The initial mass function of a massive relic galaxy

TL;DR

This study investigates the initial mass function of the relic galaxy NGC 1277, revealing a consistently bottom-heavy IMF across its radius, likely influenced by intense early star formation conditions.

Contribution

It provides detailed IMF measurements of a nearby relic galaxy, highlighting the impact of early universe star formation on stellar population properties.

Findings

The IMF in NGC 1277 is bottom-heavy at all radii.

Low-mass star fraction is at least twice that of the Milky Way.

Velocity dispersion decreases with radius, indicating other factors influence IMF variations.

Abstract

Massive relic galaxies formed the bulk of their stellar component before z~2 and have remained unaltered since then. Therefore, they represent a unique opportunity to study in great detail the frozen stellar population properties of those galaxies that populated the primitive Universe. We have combined optical to near-infrared line-strength indices in order to infer, out to 1.5 Reff, the IMF of the nearby relic massive galaxy NGC 1277. The IMF of this galaxy is bottom-heavy at all radii, with the fraction of low-mass stars being at least a factor of two larger than that found in the Milky Way. The excess of low-mass stars is present throughout the galaxy, while the velocity dispersion profile shows a strong decrease with radius. This behaviour suggests that local velocity dispersion is not the only driver of the observed IMF variations seen among nearby early-type galaxies. In addition, the excess of low-mass stars shown in NGC 1277 could reflect the effect on the IMF of dramatically different and intense star formation processes at z~2, compared to the less extreme conditions observed in the local Universe.