The 0.4 < z < 1.3 star formation history of the Universe as viewed in the far-infrared

March 2009 • 2009A&A...496...57M

Authors • Magnelli, B. • Elbaz, D. • Chary, R. R. • Dickinson, M. • Le Borgne, D. • Frayer, D. T. • Willmer, C. N. A.

Abstract • Aims: We use the deepest existing mid- and far-infrared observations (reaching ~3 mJy at 70 μm) obtained with Spitzer in the Great Observatories Origins Deep Survey (GOODS) and Far Infrared Deep Extragalactic Legacy survey (FIDEL) fields to derive the evolution of the rest-frame 15 μm, 35 μm, and total infrared luminosity functions of galaxies spanning z<1.3. We thereby quantify the fractional contribution of infrared luminous galaxies to the comoving star formation rate density over this redshift range. In comparison with previous studies, the present one takes advantage of deep 70 μm observations that provide a more robust infrared luminosity indicator than 24 μm affected by the emission of PAHs at high redshift (z∼1), and we use several independent fields to control cosmic variance.
Methods: We used a new extraction technique based on the well-determined positions of galaxies at shorter wavelengths to extract the 24 and 70 μm flux densities of galaxies. It is found that sources separated by a minimum of 0.5 × FWHM are deblended by this technique, which facilitates multi-wavelength associations of counterparts. Using a combination of photometric and spectroscopic redshifts that exist for ~80% of the sources in our sample, we are able to estimate the rest-frame luminosities of galaxies at 15 μm and 35 μm. By complementing direct detections with a careful stacking analysis, we measured the mid- and far-infrared luminosity functions of galaxies over a factor ~100 in luminosity (10¹¹~L_⊙ <∼ L_IR <∼ 10¹³~L_⊙) at z<1.3. A stacking analysis was performed to validate the bolometric corrections and to compute comoving star-formation rate densities in three redshift bins 0.4<z<0.7, 0.7<z<1.0 and, 1.0<z<1.3.
Results: We find that the average infrared spectral energy distribution of galaxies over the last 2/3 of the cosmic time is consistent with that of local galaxies, although individual sources do present significant scatter. We also measured both the bright and faint ends of the infrared luminosity functions and find no evidence for a change in the slope of the double power law used to characterize the luminosity function. The redshift evolution of infrared luminous galaxies is consistent with pure luminosity evolution proportional to (1+z)^3.6±0.4 up to z∼1.3. We do not find evidence of differential evolution between LIRGs and ULIRGs up to z∼1.3, in contrast with previous claims. The comoving number density of infrared luminous galaxies has increased by a factor of ∼100 between 0<z<1. By z∼1.0, LIRGs produce half of the total comoving infrared luminosity density.

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Ranga-Ram Chary

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