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|Mixed-Morphology Pairs as a Breeding Ground for Active Nuclei|
Mixed-morphology pairs offer a simplification of the interactionequation that involves a gas-rich fast rotator paired with a gas-poorslow rotator. In past low-resolution IRAS studies it was assumed thatthe bulk of the far-infrared (FIR) emission originated in the spiralcomponent. However, our Infrared Space Observatory studies revealed asurprising number of early-type components with significant IR emission,some of which turned out to show active nuclei. This motivated us tolook at the current statistics of active nuclei in mixed pairs using theradio-FIR continuum correlation as a diagnostic. We find a clear excessof early-type components with radio continuum emission and activenuclei. We suggest that they arise more often in mixed pairs viacross-fueling of gas from the spiral companion. This fuel is moreefficiently channeled into the nucleus of the slow-rotating receptor. Ina sample of 112 mixed-morphology pairs from the Karachentsev catalog, wefind that about 25%-30% of detected mixed pairs show a displacement fromthe radio-FIR relation defined by normal star-forming galaxies. Thelatter objects show excess radio continuum emission, while others extendthe relation to unusually high radio and FIR flux levels. Many of theoutliers or extreme emitters involve an early-type component with anactive nucleus. The paired E/S0 galaxies in the sample exhibit asignificant excess detection fraction and a marginal excess luminositydistribution compared to those of isolated unpaired E/S0 galaxies.
|A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample|
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
|Statistical Properties of the Emission in Mixed-Morphology (E+S) Pairs. I. Optical Results|
We present a statistical analysis of the optical emission properties fora mixed-morphology (E+S) sample of galaxy pairs. The sample is large anddiverse enough (~150 pairs) to permit discrimination of pairs bymorphological types. It samples a large enough volume of space tojustify derivation of the optical luminosity function. We find anaverage factor of 1.6 enhancement in the optical luminosity of thelate-type pair components relative to an isolated galaxy control sample.This is interpreted as the optical signature of the interaction-starformation connection. We find a complete absence of dwarf pairs(M_Zw>=-17.0) that is probably related to a corresponding lack ofisolated E/S0 dwarf galaxies in the control sample. The spirals in (E+S)and (S+S) pairs show similar levels of optical enhancement but fail toshow a trend toward higher luminosity with decreasing companionseparation. A first-order comparison of galaxy type distributionsbetween our pair and isolated samples suggests that (1) pairs show anexcess of elliptical and early-type spiral (Sa-b) components and (2)corresponding deficit of S0s and late-type spirals in the ``E'' and``S'' pair components, respectively. We consider both possible bias anddynamical explanations for (1) the observed (E+S) spiral-componentluminosity excess and (2) the morphology excesses/deficits.
|Accurate Positions for MCG Galaxies|
We have measured accurate celestial coordinates for 4741 extragalacticobjects, primarily drawn from a list of MCG galaxies with no recentlypublished accurate positions. The standard deviations in the newpositions depend slightly on the measurement method but are on the orderof 1.0" to 1.2". Standard deviations in the original MCG positions areconfirmed to be at the 1.5′-2.0′ level. These new positionswere integrated into NED in 1997 December.
|Double galaxy investigations. I - Observations|
Redshift information from 240 A/mm spectrograms is presented for 370double arcsec galaxy systems from the Karachentsev (1972) catalog,including all pairs in that catalog with separation less than 80 arcsec.An extensive error discussion utilizing internal and external (21 cm)comparisons provides calibration of systematic error and determines theuncertainty for a typical high weight optical redshift to be plus orminus 65 km/sec. Internal differential redshifts within single spectrausing common lines achieve accuracies of 18-30 km/sec, depending uponseparation, and are available for about 200 pairs. Extensive informationon emission and other properties is also provided.
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