Structure and dynamics of galaxies with a low surface-brightness disc – I. The stellar and ionized-gas kinematics |
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| Authors: | A Pizzella E M Corsini M Sarzi J Magorrian J Méndez-Abreu L Coccato L Morelli F Bertola |
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| Institution: | Dipartimento di Astronomia, Universitàdi Padova, vicolo dell'Osservatorio 3, I-35122 Padova, Italy;Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB;Theoretical Physics, Department of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP;Max-Planck Institut für extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany;INAF –Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, I-35122 Padova, Italy;Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, E-38206 La Laguna, Spain |
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| Abstract: | Photometry and long-slit spectroscopy are presented for a sample of six galaxies with a low surface-brightness stellar disc and a bulge. The characterizing parameters of the bulge and disc components were derived by means of a two-dimensional photometric decomposition of the images of the sample galaxies. Their surface-brightness distribution was assumed to be the sum of the contribution of a Sérsic bulge and an exponential disc, with each component being described by elliptical and concentric isophotes of constant ellipticity and position angle. The stellar and ionized-gas kinematics were measured along the major and minor axes in half of the sample galaxies, whereas the other half was observed only along two diagonal axes. Spectra along two diagonal axes were obtained also for one of the objects with major and minor axis spectra. The kinematic measurements extend in the disc region out to a surface-brightness level μ R ≈ 24 mag arcsec?2, reaching in all cases the flat part of the rotation curve. The stellar kinematics turns out to be more regular and symmetric than the ionized-gas kinematics, which often shows the presence of non-circular, off-plane and non-ordered motions. This raises the question about the reliability of the use of the ionized gas as the tracer of the circular velocity in the modelling of the mass distribution, in particular in the central regions of low surface-brightness galaxies. |
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| Keywords: | galaxies: kinematics and dynamics galaxies: photometry galaxies: spiral galaxies: structure |
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