Evidence for strong evolution of the cosmic star formation density at high redshift

Abstract

Deep HST/ACS and VLT/ISAAC data of the GOODS-South field were used to look for high-redshift galaxies in the rest-frame UV wavelength range and to study the evolution of the cosmic star-formation density at z~7. The GOODS-South area was surveyed down to a limiting magnitude of about (J+Ks)=25.5 looking for drop-out objects in the z ACS filter. The large sampled area would allow for the detection of galaxies which are 20 times less numerous and 1-2 magnitudes brighter than similar studies using HST/NICMOS near-IR data. Two objects were initially selected as promising candidates of galaxies at z~7, but have subsequently been dismissed and identified as Galactic brown dwarfs through a detailed analysis of their morphology and Spitzer colors, as well as through spectroscopic information. As a consequence, we conclude that there are no galaxies at z~7 down to our limiting magnitude in the field we investigated. Our non detection of galaxies at z~7 provides clear evidence for a strong evolution of the luminosity function between z=6 and z=7, i.e. over a time interval of only ~170 Myr. Our constraints also provide evidence for a significant decline of the total star formation rate at z=7, which must be less than 40% of that at z=3 and 40-80% of that at z=6. We also derive an upper limit to the ionizing flux at z=7, which is only marginally consistent with that required to completely ionize the Universe.

11 pages, A&A, in press. New version after proof correction

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• z~7-10 Galaxies in the HUDF and GOODS fields, and their UV Luminosity Functions
• Keeping the Universe ionised: Photo-heating and the clumping factor of the high-redshift intergalactic medium
• A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint $z\sim 7-8$ Galaxies
• The UDF05 Follow-up of the HUDF: II. Constraints on Reionization from z-dropout Galaxies
• How many supernovae are we missing at high redshift?
• Type Ia and II supernovae contributions to the metal enrichment in intra-cluster medium observed with Suzaku
• Probing the star formation history using the redshift evolution of luminosity functions
• Spitzer Spectra of a 10 mJy Galaxy Sample and the Star Formation Rate in the Local Universe
• The Most Luminous Starbursts in the Universe
• First stars and the extragalactic background light: How recent gamma-ray observations constrain the early universe
• Probing the thermal history during reionization using a semi-numerical photon-conserving code SCRIPT
• The First Billion Years project: gamma-ray bursts at z>5
• Optical-NIR spectra of quasars close to reionization (z~ 6)