Galaxy evolution from deep multi-wavelength infrared surveys: a prelude to Herschel

摘要

Context. Studies of the generation and assembly of stellarpopulations in galaxies largely benefit from far-IR observations,considering that the IR flux is a close prior to the rate ofstar formation (thebulk of which happens in dust-obscuredenvironments). At the same time, major episodes of nuclear AGNaccretion are also dust-obscured and visible in theIR. Aims. At the end of the Spitzer cryogenic mission and the onset of the Herschelera,we review our current knowledge of galaxy evolution atIRwavelengths, and model it to achieve as far as a complete viewof the evolution of cosmic sources. We also develop new tools for theanalysis of background fluctuations to constrain source counts inregimes of high confusion, asit happens for the Herschel sub-mm surveys. Methods. We analysed a wide variety of new data on galaxy evolution and high-redshift source populations from Spitzercosmological surveys, and confront them with complementary data frommmground-based observations and constraints from the far-IRdiffuse radiation, aswell as preliminary results from Herschel surveys. Results. These data confirm earlier indications about a very rapid increase in galaxy volume emissivity with redshift up to [], thefastest evolution rate observed for galaxies at any wavelengths. The observed Spitzercounts require a combination of fast evolution for the dominantpopulation and a bumpy spectrum with substantial PAHemission at to2. Number counts at long wavelengths (70through 1100m) confirm these results. All the present data require that the fast observed evolution from z=0 to 1flattens around redshift1 and then keeps approximately constant up to at least. Our estimated redshift-dependent bolometric comoving energy density keeps lower at than some previously published results based on either large extinction corrections, or large spectral extrapolations. Conclusions. The present-day IR/sub-mm data provide evidence of a distinct population of very luminous galaxies becoming dominant at z>1. Their cosmological evolution, peaking around ,shows a faster decay with cosmic time than lower luminosity systems, whose maximal activity is set around ,then supporting an earlier phase of formation for the most luminous andmassive galaxies. From a comparison of our results on the comovingIRemissivity with recent estimates of the redshift-dependentstellar mass functions of galaxies, we find that the two agree wellwith each other if we assume standard recipes for star formation(auniversal SalpeterIMF) and standard fractions ()for the contribution of obscured AGNaccretion. Systematic exploitation of the forthcoming Herschel survey data will be important for confirming allthis. Key words: surveys - galaxies: evolution - galaxies: formation - galaxies: high-redshift - infrared: galaxies - submillimeter: galaxies