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

Deep observations of the Chandra Deep Field South have been secured at 15/mu m with AKARI/IRC infrared space telescope. From these observations, we define a sample of mid infrared-selected galaxies at 15 mu m and we also obtain 15 mu m flux densities for a sample of Lyman Break Galaxies at z similar to 1 already observed at 24 mu m with Spitzer/MIPS. Number counts for the mid infrared-selected sample show a bump around a 15 mu m flux density of 0.2 mJy 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 similar to 1 we have tested the validity of the conversions from luminosities nu(f nu) at 8 mu m to total dust luminosities by comparing with luminosities estimated from 12 mu m data used as a reference. Some calibrations seem better when compared to L-dust evaluated from longer wavelength luminosities. We also find that the rest-frame 8 mu m 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 f(24)/f(15) 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 similar to 2 based on our results and added new data points at higher redshifts. The decreasing trend is amplified as compared to the previous estimate.