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|Optical spectroscopy for a sample of southern binary galaxies|
Aims.This work is part of a joint observational program aiming to getphotometric and spectroscopic information on southern pairs of galaxies.We present optical long-slit spectroscopic data on 80 probablecomponents of pairs, 61 of them collected with a spectral resolution of3.4 Å, and 19 with 12 Å. Nevertheless, our analysis takesinto account 53 components of pairs with better spectral resolution, as8 of these target galaxies actually belong to optical pairs. For thesample with better resolution, the covered wavelength range is 5724≤ λ ≤ 7036 Å. The spectroscopic and photometricinformation is gathered for an analysis relating galaxy morphologies totheir spectra. Methods: .We use Hα +[NII] and Hα equivalent widths as star formationtracers for the central region of our sample galaxies, and we classifythe spectra according to the emission lines' relative strength bylooking at their behavior. Results: . Some of our sample galaxiesexhibit high central star formation, most of them belonging to closepairs. However, not all galaxies' components of close pairs show thisbehavior. This may be a clue that besides interaction, other agents canstimulate central emission in binary galaxies. We suggest an enhancementin the number of galaxies with peculiar spectra (probably Seyferts) inour binary sample, when compared to isolated galaxies. Our dataindicates that the morphological types of interacting galaxies arerelated to their spectral characteristics, as almost all early-typegalaxies of our sample do not exhibit central optical emission. We notethat the star formation activity is most likely to take place in bothpairs' components, with a slightly higher mean strength for the lessbright component of the pair. It is interesting to point out that mostspirals exhibiting a strong HII emission line spectra present either abar or a peculiarity, but on a general basis we do not find anenhancement of star formation in our interaction sample.
|Photometric study of a sample of southern binary galaxies|
Aims.This work exhibits the basic optical photometric data for a sampleof 50 probable southern binary galaxies. Our sample covers a broad rangeof pair separations, stages of interaction, and morphologies. From theinitial list of selected pairs, using spectroscopic data from theliterature and our own data, we conclude that 84% of these systems aretrue binary galaxies. Methods: .We present residual and asymmetricmaps, R major semi-axis profiles of surface brightness, ellipticity,position-angle, harmonic Fourier coefficients of third and fourth order(b3 and b_4) for 50 probable pairs, and B-R color maps for 47of these pairs. For most galaxies, we present the profiles in twodifferent ways, aiming to verify the influence of random errors onthem. Results: . We note that random errors in position-angleprofiles are at least 2°, but a more significant result must takeinto account a variation larger than 11° for this distribution.Barred galaxies usually show a typical behavior in ellipticity andposition-angle profiles: these profiles display variations when changingfrom a bar to a disk region. In some cases, the variations also occuralong the bar. Some galaxies show distribution profiles that are commonfor their morphological type, and the interaction signature is onlyevidenced by their residual maps. Bars are usually redder and rings arebluer, when compared with the galaxy outskirts. Conclusions: .Ourdata indicates that there is a connection between interaction strengthand morphological distortions in binary galaxies. If we consider theprojected separation of a pair as an indication of interaction strength,distortions such as displaced centers, anomalous shapes of spiral arms,and twistings of external regions are easily detected in some closepairs, although not all components of close pairs show this behavior.Our data suggests that besides interaction, other parameters, likeorbital geometry and internal properties of galaxies, can stimulatebinary galaxies' peculiarities.
|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.
|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.
|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.
|A large sample of southern IRAS galaxies - Spectral classes and superclustering|
Results are presented of an extensive spectroscopic survey of IRASgalaxies, in three Southern-Hemisphere fields totaling about 0.5 sr.Spectroscopic observations have been made of 527 galaxies which arecandidates for 474 IRAS sources. Together with published data, there arenow measured redshifts for almost 850 of the 1178 selected IRAS galaxiesin these fields. This measured sample includes nearly all galaxies athigh redshifts, and hense high infrared luminosities, within thesefields. Classification of more than 350 of these galaxies usingemission-line ratios and line widths shows that about 90 percent havestarburst characteristics. Two distinct groups of starburst galaxies inthe sample display forbidden O III-line intensities which significantlyexceed those observed in optically selected starburst galaxies. One ofthese groups, with strong N II forbidden lines, may be related to linersand/or Seyfert galaxies. The other, with weak N II forbidden-lineemission, displays unusually narrow lines; this group is interpreted interms of the youngest phase of starburst activity.
|Mass-to-Light Ratios of Binary Galaxies. III. Analysis|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987ApJS...64..427S&db_key=AST
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