Investigating the clumpy star formation in an interacting dwarf irregular galaxy

TL;DR

This study uses high-resolution observations to analyze kpc-sized star-forming clumps in a nearby dwarf irregular galaxy, revealing insights into their metallicity, formation, and relation to galaxy dynamics.

Contribution

It provides detailed analysis of clump properties in a low-redshift galaxy, highlighting the role of metal-poor gas accretion in clump formation and the impact of galactic-scale mixing.

Findings

Clumps are embedded in a rotating ionised gas disk.

Younger stellar populations have lower metallicity than older ones.

Gas-phase metallicity is roughly uniform at 0.3 Z_sun.

Abstract

Clumpy morphologies are more frequent in distant and low-mass star-forming galaxies. Therefore the less numerous nearby galaxies presenting kpc-sized clumps represent unique laboratories from which to address the mechanisms driving clump formation and study why such structures become less common in the local Universe, and why they tend to exhibit smaller sizes and lower star formation rates compared to their high-$z$ counterparts. We use high spatial resolution Integral Field Unit observations from VLT/MUSE to investigate the properties of several kpc-sized clumps seen in SDSS J020536-081424, a $z \approx 0.04$ dwarf irregular galaxy interacting with its more massive companion Mrk 1172 ($\log (M/M_{\odot}) \sim 11$). H$\alpha$ channel maps reveal that the clumps are embedded within a rotating ionised gas component, possibly a disk. Self-consistent full-spectral fitting of the clump spectra with $\mathrm{FADO}$ indicates that their young ($t \leq 10$ Myr) populations have lower stellar metallicities compared to the older ($t \gtrsim 100$ Myr) ones, although these estimates are subject to significant degeneracies. The clumpy SF in SDSS J020536-081424 seems to occur in the disk, which dominates the stellar emission. Gas-phase metallicities derived through strong-line calibrations exhibit a flat distribution around $Z_{\mathrm{gas}} \approx 0.3\,Z_{\odot}$, likely caused by efficient galactic-scale metal mixing processes. There is no evidence for a strong anti-correlation between $Z_{\mathrm{gas}}$ and $\mathrm{SFR}$, although clump sizes are likely overestimated due to seeing limitations. The lower $Z_{\ast}$ of younger stellar populations compared to the disk suggests clump formation driven by accretion of metal-poor gas in SDSS J020536-081424.