The Impact of Stellar Populations on the Dynamics of Merger Remnants

TL;DR

This paper investigates how stellar populations, especially nuclear disks of RSG and AGB stars, influence the measured dynamics of galaxy merger remnants, revealing biases in mass estimates and implications for galaxy formation.

Contribution

It demonstrates the significant impact of RSG and AGB stars on dynamical measurements, highlighting the importance of wavelength choice in studying merger remnants.

Findings

Near-infrared spectra reveal nuclear disks dominated by RSG and AGB stars.

Dust obscuration affects dynamical mass estimates at different wavelengths.

LIRGs align with elliptical galaxies on the Fundamental Plane in the I-band.

Abstract

Many studies and simulations suggest gas-rich mergers do not contribute significantly to the overall star-formation rate and total mass function of galaxies. The velocity dispersions (sigma) of Luminous & Ultraluminous Infrared Galaxies measured using the 1.62 or 2.29 micron CO bandheads imply they will form m < m* ellipticals. Yet, sigma's obtained with the Calcium II triplet (CaT) at 0.85 micron suggest all types of mergers will form m > m* ellipticals. Presented here are recent results, based on high-resolution imaging and multi-wavelength spectroscopy, which demonstrate the dominance of a nuclear disk of Red Supergiants (RSG) or Asymptotic Giant Branch (AGB) stars in the near-infrared bands, where dust obscuration does not sufficiently block their signatures. The presence of these stars severely biases the dynamical mass. At I-band, where dust can sufficiently block RSG or AGB stars, LIRGs populate the Fundamental Plane over a large dynamic range and are virtually indistinguishable from elliptical galaxies.