Chemical abundances of Young Massive Clusters in NGC 1313

TL;DR

This study uses spectroscopic data of young massive clusters in NGC 1313 to measure detailed elemental abundances and gradients, revealing discrepancies with gas-phase metallicity studies and suggesting a constant star formation history with localized bursts.

Contribution

First detailed integrated-light abundance analysis of YMCs in NGC 1313, highlighting differences with gas-phase metallicity measurements and proposing explanations for the observed gradients.

Findings

Fe abundance gradient of -0.124 dex/kpc

Alpha element gradient of -0.093 dex/kpc

Evidence for constant star formation with localized bursts

Abstract

We analyze spectroscopic observations of five young massive clusters (YMCs) in the barred spiral galaxy NGC 1313 to obtain detailed abundances from their integrated light. Our sample of YMCs was observed with the X-Shooter spectrograph on the Very Large Telescope (VLT). We make use of theoretical isochrones to generate synthetic integrated-light spectra, iterating on the individual elemental abundances until converging on the best fit to the observations. We measure abundance ratios for [Ca/Fe], [Ti/Fe], [Mg/Fe], [Cr/Fe], and [Ni/Fe]. We estimate an Fe abundance gradient of $-$0.124 $\pm$ 0.034 dex kpc$^{-1}$, and a slightly shallower $\alpha$ gradient of $-$0.093 $\pm$ 0.009 dex kpc$^{-1}$. This is in contrast to previous metallicity studies that focused on the gas-phase abundances, which have found NGC 1313 to be the highest-mass barred galaxy known not to have a radial abundance gradient. We propose that the gradient discrepancy between the different studies originates from the metallicity calibrations used to study the gas-phase abundances. We also observe an age-metallicity trend which supports a scenario of constant star formation throughout the galaxy, with a possible burst in star formation in the south-west region where YMC NGC 1313-379 is located.