THE MOST LUMINOUS z ∼ 9–10 GALAXY CANDIDATES YET FOUND: THE LUMINOSITY FUNCTION, COSMIC STAR-FORMATION RATE, AND THE FIRST MASS DENSITY ESTIMATE AT 500 Myr

We present the discovery of four surprisingly bright (H160 � 26 27 mag AB) galaxy candidates at z � 9 10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data, doubling the number of z � 10 galaxy candidates that are known, just �500 Myr after the Big Bang. Two similarly bright sources are also detected in a systematic re-analysis of the GOODS-S data set. Three of the four galaxies in GOODS-N are significantly detected at 4.5 6.2� in the very deep Spitzer/IRAC 4.5µm data, as is one of the GOODS-S candidates. Furthermore, the brightest of our candidates (at z = 10.2 ± 0.4) is robustly detected also at 3.6µm (6.9�), revealing a flat UV spectral energy distribution with a slope � = 2.0±0.2, consistent with demonstrated trends with luminosity at high redshift. The abundance of such luminous candidates suggests that the luminosity function evolves more significantly in �∗ than in L∗ at z & 8 with a higher number density of bright sources than previously expected. Despite the discovery of these luminous candidates, the cosmic star formation rate density for galaxies with SFR > 0.7 M⊙ yr −1 shows an order-of-magnitude increase in only 170 Myr from z � 10 to z � 8, consistent with previous results given the dominance of low-luminosity sources to the total SFR density. Based on the IRAC detections, we derive galaxy stellar masses at z � 10, finding that these luminous objects are typically 10 9 M⊙. This allows for a first estimate of the cosmic stellar mass density at z � 10 resulting in log10 �∗ = 4.7 +0.5 −0.8 M⊙ Mpc −3 for galaxies brighter than MUV � 18. The remarkable brightness, and hence luminosity, of these z � 9 10 candidates highlights the opportunity for deep spectroscopy to determine their redshift and nature, demonstrates the value of additional search fields covering a wider area to understand star-formation in the very early universe, and highlights the opportunities for JWST to map the buildup of galaxies at redshifts much earlier than z � 10. Subject headings: galaxies: evolution — galaxies: high-redshift — galaxies: luminosity function

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