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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.
| Optical and Near-Infrared Color Profiles in Nearby Early-Type Galaxies and the Implied Age and Metallicity Gradients
We present results of an age and metallicity gradient analysis inferredfrom both optical and near-infrared surface photometry. The analysis isbased on a sample of 36 nearby early-type galaxies, obtained from theEarly Data Release of the Sloan Digital Sky Survey and the Two MicronAll Sky Survey. Surface brightness profiles were derived in each bandand used to study the color gradients of the galaxies. Using simplestellar population models with both optical and near-infrared colors, wemay interpret the color gradients in terms of age and metallicitygradients of galaxies. UsinggZ≡dlogZmet/dlogR andgA=dlog(age)/dlogR to represent the metallicity and agegradients, we found a median value of gZ=-0.25+/-0.03 for themetallicity gradient, with a dispersionσgZ=0.19+/-0.02. The corresponding valuesfor the age gradients were gA=0.02+/-0.04 andσgA=0.25+/-0.03. These results are in goodagreement with recent observational results, as well as with recentsimulations that suggest that both monolithic collapse and major mergershave played important roles in the formation of early-type galaxies. Ourresults demonstrate the potential of using multi-wave band colorsobtained from current and future optical and infrared surveys inconstraining the age and metallicity gradients of early-type galaxies.
| An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| 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
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| On the relationship between radio emission and optical properties in early-type galaxies
To study the origin of radio activity in early-type galaxies, thepossible dependence of their radio emission on basic optical parameters,such as the absolute magnitude, the central velocity dispersion sigma,and the mean surface brightness mu is explored. A sample of 743 E and SOgalaxies is used which is based on three independent radio surveys ofoptically selected galaxies with virtually complete information onmagnitudes, morphological types, redshift distances, diameters, andradio fluxes. For both E and SO galaxies, only the absolute magnitudeappears to be directly related to the radio activity, while sigma and mudo not. Also, a significant dependence of the apparent flattening onradio power is confirmed for E galaxies. Some relevant implications ofthese results are discussed.
| Radio emission of isolated single and double galaxies
The catalogs of Karachentsev (1972) and Karachentseva (1973) are used tocompare the properties of isolated single and double galaxies, andquantitative results are obtained. It is shown that spiral galaxieswhich are members of pairs have a radio luminosity exceeding that ofsingle galaxies by 2.5 times on the average. In addition, it is foundthat members of interacting pairs are more powerful emitters in theradio range and that spiral galaxies which are members of triplets haveradio luminosities on a par with those of pair members.
| A survey of galaxy redshifts. IV - The data
The complete list of the best available radial velocities for the 2401galaxies in the merged Zwicky-Nilson catalog brighter than 14.5mz and with b (II) above +40 deg or below -30 deg ispresented. Almost 60 percent of the redshifts are from the CfA surveyand are accurate to typically 35 km/s.
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