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Galaxy interactions - poor starburst triggers. III. A study of a complete sample of interacting galaxies
We report on a study of tidally triggered star formation in galaxiesbased on spectroscopic/photometric observations in the optical/near-IRof a magnitude limited sample of 59 systems of interacting and merginggalaxies and a comparison sample of 38 normal isolated galaxies. From astatistical point of view the sample gives us a unique opportunity totrace the effects of tidally induced star formation. In contrast toresults from previous investigations, our global UBV colours do notsupport a significant enhancement of starforming activity in theinteracting/merging galaxies. We also show that, contrary to previousclaims, there is no significantly increased scatter in the colours ofArp galaxies as compared to normal galaxies. We do find support formoderate (a factor of ~ 2-3) increase in star formation in the verycentres of the interacting galaxies of our sample, contributingmarginally to the total luminosity. The interacting and in particularthe merging galaxies are characterized by increased far infrared(hereafter FIR) luminosities and temperatures that weakly correlate withthe central activity. The LFIR/LB ratio however,is remarkably similar in the two samples, indicating that truestarbursts normally are not hiding in the central regions of the FIRluminous cases. The gas mass-to-luminosity ratio in optical-IR ispractically independent of luminosity, lending further support to thepaucity of true massive starburst galaxies triggered byinteractions/mergers. We estimate the frequency of such cases to be ofthe order of ~ 0.1% of the galaxies in an apparent magnitude limitedsample. Our conclusion is that interacting and merging galaxies, fromthe global star formation aspect, generally do not differ dramaticallyfrom scaled up versions of normal, isolated galaxies. No drastic changewith redshift is expected. One consequence is that galaxy formationprobably continued over a long period of time and did not peak at aspecific redshift. The effects of massive starbursts, like blowoutscaused by superwinds and cosmic reionization caused by starburstpopulations would also be less important than what is normally assumed.Based on observations collected at the European Southern Observatory, LaSilla, Chile.
| A New Look at the Holes of IC 2574
Several scenarios have been proposed to explain the existence of H Iholes in galaxies. In this work, the properties of the holes and shellsin the nearby dwarf galaxy IC 2574 are used to test the differentmodels. We report that the distribution of the kinematic ages of theholes located at the receding side of the galaxy is remarkably differentfrom the distribution for the holes situated at the approaching side.The mean values of the kinematic ages are 16.45+/-5.0 Myr and30.0+/-13.0[10.5] Myr, respectively. We estimate a probability of lessthan 4×10-3 that the age distributions were drawn atrandom. An asymmetry between both sides is also found in the photometricproperties and in the H I mass. These results are interpreted asevidence in favor of a connection between the star formation activityand the formation of holes in the interstellar medium, in accordancewith the predictions of the classical hypothesis that shells are createdby multiple supernova explosions. In addition, we find that thealternative scenarios face substantial difficulties and, so far, none ofthem can convincingly explain the observed abundance of sphericallyexpanding shells. After an examination of the different alternativemodels, we conclude that most of the holes in IC 2574 are likely theresult of multiple supernova explosions.
| High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - II. The properties of compact radio components
We discuss the properties of compact nuclear radio components in Seyfertgalaxies from the extended 12-μm AGN sample of Rush et al. Our mainresults can be summarized as follows. Type 1 and type 2 Seyferts producecompact radio components which are indistinguishable in strength andaspect, indicating that their central engines are alike, as proposed bythe unification model. Infrared IRAS fluxes are more closely correlatedwith low-resolution radio fluxes than high-resolution radio fluxes,suggesting that they are dominated by kiloparsec-scale, extranuclearemission regions; extranuclear emission may be stronger in type 2Seyferts. Early-type Seyfert galaxies tend to have stronger nuclearradio emission than late-type Seyfert galaxies. V-shaped extendedemission-line regions, indicative of `ionization cones', are usuallyfound in sources with large, collimated radio outflows. Hidden broadlines are most likely to be found in sources with powerful nuclear radiosources. Type 1 and type 2 Seyferts selected by their IRAS 12-μm fluxdensities have well-matched properties.
| Disc scalelengths of non-active and active spiral galaxies
Disc scalelengths rD are determined for a sample of 32non-active and 28 active spiral galaxies from optical CCD images. For 21of the 32 non-active galaxies and 20 of the 28 active galaxies B, V, Rand I data have been obtained, while for the remaining galaxies only Band I images have been taken. For 18 of the 21 non-active galaxies,which are measured in all four passbands, rD decreasessystematically from B to I, whereas such a decrease is found for onlyfour of the 20 active galaxies with BVRI data. For the non-activegalaxies, the ratios rD(B)/rD(I),rD(V)/rD(I) and rD(R)/rD(I)increase systematically with increasing apparent ellipticity ɛof the galaxies. For the active galaxies, no systematic variation of anyof the ratios with increasing ɛ is found. The variation ofrD(B)/rD(I) with ɛ is compared with modelcalculations. For the non-active galaxies, the data are represented bestby a model with a stellar disc that has an intrinsic colour gradient andwith a central optical depth in the B band for face-on view ofτ0B=3. For the active galaxies, the best agreement between data andmodels is found for models with a stellar disc with no intrinsic colourgradient and no dust. The best-fitting model for the non-active galaxiesdoes not reproduce the data of the active galaxies. The main conclusionof this work is that structural differences seem to exist between thediscs of non-active and active galaxies. The non-active galaxies showsignificant colour gradients within their discs, whereas the activegalaxies do not. These gradients are probably caused by a combination ofan intrinsic colour gradient within the stellar disc, and dustextinction. Furthermore, the measurements indicate that the non-activegalaxies show significant dust extinction in the centre, but they areoptically thin in the outer regions. The active galaxies do not seem tohave intrinsic colour gradients within the stellar disc and they areoptically thin throughout the disc.
| Star Formation in the Interacting Pair NGC 7733/7734
The problem of star formation within the interacting pair NGC 7733/34has been studied based on the UBVRI photometry of the source. Thedistribution of the colors of selected regions within the galaxies isused to infer an estimate for the age distribution of the star-formingregions. The results seem to indicate the presence of numerous extendedyoung star-forming regions in the disk of one of the two galaxies, NGC7733, with ages in the range 106-108 yr. However,there exists no evidence for any violent star formation activity in thepast 108 yr in the nuclei of the two galaxies. The pair seemsto be a merger-bound system with the brightest and youngest site ofstar-forming activity lying at the disk interface.
| Surface photometry of binary galaxies.
Not Available
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| CO and HI in a southern sample of interacting galaxies. I. The data
Using SEST, the Parkes antenna and the Australia Telescope CompactArray, we have made a survey of the ^12CO(1-0) and HI emission of anoptically-selected sample of ~60 southern interacting and merginggalaxies. In this paper we present the data and determine global massesof neutral gas (in molecular and atomic form) for the observed galaxies.We have detected HI in 26 systems and found that these galaxies haveless than 15% of their gas in molecular form. Figure 3 in its entirelyis only available in electronic form at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| A study of a complete sample of interacting galaxies. II. Images, colour distributions and spectra.
We present broadband images, two-colour maps and spectra of a magnitudelimited sample of interacting and merging galaxies.
| CO in paired galaxies: Star formation induced by gas flow
We present CO(1-0) observations of 51 galaxies from anoptically-selected smaple of binaries in the southern hemisphere. Datawere taken with the SEST 15m telescope (44 in beam). CO emission wasdetected from 33 galaxies, corresponding to a 65% detection rate. Thereis a strong correlation between the normalized CO and FIR luminosities.As already noted in other samples, the far infrared luminosity L(FIR)normalized to the blue luminosity and the star formation efficiency, astraced by the L(FIR)/M(H2) ratio, are enhanced, suggesting a tidaltrigger for the star-formation. The FIR luminosity normalized to theoptical surface is also enhanced. The CO luminosity is enhanced intidally perturbed objects, suggesting that the amount of molecular gasis higher in the interacting objetcs. The L(FIR)/L(B), and L(CO)/L(B)ratios correlate, although weakly, with the component separation in thebinaries, while the L(FIR)/M(H2) does not. This suggests that one of themain phenomena triggering star formation is the enhancement in the totalamount of molecular gas. The gas inflow is probably due to gravitationaltorques produced by tidal interaction. Our observations show thatinteracting galaxies have both a higher star formation efficiency and alarger mass of molecular gas available to fuel star formation.
| Southern Sky Redshift Survey - The catalog
The catalog of radial velocities for galaxies which comprise thediameter-limited sample of the Southern Sky Redshift Survey ispresented. It consolidates the data of observations carried out at theLas Campanas Observatory, Observatorio Nacional, and South AfricanAstronomical Observatory. The criteria used for the sample selection aredescribed, as well as the observational procedures and the techniqueutilized to obtain the final radial velocities. The intercomparisonbetween radial velocity measurements from different telescopes indicatesthat the final data base is fairly homogeneous with a typical error ofabout 40 km/s. The sample is at present 90 percent complete, and themissing galaxies are predominantly objects with very low surfacebrightness for which it is very difficult to obtain optical redshifts.
| A study of a complete sample of interacting galaxies. I - Presentation of the sample and the UBVRIJHK photometry
An investigation is presented on what effects galaxy-galaxy interactionhas on the properties of the involved galaxies. A magnitude limitedsample of interacting galaxies is presented, together with a controlsample of isolated galaxies. The Cousins UBVRI and Johnson JHKphotometry of all galaxies included in the samples is also presented.
| The ON-CfA redshift survey of the southern hemisphere
A redshift survey of a diameter-limited sample of southern galaxies hasbeen performed by the Observatorio Nacional in collaboration with theHarvard-Smithsonian Center for Astrophysics. Redshift data are presentedfor 442 galaxies. A relatively small mean difference of -5.2 km/s wasfound between the present redshifts and previous radio data.
| A catalogue of Seyfert galaxies.
Not Available
| New southern galaxies with active nuclei
A list of AGN candidates, identified from optical spectra taken as partof an ongoing redshift survey of southern galaxies, is presented. Theidentification, coordinates, morphological type, measured heliocentricradial velocity, and proposed emission type are given for the galaxiesshowing evidence of nonstellar nuclear activity. Using standarddiagnostics, several new Seyferts and low-ionization nuclear-emissionregions (LINERs) are identified among the emission-line galaxiesobserved.
| BV photometry and radial velocities of southern spiral galaxies
Multiaperture photoelectric photometry for 119 southern spiral galaxiesand heliocentric velocities for 98 southern spiral galaxies obtainedfrom image-tube spectrograms are presented. The data were collected in1976, 1977, and 1978 at Cerro Tololo Inter-American Observatory. Themagnitude and (B-V) color index are compared with aperture diameter inorder to determine if the present data correlate with previousmeasurements. The comparison reveals that the data correspond. Theinternal measurement error of the radial velocities is estimated; it isobserved that the internal error for one measurement is 41 km/sec.
| Southern Galaxy Catalogue.
Not Available
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