Detectability of [ C ii ] 158 μ m emission from high - redshift galaxies : predictions for ALMA and SPICA

We discuss the detectability of high-redshift galaxies via [C ii] 158μm line emission by coupling an analytic model with cosmological Smoothed Particle Hydrodynamics (SPH) simulations that are based on the concordance Λ cold dark matter (CDM) model. Our analytic model describes a multiphase interstellar medium (ISM) irradiated by the far ultra-violet (FUV) radiation from local starforming regions, and it calculates thermal and ionization equilibrium between cooling and heating. The model allows us to predict the mass fraction of a cold neutral medium (CNM) embedded in a warm neutral medium (WNM). Our cosmological SPH simulations include a treatment of radiative cooling/heating, star formation, and feedback effects from supernovae and galactic winds. Using our method, we make predictions for the [C ii] luminosity from high-redshift galaxies which can be directly compared with upcoming observations by the Atacama Large Millimeter Array (ALMA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We find that the number density of galaxies that are detectable by ALMA and SPICA via [C ii] emission depends significantly on the amount of neutral gas in high-redshift galaxies, which is highly uncertain. In a CDM universe, most [C ii] sources at z = 3 are expected to be faint objects with Sν < 0.01mJy. Our calculations suggest that Lyman-break galaxies (LBGs) brighter than RAB = 23.5 magnitude have flux densities Sν = 1− 3mJy depending on the strength of galactic wind feedback, and one has to aim at very bright LBGs to obtain a detection with ALMA and SPICA. Subject headings: cosmology: theory — stars: formation — galaxies: formation — galaxies: evolution — methods: numerical 1 Center for Astrophysics and Space Sciences, University of California, San Diego, MC 0424 9500 Gilman Dr., La Jolla, 92093-0424 Email: [email protected], [email protected] Harvard University, 60 Garden Street, Cambridge, MA 02138