# The Initial Mass Function and Other Stellar Properties Across the Core of the Hydra I Cluster

## TL;DR

This study compares the stellar populations and initial mass function of two bright galaxies in the Hydra I cluster's core, revealing similar early formation but differences in metallicity and IMF profiles linked to their kinematics.

## Contribution

It provides a detailed spectral analysis of two galaxies, showing their similar formation history and how their stellar properties vary with radius and kinematics.

## Key findings

- Inner 5 kpc regions formed simultaneously with similar star formation histories.
- Radial IMF profiles correlate with metallicity and velocity dispersion.
- Outer regions contain mixed stellar populations with diverse chemical compositions.

## Abstract

The Hydra I cluster offers an excellent opportunity to study and compare the relic old stellar populations in the core of its two brightest galaxies. In addition, the differing kinematics of the two galaxies allows a test of the local validity of general scaling relations. In this work we present a direct comparison employing full spectral fitting of new high-quality long-slit optical and NIR spectroscopic data. We retrieve age, metallicity and 19 elemental abundances out to about 12 kpc within each galaxy, as well as the IMF in their central regions. Our results suggest that the inner 5 kpc region of both galaxies, despite their different masses, formed at the same time and evolved with a similar star formation time-scale and chemical enrichment, confirming their early formation in the cluster build up. Only the overall metallicity and IMF radial profiles show differences connected with their different velocity dispersion profiles. The radial trend of the IMF positively correlates with both [Z/H] and velocity dispersion. While the trends of the IMF with metallicity agree with a global trend for both galaxies, the trends with the velocity dispersion exhibit differences. The outer regions show signs of mixed stellar populations with large differences in chemical content compared to the centers, but with similar old ages.