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

Abstract

Deep observations of the Chandra Deep Field South have been secured at 15jum with AKARI/IRC infrared space telescope. From these observations, we define a sample of mid infrared-selected galaxies at 15jum and we also obtain 15/im flux densities for a sample of Lyman Break Galaxies at z ̃ 1 already observed at 24/xm with Spitzer/MIPS. Number counts for the mid infrared-selected sample show a bump around a 15/xm 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 ̃ 1 we have tested the validity of the conversions from luminosities vf v at 8/zm to total dust luminosities by comparing with luminosities estimated from 12/μm data used as a reference. Some calibrations seem better when compared to Ldust evaluated from longer wavelength luminosities. We also find that the rest-frame 8 μm luminosities provide good estimates of Ldust- By comparing our data to several libraries of spectral energy distributions, we find that models can explain the diversity of the observed /24//15 ratio quite reasonably. However, when we analyse the luminosity dependence of this ratio, we find important discrepancies. Finally, we revisit the evolution of Ldust/Luv ratio with the redshift z by re-calibrating previous Ldust 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. © 2009 Astronomical Society of Japan.