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Abstract: Small and bright stellar disks with scale lengths of few tens of parsec areknown to reside in the center of galaxies. They are believed to have formed ina dissipational process as the end result of star formation in gas eitheraccreted in a merging or acquisition event or piled up by the secularevolution of a nuclear bar. Only few of them have been studied in detail todate. Using archival Hubble Space Telescope HST imaging, we investigated thephotometric parameters of the nuclear stellar disks hosted by three early-typegalaxies in the Virgo cluster, NGC 4458, NGC4478, and NGC4570. We aimed atconstraining the process of formation of their stars. The central surfacebrightness, scale length, inclination, and position angle of the nuclear diskswere derived by adopting the photometric decomposition method introduced byScorza and Bender and assuming the disks to be infinitesimally thin andexponential. The location, orientation, and size of the nuclear disks is thesame in all the images obtained with the Wide Field Planetary Camera 2 andAdvanced Camera for Survey and available in the HST Science Archive. The scalelength, inclination, and position angle of each disk are constant within theerrors in the observed U, B, V, and I passbands, independently of their valuesand of the properties of the host spheroid. We interpret the absence of colorgradients in the stellar population of the nuclear disks as the signature thatstar formation homogeneously occurred all through their extension. A inside-outformation scenario is, instead, expected to produce color gradients andtherefore is ruled out.



Author: L. Morelli, M. Cesetti, E. M. Corsini, A. Pizzella, E. Dalla Bontà, M. Sarzi, F. Bertola

Source: https://arxiv.org/







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