Extragalactic globular cluster near-infrared spectroscopy: II. The stellar population synthesis model zero-point problem extends to the near-infrared

TL;DR

This study reveals that stellar population synthesis models exhibit an age zero-point problem in the near-infrared, with globular cluster ages appearing older than the universe, highlighting the need for model refinement in this wavelength range.

Contribution

First application of extragalactic globular cluster NIR spectroscopy showing the age zero-point problem extends from optical to NIR, emphasizing the need to improve SPS models.

Findings

Globular clusters' NIR spectra indicate an age zero-point discrepancy.

The Paβ line at 1.28 microns is used to assess stellar ages.

SPS models require refinement to accurately interpret NIR observations.

Abstract

Many recent studies have pointed out significant discrepancies between observations and models of stellar populations in the near-infrared (NIR). With current and future observing facilities being focused in this wavelength range, properly assessing and solving these issues is of utmost importance. Here, we present the first application of the extragalactic globular cluster (GC) near-infrared spectroscopy survey, and present evidence that these GCs reveal an age zero-point problem of stellar population synthesis (SPS) models. This problem has already been identified in the optical range for the GCs of the Milky Way. Such an issue arises when derived GC spectroscopic ages appear older than the Universe itself. We extend this discussion for the first time to the NIR, specifically using the Pa$_{\rm\beta}$ line at 1.28~microns. We focus on the GCs of the nearby Centaurus~A galaxy using their NIR spectra. This work broadens our understanding of the age zero-point problem and emphasises the necessity to revisit and refine SPS models, especially in the NIR domain.