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|The 1.0 Megaparsec Galaxy Pair Sample in Low-Density Regions|
Using complete redshift catalogs, we have compiled a list of galaxypairs based solely on a pair's projected separation, rp, andvelocity difference, ΔV. We have made high-velocity precision H Iobservations of each galaxy in the sample and have reported these in theliterature. Due to the nature of the redshift catalogs, we are able toquantitatively evaluate the effects of isolation and number density ofsurrounding galaxies on each pair in the sample. For the close galaxypairs (rp<100 kpc), the degree of isolation (a measure ofthe number of near neighbors) has little effect on the median ΔV.This median is about 55 km s-1 for the 25 close pairs (ifmedium-density close pairs are omitted ΔV is even smaller, but thedifference is not statistically significant). The effect of isolation isstrong for the entire sample of galaxy pairs with separations as largeas 1.0 Mpc. For these larger separation pairs, relaxation of strictisolation requirements introduces small groups into the sample, whichdramatically increases the median ΔV. We find little evidence ofan increase in the median ΔV with decreasing rp, norwith increasing total luminosity. For our isolated pairs in low-densityregions, the overall median ΔV is only 30 km s-1. Forsimilar separations and isolation criteria, galaxy satellites withlarger luminosity ratios (i.e., less dynamical friction) in higherdensity regions have ΔV approximately twice as large. Weconjecture that our orbits are highly eccentric, so that the indirecteffect of dynamical friction leads to predominantly small ΔV.However, the halos of our galaxies may also be of low density (althoughhighly extended).
|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.
|Close galaxy pairs in low and medium density regions: The southern sky.|
We extend to the southern hemisphere a continuing program of optical andHI observations of galaxy pairs (Chengalur \etal 1993, 1994, 1995 andNordgren \etal 1997). These pairs are drawn from published redshiftcatalogs and represent a complete sample. We present new data of 15pairs observed with the Palomar 5-meter telescope, Mount Stromlo SidingSpring 40-inch telescope, Australia Telescope Compact Array and VLA Dsynthesis array. These galaxy pairs are all defined as close pairs(projected separations < 100 kpc). HI companions are found near fiveof 15 pairs.
|Surface photometry of binary galaxies. I. A multicolour study of morphologies due to the interaction.|
We present the multicolour (B, V, R) surface photometry of 53 doublegalaxies. All the pairs belong to the catalogue of Reduzzi &Rampazzo (1995) containing objects selected according to theKarachentsev (1972) criteria. We comment on the morphological,structural and photometric characteristics of pairs and their members.Different classes of interaction induced phenomena, both among early andlate-type galaxies, are considered. We found that few early-typegalaxies show fine structures. Grand design structure is more frequentlydetected in binary than in field spirals both for barred and non barred,confirming Elmegreen & Elmegreen's (1982) study. The colour of thetails is consistent with the stripping hypothesis since it is similar tothe progenitor galaxy outskirts. Among our objects we have no evidentsign of induced star formation in tails. Rings appear on average bluerthan the disc as a whole.
|Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of 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 southern redshift survey. I - Accurate redshifts for 500 galaxies observed at SAAO|
Radial velocities are presented for about 500 galaxies observed with anintensified Reticon photon-counting detector attached to the 1.9 mtelescope at the Sutherland field station of SAAO. The velocities weredetermined by cross correlation with standard velocity templates, fromthe measured wavelengths of emission lines, or from both techniques,with spectra covering the wavelength range from 3700 to 5400 A. Thefinal velocities appear to have the same zero point as H I radiovelocities, and have standard deviations of the order of 35 km/s, thoughcross-correlation velocities on their own may have significantly largererrors.
|The enhancement of infrared emission in interacting galaxies|
Selected infrared properties, based on IRAS observations, of twocategories of interacting galaxy pairs from the Arp-Madore Catalogue ofSouthern Peculiar Galaxies and Associations are examined. For pairs ofcomparably sized galaxies, a strong tendency exists for pairs with thehighest far-IR color temperatures to have the smallest separation. Thisfinding implies that galaxy interactions significantly enhance theintensity or the efficiency of star formation. No trend of far-IR colortemperature varying with pair separation is found for pairs consistingof a galaxy with a small companion. There are 10 times as many pairs inthe sample that contain one IRAS far-IR galaxy as there are pairs forwhich both galaxies were detected by IRAS, thus strengthening previousconclusions that the effect of a perturbation depends strongly on thedetailed geometry of the interaction.
|Southern Galaxy Catalogue.|
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