Deep 15µm AKARI Observations in the CDFS: Estimating Dust Luminosities for a MIR-Selected Sample and for Lyman Break Galaxies and the Evolution of L_dust/L_UV with the Redshift

Abstract

Deep observations of the Chandra Deep Field South have been secured at 15μm with AKARI/IRC infrared space telescope. From these observations, we define a sample of mid infrared-selected galaxies at 15μm and we also obtain 15μm flux densities for a sample of Lyman Break Galaxies at z ∼ 1 already observed at 24μm with Spitzer/MIPS. Number counts for the mid infrared-selected sample show a bump around a 15μm flux density of 0.2mJy that can be attributed to galaxies at z > 0.4 and at z > 0.8 for the fainter part of the bump. This bump seems to be shifted as compared to other works and a possible origin can be the Cosmic variance. On the two above samples at z ∼ 1 we have tested the validity of the conversions from luminosities ν.f_ν at 8νm to total dust luminosities by comparing with luminosities estimated from 12νm data used as a reference. Some calibrations seem better when compared to evaluated from longer wavelength luminosities. We also find that the rest-frame 8μm luminosities provide good estimates of L_dust. By comparing our data to several libraries of spectral energy distributions, we find that models can explain the diversity of the observed f₂₄/f₁₅ ratio quite reasonably. However, when we analyse the luminosity dependence of this ratio, we find important discrepancies. Finally, we revisit the evolution of L_dust/L_UV ratio with the redshift z by re-calibrating previous L_dust at z ∼ 2 based on our results and added new data points at higher redshifts. The decreasing trend is amplified as compared to the previous estimate.