# Star formation histories in mergers: The spatially resolved properties of the early-stage merger LIRGs IC 1623 and NGC 6090

## TL;DR

This study investigates early-stage galaxy mergers IC 1623 and NGC 6090, revealing enhanced, extended star formation, metallicity gradients, and gas inflow effects through detailed spectral analysis and comparison with control spirals.

## Contribution

It provides a detailed spatially resolved analysis of stellar populations, gas properties, and star formation in early-stage mergers, highlighting the impact of mergers on galaxy evolution.

## Key findings

- Merger-induced star formation is extended and recent, with young stellar populations dominating light.
- Early-stage mergers exhibit positive metallicity gradients and lower central nebular metallicity.
- Star formation rates are significantly enhanced compared to non-interacting spirals, consistent with merger effects.

## Abstract

The role of major mergers in galaxy evolution is investigated through a detailed characterization of the stellar populations, ionized gas properties, and star formation rates (SFR) in the early-stage merger LIRGs IC 1623 W and NGC 6090, by analysing optical Integral Field Spectroscopy (IFS) and high resolution HST imaging. The spectra were processed with the Starlight full spectral fitting code, and the emission lines measured in the residual spectra. The results are compared with control non-interacting spiral galaxies from the CALIFA survey. Merger-induced star formation is extended and recent, as revealed by the young ages (50-80 Myr) and high contributions to light of young stellar populations (50-90$\%$), in agreement with merger simulations in the literature. These early-stage mergers have positive central gradients of the stellar metallicity, with an average $\sim$0.6 Z$_{\odot}$. Compared to non-interacting spirals, they have lower central nebular metallicity, and flatter profiles, in agreement with the gas inflow scenario. We find that they are dominated by star formation, although shock excitation cannot be discarded in some regions, where high velocity dispersion is found (170-200 km s$^{-1}$). The average SFR in these early-stage mergers ($\sim$23-32 M$_{\odot}$ yr$^{-1}$) is enhanced with respect to main-sequence Sbc galaxies by factors of 6-9, slightly above the predictions from classical merger simulations, but still possible in about 15$\%$ of major galaxy mergers, where U/LIRGs belong.