Latest Results

HST WFC3The Hubble UltraDeep Field 2009 (HUDF09) Project was conceived in 2007. In 2008, through a highly competitive proposal process, the HUDF09 team was awarded 192 orbits (12 days) of observations on the Hubble Space Telescope with the new Wide Field InfraRed Camera (WFC3/IR). More on the HUDF09 project...

XDF

XDF thumbnailThe Hubble eXtreme Deep Field (XDF) Project has combined 50 days of observations with the Hubble Space Telescope using the Advanced Camera for Surveys Wide Field Channel and the Wide Field Camera 3 InfraRed Channel to create the deepest image of the universe. More on the XDF project ...

Recent Publications

Extremely Small Sizes for Faint z~2-8 Galaxies in the Hubble Frontier Fields: A Key Input For Establishing their Volume Density and UV Emissivity

Bouwens, R. J., Illingworth, G. D., Oesch, P. A., Atek, H., Lam, D., and Stefanon, M.

We provide the first observational constraints on the sizes of the faintest galaxies lensed by the Hubble Frontier Fields (HFF) clusters. Ionizing radiation from faint galaxies likely drives cosmic reionization, and the HFF initiative provides a key opportunity to find such galaxies. Yet, we cannot really assess their ionizing emissivity without a robust measurement of their sizes, since this is key to quantifying both their prevalence and the faint-end slope to the UV luminosity function. Here we provide the first such size constraints with 2 new techniques. The first utilizes the fact that the detectability of highly-magnified galaxies as a function of shear is very dependent on a galaxy's size. Only the most compact galaxies will remain detectable in regions of high shear (vs. a larger detectable size range for low shear), a phenomenon we carefully quantify using simulations. Remarkably, however, no correlation is found between the surface density of faint galaxies and the predicted shear, using 87 faint high-magnification mu>10 z~2-8 galaxies seen behind the first 4 HFF clusters. This can only be the case if such faint (~-15 mag) galaxies have significantly smaller sizes than luminous galaxies. We constrain their half-light radii to be <~30 mas (<160-240 pc). As a 2nd size probe, we rotate and stack 26 faint high-magnification sources along the major shear axis. Less elongation is found than even for objects with an intrinsic half-light radius of 10 mas. Together these results indicate that extremely faint z~2-8 galaxies have near point-source profiles in the HFF dataset (half-light radii conservatively <30 mas and likely 5-10 mas). These results suggest smaller completeness corrections and hence much lower volume densities for faint z~2-8 galaxies and shallower faint-end slopes than have been derived in many recent studies (by factors of ~2-3 and by dalpha>~0.1-0.3).

2016arXiv160800966B

The Hubble Legacy Fields (HLF-GOODS-S) v1.0 Data Products: Combining 2387 Orbits of GOODS-S/CDF-S Region ACS and WFC3/IR Images

Illingworth, G., Magee, D., Bouwens, R., Oesch, P., Labbe, I., van Dokkum, P., Whitaker, K., Holden, B., Franx, M., and Gonzalez, V.

We have submitted to MAST the 1.0 version data release of the Hubble Legacy Fields (HLF) project covering a 25 x 25 arcmin area over the GOOD-S (ECDF-S) region from the HST archival program AR-13252. The release combines exposures from Hubble's two main cameras, the Advanced Camera for Surveys (ACS/WFC) and the Wide Field Camera 3 (WFC3/IR), taken over more than a decade between mid-2002 to early 2016. The HLF includes essentially all optical (ACS/WFC F435W, F606W, F775W, F814W and F850LP filters) and infrared (WFC3/IR F105W, F125W, F140W, and F160W filters) data taken by Hubble over the original CDF-S region including the GOODS-S, ERS, CANDELS and many other programs (31 in total). The data has been released at https://archive.stsci.edu/prepds/hlf/ as images with a common astrometric reference frame, with corresponding inverse variance weight maps. We provide one image per filter for WFC3/IR at 60 mas per pixel resolution and two ACS/WFC images per filter, at both 30 and 60 mas per pixel. Since this comprehensive dataset combines data from 31 programs on the GOODS-S/ECDF-S, the AR proposal identified the MAST products by the global name "Hubble Legacy Field", with this region being identified by "HLF-GOODS-S". This dataset complements that of the Frontier Fields program. The total incorporated in the HLF-GOODS-S is 5.7 Msec in 7079 exposures from 2387 orbits. This is ~70% of a HST full cycle!

2016arXiv160600841I

z ≳ 7 Galaxies with Red Spitzer/IRAC [3.6]-[4.5] Colors in the Full CANDELS Data Set: The Brightest-Known Galaxies at z ~ 7-9 and a Probable Spectroscopic Confirmation at z = 7.48

Roberts-Borsani, G. W., Bouwens, R. J., Oesch, P. A., Labbe, I., Smit, R., Illingworth, G. D., van Dokkum, P., Holden, B., Gonzalez, V., Stefanon, M., Holwerda, B., and Wilkins, S.

We identify four unusually bright (H {}160,{AB} < 25.5) galaxies from Hubble Space Telescope (HST) and Spitzer CANDELS data with probable redshifts z ∼ 7–9. These identifications include the brightest-known galaxies to date at z ≳ 7.5. As Y-band observations are not available over the full CANDELS program to perform a standard Lyman-break selection of z > 7 galaxies, we employ an alternate strategy using deep Spitzer/IRAC data. We identify z ∼ 7.1–9.1 galaxies by selecting z ≳ 6 galaxies from the HST CANDELS data that show quite red IRAC [3.6]−[4.5] colors, indicating strong [O iii]+Hβ lines in the 4.5 μm band. This selection strategy was validated using a modest sample for which we have deep Y-band coverage, and subsequently used to select the brightest z ≥ 7 sources. Applying the IRAC criteria to all HST-selected optical dropout galaxies over the full ∼900 arcmin2 of the CANDELS survey revealed four unusually bright z ∼ 7.1, 7.6, 7.9, and 8.6 candidates. The median [3.6]−[4.5] color of our selected z ∼ 7.1–9.1 sample is consistent with rest-frame [O iii]+Hβ EWs of ∼1500 Å in the [4.5] band. Keck/MOSFIRE spectroscopy has been independently reported for two of our selected sources, showing Lyα at redshifts of 7.7302 ± 0.0006 and {8.683}-0.004+0.001, respectively. We present similar Keck/MOSFIRE spectroscopy for a third selected galaxy with a probable 4.7σ Lyα line at z spec = 7.4770 ± 0.0008. All three have H160-band magnitudes of ∼25 mag and are ∼0.5 mag more luminous (M 1600 ∼ −22.0) than any previously discovered z ∼ 8 galaxy, with important implications for the UV luminosity function (LF). Our three brightest and highest redshift z > 7 galaxies all lie within the CANDELS-EGS field, providing a dramatic illustration of the potential impact of field-to-field variance.

2016ApJ...823..143R

Rest-frame Optical Emission Lines in z ˜ 3.5 Lyman-break-selected Galaxies: The Ubiquity of Unusually High [OIII]/Hβ Ratios at 2 Gyr

Holden, B. P., Oesch, P. A., González, V. G., Illingworth, G. D., Labbé, I., Bouwens, R., Franx, M., van Dokkum, P., and Spitler, L.

We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z ˜ 3.2-3.7 using MOSFIRE on the Keck I telescope. Strong rest-frame optical [O iii] and Hβ emission lines were detected in 18 Lyman break galaxies (LBGs). The median flux ratio of [O iii]λ5007 to Hβ is {5.1}-0.5+0.5. This is a factor of 5-10 times higher than in local galaxies with similar stellar masses. None of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei. Combining our sample with a variety of LBGs from the literature, including 49 galaxies selected in a very similar manner, we find a high median ratio of [O iii]/Hβ = {4.8}-1.7+0.8. This high ratio seems to be a ubiquitous feature of z ˜ 3-4 LBGs, very different from typical local star-forming galaxies at similar stellar masses. The only comparable systems at z ˜ 0 are those with similarly high specific star formation rates (SSFRs), though ˜5 times lower stellar masses. High SSFRs may result in a higher ionization parameter, higher electron density, or harder ionizing radiation, which, combined different elemental abundances, result in a much higher [O iii]/Hβ line ratio. This implies a strong relation between a global property of a galaxy, the SSFR, and the local conditions of ISM in star-forming regions. Partially based on data obtained with the Hubble Space Telescope operated by AURA, Inc. for NASA under contract NAS5-26555. Partially based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407.

2016ApJ...820...73H

A Remarkably Luminous Galaxy at z=11.1 Measured with Hubble Space Telescope Grism Spectroscopy

Oesch, P. A., Brammer, G., van Dokkum, P. G., Illingworth, G. D., Bouwens, R. J., Labbé, I., Franx, M., Momcheva, I., Ashby, M. L. N., Fazio, G. G., Gonzalez, V., Holden, B., Magee, D., Skelton, R. E., Smit, R., Spitler, L. R., Trenti, M., and Willner, S. P.

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 μ {{m}}. 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}-0.12+0.08, 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 ˜109 M&sun;. This spectroscopic redshift measurement suggests that James Webb Space Telescope (JWST) 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 JWST's spectroscopy, if it is launched early enough to overlap with JWST.

2016ApJ...819..129O

VizieR Online Data Catalog: IRAC HUDF and GOODS ultradeep surveys (Labbe+, 2015)

Labbe, I., Oesch, P. A., Illingworth, G. D., van Dokkum, P. G., Bouwens, R. J., Franx, M., Carollo, C. M., Trenti, M., Holden, B., Smit, R., Gonzalez, V., Magee, D., Stiavelli, M., and Stefanon, M.

The IRAC ultradeep field and IRAC Legacy over GOODS programs are two ultradeep imaging surveys at 3.6 and 4.5μm with the Spitzer Infrared Array Camera (IRAC). The primary aim is to directly detect the infrared light of reionization epoch galaxies at z>7 and to constrain their stellar populations. The observations cover the Hubble Ultra Deep Field (HUDF), including the two HUDF parallel fields, and the CANDELS/GOODS-South, and are combined with archival data from all previous deep programs into one ultradeep data set. The resulting imaging reaches unprecedented coverage in IRAC 3.6 and 4.5μm ranging from >50hr over 150arcmin2, >100hr over 60sq arcmin2, to ~200hr over 5-10arcmin2. This paper presents the survey description, data reduction, and public release of reduced mosaics on the same astrometric system as the CANDELS/GOODS-South Wide Field Camera 3 (WFC3) data. To facilitate prior-based WFC3+IRAC photometry, we introduce a new method to create high signal-to-noise PSFs from the IRAC data and reconstruct the complex spatial variation due to survey geometry. The PSF maps are included in the release, as are registered maps of subsets of the data to enable reliability and variability studies. Simulations show that the noise in the ultradeep IRAC images decreases approximately as the square root of integration time over the range 20-200hr, well below the classical confusion limit, reaching 1σ point-source sensitivities as faint as 15nJy (28.5 AB) at 3.6μm and 18nJy (28.3 AB) at 4.5μm. The value of such ultradeep IRAC data is illustrated by direct detections of z=7-8 galaxies as faint as HAB=28. (1 data file).

2016yCat..22210023L

Ultradeep IRAC Imaging Over the HUDF and GOODS-South: Survey Design and Imaging Data Release

Labbé, I., Oesch, P. A., Illingworth, G. D., van Dokkum, P. G., Bouwens, R. J., Franx, M., Carollo, C. M., Trenti, M., Holden, B., Smit, R., González, V., Magee, D., Stiavelli, M., and Stefanon, M.

The IRAC ultradeep field and IRAC Legacy over GOODS programs are two ultradeep imaging surveys at 3.6 and 4.5 μm with the Spitzer Infrared Array Camera (IRAC). The primary aim is to directly detect the infrared light of reionization epoch galaxies at z > 7 and to constrain their stellar populations. The observations cover the Hubble Ultra Deep Field (HUDF), including the two HUDF parallel fields, and the CANDELS/GOODS-South, and are combined with archival data from all previous deep programs into one ultradeep data set. The resulting imaging reaches unprecedented coverage in IRAC 3.6 and 4.5 μm ranging from >50 hr over 150 arcmin2, >100 hr over 60 sq arcmin2, to ˜200 hr over 5-10 arcmin2. This paper presents the survey description, data reduction, and public release of reduced mosaics on the same astrometric system as the CANDELS/GOODS-South Wide Field Camera 3 (WFC3) data. To facilitate prior-based WFC3+IRAC photometry, we introduce a new method to create high signal-to-noise PSFs from the IRAC data and reconstruct the complex spatial variation due to survey geometry. The PSF maps are included in the release, as are registered maps of subsets of the data to enable reliability and variability studies. Simulations show that the noise in the ultradeep IRAC images decreases approximately as the square root of integration time over the range 20-200 hr, well below the classical confusion limit, reaching 1σ point-source sensitivities as faint as 15 nJy (28.5 AB) at 3.6 μm and 18 nJy (28.3 AB) at 4.5 μm. The value of such ultradeep IRAC data is illustrated by direct detections of z = 7-8 galaxies as faint as HAB = 28. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

2015ApJS..221...23L

Reionization After Planck: The Derived Growth of the Cosmic Ionizing Emissivity Now Matches the Growth of the Galaxy UV Luminosity Density

Bouwens, R. J., Illingworth, G. D., Oesch, P. A., Caruana, J., Holwerda, B., Smit, R., and Wilkins, S.

Thomson optical depth τ measurements from Planck provide new insights into the reionization of the universe. In pursuit of model-independent constraints on the properties of the ionizing sources, we determine the empirical evolution of the cosmic ionizing emissivity. We use a simple two-parameter model to map out the evolution in the emissivity at z ≳ 6 from the new Planck optical depth τ measurements, from the constraints provided by quasar absorption spectra and from the prevalence of Lyα emission in z ˜ 7-8 galaxies. We find the redshift evolution in the emissivity {\dot{N}}{ion}(z) required by the observations to be {({\text{}}d{{log}}10 {\dot{N}}{ion}/{dz})}z=8=-{0.15}-0.11+0.08 ({({\text{}}d{{log}}10 {\dot{N}}{ion}/{dz})}z=8=-{0.19}-0.11+0.09 for a flat prior), largely independent of the assumed clumping factor CH ii and entirely independent of the nature of the ionizing sources. The trend in {\dot{N}}{ion}(z) is well-matched by the evolution of the galaxy UV-luminosity density (d{{log}}10{ρ }{UV}/{dz}=-0.11+/- 0.04) to a magnitude limit ≳-13 mag, suggesting that galaxies are the sources that drive the reionization of the universe. The role of galaxies is further strengthened by the conversion from the UV luminosity density ρUV to {\dot{N}}{ion}(z) being possible for physically plausible values of the escape fraction fesc, the Lyman-continuum photon production efficiency ξion, and faint-end cut-off Mlim to the luminosity function. Quasars/active galactic nuclei appear to match neither the redshift evolution nor normalization of the ionizing emissivity. Based on the inferred evolution in the ionizing emissivity, we estimate that the z ˜ 10 UV-Iuminosity density is 8-4+15× lower than at z ˜ 6, consistent with the observations. The present approach of contrasting the inferred evolution of the ionizing emissivity with that of the galaxy UV luminosity density adds to the growing observational evidence that faint, star-forming galaxies drive the reionization of the universe. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

2015ApJ...811..140B

First Frontier Field Constraints on the Cosmic Star Formation Rate Density at z ∼ 10—The Impact of Lensing Shear on Completeness of High-redshift Galaxy Samples

Oesch, P. A., Bouwens, R. J., Illingworth, G. D., Franx, M., Ammons, S. M., van Dokkum, P. G., Trenti, M., and Labbé, I.

We search the complete Hubble Frontier Field data set of Abell 2744 and its parallel field for z∼ 10 sources to further refine the evolution of the cosmic star formation rate density (SFRD) between z∼ 8 and z∼ 10. We independently confirm two images of the recently discovered triply imaged z∼ 9.8 source by Zitrin et al. and set an upper limit for similar z∼ 10 galaxies with red colors of {J}125-{H}160\gt 1.2 in the parallel field of Abell 2744. We utilize extensive simulations to derive the effective selection volume of Lyman-break galaxies at z∼ 10, both in the lensed cluster field and in the adjacent parallel field. Particular care is taken to include position-dependent lensing shear to accurately account for the expected sizes and morphologies of highly magnified sources. We show that both source blending and shear reduce the completeness at a given observed magnitude in the cluster, particularly near the critical curves. These effects have a significant, but largely overlooked, impact on the detectability of high-redshift sources behind clusters, and substantially reduce the expected number of highly magnified sources. The detections and limits from both pointings result in an SFRD which is consistent within the uncertainties with previous estimates at z∼ 10 from blank fields. The combination of these new results with all other estimates is also consistent with a rapidly declining SFRD in the 170 Myr from z∼ 8 to z∼ 10 as predicted by cosmological simulations and dark-matter halo evolution in ΛCDM. Once biases introduced by magnification-dependent completeness are accounted for, the full six cluster and parallel Frontier Field program will be an extremely powerful new data set to probe the evolution of the galaxy population at z\gt 8 before the advent of the James Webb Space Telescope. Based on data obtained with the Hubble Space Telescope operated by AURA, Inc. for NASA under contract NAS5-26555.

2015ApJ...808..104O