AAS 197, January 2001
Session 65. Galaxy Evolution: High Redshift
Oral, Tuesday, January 9, 2001, 1:30-3:00pm, Pacific One

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[65.06] A Model for the Evolution of the Cosmic Star Formation Rate derived from the Mid-Infrared Luminosity Function

R. Chary (University of California, Santa Cruz), D. Elbaz (University of California, Santa Cruz & CEA-Saclay, France)

Deep extragalactic surveys with the ISOCAM instrument have revealed the presence of a population of bright mid-infrared galaxies at z~0.8. These sources have been associated with the analogs of luminous infrared galaxies (LIRGs; LIR > 1011 L\sun) that were first detected by IRAS, suggesting that LIRGs are much more numerous at high redshift than in the local Universe. However, LIRGs are known to emit more than 90% of their luminosity at far-infrared wavelengths. Thus, star formation rates derived from visible light observations of LIRGs are only a lower limit to the total SFR. This implies that estimates of the star formation history of the Universe derived from deep optical surveys underestimate the comoving SFR. The spectrum of the cosmic infrared background confirms this hypothesis.

The mid-infrared has been found to be a good tracer of the far-infrared and is less affected by extinction and by confusion. We present a backward evolution model for the comoving SFR that is based on evolution of the mid-infrared luminosity function with redshift.Our evolutionary model fits a number of observational parameters such as mid-infrared source counts from ISOCAM, the spectrum of the cosmic infrared background at mid- and far-infrared wavelengths and submillimeter number counts. Implications for MIPS/SIRTF are also presented.

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