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Date and Time of the Query: 2019-07-18 T00:38:41 PDT
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For refcode 1993MNRAS.261..718S:
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Copyright by Royal Astronomical Society. 1993MNRAS.261..718S The photometric properties of `box/peanut' galactic bulges Martin Shaw Department of Astronomy, University of Manchester Manchester M13 9PL Department of Physics, University of Sheffield, Sheffield S3 7RH Accepted 1992 October 2. Received 1992 September 17; in original form 1992 July 14 ABSTRACT Optical and near-IR photometry is presented for a sample of 14 edge-on galaxies displaying `box/peanut' bulge structure. The observed luminosity distributions are modelled using a 2D non-linear, least-squares minimization scheme, and the resulting `best-fitting' model combinations subtracted from the observational data to study the deviations from the imposed models. In all cases, the models used underestimate the observed luminosity in the region of the box/peanut distortions by typically 5-15 percent of the luminosity of the bulge as a whole in the same regions (rising to ~60 per cent in some cases). This luminosity excess appears greater in later type galaxies - whilst the bulges in such systems are small, the box/peanut components contain a larger fraction of the total luminosity of the old stellar populations. The evidence for colour gradients within the bulge components is contradictory: two systems show clear evidence of a blueing with radius and Z-height, but in four out of seven cases there is no significant gradient in those regions clearly dominated by the stellar components. Taken together with the similar lack of evidence for low surface brightness arcs, shells, filaments, etc. in the present sample, the box/peanuts do not appear to be the result of recent merger/accretion events. Moreover, isophote twists with respect to the major axes are unambiguously detected in only two out of nine galaxies, supporting a previous assertion that box/peanut bulges do not possess a significant degree of triaxiality. The Z-height of the maximum excess flux within the derived (model - data) residual maps has been measured at several radii (R). This turnover height (Z_peak_) accurately determines the position of the box/peanut distortions at each radius. Z_peak_ varies continuously with R in all galaxies, whilst Z_peak_/R falls monotonically with R. Both results are contrary to a recent theoretical analysis of the orbital families thought to be present within box/peanut bulges (such a study predicting that the zero-velocity curve increases linearly with radius, i.e. that Z_peak_/R is constant with R). This may suggest that the orbits normally used to describe this morphology are inappropriate or, more likely, that each bulge possesses several such orbital families and that their relative contributions vary with galactocentric distance. If box/peanuts are the result of the presence of a bar, regular/periodic orbits appear favoured at the expense of more chaotic orbits. However, the typical radii of the most extreme box/peanut isophotal distortions are larger than those of the inferred inner Lindblad resonances in typical barred potentials. Contrary to previous expectations, it is clear that photometry alone can be used to place valuable constraints on a theoretical understanding of this structure. Key words: galaxies: photometry - galaxies: spiral - galaxies: stellar content - galaxies: structure - infrared: galaxies.
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