# Metallicity Gradients at Large Galactocentric Radii Using the Near-infrared Calcium Triplet

## TL;DR

This paper introduces a new spectroscopic method using the near-infrared Calcium triplet to measure metallicity gradients at large galactocentric radii in early-type galaxies, providing insights into galaxy formation.

## Contribution

The study presents a novel technique combining NIR CaT features with stellar population models to extend metallicity measurements to larger galactic radii.

## Key findings

- Good agreement with previous inner region metallicity values
- Extended metallicity gradients support specific galaxy formation scenarios
- Comparison with merger simulations offers theoretical context

## Abstract

We describe a new spectroscopic technique for measuring radial metallicity gradients out to large galactocentric radii. We use the DEIMOS multi-object spectrograph on the Keck telescope and the galaxy spectrum extraction technique of Proctor et al. (2009). We also make use of the metallicity sensitive near-infrared (NIR) Calcium triplet (CaT) features together with single stellar population models to obtain metallicities. Our technique is applied as a pilot study to a sample of three relatively nearby (<30 Mpc) intermediate-mass to massive early-type galaxies. Results are compared with previous literature inner region values and generally show good agreement. We also include a comparison with profiles from dissipational disk-disk major merger simulations. Based on our new extended metallicity gradients combined with other observational evidence and theoretical predictions, we discuss possible formation scenarios for the galaxies in our sample. The limitations of our new technique are also discussed.