Near-infrared spectroscopy in NGC 7538

TL;DR

This study provides the first near-infrared spectro-photometric analysis of NGC 7538, revealing diverse stellar populations, estimating distance and age, and identifying young stellar objects within the region.

Contribution

It offers new near-infrared spectroscopic data and analysis of NGC 7538's stellar content, improving understanding of its distance, age, and star formation activity.

Findings

Distance estimated at 2.7±0.5 kpc

Age spread of 0.5-2.2 Myr

Detection of CO bandhead emission in several sources

Abstract

The characterisation of the stellar population toward young high-mass star-forming regions allows to constrain fundamental cluster properties like distance and age. These are essential when using high-mass clusters as probes to conduct Galactic studies. NGC 7538 is a star-forming region with an embedded stellar population only unearthed in the near-infrared. We present the first near-infrared spectro-photometric study of the candidate high-mass stellar content in NGC 7538. We obtained H and K spectra of 21 sources with both the multi-object and long-slit modes of LIRIS at the WHT, and complement these data with sub-arcsecond JHKs photometry of the region using the imaging mode of the same instrument. We find a wide variety of objects within the studied stellar population of NGC 7538. Our results discriminate between a stellar population associated to the HII region, but not contained within its extent, and several pockets of more recent star formation. We report the detection of CO bandhead emission toward several sources as well as other features indicative of a young stellar nature. We infer a spectro-photometric distance of 2.7+-0.5 kpc, an age spread in the range 0.5-2.2 Myr and a total mass ~1.7x10^3 Msun for the older population.