Estimation of galactic model parameters in high latitudes with SDSS

TL;DR

This study estimates the parameters of the Galactic model across 36 high-latitude SDSS fields, revealing variations linked to Galactic longitude and structural asymmetries, influenced by the Galactic bar and halo structure.

Contribution

It provides the first detailed analysis of how Galactic model parameters vary with longitude using SDSS data, highlighting the influence of the Galactic bar and halo asymmetries.

Findings

Thick disc scaleheight varies from 550 pc to 720 pc with longitude.

Halo axis ratio c/a changes from 0.55 to 0.70 across quadrants.

Star excess in certain quadrants supports the influence of the Galactic bar.

Abstract

We estimated the Galactic model parameters for a set of 36 high-latitude fields included in the currently available Data Release 5 (DR 5) of the Sloan Digital Sky Survey ({\em SDSS}), to explore their possible variation with the Galactic longitude. The thick disc scaleheight moves from $\sim$550 pc at $120^{\circ}<l<150^{\circ}$ to $\sim$720 pc at $250^{\circ}<l<290^{\circ}$, while the thin disc scaleheight is as large as $\sim$195 pc in the anticenter direction and $\sim$15% lower at $|l|<30^\circ$. Finally, the axis ratio ($c/a$) of the halo changes from a mean value of $\sim$0.55 in the two first quadrants of the Galaxy to $\sim$0.70 at $190^{\circ}<l<300^{\circ}$. For the halo, the reason for the dependence of the model parameters on the Galactic longitude arises from the well known asymmetric structure of this component. However, the variation of the model parameters of the thin and thick discs with Galactic longitude originates from the gravitational effect of the Galactic long bar. Moreover, the excess of stars in quadrant I (quadrant III) over quadrant IV (quadrant II) is in agreement with this scenario.