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|Comparative Study of Asymmetry Origin of Galaxies in Different Environments. I. Optical Observations|
This paper presents the first of two analyses about the influence ofenvironment on the formation and evolution of galaxies observed in thenearby universe. For our study, we used three different samplesrepresenting different density environments: galaxies in Compact Groups(HCGs), Isolated Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs),which were taken as references. Usingboth characteristic isophotalparameters and evidence of asymmetries in the optical and thenear-infrared, we are able to establish differences in thecharacteristics of galaxies with different morphologies in differentenvironments, allowing us to better understand their different formationhistories. In this first paper, we present the isophotal and asymmetryanalyses of a sample of 214 galaxies in different environments observedin the optical (V and I images). For each galaxy, we have determineddifferent characteristic isophotal parameters and V - I colorprofiles, as a function of semi-major axis, and performed a fullasymmetry analysis in residual images using the V filter. Evidence ofasymmetry in the optical is almost missing in the KIG sample andsignificantly more common in the KPG than in the HCG samples. Ourisophotal analysis suggests that the stellar populations in the HCGgalaxies are older and more dynamically relaxed than in the KPG. The HCGgalaxies seem to be at a more advanced stage of interaction than theKPGs. One possible explanation is that these structures formed atdifferent epochs: compact groups of galaxies would have formed beforeclose pairs of galaxies, which only began interacting recently. However,similarities in the formation process of galaxies with same morphologysuggest CGs and close pairs of galaxies share similar conditions; theyare new structures forming relatively late in low-density environments.
|Infrared Properties of Close Pairs of Galaxies|
We discuss spectroscopy and IR photometry for a complete sample of ~800galaxies in close pairs objectively selected from the second Center forAstrophysics redshift survey. We use the Two Micron All Sky Survey tocompare near-IR color-color diagrams for our sample with the NearbyField Galaxy Sample and with a set of IRAS flux-limited pairs fromSurace and coworkers. We construct a basic statistical model to explorethe physical sources of the substantial differences among these samples.The model explains the spread of near-IR colors and is consistent with apicture in which central star formation is triggered by thegalaxy-galaxy interaction before a merger occurs. For 160 galaxies wereport new, deep JHK photometry within our spectroscopic aperture, andwe use the combined spectroscopic and photometric data to explore thephysical conditions in the central bursts. We find a set of objects withH-K>=0.45 and with a large FFIR/FH. Weinterpret the very red H-K colors as evidence for 600-1000 K dust withincompact star-forming regions, perhaps similar to super star clustersidentified in individual well-studied interacting galaxies. The galaxiesin our sample are candidate ``hidden'' bursts or, possibly, ``hidden''active galactic nuclei. Over the entire pair sample, both spectroscopicand photometric data show that the specific star formation ratedecreases with the projected separation of the pair. The data suggestthat the near-IR color-color diagram is also a function of the projectedseparation; all of the objects with central near-IR colors indicative ofbursts of star formation lie at small projected separation.
|The gas content of peculiar galaxies: Strongly interacting systems|
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
|Small-Scale Systems of Galaxies. I. Photometric and Spectroscopic Properties of Members|
This paper is the first of a series addressed to the investigation ofgalaxy formation/evolution in small-scale systems of galaxies (SSSGs),which are located in low-density cosmic environments. Our algorithm forSSSG selection includes galaxy systems of two or more galaxies lyingwithin Δcz<=1000 km s-1 and a 200h-1100 kpc radius volume. We present the analysisof the photometric and spectroscopic properties of 19 member galaxiesbelonging to a sample of 11 SSSGs. In the μe-replane early-type members may be considered ``ordinary,'' rather than``bright,'' galaxies, with a significant fraction of galaxies having adisk or disky isophotes. We do not detect fine structure or signaturesof recent interaction events in the early-type galaxy population, apicture also confirmed by the spectroscopy. At odds with these findingsare several spiral members with open arm configurations, as expected ininteracting systems. At the same time, emission lines in the spectra ofspiral members fall in the H II regions regime. None of the objectsdisplays unambiguous indications of nuclear activity, although fourspiral nuclei could be ascribed to the class of Seyferts. The starformation rate seems enhanced over the average expected in spiralgalaxies only for poorer SSSGs in particular pairs (<=50Msolar yr-1) but without being in the range ofstarburst systems.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program No. 57.B-036).
|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.
|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.
|Molecular Gas in Strongly Interacting Galaxies. I. CO (1-0) Observations|
We present observations of the CO (1-0) line in 80 interacting galaxiesas part of a program to study the role of interactions and mergers intriggering starbursts. The sample, which only includes obviouslyinteracting pairs of galaxies, is the largest such sample observed inCO. The observations were carried out at the NRAO 12 m and IRAM 30 mtelescopes. CO emission was detected in 56 galaxies (of which 32 are newdetections), corresponding to a detection rate of 70%. Because mostgalaxies are slightly larger than the telescope beam, correction factorswere applied to include CO emission outside the beam. The correctionfactors were derived by fitting a Gaussian function or an exponential CObrightness distribution to galaxies with multiple pointings and byassuming an exponential model for galaxies with single pointing. Wecompared the global CO fluxes of 10 galaxies observed by us at bothtelescopes. We also compared the measured fluxes for another 10 galaxiesobserved by us with those by other authors using the NRAO 12 m and FCRAO14 m telescopes. These comparisons provide an estimate of the accuracyof our derived global fluxes, which is ~40%. Mapping observations of twoclose pairs of galaxies, UGC 594 (NGC 317) and UGC 11175 (NGC 6621), arealso presented. In subsequent papers we will report the statisticalanalyses of the molecular properties in our sample galaxies and makecomparisons between isolated spirals and interacting galaxies.
|The Updated Zwicky Catalog (UZC)|
The Zwicky Catalog of galaxies (ZC), with m_Zw<=15.5, has been thebasis for the Center for Astrophysics (CfA) redshift surveys. To date,analyses of the ZC and redshift surveys based on it have relied onheterogeneous sets of galaxy coordinates and redshifts. Here we correctsome of the inadequacies of previous catalogs by providing (1)coordinates with <~2" errors for all of the 19,369 catalog galaxies,(2) homogeneously estimated redshifts for the majority (98%) of the datataken at the CfA (14,632 spectra), and (3) an estimate of the remaining``blunder'' rate for both the CfA redshifts and for those compiled fromthe literature. For the reanalyzed CfA data we include a calibrated,uniformly determined error and an indication of the presence of emissionlines in each spectrum. We provide redshifts for 7257 galaxies in theCfA2 redshift survey not previously published; for another 5625 CfAredshifts we list the remeasured or uniformly rereduced value. Among ournew measurements, 1807 are members of UZC ``multiplets'' associated withthe original Zwicky catalog position in the coordinate range where thecatalog is 98% complete. These multiplets provide new candidates forexamination of tidal interactions among galaxies. All of the newredshifts correspond to UZC galaxies with properties recorded in the CfAredshift compilation known as ZCAT. About 1000 of our new measurementswere motivated either by inadequate signal-to-noise in the originalspectrum or by an ambiguous identification of the galaxy associated witha ZCAT redshift. The redshift catalog we include here is ~96% completeto m_Zw<=15.5 and ~98% complete (12,925 galaxies out of a total of13,150) for the right ascension ranges 20^h>=alpha_1950<=4^h and8^h>=alpha_1950<=17^h and declination range-2.5d<=delta_1950<=50^deg. This more complete region includes allof the CfA2 survey as analyzed to date. The Great Wall structurepersists throughout the northern survey region. Dedicated to the memoryof Jim Peters, whose friendship, skill, and dedication were essential tothis work.
|The CFA Redshift Survey: Data for the South Galactic CAP|
We present redshifts for a sample of 4391 galaxies with magnitudem_B(0)<=15.5 covering 20^h<=alpha<=4^h in right ascension and-2.5d<=delta<=90^deg in declination. This sample is complete forall galaxies in the merge of the Zwicky et al. and Nilson catalogs inthe south Galactic cap. Redshifts for 2964 of these were measured aspart of the second CfA Redshift Survey. The data reveal large voids inthe foreground and background of the Perseus-Pisces Supercluster. Thelargest of these voids lies at a mean velocity ~8000 km s^-1, hasdiameter ~5000 km s^-1, and is enclosed by a complex of densestructures. The large structure known as the Perseus-Pisces Superclusterforms the near side of this complex. On the far side of this large void,at a mean velocity ~12,000 km s^-1, there is another coherent densewall. The structures in this survey support the view that galaxiesgenerally lie on surfaces surrounding or nearly surrounding low-densityregions or voids.
|Morphology transformation in pairs of galaxies - the local sample|
We present photometric analysis of a local sample of 14 isolated pairsof galaxies. The photometric properties analyzed in the local pairs are:colors, morphology, tidal effects and activity. We verify that closepairs have an excess of early-type galaxies and many elliptical galaxiesin this pairs are, in fact, lenticular galaxies. Many late-pairs in oursample show strong tidal damage and blue star formation regions. Weconclude that pairs of different morphologies may have passed throughdifferent evolution processes which violently transformed theirmorphology. Pairs with at least one early-type component may bedescendents of groups of galaxies. However, late-type pairs are probablylong-lived showing clearly signs of interaction. Some of them could beseen as an early stage of mergers. These photometric databases will beused for future comparison with more distant pairs in order to studygalaxy evolution.
|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.
|IRAS observations of an optically selected sample of interacting galaxies|
IRAS observations of a large, morphologically selected sample ofstrongly interacting disk-type galaxies have demonstrated thatgalaxy-galaxy collisions can lead to enhanced infrared emission, but notin all cases. Infrared luminosities of the interacting galaxies span alarge range, but are about a factor of 2 higher, on average, than thoseof isolated disk galaxies. The data suggest the existence of a cutoff inblue luminosity, below which no galaxies show markedly enhanced infraredemission. Only the most strongly interacting systems in the sample showextreme values of infrared excess, suggesting that deep,interpenetrating collisions are necessary to drive infrared emission toextreme levels. Comparisons with optical indicators of star formationshow that infrared excess and color temperatures correlate with thelevel of star-formation activity in the interacting galaxies. Allinteracting galaxies in our sample that exhibit an infrared excess andhave higher than normal color temperatures also have optical indicatorsof high levels of star formation. It is not necessary to invokeprocesses other than star formation to account for the enhanced infraredluminosity in this sample of interacting galaxies.
|Global properties of interacting disk-type galaxies|
Optical, far-IR, and radio observations of global properties arepresented for a sample of strongly interacting disk-type galaxies.Global star formation rates (SFRs) for the galaxies span a large rangeand are, on average, a factor of 2.5 higher than similarly determinedglobal SFRs for isolated spiral galaxies. New star formation occurspreferentially in or near the nuclear regions. H I 21 cm emission-lineprofiles indicate the presence of anomalous velocity material andchaotic patterns of gas motion in many interacting systems. Few systemsshow evidence for the presence of a well-organized rotating H I disksuch as are seen in isolated spiral galaxies. Neutral hydrogen gasmass-to-blue luminosity ratios are not atypical when compared withisolated spirals. The evidence indicates that local rather than globalproperties of these galaxies govern the star-formation process. Theobservations generally support the notion that enhanced SFRs are causedby increased cloud collision rates and dissipative flows of gas to thenucleus.
|Atlas of interacting galaxies, Part. II and the concept of fragmentation of galaxies.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28....1V&db_key=AST
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