# Tracing the outer disk of NGC 300: An ultraviolet view

## TL;DR

This study uses GALEX UV observations to reveal an extended UV disk in NGC 300, showing young star populations up to 12 kpc, with implications for understanding star formation in galaxy outskirts.

## Contribution

First detailed UV analysis of NGC 300 revealing extended UV disk and young star populations beyond optical limits.

## Key findings

- UV disk extends up to 12 kpc, beyond 2R_25
- UV disk scale-length is 3.05 kpc in FUV
- Star formation rate is approximately 0.46 solar masses per year

## Abstract

We present an ultra-violet (UV) study of the galaxy NGC~300 using GALEX far-UV (FUV) and near-UV (NUV) observations. We studied the nature of UV emission in the galaxy and correlated it with optical, H~I and mid-infrared (3.6 $\mu$m) wavelengths. Our study identified extended features in the outer disk, with the UV disk extending up to radius 12 kpc ($>$2R$_{25})$. We estimated the FUV and NUV disk scale-length as 3.05$\pm$0.27 kpc and 2.66$\pm$0.20 kpc respectively. The scale-length in FUV is 2.3 times larger than that at 3.6 $\mu$m, and we also find the disk to gradually become flatter from longer to shorter wavelengths. We performed a statistical source subtraction to eliminate the background contaminants and identified 261 unresolved UV sources between the radii 5.3 kpc and 10 kpc (1 $\sim$ 2 R$_{25}$). The identified UV sources show an age range between 1 - 300 Myr with a peak at 25 Myr and a mass range between $10^3 M_{\odot}$ to $10^6 M_{\odot}$, estimated using starburst99 models. The north-eastern spiral arm is found to be populated by young low mass sources suggesting that the star formation in this spiral arm is a recent phenomenon. The UV emission beyond the R$_{25}$ radius has contribution from these low mass sources and is extended up to $\sim$ 2R$_{25}$ radius. We conclude that NGC~300 has an extended UV disk, mainly populated by young low mass sources. The star formation rate is measured to be $\sim$0.46 $M_{\odot}/yr$ which is comparable to its near optical twin M33.