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|Cosmic Masks Still Dance|
The Hubble classification scheme of galaxies is based on their opticalappearance or `masks'. As one goes from early to late type spirals, bothbarred and unbarred, the optical appearance will be dominated more andmore by the young Population I, i.e., blue stars and dust. Atlasesreveal the rich variety of responses of the Population I component ofgas and dust (the mask) to the underlying, older, stellar population.However, the gaseous Population I component, may only constitute 5percent of the dynamical mass of the galaxy. Masks of negligible massmay conceal the human face - and that of galaxy. In the near-infrared,the morphology of older star-dominated disk indicates a simpleclassification scheme: the dominant Fourier m-mode in the dustpenetrated regime, and the associated pitch angle. A ubiquity of low m=1and m=2 modes is confirmed. On the basis of deprojected H (1.65 μm)and K' (2.1μm) images, we propose that the evolved stellar disks maybe grouped into three principal dust penetrated archetypes: those withtightly wound stellar arms characterised by pitch angles at K' of ~10^° (the α class), an intermediate group with pitch angles of~ 25^° (the β class) and thirdly, those with open spiralsdemarcated by pitch angles at K' of ~ 40^° (the γ bin). Flator falling rotation curves give rise to the tightly wound α class;rising rotation curves are associated with the open γ class. Theobserved dust penetrated classes are inextricably related to the rate ofshear in the stellar disk, as determined by A/ω. Here A is thefirst Oort constant andω denotes the angular velocity. There is nocorrelation between our dust penetrated classes and optical Hubblebinning; the Hubble tuning fork does not constrain the morphology of theold stellar Population II disks. NGC 3223 and NGC 7083 (both SbI-II andalmost the same absolute blue magnitude) have identical Hubble types andidentical luminosity classes; the dust penetrated disk of NGC 3223 hastightly wrapped arms of class α, whereas the near-infrared disk ofNGC 7083 has open arms of class γ. This is in turn associated withtheir very different rotation curve shapes yielding different rates ofshear A/ω in their stellar disks. Any specific dust penetratedarchetype may be the resident disk of both an early or late type galaxy.The number of arms and the pitch angle of the arms at K' of theearly-type `a' spiral NGC 718 are almost identical to those for thelate-type `c' spiral NGC 309. We demonstrate that galaxies on oppositeends of the tuning fork can display remarkably similar evolved diskmorphologies and belong to the same dust penetrated class. In thissense, there is no differentiation between an early and late typegalaxy: the Hubble tuning fork becomes a circle. Furthermore, aprototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class3) can have an evolved disk morphology almost identical to that of NGC5861, characterised in the optical as having one of the most regularspiral patterns known and of Elmegreen class 12. Both opticallyflocculent or grand design galaxies can reside within the same dustpenetrated morphological bin. As was suggested by Block et al. (1994a),it is the gas dominated Population I component which determines theoptical types (a, b, c). This may be partially or even fully decoupledfrom the Population II disk. Those L=lopsided galaxies (where m=1 is adominant mode) are designated Lα, Lβ and Lγ accordingto the dust penetrated pitch angle; E=evensided galaxies (where m=2 isthe dominant Fourier mode) are classified into classes Eα, Eβand Eγ, according to our three principal dust penetratedarchetypes. The L and E modes are the most common morphologies in oursample, which spans a range of Hubble types from early (a) to late(irregular).
|The structure of spiral galaxies - II. Near-infrared properties of spiral arms|
We have imaged a sample of 45 face-on spiral galaxies in the K band, todetermine the morphology of the old stellar population, which dominatesthe mass in the disc. The K-band images of the spiral galaxies have beenused to calculate different characteristics of the underlying densityperturbation such as arm strengths, profiles and cross-sections, andspiral pitch angles. Contrary to expectations, no correlation was foundbetween arm pitch angle and Hubble type, and combined with previousresults this leads us to conclude that the morphology of the old stellarpopulation bears little resemblance to the optical morphology used toclassify galaxies. The arm properties of our galaxies seem inconsistentwith predictions from the simplest density wave theories, and someobservations, such as variations in pitch angle within galaxies, seemhard to reconcile even with more complex modal theories. Bars have nodetectable effect on arm strengths for the present sample. We have alsoobtained B-band images of three of the galaxies. For these galaxies wehave measured arm cross-sections and strengths, to investigate theeffects of disc density perturbations on star formation in spiral discs.We find that B-band arms lead K-band arms and are narrower than K-bandarms, apparently supporting predictions made by the large-scale shockscenario, although the effects of dust on B-band images may contributetowards these results.
|The structure of spiral galaxies - I. Near-infrared properties of bulges, discs and bars|
We present data for a sample of 45 spiral galaxies over a range ofHubble types, imaged in the near-IR JK bands. Parameters are calculateddescribing the bulge, disc and bar K-band light distributions, and welook for correlations showing the interrelation between thesecomponents. We find that bulge profiles are not well-fitted by theclassic de Vaucouleurs profile, and that exponential or R^1/2 fits arepreferred. The bulge-to-disc ratio correlates only weakly with Hubbletype. Many of the galaxies show central reddening of their J-K colours,which we interpret as due to nuclear starbursts or dusty AGN. We definea new method for measuring the strength of bars, which we call`equivalent angle'. We stress that this is better than the traditionalbar-interbar contrast, as it is not subject to seeing and resolutioneffects. Bars are found in 40 of the 45 galaxies, nine of which had beenpreviously classified as unbarred. Bar strengths are found not tocorrelate with disc surface brightness or the presence of nearneighbours, but a tendency is found for the most strongly barredgalaxies to lie within a restricted, intermediate range of bulge-to-discratio. Bar light profiles are found to be either flat or exponentiallydecreasing along their long axes, with profile type not correlatingstrongly with Hubble type. Bar short axis profiles are significantlyasymmetric, with the steeper profile being generally on the leadingedge, assuming trailing arms. In the K band we find bars with higheraxial ratios than have been found previously in optical studies.
|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.
|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 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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