Geometric Aspects and Testing of the Galactic Center Distance Determination from Spiral Arm Segments

TL;DR

This paper introduces a geometric method to determine the Galactic center distance using spiral arm segments, applying it to maser data to estimate R0 and analyze spiral arm parameters.

Contribution

A new simplified approach for estimating the Galactic center distance from spiral arm segments using maser data and median calculations.

Findings

Estimated R0 as 8.8 ± 0.5 kpc from maser data.

Confirmed differences in spiral arm pitch angles.

Found correlation between R0 and spiral arm pitch angles.

Abstract

We consider the problem of determining the geometric parameters of a Galactic spiral arm from its segment by including the distance to the spiral pole, i.e., the distance to the Galactic center ($R_0$). The question about the number of points belonging to one turn of a logarithmic spiral and defining this spiral as a geometric figure has been investigated numerically and analytically by assuming the direction to the spiral pole (to the Galactic center) to be known. Based on the results obtained, in an effort to test the new approach, we have constructed a simplified method of solving the problem that consists in finding the median of the values for each parameter from all possible triplets of objects in the spiral arm segment satisfying the condition for the angular distance between objects. Applying the method to the data on the spatial distribution of masers in the Perseus and Scutum arms (the catalogue by Reid et al. (2014)) has led to an estimate of $R_0 = 8.8 \pm 0.5$ kpc. The parameters of five spiral arm segments have been determined from masers of the same catalogue. We have confirmed the difference between the spiral arms in pitch angle. The pitch angles of the arms revealed by masers are shown to generally correlate with $R_0$ in the sense that an increase in $R_0$ leads to a growth in the absolute values of the pitch angles.