# The Next Generation Virgo cluster Survey (NGVS). XXVI. The issues of photometric age and metallicity estimates for globular clusters

## TL;DR

This study compares photometric age and metallicity estimates of globular clusters in the Milky Way and Virgo core using multi-wavelength data and synthetic models, revealing systematic differences and the need for environment-specific models.

## Contribution

It highlights the limitations of current models in accurately estimating GC ages across different environments and emphasizes the need for environment-dependent modeling approaches.

## Key findings

- Models agree on MW GC ages and metallicities
- Virgo GCs appear systematically younger in models
- Current models are insufficient without environment-specific adjustments

## Abstract

Large samples of globular clusters (GC) with precise multi-wavelength photometry are becoming increasingly available and can be used to constrain the formation history of galaxies. We present the results of an analysis of Milky Way (MW) and Virgo core GCs based on five optical-near-infrared colors and ten synthetic stellar population models. For the MW GCs, the models tend to agree on photometric ages and metallicities, with values similar to those obtained with previous studies. When used with Virgo core GCs, for which photometry is provided by the Next Generation Virgo cluster Survey (NGVS), the same models generically return younger ages. This is a consequence of the systematic differences observed between the locus occupied by Virgo core GCs and models in panchromatic color space. Only extreme fine-tuning of the adjustable parameters available to us can make the majority of the best-fit ages old. Although we cannot exclude that the formation history of the Virgo core may lead to more conspicuous populations of relatively young GCs than in other environments, we emphasize that the intrinsic properties of the Virgo GCs are likely to differ systematically from those assumed in the models. Thus, the large wavelength coverage and photometric quality of modern GC samples, such as used here, is not by itself sufficient to better constrain the GC formation histories. Models matching the environment-dependent characteristics of GCs in multi-dimensional color space are needed to improve the situation.