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The Effects of Interactions on the Structure and Morphology of Elliptical/Lenticular Galaxies in Pairs
We present a structural and photometric analysis of 42elliptical/lenticular galaxies in E/S0 + S pairs observed in the BVRIcolor bands. The aim of the analysis is to empirically determine theeffects of interactions on the galaxies' morphology, structure, andstellar populations as seen from the CAS parameters (light concentrationC, asymmetry A, and clumpiness S). We further compare these values to acontrol sample of 67 mostly isolated noninteracting E/S0 galaxies. Wefind that the paired E/S0 galaxies occupy more scattered loci in CASspace than noninteracting E/S0s and that the structural effects ofinteractions on E/S0s are minor, in contrast to disk galaxies involvedin interactions. This suggests that observational methods forrecognizing interactions, such the CAS methodology of Conselice, wouldnot detect E/S0s involved in interactions (related to early phases ofthe so-called dry mergers), and that the majority of interactinggalaxies identified at high redshift must be gas-dominated systems.However, we find statistical differences in the asymmetry index whencomparing isolated and interacting E/S0s. On average, paired E/S0galaxies have A-values 2.96+/-0.72 times larger than those ofnoninteracting E/S0s. For the subset of presumably strongly interactingE/S0s, A and S can be several times larger than the typical values ofthe isolated E/S0s. We show that the asymmetries are consistent withseveral internal and external morphological distortions. We concludethat the subsample of interacting E/S0s should be dense, gas-poorgalaxies in systems spanning a wide range of interaction stages, withtypical merging timescales >~0.1-0.5 Gyr. We use the observedphenomenology of this subsample to predict the approximate loci of drypremergers in the CAS parameter space.
| Mixed-Morphology Pairs as a Breeding Ground for Active Nuclei
Mixed-morphology pairs offer a simplification of the interactionequation that involves a gas-rich fast rotator paired with a gas-poorslow rotator. In past low-resolution IRAS studies it was assumed thatthe bulk of the far-infrared (FIR) emission originated in the spiralcomponent. However, our Infrared Space Observatory studies revealed asurprising number of early-type components with significant IR emission,some of which turned out to show active nuclei. This motivated us tolook at the current statistics of active nuclei in mixed pairs using theradio-FIR continuum correlation as a diagnostic. We find a clear excessof early-type components with radio continuum emission and activenuclei. We suggest that they arise more often in mixed pairs viacross-fueling of gas from the spiral companion. This fuel is moreefficiently channeled into the nucleus of the slow-rotating receptor. Ina sample of 112 mixed-morphology pairs from the Karachentsev catalog, wefind that about 25%-30% of detected mixed pairs show a displacement fromthe radio-FIR relation defined by normal star-forming galaxies. Thelatter objects show excess radio continuum emission, while others extendthe relation to unusually high radio and FIR flux levels. Many of theoutliers or extreme emitters involve an early-type component with anactive nucleus. The paired E/S0 galaxies in the sample exhibit asignificant excess detection fraction and a marginal excess luminositydistribution compared to those of isolated unpaired E/S0 galaxies.
| BVRI surface photometry of mixed morphology pairs of galaxies. II. The second data set
In order to analyze the photometric signature of gravitationalinteractions in spiral and elliptical galaxies, we present results ofmulticolor broad band (BVRI) surface photometry for a second set of 10mixed pairs drawn from the Karachentsev Catalogue of Isolated Pairs ofGalaxies (KPG). We report total magnitudes and colors, as well assurface brightness, color and geometric (ɛ, PA anda4/a) profiles. Most of this subsample have photometricparameters homogeneously derived for the first time. Internal andexternal data comparisons show consistency within the estimated errors.We find 1 true (E+S) pair and 4 probable (E+S) pairs ((E/S0+S) cases) inthe present sample. The remaining objects include 3 lenticular-spiral(S0+S) systems, 1 spiral-spiral (S+S) pair and 1 probable spiral-spiralpair ((S0/Sa+S) case). Four lenticular galaxies show evidence ofunderlying (perhaps induced) structures like bars/arms. Among the spiralcomponents, an over-representation of early (Sa-Sb) types was found. Abrief discussion on the existence of a Holmberg Effect is alsopresented.Based on data obtained at the 0.84 m telescope of the ObservatorioAstronómico Nacional (OAN), San Pedro Mártir, BajaCalifornia, México, operated by the Instituto deAstronomía, UNAM.Tables 1-3 and Figs. 3-12 are only available in electronic form athttp://www.edpsciences.org
| Multiwavelength Insights into Mixed-Morphology Binary Galaxies. I. ISOCAM, ISOPHOT, and Hα Imaging
We present Hα and ISO mid- and far-IR observations for a sample ofmixed-morphology galaxy pairs that reveal both the stellar andnonstellar signatures of the interaction process. A mixed-morphologypair is perhaps the simplest form of galaxy-galaxy interaction becauseit is expected to involve only a single rapidly rotating gas-richcomponent paired with a gas-poor elliptical or lenticular galaxy. Aprimary assumption that we address is whether spirals are the only IRemitter in these mixed (E+S) pairs. Our observations reveal that many ofthe early-type galaxies exhibit weak (low equivalent width) emission, asoften observed in field elliptical galaxies. These are the classicalmixed-morphology pairs. However, some of the early-type components,especially the lenticular galaxies, show evidence for significant starformation, with Hα equivalent widths and 15 μm luminositiescomparable to or exceeding those of their often much larger spiralcompanions. Our sample contains five Seyfert 2 nuclei, of which threecan be described as companions on the end of a spiral arm. The Seyfertnucleus is often accompanied by a starburst region, while other suchcompanions currently show only the starburst component. These pairs areamong the best candidates for direct interaction fuelling of bothstarbursts and active galactic nuclei.Based on observations with the Infrared Space Observatory (ISO), an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, the Netherlands and the United Kingdom) withthe participation of ISAS and NASA.
| Kinematical Observations of a Sample of Binary Galaxies
Not Available
| 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 list of some corrections to Zwicky's Catalogue of Galaxies and Clusters of Galaxies
Not Available
| Supernova rates and bursts of star formation
A new analysis of supernova (SN) rates in spiral and irregular galaxiesis presented. It is shown that the concept of a single average SN ratefor all 'normal' galaxies has to be abandoned. Normal galaxies belong totwo distinct classes with regard to the formation of SN II progenitors:most galaxies are rather inactive while a small percentage of galaxiesin a 'burst' phase is producing these massive stars vigorously. Theinitial mass function during such bursts must be notably different fromthat determined in the solar neighborhood. It has to be strongly biasedtoward stars with masses above about eight solar. The formation ofmassive stars follows a pattern fundamentally different from that of lowand intermediate-mass stars. It occurs episodically and apparently overentire disks of spirals, in particular Sc galaxies.
| 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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