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Register a new userPhotometric deprojection of edge-on galaxies
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Authors
D. Bizyaev
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Photometric deprojection is used to determine the stellardisk and bulge parameters for several edgeon galaxies from the FGC catalog. The assumption that the galaxies of our sample belonging to the fourth (i.e., lowest) surfacebrightness class in the FGC are edgeon, lowsurfacebrightness (LSB) galaxies is considered.
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Dmitry Bizyaev (Sternberg Astronomical Institute
, Moscow
, Isaac Newtonn Institute of Chile
2002
To analyze the vertical structure of edge-on galaxies, we have used images of a large uniform sample of flat galaxies that have been taken during the 2MASS all-sky survey. The photometric parameters, such as the radial scale length, the vertical scale height, and the deprojected central surface brightness of galactic disks have been obtained. We find a strong correlation between the central surface brightness and the ratio of the vertical scale height to the vertical scale length: the thinner the galaxy, the lower the central surface brightness of its disk. The vertical scale height does not increase systematically with the distance from the galaxy center in the frames of this sample.
A family of triaxial Stackel potential-density pairs is introduced. With the help of a Quadratic Programming method, a linear combination of potential-density pairs of this family which fits a given projected density distribution can be built. This deprojection strategy can be used to model the potentials of triaxial elliptical galaxies with or without dark halos. Besides, we show that the expressions for the Stackel triaxial density and potential are considerably simplified when expressed in terms of divided differences, which are convenient numerically. We present an example of triaxial deprojection for the galaxy NGC~5128 whose photometry follows the de Vaucouleurs law.
Photometric parameters of stellar disks and bulges for several edge-on galaxies from the Catalog of Flat Galaxies (FGC) were determined. We discuss a difference between photometric parameters of LSB and HSB galaxies from our sample. Also we present results of R CCD photometry of edge-on galaxy RFGC 3647. Deprojecting this galaxy we show that it has thin LSB disk (central surface brightness $22^m.2$ in R) and high ratio of radial to vertical scale lengths. It is shown that initially gaseous disk of the galaxy was unstable and its velocity dispersion was low. Stellar disk of this LSB galaxy was not heated significantly since that time.
We present a grid-based non-parametric approach to obtain a triaxial three-dimensional luminosity density from its surface brightness distribution. Triaxial deprojection is highly degenerate and our approach illustrates the resulting difficulties. Fortunately, for massive elliptical galaxies, many deprojections for a particular line of sight can be discarded, because their projection along other lines of sight does not resemble elliptical galaxies. The near-elliptical isophotes of these objects imply near ellipsoidal intrinsic shapes. In fact, deprojection is unique for densities distributed on ellipsoidal shells. The constrained non-parametric deprojection method we present here relaxes this constraint and assumes that the contours of the luminosity density are boxy/discy ellipsoids with radially varying axis ratios. With this approach we are able to reconstruct the intrinsic triaxial densities of our test models, including one drawn from an $N$-body simulation. The method also allows to compare the relative likelihood of deprojections at different viewing angles. We show that the viewing orientations of individual galaxies with nearly ellipsoidal isophotal shapes can be constrained from photometric data alone.
We present results of surface photometry for eleven edge-on galaxies observed with the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. The photometric scale length, the scale height, and the central surface brightness of the stellar disks for the galaxies were found using photometric cuts made parallel to the major and the minor axes for each galaxy. We show that four galaxies in our sample that were visually classified as objects of lowest surface brightness in the Revised Flat Galaxies Catalog have LSB (low surface brightness) disks. Stellar disks of our LSB galaxies are thinner than HSB (high surface brightness) ones. There is a good correlation between the central surface brightness of the stellar disk and its ratio of vertical to radial scales. The ratio of the disk photometric scales enables us to estimate the mass of the spherical galactic subsystem using results from numerical modeling. Combining our results with published rotation curves we determined the mass of dark halos for the galaxies in our sample. The LSB galaxies tend to harbor relatively more massive spherical subsystems than those of HSBs. Indeed, we found no systematic difference between our LSB and HSB objects in dark halo masses considering it separately from the bulge. At the same time, the inferred mass/luminosity ratio for the LSB disks appears to be systematically higher, when compared to the ratio for HSB ones.
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