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Hot-dust (690 K) Luminosity Density and Its Evolution in the Last 7.5 Gyr

H. Messias, B. Mobasher, J. Afonso

Abstract
We study the contribution of hot-dust to the luminosity density of galaxies and its evolution with cosmic time. Using the Spitzer-IRAC data over an area of 1.8 deg2 covered by the Cosmic Evolution Survey (COSMOS) field, we estimate the contribution from hot-dust at rest-frame 4.2 mum (from 0 <~ z <~ 0.2 up to 0.5 <~ z <~ 0.9). This wavelength corresponds to blackbody temperature of ~690 K. The contribution of stellar emission is estimated from the rest-frame 1.6 mum luminosity (assumed to result from stellar emission alone) and subtracted from the mid-infrared luminosity of galaxies to measure hot-dust emission. To attempt the study of the 3.3 mum polycyclic aromatic hydrocarbon (PAH) feature, we use the rest-frame 4.2 mum to infer the hot-dust flux at 3.3 mum. This study is performed for different spectral types of galaxies: early-type, late-type, starburst, and IR-selected active galactic nuclei (AGNs). We find that (1) the decrease of the hot-dust luminosity density since 0.5 <~ z <~ 1 is steeper (by at least 0.5 dex) compared with that of the cold-dust, giving support to the scenario where galaxy obscuration increases with redshift, as proposed in the literature;(2) hot-dust and PAH emission evolution seems to be correlated with stellar mass, where rest-frame 1.6 mum luminous non-AGN galaxies(i.e., massive systems) show a stronger decrement(with decreasing redshift) in hot-dust and PAH emission than the less luminous(less massive) non-AGN galaxies;(3) despite comprising <~ 3% of the total sample, AGN contribute as much as a third to the hot-dust luminosity density at z < 1 and clearly dominate the bright-end of the total hot-dust luminosity density function at 0.5 <~ z <~ 0.9;(4) the average dust-to-total luminosity ratio increases with redshift, while PAH-to-total luminosity ratio remains fairly constant;(5) at M 1.6 > -25, the dust-to-total and PAH-to-total luminosity ratios increase with decreasing luminosity, but deeper data are required to confirm this result. Future study is necessary to further enlighten the characterization of the different spectral components at play in 2-5 mum spectral regime.

Keywords
dust - extinction - galaxies: active - galaxies: evolution - galaxies: luminosity: function, mass: function - galaxies: starburst

The Astrophysical Journal
Volume 776, Number 2, Page 117_1
2013 October

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia