Solar Space Density of the Red Clump Stars and the Scale-length of the Thin Disc

TL;DR

This study estimates the thin disc's scale-length using Red Clump stars' magnitudes across various Galactic longitudes, revealing a decrease from 2 kpc to 1.6 kpc, influenced by disc inhomogeneities like warp and flare.

Contribution

It provides the first detailed measurement of the thin disc's scale-length variation with Galactic longitude using Red Clump stars.

Findings

The scale-length varies from 2 kpc to 1.6 kpc across different longitudes.

Results are consistent with the Galaxia model predictions.

Disc inhomogeneities such as warp and flare influence the scale-length distribution.

Abstract

We estimated the scale-length of the thin disc with the J and W1 magnitudes of the most probable Red Clump (RC) stars in the Galactic plane, $-0\overset{^\circ}.5 \leq b \leq +0\overset{^\circ}.5$, in 19 equal sized fields with consecutive Galactic longitudes which cover the interval $90^\circ \leq l \leq 270^\circ$. Our results are constrained with respect to the solar space density ($D^*=5.95$), which indicates that the radial variation of the density is lower for higher Galactocentric distances. The scale-length of the thin disc is 2 kpc for the fields in the Galactic anticentre direction or close to this direction, while it decreases continuously in the second and third quadrants reaching to a lower limit of $h$ = 1.6 kpc at the Galactic longitudes $l$ = 90$^\circ$ and $l$ = 270$^\circ$. The distribution of the scale-length in 19 fields is consistent with the predictions from the Galaxia model and its variation with longitude is probably due to the inhomogeneity structure of the disc caused by the accreted material or other features such as warp and flare.