Tracing young star-forming clumps in the nearby flocculent spiral galaxy NGC 7793 with UVIT imaging

TL;DR

This study uses UVIT imaging to identify and analyze young star-forming clumps in NGC 7793, revealing insights into galaxy growth, star formation history, and the properties of stellar clusters within a nearby flocculent spiral galaxy.

Contribution

First detailed UV imaging analysis of NGC 7793's star-forming regions, revealing their sizes, ages, and distribution, supporting inside-out galaxy growth and recent star formation enhancement.

Findings

Identified 2046 young star-forming clumps with radii 12-70 pc.

Most regions are younger than 20 Myr, indicating recent star formation.

Youngest regions trace the galaxy's flocculent arms.

Abstract

Star formation in galaxies is a hierarchical process with a wide range of scales from smaller clusters to larger stellar complexes. Here, we present an ultra-violet imaging study of the nearby flocculent spiral galaxy NGC 7793, observed with the Ultra-Violet Imaging Telescope (UVIT). We find that the disk scale-length estimated in Far-UV (2.64$\pm$0.16 kpc) is larger than that in Near-UV (2.21$\pm$0.21 kpc) and optical (1.08 kpc), which supports the inside-out growth scenario of the galaxy disk. The star-forming UV disk is also found to be contained within the extent of H~I gas of column density greater than $10^{21}$cm$^{-2}$. With the spatial resolution of UVIT (1 pixel $\sim$ 6.8 pc), we identified 2046 young star-forming clumps in the galaxy with radii between $\sim$ 12 - 70 pc, which matches well with the size of GMCs detected in the galaxy. Around 61\% of the regions identified in our study have age younger than 20 Myr, which points to a recent enhancement of star formation across the galaxy. We also noticed that the youngest star-forming regions, with age $<$ 10 Myr, distinctly trace the flocculent arms of the galaxy. The estimated mass of the clumps cover a range between $10^3 - 10 ^6 M_{\odot}$. We noticed a gradient in the mass distribution of identified clumps along the spiral arms. We have also studied the nuclear star cluster of the galaxy and found that the stellar populations in the cluster outskirts are younger than the inner part.