Dust and Molecules in Early Galaxies: Prediction and Strategy for Observations

The interplay between dust and molecules is of fundamental importance in early galaxy evolution. First we present the prediction for the dust emission from forming galaxies. Then we discuss the observational strategy for molecules in early galaxies by infrared absorption lines of a bright continuum source behind the clouds. By combining these two approaches, we will be able to have a coherent picture of the very early stage of galaxy evolution.Comment: 10 pages, 4 figures, to appear in the proceedings of `Hunt for Molecules', IA

The Evolution of the Visible and Hidden Star Formation in the Universe: Implication from the Luminosity Functions at FUV and FIR

Based on GALEX and IRAS/Spitzer datasets, we have found that both FUV and FIR luminosity functions (LFs) show a strong evolution from z=0 to z=1, but the FIR LF evolves much stronger than the FUV one. Consequently, the FIR/FUV luminosity density ratio increases from 4 (z=0) to 15 (z=1). It means that more than 80% of the star-forming activity in the Universe is hidden by dust at z=1. To explore this issue further, we have performed a combined analysis of the galaxy sample in FUV and FIR. For the Local Universe we used GALEX-IRAS sample, whereas at z=1 we used the Lyman-break galaxy sample selected by GALEX bands constructed by Burgarella et al. (2005), which is known to be representative of visible (i.e., non-obscured) star-forming galaxies at z=1. From these datasets, we constructed the LFs of the FUV-selected galaxies by the survival analysis to, take into account the upper-limit data properly. We discovered that the FIR LF of the Lyman-break galaxies show a significant evolution comparing with the local FIR LF, but it is a factor of 2-3 lower than the global FIR LF (Le Floc'h et al. 2005). This indicates that the evolution of visible galaxies is not strong enough to explain the drastic evolution of the FIR LF. Namely, a FIR-luminous, rapidly diminishing population of galaxies is required.Comment: 4 pages, 4 figures, conference proceedings of "At the Edge of the Universe", Sintra 9-13 October 200

A Dust Emission Model for Very Young Galaxies: Expected Properties and Far Infrared Diagnostics

Dust plays crucial roles in galaxy formation and evolution. In the early epoch of galaxy evolution dust is only supplied by supernovae (SNe). With the aid of a new physical model of dust production by SNe, we constructed a model of dust emission from forming galaxies. We show the evolution of the spectral energy distribution (SED). Then we adopt this model to a local starbursting dwarf galaxy SBS 0335$-$052. Further we discuss the SEDs of high redshift galaxies, and consider their observational feasibility.Comment: 8 pages, 4 figures, to appear in the proceedings of "Infrared Diagnostics of Galaxy Evolution

Deep 15um 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

Deep observations of the CDFS have been secured at 15um with AKARI/IRC infrared space telescope (ESA open time). From these observations, we define a sample of MIR-selected galaxies at 15um and we also obtain 15um flux densities for a sample of LBGs at z=1 already observed at 24um with Spitzer/MIPS. Number counts for the MIR-selected sample show a bump around a 15um 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. Thanks to this dataset, we have tested, on the two above samples at z=1, the validity of the conversions from monochromatic luminosities nu.f(nu) at a rest-frame wavelength of 8um by a comparison with total dust luminosities estimated from Spitzer rest-frame 12um data that we use as a reference. We find that the 8um dust luminosities are not all consistent and that some of them are better when compared to L(dust) evaluated from longer wavelength luminosities. We also find that the rest-frame 8um luminosities provide globally good estimates of L(dust). By comparing our data for the two samples to several libraries of SEDs, we find that models can explain the diversity of the observed f(24)/f(15) ratio quite reasonably for the MIR-selected sample and better for the LBG sample which are less dispersed than the MIR selection. 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.Comment: Paper accepted for publication in PAS