FIR line emission from high redshift galaxies

TL;DR

This study combines cosmological simulations with a multi-phase interstellar medium model to predict far infrared emission lines from high-redshift galaxies, providing insights into their gas metallicity and observability with ALMA.

Contribution

It introduces a detailed simulation-based method to predict FIR line emissions from z~6 galaxies, linking line properties to gas metallicity and galaxy structure.

Findings

[C II] line flux is 185 mJy km/s for Z=Z_sun.

95% of [C II] flux originates from cold H I gas.

[C II] detectable by ALMA in a few hours of observation.

Abstract

By combining high resolution, radiative transfer cosmological simulations of z~6 galaxies with a sub-grid multi-phase model of their interstellar medium we derive the expected intensity of several far infrared (FIR) emission lines ([C II] 158 micron, [O I] 63 micron, and [N II] 122 micron) for different values of the gas metallicity, Z. For Z = Z_sun the [C II] spectrum is very complex due to the presence of several emitting clumps of individual size < 3 kpc; the peak is displaced from the galaxy center by ~100 km/s. While the [O I] spectrum is also similarly displaced, the [N II] line comes predominantly from the central ionized regions of the galaxy. When integrated over ~500 km/s, the [C II] line flux is 185 mJy km/s; 95% of such flux originates from the cold (T~250 K) H I phase, and only 5% from the warm (T~5000 K) neutral medium. The [O I] and [N II] fluxes are ~6 and ~90 times lower than the [C II] one, respectively. By comparing our results with observations of Himiko, the most extended and luminous Lyman Alpha Emitter (LAE) at z = 6.6, we find that the gas metallicity in this source must be sub-solar. We conclude that the [C II] line from z~6 galaxies is detectable by the ALMA full array in 1.9 < t_ON < 7.7 hr observing time, depending on Z.