Study of Galactic Structure Using UVIT/AstroSat Star Counts

TL;DR

This study uses UV star counts from AstroSat's UVIT to analyze the structure of the Milky Way, estimating scale lengths and heights of its disc components through observations and simulations.

Contribution

It provides new measurements of the Galactic disc scale length and scale height using UV star counts and compares them with stellar population models.

Findings

Thick disc scale length ranges from 3.11 to 5.40 kpc.

Thick disc scale height ranges from 530 to 630 pc.

Thin disc scale height ranges from 230 to 330 pc.

Abstract

The structure of our Galaxy has been studied from ultraviolet (UV) star counts obtained with the Ultra-Violet Imaging Telescope (UVIT) on board the {\em AstroSat} satellite, in Far-UV (FUV) and Near-UV (NUV) bands. The F154W (BaF2) and N263M (NUVB4) filters were used in the FUV and NUV bands, respectively. The point sources are separated from the extra-galactic sources of UVIT observations using infrared (IR) color cut method. The observed UVIT star counts match well with the simulations obtained from the Besan\c{c}on model of stellar population synthesis towards several Galactic directions. We also estimated the scale length and scale height of the thick disc and the scale height of the thin disc using the space density function and the exponential density law for the stars of intermediate Galactic latitudes. The scale length of the thick disc ranges from 3.11 to 5.40 kpc whereas the scale height ranges from 530$\pm$32 pc to 630$\pm$29 pc. The scale height of the thin disc comes out to be in the range of 230$\pm$20 pc to 330$\pm$11 pc.