decreases significantlyfor ~1-2Gyr, but subsequent evolution toward evolved elliptical systemssees very little change. This trend can be attributed to an initial gasdepletion by strong star formation, which subsequently declines toquiescent rates. This explanation is consistent with the merger picturefor the formation of elliptical galaxies. We also explore the relationbetween the HI-to-H2 mass ratio and spectroscopic galaxy age,but find no evidence for a statistically significant trend. Thissuggests little net HI-to-H2 conversion for the systems inthe present sample.
| 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.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Do galaxy mergers form elliptical galaxies? A comparison of kinematic and photometric properties
We present near-infrared K-band imaging and spectroscopy of a sample ofgalaxy mergers, which we use to derive light profile indices, absolutemagnitudes and central velocity dispersions. We find that the lightdistributions of mergers more nearly resemble those of ellipticals thanthose of bulges, but that the mergers lie well away from the FundamentalPlane defined by the ellipticals. We interpret this as being due toenhancement of the K-band surface brightness of the mergers by asignificant population of supergiant stars, and independent evidence forsuch a population is inferred from measurements of the depth of the2.3-μm CO absorption feature.
| 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.
| 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.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| A Spectrophotometric Survey of Merging Galaxies
We present long-slit spectrophotometry of 40 merging or stronglyinteracting galaxy systems in the wavelength range 3650-7100 A. Alongwith optically selected objects, the sample includes 10 ultraluminousIRAS galaxies with evidence of ongoing merger activity. The data show awide variety of phenomena, with spectra resembling those of isolatedelliptical galaxies, early and late-type spiral galaxies, activegalactic nuclei starbursts, and poststarburst systems.
| Spectrophotometric Properties of Merging Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...450..547L&db_key=AST
| Binaries in the Universe. Possible Dynamical Mechanisms of Formation, Evolution and Disruption of Different Kinds of Constituents of the Universe
Not Available
| The Local Merger Rate of Disk Galaxies
We consider the local population of galaxy merger remnants, morespecifically the remnants of disk-disk mergers for which there arediagnostic features (such as tails) that might be catalogued in a fairlycomplete manner. We estimate the current rate of mergers for suchgalaxies by comparing the luminosity function for mergers with those ofspiral-spiral pairs (their most common precursors) and for all diskgalaxies, incorporating the effects of changing crossing time withluminosity. These are connected via the time scale for mergers, which weestimate from the dynamical properties of our sample and publishedn-body models. We derive a merger rate for spirals in pairs, at thepresent epoch, of 4.2 per Hubble time (2.8 over the age of the Universeat critical density, or extrapolated to all spirals, 0.33 per Hubbletime). Given this large difference, depending on which precursorpopulation is considered, a two-component model seems most appropriateto assess the effects of mergers on galaxy evolution - one for galaxiesoriginally in pairs or small groups, and a second for galaxies whichhave never been in environments so susceptible to merging.Distinguishing the initial contributions of each to the overall galaxypopulations will require samples at high redshift. We also evaluate thehistory of several indicators of observable star formation, using thedynamical state of each remnant as an age estimate. With large scatter,we see evidence that star formation builds up to the time of mergerrather slowly, with a rapid decline thereafter. For most systems, dustseems to be so important in obscuring much of the starburst's opticalradiation that the luminosity increase of a merger over its initialcomponents does not have a profound effect on either our derived mergerrate or on higher-redshift counts. This rapid fading means that mergersper se can be at most a minor contributor to the Butcher-Oemler effect;most blue galaxies in systems fated to merge will be observed during theinteractions that precede the final merging event. Further observationsof the dynamical state of high-redshift systems are clearly needed toassess the time- integrated impact of merging on the overall galaxypopulation; the crude estimates given per Hubble time must be lowerlimits under most conditions. An Appendix describes the luminosityfunction of "field" galaxies of various morphological types, derivedfrom a new analysis of the CfA survey in the B_t_^0^ system.
| A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow field
A new identification of groups and clusters in the CfA1 Catalog ofHuchra et al. is presented, using a percolation algorithm to identifydensity enhancements. It is shown that in the resulting catalog,contamination by interlopers is significantly reduced. The Schechterluminosity function is redetermined, including the Malmquist bias.
| The frequency of mergers in compact groups
The far-infrared colors, optical morphologies, and emission-linerotation curves of galaxies in compact groups are used to estimate thenumber of these galaxies which are currently merging. Each of theseindependent methods indicates that roughly 7 percent of the galaxies incompact groups are in the process of merging. Although each technique issomewhat uncertain, the agreement among the independent methods for thefraction of ongoing mergers and the generally good correlation betweendifferent measures of merging for individual systems lend added weightto the results. The combination of this fraction of galaxies in compactgroups which are currently merging with previous studies of theproperties of elliptical galaxies in compact groups leads to theconclusion that the dynamical evolution of compact groups throughmerging occurs on a time scale significantly longer than the observedcrossing time.
| A near-infrared imaging survey of interacting galaxies - The small angular-size ARP systems
Near-IR images of a large sample of interacting galaxies selected fromthe Atlas of Peculiar Galaxies by Arp (1966) have been obtained.Approximately 180 systems have been imaged in at least two, and usuallythree of the standard JHK bands. The survey and the observing and datareduction procedures, are described, and contour plots and aperturephotometry are presented. Future papers will analyze the imaging data bygroupings based on interaction type, stage, and progenitors. The goalsof the analysis are to explore the relationships between galaxyinteractions, activity, and morphology by studying the structure of thenear-IR luminosity distribution, where extinction effects are muchreduced relative to the optical and the major stellar mass component ofgalaxies dominates the observed light.
| The far-infrared properties of the CfA galaxy sample. I - The catalog
IRAS flux densities are presented for all galaxies in the Center forAstrophysics magnitude-limited sample (mB not greater than 14.5)detected in the IRAS Faint Source Survey (FSS), a total of 1544galaxies. The detection rate in the FSS is slightly larger than in thePSC for the long-wavelength 60- and 100-micron bands, but improves by afactor of about 3 or more for the short wavelength 12- and 25-micronbands. This optically selected sample consists of galaxies which are, onaverage, much less IR-active than galaxies in IR-selected samples. Itpossesses accurate and complete redshift, morphological, and magnitudeinformation, along with observations at other wavelengths.
| Periodicities in galaxy redshifts
Using new data for unassociated galaxies with wide H I profiles andvalues of period and solar motion predicted by Tifft and Cocke (1984), aperiodicity has been found which is significant at the conventional 5percent level. Together with Tifft's work on galaxy pairs and smallgroups, this result appears to provide evidence in favor of thehypothesis that measured galaxy redshifts occur in steps of a littlemore than 72 km/s or a simple multiple of this period.
| Structure of superclusters and supercluster formation. V - Spatial correlation and voids
The galaxian spatial correlation function is calculated for variousobservational samples having different sample volume. It is demonstratedthat the correlation length increases with sample volume. For volumesconsiderably smaller than the size of the Local Supercluster thecorrelation length is about half the conventional value, 5/h Mpc, whichcorresponds to sizes of intermediate samples, containing the wholesupercluster. Samples containing several superclusters have correlationlengths twice the conventional one. Similar calculations have beencarried out for various theoretical models. Samples representingluminous matter in a neutrino-dominated universe and having differentsample volumes have correlation length which increases with volume untilthe sample size reaches the average size of voids. Further increase inthe sample size does not change the correlation length, indicating thatfair samples of the model universe have been reached. These calculationsand simple theoretical estimates indicate that the value of thecorrelation length reflects the filling factor of the sample and thepresence of large voids in galaxy distribution. The observed correlationfunction of galaxies reflects the distribution of luminous matter. Aftercorrecting for the difference between the correlation functions of truemass and galaxies, the correlation length for a fair sample of theuniverse is estimated to be 10/h Mpc.
| A study of the large-scale structure in the distribution of galaxies in a region centered about the Cancer cluster. I - Initial observational results. II - Further observational results
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986AJ.....91..705B&db_key=AST
| Radio emission of isolated single and double galaxies
The catalogs of Karachentsev (1972) and Karachentseva (1973) are used tocompare the properties of isolated single and double galaxies, andquantitative results are obtained. It is shown that spiral galaxieswhich are members of pairs have a radio luminosity exceeding that ofsingle galaxies by 2.5 times on the average. In addition, it is foundthat members of interacting pairs are more powerful emitters in theradio range and that spiral galaxies which are members of triplets haveradio luminosities on a par with those of pair members.
| The nuclear activity of interacting galaxies
A search for active galactic nuclei among interacting galaxies isreported. A sample of 167 systems of interacting and asymmetric galaxieswas observed spectrophotometrically in the spectral range 4700-7100 A.The results are compared with a sample of isolated galaxies. It is foundthat (1) there are no Seyfert nuclei in elliptical or dwarf irregulargalaxies of the sample; (2) there is an excess of Seyfert nuclei amonginteracting spirals, but it is only at the 90 percent confidence level;(3) this excess becomes statistically significant (98 percent) when onlystrongly interacting spirals are included (four new Seyfert nuclei arepresented); (4) in the subgroup of galaxies with extreme tidaldistortions, no Seyfert nuclei were found.
| Structure of superclusters and superclusters formation. IV Spatial distribution of clusters of galaxies in the Coma supercluster and its large-scale environment
The Coma-A1367 Supercluster and its large-scale environment areinvestigated. The Zwicky et al. (1961-68) clusters are used assupercluster tracers; superclusters are defined not by visual impressionbut on the basis of cluster analysis. Attention is restricted to an areaof the sky where RA is between 9h and 15h, with Dec. greater than -3deg. Clustering analysis is applied to study the spatial distribution.At neighborhood radii R = 15-25 Mpc (for Hubble constant H = 50 km per sper Mpc), the clusters form chains and superclusters of galaxies. It isnoted that at R = 26-28 Mpc, superclusters merge to a single connectednetwork. Cluster chains link the Coma-A1367 Supercluster with the LocalSupercluster, A779, and Hercules Superclusters. The Coma-A1367Supercluster comprises four cluster chains, and its diameter is greaterthan 100 Mpc. It is noted that a typical cluster chain has eight Zwickyclusters and is 80 Mpc in length. Most, if not all, of the clusters formconnected systems. Empty regions devoid of clusters have diameters up to100 Mpc in this region of the sky. The morphology distribution of brightgalaxies and the mean absolute magnitude of first ranked galaxies inZwicky clusters are found to be similar to the respective quantities inAbell clusters.
| Enhanced radio emission in binary spiral galaxies
A comparison is conducted between the radio emission characteristics ofa sample of isolated pairs of spiral galaxies and those of a sample ofisolated spiral galaxies for which complete distance information isavailable. It is noted that double galaxy total emission is, on average,a factor of 2 more powerful than that of isolated spiral galaxies ofcomparable luminosity. The radio emission enhancement in these doublegalaxies is correlated with a tidal index, in keeping with a tidalorigin for the enhancement.
| Very large spiral galaxies
As a first step in the systematic study of large spirals, which may beuseful in cosmological tests and studies of galaxy evolution, a catalogof the 107 largest known spiral galaxies is presented. Catalog galaxieshave isophotal diameters greater than 90 kpc, assuming an H(zero) valueof 50 km/sec per Mpc. UBVR photoelectric photometry is presented for 20of these galaxies, and absolute magnitudes are derived for all galaxiesin the catalog by transforming Zwicky magnitudes to the B(T) system.
| A 21 centimeter line survey of a complete sample of interacting and isolated galaxies
The paper presents 21 cm line observations of a complete sample ofinteracting and isolated galaxies made with the National Radio AstronomyObservatory 91 and 43 m telescopes and the Arecibo 3035 m telescope. The21 cm line data are combined with a homogeneous set of optical data onangular diameters, axial ratios, magnitudes, and colors, and integralproperties are calculated for the galaxies in both samples. In thispaper, the sample selection procedures, the method of observation, thedata reduction, and the observational errors are described. Thedetection percentages are presented for both samples.
| A survey of galaxy redshifts. IV - The data
The complete list of the best available radial velocities for the 2401galaxies in the merged Zwicky-Nilson catalog brighter than 14.5mz and with b (II) above +40 deg or below -30 deg ispresented. Almost 60 percent of the redshifts are from the CfA surveyand are accurate to typically 35 km/s.
| Enhanced radio emission in merging galaxies
The list of examples selected by Toomre (1977) is supplemented withmorphologically similar systems from the Arp Atlas of Peculiar Galaxies(1966). This sample of mergers is compared with two samples of spiralgalaxies in terms of radio power. The first comparison sample comprisesgalaxies with the same optical luminosities as the mergers. The secondis that subset of the first sample in which the galaxy forms part of adouble or multiple system. The mergers are found to be approximatelyeight times more likely to be radio-loud (radio power greater than orequal to 10 to the 22nd W/Hz at 1.4 GHz) than the members of the firstsample and two to three times more likely to be radio-loud than those ofthe second sample. The merger either involves a unique mechanism forstimulating radio emission or makes more extensive use of the samemechanism that enhances radio emission in galaxies in double or multiplesystems.
| Observations of neutral hydrogen in radio-loud and interacting galaxies
The results of a survey of H I in radio-loud and interacting galaxies ispresented. Four cases of H I absorption and five of emission arereported. The interesting features found for individual galaxies aredescribed, and the systematic properties are discussed. Column densitiesof absorbing gas generally exceed those expected for a 'Milky Way' H Idisk by more than an order of magnitude. The absorbing gas must have aflattened, disklike morphology oriented roughly parallel to the opticaldisk of the galaxy. Turbulent noncircular gas motions are evidentlypresent, which are shown to be almost certainly induced by galaxy-galaxyinteractions. The set of galaxies in which H I absorption has beendetected is dominated by morphologically peculiar objects. It isconcluded that the detection of H I seen in absorption against a nuclearradio source permits direct determination of the sense of radial flow ofextranuclear material, and is direct evidence that potential 'food' fora compact object in the nucleus exists in the galaxy.
| Double galaxy investigations. I - Observations
Redshift information from 240 A/mm spectrograms is presented for 370double arcsec galaxy systems from the Karachentsev (1972) catalog,including all pairs in that catalog with separation less than 80 arcsec.An extensive error discussion utilizing internal and external (21 cm)comparisons provides calibration of systematic error and determines theuncertainty for a typical high weight optical redshift to be plus orminus 65 km/sec. Internal differential redshifts within single spectrausing common lines achieve accuracies of 18-30 km/sec, depending uponseparation, and are available for about 200 pairs. Extensive informationon emission and other properties is also provided.
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