The innermost globular clusters of M87

TL;DR

This study provides a detailed multiwavelength photometric analysis of the innermost globular clusters in M87, revealing their old ages, low metallicities, and supporting early formation of the galaxy's central regions.

Contribution

It offers the first comprehensive SED analysis of M87's inner GCs using high-resolution multiwavelength data, comparing them with Milky Way clusters and stellar population models.

Findings

Inner GCs are older than 10 Gyr.

They have low metallicity around -0.6 dex.

Data do not support recent wet merging events.

Abstract

We present a comprehensive multiwavelength photometric analysis of the innermost (3x3 square kpc) 110 globular clusters (GCs) of M87. Their spectral energy distributions (SEDs) were built taking advantage of new ground-based high resolution near-IR imaging aided by adaptive optics at the Very Large Telescope (VLT) combined with Hubble Space Telescope (HST) ultraviolet--optical archival data. These GC SEDs are among the best photometrically sampled extragalactic GC SEDs. To compare with our SEDs we constructed equally sampled SEDs of Milky Way GCs. Using both these Milky Way cluster templates and different stellar population models, ages of >10 Gyr and metallicities of [Fe/H] -0.6 dex are consistently inferred for the inner GCs of M87. In addition, the metallicity of these GCs is low (Dif([Fe/H]) 0.8 dex) compared to that of their host galaxy. These results agree with the idea that the GC formation in M87 ceased earlier than that of the bulk of the stars of the central part of the galaxy. The ages of the inner GCs of M87 support the idea that these central parts of the galaxy formed first. Our data do not support evidence of recent wet merging.