Search

We study the rest-frame ultraviolet (UV) continuum slopes (β) of galaxies at redshifts 8 < z < 16 (〈 z 〉 = 10), using a combination of JWST ERO and ERS NIRCam imaging and ground-based near-infrared imaging of the COSMOS field. The combination of JWST and ground-based imaging provides a wide baseline in both redshift and absolute UV magnitude (−22.6 < M UV < −17.9), sufficient to allow a meaningful comparison to previous results at lower redshift. Using a power-law fitting technique, we find that our full sample (median M UV = −19.3 ± 1.3) returns an inverse-variance weighted mean value of 〈β〉 = −2.10 ± 0.05, with a corresponding median value of β  = −2.29 ± 0.09. These values imply that the UV colours of galaxies at z > 8 are, on average , no bluer than the bluest galaxies in the local universe (e.g. NGC 1705; β  = −2.46). We find evidence for a β − M UV relation, such that brighter UV galaxies display redder UV slopes (⁠|$\rm {d}\beta / \rm {d} M_{\rm UV} = -0.17 \pm 0.05$|⁠). Comparing to results at lower redshift, we find that the slope of our β − M UV relation is consistent with the slope observed at z ≃ 5 and that, at a given M UV, our 8 < z < 16 galaxies are bluer than their z ≃ 5 counterparts, with an inverse-variance weighted mean offset of 〈Δβ〉 = −0.38 ± 0.09. We do not find strong evidence that any objects in our sample display ultra-blue UV continuum slopes (i.e. β ≲ −3) that would require their UV emission to be dominated by ultra-young, dust-free stellar populations with high Lyman-continuum escape fractions. Comparing our results to the predictions of theoretical galaxy formation models, we find that the galaxies in our sample are consistent with the young, metal-poor, and moderately dust-reddened galaxies expected at z > 8. [ABSTRACT FROM AUTHOR]

We reduce and analyse the available JWST ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range z  = 8 − 15. This yields a new estimate of the evolution of UV luminosity density (ρUV), and hence cosmic star formation rate density (ρSFR) out to within <300 Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power law (rather than a Schechter) function up to z ∼ 10, and that the LF and the resulting derived ρUV (and thus ρSFR), continues to decline gradually and steadily up to z ∼ 15 (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). We provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at z ≥ 12, one of which appears to set a new redshift record as an apparently robust galaxy candidate at z ≃ 16.4, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe. [ABSTRACT FROM AUTHOR]

We present a first-look analysis of the JWST ERO data in the SMACS J0723.3-7327 cluster field. We begin by reporting 10 new spectroscopic redshifts from λobs = 1.8–5.2 μm NIRSpec medium-resolution (R  = λ/Δλ = 1000) data. These are determined via multiple high-SNR emission line detections with five objects at 1 < z < 3 displaying multiple rest-frame near-infrared Hydrogen Paschen lines, and five objects at 5 < z < 9 displaying rest-frame optical Oxygen and Hydrogen Balmer lines. For the five higher-redshift galaxies we extract fluxes in six NIRCam bands spanning λobs = 0.8–5 μm and perform spectral energy distribution fitting in combination with existing HST photometry. The 7 < z < 9 objects exhibit a U-shaped pattern across the F 277 W, F 356 W , and F 444 W bands, indicating a Balmer break seen in emission (Balmer jump) and high-equivalent-width [O  iii ] emission. This indicates an extremely young stellar population with the bulk of the current mass having formed within the past 10 Myr. We report robust stellar masses and mean stellar ages from our spectral fitting with the four z > 6 galaxies exhibiting low-stellar masses from log10 (M */M⊙) = 7.1–8.2, and correspondingly young mean stellar ages of only a few Myr. This work highlights the critical importance of combining large upcoming NIRCam surveys with NIRSpec follow-up to measure the spectroscopic redshifts necessary to robustly constrain physical parameters. [ABSTRACT FROM AUTHOR]

We present deep ALMA dust continuum observations for a sample of luminous (M UV < −22) star-forming galaxies at z ≃ 7. We detect five of the six sources in the far-infrared (FIR), providing key constraints on the obscured star formation rate (SFR) and the infrared-excess-β (IRX–β) relation without the need for stacking. Despite the galaxies showing blue rest-frame ultraviolet (UV) slopes (β ≃ −2) we find that 35–75 per cent of the total SFR is obscured. We find the IRX–β relation derived for these z ≃ 7 sources is consistent with that found for local starburst galaxies. Using our relatively high-resolution (FWHM |$\simeq 0.7\, {\rm arcsec}$|⁠) observations we identify a diversity of dust morphologies in the sample. We find both compact emission that appears offset relative to the unobscured components and extended dust emission that is co-spatial with the rest-frame UV light. In the majority of the sources, we detect strong rest-frame UV colour gradients (with up to Δβ ≃ 0.7–1.4) as probed by the multiband UltraVISTA ground-based data. The observed redder colours are spatially correlated with the location of the FIR detection. Our results show that even in bright Lyman-break galaxies at z ≃ 7 the peak of the star formation is typically hosted by the fainter, redder, regions in the rest-frame UV, which have an obscured fraction of f obs ≥ 0.8. As well as demonstrating the importance of dust obscured star formation within the Epoch of Reionization, these observations provide an exciting taster of the rich spatially resolved data sets that will be obtained from  JWST and high-resolution ALMA follow-up at these redshifts. [ABSTRACT FROM AUTHOR]

We present a new determination of the galaxy stellar-mass function (GSMF) over the redshift interval 0.25 ≤ z ≤ 3.75, derived from a combination of ground-based and Hubble Space Telescope (HST) imaging surveys. Based on a near-IR-selected galaxy sample selected over a raw survey area of 3 deg2 and spanning ≥4 dex in stellar mass, we fit the GSMF with both single and double Schechter functions, carefully accounting for Eddington bias to derive both observed and intrinsic parameter values. We find that a double Schechter function is a better fit to the GSMF at all redshifts, although the single and double Schechter function fits are statistically indistinguishable by z  = 3.25. We find no evidence for significant evolution in M ⋆, with the intrinsic value consistent with |$\log _{10}(M^{\star }/\hbox{$\rm \, M_{\odot }$})=10.55\pm {0.1}$| over the full redshift range. Overall, our determination of the GSMF is in good agreement with recent simulation results, although differences persist at the highest stellar masses. Splitting our sample according to location on the UVJ plane, we find that the star-forming GSMF can be adequately described by a single Schechter function over the full redshift range, and has not evolved significantly since z ≃ 2.5. In contrast, both the normalization and the functional form of the passive GSMF evolve dramatically with redshift, switching from a single to a double Schechter function at z ≤ 1.5. As a result, we find that while passive galaxies dominate the integrated stellar-mass density at z ≤ 0.75, they only contribute ≲10 per cent by z ≃ 3. Finally, we provide a simple parametrization that provides an accurate estimate of the GSMF, both observed and intrinsic, at any redshift within the range 0 ≤ z ≤ 4. [ABSTRACT FROM AUTHOR]

We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and  Spitzer data, to search for bright star-forming galaxies at z ≳ 7.5. Using a full photometric redshift fitting analysis applied to the ∼6 |$\, {\rm deg}^2$|  of imaging searched, we find 27 Lyman break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range 7.4 < z < 9.1. From this sample, we derive the rest-frame UV luminosity function at z = 8 and z = 9 out to extremely bright UV magnitudes (M UV ≃ −23) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright (M UV ∼ −23) LBGs between z ≃ 5 and z ≃ 9. The tentative detection of an LBG with best-fitting photometric redshift of z = 10.9 ± 1.0 in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude (Δ M */Δ z ≃ −0.5) and a steadily steepening bright-end slope (Δβ/Δ z ≃ −0.5) provides a good description of the z > 5 data over a wide range in absolute UV magnitude (−23 < M UV < −17). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first |${\sim}1 \, {\rm Gyr}$| of galaxy evolution. [ABSTRACT FROM AUTHOR]

We present the results of a new study of the relationship between infrared excess (IRX ≡ L IR/ L UV), ultraviolet (UV) spectral slope (β) and stellar mass at redshifts 2 <  z  < 3, based on a deep Atacama Large Millimeter Array (ALMA) 1.3-mm continuum mosaic of the Hubble Ultra Deep Field. Excluding the most heavily obscured sources, we use a stacking analysis to show that z ≃ 2.5 star-forming galaxies in the mass range |$9.25\le \log (M_{\ast }/\rm M_{{\odot }}) \le 10.75$| are fully consistent with the IRX–β relation expected for a relatively grey attenuation curve, similar to the commonly adopted Calzetti law. Based on a large, mass-complete sample of 2 ≤ z ≤ 3 star-forming galaxies drawn from multiple surveys, we proceed to derive a new empirical relationship between β and stellar mass, making it possible to predict UV attenuation (A 1600) and IRX as a function of stellar mass, for any assumed attenuation law. Once again, we find that z ≃ 2.5 star-forming galaxies follow A 1600– M * and IRX– M * relations consistent with a relatively grey attenuation law, and find no compelling evidence that star-forming galaxies at this epoch follow a reddening law as steep as the Small Magellanic Cloud (SMC) extinction curve. In fact, we use a simple simulation to demonstrate that previous determinations of the IRX–β relation may have been biased towards low values of IRX at red values of β, mimicking the signature expected for an SMC-like dust law. We show that this provides a plausible mechanism for reconciling apparently contradictory results in the literature and that, based on typical measurement uncertainties, stellar mass provides a cleaner prediction of UV attenuation than β. Although the situation at lower stellar masses remains uncertain, we conclude that for 2 <  z  < 3 star-forming galaxies with |$\log (M_{\ast }/\rm M_{{\odot }}) \ge 9.75$|⁠, both the IRX–β and IRX– M * relations are well described by a Calzetti-like attenuation law. [ABSTRACT FROM AUTHOR]

We present a new measurement of the evolving galaxy far-IR luminosity function (LF) extending out to redshifts z ≃ 5, with resulting implications for the level of dust-obscured star formation density in the young Universe. To achieve this, we have exploited recent advances in sub-mm/mm imaging with SCUBA-2 on the James Clerk Maxwell Telescope and the Atacama Large Millimeter/Submillimeter Array, which together provide unconfused imaging with sufficient dynamic range to provide meaningful coverage of the luminosity-redshift plane out to z > 4. Our results support previous indications that the faint-end slope of the far-IR LF is sufficiently flat that comoving luminosity density is dominated by bright objects (≃L*). However, we find that the number density/luminosity of such sources at high redshifts has been severely overestimated by studies that have attempted to push the highly confused Herschel SPIRE surveys beyond z ≃ 2. Consequently, we confirm recent reports that cosmic star formation density is dominated by UV-visible star formation at z > 4. Using both direct (1/Vmax) and maximum likelihood determinations of the LF, we find that its high-redshift evolution is well characterized by continued positive luminosity evolution coupled with negative density evolution (with increasing redshift). This explains why bright sub-mm sources continue to be found at z > 5, even though their integrated contribution to cosmic star formation density at such early times is very small. The evolution of the far-IR galaxy LF thus appears similar in form to that already established for active galactic nuclei, possibly reflecting a similar dependence on the growth of galaxy mass. [ABSTRACT FROM AUTHOR]

The z = 6.6 Lyman α emitter ‘CR7’ has been claimed to have a Population III (Pop III) like stellar population, or alternatively, be a candidate direct collapse black hole (DCBH). In this paper, we investigate the evidence for these exotic scenarios using recently available, deeper, optical, near-infrared and mid-infrared imaging.We find strong Spitzer/Infrared Array Camera detections for the main component of CR7 at 3.6 and 4.5 μm, and show that it has a blue colour ([3.6] − [4.5]=−1.2 ± 0.3). This colour cannot be reproduced by current Pop III or pristine DCBH models. Instead, the results suggest that the [3.6] band is contaminated by the [O III]λλ 4959, 5007 emission line with an implied rest-frame equivalent width of EW0(H β + [O III]) ≳ 2000 Å. Furthermore, we find that new near-infrared data from the UltraVISTA survey supports a weaker He II λ1640 emission line than previously measured, with EW0 = 40 ± 30 Å. For the fainter components of CR7 visible in Hubble Space Telescope imaging, we find no evidence that they are particularly red as previously claimed, and show that the derived masses and ages are considerably uncertain. In light of the likely detection of strong [O III] emission in CR7, we discuss other more standard interpretations of the system that are consistent with the data. We find that a low-mass, narrow-line active galactic nucleus can reproduce the observed features of CR7, including the lack of radio and X-ray detections. Alternatively, a young, low-metallicity (∼1/200 Z⊙) starburst, modelled including binary stellar pathways, can reproduce the inferred strength of the He II line and simultaneously the strength of the observed [OIII] emission, but only if the gas shows supersolar α-element abundances (O/Fe ≃ 5 (O/Fe)⊙). [ABSTRACT FROM AUTHOR]

We present physical properties [redshifts (z), star-formation rates (SFRs) and stellar masses (Mstar)] of bright (S850 ≥ 4 mJy) submm galaxies in the ≃2 deg2 COSMOS and UDS fields selected with SCUBA-2/JCMT.We complete the galaxy identification process for all (≃2000) S/N ≥ 3.5 850-μm sources, but focus our scientific analysis on a high-quality subsample of 651 S/N ≥ 4 sources with complete multiwavelength coverage including 1.1-mm imaging. We check the reliability of our identifications, and the robustness of the SCUBA-2 fluxes by revisiting the recent ALMA follow-up of 29 sources in our sample. Considering >4mJy ALMA sources, our identification method has a completeness of ≃86 per cent with a reliability of ≃92 per cent, and only ≃15–20 per cent of sources are significantly affected by multiplicity (when a secondary component contributes >1/3 of the primary source flux). The impact of source blending on the 850-μmsource counts as determined with SCUBA-2 ismodest; scaling the single-dish fluxes by ≃0.9 reproduces the ALMA source counts. For our final SCUBA- 2 sample, we find median z = 2.40+0.10 −0.04, SFR = 287 ± 6M⊫ yr−1 and log(Mstar/M⊫) = 11.12 ± 0.02 (the latter for 349/651 sources with optical identifications). These properties clearly locate bright submm galaxies on the high-mass end of the ‘main sequence’ of starforming galaxies out to z ≃ 6, suggesting that major mergers are not a dominant driver of the high-redshift submm-selected population. Their number densities are also consistent with the evolving galaxy stellar mass function. Hence, the submm galaxy population is as expected, albeit reproducing the evolution of the main sequence of star-forming galaxies remains a challenge for theoretical models/simulations. [ABSTRACT FROM AUTHOR]

We present new Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) imaging of 25 extremely luminous (-23.2 ≤ MUV ⩽ -21.2) Lyman-break galaxies (LBGs) at z≃ 7. The sample was initially selected from 1.65 deg2 of ground-based imaging in the UltraVISTA/ COSMOS and UDS/SXDS fields, and includes the extreme Lyman α emitters, 'Himiko' and 'CR7'. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW0(Hβ + [O III]) > 600 Å). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (fmulti > 0.4) in bright z≃ 7 galaxies, and ubiquitous at the very bright end (MUV <-22.5). The galaxies have half-light radii in the range r1/2 ∼0.5- 3 kpc. The size measurements provide the first determination of the size-luminosity relation at z≃ 7 that extends to MUV ∼ -23. We find the relation to be steep with r1/2 αL1/2. Excluding clumpy, multicomponent galaxies however, we find a shallower relation that implies an increased star formation rate surface density in bright LBGs. Using the new, independent, HST/WFC3 data we confirm that the rest-frame UV luminosity function at z≃ 7 favours a power-law decline at the bright end, compared to an exponential Schechter function drop-off. Finally, these results have important implications for the Euclid mission, which we predict will detect >1000 similarly bright galaxies at z≃ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination. [ABSTRACT FROM AUTHOR]

We investigate the redshift evolution of the [O III]/H β nebular emission line ratio for a sample of galaxies spanning the redshift range 0 < z < 4. We compare the observed evolution to a set of theoretical models which account for the independent evolution of chemical abundance, ionization parameter and interstellar medium (ISM) pressure in star-forming galaxies with redshift. Accounting for selection effects in the combined data sets, we show that the evolution to higher [O III]/H β ratios with redshift is a real physical effect which is best accounted for by a model in which the ionization parameter is elevated from the average values typical of local star-forming galaxies, with a possible simultaneous increase in the ISM pressure. We rule out the possibility that the observed [O III]/H β evolution is purely due to metallicity evolution. We discuss the implications of these results for using local empirical metallicity calibrations to measure metallicities at high redshift, and briefly discuss possible theoretical implications of our results. [ABSTRACT FROM AUTHOR]

We investigate the properties of the galaxies selected from the deepest 850-µm survey undertaken to date with (Submillimetre Common-User Bolometer Array 2) SCUBA-2 on the James Clerk Maxwell Telescope as part of the SCUBA-2 Cosmology Legacy Survey. A total of 106 sources (>5s) were uncovered at 850 µm from an area of ≃150 arcmin² in the centre of the COSMOS/UltraVISTA/Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field, imaged to a typical depth of s850 ≃ 0.25 mJy. We utilize the available multifrequency data to identify galaxy counterparts for 80 of these sources (75 per cent), and to establish the complete redshift distribution for this sample, yielding z = 2.38 ± 0.09. We have also been able to determine the stellar masses of the majority of the galaxy identifications, enabling us to explore their location on the star formation rate:stellar mass (SFR:M *) plane. Crucially, our new deep 850-µm-selected sample reaches flux densities equivalent to SFR 100M&#9737 yr-1, enabling us to confirm that sub-mm galaxies form the high-mass end of the 'main sequence' (MS) of star-forming galaxies at z > 1.5 (with a mean specific SFR of sSFR = 2.25 ± 0.19 Gyr-1 at z ≃ 2.5). Our results are consistent with no significant flattening of the MS towards high masses at these redshifts. However, our results add to the growing evidence that average sSFR rises only slowly at high redshift, resulting in log10sSFR being an apparently simple linear function of the age of the Universe. [ABSTRACT FROM AUTHOR]

We present the results of a search for bright (-22.7 ≤ MUV ≤ -20.5) Lyman-break galaxies at z ≃ 6 within a total of 1.65 deg² of imaging in the UltraVISTA/Cosmological Evolution Survey (COSMOS) and United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) fields. The deep near-infrared imaging available in the two independent fields, in addition to deep optical (including z'-band) data, enables the sample of z ≃ 6 star-forming galaxies to be securely detected longward of the break (in contrast to several previous studies). We show that the expected contamination rate of our initial sample by cool Galactic brown dwarfs is ≲3 per cent and demonstrate that they can be effectively removed by fitting brown dwarf spectral templates to the photometry. At z ≃ 6, the galaxy surface density in the UltraVISTA field exceeds that in the UDS by a factor of ≃ 1.8, indicating strong cosmic variance even between degree-scale fields at z > 5. We calculate the bright end of the rest-frame Ultraviolet (UV) luminosity function (LF) at z ≃ 6. The galaxy number counts are a factor of ~1.7 lower than predicted by the recent LF determination by Bouwens et al. In comparison to other smaller area studies, we find an evolution in the characteristic magnitude between z ≃ 5 and z ≃ 7 of ΔM* ~ 0.4, and show that a double power law or a Schechter function can equally well describe the LF at z = 6. Furthermore, the bright end of the LF appears to steepen from z ≃ 7 to z ≃ 5, which could indicate the onset of mass quenching or the rise of dust obscuration, a conclusion supported by comparing the observed LFs to a range of theoretical model predictions. [ABSTRACT FROM AUTHOR]

We present the results of a new search for galaxies at redshift z ≃ 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift solutions, and to minimize incompleteness, we confine our search to objects with σ160 < 28.6 (AB mag), consider only image regions with anrms noise σ160 > 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H160 and J140. The result is a survey covering an effective area (after accounting for magnification) of 10.9 arcmin², which yields 12 galaxies at 8.4 < z < 9.5. Within the Abell-2744 cluster and parallel fields, we confirm the three brightest objects reported by Ishigaki et al., but recover only one of the four z > 8.4 sources reported by Zheng et al. In the MACSJ0416.1-240 cluster field, we report five objects, and explain why each of these eluded detection or classification as z ≃ 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z ≃ 9 galaxies from the MACSJ0416.1-240 parallel field. Based on the published magnification maps, we find that only one of these 12 galaxies is likely boosted by more than a factor of 2 by gravitational lensing. Consequently, we are able to perform a fairly straightforward reanalysis of the normalization of the z ≃ 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star formation rate density) from z â€" 8 to 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization. [ABSTRACT FROM AUTHOR]

We present the results of a study investigating the rest-frame ultraviolet (UV) spectral slopes of redshift z ≈ 5 Lyman-break galaxies (LBGs). By combining deep Hubble Space Telescope imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and Hubble Ultra-Deep Field with ground-based imaging from the UKIRT Infrared Deep Sky Survey Ultra Deep Survey, we have produced a large sample of z ≈ 5 LBGs spanning an unprecedented factor of >100 in UV luminosity. Based on this sample we find a clear colour–magnitude relation (CMR) at z ≈ 5, such that the rest-frame UV slopes (β) of brighter galaxies are notably redder than their fainter counterparts. We determine that the z ≈ 5 CMR is well described by a linear relationship of the form: dβ = (−0.12 ± 0.02)dMUV, with no clear evidence for a change in CMR slope at faint magnitudes (i.e. MUV ≥ −18.9). Using the results of detailed simulations we are able, for the first time, to infer the intrinsic (i.e. free from noise) variation of galaxy colours around the CMR at z ≈ 5. We find significant (12σ) evidence for intrinsic colour variation in the sample as a whole. Our results also demonstrate that the width of the intrinsic UV slope distribution of z ≈ 5 galaxies increases from Δβ ≃ 0.1 at MUV = −18 to Δβ ≃ 0.4 at MUV = −21. We suggest that the increasing width of the intrinsic galaxy colour distribution and the CMR itself are both plausibly explained by a luminosity-independent lower limit of β ≈ −2.1, combined with an increase in the fraction of red galaxies in brighter UV-luminosity bins. [ABSTRACT FROM AUTHOR]

Context. The exploration of the relation between galaxy sizes and other physical parameters (luminosity, mass, star formation rate) has provided important clues for understanding galaxy formation, but such exploration has until recently been limited to intermediate redshift objects. Aims. We use the currently available CANDELS Deep+Wide surveys in the GOODS-South, UDS and EGS fields, complemented by data from the HUDF09 program, to address the relation between size and luminosity at z ∼ 7. Methods. The six different fields used for this study are characterized by a wide combination of depth and areal coverage, well suited for reducing the biases on the observed size-magnitude plane. From these fields, we select 153 z-band dropout galaxies. Detailed simulations have been carried out for each of these six fields, inserting simulated galaxies at different magnitudes and half light radius in the two dimensional images for all the Hubble Space Telescope (HST) bands available and recovering them as carried out for the real galaxies. These simulations allow us to derive precisely the completeness as a function of size and magnitude and to quantify measurements errors/biases, under the assumption that the 2D profile of z = 7 galaxies is well represented by an exponential disk function. Results. We find in a rather robust way that the half light radius distribution function of z ∼ 7 galaxies fainter than J = 26.6 is peaked at ⩽0.1 arcsec (or equivalently 0.5 kpc proper), while at brighter magnitudes high-z galaxies are typically larger than ∼0.15 arcsec.We also find a well defined size-luminosity relation, Rh ∝ L1/2. We compute the luminosity function (LF) in the HUDF and P12HUDF fields, finding large spatial variation on the number density of faint galaxies. Adopting the size distribution and the size-luminosity relation found for faint galaxies at z = 7, we derive a mean slope of -1.7 ± 0.1 for the LF of LBGs at this redshift. Conclusions. Using this LF, we find that the number of ionizing photons emitted from galaxies at z ∼ 7 cannot keep the Universe re-ionized if the IGM is clumpy (CHII ⩾ 3) and the Lyman continuum escape fraction of high-z LBGs is relatively low ( fesc ⩽ 0.3). If these results are confirmed and strengthened by future CANDELS data, in particular by the forthcoming deep observations in GOODS-South and North and the wide field COSMOS, we can put severe limits to the role of galaxies in the reionization of the Universe [ABSTRACT FROM AUTHOR]

ABSTRACT We present spectroscopic confirmation of 10 highly luminous ( L≥ 2 L★) Lyα emitters (LAEs) in the redshift range 6.01 < z < 6.49 (nine galaxies and one active galactic nucleus), initially drawn from a sample of 14 zphot≥ 6 Lyman-break galaxies (LBGs) selected from an area of 0.25 deg2 within the UK Infrared Deep Sky Survey (UKIDSS) Ultra-Deep Survey (UDS). Overall, our high rate of spectroscopic confirmation (≥71 per cent) and low rate of contamination provides a strong vindication of the photometric redshift analysis used to define the original sample. By considering star formation rate estimates based on the Lyα and ultraviolet continuum luminosity we conclude that our sample is consistent with a Lyα escape fraction of ≃25 per cent. Moreover, after careful consideration of the potential uncertainties and biases, we find that 40-50 per cent of our sample of L≥ 2 L★ galaxies at 6.0 < z < 6.5 display strong Lyα emission (rest-frame equivalent width ≥25 Å), a fraction which is a factor of ≃2 higher than previously reported for L≤ L★ galaxies at z≃ 6. Our results suggest that, as the epoch of reionization is approached, it is plausible that the LAE fraction amongst luminous ( L≥ 2 L★) LBGs shows a similarly sharp increase to that observed in their lower luminosity ( L≤ L★) counterparts. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the results of a photometric redshift analysis designed to identify z≥ 6 galaxies from the near-infrared Hubble Space Telescope imaging in three deep fields [ Hubble Ultra Deep Field (HUDF), HUDF09-2 and Early Release Science] covering a total area of 45 square arcmin. By adopting a rigorous set of criteria for rejecting low-redshift interlopers, and by employing a deconfusion technique to allow the available ultradeep IRAC imaging to be included in the candidate-selection process, we have derived a robust sample of 70 Lyman break galaxies (LBGs) spanning the redshift range 6.0 < z < 8.7. Based on our final sample, we investigate the distribution of ultraviolet (UV) spectral slopes ( fλ∝λβ), finding a variance-weighted mean value of 〈β〉=−2.05 ± 0.09 which, contrary to some previous results, is not significantly bluer than displayed by lower redshift starburst galaxies. We confirm the correlation between UV luminosity and stellar mass reported elsewhere, but based on fitting galaxy templates featuring a range of star formation histories (SFHs), metallicities and reddening, we find that, at z≥ 6, the range in mass-to-light ratio ( M★/ LUV) at a given UV luminosity could span a factor of ≃50. Focusing on a subsample of 21 candidates with IRAC detections at m, we find that L★ LBGs at z≃ 6.5 have a median stellar mass of M★= (2.1 ± 1.1) × 109 M⊙ (Chabrier initial mass function) and a median specific star formation rate (sSFR) of 1.9 ± 0.8 Gyr−1. Using the same subsample, we have investigated the influence of nebular continuum and line emission, finding that for the majority of candidates (16 out of 21), the best-fitting stellar masses are reduced by less than a factor of 2.5. However, galaxy template fits exploring a plausible range of SFHs and metallicities provide no compelling evidence of a clear connection between SFR and stellar mass at these redshifts. Finally, a detailed comparison of our final sample with the results of previous studies suggests that, at faint magnitudes, several high-redshift galaxy samples in the literature are significantly contaminated by low-redshift interlopers. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the environments of both X-ray and radio-loud active galactic nuclei (AGN) within the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Ultra-deep Survey (UDS) using deep infrared selection to sample the galaxy density field in the redshift range 1.0 ≤ z≤ 1.5. Using angular cross-correlation techniques we find that both X-ray and radio-loud AGN preferentially reside in overdense environments. We also find that both types of AGN cluster more strongly with those galaxies classified as 'passive' rather than those that are actively star forming. We infer clustering scalelengths comparable to those of passive red galaxies, suggesting that typical AGN at these epochs reside in dark matter haloes of mass M≳ 1013 M⊙. A closer look at the small-scale environments of the AGN reveals that the neighbouring galaxies of radio-loud AGN have U− B colours more skewed towards the 'green valley' and the red sequence, whereas the neighbours of X-ray AGN show no difference to the general galaxy population. This suggests that although both AGN types live in overdense environments, the radio-loud AGN may be preferentially located in more evolved cluster cores, in a similar environment to low-powered radio AGN in the local Universe. [ABSTRACT FROM AUTHOR]

We present a study of galaxy environments to , based on a sample of over 33 000 K-band-selected galaxies detected in the UKIDSS Ultra Deep Survey (UDS). The combination of infrared depth and area in the UDS allows us to extend previous studies of galaxy environment to without the strong biases associated with optical galaxy selection. We study the environments of galaxies divided by rest-frame colours, in addition to 'passive' and 'star-forming' subsets based on template fitting. We find that galaxy colour is strongly correlated with galaxy overdensity on small scales (<1-Mpc diameter), with red/passive galaxies residing in significantly denser environments than blue/star-forming galaxies to . On smaller scales (<0.5-Mpc diameter) we also find a relationship between galaxy luminosity and environment, with the most luminous blue galaxies at inhabiting environments comparable to red, passive systems at the same redshift. Monte Carlo simulations demonstrate that these conclusions are robust to the uncertainties introduced by photometric redshift errors. [ABSTRACT FROM AUTHOR]

ABSTRACT We have analysed a sample of 1292 4.5- μm-selected galaxies at z≥ 3, over 0.6 deg 2 of the UKIRT Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS). Using photometry from the U band through 4.5 μm, we have obtained photometric redshifts and derived stellar masses for our sources. Only two of our galaxies potentially lie at z > 5. We have studied the galaxy stellar mass function at 3 ≤ z < 5, based on the 1213 galaxies in our catalogue with 4.5- μm magnitudes ≤ 24.0. We find that (i) the number density of galaxies increased by a factor of > 10 between z= 5 and 3, indicating that the assembly rate of these galaxies proceeded > 20 times faster at these redshifts than at 0 < z < 2; (ii) the Schechter function slope α is significantly steeper than that displayed by the local stellar mass function, which is a consequence of both the steeper faint end and the absence of a pure exponential decline at the high-mass end; and (iii) the evolution of the comoving stellar mass density from z= 0 to 5 can be modelled as log10ρM=−(0.05 ± 0.09) z2−(0.22 ∓ 0.32) z+ 8.69. At 3 ≤ z < 4, more than 30 per cent of the galaxies would be missed by optical surveys with R < 27 or z < 26. Thus, our study demonstrates the importance of deep mid-infrared surveys over large areas to perform a complete census of massive galaxies at high z and trace the early stages of massive galaxy assembly. [ABSTRACT FROM AUTHOR]

We use the UKIDSS Ultra Deep Survey to trace the evolution of galaxy clustering to . Using photometric redshifts derived from data covering the wavelength range , we examine this clustering as a function of absolute K-band luminosity, colour and star formation rate. Comparing the deprojected clustering amplitudes, we find that red galaxies are more strongly clustered than blue galaxies out to at least , irrespective of rest-frame K-band luminosity. We then construct passive and star-forming samples based on stellar age, colour and star formation histories calculated from the best-fitting templates. The clustering strength of star-forming galaxies declines steadily from Mpc at to Mpc at , while passive galaxies have clustering strengths up to a factor of 2 higher. Within the passive and star-forming subsamples, however, we find very little dependence of galaxy clustering on K-band luminosity. Galaxy ‘passivity’ appears to be the strongest indicator of clustering strength. We compare these clustering measurements with those predicted for dark matter haloes and conclude that passive galaxies typically reside in haloes of mass while luminous star-forming galaxies occupy haloes an order of magnitude less massive over the range . The decline in the clustering strength of star-forming galaxies with decreasing redshift indicates a decline in the hosting halo mass for galaxies of a given luminosity. We find evidence for convergence of clustering in star-forming and passive galaxies around , which is consistent with this being the epoch at which the red sequence of galaxies becomes distinct. [ABSTRACT FROM AUTHOR]

We present the results of a systematic search for galaxies in the redshift range , within the new, deep, near-infrared imaging of the Hubble Ultra Deep Field provided by the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. We have performed full spectral energy distribution fitting to the optical+infrared photometry of all high-redshift galaxy candidates detected at significance in at least one of the WFC3/IR broad-band filters. After careful rejection of contaminants, the result is a sample of 49 galaxies with primary photometric redshift solutions , within the 4.5 arcmin2 field covered by the new near-infrared imaging. Our sample, selected without recourse to specific colour cuts, reselects all but the faintest one of the 16 z850-drops selected by Oesch et al., recovers all five of the Y105-drops reported by Bouwens et al. and adds a further 29 equally plausible galaxy candidates, of which 12 lie beyond and four lie beyond . However, we also present confidence intervals on our photometric redshift estimates, including alternative secondary redshift solutions. As a result of this analysis, we caution that acceptable low-redshift solutions exist for 28 out of the 37 galaxies at and in particular for all eight of the galaxy candidates reported here at . Nevertheless, we note that the very highest redshift candidates appear to be strongly clustered in the field. Based on our photometric redshift analysis, we derive new estimates of the ultraviolet galaxy luminosity function at and 8. Where our results are most robust, at a characteristic luminosity (AB), we find that the comoving number density of galaxies declines by a factor of between and 7 and by a further factor of by . These results suggest that it is difficult for the observed population of high-redshift star-forming galaxies to achieve re-ionization by without a significant contribution from galaxies well below the detection limits, plus alterations in the escape fraction of ionizing photons and/or continued vigorous star formation at . [ABSTRACT FROM AUTHOR]

We present the results of a study of a large sample of luminous Lyman-break galaxies (LBGs) in the redshift interval , selected from a contiguous 0.63 deg2 area covered by the UKIRT Infrared Deep Sky Survey Ultra Deep Survey and the Subaru XMM–Newton Survey. Utilizing the large area coverage and the excellent available optical+near-infrared data, we use a photometric redshift analysis to derive a new, robust, measurement of the bright end of the ultraviolet-selected luminosity function at high redshift. When combined with literature studies of the fainter LBG population, our new sample provides improved constraints on the luminosity function of redshift LBGs over the luminosity range . A maximum likelihood analysis returns best-fitting Schechter function parameters of and for the luminosity function at , and and at . In addition, an analysis of the angular clustering properties of our LBG sample demonstrates that luminous LBGs are strongly clustered , and consistent with the occupation of dark matter haloes with masses of . Moreover, by stacking the available multiwavelength imaging data for the high-redshift LBGs, it is possible to place useful constraints on their typical stellar mass. The results of this analysis suggest that luminous LBGs at have an average stellar mass of , consistent with the results of the clustering analysis assuming plausible values for the ratio of stellar to dark matter. Finally, by combining our luminosity function results with those of the stacking analysis we derive estimates of and for the stellar mass density at and 6, respectively. [ABSTRACT FROM AUTHOR]

We use the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Ultra-deep survey (UDS), currently the deepest panoramic near-infrared survey, together with deep Subaru optical imaging to measure the clustering, number counts and luminosity function of galaxies at selected using the BzK selection technique. We find that both star-forming (s BzK) and passive (p BzK) galaxies, to a magnitude limit of , are strongly clustered. The passive galaxies are the most strongly clustered population, with scalelengths of compared with for star-forming galaxies. The direct implication is that passive galaxies inhabit the most massive dark matter haloes, and are thus identified as the progenitors of the most massive galaxies at the present day. In addition, the p BzKs exhibit a sharp flattening and potential turnover in their number counts, in agreement with other recent studies. This plateau cannot be explained by the effects of incompleteness. We conclude that only very massive galaxies are undergoing passive evolution at this early epoch, consistent with the downsizing scenario for galaxy evolution. Assuming a purely passive evolution for the p BzKs from their median redshift to the present day, their luminosity function suggests that only ∼2.5 per cent of present-day massive ellipticals had a p BzK as a main progenitor. [ABSTRACT FROM AUTHOR]

Motivated by the claimed discovery of a very massive galaxy (HUDF-JD2; M≃ 5 × 1011 M⊙) at extreme redshift within the Hubble Ultra Deep Field (HUDF), we have completed a systematic search for comparably massive galaxies with among the 2688 galaxies in our (AB) catalogue within the CDFS/GOODS-South field. This search was conducted using redshift estimates based on the recently completed, uniquely-deep 11-band ( B, V, i, z, J, H, KS, 3.6 μ m, 4.5 μm, 5.8 μm, 8.0 μm) imaging in this 125-arcmin2 field, ≃ 25 times larger than the NICMOS HUDF. To ensure completeness, our approach places no special emphasis on the standard V-drop, i-drop or z-drop criteria commonly used to pre-select candidate high-redshift galaxies. Initial spectral fitting, based on published catalogueSExtractor photometry, led us to conclude that at least 2669 of the galaxies in our sample lie at . This list includes several galaxies for which redshifts have been previously proposed. We carried out a detailed investigation of the 19 remaining candidates, performing aperture photometry on all images, and including marginal detections and formal non-detections in the fitting process. This led to the rejection of a further 13 galaxies to lower redshift. Moreover, subjecting HUDF-JD2 to the same analysis, we find that it almost certainly lies at , rather than the extreme redshift favoured by Mobasher et al. The six remaining candidates appear to be credible examples of galaxies in the redshift range , with plausible stellar ages. However, refitting with allowance for extreme values of extinction, we find that, even for these objects, statistically acceptable solutions can be found at . In fact, only two galaxies retain formally preferred high-redshift solutions. Moreover, the recently released Spitzer MIPS imaging in GOODS-South has revealed that five out of our six final candidates are detected at 24 μm. This was also the case for HUDF-JD2, and provides further circumstantial evidence in favour of the moderate-redshift dusty solutions. We conclude that there is no convincing evidence for any galaxy with and within the 125-arcmin2 GOODS-South field. We briefly discuss the implications of this null result, and revised expectations for the much larger (0.8 deg2), and deeper near-infrared UKIDSS Ultra Deep Survey now underway with the WFCAM on the UKIRT. [ABSTRACT FROM AUTHOR]

We present the first cluster catalogue extracted from the UKIRT Infrared Deep Sky Survey (UKIDSS) Early Data Release. The catalogue is created using UKIDSS Ultra Deep Survey infrared J and K data combined with 3.6- and 4.5-μm Spitzer bands and optical BVRi′ z′ imaging from the Subaru Telescope over 0.5 deg2 in the Subaru XMM–Newton Deep Field. We have created a new cluster detection algorithm, based on the friends-of-friends and Voronoi tessellation methods, which utilizes probability distribution functions derived from a photometric redshift analysis. We employ mock catalogues to understand the selection effects and contamination associated with the algorithm. The cluster catalogue contains 13 clusters at redshifts with luminosities , corresponding to masses for . The measured sky surface density of for high-redshift , massive clusters is precisely in line with theoretical predictions presented by Kneissl et al. [ABSTRACT FROM AUTHOR]

We have exploited the large area coverage of the combined UKIDSS Ultra Deep Survey (UDS) and Subaru/ XMM–Newton Deep Survey (SXDS) to search for bright Lyman-break galaxies (LBGs) at z≥ 5. Using the available optical + near-infrared photometry to efficiently exclude low-redshift contaminants, we identify nine z≥ 5 LBG candidates brighter than within the 0.6-deg2 overlap region between the UDS early data release and the optical coverage of the SXDS. Accounting for selection incompleteness, we estimate the corresponding surface density of with to be . Modelling of the optical + near-infrared photometry constrains the candidates' redshifts to lie in the range , and provides estimates for their stellar masses. Although the stellar mass estimates are individually uncertain, a stacking analysis suggests that the typical stellar mass of the LBG candidates is which, if confirmed, places them amongst the most massive galaxies currently known at z≥ 5. It is found that Lambda cold dark matter structure formation can produce sufficient numbers of dark matter haloes at z≥ 5 to accommodate our estimated number density of massive LBGs for plausible values of σ8 and the ratio of stellar to dark matter. Moreover, it is found that recent galaxy formation models can also account for the existence of such massive galaxies at z≥ 5. Finally, no evidence is found for the existence of LBGs with stellar masses in excess of at this epoch, despite the large comoving volume surveyed. [ABSTRACT FROM AUTHOR]

We present the results of a study which uses the 3C RR sample of radio-loud active galactic nuclei to investigate the evolution of the black hole:spheroid mass ratio in the most massive early-type galaxies from . Radio-loud unification is exploited to obtain virial (linewidth) black hole mass estimates from the 3C RR quasars, and stellar mass estimates from the 3C RR radio galaxies, thereby providing black hole and stellar mass estimates for a single population of early-type galaxies. At low redshift , the 3C RR sample is consistent with a black hole:spheroid mass ratio of , in good agreement with that observed locally for quiescent galaxies of similar stellar mass . However, over the redshift interval the 3C RR black hole:spheroid mass ratio is found to evolve as , reaching by redshift . This evolution is found to be inconsistent with the local black hole:spheroid mass ratio remaining constant at a moderately significant level (98 per cent). If confirmed, the detection of evolution in the 3C RR black hole:spheroid mass ratio further strengthens the evidence that, at least for massive early-type galaxies, the growth of the central supermassive black hole may be completed before that of the host spheroid. [ABSTRACT FROM AUTHOR]

We have selected and analysed the properties of a sample of galaxies in of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the evolution of Ks-selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5-μm bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimized redshift catalogue for our galaxy sample. We computed the Ks-band luminosity function and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from to . We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (∼85–90 per cent) of the most massive local galaxies appear to be in place before redshift . Around 65–70 per cent of the total assemble between redshifts and 3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short-time-scale bursts. The remaining fraction (up to ∼20 per cent) could be in place at even higher redshifts , pushing the first epoch of formation of massive galaxies beyond the limits of current near-IR surveys. [ABSTRACT FROM AUTHOR]

We present estimated redshifts and derived properties of a sample of 1663 galaxies with (Vega), selected from of the Great Observatories Origins Deep Survey/ Chandra Deep Field South (GOODS/CDFS) field with deep Infrared Spectrometer and Array Camera (ISAAC) imaging, and make an extensive comparison of their properties with those of the extremely red galaxies (ERGs) selected in the same field. We study in detail the evolution of -selected galaxies up to redshifts , and clarify the role of ERGs within the total -band galaxy population. We compute the total -band luminosity function (LF) and compare its evolution with the ERG LF. Up to , the bright end of the -band LF shows no sign of decline, and is progressively well reproduced by the ERGs with increasing redshift. We also explore the evolution of massive systems present in our sample: up to 20–25 per cent of the population of local galaxies with assembled stellar mass has been formed before redshift , and contains ∼45–70 per cent of the stellar mass density of the Universe at that redshift. Within our sample, the comoving number density of these massive systems is then essentially constant down to redshift , by which point most of them have apparently evolved into -selected ERGs. The remaining massive systems observed in the local Universe are assembled later, at redshifts . Our results therefore suggest a twofold assembly history for massive galaxies, in which galaxy/star formation proceeds very efficiently in high mass haloes at very high redshift. [ABSTRACT FROM AUTHOR]

A new technique is presented for determining the black hole masses of high-redshift quasars from optical spectroscopy. The new method utilizes the full-width at half-maximum (FWHM) of the low-ionization Mg II emission line and the correlation between the broad-line region (BLR) radius and the continuum luminosity at 3000 Å. Using archival ultraviolet (UV) spectra it is found that the correlation between BLR radius and 3000-Å luminosity is tighter than the established correlation with 5100-Å luminosity. Furthermore, it is found that the correlation between BLR radius and 3000-Å continuum luminosity is consistent with a relation of the form R[sub BLR] &prop λL[sup ½, sub λ], as expected for a constant ionization parameter. Using a sample of objects with broad-line radii determined from reverberation mapping it is shown that the FWHM of Mg II and Hβ are consistent with following an exact one-to-one relation, as expected if both Hβ and Mg II are emitted at the same radius from the central ionizing source. The resulting virial black hole mass estimator based on rest-frame UV observables is shown to reproduce black hole mass measurements based on reverberation mapping to within a factor of 2.5 (1σ). Finally, the new UV black hole mass estimator is shown to produce identical results to the established optical (Hβ) estimator when applied to 128 intermediate-redshift (0.3 < z < 0.9) quasars drawn from the Large Bright Quasar Survey and the radio-selected Molonglo quasar sample. We therefore conclude that the new UV virial black hole mass estimator can be reliably used to estimate the black hole masses of quasars from z ∼ 0.25 through to the peak epoch of quasar activity at z ∼ 2.5 via optical spectroscopy alone. [ABSTRACT FROM AUTHOR]

We investigate colour selection techniques for high-redshift galaxies in the UKIRT Infrared Deep Sky Survey (UKIDSS) Ultra Deep Survey Early Data Release (UDS EDR). Combined with very deep Subaru optical photometry, the depth and area (0.62 deg2) of the UDS EDR allow us to investigate optical/near-infrared selection using a large sample of over 30 000 objects. By using the B− z′, z′− K colour–colour diagram (the BzK technique) we identify over 7500 candidate galaxies at , which can be further separated into passive and star-forming systems (pBzKs and sBzKs respectively). Our unique sample allows us to identify a new feature not previously seen in BzK diagrams, consistent with the passively evolving track of early-type galaxies at . We also compare the BzK technique with the R− K colour selection of extremely red objects (EROs) and the J− K selection of distant red galaxies (DRGs), and quantify the overlap between these populations. We find that the majority of DRGs at these relatively bright magnitudes are also EROs. Since previous studies have found that DRGs at these magnitudes have redshifts of z∼ 1, we determine that these DRGs/EROs have spectral energy distributions consistent with being dusty star-forming galaxies or active galactic nuclei at . Finally, we observe a flattening in the number counts of pBzK galaxies, similar to other studies, which may indicate that we are sampling the luminosity function of passive galaxies over a narrow redshift range. [ABSTRACT FROM AUTHOR]