DSS Images Other Images
|Analysis of Resonances in Grand Design Spiral Galaxies|
We have searched for corotation resonances (CRs) in three southern granddesign spiral galaxies: NGC 1365, NGC 1566, and NGC 2997. We have alsointroduced a method of quantifying errors in the phase diagram used todetect CRs. We established the m=2 pattern CR at 12.1, 9.4, and 7 kpcfor NGC 1365, NGC 1566, and NGC 2997, respectively. By using publishedrotation curves, we could determine spiral pattern angular speeds of25.0, 12.2, and 17.6 km s-1 kpc-1, respectively. Athree-armed component has been detected in NGC 2997, with the CR placedat 8.7 kpc with a pattern angular speedΩCR3=12.7 km s-1kpc-1. An m=1 component was detected in NGC 1566. We warilylocate the CR at 7.1 kpc, with a pattern angular speedΩCR~=16.6 km s-1 kpc-1. Thispattern does not present inner Lindblad resonance. Ages have beendetermined by studying the radial density profile of the m=2 Fouriercomponents in g (newly formed stars) and i (perturbing spiral densitywave supported by the disk of old stars), aided by the global aspect ofthe real spiral pattern in comparison with numerical simulations. Thepattern is ~1200 Myr old in NGC 1365, ~800 Myr old in NGC 1566, andyounger than 80 Myr in NGC 2997.
|Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies|
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
|Optical tracers of spiral wave resonances in galaxies. II - Hidden three-arm spirals in a sample of 18 galaxies|
An improved algorithm for extracting various types of symmetries fromgalaxy images is introduced. It preserves the nonlinear shapes of thespiral arms without introducing false interarm components, and itdisplays the m = 2, 3, 4, etc. subcomponents in whole galaxies all atonce to avoid confusion with localized star formation and foregroundstars. The algorithm is applied to 18 galaxies with various types ofspirals. Conventional Fourier transform techniques are also used tostudy the arm structures. Underlying three-arm spirals are found to becommon in the present sample, and a few galaxies have a complex four- orfive-arm system, too. To check whether this structure is sensible, thetermination radii of the two-, three-, and four-arm spirals are comparedto the corresponding resonance radii predicted from theory. Thesymmetric components in nearly all of the galaxies are found to end attheir outer wave-epicycle resonances.
|Southern Galaxy Catalogue.|
|H I line studies of galaxies. III - Distance moduli of 822 disk galaxies|
The distance scale established on the basis of a distance moduli catalog(for 822 galaxies) that was derived from 21-cm line widths via theB-band Tully-Fisher relation is compared with several independent scaleshaving a common zero point, that are based on the indicators forluminosity index, redshift, ring diameters, brightest superassociations,and effective diameters. These are in excellent systematic agreement,and confirm the linearity of the H I scale in the 24-35 modulusinterval, but indicate a small systematic zero point difference of about0.2 mag, which must be added to the H I moduli to place them on the same'short' distance scale defined by the others.