Nuclear stellar discs in early-type galaxies — II. Photometric properties |
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| Authors: | Cecilia Scorza & Frank C van den Bosch |
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| Institution: | Landessternwarte, Ko¨nigstuhl, D-69117 Heidelberg, Germany,;Centro de Investigaciones de Astronomia CIDA, Merida, Venezuela,;Department of Astronomy, University of Washington, Seattle, WA 98195, USA |
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| Abstract: | Hubble Space Telescope images of two early-type galaxies harbouring both nuclear and outer stellar discs are studied in detail. By means of a photometric decomposition, the images of NGC 4342 and 4570 are analysed and the photometric properties of the nuclear discs investigated. We find a continuity of properties in the parameter space defined by the central surface brightness μ0 and the scalelength R d of discs in spirals, S0s and embedded discs in ellipticals, in the sense that the nuclear discs extend the observed disc properties even further towards smaller scalelengths and brighter central surface brightnesses. When including the nuclear discs, disc properties span more than four orders of magnitude in both scalelength and central surface brightness. The nuclear discs studied here are the smallest and brightest stellar discs known, and as such, they are as extreme in their photometric properties as Malin I, when compared with typical galactic discs that obey Freeman's law. We discuss a possible formation scenario in which the double-disc structure observed in these galaxies has been shaped by now dissolved bars. Based on the fact that the black holes known to exist in some of these galaxies have masses comparable to those of the nuclear discs, we explore a possible link between the black holes and the nuclear discs. |
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| Keywords: | galaxies: elliptical and lenticular cD galaxies: individual: NGC 4342 galaxies: individual: NGC 4570 galaxies: photometry galaxies: structure |
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