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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.
| BVRI surface photometry of mixed morphology pairs of galaxies. I. The first data set
We present multicolor broad band (BVRI) photometry for a sample of 11mixed morphology (E/S0+S) binary galaxies drawn from the KarachentsevCatalogue of Isolated Pairs of Galaxies (KPG). The data is part of anobservational programme devoted to the systematic photometric study ofone of the most complete and homogeneous pair samples available in theliterature. We present B band, B-filtered images, B, V, R and I surfacebrightness and (B-V), (B-R) and (B-I) color profiles as well asgeometric (epsilon = 1 - b/a, PA and a4/a) profiles for eachcomponent pair. In addition, integrated corrected B, V, R and Imagnitudes and integrated (B-V), (B-R) and (B-I) colors are alsopresented. Internal and external data comparisons show consistencywithin the estimated errors. Most of this subsample have photometricparameters homogeneously derived for the first time. Geometric profilesfrom our surface photometry along with the broad-band imaging and colorinformation have been used to re-evaluate morphology in all pairs. Wefind an important number of true mixed pairs with 5/11 (E+S) pairs inthe present sample. The remaining objects include 3 disky pairs(composed of S0 and S members), 2 early-type pair comprising E and S0members and 1 spiral-irregular pair. The measurements will be used in aseries of forthcoming papers where we try to identify and isolate themain structural and photometric properties of disk and ellipticalgalaxies at different stages of interaction.Based on data obtained at the 0.84 m and 1.5 m telescopes of theObservatorio Astronómico Nacional, San Pedro Mártir, BajaCalifornia, México, operated by the Instituto deAstronomía, UNAM.Tables 1-3 and Figs. 5 to 15 are only available in electronic form athttp://www.edpsciences.org
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
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