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South Pole Telescope eyes birth of first massive galaxies

New data from the South Pole Telescope (SPT) indicate that the birth of the first massive galaxies that lit up the early universe was an explosive event, happening faster and ending sooner than suspected.
Extremely bright, active galaxies formed and fully illuminated the universe by the time it was 750 million years old, or about 13 billion years ago, according to a new report published in the Sept. 1 print edition of The Astrophysical Journal.

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Title: The Most Massive Galaxies at 3.0<z<4.0 in the NEWFIRM Medium-Band Survey: Properties and Improved Constraints on the Stellar Mass Function
Authors: Danilo Marchesini, Katherine E. Whitaker, Gabriel Brammer, Pieter G. van Dokkum, Ivo Labbe, Adam Muzzin, Ryan F. Quadri, Mariska Kriek, Kyoung-Soo Lee, Gregory Rudnick, Marijn Franx, Garth D. Illingworth, David Wake
(Version v2)

We use the NEWFIRM Medium-Band Survey (NMBS) to characterise the properties of a mass-complete sample of 14 galaxies at 3.0<z<4.0 with M_star>2.5x10^11 Msun, and to derive more accurate measurements of the high-mass end of the stellar mass function (SMF) of galaxies at z=3.5, with significantly reduced contributions from photometric redshift errors and cosmic variance to the total error budget of the SMF. The typical very massive galaxy at z=3.5 is red and faint in the observer's optical, with median r=26.1, and rest-frame U-V=1.6. About 60% of the sample have optical colors satisfying either the U- or the B-dropout colour criteria, although ~50% of these galaxies have r>25.5. About 30% of the sample has SFRs from SED modelling consistent with zero. However, >80% of the sample is detected at 24 micron, with total infrared luminosities in the range (0.5-4.0)x10^13 Lsun. This implies the presence of either dust-enshrouded starburst activity (with SFRs of 600-4300 Msun/yr) and/or highly-obscured active galactic nuclei (AGN). The contribution of galaxies with M_star>2.5x10^11 Msun to the total stellar mass budget at z=3.5 is ~8%. We find an evolution by a factor of 2-7 and 3-22 from z~5 and z~6, respectively, to z=3.5. The previously found disagreement at the high-mass end between observed and model-predicted SMFs is now significant at the 3sigma level. However, systematic uncertainties dominate the total error budget, with errors up to a factor of ~8 in the densities, bringing the observed SMF in marginal agreement with the predicted SMF. Additional systematic uncertainties on the high-mass end could be introduced by either 1) the intense star-formation and/or the very common AGN activities as inferred from the MIPS 24 micron detections, and/or 2) contamination by a significant population of massive, old, and dusty galaxies at z~2.6.

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First results from the GOODS NICMOS survey, the largest Hubble Space Telescope programme ever led from outside of the United States, reveal how the most massive galaxies in the early Universe assembled to form the most massive objects in the Universe today. Dr Chris Conselice from the University of Nottingham will present the results at the European Week of Astronomy and Space Science at the University of Hertfordshire on Wednesday 22nd April.

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