Understanding star formation in NGC 4571 using UVIT and SDSS

Abstract

Star formation is one of the key processes through which galaxies convert their gas into stars, and that in turn leads to the stellar mass growth of a galaxy. Not only that, star formation is the key parameter that divides the galaxy into two primary categories: star-forming galaxies and quenched galaxies. A comprehensive multi-wavelength study is necessary in order to gain critical insights on the physical properties of a galaxy. This thesis investigates the nature of star formation in the flocculent galaxy NGC 4571 using multi-band observations taken from the Ultra-Violet Imaging Telescope (UVIT) in 2 filters - F154W and N263M and the Sloan Digital Sky Survey (SDSS) in 5 filters - u, g, r, i, z. We perform image analysis using a variety of tools such as SExtractor, ds9, topcat. We also use various python libraries such as astropy and photutils for photometry. With the superior spatial resolution of UVIT (∼ 1.4 00 ), we identified 172 bright young star-forming regions in the UVIT bands within the galaxy, most of them having sizes between ∼ 100 − 400 pc. These regions were also found to be clumpy in nature. Around 53% of the sources are younger than ∼ 20 Myr, which points towards a recent spike in star formation. We also noticed that the younger sources are distributed throughout the galaxy, which is an indicator of recent star formation across the galaxy. We also found that most of the sources are roughly circular, with ellipticity ε < 0.5 and that there is no specific trend observed with regards to the orientation of the major axis of the identified sources. We further derived the radial surface brightness profile in UV and optical, the radial FUV-NUV color profile, and the radial SFR density profile of the galaxy, which provide further evidence for star formation occurring throughout the galaxy. Based on the UVIT data, the star formation rate in NGC 4571 is found to be ∼ 0.01605 M /yr.