Models for the 3D axisymmetric gravitational potential of the Milky Way galaxy

A detailed modelling of the Galactic disk

¹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Cidade Universitária, 05508-090 São Paulo, SP, Brasil
e-mail: douglas.barros@iag.usp.br
² UNIFEI, Instituto de Ciências Exatas, Universidade Federal de Itajubá, Av. BPS 1303 Pinheirinho, 37500-903 Itajubá, MG, Brasil

Received: 10 October 2015
Accepted: 7 July 2016

Abstract

Aims. Galaxy mass models based on simple and analytical functions for density and potential pairs have been widely proposed in the literature. Disk models that are constrained solely by kinematic data only provide information about the global disk structure very near the Galactic plane. We attempt to circumvent this issue by constructing disk mass models whose three-dimensional structures are constrained by a recent Galactic star counts model in the near-infrared and also by observations of the hydrogen distribution in the disk. Our main aim is to provide models for the gravitational potential of the Galaxy that are fully analytical but also give a more realistic description of the density distribution in the disk component.

Methods. We produced fitted mass models from the disk model, which is directly based on the observations divided into thin and thick stellar disks and H I and H₂ disks subcomponents, by combining three Miyamoto-Nagai disk profiles of any model order (1, 2, or 3) for each disk subcomponent. The Miyamoto-Nagai disks are combined with models for the bulge and dark halo components and the total set of parameters is adjusted by observational kinematic constraints. A model that includes a ring density structure in the disk, beyond the solar Galactic radius, is also investigated.

Results. The Galactic mass models return very good matches to the imposed observational constraints. In particular, the model with the ring density structure provides a greater contribution of the disk to the rotational support inside the solar circle. The gravitational potential models and their associated force-fields are described in analytically closed forms.

Conclusions. The simple and analytical models for the mass distribution in the Milky Way and their associated three-dimensional gravitational potential are able to reproduce the observed kinematic constraints and, in addition, they are also compatible with our best knowledge of the stellar and gas distributions in the disk component. The gravitational potential models are suited for investigations of orbits in the Galactic disk.