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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.
| Tidally Triggered Star Formation in Close Pairs of Galaxies. II. Constraints on Burst Strengths and Ages
Galaxy-galaxy interactions rearrange the baryons in galaxies and triggersubstantial star formation; the aggregate effects of these interactionson the evolutionary histories of galaxies in the universe are poorlyunderstood. We combine B- and R-band photometry and optical spectroscopyto estimate the strengths and timescales of bursts of triggered starformation in the centers of 190 galaxies in pairs and compact groups.Based on an analysis of the measured colors and EW(Hα), wecharacterize the preexisting and triggered populations separately. Thebest-fitting burst scenarios assume stronger reddening corrections forline emission than for the continuum and continuous star formationlasting for >~100 Myr. The most realistic scenarios require aninitial mass function that is deficient in the highest mass stars. Thecolor of the preexisting stellar population is the most significantsource of uncertainty. Triggered star formation contributessubstantially (probably >~50%) to the R-band flux in the centralregions of several galaxies; tidal tails do not necessarily accompanythis star formation. Many of the galaxies in our sample have bluercenters than outskirts, suggesting that pre- or nonmerger interactionsmay lead to evolution along the Hubble sequence. These objects wouldappear blue and compact at higher redshifts; the older, redder outskirtsof the disks would be difficult to detect. Our data indicate thatgalaxies with larger separations on the sky contain weaker, and probablyolder, bursts of star formation on average. However, confirmation ofthese trends requires further constraints on the colors of the olderstellar populations and on the reddening for individual galaxies.
| The Tully-Fisher Relation as a Measure of Luminosity Evolution: A Low-Redshift Baseline for Evolving Galaxies
We use optical rotation curves to investigate the R-band Tully-Fisherproperties of a sample of 90 spiral galaxies in close pairs, covering arange of luminosities, morphological types, and degrees of tidaldistortion. The galaxies follow the Tully-Fisher relation remarkablywell, with the exception of eight distinct ~3 σ outliers. Althoughmost of the outliers show signs of recent star formation, gasdynamicaleffects are probably the dominant cause of their anomalous Tully-Fisherproperties. Four outliers with small emission-line widths have verycentrally concentrated line emission and truncated rotation curves; thecentral emission indicates recent gas infall after a close galaxy-galaxypass. These four galaxies may be local counterparts to compact, bluegalaxies at intermediate redshift. The remaining galaxies have anegligible offset from the reference Tully-Fisher relation, but ashallower slope (2.6 σ significance) and a 25% larger scatter. Weargue that triggered star formation is a significant contributor to theslope difference. We characterize the nonoutlier sample with measures ofdistortion and star formation to search for third-parameter dependencein the residuals of the TF relation. Severe kinematic distortion is theonly significant predictor of TF residuals; this distortion is not,however, responsible for the slope difference from the referencedistribution. Because the outliers are easily removed by sigma clipping,we conclude that even in the presence of some tidal distortion,detection of moderate (>~0.5 mag in rest-frame R) luminosityevolution should be possible with high-redshift samples the size of this90-galaxy study. The slope of the TF relation, although difficult tomeasure, is as fundamental for quantifying luminosity evolution as thezero-point offset. Some observations reported in this paper wereobtained at the Multiple Mirror Telescope Observatory, a facilityoperated jointly by the University of Arizona and the SmithsonianInstitution.
| 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.
| Mapping Infrared Enhancements in Closely Interacting Spiral-Spiral Pairs. I. ISO CAM and ISO SWS Observations
Mid-infrared (MIR) imaging and spectroscopic observations are presentedfor a well-defined sample of eight closely interacting (CLO) pairs ofspiral galaxies that have overlapping disks and show enhancedfar-infrared (FIR) emission. The goal is to study the star formationdistribution in CLO pairs, with special emphasis on the role of``overlap starbursts.'' Observations were made with the Infrared SpaceObservatory (ISO) using the CAM and SWS instruments. The ISO CAM maps,tracing the MIR emission of warm dust heated by young massive stars, arecompared to new ground-based Hα and R-band images. We identifythree possible subgroups in the sample, classified according to the starformation morphology: (1) advanced mergers (Arp 157, Arp 244, and Arp299), (2) severely disturbed systems (Arp 81 and Arp 278), and (3) lessdisturbed systems (Arp 276, KPG 347, and KPG 426). Localized starburstsare detected in the overlap regions in all five pairs of subgroups (1)and (2), suggesting that they are a common property in collidingsystems. Except for Arp 244, the ``overlap starburst'' is usuallyfainter than the major nuclear starburst in CLO pairs. Star formation in``less disturbed systems'' is often distributed throughout the disks ofboth galaxies with no ``overlap starburst'' detected in any of them.These systems also show less enhanced FIR emission, suggesting that theyare in an earlier interaction stage when the direct disk collisions haveprobably not yet occurred. Based on observations made with ISO, an ESAproject with instruments funded by ESA Member States and with theparticipation of ISAS and NASA.
| 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.
| An X-Ray Survey of Galaxies in Pairs
Results are reported from the first survey of X-ray emission fromgalaxies in pairs. The sample consists of 52 pairs of galaxies from theCatalog of Paired Galaxies whose coordinates overlap the ROSAT PositionSensitive Proportional Counter pointed observations. The mean observedlogl_X for early-type pairs is 41.35+/-0.21, while the mean logl_Xpredicted using the l_X-l_b relationship for isolated early-typegalaxies is 42.10+/-0.19. With 95% confidence, the galaxies in pairs areunderluminous in the X-ray, compared with isolated galaxies, for thesame l_b. A significant fraction of the mixed pair sample also appearssimilarly underluminous. A spatial analysis shows that the X-rayemission from pairs of both types typically has an extent of ~10-50 kpc,much smaller than the group intergalactic medium, and thus likelyoriginates from the galaxies. CPG 564, the most X-ray luminousearly-type pair, 4.7x10^42 ergs s^-1, is an exception. The extent of itsX-ray emission, greater than 169 kpc, and HWHM, ~80 kpc, is comparableto that expected from an intergalactic medium. The sample shows only aweak correlation, ~81% confidence, between l_X and l_b, presumably dueto variations in gas content within the galaxies. No correlation betweenl_X and the pair velocity difference (Deltav), separation (Deltar), orfar-infrared luminosity (l_fir) is found, although the detection rate islow, 22%.
| 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.
| Tidally-triggered disk thickening. II. Results and interpretations.
We have reported in a previous paper (Paper I, Reshetnikov and Combes,1996A&AS..116..417R) B,V and I band photometric data for a sample of24 edge-on interacting spiral galaxies, together with a control sampleof 7 edge-on isolated galaxies. We discuss here the main result found inthis study: the ratio h/z_0_ of the radial exponential scalelength h tothe constant scaleheight z_0_ is about twice smaller for interactinggalaxies. This is found to be due both to a thickening of the plane, andto a radial stripping or shrinking of the stellar disk. If we believethat any galaxy experienced a tidal interaction in the past, we mustconclude that continuous gas accretion and subsequent star formation canbring back the ratio h/z_0_ to higher values, in a time scale of 1Gyr.
| A 1.425 GHz Atlas of the IRAS Bright Galaxy Sample, Part II
Galaxies with δ >= -45^deg^ and |b| >= 10^deg^ in the IRASBright Galaxy Sample, Part II, were observed at 1.425 GHz by the VeryLarge Array in its B, CnB, C, DnC, and D configurations. An atlas ofradio contour maps and a table listing the principal radio sourceparameters (position, flux density, angular size) are given. This atlasof 187 galaxies supplements the 1.49 GHz atlas of 313 galaxies in therevised Bright Galaxy Sample, Part I. Together, they are complete forextragalactic sources stronger than S = 5.24Jy at λ = 60 micronsin the area |b| > 10^deg^, δ > -45^deg^. To the extent thatthe far-infrared and radio brightness distributions overlap, these radiomaps provide the most accurate positions and high-resolution images ofthe brightest extragalactic far-infrared sources.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Tidally-triggered disk thickening. I. Observations.
As part of an investigation on what effect galaxy interactions have onthe z-structure of the disks of involved galaxies, we present here newphotometric data in the B, V, I passbands for a sample of 24 interactingsystems and 7 non-interacting galaxies. Isophotes, total magnitudes andcolours of all sample galaxies (67) are determined. Our estimates andthe comparison with the published results show that the accuracy of ourphotometry is about 0.15mag.
| The IRAS Bright Galaxy Survey - Part II: Extension to Southern Declinations (delta ~< -30), and Low Galactic Latitudes (f<|b|
Complete IRAS Observations and redshifts are reported for all sourcesidentified in the IRAS Bright Galaxy Survey-Part II (hereafter referredto as BGS_2_). Source positions, radial velocities, optical magnitudes,and total flux densities, peak flux densities, and spatial extents at12, 25, and 100 ,microns are reported for 288 sources having 60 micronflux densities > 5.24 Jy, the completeness limit of the originalBright Galaxy Survey [Soifer et al., AJ, 98,766(1989)], hereafterreferred to as BGS_1_. These new data represent the extension of theIRAS Bright Galaxy Survey to southern declinations,δ<~-30^deg^, and low Galactic latitudes,5^deg^<|b|<30^deg^. Although the sky coverage of the BGS_2_ (~19935 deg^2^) is 37% larger than the sky coverage of the BGS_1_, thenumber of sources is 8% smaller due primarily to large scale structurein the local distribution of galaxies. Otherwise, the sources in theBGS_2_ show similar relationships between number counts and flux densityas observed for the 313 sources in the BGS_1_. The BGS_2_ along with theearlier BGS, represents the best sample currently available for definingthe infrared properties of galaxies in the local (z <~ 0.1) Universe.
| Radio Identifications of Extragalactic IRAS Sources
Extragalactic sources detected at λ= 60 microns were selectedfrom the IRAS Faint Source Catalog, Version 2 by the criterion S_60microns_ >= S_12_ microns. They were identified by positioncoincidence with radio sources stronger than 25 mJy at 4.85 GHz in the6.0 sr declination band 0^deg^ < δ < +75^deg^ (excluding the0.05 sr region 12^h^40^m^< α < 14^h^40^m^, 0^deg^<+5^deg^) and with radio sources stronger than 80 mJy in the 3.4 sr areao^h^ <α < 2o^h^, -40^deg^ < δ < 0^deg^ (plus theregion 12^h^40^m^ < α < 14^h^40^m^, 0^deg^<δ<+5^deg^). Fields containing new candidate identifications weremapped by the VLA at 4.86 GHz with about 15" FWHM resolution. Difficultcases were confirmed or rejected with the aid of accurate (σ ~ 1")radio and optical positions. The final sample of 354 identifications in{OMEGA} = 9.4 sr is reliable and large enough to contain statisticallyuseful numbers of radio-loud FIR galaxies and quasars. The logarithmicFIR radio flux ratio parameter q can be used to distinguish radiosources powered by "starbursts" from those powered by "monsters."Starbursts and normal spiral galaxies in a λ = 60 micronflux-limited sample have a narrow (σ_q_ = 0.14 +/- 0.01) qdistribution with mean = 2.74 +/- 0.01, and none have "warm"FIR spectra [α(25 microns, 60 microns) < 1.5]. The absence ofradio- quiet (but not completely silent) blazars indicates that nearlyall blazars become optically thin at frequencies v<~100 GHz.Nonthermal sources with steep FIR/optical spectra and dusty-embeddedsources visible only at FIR and radio wavelengths must be very rare.
| Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
| A photometric study of interacting galaxies. I - Observations
As part of an investigation on what effect galaxy-galaxy interaction hason the global photometric properties of the involved galaxies, wepresent here new photometric data in the Cousins R-prime system for asample of 35 interacting systems. Isophotes, equivalent profiles, andtotal magnitudes of all sample galaxies (73) are determined. Ourestimates and the comparison with the published results show that theaccuracy of our photometry is about 0.2-0.3 mag. A later paper willpresent the interpretation of the data.
| A photometric study of interacting galaxies. 2: Analysis of the results
We present the results of a detailed photometric study in theRC band of 73 galaxies in close interacting systems. Thesample for this study was selected mainly from the Atlas of PeculiarGalaxies by Arp on the basis of the optical morphology of galaxies. Theobserved systems exhibit: an excess of early type spirals (Sa) anddeficiency of late type ones (Sm/Irr), and excess of brighter galaxiesas compared with field galaxies. From the decomposition of theequivalent profiles we found the following principal results: (a)Interacting ellipticals and bulges of SO galaxies are systematicallydisplaced in the plane mue - Re from the relationfor normal galaxies. This displacement may be explained in terms ofbulges of interacting galaxies being more compact. (b) Bulges ofinteracting spirals are located in the effective parameters plane in thesame region of bulges of non-interacting galaxies. (c) Disks of stronglyinteracting spirals are 2-3 times thicker as compared with disks ofnormal galaxies. (d) The central surface brightnesses (mu0 ofthe disks of interacting galaxies are, on average, brighter than forfield spirals. (e) There is no clear dependence of the globalphotometric characteristics of galaxies on the interaction strength.There is a weak tendency for galactic disks to be slightly brighter andshorter than in strongly interacting systems.
| Hydroxyl in galaxies. I - Surveys with the NRAO 300 FT telescope
Results are presented of a search for 1667- and 1665-MHz mainline OHtransitions for 321 galaxies, which were observed during four separatesessions at the NRAO 300-ft telescope in the period 1984-1987. Threedetections of OH megamasers are reported, as well as detections of threenew OH absorption sources. The observational sample contains sourcesfrom a variety of catalogs and represents different criteria. Theresults for the whole sample confirm that FIR luminosity and colorcriteria used for these surveys are indeed optimized for findingmegamasers. The results also confirm that detecting distant highluminosity OH megamasers is considerably more successful than findingnearby weak masers.
| Accurate Positions of Zwicky Galaxies - Part Four
Accurate optical positions are given for about 2830 galaxies containedin 44 fields of the Zwicky Catalogue.
| An extragalactic data base. II - The HI data
A compilation of raw H I data has been made as a part of a big projectof collecting astrophysical parameters for more than 70000 galaxies.Corrections to produce homogenized H I parameters are deduced from thecompilation made for the Extragalactic Data Base. All raw 21-cm linewidths are reduced to a common system of widths at 20 percent and 50percent of the peak. They are corrected for velocity resolution effectand tested for homogeneity reference by reference. The H I fluxesconverted to uniform units system are corrected, when necessary, forbeam-filling effect. The homogenized mean fluxes are tested for scaleand zero-point errors and also for a reference effect. Heliocentric HI-velocities are reduced in the same way. These results have been usedto produce a catalogue of weighted mean H I parameters for 6439galaxies.
| IRAS observations of an optically selected sample of interacting galaxies
IRAS observations of a large, morphologically selected sample ofstrongly interacting disk-type galaxies have demonstrated thatgalaxy-galaxy collisions can lead to enhanced infrared emission, but notin all cases. Infrared luminosities of the interacting galaxies span alarge range, but are about a factor of 2 higher, on average, than thoseof isolated disk galaxies. The data suggest the existence of a cutoff inblue luminosity, below which no galaxies show markedly enhanced infraredemission. Only the most strongly interacting systems in the sample showextreme values of infrared excess, suggesting that deep,interpenetrating collisions are necessary to drive infrared emission toextreme levels. Comparisons with optical indicators of star formationshow that infrared excess and color temperatures correlate with thelevel of star-formation activity in the interacting galaxies. Allinteracting galaxies in our sample that exhibit an infrared excess andhave higher than normal color temperatures also have optical indicatorsof high levels of star formation. It is not necessary to invokeprocesses other than star formation to account for the enhanced infraredluminosity in this sample of interacting galaxies.
| The Photometric Investigation of the Interacting System VORONTSOV-VELYAMINOV:242 / VV:242
Not Available
| A 21 CM survey of the Pisces-Perseus supercluster. I - The declination zone +27.5 to +33.5 degrees
Neutral-hydrogen 21 cm line data for a sample of galaxies in the regionbounded by 22 h less than R.A. less than 04h, + 27 deg 30 arcmin Dec.less than + 33 deg 30 arcmin are presented as the first installment of asurvey of galaxies in the region of the Pisces-Perseus supercluster. Ofthe 415 galaxies observed in this strip with the Arecibo 305 mtelescope, 342 have been detached in the 21 cm line; another ten haveuseful upper limits to their H I content. The sample includes mostspiral, irregular, and dwarf galaxies larger than 1 arcmin; in selectedareas, spirals to a limiting magnitude of + 15.7 have been observed. Thevelocity distribution of the 511 galaxies with known redshift in thiszone deviates markedly from that expected for a similar sample ofrandomly placed objects. The region contains significant clustering inall three dimensions.
| 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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