Extragalactic globular cluster near-infrared spectroscopy

II. The stellar population synthesis model zero-point problem extends to the near-infrared

¹ Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
² Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain
³ School of Astronomy, Institute for Research in Fundamental Sciences – IPM, 19395-5531 Tehran, Iran
⁴ Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves, 9500 Porto Alegre, RS, Brazil
⁵ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China
⁶ Centre for Astrophysics and Supercomputing, Swinburne University, John Street, Hawthorn, VIC 3122, Australia
⁷ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
⁸ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
⁹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05508-900 São Paulo, Brazil

^⋆ Corresponding author; eftekhari.eli@gmail.com

Received: 11 February 2024
Accepted: 1 December 2024

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 Paβ 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.