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|Scale Heights of Non-Edge-on Spiral Galaxies|
We present a method of calculating the scale height of non-edge-onspiral galaxies, together with a formula for errors. The method is basedon solving Poisson's equation for a logarithmic disturbance of matterdensity in spiral galaxies. We show that the spiral arms can not extendto inside the ``forbidden radius'' r0, due to the effect ofthe finite thickness of the disk. The method is tested by re-calculatingthe scale heights of 71 northern spiral galaxies previously calculatedby Ma, Peng & Gu. Our results differ from theirs by less than 9%. Wealso present the scale heights of a further 23 non-edge-on spiralgalaxies.
|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.
|HI, HII, and R-Band Observations of a Galactic Merger Sequence|
bWe present high-quality aperture synthesis observations of the neutralhydrogen distribution in a sample of five galactic systems believed tobe involved in progressive stages of merging: Arp 295, NGC 4676, NGC520, NGC 3921, and NGC 7252. This is the first time that the atomichydrogen in such a broad range of disk mergers has been imaged. Thesedata are supplemented by wide-field images taken through a narrowbandHα filter, and by deep (μ_R_ > 26.5 mag arcsec^-2^) R-bandsurface photometry. We identify several trends along the mergingsequence. In the early stages, large amounts of HI still exist withinthe galactic disks and star formation is widespread. The ionized gasemission often takes on the appearance of plumes and arcs emanating fromthe nuclear regions, which are presumably the sites ofinteraction-induced starbursts. In the final stages there is little ifany H I within the remnant bodies, and tidal material is seen movinginward. We conclude that as the merger rearranges the light profiles ofthe progenitor disk galaxies into r^1/4^ profiles, it leads to anefficient conversion of the atomic gas into other forms within the mainbodies of the merger remnants. This suggests that these remnants willevolve into elliptical galaxies in their atomic gas contents as well astheir photometric properties. However, the observations of NGC 520reveal an extensive rotating gaseous disk, suggesting that perhaps somemergers will not destroy the atomic gas disks of the progenitors. Themorphological similarity between the gaseous and stellar tails and thesmooth gas kinematics confirm that gravity plays the dominant role inproducing them. There are, however, some striking differences betweenthe faint gas and light distributions. H I mapping often reveals gaseousextension not at all apparent optically, and tidal features of differentoptical morphologies have different gas characteristics: Theedge-brightened tails are gas rich, while the featureless plumes andhalos are gas poor. Some of these features may be explained by thedifferent velocity dispersions of the gas and stars, some by differentgas contents in the progenitors, and some remain unexplained. Overall,large quantities of both gas and starlight (M_H I_ > 10^9^h^-2^M_sun_, L_R_ > 10^9^h^-2^ L_sun_) are seen at large radii (r > 50h^-1^ kpc). Since this material evolves on very long time scales, it mayleave observable signatures for many Gyr.
|Colliding and Merging Galaxies. III. The Dynamically Young Merger Remnant NGC 3921|
This paper presents imaging, photometric, and spectroscopic observationsof NGC 3921 = Mrk 430 gathered over many years with five opticaltelescopes. This luminous galaxy (M_V_= -22.8 for H_0_ = 50) atcz_hel_=5926 +/- 15 km s^-1^ features a single nucleus, a main body withcomplex fine structure (ripples, loops, fan-shaped protrusions), and apair of ~100 kpc long, crossed tidal tails indicative of two former diskgalaxies of near-equal mass. These galaxies have essentially merged. Themain body of the remnant shows a typical post-starburst spectrumdominated in the blue by A 3-5 V stars. The inferred burst age is 0.5-1Gyr and the burst strength ~10% (by mass). Surrounding the nucleus isextremely centrally concentrated ionized gas that can be traced out to~12" (7 kpc), emits ~> 1.5 x 10^41^ ergs s^-1^ in Hα, and showssigns of both rotational and chaotic motions. The bright semistellarnucleus appears strikingly off-centered relative to the main body, whichitself features "sloshing" isophotes. That is, the centers of successiveisophotes shift position by ~>2 kpc, causing the nucleus to appeareccentric by up to 23% relative to a nearly half-light isophote. Theluminous matter has clearly not yet equilibrated, and this mergerremnant is dynamically young. Nevertheless, the mean light distributionof the main body is already well described by an r^1/4^ law. Thisdistribution plus the luminosity, UBV colors, color gradients, velocitydispersion, spectroscopic line strengths, and fine-structure index allagree with the notion that NGC 3921, which is a member of a small, tightgroup of four galaxies, is a 0.7+/-0.3 Gyr old protoelliptical (reckonedsince close passage that started the merger). Both it and its kin NGC7252 are nearby analogs of distant galaxies with "E+A"-type spectra inButcher-Oemler clusters. A search for star clusters and associations inNGC 3921 reveals 19 candidate OB associations, but only five candidateyoung globular clusters with M_V_ = -12 to -14. Thus, NGC 3921 appearsto have distinctly fewer and certainly less luminous young globularclusters than NGC 7252. This less extreme population of young globularsmay reflect a paucity of gas in one of the two merging component disksof this suspected S0-Sc or Sa-Sc merger (Hibbard & van Gorkom, AJ,in press). Such gas paucity may explain the weaker starburst and mayhave supplied fewer giant molecular clouds for globular clusterformation. Hence, the Hubble types and gas contents of componentgalaxies appear to play an important role in determining the clusterpopulations in merger remnants.
|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.
|HI observations of galaxies in nearby Zwicky clusters|
The results of a long term project of H I observations of galaxieswithin the boundaries of nearby Zwicky clusters are presented. Thedetection rate is rather low (233 out of 618, i.e., 38 percent) ascompared to other surveys carried out recently. Most of the radialvelocities of the detected galaxies are new determinations. The largespread in radial velocities for many of these clusters is a strongindication for the presence of several foreground and/or backgroundgalaxies.
|A Bowl Full of Galaxies|
|The Asiago Supernova Catalogue|
A Catalogue of Supernovae (SNe) is presented which tabulates the maindata relative to all extragalactic SNe discovered up to 1988 December31, and to their parent galaxies. In total 661 SNe are listed of which267 are classified. For an easier consultation, two lists are givenwhere the SNe are ordered chronologically and by Right Ascension,respectively. The overall distribution of classified supernovae over themorphological types of their parent galaxies is also presented in asummary table.
|A Checklist of Supernovae in the NGC and IC Galaxies Through 1985|
This Checklist of Supernovae in the NGC and IC Galaxies Through 1985 ispresented to assist those interested in undertaking a visual orphotographic search for extragalactic supernovae. Some galaxies appearto have had more than one or two supernovae, and these should bemonitored closely for any new outbursts.
|A revised supernova catalogue|
Essential data for 568 supernovae, discovered since 1885 up to 1983, andtheir parent galaxies are presented. This catalogue updates and revisesprevious listings, and some of its information is summarized in tabularand graphical form and briefly discussed. An appendix listing the mainreferences to observations of supernovae outside the optical range isprovided.
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