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

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±0.16 kpc) is larger than that in Near-UV (2.21±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 ∼ 6.8 pc), we identified 2046 young star-forming clumps in the galaxy with radii between ∼ 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 . 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.

A Multi-Wavelength Study of Star Formation in 15 Local Star-Forming Galaxies

“…A maximum size of 1.5 kpc was allowed, so sources larger than this were split up into smaller regions. A recent study of the NGC 7793 found UV clumps sized 12-70 pc (Mondal et al 2021). In comparison, the smallest size permitted for NGC 7793 in this project was ~40 pc.…”