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arXiv · 1102.3689

K+A Galaxies as the Aftermath of Gas-Rich Mergers: Simulating the Evolution of Galaxies as Seen by Spectroscopic Surveys

Gregory F. Snyder·Thomas J. Cox·Christopher C. Hayward·Lars Hernquist·Patrik Jonsson
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Abstract

Models of poststarburst (or "K+A") galaxies are constructed by combining fully three-dimensional hydrodynamic simulations of galaxy mergers with radiative transfer calculations of dust attenuation. Spectral line catalogs are generated automatically from moderate-resolution optical spectra calculated as a function of merger progress in each of a large suite of simulations. The mass, gas fraction, orbital parameters, and mass ratio of the merging galaxies are varied systematically, showing that the lifetime and properties of the K+A phase are strong functions of merger scenario. K+A durations are generally less than ~0.1-0.3 Gyr, significantly shorter than the commonly assumed 1 Gyr, which is obtained only in rare cases, owing to a wide variation in star formation histories resulting from different orbital and progenitor configurations. Combined with empirical merger rates, the model lifetimes predict rapidly-rising K+A fractions as a function of redshift that are consistent with results of large spectroscopic surveys, resolving tension between the observed K+A abundance and that predicted when one assumes the K+A duration is the lifetime of A stars (~1 Gyr). The effects of dust attenuation, viewing angle, and aperture bias on our models are analyzed. In some cases, the K+A features are longer-lived and more pronounced when AGN feedback removes dust from the center, uncovering the young stars formed during the burst. In this picture, the K+A phase begins during or shortly after the bright starburst/AGN phase in violent mergers, and thus offers a unique opportunity to study the effects of quasar and star formation feedback on the gas reservoir and evolution of the remnant. Analytic fitting formulae are provided for the estimates of K+A incidence as a function of merger scenario.

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Gregory F. Snyder, Thomas J. Cox, Christopher C. Hayward, Lars Hernquist, Patrik Jonsson. 2011-02-17. K+A Galaxies as the Aftermath of Gas-Rich Mergers: Simulating the Evolution of Galaxies as Seen by Spectroscopic Surveys. https://doi.org/10.1088/0004-637x/741/2/77

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