Red Supergiants as Cosmic Abundance Probes: The First Direct Metallicity Determination of NGC 4038 in the Antennae

Abstract

We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D = 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not affected by the biases and poorly understood systematics inherent to strong line H II methods which are routinely applied to massive data sets of galaxies. We find [Z]= +0.07 ± 0.03 and compare our measurements to H II strong line calibrations. Our abundances and literature data suggest the presence of a flat metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.

Detailed abundance analysis of globular clusters in the Local Group

“…Subsequently we applied our technique to the lone GC in the Wolf-Lundmark-Melotte (WLM) galaxy, which was also found to be metal-poor ([Fe/H] ≈ −2) and with chemical abundance patterns similar to those in Milky Way GCs (Larsen et al 2014a, L14). We note that similar techniques have also been applied to young star clusters in external star-forming galaxies (Larsen et al 2006(Larsen et al , 2008Gazak et al 2014;Lardo et al 2015;Cabrera-Ziri et al 2016;Hernandez et al 2017Hernandez et al , 2018 where they provide a welcome alternative to more traditional tracers of the chemical composition of young stellar populations (e.g., H ii regions).…”

Searching for globular cluster-like abundance patterns in young massive clusters – II. Results from the Antennae galaxies

“…Our sample consists of the three YMCs presented in in Lardo et al (2015). Their masses, metallicities, and ages are listed in Table 1 along with other useful information.…”

“…KMOS IFU data cubes were flat fielded, wavelength calibrated, and telluric corrected 1 using the standard KMOS/esorex routines. Additionally, spectra were corrected for variations in spectral resolution and wavelength calibration across the field-of-view of each IFU (see Lardo et al 2015, for details).…”

“…As a matter of fact, such approach has been successfully used to measure metallicities an abundances of YMCs in external galaxies (e.g. Larsen et al 2006Larsen et al , 2008Gazak et al 2014;Lardo et al 2015).…”

“…In Lardo et al (2015) we targeted three YMCs in NGC 4038, a galaxy part of the Antennae merging systems, to directly measure their metallicities of from low-resolution (R [λ∆λ] 3200) KMOS spectra. The analysed spectra also include the above-mentioned Al doublet.…”