The remarkable Hubble Space Telescope(HST) data sets from the CANDELS, HUDF09, HUDF12, ERS, and BoRG/HIPPIES programs have allowed us to map the evolution of the rest-frame UV luminosity function (LF) fromz 10 toz 4. We develop new color criteria that more optimally utilize the full wavelength coverage from the optical, near-IR, and mid-IR observations over our search fields, while simultaneously minimizing the incompleteness and eliminating redshift gaps. We have identified 5859, 3001, 857, 481, 217, and 6 galaxy candidates atz 4,z 5,z 6,z 7,z 8, andz 10, respectively, from the ∼1000 arcmin 2 area covered by these data sets. This sample of >10,000 galaxy candidates at ⩾ z 4 is by far the largest assembled to date with HST. The selection ofz 4-8 candidates over the five CANDELS fields allows us to assess the cosmic variance; the largest variations are at ⩾ z 7. Our new LF determinations atz 4 andz 5 span a 6 mag baseline and reach to -16 AB mag. These determinations agree well with previous estimates, but the larger samples and volumes probed here result in a more reliable sampling of >L* galaxies and allow us to reassess the form of the UV LFs. Our new LF results strengthen our earlier findings to s 3.4 significance for a steeper faint-end slope of the UV LF at > z 4, with α evolving from a = - 1.64 0.04 atz 4 to a = - 2.06 0.13 atz 7 (and a = - 2.02 0.23 atz 8), consistent with that expected from the evolution of the halo mass function. We find less evolution in the characteristic magnitude M * fromz 7 toz 4; the observed evolution in the LF is now largely represented by changes in f*. No evidence for a non-Schechter-like form to the z ∼ 4-8 LFs is found. A simple conditional LF model based on halo growth and evolution in the M/L ratio µ +z ( ( 1) ) 1.5 of halos provides a good representation of the observed evolution.

We explore star formation histories (SFHs) of galaxies based on the evolution of the star formation rate stellar mass relation (SFR-M * ). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR-M * relation at 0.5 < z < 4. Similar to recent works we find that the average infrared spectral energy distributions of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that the SFR-M * relation is not consistent with a single power law of the form M SFR * µ a at any redshift; it has a power law slope of α ∼ 1 at low masses, and becomes shallower above a turnover mass (M 0 ) that ranges from 10 9.5 to 10 10.8 M e , with evidence that M 0 increases with redshift. We compare our measurements to results from state-of-the-art cosmological simulations, and find general agreement in the slope of the SFR-M * relation albeit with systematic offsets. We use the evolving SFR-M * sequence to generate SFHs, finding that typical SFRs of individual galaxies rise at early times and decline after reaching a peak. This peak occurs earlier for more massive galaxies. We integrate these SFHs to generate mass growth histories and compare to the implied mass growth from the evolution of the stellar mass function (SMF). We find that these two estimates are in broad qualitative agreement, but that there is room for improvement at a more detailed level. At early times the SFHs suggest mass growth rates that are as much as 10× higher than inferred from the SMF. However, at later times the SFHs under-predict the inferred evolution, as is expected in the case of additional growth due to mergers.

We present Hubble WFC3/IR slitless grism spectra of a remarkably bright z 10 galaxy candidate, GN-z11, identified initially from CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is detected at λ = 1.47 ± 0.01 µm. The new grism data, combined with the photometric data, rule out all plausible lower redshift solutions for this source. The only viable solution is that this continuum break is the Lyα break redshifted to z grism = 11.09 +0.08 −0.12 , just ∼400 Myr after the Big Bang. This observation extends the current spectroscopic frontier by 150 Myr to well before the Planck (instantaneous) cosmic reionization peak at z ∼ 8.8, demonstrating that galaxy build-up was well underway early in the reionization epoch at z > 10. GN-z11 is remarkably and unexpectedly luminous for a galaxy at such an early time: its UV luminosity is 3× larger than L * measured at z ∼ 6 − 8. The Spitzer IRAC detections up to 4.5 µm of this galaxy are consistent with a stellar mass of ∼ 10 9 M . This spectroscopic redshift measurement suggests that the James Webb Space Telescope (JW ST ) will be able to similarly and easily confirm such sources at z > 10 and characterize their physical properties through detailed spectroscopy. Furthermore, WFIRST, with its wide-field near-IR imaging, would find large numbers of similar galaxies and contribute greatly to JW ST 's spectroscopy, if it is launched early enough to overlap with JW ST .