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 L _(dust) /L_(UV) with the Redshift

摘要

Deep observations of the Chandra Deep Field South have been secured at 15 Am with AKARI/RC infrared space telescope. From these observations, we define a sample of mid infrared-selected galaxies at 15 /μm and we also obtain 15 μm flux densities for a sample of Lyman Break Galaxies at z 1 already observed at 24 Am with Spitzer/MIPS. Number counts for the mid infrared-selected sample show a bump around a 15 Am 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 Am 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 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 ～ 2 based on our results and added new data points at higher redshifts. The decreasing trend is amplified as compared to the previous estimate.