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On the morphology of peculiar ring galaxies
It is proposed that peculiar ring galaxies can be divided into fiveprincipal types according to the morphology of the ring and bulge, basedon the visual inspection of 489 selected objects. Those objects havebeen named ``peculiar'' following the ``Catalogue of Southern PeculiarGalaxies and Associations'' by \cite[Arp & Madore (1986]{am6}) Table2 with its notes is only available electronically via anonymous ftp130.79.128.5 or http://cdsweb.u-strasbg.fr.
| Wheels of Fire. III. Massive Star Formation in the ``Double-ringed'' Ring Galaxy AM 0644-741
We have used H alpha CCD imaging to map the distribution and intensityof massive star formation (MSF) in AM 0644-741, a large southern ringgalaxy. MSF is restricted to a pair of interlocked 30 kpc diameterrings, with less than 1% contributed by a nuclear point source. Fiftypercent of the total H alpha emission originates in a crescent-shapedregion defining the southwest quadrant of the most prominent ring("A-ring"). North of the nucleus, MSF bifurcates into closely spacedrings of H II complexes. Particularly strong MSF occurs where theyintersect. A broad continuum ring spans the disk south of the nucleus("B-ring"). No diffuse MSF is found over the enclosed disk above an SFRper unit area of 0.15 Mȯ Gyr-1 pc-2 (3 sigma ), which is similar tolimits set in the disks of S0 galaxies. However, low H alpha surfacebrightness ( Sigma H alpha ) complexes are found beyond the southwestA-ring. We derive a total H alpha luminosity (LH alpha ) of 3.0 x 1041ergs s-1 (H0 = 100 km s-1 Mpc-1), and a total SFR of 3 Mȯ yr-1.Both values are significantly larger than those of field spirals andcomparable to those found in interacting disk systems. The integrated Halpha equivalent width (EWH alpha ) is 14 Angstroms, which is similar tovalues derived for noninteracting spirals. Systematic changes in LHalpha and EWH alpha with ring position angle were found in the A-ring,although much less pronounced than the Cartwheel's (Higdon 1995). BothA-rings and B-rings show only small azimuthal changes in red continuum.We have measured LH alpha and EWH alpha for 54 ring H II complexes.While their LH alpha tend to be higher than those commonly found inspiral galaxies, their EWH alpha are very similar. The H II luminosityfunction possesses a flat slope and large peak LH alpha , similar tothose of irregular galaxies. We conclude that MSF in AM 0644-741 hasbeen enhanced (~3x) and redistributed as a result of the intruder'spassage and that the ring galaxy was originally an Sa--Sab spiral. Weinterpret the distribution of Sigma H alpha around the rings and faint Halpha emission beyond the southwest A-ring in terms of MSF triggered onthe outer edge of a primarily gaseous ring density wave. We suggest thatthe unique double-ring structure reflects strong caustics along theinner and outer edges of a single-ring density wave. The much lessextreme MSF properties in AM 0644 relative to the Cartwheel likely arisefrom a combination of a weaker orbit crowding in the ring, highermetallicity, and a thicker precollision disk. We compare our resultswith ring galaxy models, where we find mixed results: the basicdistribution and kinematics of material in ring galaxies appear to bedescribed reasonably well. However, recent models fail to reproduce theobserved distribution of star forming regions.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| Two-dimensional caustics in disturbed galaxy disks
Interacting galaxies show a variety of exotic morphologies besides thewell-known rings, spirals, and bars. It is proposed that many of thesecan be identified with nonlinear, caustic structures that are known fromsingularity theory to be generic in collisionless dynamics. A simplekinematical model for stellar orbits is used to study the development ofcaustic waveforms in galaxy disks following impulsive, nonaxiallysymmetric (collisional) disturbances. It appears that all of thecaustics known from singularity theory to be generic in two dimensionsdevelop as transient forms in at least some moderately off-centercollisions. The more complex, higher-order caustics appear mostprominently in the more off-center and larger amplitude disturbances. Itis further suggested that the highly nonlinear caustic waves may play animportant role in interaction-induced star formation.
| Star formation rates in ring galaxies from IRAS observations
IRAS and optical data for a sample of 26 ring galaxies are analyzed, andit is found that: (1) relatively high average values of far-infraredluminosity L(FIR), infrared to blue luminosity ratio L(FIR)/L(B), andcolor temperature compared to normal galaxies, implying a high recentstar formation rate; (2) evidence that a large fraction of the youngstars are located in the rings, indicating a very extended, coherentstarburst; and (3) a possible trend of the dispersion of L(FIR) amongrings as a function of ring diameter. Thus, within the uncertaintiesinherent in the study of this relatively small sample, it appears thatring galaxies represent a unique class of nonnuclear coherentstarbursts.
| Southern Galaxy Catalogue.
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