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The observations and studies of OH megamasers associated with external galaxies
During the thirty years since the first discovery of OH megamaserassociated with external galaxies, a great progress of observations andstudies for OH megamasers associated with external galaxies has beenproceeded. So far 106 OH megamasers associated with external galaxieshave been found, including 59 higher red-shifted ones. The observationsand studies of the OH megamasers associated with AGN and starburstgalaxies are the very efficient tools to investigate characteristics oftheir central sources and circumnuclear discs. A review on the currentprogress concerning surveys, observations and theoretical investigationson extragalactic OH megamaser sources is given in this paper.
| A study of the infrared characteristics of host IRAS sources with OH megamasers
OH megamasers are the most luminous cosmic maser sources known. So farpowerful OH maser emission has been discovered from 90 extragalacticobjects. An important observational characteristic of the OH megamasersources is their relationship between L(OH) and L(IR). We study therelationship between logL(OH) and logL(IR) for the 67 OH megamasersources for which there are data on L(OH) and L(IR). Accounting forMalmquist bias, the relationship L(OH) ~L(IR)1.41 isobtained. We use the largest sample currently available to study therelationship between L(OH) and L(IR) for OH megamaser sources. Ourresults agree with Kandalian's results within the uncertainties.The infrared properties of the host IRAS sources with OH megamasers arealso studied. The most striking features are the anticorrelation of S(12μm)/S(25 μm) versus S(60 μm)/S(100 μm) and the correlationof S(12 μm)/S(25 μm) versus S(25 μm)/S(60 μm). They areconsistent with Henkel, Wouterlooy & Bally's finding that S(12μm)/S(25 μm) is anticorrelated with S(60 μm)/S(100 μm), butare the opposite of Henkel et al.'s result that S(12 μm)/S(25 μm)is correlated with S(25 μm)/S(60 μm). This is an interestingdifference. Our colour-colour plots suggest that the peak of theinfrared spectra of our sample of OH sources is at a longer wavelengththan the peak in the sample of Henkel et al. This suggests that infraredradiation from our sample is dominated by emission from material atgreater separations from the central source.
| 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.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| 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.
| Optical Classification of Megamaser Galaxies
We have obtained spectroscopic observations of the nuclear regions of 42galaxies known to harbor strong OH masers. These megamaser galaxiesrepresent a subsample of FIR (ultra)luminous galaxies, which typicallyhave FIR luminosities in excess of 10^11 L_ȯ. The primary goal ofthis study is to investigate the nuclear activity sources of OHmegamaser galaxies. We are able to classify the nuclear emission-linespectra of all but one of our sample, and we find that this class ofgalaxies is dominated by active galactic nuclei (AGNs), althoughstarburst galaxies do make up an appreciable fraction of the megamasersas well. Fully 45% of the megamasers exhibit Seyfert or LINER spectra,predominantly of Seyfert 2 type, although two galaxies with broad linesare observed. This observation is consistent with the currentunification models for the two types of Seyfert activity, since theassumed geometry necessary to detect a megamaser places the Seyfertnucleus behind a high column density of molecular gas (i.e., themolecular torus). Starburst-nucleus galaxies comprise 32.5% of oursample, while 22.5% are classified as ``composite nuclear spectra''(CSN) sources, showing evidence of both AGN and starburst activity. Anumber of objects show unusual emission-line ratios, not surprising fora group of galaxies that are known a priori to possess substantialabsorbing material along the line of sight to their nuclei. Our resultsare compared to previous studies of FIR-selected galaxy samples, as wellas to radio-continuum observations of these galaxies. The activityclassification obtained from the radio data disagrees with the opticalclassifications in roughly 25% of the sources; we discuss possibleexplanations for these discrepancies.
| 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.
| A comparative study of morphological classifications of APM galaxies
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
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