A systematic search for very massive galaxies at z > 4

The Hubble Ultra Deep Field (HUDF) offers a unique opportunity to study high-redshift starbursts with high spatial resolution. The combination of ACS optical and NICMOS near-IR images provide a measure of the redshift, intrinsic SED and extinction. This analysis finds 39 galaxies with SFRs in excess of 50 M☉ yr−1. The typical starburst galaxy has a very blue SED and relatively high extinction. All of the HUDF starburst galaxies have redshifts higher than 0.9 but no starburst galaxies lie at redshifts greater than 3.5. The highest SFR in the HUDF is 560 M☉ yr−1. The top ten SFR galaxies, all with SFRs exceeding 100 M☉ yr−1 lie in the redshift range between 1.7 and 3.1. This defines an epoch of massive galaxy assembly similar to that seen in the Northern Hubble Deep Field (NHDF). Unlike the HUDF, however, the NHDF contains starburst galaxies up to the analysis redshift limit of 6. Both fields subtend small areas and any conclusions relative to universal star formation should be viewed with caution.

We report on a complete sample of 7 luminous early-type galaxies in the Hubble Ultra Deep Field (UDF) with spectroscopic redshifts between 1.39 and 2.47 and to K<23 AB. Using the BzK selection criterion we have pre-selected a set of objects over the UDF which fulfill the photometric conditions for being passively evolving galaxies at z>1.4. Low-resolution spectra of these objects have been extracted from the HST+ACS grism data taken over the UDF by the GRAPES project. Redshift for the 7 galaxies have been identified based on the UV feature at rest frame 2640<lambda<2850 AA. This feature is mainly due to a combination of FeII, MgI and MgII absorptions which are characteristic of stellar populations dominated by stars older than about 0.5 Gyr. The redshift identification and the passively evolving nature of these galaxies is further supported by the photometric redshifts and by the overall spectral energy distribution (SED), with the ultradeep HST+ACS/NICMOS imaging revealing compact morphologies typical of elliptical/early-type galaxies. From the SED we derive stellar masses of 10^{11}Msun or larger and ages of about 1 Gyr. Their space density at < z >=1.7 appears to be roughly a factor of 2--3 smaller than that of their local counterparts, further supporting the notion that such massive and old galaxies are already ubiquitous at early cosmic times. Much smaller effective radii are derived for some of the objects compared to local massive ellipticals, which may be due to morphological K corrections, evolution, or the presence of a central point-like source. Nuclear activity is indeed present in a subset of the galaxies, as revealed by them being hard X-ray sources, hinting to AGN activity having played a role in discontinuing star formation.

Multiwavelength data are essential in order to provide a complete picture of galaxy evolution and to inform studies of galaxies' morphological properties across cosmic time. Here we present results of a multiwavelength investigation of the morphologies of "tadpole" galaxies at intermediate redshift (0.314

It remains a challenge to assess the merger fraction of galaxies at different cosmic epochs in order to probe the evolution of their mass assembly. Using the ILLUSTRIS cosmological simulation project, we investigate the relation between the separation of galaxies in a pair, both in velocity and projected spatial separation space, and the probability that these interacting galaxies will merge in the future. From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction. We then probe the evolution of the major and minor merger fraction using the latest Multi-Unit Spectroscopic Explorer (MUSE) deep observations over the Hubble Ultra Deep Field, Hubble Deep Field South, COSMOS-Gr30, and Abell 2744 regions. From a parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366 close pairs spread over a large range of redshifts (0.2 &lt; z &lt; 6) and stellar masses (107 − 1011M⊙). Using the stellar mass ratio between the secondary and primary galaxy as a proxy to split the sample into major, minor, and very minor mergers, we found a total of 183 major, 142 minor, and 47 very minor close pairs corresponding to a mass ratio range of 1:1–1:6, 1:6–1:100, and lower than 1:100, respectively. Due to completeness issues, we do not consider the very minor pairs in the analysis. Overall, the major merger fraction increases up to z ≈ 2−3 reaching 25% for pairs where the most massive galaxy has a stellar mass M⋆ ≥ 109.5 M⊙. Beyond this redshift, the fraction decreases down to ∼5% at z ≈ 6. The major merger fraction for lower-mass primary galaxies with M⋆ ≤ 109.5 M⊙ seems to follow a more constant evolutionary trend with redshift. Thanks to the addition of new MUSE fields and new selection criteria, the increased statistics of the pair samples allow us to significantly shorten the error bars compared to our previous analysis. The evolution of the minor merger fraction is roughly constant with cosmic time, with a fraction of 20% at z &lt; 3 and a slow decrease to 8−13% in the redshift range 3 ≤ z ≤ 6.

Following the discovery of the first significant samples of galaxies at z > 6.5 with Wide Field Camera 3/Infra-Red (WFC3/IR) on board Hubble Space Telescope (HST), it has been claimed that the faintest high-redshift galaxies display extremely blue ultraviolet (UV) continuum slopes, with a UV power-law index β≃−3 (where fλ∝λβ). Such slopes are bluer than previously reported for any other galaxy population, and are most readily explained theoretically by extinction-free, young and very low metallicity stellar populations with a high ionizing photon escape fraction. Here we undertake a critical study of the evidence for such extreme values of β, combining three new WFC3/IR-selected samples of galaxies spanning nearly two decades in UV luminosity over the redshift range z≃ 4.5–8. We explore the impact of inclusion/exclusion of less robust high-redshift candidates and use the varying depths of the samples to explore the effects of noise and selection bias at a given UV luminosity. Simple data-consistency arguments suggest that artificially blue average values of β can result when the analysis is extended into the deepest ≃0.5 mag bin of these WFC3/IR-selected galaxy samples, regardless of the actual luminosity or redshift range probed. By confining attention to robust high-redshift galaxy candidates, with at least one 8σ detection in the WFC3/IR imaging, we find that the average value of β is consistent with 〈β〉=−2.05 ± 0.10 over the redshift range z= 5–7 and the UV absolute magnitude range −22 < MUV,AB < − 18, and that 〈β〉 shows no significant trend with either redshift or MUV. We create and analyse a set of simple end-to-end simulations based on the WFC3/IR+ACS Hubble Ultra Deep Field (HUDF) and Early Release Science data sets which demonstrate that a bias towards artificially low/blue average values of β is indeed ‘expected’ when the UV slope analysis is extended towards the source detection threshold, and conclude that there is as yet no clear evidence for UV slopes significantly bluer than β≃−2, the typical value displayed by the bluest star-forming galaxies at more modest redshifts. A robust measurement of 〈β〉 for the faintest galaxies at z≃ 7 (and indeed z≃ 8) remains a key observational goal, as it provides a fundamental test for high escape fractions from a potentially abundant source of re-ionizing photons. This goal is achievable with HST, but requires still deeper WFC3/IR imaging in the HUDF.

Color-color diagrams for the clump and interclump emission in 10 clump-cluster galaxies of the Hubble Ultra Deep Field (UDF) are made from B,V, i, and z images and compared with models to determine redshifts, star formation histories, and galaxy masses. These galaxies are members of a class dominated by 5-10 giant clumps, with no exponential disk or bulge. The redshifts are found to be in the range from 1.6 to 3. The clump emission is typically 40% of the total galaxy emission, and the luminous clump mass is 19% of the total galaxy mass. The clump colors suggest declining star formation over the last ~0.3 Gyr, while the interclump emission is redder than the clumps, corresponding to a greater age. The clump luminous masses are typically 6 × 108 M☉, and their diameters average 1.8 kpc, making their average density ~0.2 M☉ pc-3. Including the interclump populations, assumed to begin forming at z = 6, the total galaxy luminous masses average 6.5 × 1010 M☉ and their diameters average 19 kpc to the 2 σ noise level. The expected galaxy rotation speeds average ~150 km s-1 if they are uniformly rotating disks. The ages of the clumps are longer than their internal dynamical times by a factor of ~8, so they are stable star clusters, but the clump densities are only ~10 times the limiting tidal densities, so they could be deformed by tidal forces. This is consistent with the observation that some clumps have tails. The clumps could form by gravitational instabilities in accreting disk gas and then disperse on a ~1 Gyr timescale, building up the interclump disk emission, or they could be captured as gas-rich dwarf galaxies, flaring up with star formation at first and then dispersing. Support for this second possibility comes from the high abundance of nearly identical clumps in the UDF, smaller than 6 pixels, whose distributions on color-magnitude and color-color plots are the same as the galaxy clumps studied here. The distribution of axial ratios for the combined population of chain and clump-cluster galaxies in the UDF is compared with models and shown to be consistent with a thick-disk geometry. If these galaxies evolve into today's disk galaxies, then we are observing a stage in which accretion and star formation are extremely clumpy and the resulting high velocity dispersions form thick disks. Several clump-clusters have disk densities that are much larger than in local disks, however, suggesting an alternate model in which they do not survive until today, but get converted into ellipticals by collisions.

Elliptical galaxies larger than 10 pixels in the Hubble Ultra Deep Field (UDF) were surveyed for internal structure; 30 out of 100 in a sample of 884 morphologically classified galaxies exhibit large blue clumps near their centers. Unsharp-masked images of the clearest cases are presented. The distributions of the clumps on color-color and color-magnitude diagrams are about the same as the distributions of isolated objects in the UDF with the same size, suggesting a possible accretion origin. In the few cases for which redshifts have been published, the clump masses and star formation ages were determined from stellar evolution models, as were the galaxy masses. The clump mass scales with galaxy mass, probably because of selection effects, and ranges from 106 to 108 M☉ for galaxies with masses from 109 to 1011 M☉. The clump star formation age ranges between 107 and 2 × 108 yr. With partial evaporation and core contraction in the intervening years, some of these clumps could resemble globular clusters today. Stars that evaporate will contribute to the field population in the elliptical galaxies.

We have conducted a two-layered spectroscopic survey (1′ × 1′ ultra deep and 3′ × 3′ deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for Hubble Space Telescope (HST) continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z&gt; 3 and to HST/F775W magnitudes as faint as ≈ 30 mag (AB, 1σ). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [O ii] at z&lt; 1.5 (473 objects) and Lyα at 2.9 &lt;z&lt; 6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains ≳ 20% up to 28–29 mag and ≈ 27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ≈ 80% of the targeted z ~ 2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ≈ 20–40%. We empirically redefine the selection boundaries to make an attempt to improve them to ≈ 60%. The revised boundaries allow bluer colors that capture Lyα emitters with high Lyα equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.

Accretion disks around supermassive black holes (SMBH) in the centers of galaxies are the central engines of active galactic nuclei (AGN), which are observable over the entire electromagnetic spectrum and out to the beginning of galaxy formation. The gradual assembly of galaxies is believed to have resulted in SMBH today. The growth of SMBH is largely hidden by dust, and possibly by large time delays between galaxy mergers and the feeding of the central monster, so the connection between galaxy assembly and SMBH growth is currently at best circumstantial. Facilities like HST WFC3 and the James Webb Space Telescope (JWST) are needed to trace this process from the epoch of reionization to the present.Using panchromatic deep HST WFC3+ACS imaging data, grism spectra, and ground‐based spectroscopy in GOODS and the Hubble Ultra Deep Field (HUDF), we address this issue through the epoch‐dependent rate of major mergers in massive galaxies in the HUDF, and through SED‐fitting of objects with and without (known) AGN in GOODS. On average, the field galaxy population at z = 1–6 has an underlying star‐forming SED with typical ages of 0.1–0.2 Gyr. However, most AGN‐dominated objects at z = 0.5–1.5 have an underlying stellar SED age of ∼1 Gyr on average. This suggests that AGN growth and SMBH feeding may become visible 0.5–1 Gyr after the dynamical event which triggers the dominant starburst at these redshifts. This may also be reflected in the peak in the massive galaxy major merger rate compared to the peak in the redshift distribution of weak AGN. Finally, we discuss how JWST will expand on this topic in the next decade from the epoch of first light to the present.

We present a search for [C ii] line and dust continuum emission from optical dropout galaxies at z &gt; 6 using ASPECS, our Atacama Large Millimeter submillimeter Array Spectroscopic Survey in the Hubble Ultra-deep Field (UDF). Our observations, which cover the frequency range of 212–272 GHz, encompass approximately the range of 6 &lt; z &lt; 8 for [C ii] line emission and reach a limiting luminosity of L [C ii] ∼ (1.6–2.5) × 108 L ⊙. We identify 14 [C ii] line emitting candidates in this redshift range with significances &gt;4.5σ, two of which correspond to blind detections with no optical counterparts. At this significance level, our statistical analysis shows that about 60% of our candidates are expected to be spurious. For one of our blindly selected [C ii] line candidates, we tentatively detect the CO(6-5) line in our parallel 3 mm line scan. None of the line candidates are individually detected in the 1.2 mm continuum. A stack of all [C ii] candidates results in a tentative detection with S 1.2 mm = 14 ± 5 μJy. This implies a dust-obscured star-formation rate (SFR) of (3 ± 1) M ⊙ yr−1. We find that the two highest-SFR objects have candidate [C ii] lines with luminosities that are consistent with the low-redshift L [C ii] versus SFR relation. The other candidates have significantly higher [C ii] luminosities than expected from their UV-based SFR. At the current sensitivity, it is unclear whether the majority of these sources are intrinsically bright [C ii] emitters, or spurious sources. If only one of our line candidates was real (a scenario greatly favored by our statistical analysis), we find a source density for [C ii] emitters at 6 &lt; z &lt; 8 that is significantly higher than predicted by current models and some extrapolations from galaxies in the local universe.

We report molecular gas mass estimates obtained from a stacking analysis of CO line emission in the ALMA Spectroscopic Survey (ASPECS) using the spectroscopic redshifts from the optical integral field spectroscopic survey by the Multi Unit Spectroscopic Explorer (MUSE) of the Hubble Ultra Deep Field (HUDF). Stacking was performed on subsets of the sample of galaxies classified by their stellar mass and position relative to the main-sequence relation (on, above, below). Among all the CO emission lines, from CO(2–1) to CO(6–5), with redshifts accessible via the ASPECS Band 3 and the MUSE data, CO(2–1) provides the strongest constraints on the molecular gas content. We detect CO(2–1) emission in galaxies down to stellar masses of . Below this stellar mass, we present a new constraint on the molecular gas content of main-sequence galaxies by stacking based on the MUSE detections. We find that the molecular gas mass of main-sequence galaxies continuously decreases with stellar mass down to . Assuming a metallicity-based CO–to–H 2 conversion factor, the molecular gas-to-stellar mass ratio from to ∼10.0 does not seem to decrease as fast as for , which is in line with simulations and studies at lower redshift. The inferred molecular gas density of MUSE-selected galaxies at is comparable with the one derived in the HUDF with a different CO selection. Using the MUSE data we recover most of the CO emission in our deep ALMA observations through stacking, demonstrating the synergy between volumetric surveys obtained at different wave bands.

We present photometry and derived redshifts from up to eleven bandpasses for 9927 galaxies in the Hubble Ultra Deep field (UDF), covering an observed wavelength range from the near-ultraviolet (NUV) to the near-infrared (NIR) with Hubble Space Telescope observations. Our Wide Field Camera 3 (WFC3)/UV F225W, F275W, and F336W image mosaics from the ultra-violet UDF (UVUDF) imaging campaign are newly calibrated to correct for charge transfer inefficiency, and use new dark calibrations to minimize background gradients and pattern noise. Our NIR WFC3/IR image mosaics combine the imaging from the UDF09 and UDF12 campaigns with CANDELS data to provide NIR coverage for the entire UDF field of view. We use aperture-matched point-spread function corrected photometry to measure photometric redshifts in the UDF, sampling both the Lyman break and Balmer break of galaxies at z~0.8-3.4, and one of the breaks over the rest of the redshift range. Our comparison of these results with a compilation of robust spectroscopic redshifts shows an improvement in the galaxy photometric redshifts by a factor of two in scatter and a factor three in outlier fraction over previous UDF catalogs. The inclusion of the new NUV data is responsible for a factor of two decrease in the outlier fraction compared to redshifts determined from only the optical and NIR data, and improves the scatter at z<0.5 and at z>2. The panchromatic coverage of the UDF from the NUV through the NIR yields robust photometric redshifts of the UDF, with the lowest outlier fraction available.

The IRAC ultradeep field (IUDF) and IRAC Legacy over GOODS (IGOODS) programs are two ultradeep imaging surveys at 3.6{\mu}m and 4.5{\mu}m 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 dataset. The resulting imaging reaches unprecedented coverage in IRAC 3.6{\mu}m and 4.5{\mu}m ranging from > 50 hour over 150 arcmin^2, > 100 hour over 60 sq arcmin2, to 200 hour over 5 - 10 arcmin$^2$. This paper presents the survey description, data reduction, and public release of reduced mosaics on the same astrometric system as the CANDELS/GOODS-South 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 hours, well below the classical confusion limit, reaching 1{\sigma} point source sensitivities as faint as of 15 nJy (28.5 AB) at 3.6{\mu}m and 18 nJy (28.3 AB) at 4.5{\mu}m. The value of such ultradeep IRAC data is illustrated by direct detections of z = 7 - 8 galaxies as faint as HAB = 28.

We summarize the properties and initial data release of the JADES Origins Field (JOF), the longest single pointing yet imaged with the James Webb Space Telescope (JWST). This field falls within the GOODS-S region about 8′ southwest of the Hubble Ultra Deep Field (HUDF), where it was formed initially in Cycle 1 as a parallel field of HUDF spectroscopic observations within the JWST Advanced Deep Extragalactic Survey (JADES). This imaging was greatly extended in Cycle 2 program 3215, which observed the JOF for 5 days in six medium-band filters, seeking robust candidates for z &gt; 15 galaxies. This program also includes ultradeep parallel NIRSpec spectroscopy (up to 91 hr on source, summing over the dispersion modes) on the HUDF. Cycle 3 observations from program 4540 added 20 hr of NIRCam slitless spectroscopy and F070W imaging to the JOF. With these three campaigns, the JOF was observed for 380 open-shutter hours with NIRCam using 15 imaging filters and two grism bandpasses. Further, parts of the JOF have deep 43 hr MIRI observations in F770W. Taken together, the JOF is one of the most compelling deep fields available with JWST and a powerful window into the early Universe. This paper presents the second data release from JADES, featuring the imaging and catalogs from the year 1 JOF observations.

Using new ultradeep Spitzer/InfraRed Array Camera (IRAC) photometry from the IRAC Ultra Deep Field program, we investigate the stellar populations of a sample of 63 Y-dropout galaxy candidates at z \\~{} 8, only 650 Myr after the big bang. The sources are selected from HST/ACS+WFC3/IR data over the Hubble Ultra Deep Field (HUDF), two HUDF parallel fields, and wide area data over the CANDELS/GOODS-South. The new Spitzer/IRAC data increase the coverage in [3.6] and [4.5] to \\~{}120h over the HUDF reaching depths of \\~{}28 (AB,1{$σ$}). The improved depth and inclusion of brighter candidates result in direct {\\gt}=3{$σ$} InfraRed Array Camera (IRAC) detections of 20/63 sources, of which 11/63 are detected at {\\gt}=5{$σ$}. The average [3.6]-[4.5] colors of IRAC detected galaxies at z \\~{} 8 are markedly redder than those at z \\~{} 7, observed only 130 Myr later. The simplest explanation is that we witness strong rest-frame optical emission lines (in particular [O III] {$λ$}{$λ$}4959, 5007 + H{$β$}) moving through the IRAC bandpasses with redshift. Assuming that the average rest-frame spectrum is the same at both z \\~{} 7 and z \\~{} 8 we estimate a rest-frame equivalent width of $\\{$W$\\}$\\_$\\{$[O$\\backslash$,$\\backslash$scriptsize$\\{$III$\\}$]$\\backslash$ $\\backslash$lambda $\\backslash$lambda 4959,5007+H$\\backslash$beta $\\}$=670\\^{}$\\{$+260$\\}$\\_$\\{$-170$\\}$ Å contributing 0.56\\^{}$\\{$+0.16$\\}$\\_$\\{$-0.11$\\}$ mag to the [4.5] filter at z \\~{} 8. The corresponding $\\{$W$\\}$\\_$\\{$H$\\backslash$alpha $\\}$=430\\^{}$\\{$+160$\\}$\\_$\\{$-110$\\}$ Å implies an average specific star formation rate of sSFR=11\\_$\\{$-5$\\}$\\^{}$\\{$+11$\\}$ Gyr$^{–1}$ and a stellar population age of 100\\_$\\{$-50$\\}$\\^{}$\\{$+100$\\}$ Myr. Correcting the spectral energy distribution for the contribution of emission lines lowers the average best-fit stellar masses and mass-to-light ratios by \\~{}3 {\\times}, decreasing the integrated stellar mass density to $\\backslash$rho \\^{}*(z=8,M\\_$\\{$$\\backslash$rm$\\{$UV$\\}$$\\}${\\lt}-18)=0.6\\^{}$\\{$+0.4$\\}$\\_$\\{$-0.3$\\}$$\\backslash$times 10\\^{}6 $\\backslash$,M\\_$\\backslash$odot Mpc$^{–3}$. 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. These observations are associated with programs \\#11563, 9797. Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through contract 125790 issued by JPL/Caltech. Based on service mode observations collected at the European Southern Observatory, Paranal, Chile (ESO Program 073.A-0764A). Based on data gathered with the 6.5{\\nbsp}m Magellan Telescopes located at Las Campanas Observatory, Chile.