Tracing the outer disk of NGC 300: An ultraviolet view

• Published in: Journal of astrophysics and astronomy Vol. 40; no. 4; pp. 1 - 17
• Main Authors: Mondal, Chayan, Subramaniam, Annapurni, George, Koshy
• Format: Journal Article
• Language: English
• Published: New Delhi Springer India 01.08.2019; Springer Nature B.V
• Subjects: Astronomy; Astrophysics and Astroparticles; Contaminants; Emission analysis; Emissions; Galaxies; Observations and Techniques; Physics; Physics and Astronomy; Spiral galaxies; Star & galaxy formation; Star formation; Star formation rate; Subtraction; Wavelengths; star formation; Individual galaxies; spiral galaxies; XUV disk
• ISSN: 0250-6335; 0973-7758
• DOI: 10.1007/s12036-019-9603-4

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 μ m) wavelengths. Our study identified extended features in the outer disk, with the UV disk extending up to a radius of 12 kpc ( > 2 R 25 ). We estimated the FUV and NUV disk scale-length as 3.05 ± 0.27 kpc and 2.66 ± 0.20 kpc respectively. The scale-length in FUV is 2.3 times larger than that at 3.6 μ 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 ∼ 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 ⊙ to 10 6 M ⊙ , 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 ∼ 2 R 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 ∼ 0.46 M ⊙ /yr which is comparable to its near optical twin M33.