The stellar dynamics of "box/peanut" galactic bulges. I. NGC 3079.
Abstract
This paper presents multicolour CCD photometry and extensive 2 D longslit spectroscopy of the edgeon Sbc galaxy NGC 3079, a system which displays a striking "peanut"shaped galactic bulge. in common with all other such systems observed to date, the peanut bulge displays a velocity field which shows "cylindrical rotation" to the limit of the data (a Zheight ~ 1.6 kpc). The velocity dispersion distribution is strongly peaked to the centre (σ_cen_ ~ 150 + 10 kms^1^), falling to the intrinsic resolution of ~60 km s^1^ exterior to the central 10". We model the observational properties of the bulge with self consistent numerical simulations specifically tailored to objects of this type, using the photometry and kinematics to constrain the parameters of these models in a statistically rigorous fashion. Surfaces of the sumof squares of the residuals between the model and observed photometry and kinematics are used to define the preferred solution or range of solutions appropriate to the present dataset. The surfaces thus constructed are insensitive to the data analysis procedure used to derive the kinematic results or to the nature of the disc component imposed. Within the uncertainties in these data, specific solutions cannot be defined  only regions in these surfaces of sumofsquares of residuals can be excluded. Even so, the description of NGC 3079 afforded by the imposed axisymmetric model shows that, within these uncertainties, the box/peanut morphology in this system can be accounted for solely by a distribution function comprising two integrals of the motion [namely the total energy and the vertical (Z) component of angular momentum], i.e. without recourse to a significant contribution from a third integral. This appears to distinguish the peanut bulge morphology in this system from the boxiness generally found in ellipticals. Moreover, it is unnecessary to invoke a significant degree of triaxiality within the bulge component to explain the observations. Criteria are presented which future observational data of similar systems must satisfy before more detailed (e.g. nonlinear leastsquares, simplex) minimisation routines can be expected to achieve convergence to a specific solution. These are minimum criteria necessary to distinguish between a variety of distribution functions, and/or between axisymmetric and nonaxisymmetric models of this morphology.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 1993
 Bibcode:
 1993A&A...268..511S
 Keywords:

 Galactic Bulge;
 Galactic Structure;
 Spiral Galaxies;
 Stellar Physics;
 Astronomical Models;
 Astronomical Photometry;
 Astronomical Spectroscopy;
 Charge Coupled Devices;
 Density Distribution;
 Galactic Rotation;
 Kinematics;
 Astrophysics